Arctic Sea Ice : Forum

AGW in general => Science => Topic started by: AbruptSLR on September 03, 2015, 04:35:05 PM

Title: The Science of Aerosols
Post by: AbruptSLR on September 03, 2015, 04:35:05 PM
As discussions of the influence of aerosols is rather scattered though out this forum, I thought that it would be helpful to open a thread focused on this important anthropogenic forcing mechanism, and I open this thread with the following about contrails:

The linked article (with an open access pdf) discusses how global warming will increase the potential formation of contrails in some parts of the world and decrease it in other parts.

Irvine, E. A. and Shine, K. P.: Ice supersaturation and the potential for contrail formation in a changing climate, Earth Syst. Dynam., 6, 555-568, doi:10.5194/esd-6-555-2015, 2015.

http://www.earth-syst-dynam.net/6/555/2015/esd-6-555-2015.html (http://www.earth-syst-dynam.net/6/555/2015/esd-6-555-2015.html)

Abstract. Ice supersaturation (ISS) in the upper troposphere and lower stratosphere is important for the formation of cirrus clouds and long-lived contrails. Cold ISS (CISS) regions (taken here to be ice-supersaturated regions with temperature below 233 K) are most relevant for contrail formation. We analyse projected changes to the 250 hPa distribution and frequency of CISS regions over the 21st century using data from the Representative Concentration Pathway 8.5 simulations for a selection of Coupled Model Intercomparison Project Phase 5 models. The models show a global-mean, annual-mean decrease in CISS frequency by about one-third, from 11 to 7% by the end of the 21st century, relative to the present-day period 1979–2005. Changes are analysed in further detail for three subregions where air traffic is already high and increasing (Northern Hemisphere mid-latitudes) or expected to increase (tropics and Northern Hemisphere polar regions). The largest change is seen in the tropics, where a reduction of around 9 percentage points in CISS frequency by the end of the century is driven by the strong warming of the upper troposphere. In the Northern Hemisphere mid-latitudes the multi-model-mean change is an increase in CISS frequency of 1 percentage point; however the sign of the change is dependent not only on the model but also on latitude and season. In the Northern Hemisphere polar regions there is an increase in CISS frequency of 5 percentage points in the annual mean. These results suggest that, over the 21st century, climate change may have large impacts on the potential for contrail formation; actual changes to contrail cover will also depend on changes to the volume of air traffic, aircraft technology and flight routing.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 05, 2015, 06:31:29 PM
The linked reference (with an open access preprint) provides a discussion of a new framework for understanding climate sensitivity using adjustments that are responses to forcings that are not controlled by global mean warming.  This new approach offers the promise of reducing some of the uncertainties associated with the range of climate sensitivity and is particularly well suited for clarifying the uncertainties associated with aerosols:

Sherwood, S. C., S. Bony, O. Boucher, C. Bretherton, P. M. Forster, J. M. Gregory and B. Stevens, (2014), "Adjustments in the forcing-feedback framework for understanding climate change", Bull. Amer. Meteorol. Soc., doi: http://dx.doi.org/10.1175/BAMS-D-13-00167.1 (http://dx.doi.org/10.1175/BAMS-D-13-00167.1)


http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-13-00167.1 (http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-13-00167.1)

For an open access pre-print:

http://web.science.unsw.edu.au/~stevensherwood/forcefeed_v2.2.1.pdf (http://web.science.unsw.edu.au/~stevensherwood/forcefeed_v2.2.1.pdf)

Abstract: "The traditional forcing-feedback framework has provided an indispensable basis for discussing global climate changes. However, as analysis of model behavior has become more detailed, shortcomings and ambiguities in the framework have become more evident and physical effects unaccounted for by the traditional framework have become interesting. In particular, the new concept of adjustments, which are responses to forcings that are not mediated by the global mean temperature, has emerged. This concept, related to the older ones of climate efficacy and stratospheric adjustment, is a more physical way of capturing unique responses to specific forcings. We present a pedagogical review of the adjustment concept, why it is important, and how it can be used. The concept is particularly useful for aerosols, where it helps to organize what has become a complex array of forcing mechanisms.  It also helps clarify issues around cloud and hydrological response, transient vs. equilibrium climate change, and geoengineering."

Hopefully in AR6 the IPCC will include some of Sherwood et al 2014's thinking about adjustments to the forcing-feedback framework.  In this regards I make the following comments:

1.  The current anthropogenic aerosol allowances within the RCP scenario are dependent on the amount of economic activity assumed within the scenario.  Thus RCP 8.5 has a large amount of negative feedback from large anthropogenic aerosols.  As we now know that at least China will make a dramatic effort to cut aerosol emissions while maintaining a relatively high consumption-driven economic level; hopefully the IPCC will break-out the anthropogenic aerosol forcing component to allow scientists to reduce these large negative feedbacks from their forcing models; and,

2. Ocean acidification can act as a positive feedback by encouraging the reproduction of smaller plankton that do not sink down to remove carbon from the atmospheric cycle, and at high levels can kill many types of plankton.  Furthermore, nanoplankton (& dead plankton) produce less dimethyl sulfide, DSM, which is a natural aerosol that acts as a negative forcing agent.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 05, 2015, 06:39:34 PM
The linked reference provides evidence that aerosols have recently played a large role in masking Arctic Amplification, thus as China cleans-up its aerosol emissions, we can expect Arctic Amplification to accelerate:

Mohammad Reza Najafi, Francis W. Zwiers and Nathan P. Gillett (February 2015), "Attribution of Arctic temperature change to greenhouse-gas and aerosol influences", Nature Climate Change, DOI:10.1038/NCLIMATE2524

http://www.nature.com/nclimate/journal/v5/n3/full/nclimate2524.html (http://www.nature.com/nclimate/journal/v5/n3/full/nclimate2524.html)

Abstract: "The Arctic has warmed significantly more than global mean surface air temperature over recent decades, as expected from amplification mechanisms. Previous studies have attributed the observed Arctic warming to the combined effect of greenhouse gases and other anthropogenic influences4. However, given the sensitivity of the Arctic to external forcing and the intense interest in the effects of aerosols on its climate, it is important to examine and quantify the effects of individual groups of anthropogenic forcing agents. Here we quantify the separate contributions to observed Arctic land temperature change from greenhouse gases, other anthropogenic forcing agents (which are dominated by aerosols) and natural forcing agents. We show that although increases in greenhouse-gas concentrations have driven the observed warming over the past century, approximately 60% of the greenhouse-gas-induced warming has been offset by the combined response to other anthropogenic forcings, which is substantially greater than the fraction of global greenhouse-gas-induced warming that has been offset by these forcings. The climate models considered on average simulate the amplitude of response to anthropogenic forcings well, increasing confidence in their projections of profound future Arctic climate change."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 06, 2015, 09:05:34 PM
The Sherwood (2015) presentation focuses on the influence of aerosols on the radiative forcing over the Southern Ocean, which were not previously recognized.
Steven Sherwood (2015) "Radiosonde trends and a (perhaps) unexpected aerosol forcing mechanism", Ringberg workshop:

http://www.mpimet.mpg.de/fileadmin/atmosphaere/WCRP_Grand_Challenge_Workshop/Ringberg_2015/Talks/Sherwood_24032015.pdf (http://www.mpimet.mpg.de/fileadmin/atmosphaere/WCRP_Grand_Challenge_Workshop/Ringberg_2015/Talks/Sherwood_24032015.pdf)


The first image shows that the cloud cover over the Southern Ocean is particularly susceptible to sulfate-induced changes in cloud radiative effect from a doubling of CO₂.
The second image shows a 7%/decade increase in Southern Ocean cloud condensation nuclei (CNN) from 1990 to 2005.
The third image shows observed data from the Southern Ocean comparing aerosol optical depth, AOD, to rainfall rates, cloud top pressure, cloud top temperature and cloud fraction and concludes that at low values of CNN that cloud fraction is proportional to CCN.
The fourth image summarizes Shewood Ringberg (2015) findings that since 1979 the Southern Ocean cloud fraction has increased by 10% per decade largely due to an increase in wind strength associated with the ozone hole over Antarctic; which has resulted in a zonal mean trend decrease of annual mean reflected shortwave forcing of about 1 W/m² per decade.

Extract:
"- We should not assume aerosol effects can only be in the northern hemisphere.
- Possible that greenhouse forcing in SH-extratropics has been negated by aerosol (or sea-ice) increases for some time. Deserves further attention?
- Would help to explain both (a) sluggish recent warming and (b) weird SH-NH contrast since 1979.
- Ozone depletion is the most likely culprit for the wind increase—would make this a rapid adjustment to ozone forcing."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 07, 2015, 12:03:57 AM
This post is a follow-up to my last post about Sherwood Ringberg (2015) findings about aerosols and the Southern Ocean.  McCoy et al. (2015) found that seasonal variations in plankton emitted dimethyl sulfide result in an estimated increase the local summertime mean reflected solar radiation in excess of 10 W m–2 over parts of the Southern Ocean, which is comparable to the annual mean increases expected from anthropogenic aerosols over heavily polluted regions of the Northern Hemisphere.  If future dimethyl sulfide emissions decrease say due to ocean acidification and/or a decrease in the size of Southern Ocean plankton due to ocean warming and/or freshening, then global warming would accelerate faster than currently expected:


Daniel T. McCoy, Susannah M. Burrows, Robert Wood, Daniel P. Grosvenor, Scott M. Elliott, Po-Lun Ma, Phillip J. Rasch and Dennis L. Hartmann (17 Jul 2015), "Natural aerosols explain seasonal and spatial patterns of Southern Ocean cloud albedo", Science Advances, Vol. 1, no. 6, e1500157, DOI: 10.1126/sciadv.1500157


http://advances.sciencemag.org/content/1/6/e1500157 (http://advances.sciencemag.org/content/1/6/e1500157)


Abstract: "Atmospheric aerosols, suspended solid and liquid particles, act as nucleation sites for cloud drop formation, affecting clouds and cloud properties—ultimately influencing the cloud dynamics, lifetime, water path, and areal extent that determine the reflectivity (albedo) of clouds. The concentration Nd of droplets in clouds that influences planetary albedo is sensitive to the availability of aerosol particles on which the droplets form. Natural aerosol concentrations affect not only cloud properties themselves but also modulate the sensitivity of clouds to changes in anthropogenic aerosols. It is shown that modeled natural aerosols, principally marine biogenic primary and secondary aerosol sources, explain more than half of the spatiotemporal variability in satellite-observed Nd. Enhanced Nd is spatially correlated with regions of high chlorophyll a, and the spatiotemporal variability in Nd is found to be driven primarily by high concentrations of sulfate aerosol at lower Southern Ocean latitudes (35o to 45oS) and by organic matter in sea spray aerosol at higher latitudes (45o to 55oS). Biogenic sources are estimated to increase the summertime mean reflected solar radiation in excess of 10 W m–2 over parts of the Southern Ocean, which is comparable to the annual mean increases expected from anthropogenic aerosols over heavily polluted regions of the Northern Hemisphere."


See also:

http://www.livescience.com/51598-marine-aerosols-clouds-climate-change.html (http://www.livescience.com/51598-marine-aerosols-clouds-climate-change.html)

Extract: "Since the aerosols are difficult to distinguish when viewed from space, the researchers used models that tracked the compound dimethyl sulfide, which is released by phytoplankton and turns into a sulfate aerosol in the atmosphere. They also designed a model that included simulations of the process by which salty water known as "sea spray" is enriched with organic matter produced by phytoplankton (essentially, phytoplankton poop).
Not all aerosols attract water droplets, said Susannah Burrows, the other lead author of the study and a climate scientist at the Department of Energy's Pacific Northwest National Laboratory. Although most aerosols are carried up by the same atmospheric circulation patterns, their chemical and physical properties determine whether or not they become "cloud condensation nuclei," which are the points around which droplets form before they become cloud droplets.
Smaller aerosols may have a harder time attracting water droplets than do larger ones, Burrows said. Solubility also plays a role in determining how easily the aerosol will take up water vapor from the atmosphere. Sea salt is very soluble and "likes to suck up water vapor from the atmosphere, so organic particles are less effective cloud-condensation nuclei than salt," Burrows told Live Science.
The researchers found that they could predict the observed concentration of cloud droplets with their model. The results were "interesting in a climate sense, because the amount of sunlight that is being reflected by these clouds is to some extent determined by the number of cloud droplets," McCoy told Live Science.
The scientists calculated the amount of light reflected by the clouds and determined that "it ends up being a 60 percent increase in cloud droplets throughout the year, doubling in summer, when the phytoplankton are most active, translating to a 4-watt-per-meter-squared increase in reflected sunlight, and 10-watt-per-meter-squared increase during the summer," McCoy said."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 07, 2015, 12:11:42 AM
The following two linked references point out that forests emit large quantities of volatile organic compounds (VOCs) to the atmosphere. Their condensable oxidation products can form secondary organic aerosol, a significant and ubiquitous component of atmospheric aerosol, which is known to affect the Earth’s radiation balance by scattering solar radiation and by acting as cloud condensation nuclei, and thus act as a negative feedback mechanism.

It is not pointed out in either of the two following linked references that as current estimates of "climate sensitivity" do not include this negative feedback; in order for Global Circulation Models, GCM's including this negative feedback to match historical records they will need to utilize higher effective "climate sensitivity" values; which should resulting in higher projections of global temperature increase, if plant growth/activity does not keep pace with the rate of future green house gas, GHC, emissions.

Mikael Ehn, Joel A. Thornton, Einhard Kleist, Mikko Sipilä, Heikki Junninen, Iida Pullinen, Monika Springer, Florian Rubach, Ralf Tillmann, Ben Lee, Felipe Lopez-Hilfiker, Stefanie Andres, Ismail-Hakki Acir, Matti Rissanen, Tuija Jokinen, Siegfried Schobesberger, Juha Kangasluoma, Jenni Kontkanen, Tuomo Nieminen, Theo Kurtén, Lasse B. Nielsen, Solvejg Jørgensen, Henrik G. Kjaergaard, Manjula Canagaratna, Miikka Dal Maso et al (2014), " A large source of low-volatility secondary organic aerosol", Nature, 506, 476–479, doi:10.1038/nature13032


http://www.nature.com/nature/journal/v506/n7489/full/nature13032.html (http://www.nature.com/nature/journal/v506/n7489/full/nature13032.html)

Also, see:
http://www.bbc.com/news/science-environment-26340038 (http://www.bbc.com/news/science-environment-26340038)


Abstract: "Forests emit large quantities of volatile organic compounds (VOCs) to the atmosphere. Their condensable oxidation products can form secondary organic aerosol, a significant and ubiquitous component of atmospheric aerosol, which is known to affect the Earth’s radiation balance by scattering solar radiation and by acting as cloud condensation nuclei. The quantitative assessment of such climate effects remains hampered by a number of factors, including an incomplete understanding of how biogenic VOCs contribute to the formation of atmospheric secondary organic aerosol. The growth of newly formed particles from sizes of less than three nanometres up to the sizes of cloud condensation nuclei (about one hundred nanometres) in many continental ecosystems requires abundant, essentially non-volatile organic vapours, but the sources and compositions of such vapours remain unknown. Here we investigate the oxidation of VOCs, in particular the terpene α-pinene, under atmospherically relevant conditions in chamber experiments. We find that a direct pathway leads from several biogenic VOCs, such as monoterpenes, to the formation of large amounts of extremely low-volatility vapours. These vapours form at significant mass yield in the gas phase and condense irreversibly onto aerosol surfaces to produce secondary organic aerosol, helping to explain the discrepancy between the observed atmospheric burden of secondary organic aerosol and that reported by many model studies. We further demonstrate how these low-volatility vapours can enhance, or even dominate, the formation and growth of aerosol particles over forested regions, providing a missing link between biogenic VOCs and their conversion to aerosol particles. Our findings could help to improve assessments of biosphere–aerosol–climate feedback mechanisms, and the air quality and climate effects of biogenic emissions generally."

Also, see the link to the following related reference:

Paasonen, P., et. al. (2013), "Evidence for negative climate feedback: warming increases aerosol number concentrations,", Nature Geoscience, 6, Pages: 438–442, doi: 10.1038/NGEO1800

http://www.nature.com/ngeo/journal/v6/n6/full/ngeo1800.html (http://www.nature.com/ngeo/journal/v6/n6/full/ngeo1800.html)
Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 07, 2015, 12:17:43 AM
This post is a follow-up to my last two posts about how organic emissions from both forests, and from plankton in the Southern Ocean, are currently masking the climate sensitivity to GHG emissions.  The following linked reference cites new evidence that many trees also emit extremely low volatility organic compounds (ELVOC); which are suggested to promote aerosol particle formation and cloud condensation nuclei (CCN) production in the atmosphere, that are also currently masking the true magnitude of Equilibrium Climate Sensitivity, ECS, considering that forests are projected to decline rapidly with continued global warming:


Tuija Jokinen, Torsten Berndt, Risto Makkonen, Veli-Matti Kerminen, Heikki Junninen, Pauli Paasonen, Frank Stratmann, Hartmut Herrmann, Alex B. Guenther, Douglas R. Worsnop, Markku Kulmala, Mikael Ehn, and Mikko Sipilä (June 9, 2015), "Production of extremely low-volatile organic compounds from biogenic emissions: measured yields and atmospheric implications", PNAS, vol. 112 no. 23 7123-7128, doi: 10.1073/pnas.1423977112


http://www.pnas.org/content/112/23/7123 (http://www.pnas.org/content/112/23/7123)

Significance: "Extremely low volatility organic compounds (ELVOC) are suggested to promote aerosol particle formation and cloud condensation nuclei (CCN) production in the atmosphere. We show that the capability of biogenic VOC (BVOC) to produce ELVOC depends strongly on their chemical structure and relative oxidant levels. BVOC with an endocyclic double bond, representative emissions from, e.g., boreal forests, efficiently produce ELVOC from ozonolysis. Compounds with exocyclic double bonds or acyclic compounds including isoprene, emission representative of the tropics, produce minor quantities of ELVOC, and the role of OH radical oxidation is relatively larger. Implementing these findings into a global modeling framework shows that detailed assessment of ELVOC production pathways is crucial for understanding biogenic secondary organic aerosol and atmospheric CCN formation."

Abstract: "Oxidation products of monoterpenes and isoprene have a major influence on the global secondary organic aerosol (SOA) burden and the production of atmospheric nanoparticles and cloud condensation nuclei (CCN). Here, we investigate the formation of extremely low volatility organic compounds (ELVOC) from O3 and OH radical oxidation of several monoterpenes and isoprene in a series of laboratory experiments. We show that ELVOC from all precursors are formed within the first minute after the initial attack of an oxidant. We demonstrate that under atmospherically relevant concentrations, species with an endocyclic double bond efficiently produce ELVOC from ozonolysis, whereas the yields from OH radical-initiated reactions are smaller. If the double bond is exocyclic or the compound itself is acyclic, ozonolysis produces less ELVOC and the role of the OH radical-initiated ELVOC formation is increased. Isoprene oxidation produces marginal quantities of ELVOC regardless of the oxidant. Implementing our laboratory findings into a global modeling framework shows that biogenic SOA formation in general, and ELVOC in particular, play crucial roles in atmospheric CCN production. Monoterpene oxidation products enhance atmospheric new particle formation and growth in most continental regions, thereby increasing CCN concentrations, especially at high values of cloud supersaturation. Isoprene-derived SOA tends to suppress atmospheric new particle formation, yet it assists the growth of sub-CCN-size primary particles to CCN. Taking into account compound specific monoterpene emissions has a moderate effect on the modeled global CCN budget."

Also see:
http://www.science20.com/news_articles/lowvolatility_organic_compounds_how_forests_can_effect_clouds_and_climate-155798 (http://www.science20.com/news_articles/lowvolatility_organic_compounds_how_forests_can_effect_clouds_and_climate-155798)

Extract: "According to a new global-scale projection, terrestrial vegetation emits several million tons of extremely low-volatility organic compounds (ELVOCs) per year to the atmosphere, which affect cloud seeds via formation of low-volatility vapors. These oxidation products of compounds such as monoterpenes results in an increase of condensing vapors that can further form cloud condensation nuclei over the continents and have an influence on the formation of clouds.

The results show how a number of natural compounds, which together account for around 70 percent of the biological hydrocarbon emissions, produce low-volatility products and how they can possibly effect the climate via aerosol particles.

Aerosol particles act as cloud droplets and thus reflect solar radiation back to space cooling down the planet. They play a crucial role in cloud formation and therefore also affect rainfall, cloud cover and climate in general. The tiny aerosol particles can originate dust, pollen or sea spray, and are emitted straight into the atmosphere or they can be formed from precursor gases. This gas-to-particle conversion is a complicated process and some parts of its first steps still remain unsolved by scientist.
This includes the role of oxidized volatile organic compounds, such as limonene and alpha-pinene, the typical scents of the citrus fruits and coniferous forests, in aerosol formation.

These compounds are first emitted by plants into the atmosphere and then oxidized by common oxidants, ozone or the OH-radicals. Whether these reactions produce condensing vapors that can condense onto the smallest particles or even molecules can have strong impacts on aerosol formation. As long as these processes are poorly understood, it is difficult to give accurate predictions of the future climate by modern climate models.

The discovery of the extremely low-volatility organic compounds (ELVOCs) was published last year in Nature, which observed highly oxygenated organics or ELVOC's that can explain the contribution of organic compounds in aerosol formation. The other discovery was made by the Leipzig-Helsinki team who found the mechanism leading to the rapid formation of these oxidized organic compounds. Auto-oxidation, which can spoil plastics or food, also plays an important role in the atmospheric aerosol formation. In the new paper, the team outlines how different biogenic compounds produce ELVOC's and how relevant these compounds are for the atmospheric processes. For the first time they could estimate the global effects of ELVOC in cloud condensation nuclei production.

In order to investigate the formation of the extremely low-volatility organic compounds the team has studied five abundant biogenic organic compounds with different chemical structures. The compounds all reacted with ozone and OH-radicals producing ELVOC. They found that the ELVOC formation happens very fast and that the chemical structure of the precursor gases determines how effectively they form ELVOC's.
"The structure of biogenic compounds that are emitted into the atmosphere influences how they are oxidized in the air and if they produce vapours that can condensate," says lead author Tuija Jokinen of the University of Helsinki, who carried out these studies in Leipzig at TROPOS. In the experiments, five biogenic organic gases (limonene, α-pinene, β-pinene, myrcene and isoprene) were passed through the laminar flow tube and then examined by a CI-APi-TOF mass spectrometer. "Our results show that the ozonolysis of monoterpenes like α-pinene or limonene leads to a greater efficiency of ELVOC production than a well-known oxidation via OH-radicals. On the other hand, β-pinene, myrcene and isoprene, produce much less ELVOC's, which are an important biogenic sources for the formation of particles in the atmosphere," emphasizes Dr. Torsten Berndt of TROPOS, who was involved in all three publications.

The results from the experiments were incorporated into a global atmospheric model to assess the impact of ELVOC on the particle formation and growth in the atmosphere. The international team used ECHAM5-HAM, an aerosol climate model, which was originally developed at the Max Planck Institute for Meteorology in Hamburg. According to the researchers, the extended model in the study is the first global aerosol model that combines the formation processes of secondary organic aerosol (SOA) with the ELVOC production from experiments."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 07, 2015, 12:27:52 AM
The linked reference highlights one aspect of the complex influence of aerosols on climate sensitivity (in addition to my prior posts about: contrails, VOCs, SOAs, DSM, ELVOCs, Arctic Amplification, etc.; via their influence on warm convective clouds.  This research indicates that depending on aerosol concentrations they can either interact with warm convective clouds to result in either positive, or negative, feedback.  It is important that new state-of-the-art climate models like ACME, incorporate such findings in their forthcoming climate projections.

G. Dagan, I. Koren, and O. Altaratz (2015), "Competition between core and periphery-based processes in warm convective clouds – from invigoration to suppression", Atmos. Chem. Phys., 15, 2749–2760, doi:10.5194/acp-15-2749-2015

http://www.atmos-chem-phys.net/15/2749/2015/acp-15-2749-2015.pdf (http://www.atmos-chem-phys.net/15/2749/2015/acp-15-2749-2015.pdf)

Abstract. How do changes in the amount and properties of aerosol affect warm clouds? Recent studies suggest that they have opposing effects. Some suggest that an increase in aerosol loading leads to enhanced evaporation and therefore smaller clouds, whereas other studies suggest clouds’ invigoration.  In this study, using an axisymmetric bin-microphysics cloud model, we propose a theoretical scheme that analyzes the evolution of key processes in warm clouds, under different aerosol loading and environmental conditions, to explain this contradiction.
Such an analysis of the key processes reveals a robust reversal in the trend of the clouds’ response to an increase in aerosol loading. When aerosol conditions are shifted from superpristine to slightly polluted, the clouds formed are deeper and have larger water mass. Such a trend continues up to an optimal concentration (Nop) that allows the cloud to achieve a maximal water mass. Hence, for any concentration below Nop the cloud formed contains less mass and therefore can be considered as aerosol-limited, whereas for concentrations greater than Nop cloud periphery processes, such as enhanced entrainment and evaporation, take over leading to cloud suppression. We show that Nop is a function of the thermodynamic conditions (temperature and humidity profiles).  Thus, profiles that favor deeper clouds would dictate larger values of Nop, whereas for profiles of shallow convective clouds, Nop corresponds to the pristine range of the aerosol loading.  Such a view of a trend reversal, marked by the optimal concentration, Nop, helps one to bridge the gap between the contradictory results of numerical models and observations.  Satellite studies are biased in favor of larger clouds that are characterized by larger Nop values and therefore invigoration is observed. On the other hand, modeling studies of cloud fields are biased in favor of small, mostly trade-like convective clouds, which are characterized by low Nop values (in the pristine range) and, therefore, cloud suppression is mostly reported as a response to an increase in aerosol loading."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 07, 2015, 12:40:22 AM
The linked reference indicates that not only can aerosol have complex effects on climate globally, they can also have pronounced local effects:

Jiwen Fan, Daniel Rosenfeld, Yan Yang, Chun Zhao, L. Ruby Leung and Zhanqing Li (July 2015), "Substantial contribution of anthropogenic air pollution to catastrophic floods in Southwest China", Geophysical Research Letters, DOI: 10.1002/2015GL064479


http://onlinelibrary.wiley.com/doi/10.1002/2015GL064479/full (http://onlinelibrary.wiley.com/doi/10.1002/2015GL064479/full)


Abstract: "Extreme weather events have become more frequent and are likely linked to increases in greenhouse gases and aerosols, which alter the Earth's radiative balance and cloud processes. On 8–9 July 2013, a catastrophic flood devastated the mountainous area to the northwest of the Sichuan Basin. Atmospheric simulations at a convection-permitting scale with aerosols and chemistry included show that heavy air pollution trapped in the basin significantly enhances the rainfall intensity over the mountainous areas through “aerosol-enhanced conditional instability.” That is, aerosols suppress convection by absorbing solar radiation and increasing atmospheric stability in the basin during daytime. This allows excess moist air to be transported to the mountainous areas and orographically lifted, generating strong convection and extremely heavy precipitation at night. We show that reducing pollution in the Sichuan Basin can effectively mitigate floods. It is suggested that coupling aerosol with meteorology can be crucial to improve weather forecast in polluted regions."


See also:

http://news.sciencemag.org/asiapacific/2015/07/catastrophic-chinese-floods-triggered-air-pollution (http://news.sciencemag.org/asiapacific/2015/07/catastrophic-chinese-floods-triggered-air-pollution)

Extract: "Air pollution can affect precipitation in many ways. Sometimes, the aerosol particles in smoke can reduce or delay rain. Sometimes, they can make thunderstorms more intense. Their best understood interaction is in changing how water vapor condenses to form droplets in clouds. But Fan and her team have proposed a first: that pollution also changes some air circulation patterns that lead to rainclouds.
In the case of the Sichuan storms, they write in a paper published online before print in Geophysical Research Letters, soot in particular contributed to the catastrophic flooding. It prevented rainclouds from forming over the basin during the day, leading to more intense rainfall in the mountains that evening. “We were amazed at the scale of the effect the pollution had,” Fan says. “Effectively it redistributed the precipitation from the wide area of the basin into the mountains.”"

Title: Re: The Science of Aerosols
Post by: jai mitchell on September 07, 2015, 07:42:28 PM
Fantastic work ASLR!  THANKS!
 ;D
Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 08, 2015, 03:39:16 AM
Fantastic work ASLR!  THANKS!
 ;D
Feel free to jump, the water is fine!  :)
Title: Re: The Science of Aerosols
Post by: jai mitchell on September 08, 2015, 09:14:58 PM
The linked reference provides a series of potential model runs of future aerosol emission reduction due to current legislative practice (minimum values) and technical feasible potential (maximum).  It shows that the potential for aerosol reductions from fossil fuel conversions to clean energy will potentially provide as much additional radiative forcing as is currently being experienced by the earth on a globally averaged scale.

it should be noted that this is a direct impact of aerosols only which will also produce significant warming and the water vapor and lapse rate feedbacks will reach a maximum potential after 10 years post emission reductions.  This additional feedback will be significant, possibly doubling or tripling the resultant forcing values.

http://www.atmos-chem-phys.net/15/5501/2015/acp-15-5501-2015.html (http://www.atmos-chem-phys.net/15/5501/2015/acp-15-5501-2015.html)

Atmos. Chem. Phys., 15, 5501-5519, 2015
www.atmos-chem-phys.net/15/5501/2015/ (http://www.atmos-chem-phys.net/15/5501/2015/)
doi:10.5194/acp-15-5501-2015

J.-P. Pietikäinen1, K. Kupiainen2,3, Z. Klimont2, R. Makkonen4, H. Korhonen1, R. Karinkanta1, A.-P. Hyvärinen1, N. Karvosenoja3, A. Laaksonen1, H. Lihavainen1, and V.-M. Kerminen4
1Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
2International Institute for Applied Systems Analysis, Schlossplatz 1, 2361 Laxenburg, Austria
3Finnish Environment Institute SYKE, P.O. Box 140, 00251 Helsinki, Finland
4Department of Physics, University of Helsinki, P.O. Box 44, 00014 Helsinki, Finland

Abstract. The global aerosol–climate model ECHAM-HAMMOZ was used to investigate changes in the aerosol burden and aerosol radiative effects in the coming decades. Four different emissions scenarios were applied for 2030 (two of them applied also for 2020) and the results were compared against the reference year 2005. Two of the scenarios are based on current legislation reductions: one shows the maximum potential of reductions that can be achieved by technical measures, and the other is targeted to short-lived climate forcers (SLCFs). We have analyzed the results in terms of global means and additionally focused on eight subregions. Based on our results, aerosol burdens show an overall decreasing trend as they basically follow the changes in primary and precursor emissions. However, in some locations, such as India, the burdens could increase significantly. The declining emissions have an impact on the clear-sky direct aerosol effect (DRE), i.e. the cooling effect. The DRE could decrease globally 0.06–0.4 W m−2 by 2030 with some regional increases, for example, over India (up to 0.84 W m−2). The global changes in the DRE depend on the scenario and are smallest in the targeted SLCF simulation. The aerosol indirect radiative effect could decline 0.25–0.82 W m−2 by 2030. This decrease takes place mostly over the oceans, whereas the DRE changes are greatest over the continents. Our results show that targeted emission reduction measures can be a much better choice for the climate than overall high reductions globally. Our simulations also suggest that more than half of the near-future forcing change is due to the radiative effects associated with aerosol–cloud interactions.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 08, 2015, 11:59:44 PM
Nice reference jai.

The following is a listing of some recent papers from the Center for Aerosol Impacts on Climate and the Environment

Microbial Control of Sea Spray Aerosol Composition: A Tale of Two Blooms
Xiaofei Wang, Camille M. Sultana, Jonathan Trueblood, Thomas C.J. Hill, Francesca Malfatti, Christopher Lee, Olga Laskina, Kathryn A. Moore, Charlotte M. Beall, Christina S. McCluskey, Gavin C. Cornwell, Yanyan Zhou, Joshua L. Cox, Matthew A. Pendergraft, Mitchell V. Santander, Timothy H. Bertram, Christopher D. Cappa, Farooq Azam, Paul J. DeMott, Vicki H. Grassian, Kimberly A. Prather, ACS Cent. Sci., 1(3), 124-131, 2015.

Chemistry’s Contributions to Our Understanding of Atmospheric Science and Climate
Vicki H. Grassian and Elizabeth A. Stone, J. Chem. Educ., 92(4), 595-597, 2015.

Chemistry and Related Properties of Freshly Emitted Sea Spray Aerosol
Patricia K. Quinn, Douglas B. Collins, Vicki H. Grassian, Kimberly A. Prather, Timothy S. Bates, Chem. Rev., 115(10), 4383-4399, 2015.

Atmospheric Processes and Their Controlling Influence on Cloud Condensation Nuclei Activity
Delphine K. Farmer, Christopher D. Cappa, Sonia M. Kreidenweis, Chem. Rev., 115(10), 4199-4217, 2015.

Humidity-Dependent Surface Tension Measurements of Individual Inorganic and Organic Submicrometre Liquid Particles
Holly Morris, Vicki H. Grassian, Alexei V. Tivanski, Chem. Sci., 6, 3242-3247, 2015


See also:
http://caice.ucsd.edu/ (http://caice.ucsd.edu/)
Title: Re: The Science of Aerosols
Post by: jai mitchell on September 11, 2015, 11:53:51 PM
Does anyone really know the impacts of aerosol emission reductions on future warming?


Has there been attempts to model lapse rate and associated water vapor feedback responses subsequent to a "negative pulse" of  anthropogenic aerosols?  To my knowledge these feedbacks are not considered in the calculation of aerosol negative forcings.  There are indications that aerosols have a significant effect on lapse rate due to the inherent cooling that is targeted to the upper troposphere. see: "Global indirect aerosol effects: a review", U. Lohhmann (2005)  This indicates that the lapse rate and water vapor feedbacks from aerosol reductions would be more that the response for an identical Carbon Dioxide pulse.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 12, 2015, 01:16:52 AM
The linked reference discusses the calibration of the CSW _v2.0 algorithm to account for temperature lapse rate due to water vapor & aerosol effects:

A-Ra Cho, Youn-Young Choi and Myoung-Seok Suh (2015), "Improvements of a COMS Land Surface Temperature Retrieval Algorithm Based on the Temperature Lapse Rate and Water Vapor/Aerosol Effect", Remote Sens., 7(2), 1777-1797; doi:10.3390/rs70201777

http://www.mdpi.com/2072-4292/7/2/1777 (http://www.mdpi.com/2072-4292/7/2/1777)

Abstract: "The National Meteorological Satellite Center in Korea retrieves land surface temperature (LST) by applying the split-window LST algorithm (CSW_v1.0) to Communication, Ocean, and Meteorological Satellite (COMS) data. Considerable errors were detected under conditions of high water vapor content or temperature lapse rates during validation with Moderate Resolution Imaging Spectroradiometer (MODIS) LST because of the too simplified LST algorithm. In this study, six types of LST retrieval equations (CSW_v2.0) were developed to upgrade the CSW_v1.0. These methods were developed by classifying “dry,” “normal,” and “wet” cases for day and night and considering the relative sizes of brightness temperature difference (BTD) values. Similar to CSW_v1.0, the LST retrieved by CSW_v2.0 had a correlation coefficient of 0.99 with the prescribed LST and a slightly larger bias of −0.03 K from 0.00K; the root mean square error (RMSE) improved from 1.41 K to 1.39 K. In general, CSW_v2.0 improved the retrieval accuracy compared to CSW_v1.0, especially when the lapse rate was high (mid-day and dawn) and the water vapor content was high. The spatial distributions of LST retrieved by CSW_v2.0 were found to be similar to the MODIS LST independently of the season, day/night, and geographic locations. The validation using one year’s MODIS LST data showed that CSW_v2.0 improved the retrieval accuracy of LST in terms of correlations (from 0.988 to 0.989), bias (from −1.009 K to 0.292 K), and RMSEs (from 2.613 K to 2.237 K)."
Title: Re: The Science of Aerosols
Post by: jai mitchell on September 12, 2015, 03:39:40 AM
Thanks ASLR

interesting but it seems that the paper addresses extreme aerosol and lapse rate conditions to increase model sensitivity but does not address specifically the interactive effects of these two, nor does it look at the expected feedback response to aerosol reductions.  Again, it seems that the lapse rate/water vapor feedbacks will be larger for aerosols than for GHGs due to the cooling effect of aerosols in the upper troposphere (allowing for a reduction in the lapse rate feedback being induced by greenhouse gasses.  in absence of aerosols this lapse rate effect will rebound and then warming of the biosphere will further increase these feedbacks!

I feel like the conservative scientists thread is bleeding into this one. 

These interactive effects of aerosols are not included in the CMIP5 model runs, to my knowledge.  In fact they are, as yet, relatively undefined.
Title: Re: The Science of Aerosols
Post by: jai mitchell on September 12, 2015, 07:31:59 PM
Quote
The overall effect of the aerosol forcing is a cooling near the surface in the polluted regions of the Northern Hemisphere that stabilizes the lower atmosphere whereas the near surface changes in temperature are smaller in the tropics and the mid-latitudes of the Southern Hemisphere. The implications of these aerosol induced lapse rate changes on other climate feedbacks such as the water vapor feedback are, however, not quantified yet.

http://www.atmos-chem-phys.net/5/715/2005/acp-5-715-2005.pdf (http://www.atmos-chem-phys.net/5/715/2005/acp-5-715-2005.pdf)

Global indirect aerosol effects: a review
U. Lohmann1 and J. Feichter2

Atmos. Chem. Phys., 5, 715–737, 2005
www.atmos-chem-phys.org/acp/5/715/ (http://www.atmos-chem-phys.org/acp/5/715/)
SRef-ID: 1680-7324/acp/2005-5-715
European Geosciences Union


Abstract:

Aerosols affect the climate system by changing cloud characteristics in many ways. They act as cloud condensation and ice nuclei, they may inhibit freezing and they could have an influence on the hydrological cycle. While the cloud albedo enhancement (Twomey effect) of warm clouds received most attention so far and traditionally is the only indirect aerosol forcing considered in transient climate simulations, here we discuss the multitude of effects. Different
approaches how the climatic implications of these aerosol effects can be estimated globally as well as improvements that are needed in global climate models in order to better represent
indirect aerosol effects are discussed in this paper.


Title: Re: The Science of Aerosols
Post by: jai mitchell on September 22, 2015, 09:22:19 PM
This paper shows that updated models indicate that the global impact of natural Dimethyl Sulfide emissions are underrepressented by up to 20%.

67- Quantifying the impacts of an updated global dimethyl sulfide climatology on cloud microphysics and aerosol radiative forcing

Anoop S. Mahajan, Suvarna Fadnavis, Manu A. Thomas, Luca Pozzoli, Smrati Gupta, Sarah-Jeanne Royer, Alfonso Saiz-Lopez, Rafel Simó.

J. Geophys. Res. 120, 6, 2524-2536. DOI: 10.1002/2014JD022687

http://ac2.iqfr.csic.es/es/component/content/category/images/pdf/2008/acp-8-4855-2008.pdf (http://ac2.iqfr.csic.es/es/component/content/category/images/pdf/2008/acp-8-4855-2008.pdf)

Abstract. One of the critical parameters in assessing the global impacts of dimethyl sulfide (DMS) on cloud properties and the radiation budget is the estimation of phytoplankton-induced ocean emissions, which are derived from prescribed, climatological surface seawater DMS concentrations. The most widely used global ocean DMS climatology was published 15 years ago and has recently been updated using a much larger database of observations. The updated climatology displays significant differences in terms of the global distribution and regional monthly averages of sea surface DMS. In this study, we use the ECHAM5-HAMMOZ aerosol-chemistry-climate general circulation model to quantify the influence of the updated DMS climatology in computed atmospheric properties, namely, the spatial and temporal distributions of atmospheric DMS concentration, sulfuric acid concentration, sulfate aerosols, number of activated aerosols, cloud droplet number concentration, and the aerosol radiative forcing at the top of the atmosphere. Significant differences are observed for all the modeled variables. Comparison with observations of atmospheric DMS and total sulfate also shows that in places with large DMS emissions, the updated climatology shows a better match with the observations. This highlights the importance of using the updated climatology for projecting future impacts of oceanic DMS emissions, especially considering that the relative importance of the natural sulfur fluxes is likely to increase due to legislation to “clean up” anthropogenic emissions. The largest estimated differences are in the Southern Ocean, Indian Ocean, and parts of the Pacific Ocean, where the climatologies differ in seasonal concentrations over large geographical areas. The model results also indicate that the former DMS climatology underestimated the effect of DMS on the globally averaged annual aerosol radiative forcing at the top of the atmosphere by about 20%.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 24, 2015, 01:01:52 PM
This paper shows that updated models indicate that the global impact of natural Dimethyl Sulfide emissions are underrepressented by up to 20%.

67- Quantifying the impacts of an updated global dimethyl sulfide climatology on cloud microphysics and aerosol radiative forcing

Anoop S. Mahajan, Suvarna Fadnavis, Manu A. Thomas, Luca Pozzoli, Smrati Gupta, Sarah-Jeanne Royer, Alfonso Saiz-Lopez, Rafel Simó.

J. Geophys. Res. 120, 6, 2524-2536. DOI: 10.1002/2014JD022687

http://ac2.iqfr.csic.es/es/component/content/category/images/pdf/2008/acp-8-4855-2008.pdf (http://ac2.iqfr.csic.es/es/component/content/category/images/pdf/2008/acp-8-4855-2008.pdf)

Abstract. One of the critical parameters in assessing the global impacts of dimethyl sulfide (DMS) on cloud properties and the radiation budget is the estimation of phytoplankton-induced ocean emissions, which are derived from prescribed, climatological surface seawater DMS concentrations. The most widely used global ocean DMS climatology was published 15 years ago and has recently been updated using a much larger database of observations. The updated climatology displays significant differences in terms of the global distribution and regional monthly averages of sea surface DMS. In this study, we use the ECHAM5-HAMMOZ aerosol-chemistry-climate general circulation model to quantify the influence of the updated DMS climatology in computed atmospheric properties, namely, the spatial and temporal distributions of atmospheric DMS concentration, sulfuric acid concentration, sulfate aerosols, number of activated aerosols, cloud droplet number concentration, and the aerosol radiative forcing at the top of the atmosphere. Significant differences are observed for all the modeled variables. Comparison with observations of atmospheric DMS and total sulfate also shows that in places with large DMS emissions, the updated climatology shows a better match with the observations. This highlights the importance of using the updated climatology for projecting future impacts of oceanic DMS emissions, especially considering that the relative importance of the natural sulfur fluxes is likely to increase due to legislation to “clean up” anthropogenic emissions. The largest estimated differences are in the Southern Ocean, Indian Ocean, and parts of the Pacific Ocean, where the climatologies differ in seasonal concentrations over large geographical areas. The model results also indicate that the former DMS climatology underestimated the effect of DMS on the globally averaged annual aerosol radiative forcing at the top of the atmosphere by about 20%.

This clearly raises the risk that if the ocean's plankton are disrupted (by both warming & acidification) that the effective ECS will prove to be higher than previously realized.
Title: Re: The Science of Aerosols
Post by: jai mitchell on September 24, 2015, 05:17:29 PM
In addition, boreal forest and amazon basin carbon cycle response (as well as indonesia) will further exacerbate the reduction of this potent naturally occurring aerosol in coming years.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 25, 2015, 08:26:10 PM
The linked reference shows that the errors incurred due to ignoring temporal sampling of aerosols, and show they are of similar magnitude as (but smaller than) actual model errors (20–60 %). This indicates that our ignorance about the impact of aerosols are higher than previously appreciated:

Schutgens, N. A. J., Partridge, D. G., and Stier, P. (2015), "The importance of temporal collocation for the evaluation of aerosol models with observations", Atmos. Chem. Phys. Discuss., 15, 26191-26230, doi:10.5194/acpd-15-26191-2015.

http://www.atmos-chem-phys-discuss.net/15/26191/2015/acpd-15-26191-2015.html (http://www.atmos-chem-phys-discuss.net/15/26191/2015/acpd-15-26191-2015.html)

Abstract: "It is often implicitly assumed that over suitably long periods the mean of observations and models should be comparable, even if they have different temporal sampling. We assess the errors incurred due to ignoring temporal sampling and show they are of similar magnitude as (but smaller than) actual model errors (20–60 %).

Using temporal sampling from remote sensing datasets (the satellite imager MODIS and the ground-based sun photometer network AERONET) and three different global aerosol models, we compare annual and monthly averages of full model data to sampled model data. Our results show that sampling errors as large as 100 % in AOT (Aerosol Optical Thickness), 0.4 in AE (Ångström Exponent) and 0.05 in SSA (Single Scattering Albedo) are possible. Even in daily averages, sampling errors can be significant. More-over these sampling errors are often correlated over long distances giving rise to artificial contrasts between pristine and polluted events and regions. Additionally, we provide evidence that suggests that models will underestimate these errors. To prevent sampling errors, model data should be temporally collocated to the observations before any analysis is made.

We also discuss how this work has consequences for in-situ measurements (e.g. aircraft campaigns or surface measurements) in model evaluation."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on October 05, 2015, 06:16:21 PM
The linked Carbon Brief article discusses how skeptics misinterpreted findings by Ciuraru et al. (2015) about the influence of isoprene on aerosols:

http://www.carbonbrief.org/blog/2015/10/factcheck-aerosols-research-misinterpreted/ (http://www.carbonbrief.org/blog/2015/10/factcheck-aerosols-research-misinterpreted/)

Ciuraru, R. et al. (2015) Unravelling New Processes at Interfaces: Photochemical Isoprene Production at the Sea Surface, Environmental Science & Technology, doi: 10.1021/acs.est.5b02388

Title: Re: The Science of Aerosols
Post by: AbruptSLR on October 14, 2015, 01:12:49 AM
Normally the findings of the linked reference about the negative feedback associated with biogenic secondary organic aerosol (BSOA), could be considered as good news; however, given the dire condition of the boreal forests; this research could indicate that climate sensitivity could increase faster than previously thought if the boreal forests continue to degrade rapidly:

Heikki Lihavainen, Eija Asmi, Veijo Aaltonen, Ulla Makkonen and Veli-Matti Kerminen (Published 8 October 2015), "Direct radiative feedback due to biogenic secondary organic aerosol estimated from boreal forest site observations" Environmental Research Letters, Volume 10, Number 10


http://iopscience.iop.org/article/10.1088/1748-9326/10/10/104005/meta (http://iopscience.iop.org/article/10.1088/1748-9326/10/10/104005/meta)

http://iopscience.iop.org/article/10.1088/1748-9326/10/10/104005/pdf (http://iopscience.iop.org/article/10.1088/1748-9326/10/10/104005/pdf)

Abstract: "We used more than five years of continuous aerosol measurements to estimate the direct radiative feedback parameter associated with the formation of biogenic secondary organic aerosol (BSOA) at a remote continental site at the edge of the boreal forest zone in Northern Finland. Our upper-limit estimate for this feedback parameter during the summer period (ambient temperatures above 10 °C) was −97 ± 66 mW m−2 K−1 (mean ± STD) when using measurements of the aerosol optical depth (fAOD) and −63 ± 40 mW m−2 K−1 when using measurements of the 'dry' aerosol scattering coefficient at the ground level (fσ). Here STD represents the variability in f caused by the observed variability in the quantities used to derive the value of f. Compared with our measurement site, the magnitude of the direct radiative feedback associated with BSOA is expected to be larger in warmer continental regions with more abundant biogenic emissions, and even larger in regions where biogenic emissions are mixed with anthropogenic pollution."
Title: Re: The Science of Aerosols
Post by: jai mitchell on October 16, 2015, 03:05:24 AM
This work on boreal forest aerosols has significant impact on paleoclimate modeling, as the boreal forest network during the eemian maximum was approximately 300% of the current value.  It is clear that the aerosol uncertainty will produce another revision to the paleocolimate estimate of ECS. (higher)
Title: Re: The Science of Aerosols
Post by: AbruptSLR on October 16, 2015, 06:58:11 PM
The linked reference cites new research regarding condensation particle (CP) concentrations at the coastal Neumayer Antarctic station, which is associated with cloud cover formation.  The AR5 model projections have particularly poor skill levels with regards to projecting Antarctic cloud formation, and reading between the lines, this research supports the idea that DSM is important w.r.t. Antarctic cloud formation, as the other CP concentrations appear to be insufficient to account for the discrepancy between model projections & observations:

Weller, R., Schmidt, K., Teinilä, K., and Hillamo, R.: Natural new particle formation at the coastal Antarctic site Neumayer, Atmos. Chem. Phys., 15, 11399-11410, doi:10.5194/acp-15-11399-2015, 2015.

http://www.atmos-chem-phys.net/15/11399/2015/acp-15-11399-2015.html (http://www.atmos-chem-phys.net/15/11399/2015/acp-15-11399-2015.html)

Abstract. We measured condensation particle (CP) concentrations and particle size distributions at the coastal Antarctic station Neumayer (70°39´ S, 8°15´ W) during two summer campaigns (from 20 January to 26 March 2012 and 1 February to 30 April 2014) and during the polar night between 12 August and 27 September 2014 in the particle diameter (Dp) range from 2.94 to 60.4 nm (2012) and from 6.26 to 212.9 nm (2014). During both summer campaigns we identified all in all 44 new particle formation (NPF) events. From 10 NPF events, particle growth rates could be determined to be around 0.90 ± 0.46 nm h−1 (mean ± SD; range: 0.4–1.9 nm h−1). With the exception of one case, particle growth was generally restricted to the nucleation mode (Dp < 25 nm) and the duration of NPF events was typically around 6.0 ± 1.5 h (mean ± SD; range: 4–9 h). Thus, in the surrounding area of Neumayer, particles did not grow up to sizes required for acting as cloud condensation nuclei. NPF during summer usually occurred in the afternoon in coherence with local photochemistry. During winter, two NPF events could be detected, though showing no ascertainable particle growth. A simple estimation indicated that apart from sulfuric acid, the derived growth rates required other low volatile precursor vapours.

Title: Re: The Science of Aerosols
Post by: AbruptSLR on October 17, 2015, 08:15:39 PM
The linked reference indicates that satellite observations indicate that aerosols can darken the albedo of subtropical marine stratocumulus clouds:

Frida Bender, Anders Engström, and Johannes Karlsson (2015), "Factors controlling cloud albedo in marine subtropical stratocumulus regions in climate models and satellite observations", Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-15-0095.1 (http://dx.doi.org/10.1175/JCLI-D-15-0095.1)

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0095.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0095.1)

Abstract: "This study focuses on the radiative properties of five subtropical marine stratocumulus cloud regions, on monthly mean scale. Through examination of the relation between total albedo and cloud fraction, and its variability and relation to other parameters, some of the factors controlling the reflectivity, or albedo, of the clouds in these regions are investigated. It is found that the main part of the variability in albedo at a given cloud fraction can be related to temporal, rather than spatial variability, indicating spatial homogeneity in cloud radiative properties in the studied regions. This is seen most clearly in satellite observations, but also in an ensemble of climate models. Further comparison between satellite data and output from climate models shows that there is good agreement with respect to the role of liquid water path, the parameter that can be assumed to be the primary source of variability in cloud reflectivity for a given cloud fraction. On the other hand, the influence of aerosol loading on cloud albedo differs between models and observations. The cloud-albedo effect, or cloud brightening caused by aerosol through its coupling to cloud droplet number concentration and droplet size, is found not to dominate in the satellite observations on monthly mean scale, as it appears to do on this scale in the climate models. The disagreement between models and observations is particularly strong in regions with frequent occurrence of absorbing aerosols above clouds, where satellite data contrary to the climate models indicate a scene darkening with increasing aerosol loading."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on October 17, 2015, 08:46:51 PM
The linked reference confirms many of the warns provided by jai in this thread, i. e. that even if CoP21 reduces anthropogenic forcing down to the RCP 6.0 scenario that future aerosol mitigation efforts will likely increase Polar Amplification and will have substantial local climate effect and will promote telecommunication of energy to more remote regions (like high-latitude regions):

Clifford Chuwah, Twan van Noije, Detlef P. van Vuuren, Philippe Le Sager and Wilco Hazeleger (2015), "Global and regional climate impacts of future aerosol mitigation in an RCP6.0-like scenario in EC-Earth", Climatic Change, pp 1-14, doi:10.1007/s10584-015-1525-9


http://rd.springer.com/article/10.1007%2Fs10584-015-1525-9 (http://rd.springer.com/article/10.1007%2Fs10584-015-1525-9)


Abstract: "Future changes in aerosol concentrations will influence the climate system over the coming decades. In this study we evaluate the equilibrium climate response to aerosol reductions in different parts of the world in 2050, using the global climate model EC-Earth. The aerosol concentrations are based on a set of scenarios similar to RCP6.0, developed using the IMAGE integrated assessment model and exploring stringent and weaker air pollution control. Reductions in aerosol concentrations lead to an increase in downward surface solar radiation under all-sky conditions in various parts of the world, especially in Asia where the local brightening may reach about 10 Wm−2. The associated increase in surface temperature may be as high as 0.5 °C. This signal is dominated by the reduced cooling effect of sulphate which in some areas is partially compensated by the decreased warming effect of black carbon. According to our simulations, the mitigation of BC may lead to decreases in mean summer surface temperature of up to 1 °C in central parts of North America and up to 0.3 °C in northern India. Aerosol reductions could significantly affect the climate at high latitudes especially in the winter, where temperature increases of up to 1 °C are simulated. In the Northern Hemisphere, this strong surface temperature response might be related to changes in circulation patterns and precipitation at low latitudes, which can give rise to a wave train and induce changes in weather patterns at high latitudes. Our model does not include a parameterization of aerosol indirect effects so that responses could be stronger in reality. We conclude that different, but plausible, air pollution control policies can have substantial local climate effects and induce remote responses through dynamic teleconnections."
Title: Re: The Science of Aerosols
Post by: jai mitchell on October 18, 2015, 02:35:19 PM
Our model does not include a parameterization of aerosol indirect effects so that responses could be stronger in reality.

"could" = will

Title: Re: The Science of Aerosols
Post by: AbruptSLR on October 19, 2015, 07:08:40 PM
The linked open access reference presents field observations of secondary organic aerosols (BSOA) from a coniferous forest mountain region at Whistler, British Columbia.  This field work indicates laboratory measures of BSOA level may not adequately characterize the full extent of BSOA emissions from coniferous (boreal) forests; which indicates that true levels of BSOA may be masking the true magnitude of TCR & ECS, so that if the boreal forest degrade rapidly in the next few decades, the world could be subjected to higher climate sensitivity values than currently accounted for in climate models:

Lee, A. K. Y., Abbatt, J. P. D., Leaitch, W. R., Li, S.-M., Sjostedt, S. J., Wentzell, J. J. B., Liggio, J., and Macdonald, A. M. (2015), "Substantial secondary organic aerosol formation in a coniferous forest: observations of both day and night time chemistry", Atmos. Chem. Phys. Discuss., 15, 28005-28035, doi:10.5194/acpd-15-28005-2015.

http://www.atmos-chem-phys-discuss.net/15/28005/2015/acpd-15-28005-2015.html (http://www.atmos-chem-phys-discuss.net/15/28005/2015/acpd-15-28005-2015.html)

Abstract: "Substantial biogenic secondary organic aerosol (BSOA) formation was investigated in a coniferous forest mountain region at Whistler, British Columbia. A largely biogenic aerosol growth episode was observed, providing a unique opportunity to investigate BSOA formation chemistry in a forested environment with limited influence from anthropogenic emissions. Positive matrix factorization of aerosol mass spectrometry (AMS) measurement identified two types of BSOA (BSOA-1 and BSOA-2), which were primarily generated by gas-phase oxidation of monoterpenes and perhaps sesquiterpenes. The temporal variations of BSOA-1 and BSOA-2 can be explained by gas-particle partitioning in response to ambient temperature and the relative importance of different oxidation mechanisms between day and night. While BSOA-1 will arise from gas-phase ozonolysis and nitrate radical chemistry at night, BSOA-2 is less volatile than BSOA-1 and consists of products formed via gas-phase oxidation by the OH radical and ozone during the day. Organic nitrates produced through nitrate radical chemistry can account for 22–33 % of BSOA-1 mass at night. The mass spectra of BSOA-1 and BSOA-2 have higher values of the mass fraction of m/z 91 (f91) compared to the background organic aerosol, and so f91 is used as an indicator of BSOA formation pathways. A comparison between laboratory studies in the literature and our field observations highlights the potential importance of gas-phase formation chemistry of BSOA-2 type materials that may not be captured in smog chamber experiments, perhaps due to the wall loss of gas-phase intermediate products."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on October 23, 2015, 12:36:54 AM
The linked open access reference provides evidence that air pollution will likely extend the life of Arctic sea ice (from climate change) for about one extra decade.  On the other hand this implies that the true strength of Arctic Amplification is stronger than we are currently experiencing, which will become apparent as the air pollution is cleaned-up (furthermore this research may well err on the side of least drama):

Gagné, M.-È., N. P. Gillett, and J. C. Fyfe (2015), "Impact of aerosol emission controls on future Arctic sea ice cover", Geophys. Res. Lett., 42, doi:10.1002/2015GL065504

http://onlinelibrary.wiley.com/doi/10.1002/2015GL065504/pdf (http://onlinelibrary.wiley.com/doi/10.1002/2015GL065504/pdf)

Abstract: "We examine the response of Arctic sea ice to projected aerosol and aerosol precursor emission changes under the Representative Concentration Pathway (RCP) scenarios in simulations of the Canadian Earth System Model. The overall decrease in aerosol loading causes a warming, largest over the Arctic, which leads to an annual mean reduction in sea ice extent of approximately 1 million km2 over the 21st century in all RCP scenarios. This accounts for approximately 25% of the simulated reduction in sea ice extent in RCP 4.5, and 40% of the reduction in RCP 2.5. In RCP 4.5, the Arctic ocean is projected to become ice-free during summertime in 2045, but it does not become ice-free until 2057 in simulations with aerosol precursor emissions held fixed at 2000 values. Thus, while reductions in aerosol emissions have significant health and environmental benefits, their substantial contribution to projected Arctic climate change should not be overlooked."


See also:

http://www.climatecentral.org/news/pollution-arctic-sea-ice-19583 (http://www.climatecentral.org/news/pollution-arctic-sea-ice-19583)

Extract: "The main driver for Arctic sea ice’s disappearing act is the rising ocean and air temperatures driven by human greenhouse gas emissions. But that isn’t the only factor affecting Arctic sea ice. Air pollution also plays a role and can actually slow down warming.
In the tug of war, aerosols don’t necessarily counter the impacts of climate change on sea ice (or the planet as a whole for that matter). But new research shows that air pollution could buy the planet a decade of ice in the Arctic."
Title: Re: The Science of Aerosols
Post by: Bruce Steele on October 23, 2015, 05:15:19 AM
ASLR, Same paper covered in Scientific American. I got a little amusement with the magazine comment in parenthesis .
 " Using a middle of the road emissions scenario ( which is a little optimistic given currently pledges)
as well as rising aerosols Gillet and his team shows that the Arctic is likely to see an ice-free summer around 2057."

http://www.scientificamerican.com/article/pollution-could-buy-an-extra-decade-of-arctic-sea-ice/ (http://www.scientificamerican.com/article/pollution-could-buy-an-extra-decade-of-arctic-sea-ice/)

Title: Re: The Science of Aerosols
Post by: AbruptSLR on October 27, 2015, 04:36:42 PM
The linked research presents finding of unexpected high ultrafine aerosols concentrations above East Antarctic sea ice.  The ultrafine aerosols were found to be transported to the surface boundary layer from the free troposphere by cyclones, and that the aerosols help to explain differences between observed and simulated Southern Ocean cloud cover:

Humphries, R. S., Klekociuk, A. R., Schofield, R., Keywood, M., Ward, J., and Wilson, S. R. (2015), "Unexpectedly high ultrafine aerosol concentrations above East Antarctic sea-ice", Atmos. Chem. Phys. Discuss., 15, 29125-29170, doi:10.5194/acpd-15-29125-2015.

http://www.atmos-chem-phys-discuss.net/15/29125/2015/acpd-15-29125-2015.html (http://www.atmos-chem-phys-discuss.net/15/29125/2015/acpd-15-29125-2015.html)

Abstract. The effect of aerosols on clouds and their radiative properties is one of the largest uncertainties in our understanding of radiative forcing. A recent study has concluded that better characterisation of pristine, natural aerosol processes leads to the largest reduction in these uncertainties. Antarctica, being far from anthropogenic activities, is an ideal location for the study of natural aerosol processes. Aerosol measurements in Antarctica are often limited to boundary layer air-masses at spatially sparse coastal and continental research stations, with only a handful of studies in the sea ice region. In this paper, the first observational study of sub-micron aerosols in the East Antarctic sea ice region is presented. Measurements were conducted aboard the ice-breaker Aurora Australis in spring 2012 and found that boundary layer condensation nuclei (CN3) concentrations exhibited a five-fold increase moving across the Polar Front, with mean Polar Cell concentrations of 1130 cm−3 – higher than any observed elsewhere in the Antarctic and Southern Ocean region. The absence of evidence for aerosol growth suggested that nucleation was unlikely to be local. Air parcel trajectories indicated significant influence from the free troposphere above the Antarctic continent, implicating this as the likely nucleation region for surface aerosol, a similar conclusion to previous Antarctic aerosol studies. The highest aerosol concentrations were found to correlate with low pressure systems, suggesting that the passage of cyclones provided an accelerated pathway, delivering air-masses quickly from the free-troposphere to the surface. After descent from the Antarctic free troposphere, trajectories suggest that sea ice boundary layer air-masses travelled equator-ward into the low albedo Southern Ocean region, transporting with them emissions and these aerosol nuclei where, after growth, may potentially impact on the region's radiative balance. The high aerosol concentrations and their transport pathways described here, could help reduce the discrepancy currently present between simulations and observations of cloud and aerosol over the Southern Ocean.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on November 09, 2015, 10:43:18 PM
The linked (open access) reference provides satellite data that indicates that China's efforts to reduce sulfur dioxide emissions from its coal-fired power plants has not been as effective as previously expected, probably due to poor implementation of regulations:

Siwen Wang, Qiang Zhang, Randall V Martin, Sajeev Philip, Fei Liu, Meng Li, Xujia Jiang and Kebin He (2015), "Satellite measurements oversee China's sulfur dioxide emission reductions from coal-fired power plants", Environmental Research Letters, Volume 10, Number 11 , doi:10.1088/1748-9326/10/11/11401


http://iopscience.iop.org/article/10.1088/1748-9326/10/11/114015 (http://iopscience.iop.org/article/10.1088/1748-9326/10/11/114015)


Abstract: "To evaluate the real reductions in sulfur dioxide (SO2) emissions from coal-fired power plants in China, Ozone Monitoring Instrument (OMI) remote sensing SO2 columns were used to inversely model the SO2 emission burdens surrounding 26 isolated power plants before and after the effective operation of their flue gas desulfurization (FGD) facilities. An improved two-dimensional Gaussian fitting method was developed to estimate SO2 burdens under complex background conditions, by using the accurate local background columns and the customized fitting domains for each target source. The OMI-derived SO2 burdens before effective FGD operation were correlated well with the bottom-up emission estimates (R = 0.92), showing the reliability of the OMI-derived SO2 burdens as a linear indicator of the associated source strength. OMI observations indicated that the average lag time period between installation and effective operation of FGD facilities at these 26 power plants was around 2 years, and no FGD facilities have actually operated before the year 2008. The OMI estimated average SO2 removal equivalence (56.0%) was substantially lower than the official report (74.6%) for these 26 power plants. Therefore, it has been concluded that the real reductions of SO2 emissions in China associated with the FGD facilities at coal-fired power plants were considerably diminished in the context of the current weak supervision measures."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on November 13, 2015, 07:43:38 PM
The linked (open access) reference discusses progress in modeling aerosol-cloud interactions, and concludes that it is important to include these better characterized interactions in future climate model projections:

Gettelman, A.: Putting the clouds back in aerosol–cloud interactions, Atmos. Chem. Phys., 15, 12397-12411, doi:10.5194/acp-15-12397-2015, 2015

http://www.atmos-chem-phys.net/15/12397/2015/acp-15-12397-2015.html (http://www.atmos-chem-phys.net/15/12397/2015/acp-15-12397-2015.html)

Abstract. Aerosol–cloud interactions (ACI) are the consequence of perturbed aerosols affecting cloud drop and crystal number, with corresponding microphysical and radiative effects. ACI are sensitive to both cloud microphysical processes (the "C" in ACI) and aerosol emissions and processes (the "A" in ACI). This work highlights the importance of cloud microphysical processes, using idealized and global tests of a cloud microphysics scheme used for global climate prediction. Uncertainties in key cloud microphysical processes examined with sensitivity tests cause uncertainties of nearly −30 to +60 % in ACI, similar to or stronger than uncertainties identified due to natural aerosol emissions (−30 to +30 %). The different dimensions and sensitivities of ACI to microphysical processes identified in previous work are analyzed in detail, showing that precipitation processes are critical for understanding ACI and that uncertain cloud lifetime effects are nearly one-third of simulated ACI. Buffering of different processes is important, as is the mixed phase and coupling of the microphysics to the condensation and turbulence schemes in the model.


Extract: " The overall conclusion is that getting better a representation of ACI is critical for reducing uncertainty in anthropogenic climate forcing: cloud microphysical development needs to go hand in hand with better constraints on aerosol emissions to properly constrain ACI and total forcing."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on November 19, 2015, 11:49:37 PM
The linked (open access) reference indicates that secondary organic aerosols (SOAs) have production rates 4 times higher and sinks a factor of 3.7 more efficient than in the base model; which, corresponds to a direct radiative forcing at top of the atmosphere of: −0.35 W m−2

Hodzic, A., Kasibhatla, P. S., Jo, D. S., Cappa, C., Jimenez, J. L., Madronich, S., and Park, R. J. (2015), "Rethinking the global secondary organic aerosol (SOA) budget: stronger production, faster removal, shorter lifetime", Atmos. Chem. Phys. Discuss., 15, 32413-32468, doi:10.5194/acpd-15-32413-2015.

http://www.atmos-chem-phys-discuss.net/15/32413/2015/acpd-15-32413-2015.html (http://www.atmos-chem-phys-discuss.net/15/32413/2015/acpd-15-32413-2015.html)

Abstract: "Recent laboratory studies suggest that secondary organic aerosol (SOA) formation rates are higher than assumed in current models. There is also evidence that SOA removal by dry and wet deposition occurs more efficiently than some current models suggest, and that photolysis and heterogeneous oxidation may be important (but currently ignored) SOA sinks. Here, we have updated the global GEOS-Chem model to include this new information on formation (i.e. wall-corrected yields and emissions of semi-volatile and intermediate volatility organic compounds) and on removal processes (photolysis and heterogeneous oxidation). We compare simulated SOA from various model configurations against ground, aircraft and satellite measurements to assess the extent to which these improved representations of SOA formation and removal processes are consistent with observed characteristics of the SOA distribution. The updated model presents a more dynamic picture of the lifecycle of atmospheric SOA, with production rates 4 times higher and sinks a factor of 3.7 more efficient than in the base model. In particular, the updated model predicts larger SOA concentrations in the boundary layer and lower concentrations in the upper troposphere, leading to better agreement with surface and aircraft measurements of organic aerosol compared to the base model. Our analysis thus suggests that the long-standing discrepancy in model predictions of the vertical SOA distribution can now be resolved, at least in part, by a stronger source and stronger sinks leading to a shorter lifetime. The predicted global SOA burden in the updated model is 0.95 Tg and the corresponding direct radiative forcing at top of the atmosphere is −0.35 W m−2, which is comparable to recent model estimates constrained by observations. The updated model predicts a population-weighed global mean surface SOA concentration that is a factor of 2 higher than in the base model, suggesting the need for a reanalysis of the contribution of SOA to PM pollution-related human health effects. The potential importance of our estimates highlights the need for more extensive field and laboratory studies focused on characterizing organic aerosol removal mechanisms and rates."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on November 20, 2015, 06:26:03 PM
The linked reference confirms that current UN projections for future global warming underestimate the influence of the expected aerosol reductions anticipated in the RCP scenarios; which will require more strenuous efforts than the UN is currently contemplating if the world is to remain below the 2C "limit".

Westervelt, D. M., Horowitz, L. W., Naik, V., Golaz, J.-C., and Mauzerall, D. L. (2015), "Radiative forcing and climate response to projected 21st century aerosol decreases", Atmos. Chem. Phys., 15, 12681-12703, doi:10.5194/acp-15-12681-2015

http://www.atmos-chem-phys.net/15/12681/2015/acp-15-12681-2015.html (http://www.atmos-chem-phys.net/15/12681/2015/acp-15-12681-2015.html)

Abstract: "It is widely expected that global emissions of atmospheric aerosols and their precursors will decrease strongly throughout the remainder of the 21st century, due to emission reduction policies enacted to protect human health. For instance, global emissions of aerosols and their precursors are projected to decrease by as much as 80 % by the year 2100, according to the four Representative Concentration Pathway (RCP) scenarios. The removal of aerosols will cause unintended climate consequences, including an unmasking of global warming from long-lived greenhouse gases. We use the Geophysical Fluid Dynamics Laboratory Coupled Climate Model version 3 (GFDL CM3) to simulate future climate over the 21st century with and without the aerosol emission changes projected by each of the RCPs in order to isolate the radiative forcing and climate response resulting from the aerosol reductions. We find that the projected global radiative forcing and climate response due to aerosol decreases do not vary significantly across the four RCPs by 2100, although there is some mid-century variation, especially in cloud droplet effective radius, that closely follows the RCP emissions and energy consumption projections. Up to 1 W m−2 of radiative forcing may be unmasked globally from 2005 to 2100 due to reductions in aerosol and precursor emissions, leading to average global temperature increases up to 1 K and global precipitation rate increases up to 0.09 mm day−1. However, when using a version of CM3 with reduced present-day aerosol radiative forcing (−1.0 W m−2), the global temperature increase for RCP8.5 is about 0.5 K, with similar magnitude decreases in other climate response parameters as well. Regionally and locally, climate impacts can be much larger than the global mean, with a 2.1 K warming projected over China, Japan, and Korea due to the reduced aerosol emissions in RCP8.5, as well as nearly a 0.2 mm day−1 precipitation increase, a 7 g m−2 LWP decrease, and a 2 μm increase in cloud droplet effective radius. Future aerosol decreases could be responsible for 30–40 % of total climate warming (or 10–20 % with weaker aerosol forcing) by 2100 in East Asia, even under the high greenhouse gas emissions scenario (RCP8.5). The expected unmasking of global warming caused by aerosol reductions will require more aggressive greenhouse gas mitigation policies than anticipated in order to meet desired climate targets."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on January 23, 2016, 01:03:52 AM
I am not such that I understand the linked open access reference, that seems to indicate that anthropogenic direct aerosol forcing is near zero, and apparently, per the attached associated image, that the direct anthropogenic direct aerosol forcing is concentrated near equatorial Africa, as neither of these findings make much sense to me:

Chung, Chul E., Chu, Jung-Eun, Lee, Yunha, van Noije, Twan, Jeoung, Hwayoung, Ha, Kyung-Ja, and Marks, Marguerite: Global direct aerosol radiative forcing, as constrained by comprehensive observations, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-30, in review, 2016.

http://www.atmos-chem-phys-discuss.net/acp-2016-30/ (http://www.atmos-chem-phys-discuss.net/acp-2016-30/)

Abstract. Aerosols directly affect the radiative balance of the Earth through absorption and scattering of solar radiation. Although the contributions of absorption (heating) and scattering (cooling) of sunlight have proved difficult to quantify, the consensus is that anthropogenic aerosols cool the climate, partially offsetting the warming by rising greenhouse gas concentrations. Recent estimates of global direct aerosol radiative forcing are −0.35 ± 0.5 Wm−2, and these estimates depend either entirely or heavily on aerosol simulation. Here, we integrate a comprehensive suite of satellite and ground-based observations to constrain total AOD, its fine-mode fraction, the vertical distribution of aerosols and clouds, and the co-location of clouds and overlying aerosols. We find that fine-mode forcing is −0.46 Wm−2 (−0.54 ~ −0.39 Wm−2). Fine-mode aerosols include sea salt and dust aerosols, and we find that these natural aerosols pose a very large cooling (−0.44 ~ −0.26 Wm−2) when constrained by observations. When the contribution of these natural aerosols is subtracted from the fine-mode forcing, the net becomes −0.10 (−0.28 ~ +0.05) Wm−2. The net forcing arises from carbonaceous, sulfate and nitrate aerosols. Despite uncertainties in the anthropogenic fraction of these aerosols, this −0.28 ~ +0.05 Wm−2 range compels the direct aerosol forcing to be near zero.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on January 28, 2016, 06:59:17 PM
The linked reference provides a summary of the latest IPCC thinking on anthropogenic aerosols & their impact on global climate:

Hua Zhang, Shuyun Zhao, Zhili Wang, Xiaoye Zhang & Lianchun Song (25 January 2016), "The updated effective radiative forcing of major anthropogenic aerosols and their effects on global climate at present and in the future", International Journal of Climatology, DOI: 10.1002/joc.4613

http://onlinelibrary.wiley.com/doi/10.1002/joc.4613/abstract (http://onlinelibrary.wiley.com/doi/10.1002/joc.4613/abstract)

Abstract: "The effective radiative forcing (ERF), as newly defined in the Intergovernmental Panel on Climate Change's Fifth Assessment Report (IPCC AR5), of three anthropogenic aerosols [sulphate (SF), black carbon (BC), and organic carbon (OC)] and their comprehensive climatic effects were simulated and discussed, using the updated aerosol-climate online model of BCC_AGCM2.0.1_CUACE/Aero. From 1850 to 2010, the total ERF of these anthropogenic aerosols was −2.49 W m−2, of which the aerosol–radiation interactive ERF (ERFari) and aerosol–cloud interactive ERF (ERFaci) were ∼ −0.30 and −2.19 W m−2, respectively. SF was the largest contributor to the total ERF, with an ERF of −2.37 W m−2. The ERF of BC and OC were 0.12 and −0.31 W m−2, respectively. From 1850 to 2010, anthropogenic aerosols brought about a decrease of ∼2.53 K and ∼0.20 mm day−1 in global annual mean surface temperature and precipitation, respectively. Surface cooling was most obvious over mid- and high latitudes in the northern hemisphere (NH). Precipitation change was most pronounced near the equator, with decreased and increased rainfall to the north and south of the equator, respectively; this might be largely related to the enhanced Hadley Cell in the NH. Relative humidity near surface was increased, especially over land, due to surface cooling induced by anthropogenic aerosols. Cloud cover and water path were increased, especially in or near the source regions of anthropogenic aerosols. Experiments based on the Representative Concentration Pathway (RCP) 4.5 given in IPCC AR5 shows the dramatic decrease in three anthropogenic aerosols in 2100 will lead to an increase of ∼2.06 K and 0.16 mm day−1 in global annual mean surface temperature and precipitation, respectively, compared with those in 2010."
Title: Re: The Science of Aerosols
Post by: Richard Rathbone on January 29, 2016, 07:53:51 PM
i.e if we'd cleaned up our aerosol act we'd already have broken 3 degrees?
Title: Re: The Science of Aerosols
Post by: AbruptSLR on January 29, 2016, 08:17:19 PM
i.e if we'd cleaned up our aerosol act we'd already have broken 3 degrees?

The attached NOAA images shows the projected temperature increases (baselined to 2000) for the different RCP scenarios.  As the scenario numbers (e.g. 4.5) is the assumed radiative forcing, if you clean-up the aerosols faster then you need to clean-up the emissions faster to maintain the assumed forcing (otherwise you need to follow a different pathway say RCP 8.5).

Per the paper: "Experiments based on the Representative Concentration Pathway (RCP) 4.5 given in IPCC AR5 shows the dramatic decrease in three anthropogenic aerosols in 2100 will lead to an increase of ∼2.06 K and 0.16 mm day−1 in global annual mean surface temperature and precipitation, respectively, compared with those in 2010."
Title: Re: The Science of Aerosols
Post by: Richard Rathbone on January 30, 2016, 12:31:34 PM
Its the 2010 number  (2.53K higher without aerosols) that seems incredible to me.
Title: Re: The Science of Aerosols
Post by: jai mitchell on February 18, 2016, 07:16:18 PM
Its the 2010 number  (2.53K higher without aerosols) that seems incredible to me.

that doesn't sound right to me either, if it is, knowing that aerosols are preventing approximately 50% of the total atmospheric forcing from GHGs then our current climate response to a complete cessation of fossil fuels today would lead to a 4C increase in temperatures above pre-industrial.

I would have to assume that they mean, with feedbacks that this is by 2100. . .not sure though.
Title: Re: The Science of Aerosols
Post by: Steven on February 19, 2016, 02:20:09 PM
Its the 2010 number  (2.53K higher without aerosols) that seems incredible to me.

That paper seems to be an outlier.  Their climate model seems to have an excessively strong aerosol-cloud interaction.  In the abstract they say:

Quote
From 1850 to 2010, the total ERF [Effective Radiative Forcing] of these anthropogenic aerosols was −2.49 W m−2, of which the aerosol–radiation interactive ERF (ERFari) and aerosol–cloud interactive ERF (ERFaci) were ~ −0.30 and −2.19 W m−2, respectively.
http://onlinelibrary.wiley.com/doi/10.1002/joc.4613/abstract (http://onlinelibrary.wiley.com/doi/10.1002/joc.4613/abstract)


Their estimate of −2.19 W m−2 for aerosol-cloud interactive ERF is unrealistic.  (And hence their estimate of −2.49 W m−2 for total aerosol forcing is also unrealistic.)

For comparison, the IPCC's estimate for the effective radiative forcing from aerosol-cloud interaction for the year 2011 (compared to pre-industrial) is  –0.45 W m−2, with 90% confidence interval –1.2 to 0.0 W m−2:


(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi.imgur.com%2Frzq5oom.png&hash=57d5651745d40cc694f6000ae65b8863)
(Source: IPCC AR5 Fig. 8.15 (http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf)).
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 21, 2016, 01:30:28 AM

That paper seems to be an outlier.  Their climate model seems to have an excessively strong aerosol-cloud interaction.  In the abstract they say:


While it certainly is possible that the Zhang et al (2016) paper is an outlier and should be discounted.  It is also possible that it represents an upper bound value.  Certainly, citing AR5 values as poof that Zhang is an outlier cannot be valid as AR5 merely catalogs the findings available well before its publication.  Furthermore, it is well understood that AR5 included values of climate sensitivity that were too low by unbiased standards; which raises the possibility that aerosol negative forcing is stronger than AR5 considered.  For example, Marvel et al (2015) found that the most likely value for TCR is 1.7C (which is above the AR5 most likely value); but the the following Storelvmo et al (2015)research cites a most likely value for TCR of 1.9C (with a 95% CL interval of 1.2C to 2.7C); which again raises the possibility that aerosol negative forcing is stronger than AR5 considers.

Storelvmo, Trude; Leirvik, Thomas; Phillips, Petter; Lohmann, Ulrike; Wild, Martin (2015), "Disentangling Aerosol Cooling and Greenhouse Warming to Reveal Earth's Climate Sensitivity", GU General Assembly 2015, held 12-17 April, 2015 in Vienna, Austria. id.4326, Bibliographic Code: 2015EGUGA..17.4326S

Abstract: "Earth's climate sensitivity has been the subject of heated debate for decades, and recently spurred renewed interest after the latest IPCC assessment report suggested a downward adjustment of the most likely range of climate sensitivities. Here, we present a study based on the time period 1964 to 2010, which is unique in that it does not rely on global climate models (GCMs) in any way. The study uses surface observations of temperature and incoming solar radiation from approximately 1300 surface sites, along with observations of the equivalent CO2 concentration (CO2,eq) in the atmosphere, to produce a new best estimate for the transient climate sensitivity of 1.9K (95% confidence interval 1.2K - 2.7K). This is higher than other recent observation-based estimates, and is better aligned with the estimate of 1.8K and range (1.1K - 2.5K) derived from the latest generation of GCMs. The new estimate is produced by incorporating the observations in an energy balance framework, and by applying statistical methods that are standard in the field of Econometrics, but less common in climate studies. The study further suggests that about a third of the continental warming due to increasing CO2,eq was masked by aerosol cooling during the time period studied."

Furthermore, the following linked Zhang et al (2015) research shows that the uncertainties of aerosol indirect effects (AIE) is larger in local dynamic regimes than for the global average case.  As the dynamic area are more subject to non-linear positive feedback acceleration, this implies that we are at greater risk of accelerating ECS than previously understood:

Zhang, S., Wang, M., Ghan, S. J., Ding, A., Wang, H., Zhang, K., Neubauer, D., Lohmann, U., Ferrachat, S., Takeamura, T., Gettelman, A., Morrison, H., Lee, Y. H., Shindell, D. T., Partridge, D. G., Stier, P., Kipling, Z., and Fu, C.: On the characteristics of aerosol indirect effect based on dynamic regimes in global climate models, Atmos. Chem. Phys. Discuss., 15, 23683-23729, doi:10.5194/acpd-15-23683-2015, 2015.


http://www.atmos-chem-phys-discuss.net/15/23683/2015/acpd-15-23683-2015.html (http://www.atmos-chem-phys-discuss.net/15/23683/2015/acpd-15-23683-2015.html)

Also I feel that it is premature to brand Zhang et al (2016) as an outlier, when researchers like Myhre et al (2015) cann't even cut the uncertainty associated with TCR in half before 2030.

Gunnar Myhre, Olivier Boucher, François-Marie Bréon, Piers Forster & Drew Shindell, (2015), "Declining uncertainty in transient climate response as CO2 forcing dominates future climate change", Nature Geoscience, doi:10.1038/ngeo2371

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2371.html (http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2371.html)

Abstract: "Carbon dioxide has exerted the largest portion of radiative forcing and surface temperature change over the industrial era, but other anthropogenic influences have also contributed. However, large uncertainties in total forcing make it difficult to derive climate sensitivity from historical observations. Anthropogenic forcing has increased between the Fourth and Fifth Assessment Reports of the Intergovernmental Panel of Climate Change (IPCC) although its relative uncertainty has decreased. Here we show, based on data from the two reports, that this evolution towards lower uncertainty can be expected to continue into the future. Because it is easier to reduce air pollution than carbon dioxide emissions and because of the long lifetime of carbon dioxide, the less uncertain carbon dioxide forcing is expected to become increasingly dominant. Using a statistical model, we estimate that the relative uncertainty in anthropogenic forcing of more than 40% quoted in the latest IPCC report for 2011 will be almost halved by 2030, even without better scientific understanding. Absolute forcing uncertainty will also decline for the first time, provided projected decreases in aerosols occur. Other factors being equal, this stronger constraint on forcing will bring a significant reduction in the uncertainty of observation-based estimates of the transient climate response, with a 50% reduction in its uncertainty range expected by 2030."

Finally, I note that the linked 2015 The Guardian article points to evidence that climate sensitivity is likely higher than most mainstream climate scientists are willing to admit to publicly; which again raises the possibility that aerosol negative radiative forcing may be higher than the range that AR5 cataloged from several year old research.

http://www.theguardian.com/environment/climate-consensus-97-per-cent/2015/apr/30/overlooked-evidence-global-warming-may-proceed-faster-than-expected (http://www.theguardian.com/environment/climate-consensus-97-per-cent/2015/apr/30/overlooked-evidence-global-warming-may-proceed-faster-than-expected)

Title: Re: The Science of Aerosols
Post by: jai mitchell on February 22, 2016, 06:48:32 AM
It must be here stated that the GHG Radiative Forcing values include the lapse rate and water vapor feedbacks in their calculation.  These associated feedbacks represent about 3/4 of the total forcing produced by a given amount of GHG emissions.

To my current understanding, I have looked but not found definitive proof, the radiative forcing values associated with aerosols are ONLY associated with immediate effects and the lapse rate and water vapor feedbacks are not included in their calculation.

If the total anthropogenic aerosol radiative forcing term is -0.5 W/m^2 then these feedbacks would produce the effective warming of +2.0 W/m^2 if those aerosols are removed.

If indeed the anthropogenic aerosol values are -2.4 W/m^2 then with the removal of those emissions, within about 10 years, we would see an effective forcing of +9.6 W/m^2.

iff this is true then our collective geese are truly cooked.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 22, 2016, 11:17:33 AM
It must be here stated that the GHG Radiative Forcing values include the lapse rate and water vapor feedbacks in their calculation.  These associated feedbacks represent about 3/4 of the total forcing produced by a given amount of GHG emissions.

To my current understanding, I have looked but not found definitive proof, the radiative forcing values associated with aerosols are ONLY associated with immediate effects and the lapse rate and water vapor feedbacks are not included in their calculation.

If the total anthropogenic aerosol radiative forcing term is -0.5 W/m^2 then these feedbacks would produce the effective warming of +2.0 W/m^2 if those aerosols are removed.

If indeed the anthropogenic aerosol values are -2.4 W/m^2 then with the removal of those emissions, within about 10 years, we would see an effective forcing of +9.6 W/m^2.

iff this is true then our collective geese are truly cooked.

jai,

Thank you for the clarifications.  As Zhang et al (2016) has been peer reviewed, it is advisable to evaluate its implications seriously, rather than to simply label it an "outlier" as Steven's post implied.

Best,
ASLR
Title: Re: The Science of Aerosols
Post by: Steven on February 22, 2016, 10:05:10 PM
It must be here stated that the GHG Radiative Forcing values include the lapse rate and water vapor feedbacks in their calculation.

No, they are not included.  Forcings and feedbacks are treated separately.  The IPCC graphic that I posted upthread shows forcings, no feedbacks.  The concept of Effective Radiative Forcing (ERF) does include some "rapid adjustments", but those rapid adjustments are different from the usual feedbacks such as the water vapor and lapse rate feedbacks.

From IPCC AR5:


Quote
7.1.3   Forcing, Rapid Adjustments and Feedbacks


Forcings associated with agents such as greenhouse
gases (GHGs) and aerosols act on global mean surface temperature
through the global radiative (energy) budget.  Rapid adjustments
(sometimes called rapid responses) arise when forcing agents, by alter-
ing flows of energy internal to the system, affect cloud cover or other
components of the climate system and thereby alter the global budget
indirectly. Because these adjustments do not operate through changes
in the global mean surface temperature (ΔT), which are slowed by the
massive heat capacity of the oceans, they are generally rapid and most
are thought to occur within a few weeks. Feedbacks are associated
with changes in climate variables that are mediated by a change in
global mean surface temperature

...

In principle rapid adjustments are independent of ΔT, while feedbacks
operate purely through ΔT.

...

Furthermore, one
can distinguish between the traditional concept of radiative forcing
(RF) and the relatively new concept of effective radiative forcing (ERF)
that also includes rapid adjustments.
http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter07_FINAL.pdf (http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter07_FINAL.pdf)
Title: Re: The Science of Aerosols
Post by: Steven on February 22, 2016, 10:41:58 PM
For example, Marvel et al (2015) found that the most likely value for TCR is 1.7C (which is above the AR5 most likely value); but the the following Storelvmo et al (2015)research cites a most likely value for TCR of 1.9C (with a 95% CL interval of 1.2C to 2.7C); which again raises the possibility that aerosol negative forcing is stronger than AR5 considers.

Those Marvel and Storelvmo papers are both in good agreement with the IPCC consensus.  According to the IPCC AR5 report: "The transient climate response is likely in the range of 1.0°C to 2.5°C (high confidence) and extremely unlikely greater than 3°C".


Also I feel that it is premature to brand Zhang et al (2016) as an outlier, when researchers like Myhre et al (2015) cann't even cut the uncertainty associated with TCR in half before 2030.

Gunnar Myhre, Olivier Boucher, François-Marie Bréon, Piers Forster & Drew Shindell, (2015), "Declining uncertainty in transient climate response as CO2 forcing dominates future climate change", Nature Geoscience, doi:10.1038/ngeo2371

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2371.html (http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2371.html)

Abstract: "Carbon dioxide has exerted the largest portion of radiative forcing and surface temperature change over the industrial era, but other anthropogenic influences have also contributed. However, large uncertainties in total forcing make it difficult to derive climate sensitivity from historical observations. Anthropogenic forcing has increased between the Fourth and Fifth Assessment Reports of the Intergovernmental Panel of Climate Change (IPCC) although its relative uncertainty has decreased. Here we show, based on data from the two reports, that this evolution towards lower uncertainty can be expected to continue into the future. Because it is easier to reduce air pollution than carbon dioxide emissions and because of the long lifetime of carbon dioxide, the less uncertain carbon dioxide forcing is expected to become increasingly dominant. Using a statistical model, we estimate that the relative uncertainty in anthropogenic forcing of more than 40% quoted in the latest IPCC report for 2011 will be almost halved by 2030, even without better scientific understanding. Absolute forcing uncertainty will also decline for the first time, provided projected decreases in aerosols occur. Other factors being equal, this stronger constraint on forcing will bring a significant reduction in the uncertainty of observation-based estimates of the transient climate response, with a 50% reduction in its uncertainty range expected by 2030."

What Myhre et al. actually say is that the stronger constraint on anthropogenic forcing by 2030 will reduce the uncertainty for TCR by almost 50%, even without better scientific understanding.  In addition, it's possible that advances in scientific understanding could reduce the uncertainty even further.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 22, 2016, 11:15:10 PM
Its the 2010 number  (2.53K higher without aerosols) that seems incredible to me.

That paper seems to be an outlier.  Their climate model seems to have an excessively strong aerosol-cloud interaction.  In the abstract they say:

Quote
From 1850 to 2010, the total ERF [Effective Radiative Forcing] of these anthropogenic aerosols was −2.49 W m−2, of which the aerosol–radiation interactive ERF (ERFari) and aerosol–cloud interactive ERF (ERFaci) were ~ −0.30 and −2.19 W m−2, respectively.
http://onlinelibrary.wiley.com/doi/10.1002/joc.4613/abstract (http://onlinelibrary.wiley.com/doi/10.1002/joc.4613/abstract)


Their estimate of −2.19 W m−2 for aerosol-cloud interactive ERF is unrealistic.  (And hence their estimate of −2.49 W m−2 for total aerosol forcing is also unrealistic.)

For comparison, the IPCC's estimate for the effective radiative forcing from aerosol-cloud interaction for the year 2011 (compared to pre-industrial) is  –0.45 W m−2, with 90% confidence interval –1.2 to 0.0 W m−2:


(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi.imgur.com%2Frzq5oom.png&hash=57d5651745d40cc694f6000ae65b8863)
(Source: IPCC AR5 Fig. 8.15 (http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf)).

I note that per the linked pdf (& attached image) that Hua Zhang was one of the lead others of the WG1 AR5 Chapter 8, and thus likely has some idea of what he is talking about, and should not be dismissed as an outlier.  Furthermore, the Effective Radiative Forcing likely includes the aerosol-cloud interaction and the aerosol-radiation interaction:

http://www.climatechange2013.org/images/report/WG1AR5_Chapter08_FINAL.pdf (http://www.climatechange2013.org/images/report/WG1AR5_Chapter08_FINAL.pdf)
Title: Re: The Science of Aerosols
Post by: Steven on February 22, 2016, 11:51:12 PM

I note that per the linked pdf (& attached image) that Hua Zhang was one of the lead others of the WG1 AR5 Chapter 8, and thus likely has some idea of what he is talking about, and should not be dismissed as an outlier.

http://www.climatechange2013.org/images/report/WG1AR5_Chapter08_FINAL.pdf (http://www.climatechange2013.org/images/report/WG1AR5_Chapter08_FINAL.pdf)

Actually Hua Zhang is female.  Moreover, no one in this thread has claimed that Zhang et al. are outliers who have no idea what they are talking about.  The point is that in this particular Zhang et al. 2016 paper, their climate model has a total anthropogenic aerosol forcing that is aberrant compared to the scientific consensus.  (More precisely, the contribution from aerosol-radiation interactions in their climate model is in good agreement with the consensus, but the contribution from aerosol-cloud interactions is clearly not.)  If you read the Zhang et al. 2016 paper (pdf-file here (https://www.researchgate.net/profile/Hua_Zhang35/publication/291949505_The_updated_effective_radiative_forcing_of_major_anthropogenic_aerosols_and_their_effects_on_global_climate_at_present_and_in_the_future/links/56aeb89408ae28588c61e660.pdf)), you'll see that they discuss this a bit further in the last paragraph of Section 3.2 of the paper:


Quote
ERFaci can be considered as the residual between ERF
and ERFari ∼ −2.19 W m−2, which is close to the anthropogenic
aerosol indirect effects (AIE) in Wang et al.
(2014) and the simulated AIE by CAM5 (Ghan et al.,
2012), but much larger than the values given by IPCC
(2013) [−0.45 (−1.2, 0) W m−2]. Hoose et al. (2009)
found that the AIE was very sensitive to the lower bound
of cloud droplet number concentration (CDNCmin), and
the absolute value of AIE decreased rapidly when the
CDNCmin increased from 0 to 40 cm−3. Many models
have adopted different CDNCmin, but CDNCmin was set
at 0 in this study
, as the prescription of CDNCmin is still
physically unclear (Hoose et al., 2009). This is the main
reason for the much larger simulated ERFaci
.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 23, 2016, 01:16:21 AM
... their climate model has a total anthropogenic aerosol forcing that is aberrant compared to the scientific consensus.  (More precisely, the contribution from aerosol-radiation interactions in their climate model is in good agreement with the consensus, but the contribution from aerosol-cloud interactions is clearly not.)

As this is a peer reviewed paper it will be included in AR6, so what does "aberrant" mean, and what does "scientific consensus" mean?  This paper is an update on old science, so does aberrant mean new/updated and consensus mean old/out-of-date?

Edit: Some of your posts read like AR5 represents "settled-science", which it does not.
Title: Re: The Science of Aerosols
Post by: Theta on February 23, 2016, 10:19:05 AM
It must be here stated that the GHG Radiative Forcing values include the lapse rate and water vapor feedbacks in their calculation.  These associated feedbacks represent about 3/4 of the total forcing produced by a given amount of GHG emissions.

To my current understanding, I have looked but not found definitive proof, the radiative forcing values associated with aerosols are ONLY associated with immediate effects and the lapse rate and water vapor feedbacks are not included in their calculation.

If the total anthropogenic aerosol radiative forcing term is -0.5 W/m^2 then these feedbacks would produce the effective warming of +2.0 W/m^2 if those aerosols are removed.

If indeed the anthropogenic aerosol values are -2.4 W/m^2 then with the removal of those emissions, within about 10 years, we would see an effective forcing of +9.6 W/m^2.

iff this is true then our collective geese are truly cooked.

Taking this factor alone into consideration means that we shouldn't dismiss it as an outlier because it basically means that there is no way to actually fix the problems that we face with Climate Change because if we stop burning fossil fuels, then Guy McPherson's statements on 4C within weeks, are guaranteed and we'd be dead within months or a few years. So, what we have is a hopeless situation where the best we can do is give up on fighting Climate Change and continue on hoping that by prolonging the lifetime of civilisation, we can find some kind of miracle technology, but even that seems unlikely with civilisation just about to fall off the cliff into oblivion with the economy in shambles.
Title: Re: The Science of Aerosols
Post by: Richard Rathbone on February 23, 2016, 02:01:08 PM
What Hoose et al say, is that CNDCmin is effectively a tuning parameter for the indirect effect. So you decide, based on your expert judgement, what the indirect effect should be, and then choose CNDCmin to deliver that value. i.e. aerosol models aren't good enough to tell you what the indirect effect is.

Zhang et al have decided that the indirect effect should be as large as their model can make it and set CNDCmin to deliver that value. Consequently its an outlier.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 23, 2016, 04:30:15 PM
What Hoose et al say, is that CNDCmin is effectively a tuning parameter for the indirect effect. So you decide, based on your expert judgement, what the indirect effect should be, and then choose CNDCmin to deliver that value. i.e. aerosol models aren't good enough to tell you what the indirect effect is.

Zhang et al have decided that the indirect effect should be as large as their model can make it and set CNDCmin to deliver that value. Consequently its an outlier.

Outlier, or upper-bound?
Title: Re: The Science of Aerosols
Post by: Richard Rathbone on February 24, 2016, 01:19:59 PM
What Hoose et al say, is that CNDCmin is effectively a tuning parameter for the indirect effect. So you decide, based on your expert judgement, what the indirect effect should be, and then choose CNDCmin to deliver that value. i.e. aerosol models aren't good enough to tell you what the indirect effect is.

Zhang et al have decided that the indirect effect should be as large as their model can make it and set CNDCmin to deliver that value. Consequently its an outlier.

Outlier, or upper-bound?

Outlier.

If they were choosing CNDCmin for the purpose of establishing an upper bound, it should have been non-zero and their estimate of the upper bound would have been smaller.

However, its really a demonstration that aerosol models aren't good enough to come up with values for the indirect effect. They need to know what it is in advance and be tuned to give that result and taking the range over which they can be tuned as indicating uncertainty in the indirect effect is the wrong way round. Establishing the range over which its reasonable to tune them from uncertainty in other estimates is the way to establish bounds.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 24, 2016, 06:20:24 PM
The linked (open access) reference points to new development in aerosol-cloud interaction modeling, indicating that some of the older (AR5) models need to be updated:


Zhou, C., Zhang, X., Gong, S., Wang, Y., and Xue, M.: Improving aerosol interaction with clouds and precipitation in a regional chemical weather modeling system, Atmos. Chem. Phys., 16, 145-160, doi:10.5194/acp-16-145-2016, 2016.


http://www.atmos-chem-phys.net/16/145/2016/ (http://www.atmos-chem-phys.net/16/145/2016/)

http://www.atmos-chem-phys.net/16/145/2016/acp-16-145-2016.pdf (http://www.atmos-chem-phys.net/16/145/2016/acp-16-145-2016.pdf)

Abstract: "A comprehensive aerosol–cloud–precipitation interaction (ACI) scheme has been developed under a China Meteorological Administration (CMA) chemical weather modeling system, GRAPES/CUACE (Global/Regional Assimilation and PrEdiction System, CMA Unified Atmospheric Chemistry Environment). Calculated by a sectional aerosol activation scheme based on the information of size and mass from CUACE and the thermal-dynamic and humid states from the weather model GRAPES at each time step, the cloud condensation nuclei (CCN) are interactively fed online into a two-moment cloud scheme (WRF Double-Moment 6-class scheme – WDM6) and a convective parameterization to drive cloud physics and precipitation formation processes. The modeling system has been applied to study the ACI for January 2013 when several persistent haze-fog events and eight precipitation events occurred.

The results show that aerosols that interact with the WDM6 in GRAPES/CUACE obviously increase the total cloud water, liquid water content, and cloud droplet number concentrations, while decreasing the mean diameters of cloud droplets with varying magnitudes of the changes in each case and region. These interactive microphysical properties of clouds improve the calculation of their collection growth rates in some regions and hence the precipitation rate and distributions in the model, showing 24 to 48 % enhancements of threat score for 6 h precipitation in almost all regions. The aerosols that interact with the WDM6 also reduce the regional mean bias of temperature by 3 °C during certain precipitation events, but the monthly means bias is only reduced by about 0.3 °C."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 24, 2016, 06:38:02 PM
However, its really a demonstration that aerosol models aren't good enough to come up with values for the indirect effect. They need to know what it is in advance and be tuned to give that result and taking the range over which they can be tuned as indicating uncertainty in the indirect effect is the wrong way round. Establishing the range over which its reasonable to tune them from uncertainty in other estimates is the way to establish bounds.

The linked reference indicates that different modeling approaches to the same input result in significantly different aerosol-cloud interaction projections.  Therefore, it is not good risk management for AR5 to lump the poor model forecasts together with the better model forecasts in order to publish a dumbed-down message to the public.  Hopefully, scientists will follow some of the advise of Feingold et al (2016) so that they can converge more rapidly to selecting the better model approaches, rather than merely transferring climate change risk to the general public, who have very little idea of what is going on.


Graham Feingold, Allison McComiskey, Takanobu Yamaguchi, Jill S. Johnson, Kenneth S. Carslaw, and K. Sebastian Schmidt (February 1, 2016), "New approaches to quantifying aerosol influence on the cloud radiative effect", PNAS, doi: 10.1073/pnas.1514035112


http://www.pnas.org/content/early/2016/01/25/1514035112 (http://www.pnas.org/content/early/2016/01/25/1514035112)


Abstract: "The topic of cloud radiative forcing associated with the atmospheric aerosol has been the focus of intense scrutiny for decades. The enormity of the problem is reflected in the need to understand aspects such as aerosol composition, optical properties, cloud condensation, and ice nucleation potential, along with the global distribution of these properties, controlled by emissions, transport, transformation, and sinks. Equally daunting is that clouds themselves are complex, turbulent, microphysical entities and, by their very nature, ephemeral and hard to predict. Atmospheric general circulation models represent aerosol−cloud interactions at ever-increasing levels of detail, but these models lack the resolution to represent clouds and aerosol−cloud interactions adequately. There is a dearth of observational constraints on aerosol−cloud interactions. We develop a conceptual approach to systematically constrain the aerosol−cloud radiative effect in shallow clouds through a combination of routine process modeling and satellite and surface-based shortwave radiation measurements. We heed the call to merge Darwinian and Newtonian strategies by balancing microphysical detail with scaling and emergent properties of the aerosol−cloud radiation system."

See also:
http://www.esrl.noaa.gov/csd/news/2016/179_0201.html (http://www.esrl.noaa.gov/csd/news/2016/179_0201.html)

Extract: "The authors focus on modeling how the aerosol affects the clouds' reflection and absorption of sunlight, using a set of inputs that describe both the aerosol and meteorology. They first illustrate the problem by making use of two different approaches that differ only in the co-variability between the meteorological conditions and aerosols. They get different outcomes for the role of the aerosols, even though both approaches used the same inputs. "This perplexing outcome motivated us to look further into how to model the complex system of clouds, aerosol, meteorology, and radiation," said Feingold.

To quantify the aerosol-cloud radiative effect the authors argue for studies that consider how the system would respond to inputs that are allowed to co-vary in a natural way, more accurately representing real-world conditions. They call for routine process model simulations in which the initial inputs for aerosol and meteorology are derived from observations – and hence are varying simultaneously in space and time. With a large volume of observations and successful model simulations of this kind, the authors argue that this approach could advance the study of aerosol-cloud interactions and their implications for the warming or cooling effects of clouds.

The new paper gives a good start on advancing the science on this topic, but it is far from the end of the story, notes Feingold. "To really quantify the warming and cooling effects of clouds, we will have to apply this approach in different cloud regimes in different places on the globe.""
Title: Re: The Science of Aerosols
Post by: Steven on February 24, 2016, 11:15:18 PM
Taking this factor alone into consideration means that we shouldn't dismiss it as an outlier because it basically means that there is no way to actually fix the problems that we face with Climate Change because if we stop burning fossil fuels, then Guy McPherson's statements on 4C within weeks, are guaranteed and we'd be dead within months or a few years.

Guy McPherson is an unreliable source, and his claims about "4C within weeks" are not even remotely plausible.

Here is a 2012 scientific paper about this topic:

H. Matthews and K. Zickfeld, "Climate response to zeroed emissions of greenhouse gases and aerosols"

http://www.nature.com/nclimate/journal/v2/n5/full/nclimate1424.html (http://www.nature.com/nclimate/journal/v2/n5/full/nclimate1424.html)

That paper suggests that, if we were to abruptly eliminate anthropogenic aerosol and GHG emissions, then the global temperature would increase by a few tenths of a degree (most likely between 0.25 and 0.5 °C) over the decade immediately following zeroed emissions. 
Title: Re: The Science of Aerosols
Post by: Steven on February 24, 2016, 11:26:32 PM
As this is a peer reviewed paper it will be included in AR6, so what does "aberrant" mean, and what does "scientific consensus" mean?  This paper is an update on old science, so does aberrant mean new/updated and consensus mean old/out-of-date?

The text I quoted in Reply #49 explains why the Zhang et al. 2016 paper is an outlier.  See also Richard Rathbone's interpretation.



Therefore, it is not good risk management for AR5 to lump the poor model forecasts together with the better model forecasts in order to publish a dumbed-down message to the public. 

They are not "lumping together" the forecasts.  The AR5 assessment (and confidence intervals) for aerosol forcing are based on expert judgement, which gives less weight to the older and more primitive models than to the more comprehensive modeling studies.  Moreover, it gives more weight to observationally based (especially satellite) studies.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 24, 2016, 11:46:14 PM

The text I quoted in Reply #49 explains why the Zhang et al. 2016 paper is an outlier.  See also Richard Rathbone's interpretation.


Obviously, the peer reviewers disagreed with both yourself and Richard Rathbone, otherwise a outlier would be thrown out by the review process.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 25, 2016, 11:17:17 AM
For example, Marvel et al (2015) found that the most likely value for TCR is 1.7C (which is above the AR5 most likely value); but the the following Storelvmo et al (2015)research cites a most likely value for TCR of 1.9C (with a 95% CL interval of 1.2C to 2.7C); which again raises the possibility that aerosol negative forcing is stronger than AR5 considers.

Those Marvel and Storelvmo papers are both in good agreement with the IPCC consensus.  According to the IPCC AR5 report: "The transient climate response is likely in the range of 1.0°C to 2.5°C (high confidence) and extremely unlikely greater than 3°C".


In reality only one TCR is correct, but due to uncertainty one needs to compare PDFs from different researchers such as the attached image from Marvel et al (2015).  In this regards the Storelvmo et al (2015) range of for TCR of 1.9C (with a 95% CL interval of 1.2C to 2.7C), is much different than the Marvel findings.  Thus when AR6 is published they should have a new & different PDF for TCR than did AR5, due to new findings.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 25, 2016, 11:26:46 AM

Therefore, it is not good risk management for AR5 to lump the poor model forecasts together with the better model forecasts in order to publish a dumbed-down message to the public. 

They are not "lumping together" the forecasts.  The AR5 assessment (and confidence intervals) for aerosol forcing are based on expert judgement, which gives less weight to the older and more primitive models than to the more comprehensive modeling studies.  Moreover, it gives more weight to observationally based (especially satellite) studies.

I do not believe that Feingold et al 2016 is talking about the difference between more primitive models and more comprehensive models.  They provided the same input to two different more comprehensive models and they got significantly different projects.  What is needed to make progress is not more reliance on expert judgement, but we need to: "... heed the call to merge Darwinian and Newtonian strategies by balancing microphysical detail with scaling and emergent properties of the aerosol−cloud radiation system.

Furthermore, I note that AR5's inclusion of climate sensitivity values that were too low, was largely due to their over reliance on satellite data without adequately understanding the physics involved.
Title: Re: The Science of Aerosols
Post by: Richard Rathbone on February 25, 2016, 02:04:23 PM

The text I quoted in Reply #49 explains why the Zhang et al. 2016 paper is an outlier.  See also Richard Rathbone's interpretation.


Obviously, the peer reviewers disagreed with both yourself and Richard Rathbone, otherwise a outlier would be thrown out by the review process.

Outliers are not necessarily without merit. I think the way some of their argument is structured is disingenuous, but I wouldn't have refused it publication. The necessary references to allow an informed reader to draw their own conclusions are in there.

The main conclusion I draw is that its not possible at the moment to come up with a well constrained value for the indirect effect from aerosols models. As one of the other papers you quote says "There is a dearth of observational constraints on aerosol−cloud interactions." and until that is remedied and models that fit those observations are in place, any published value for indirect aerosol effects needs to be taken with a large pinch of sulphate.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 25, 2016, 04:50:17 PM

The text I quoted in Reply #49 explains why the Zhang et al. 2016 paper is an outlier.  See also Richard Rathbone's interpretation.


Obviously, the peer reviewers disagreed with both yourself and Richard Rathbone, otherwise a outlier would be thrown out by the review process.

Outliers are not necessarily without merit. I think the way some of their argument is structured is disingenuous, but I wouldn't have refused it publication. The necessary references to allow an informed reader to draw their own conclusions are in there.

The main conclusion I draw is that its not possible at the moment to come up with a well constrained value for the indirect effect from aerosols models. As one of the other papers you quote says "There is a dearth of observational constraints on aerosol−cloud interactions." and until that is remedied and models that fit those observations are in place, any published value for indirect aerosol effects needs to be taken with a large pinch of sulphate.

Richard,

While I am not questioning your judgment, or skill set, I do note that approving papers presenting disingenuous arguments for publication seems to create a playground for climate skeptics to sow sufficient doubt to delay effective climate action for decades to come.

Best regards,
ASLR
Title: Re: The Science of Aerosols
Post by: Steven on February 25, 2016, 08:28:44 PM
They are not "lumping together" the forecasts.  The AR5 assessment (and confidence intervals) for aerosol forcing are based on expert judgement, which gives less weight to the older and more primitive models than to the more comprehensive modeling studies.  Moreover, it gives more weight to observationally based (especially satellite) studies.

I do not believe that Feingold et al 2016 is talking about the difference between more primitive models and more comprehensive models.  They provided the same input to two different more comprehensive models and they got significantly different projects.  What is needed to make progress is not more reliance on expert judgement, but we need to: "... heed the call to merge Darwinian and Newtonian strategies by balancing microphysical detail with scaling and emergent properties of the aerosol−cloud radiation system.

Furthermore, I note that AR5's inclusion of climate sensitivity values that were too low, was largely due to their over reliance on satellite data without adequately understanding the physics involved.

I have no idea what satellite data you have in mind in that boldface sentence.  In the text you quoted, I was not talking about climate sensitivity, but about aerosol forcing.  What I meant with "observationally based (especially satellite) studies", is studies that try to infer aerosol–cloud interactions from e.g. the variability in the present-day satellite record, using e.g. MODIS or CERES satellite data.  The image below from AR5 gives more information about papers that were used in their expert judgement of anthropogenic aerosol forcing: the list contains 7 model-based (GCM) and 6 satellite-based papers.


Regarding the other part of your comment:  from my reading of that Feingold et al. 2016 (http://www.pnas.org/content/early/2016/01/25/1514035112.abstract) paper, the paper uses only 1 model, for simulating certain aspects of cloud systems.  They compare 2 different methods for sampling initial conditions (cloud-controlling parameters) for that model.  However, they mention that neither of their 2 methods is supposed to be a realistic sampling of actual atmospheric conditions.  In fact it looks like the results in that Feingold paper are merely conceptual, and it remains to be seen whether their approach can be used to obtain a concrete constraint on aerosol-cloud interactions.  Perhaps they will be able to do that in a future paper...


(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FweVOBUp.png&hash=e582aa6835063ff2e6e896c27675e849)
http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter07_FINAL.pdf (http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter07_FINAL.pdf)
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 25, 2016, 08:53:26 PM
They are not "lumping together" the forecasts.  The AR5 assessment (and confidence intervals) for aerosol forcing are based on expert judgement, which gives less weight to the older and more primitive models than to the more comprehensive modeling studies.  Moreover, it gives more weight to observationally based (especially satellite) studies.

I do not believe that Feingold et al 2016 is talking about the difference between more primitive models and more comprehensive models.  They provided the same input to two different more comprehensive models and they got significantly different projects.  What is needed to make progress is not more reliance on expert judgement, but we need to: "... heed the call to merge Darwinian and Newtonian strategies by balancing microphysical detail with scaling and emergent properties of the aerosol−cloud radiation system.

Furthermore, I note that AR5's inclusion of climate sensitivity values that were too low, was largely due to their over reliance on satellite data without adequately understanding the physics involved.

I have no idea what satellite data you have in mind in that boldface sentence.  In the text you quoted, I was not talking about climate sensitivity, but about aerosol forcing.  What I meant with "observationally based (especially satellite) studies", is studies that try to infer aerosol–cloud interactions from e.g. the variability in the present-day satellite record, using e.g. MODIS or CERES satellite data.  The image below from AR5 gives more information about papers that were used in their expert judgement of anthropogenic aerosol forcing: the list contains 7 model-based (GCM) and 6 satellite-based papers.

I had previously pointed out a high climate sensitivity could be masking the influence of a highly negative aerosol-cloud interaction forcing.  But my basic point is not that the use satellite data is substandard, but that since the climate change observing satellite era began in the 1990's the global mean surface temperature has been dominated by the faux hiatus.  The linked reference indicates that research that points at the low end of AR5's ECS like range (1.5 to 4.5C); are likely in error because they do not adequately consider decadal feedback.  The reference indicates that the best way to address this matter is by diagnosing the role played by effective radiative forcing (ERF) within climate models:

Piers M. Forster (Volume publication date June 2016), "Inference of Climate Sensitivity from Analysis of Earth's Energy Budget", Annual Review of Earth and Planetary Sciences, Vol. 44


http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-060614-105156 (http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-060614-105156)

Abstract: "Recent attempts to diagnose Equilibrium Climate Sensitivity (ECS) from changes in Earth’s energy budget point towards values at the low-end of the Intergovernmental Panel on Climate Change Fifth Assessment Report’s (AR5) likely range (1.5 to 4.5 K). These studies employ observations but still require an element of modeling to infer ECS. Their diagnosed effective ECS over the historic period of around 2 K holds up to scrutiny but there is tentative evidence that this underestimates the true ECS from a doubling of carbon dioxide. Different choices of energy imbalance data explain most of the difference between published best estimates while effective radiative forcing (ERF) dominates the overall uncertainty. For decadal analyses the largest source of uncertainty comes from a poor understanding of the relationship between ECS and decadal feedback. Considerable progress could be made by diagnosing ERF in models."

If it is not clear what decadal feedbacks are, they are associated with such phenomena as the PDO/IPO, AMO, etc.  As we have just left a period of negative PDO and are now in a period of positive PDO, we can expect El Ninos to keep driving up estimates of the ECS based on the future satellite record.
Title: Re: The Science of Aerosols
Post by: Richard Rathbone on February 26, 2016, 01:51:29 PM

The text I quoted in Reply #49 explains why the Zhang et al. 2016 paper is an outlier.  See also Richard Rathbone's interpretation.


Obviously, the peer reviewers disagreed with both yourself and Richard Rathbone, otherwise a outlier would be thrown out by the review process.

Outliers are not necessarily without merit. I think the way some of their argument is structured is disingenuous, but I wouldn't have refused it publication. The necessary references to allow an informed reader to draw their own conclusions are in there.

The main conclusion I draw is that its not possible at the moment to come up with a well constrained value for the indirect effect from aerosols models. As one of the other papers you quote says "There is a dearth of observational constraints on aerosol−cloud interactions." and until that is remedied and models that fit those observations are in place, any published value for indirect aerosol effects needs to be taken with a large pinch of sulphate.

Richard,

While I am not questioning your judgment, or skill set, I do note that approving papers presenting disingenuous arguments for publication seems to create a playground for climate skeptics to sow sufficient doubt to delay effective climate action for decades to come.

Best regards,
ASLR

That's the editor's responsibility. The authors submit, the reviewers comment, the authors respond and the editor decides. For all I know, the argument got twisted to meet the comment of a reviewer and the authors aren't exactly happy with it either. Reviewers get to comment on the submission, not the revised version. 

Its an outlier, its explicit in the paper that its an outlier, there are references to follow up on if you want to form your own judgement as to whether you prefer the outlier or the consensus. That is really all you can ask a reviewer to insist on, and its there.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 26, 2016, 05:49:59 PM
That's the editor's responsibility. The authors submit, the reviewers comment, the authors respond and the editor decides. For all I know, the argument got twisted to meet the comment of a reviewer and the authors aren't exactly happy with it either. Reviewers get to comment on the submission, not the revised version. 

Its an outlier, its explicit in the paper that its an outlier, there are references to follow up on if you want to form your own judgement as to whether you prefer the outlier or the consensus. That is really all you can ask a reviewer to insist on, and its there.

It is not surprising that denialists have proven very effective at manipulating this process in the past, and I imagine that they will prove successful in manipulating this process to make sure that the input to AR6 can continue to err on the side of least drama.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 26, 2016, 11:48:52 PM
The linked reference discusses challenges in constraining anthropogenic radiative forcing for aerosol – cloud interaction.  The reference points out that not only do we have a limited understanding of the current interactions, but we also have an even poorer understanding of the preindustrial condition that researchers are trying to use as a baseline.

Steven Ghan, Minghuai Wang, Shipeng Zhang, Sylvaine Ferrachat, Andrew Gettelman, Jan Griesfeller, Zak Kipling, Ulrike Lohmann, Hugh Morrison, David Neubauer, Daniel G. Partridge, Philip Stier, Toshihiko Takemura, Hailong Wang and Kai Zhang (February 26 2016), "Challenges in constraining anthropogenic aerosol effects on cloud radiative forcing using present-day spatiotemporal variability", PNAS, doi: 10.1073/pnas.1514036113


http://www.pnas.org/content/early/2016/02/25/1514036113.abstract (http://www.pnas.org/content/early/2016/02/25/1514036113.abstract)


Abstract: "A large number of processes are involved in the chain from emissions of aerosol precursor gases and primary particles to impacts on cloud radiative forcing. Those processes are manifest in a number of relationships that can be expressed as factors dlnX/dlnY driving aerosol effects on cloud radiative forcing. These factors include the relationships between cloud condensation nuclei (CCN) concentration and emissions, droplet number and CCN concentration, cloud fraction and droplet number, cloud optical depth and droplet number, and cloud radiative forcing and cloud optical depth. The relationship between cloud optical depth and droplet number can be further decomposed into the sum of two terms involving the relationship of droplet effective radius and cloud liquid water path with droplet number. These relationships can be constrained using observations of recent spatial and temporal variability of these quantities. However, we are most interested in the radiative forcing since the preindustrial era. Because few relevant measurements are available from that era, relationships from recent variability have been assumed to be applicable to the preindustrial to present-day change. Our analysis of Aerosol Comparisons between Observations and Models (AeroCom) model simulations suggests that estimates of relationships from recent variability are poor constraints on relationships from anthropogenic change for some terms, with even the sign of some relationships differing in many regions. Proxies connecting recent spatial/temporal variability to anthropogenic change, or sustained measurements in regions where emissions have changed, are needed to constrain estimates of anthropogenic aerosol impacts on cloud radiative forcing."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 27, 2016, 10:31:10 AM
Conventional thinking is that reducing BC emissions would help to cool the Earth; however, the linked reference indicates: "… that a reduction in BC emission can lead to an unexpected warming on the Earth's climate system in the future."

Wang, Z. L., Zhang, H., and Zhang, X. Y.: Simultaneous reductions in emissions of black carbon and co-emitted species will weaken the aerosol net cooling effect, Atmos. Chem. Phys., 15, 3671-3685, doi:10.5194/acp-15-3671-2015, 2015.

http://www.atmos-chem-phys.net/15/3671/2015/acp-15-3671-2015.html (http://www.atmos-chem-phys.net/15/3671/2015/acp-15-3671-2015.html)

Abstract: "Black carbon (BC), a distinct type of carbonaceous material formed from the incomplete combustion of fossil and biomass based fuels under certain conditions, can interact with solar radiation and clouds through its strong light-absorption ability, thereby warming the Earth's climate system. Some studies have even suggested that global warming could be slowed down in the short term by eliminating BC emission due to its short lifetime. In this study, we estimate the influence of removing some sources of BC and other co-emitted species on the aerosol radiative effect by using an aerosol–climate atmosphere-only model BCC_AGCM2.0.1_CUACE/Aero with prescribed sea surface temperature and sea ice cover, in combination with the aerosol emissions from the Representative Concentration Pathways (RCPs) scenarios. We find that the global annual mean aerosol net cooling effect at the top of the atmosphere (TOA) will be enhanced by 0.12 W m−2 compared with recent past year 2000 levels if the emissions of only BC are reduced to the level projected for 2100 based on the RCP2.6 scenario. This will be beneficial for the mitigation of global warming. However, both aerosol negative direct and indirect radiative effects are weakened when BC and its co-emitted species (sulfur dioxide and organic carbon) are simultaneously reduced. Relative to year 2000 levels, the global annual mean aerosol net cooling effect at the TOA will be weakened by 1.7–2.0 W m−2 if the emissions of all these aerosols are decreased to the levels projected for 2100 in different ways based on the RCP2.6, RCP4.5, and RCP8.5 scenarios. Because there are no effective ways to remove the BC exclusively without influencing the other co-emitted components, our results therefore indicate that a reduction in BC emission can lead to an unexpected warming on the Earth's climate system in the future."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on March 01, 2016, 07:58:53 PM
The linked website contains numerous links to recorded presentations at the January 2016 Eighth Symposium on Aerosol–Cloud–Climate Interactions in New Orleans.  There are too many presentations to look at, let alone summarize:

https://ams.confex.com/ams/96Annual/webprogram/8AEROSOL.html
Title: Re: The Science of Aerosols
Post by: AbruptSLR on March 08, 2016, 05:52:35 PM
The linked reference indicates that Biogenic volatile organic compounds (BVOC) can either create positive, or negative, radiative forcing feedback, and that with continued global warming the Arctic tundra will become a major (as yet unaccounted for) source of BVOC which may be four-time higher than current emission levels.  Therefore, it is important that future state-of-the-art ESM projections include this feedback mechanism:

Frida Lindwall, Michelle Schollert, Anders Michelsen, Daan Blok & Riikka Rinnan (4 March 2016), "Arctic summer warming causes four-fold higher tundra volatile emissions", Biogeosciences, DOI: 10.1002/2015JG003295

http://onlinelibrary.wiley.com/doi/10.1002/2015JG003295/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2015JG003295/abstract)

Abstract: "Biogenic volatile organic compounds (BVOCs), which are mainly emitted by vegetation, may create either positive or negative climate forcing feedbacks. In the Subarctic, BVOC emissions are highly responsive to temperature, but the effects of climatic warming on BVOC emissions have not been assessed in more extreme arctic ecosystems. The Arctic undergoes rapid climate change, with air temperatures increasing at twice the rate of the global mean. Also, the amount of winter precipitation is projected to increase in large areas of the Arctic, and it is unknown how winter snow depth affects BVOC emissions during summer. Here, we examine the responses of BVOC emissions to experimental summer warming and winter snow addition – each treatment alone and in combination - in an arctic heath during two growing seasons. We observed a three-fold increase relative to ambient in BVOC emissions in response to a 4 °C summer warming. Snow addition had minor effects on growing season BVOC emissions after one winter, but decreased BVOC emissions after the second winter. We also examined differences between canopy and air temperatures, and found that the tundra canopy surface was on average 7.7 °C and maximum 21.6 °C warmer than air. This large difference suggests that the tundra surface temperature is an important driver for emissions of BVOCs, which are temperature-dependent. Our results demonstrate a strong response of BVOC emissions to increasing temperatures in the Arctic, suggesting that emission rates will increase with climate warming and thereby feed back to regional climate change."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on March 09, 2016, 07:13:12 PM
The linked article indicates that the direct aerosol-climate feedback (not the radiative forcing) is negative, and that the indirect aerosol-climate feedback is likely even more negative, than previously realized.  This indicates that in order to match the observed Anthropocene GMST history, that other Earth System feedbacks have been more positive than previously assumed.  Thus as people reduce their aerosol emissions in order to control air pollution, the negative aerosol-climate feedback contribution will be reduced while the positive Earth System feedbacks will likely accelerate, thus possibly resulting in a higher rate of global warming than previously assumed:

Robert J. Allen, William Landuyt & Steven T. Rumbold (2016), "An increase in aerosol burden and radiative effects in a warmer world", Nature Climate Change, Volume: 6, Pages: 269–274, doi:10.1038/nclimate2827


http://www.nature.com/nclimate/journal/v6/n3/full/nclimate2827.html (http://www.nature.com/nclimate/journal/v6/n3/full/nclimate2827.html)


Abstract: "Atmospheric aerosols are of significant environmental importance, due to their effects on air quality, as well as their ability to alter the planet’s radiative balance. Recent studies characterizing the effects of climate change on air quality and the broader distribution of aerosols in the atmosphere show significant, but inconsistent results, including the sign of the effect. Using a suite of state-of-the-art climate models, we show that climate change is associated with a negative aerosol–climate feedback of −0.02 to −0.09 W m−2 K−1 for direct radiative effects, with much larger values likely for indirect radiative effects. This is related to an increase in most aerosol species, particularly over the tropics and Northern Hemisphere midlatitudes, largely due to a decrease in wet deposition associated with less large-scale precipitation over land. Although simulation of aerosol processes in global climate models possesses uncertainty, we conclude that climate change may increase aerosol burden and surface concentration, which may have implications for future air quality."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on March 15, 2016, 11:07:22 PM
The linked article indicates that Europe's reductions in air pollution since 1980 has added about 0.5C of surface temperature increase to Arctic Amplification.  Just imagine how much greater impact there will be on GMST as Asia continues to reduce its air pollution:

J. C. Acosta Navarro, V. Varma, I. Riipinen, Ø. Seland, A. Kirkevåg, H. Struthers, T. Iversen, H.-C. Hansson & A. M. L. Ekman (2016), "Amplification of Arctic warming by past air pollution reductions in Europe", Nature Geoscience, doi:10.1038/ngeo2673


http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2673.html (http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2673.html)

Abstract: "The Arctic region is warming considerably faster than the rest of the globe, with important consequences for the ecosystems and human exploration of the region. However, the reasons behind this Arctic amplification are not entirely clear. As a result of measures to enhance air quality, anthropogenic emissions of particulate matter and its precursors have drastically decreased in parts of the Northern Hemisphere over the past three decades5. Here we present simulations with an Earth system model with comprehensive aerosol physics and chemistry that show that the sulfate aerosol reductions in Europe since 1980 can potentially explain a significant fraction of Arctic warming over that period. Specifically, the Arctic region receives an additional 0.3 W m−2 of energy, and warms by 0.5 °C on annual average in simulations with declining European sulfur emissions in line with historical observations, compared with a model simulation with fixed European emissions at 1980 levels. Arctic warming is amplified mainly in fall and winter, but the warming is initiated in summer by an increase in incoming solar radiation as well as an enhanced poleward oceanic and atmospheric heat transport. The simulated summertime energy surplus reduces sea-ice cover, which leads to a transfer of heat from the Arctic Ocean to the atmosphere. We conclude that air quality regulations in the Northern Hemisphere, the ocean and atmospheric circulation, and Arctic climate are inherently linked."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on March 18, 2016, 02:45:24 PM
According to the IPCC AR5 report: "The transient climate response is likely in the range of 1.0°C to 2.5°C (high confidence) and extremely unlikely greater than 3°C"; however, the linked reference uses only observed data (corrected for aerosol effects) to indicate that TCR is 2.0 +/- 0.8C.


T. Storelvmo, T. Leirvik, U. Lohmann, P. C. B. Phillips & M. Wild (2016), "Disentangling greenhouse warming and aerosol cooling to reveal Earth’s climate sensitivity", Nature Geoscience, doi:10.1038/ngeo2670


http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2670.html (http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2670.html)

Abstract: "Earth’s climate sensitivity has long been subject to heated debate and has spurred renewed interest after the latest IPCC assessment report suggested a downward adjustment of its most likely range. Recent observational studies have produced estimates of transient climate sensitivity, that is, the global mean surface temperature increase at the time of CO2 doubling, as low as 1.3 K, well below the best estimate produced by global climate models (1.8 K). Here, we present an observation-based study of the time period 1964 to 2010, which does not rely on climate models. The method incorporates observations of greenhouse gas concentrations, temperature and radiation from approximately 1,300 surface sites into an energy balance framework. Statistical methods commonly applied to economic time series are then used to decompose observed temperature trends into components attributable to changes in greenhouse gas concentrations and surface radiation. We find that surface radiation trends, which have been largely explained by changes in atmospheric aerosol loading, caused a cooling that masked approximately one-third of the continental warming due to increasing greenhouse gas concentrations over the past half-century. In consequence, the method yields a higher transient climate sensitivity (2.0  ±  0.8 K) than other observational studies."


However, I note that Shindell (2014) indicates that it is very unlikely that TCR is less than 1.3C
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140011847.pdf (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140011847.pdf)
Title: Re: The Science of Aerosols
Post by: AbruptSLR on March 18, 2016, 03:20:55 PM
The linked reference confirms, and quantifies, what we have long known; which is that as China cleans-up its aerosol emissions, GMST will increase due to CO₂ that is already in the atmosphere:

Bengang Li, Thomas Gasser, Philippe Ciais, Shilong Piao, Shu Tao, Yves Balkanski, Didier Hauglustaine, Juan-Pablo Boisier, Zhuo Chen, Mengtian Huang, Laurent Zhaoxin Li, Yue Li, Hongyan Liu, Junfeng Liu, Shushi Peng, Zehao Shen, Zhenzhong Sun, Rong Wang, Tao Wang, Guodong Yin, Yi Yin, Hui Zeng, Zhenzhong Zeng & Feng Zhou (17 March 2016), "The contribution of China’s emissions to global climate forcing", Nature, Volume: 531, Pages: 357–361, doi:10.1038/nature17165


http://www.nature.com/nature/journal/v531/n7594/full/nature17165.html (http://www.nature.com/nature/journal/v531/n7594/full/nature17165.html)


Abstract: "Knowledge of the contribution that individual countries have made to global radiative forcing is important to the implementation of the agreement on “common but differentiated responsibilities” reached by the United Nations Framework Convention on Climate Change. Over the past three decades, China has experienced rapid economic development, accompanied by increased emission of greenhouse gases, ozone precursors and aerosols, but the magnitude of the associated radiative forcing has remained unclear. Here we use a global coupled biogeochemistry–climate model and a chemistry and transport model to quantify China’s present-day contribution to global radiative forcing due to well-mixed greenhouse gases, short-lived atmospheric climate forcers and land-use-induced regional surface albedo changes. We find that China contributes 10% ± 4% of the current global radiative forcing. China’s relative contribution to the positive (warming) component of global radiative forcing, mainly induced by well-mixed greenhouse gases and black carbon aerosols, is 12% ± 2%. Its relative contribution to the negative (cooling) component is 15% ± 6%, dominated by the effect of sulfate and nitrate aerosols. China’s strongest contributions are 0.16 ± 0.02 watts per square metre for CO2 from fossil fuel burning, 0.13 ± 0.05 watts per square metre for CH4, −0.11 ± 0.05 watts per square metre for sulfate aerosols, and 0.09 ± 0.06 watts per square metre for black carbon aerosols. China’s eventual goal of improving air quality will result in changes in radiative forcing in the coming years: a reduction of sulfur dioxide emissions would drive a faster future warming, unless offset by larger reductions of radiative forcing from well-mixed greenhouse gases and black carbon."


See also (& image):
http://www.carbonbrief.org/21000-2 (http://www.carbonbrief.org/21000-2)
Title: Re: The Science of Aerosols
Post by: Richard Rathbone on March 19, 2016, 01:04:08 PM
Storelvmo et al should be worth the read if you have access to it (I don't). It really needs the range of the constraint halved to bring some reality into the models, but they seem to be gathering the right sort of data to do that eventually.

Title: Re: The Science of Aerosols
Post by: Steven on March 19, 2016, 06:26:01 PM
Storelvmo et al should be worth the read if you have access to it (I don't).

The pdf-file of that paper is here:  http://sci-hub.io/10.1038/ngeo2670 (http://sci-hub.io/10.1038/ngeo2670)

The paper uses:

Quote
Downward solar radiation at the surface (DSRS, measured in W m-2) reported at approximately 1,300 surface stations over the time period 1964-2010 (Fig. 1a,b)

"Figure 1: Radiation measurements from 1,300 surface stations":
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FDGoRKyd.png&hash=1cca11cebe1617fd587f12b3d5ed18d4)
Title: Re: The Science of Aerosols
Post by: Richard Rathbone on March 20, 2016, 07:12:42 PM
That link just takes me to a request to donate. (and some Russian that Google can't translate)
Title: Re: The Science of Aerosols
Post by: Csnavywx on March 20, 2016, 08:31:17 PM
I'm really late to this party, but Hoose et. al 2009 was referenced by the study in question:

Quote
Global aerosol-climate models with prognostic treatment of cloud droplet number concentration (CDNC) often prescribe lower bounds for CDNC or aerosol concentrations. Here we demonstrate that this possibly unphysical constraint reduces the simulated aerosol indirect effect by up to 80%, caused by extensively uniform CDNCs. In present-day conditions, the impact of the prescribed lower bound for CDNC is mainly visible over oceans, while with preindustrial emissions, large parts of both land and ocean areas are influenced. We furthermore show that imposing the same constraints on aerosol instead of on CDNC reduces the aerosol indirect effect to a lesser extent.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on May 02, 2016, 09:23:12 PM
The linked article indicates that in subtropical regions satellite data indicate strong negative forcing due to aerosols than assumed by most climate models:

Frida A.-M. Bender, Anders Engström, and Johannes Karlsson (2016), "Factors Controlling Cloud Albedo in Marine Subtropical Stratocumulus Regions in Climate Models and Satellite Observations", Journal of Climate, DOI: http://dx.doi.org/10.1175/JCLI-D-15-0095.1 (http://dx.doi.org/10.1175/JCLI-D-15-0095.1)


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0095.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0095.1)

Abstract: "This study focuses on the radiative properties of five subtropical marine stratocumulus cloud regions, on monthly mean scale. Through examination of the relation between total albedo and cloud fraction, and its variability and relation to other parameters, some of the factors controlling the reflectivity, or albedo, of the clouds in these regions are investigated. It is found that the main part of the variability in albedo at a given cloud fraction can be related to temporal rather than spatial variability, indicating spatial homogeneity in cloud radiative properties in the studied regions. This is seen most clearly in satellite observations but also appears in an ensemble of climate models. Further comparison between satellite data and output from climate models shows that there is good agreement with respect to the role of liquid water path, the parameter that can be assumed to be the primary source of variability in cloud reflectivity for a given cloud fraction. On the other hand, the influence of aerosol loading on cloud albedo differs between models and observations. The cloud-albedo effect, or cloud brightening caused by aerosol through its coupling to cloud droplet number concentration and droplet size, is found not to dominate in the satellite observations on monthly mean scale, as it appears to do on this scale in the climate models. The disagreement between models and observations is particularly strong in regions with frequent occurrence of absorbing aerosols above clouds, where satellite data, in contrast to the climate models, indicate a scene darkening with increasing aerosol loading."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on May 11, 2016, 08:59:10 PM
The linked "Bits of Science" article indicates that global dimming could be masking 50% of GHG potential warming:

http://www.bitsofscience.org/real-global-temperature-trend-global-dimming-still-masks-50-percent-co2-warming-6990/ (http://www.bitsofscience.org/real-global-temperature-trend-global-dimming-still-masks-50-percent-co2-warming-6990/)
Title: Re: The Science of Aerosols
Post by: Theta on May 11, 2016, 10:58:28 PM
The linked "Bits of Science" article indicates that global dimming could be masking 50% of GHG potential warming:

http://www.bitsofscience.org/real-global-temperature-trend-global-dimming-still-masks-50-percent-co2-warming-6990/ (http://www.bitsofscience.org/real-global-temperature-trend-global-dimming-still-masks-50-percent-co2-warming-6990/)

So, from my understanding of this article, if industrial civilisation collapsed tomorrow, we would instantly hit 2C?
Title: Re: The Science of Aerosols
Post by: AbruptSLR on May 11, 2016, 11:10:25 PM
The linked "Bits of Science" article indicates that global dimming could be masking 50% of GHG potential warming:

http://www.bitsofscience.org/real-global-temperature-trend-global-dimming-still-masks-50-percent-co2-warming-6990/ (http://www.bitsofscience.org/real-global-temperature-trend-global-dimming-still-masks-50-percent-co2-warming-6990/)

So, from my understanding of this article, if industrial civilisation collapsed tomorrow, we would instantly hit 2C?

Considering both lag-time and the current positive PDO phase, it is safe to say if we stopped GHG & aerosol emissions tomorrow, we would exceed a 2C increase within 6 to 7 years.  However, this article assumes that ECS is about 3C; so if ECS is higher, then the coming increase would also be higher.
Title: Re: The Science of Aerosols
Post by: Theta on May 11, 2016, 11:11:53 PM
The linked "Bits of Science" article indicates that global dimming could be masking 50% of GHG potential warming:

http://www.bitsofscience.org/real-global-temperature-trend-global-dimming-still-masks-50-percent-co2-warming-6990/ (http://www.bitsofscience.org/real-global-temperature-trend-global-dimming-still-masks-50-percent-co2-warming-6990/)

So, from my understanding of this article, if industrial civilisation collapsed tomorrow, we would instantly hit 2C?

Considering both lag-time and the current positive PDO phase, it is safe to say if we stopped GHG & aerosol emissions tomorrow, we would exceed a 2C increase within 6 to 7 years.  However, this article assumes that ECS is about 3C; so if ECS is higher, then the coming increase would also be higher.

Interesting, I was under the impression that it would be weeks to months.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on May 11, 2016, 11:23:27 PM
Interesting, I was under the impression that it would be weeks to months.

You can study the linked Hansen et al (2013) if you want to understand the response rates & inertia of the various Earth Systems:

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0081648 (http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0081648)
Title: Re: The Science of Aerosols
Post by: Theta on May 11, 2016, 11:26:36 PM
Interesting, I was under the impression that it would be weeks to months.

You can study the linked Hansen et al (2013) if you want to understand the response rates & inertia of the various Earth Systems:

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0081648 (http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0081648)

Cool, thanks
Title: Re: The Science of Aerosols
Post by: AbruptSLR on May 19, 2016, 07:10:59 PM
The linked open access reference indicates that uncertainty on the aerosol indirect effect (AIE) is greater in local regions than it is globally, which points to a need to better understand AIE for specific different conditions:

Shipeng Zheng, Minghuai Wang, Steven J Ghan, Aijun Ding, Hailong Wang, Kai Zhang, David Neubauer, Ulrike Lohmann, Sylvaine Ferrachat, Toshihiko Takeamura, Andrew Gettelman, Hugh Morrison, Yunha Lee, Drew T Shindell, Daniel G Partridge, Philip Stier, Zak Kipling & Congbin Fu (2016), "On the Characteristics of Aerosol Indirect Effect Based on Dynamic Regimes in Global Climate Models", Atmospheric Chemistry and Physics;16:2765-2783, DOI: 10.5194/acp-16-2765-2016

http://www.atmos-chem-phys.net/16/2765/2016/acp-16-2765-2016.html (http://www.atmos-chem-phys.net/16/2765/2016/acp-16-2765-2016.html)

Abstract: "Aerosol–cloud interactions continue to constitute a major source of uncertainty for the estimate of climate radiative forcing. The variation of aerosol indirect effects (AIE) in climate models is investigated across different dynamical regimes, determined by monthly mean 500 hPa vertical pressure velocity (ω500), lower-tropospheric stability (LTS) and large-scale surface precipitation rate derived from several global climate models (GCMs), with a focus on liquid water path (LWP) response to cloud condensation nuclei (CCN) concentrations. The LWP sensitivity to aerosol perturbation within dynamic regimes is found to exhibit a large spread among these GCMs. It is in regimes of strong large-scale ascent (ω500  <  −25 hPa day−1) and low clouds (stratocumulus and trade wind cumulus) where the models differ most. Shortwave aerosol indirect forcing is also found to differ significantly among different regimes. Shortwave aerosol indirect forcing in ascending regimes is close to that in subsidence regimes, which indicates that regimes with strong large-scale ascent are as important as stratocumulus regimes in studying AIE. It is further shown that shortwave aerosol indirect forcing over regions with high monthly large-scale surface precipitation rate (> 0.1 mm day−1) contributes the most to the total aerosol indirect forcing (from 64 to nearly 100 %). Results show that the uncertainty in AIE is even larger within specific dynamical regimes compared to the uncertainty in its global mean values, pointing to the need to reduce the uncertainty in AIE in different dynamical regimes."

Title: Re: The Science of Aerosols
Post by: AbruptSLR on May 26, 2016, 05:09:54 PM
I have frequently cited research on secondary aerosol particles, and while the linked reference concludes that cloud formation associated with such secondary aerosol particles will slightly reduce climate sensitivity; another way of looking at this research is that if/when the source of such secondary aerosol particles is reduced/degraded (such as by deforestation and wildfires), then near future climate sensitivity values will actually be higher that what AR5 reported/assumes.

Jasper Kirkby, Jonathan Duplissy, Kamalika Sengupta, Carla Frege, Hamish Gordon, Christina Williamson, Martin Heinritzi, Mario Simon, Chao Yan, João Almeida, Jasmin Tröstl, Tuomo Nieminen, Ismael K. Ortega, Robert Wagner, Alexey Adamov, Antonio Amorim, Anne-Kathrin Bernhammer, Federico Bianchi, Martin Breitenlechner, Sophia Brilke, Xuemeng Chen, Jill Craven, Antonio Dias, Sebastian Ehrhart, Richard C. Flagan, Alessandro Franchin, Claudia Fuchs, Roberto Guida, Jani Hakala, Christopher R. Hoyle, Tuija Jokinen, Heikki Junninen, Juha Kangasluoma, Jaeseok Kim, Manuel Krapf, Andreas Kürten, Ari Laaksonen , Katrianne Lehtipalo, Vladimir Makhmutov, Serge Mathot, Ugo Molteni, Antti Onnela, Otso Peräkylä, Felix Piel, Tuukka Petäjä, Arnaud P. Praplan, Kirsty Pringle, Alexandru Rap, Nigel A. D. Richards, Ilona Riipinen, Matti P. Rissanen, Linda Rondo, Nina Sarnela, Siegfried Schobesberger, Catherine E. Scott, John H. Seinfeld, Mikko Sipilä , Gerhard Steiner, Yuri Stozhkov, Frank Stratmann, Antonio Tomé, Annele Virtanen, Alexander L. Vogel, Andrea C. Wagner, Paul E. Wagner, Ernest Weingartner, Daniela Wimmer, Paul M. Winkler, Penglin Ye, Xuan Zhang, Armin Hansel, Josef Dommen, Neil M. Donahue, Douglas R. Worsnop, Urs Baltensperger, Markku Kulmala, Kenneth S. Carslaw, & Joachim Curtius, et al. (26 May 2016), "Ion-induced nucleation of pure biogenic particles", Nature, Volume: 533, Pages: 521–526, doi:10.1038/nature17953


http://www.nature.com/nature/journal/v533/n7604/full/nature17953.html (http://www.nature.com/nature/journal/v533/n7604/full/nature17953.html)

Abstract: "Atmospheric aerosols and their effect on clouds are thought to be important for anthropogenic radiative forcing of the climate, yet remain poorly understood. Globally, around half of cloud condensation nuclei originate from nucleation of atmospheric vapours. It is thought that sulfuric acid is essential to initiate most particle formation in the atmosphere, and that ions have a relatively minor role. Some laboratory studies, however, have reported organic particle formation without the intentional addition of sulfuric acid, although contamination could not be excluded. Here we present evidence for the formation of aerosol particles from highly oxidized biogenic vapours in the absence of sulfuric acid in a large chamber under atmospheric conditions. The highly oxygenated molecules (HOMs) are produced by ozonolysis of α-pinene. We find that ions from Galactic cosmic rays increase the nucleation rate by one to two orders of magnitude compared with neutral nucleation. Our experimental findings are supported by quantum chemical calculations of the cluster binding energies of representative HOMs. Ion-induced nucleation of pure organic particles constitutes a potentially widespread source of aerosol particles in terrestrial environments with low sulfuric acid pollution."


http://www.businessinsider.com/new-climate-change-study-about-clouds-2016-5 (http://www.businessinsider.com/new-climate-change-study-about-clouds-2016-5)

Also see:
Extract: "So, what's the deal with aerosols? Turns out that there are two sources of the particles:
1.   Direct aerosol particles: produced by dust, sea-salt spray, or the burning of biomass
2.   Secondary aerosol particles: formed when gas is converted into a particle — these are the type the scientists of the new study are interested in
Unlike what happens with direct aerosol particles, gas to particle conversion occurs everywhere. As a result, more than half of all the cloud seeds in the atmosphere are secondary aerosol particles!
This is where it gets tricky. Up until now, scientists believed that sulfuric acid, which is mainly produced from fossil-fuel emissions — cars, factories, etc. — were necessary for the formation of secondary aerosols. But in this new study, a group of scientists shows that Earth can actually produce these particles without any help from humans.
Instead, it gets made from a mix of tree vapors and highly energetic particles that bombard our atmosphere from outer space called cosmic rays.

This is where it gets tricky. Up until now, scientists believed that sulfuric acid, which is mainly produced from fossil-fuel emissions — cars, factories, etc. — were necessary for the formation of secondary aerosols. But in this new study, a group of scientists shows that Earth can actually produce these particles without any help from humans.
Instead, it gets made from a mix of tree vapors and highly energetic particles that bombard our atmosphere from outer space called cosmic rays."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on May 26, 2016, 05:10:30 PM
The linked reference indicates that aerosols in the Arctic have a “profound” impact on the global climate system. Climate models often underestimate the extent to which aerosols from industrial air pollution (especially those containing black carbon) warm the atmosphere because they assume Arctic air is cleaner than it actually is:

Yousuke Sato, Hiroaki Miura, Hisashi Yashiro, Daisuke Goto, Toshihiko Takemura, Hirofumi Tomita, Teruyuki Nakajima. Unrealistically pristine air in the Arctic produced by current global scale models. Scientific Reports, 2016; 6: 26561 DOI: 10.1038/srep26561

http://www.nature.com/articles/srep26561 (http://www.nature.com/articles/srep26561)

See also:
https://www.sciencedaily.com/releases/2016/05/160525083925.htm (https://www.sciencedaily.com/releases/2016/05/160525083925.htm)

Summary: "Black carbon aerosols are important for understanding climate change. Unfortunately, current simulation models consistently underestimate the amount of these aerosols in the Arctic compared to actual measurements. Now, scientists used the K computer to perform fine-grained simulations of how black carbon aerosols are transported to and distributed in the Arctic region. By using smaller grids they were able to show that they could more realistically model the amount of black carbon aerosols."

Also see:
http://www.climatecentral.org/news/tar-sands-impact-climate-air-quality-20376 (http://www.climatecentral.org/news/tar-sands-impact-climate-air-quality-20376)

Extract: "Aerosols from the production of heavy oil is a growing climate and pollution concern because new tar sands developments are on the drawing board in Venezuela, Utah and elsewhere, the study says. Today, heavy oil accounts for 10 percent of global crude oil production worldwide, mostly in Canada, which produced about 1.1 billion barrels of oil in 2014.
“The results indicate that the environmental impacts of Canadian tar sands are much larger than previously recognized,” said Allen Robinson, a mechanical engineering professor at Carnegie Mellon University who is unaffiliated with the study. “What is so novel about this paper is that tar sands were not on anybody’s radar as a major source of aerosol.”"
Title: Re: The Science of Aerosols
Post by: AbruptSLR on June 21, 2016, 05:25:50 PM
The linked reference concludes with regards to the faux hiatus and implications of aerosol reductions in the future that: "Our results suggest that a slowdown in GMST trends could have been predicted in advance, and that future reduction of anthropogenic aerosol emissions, particularly from China, would promote a positive PDO and increased GMST trends over the coming years."

Doug M. Smith, Ben B. B. Booth, Nick J. Dunstone, Rosie Eade, Leon Hermanson, Gareth S. Jones, Adam A. Scaife, Katy L. Sheen & Vikki Thompson (2016), "Role of volcanic and anthropogenic aerosols in the recent global surface warming slowdown", Nature Climate Change, doi:10.1038/nclimate3058

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate3058.html (http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate3058.html)

Abstract: "The rate of global mean surface temperature (GMST) warming has slowed this century despite the increasing concentrations of greenhouse gases. Climate model experiments show that this slowdown was largely driven by a negative phase of the Pacific Decadal Oscillation (PDO), with a smaller external contribution from solar variability, and volcanic and anthropogenic aerosols. The prevailing view is that this negative PDO occurred through internal variability. However, here we show that coupled models from the Fifth Coupled Model Intercomparison Project robustly simulate a negative PDO in response to anthropogenic aerosols implying a potentially important role for external human influences. The recovery from the eruption of Mount Pinatubo in 1991 also contributed to the slowdown in GMST trends. Our results suggest that a slowdown in GMST trends could have been predicted in advance, and that future reduction of anthropogenic aerosol emissions, particularly from China, would promote a positive PDO and increased GMST trends over the coming years. Furthermore, the overestimation of the magnitude of recent warming by models is substantially reduced by using detection and attribution analysis to rescale their response to external factors, especially cooling following volcanic eruptions. Improved understanding of external influences on climate is therefore crucial to constrain near-term climate predictions."

See also:
http://www.carbonbrief.org/aerosol-emissions-key-to-the-surface-warming-slowdown-study-says (http://www.carbonbrief.org/aerosol-emissions-key-to-the-surface-warming-slowdown-study-says)

Extract: "Human-caused aerosols are, therefore, at least another factor to add to the list of those that have contributed to the global surface warming slowdown …"
Title: Re: The Science of Aerosols
Post by: AbruptSLR on August 03, 2016, 06:24:15 PM
The linked reference indicates that emissions twenty-first century of SO2, BC, and OC are expected to decrease much more rapidly than GHG emissions; which should result in a net increase in positive radiative forcing for realistic emission pathways:

Smith et al, (2016), "Future aerosol emissions: a multi-model comparison", Climate Change, doi: 10.1007/s10584-016-1733-y

http://link.springer.com/article/10.1007%2Fs10584-016-1733-y (http://link.springer.com/article/10.1007%2Fs10584-016-1733-y)

Abstract: "This paper compares projections over the twenty-first century of SO2, BC, and OC emissions from three technologically detailed, long-term integrated assessment models. The character of the projections and the response of emissions due to a comprehensive climate policy are discussed focusing on the sectoral level. In a continuation of historical experience, aerosol and precursor emissions are increasingly decoupled from carbon dioxide emissions over the twenty-first century due to a combination of emission controls and technology shifts over time. Implementation of a comprehensive climate policy further reduces emissions, although there is significant variation in this response by sector and by model: the response has many similarities between models for the energy transformation and transportation sectors, with more diversity in the response for the building and industrial sectors. Much of these differences can be traced to specific characteristics of reference case end-use and supply-side technology deployment and emissions control assumptions, which are detailed by sector."
Title: Re: The Science of Aerosols
Post by: sidd on August 03, 2016, 09:24:33 PM
That Smith paper on aerosols disappoints. Two yers since Cowtan and Way debunked the hiatus, and we see aguments  made on the basis of the non existent hiatus ...

Referees are slacking at that journal.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on August 05, 2016, 04:50:23 PM
The linked reference indicates that aerosol forcing plays a significant role in modeled climate-cloud feedback variance & reducing the uncertainties associated with aerosol interactions would help to narrow the large range of climate sensitivity recognized by the IPCC:

A. Gettelman, B. Medeiros & J. Olson (2016), "Climate Feedback Variance and the Interaction of Aerosol Forcing and Feedbacks", Journal of Climate, DOI: http://dx.doi.org/10.1175/JCLI-D-16-0151.1 (http://dx.doi.org/10.1175/JCLI-D-16-0151.1)

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0151.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0151.1)

Abstract: "Aerosols can influence cloud radiative effects, and thus may alter interpretation of how the earth’s radiative budget responds to climate forcing. Three different ensemble experiments from the same climate model with different greenhouse gas and aerosol scenarios are used to analyze the role of aerosols in climate feedbacks and their spread across initial condition ensembles of transient climate simulations. The standard deviation of global feedback parameters across ensemble members is low, typically 0.02 Wm−2 K−1. Feedbacks from high (8.5 Wm−2) and moderate (4.5 Wm−2) year 2100 forcing cases are nearly identical. An aerosol kernel is introduced to remove effects of aerosol cloud interactions that alias into cloud feedbacks. Adjusted cloud feedbacks indicate an ‘aerosol feedback’ resulting from changes to climate that increase sea-salt emissions, mostly in the S. Ocean. Ensemble simulations also indicate higher tropical cloud feedbacks with higher aerosol loading. These effects contribute to a difference in cloud feedbacks of nearly 50% between ensembles of the same model. These two effects are also seen in aquaplanet simulations with varying fixed drop number. Thus aerosols can be a significant modifier of cloud feedbacks, and different representations of aerosols and their interactions with clouds may contribute to multi-model spread in climate feedbacks and climate sensitivity in multi model archives."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on August 06, 2016, 05:14:40 PM
The linked reference states: "The model with the strongest response (HadGEM3-GA4) compares best with observations of AOD regionally, …". This indicates that as scientists improve their CMIP6 models to better match observations, we can expect to see more projections of accelerating global warming beyond the CMIP5 projections due to the continuing reductions of sulfur dioxide emissions from China:

Kasoar, M., Voulgarakis, A., Lamarque, J.-F., Shindell, D. T., Bellouin, N., Collins, W. J., Faluvegi, G., and Tsigaridis, K.: Regional and global temperature response to anthropogenic SO2 emissions from China in three climate models, Atmos. Chem. Phys., 16, 9785-9804, doi:10.5194/acp-16-9785-2016, 2016.

http://www.atmos-chem-phys.net/16/9785/2016/ (http://www.atmos-chem-phys.net/16/9785/2016/)

Abstract. We use the HadGEM3-GA4, CESM1, and GISS ModelE2 climate models to investigate the global and regional aerosol burden, radiative flux, and surface temperature responses to removing anthropogenic sulfur dioxide (SO2) emissions from China. We find that the models differ by up to a factor of 6 in the simulated change in aerosol optical depth (AOD) and shortwave radiative flux over China that results from reduced sulfate aerosol, leading to a large range of magnitudes in the regional and global temperature responses. Two of the three models simulate a near-ubiquitous hemispheric warming due to the regional SO2 removal, with similarities in the local and remote pattern of response, but overall with a substantially different magnitude. The third model simulates almost no significant temperature response. We attribute the discrepancies in the response to a combination of substantial differences in the chemical conversion of SO2 to sulfate, translation of sulfate mass into AOD, cloud radiative interactions, and differences in the radiative forcing efficiency of sulfate aerosol in the models. The model with the strongest response (HadGEM3-GA4) compares best with observations of AOD regionally, however the other two models compare similarly (albeit poorly) and still disagree substantially in their simulated climate response, indicating that total AOD observations are far from sufficient to determine which model response is more plausible. Our results highlight that there remains a large uncertainty in the representation of both aerosol chemistry as well as direct and indirect aerosol radiative effects in current climate models, and reinforces that caution must be applied when interpreting the results of modelling studies of aerosol influences on climate. Model studies that implicate aerosols in climate responses should ideally explore a range of radiative forcing strengths representative of this uncertainty, in addition to thoroughly evaluating the models used against observations.

Title: Re: The Science of Aerosols
Post by: AbruptSLR on August 15, 2016, 09:57:53 PM
Per the linked reference current climate change models do not adequately account for the influence of secondary organic aerosols, SOAs (including those from trees). Thus we may well all be in for an unpleasant surprise as increasing wildfires, drought, pests, and heat/seasonal stress reduce the current negative forcing associated with such SOAs:

Manish Shrivastava et al. Sensitivity Analysis of Simulated SOA Loadings Using a Variance-Based Statistical Approach, Journal of Advances in Modeling Earth Systems (2016). DOI: 10.1002/2015MS000554


http://onlinelibrary.wiley.com/doi/10.1002/2015MS000554/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2015MS000554/abstract)

Abstract: "We investigate the sensitivity of secondary organic aerosol (SOA) loadings simulated by a regional chemical transport model to seven selected model parameters using a modified volatility basis-set (VBS) approach: four involving emissions of anthropogenic and biogenic volatile organic compounds, anthropogenic semivolatile and intermediate volatility organics (SIVOCs), and NOx; two involving dry deposition of SOA precursor gases, and one involving particle-phase transformation of SOA to low volatility. We adopt a quasi-Monte Carlo sampling approach to effectively sample the high-dimensional parameter space, and perform a 250 member ensemble of simulations using a regional model, accounting for some of the latest advances in SOA treatments based on our recent work. We then conduct a variance-based sensitivity analysis using the generalized linear model method to study the responses of simulated SOA loadings to the model parameters. Analysis of SOA variance from all 250 simulations shows that the volatility transformation parameter, which controls whether or not SOA that starts as semivolatile is rapidly transformed to nonvolatile SOA by particle-phase processes such as oligomerization and/or accretion, is the dominant contributor to variance of simulated surface-level daytime SOA (65% domain average contribution). We also split the simulations into two subsets of 125 each, depending on whether the volatility transformation is turned on/off. For each subset, the SOA variances are dominated by the parameters involving biogenic VOC and anthropogenic SIVOC emissions. Furthermore, biogenic VOC emissions have a larger contribution to SOA variance when the SOA transformation to nonvolatile is on, while anthropogenic SIVOC emissions have a larger contribution when the transformation is off. NOx contributes less than 4.3% to SOA variance, and this low contribution is mainly attributed to dominance of intermediate to high NOx conditions throughout the simulated domain. However, we note that SOA yields have a more complex nonlinear dependence on NOx levels, which needs to be addressed by more integrated model-measurement approaches focused on gaining a better process-level understanding of anthropogenic-biogenic interactions. The two parameters related to dry deposition of SOA precursor gases also have very low contributions to SOA variance. This study highlights the large sensitivity of SOA loadings to the particle-phase processes such as oligomerization that rapidly cause large decrease in the volatility of SOA, which is neglected in most previous models."

See also:
http://phys.org/news/2016-06-plain-sighta-less-explored-secret-secondary.html (http://phys.org/news/2016-06-plain-sighta-less-explored-secret-secondary.html)

Extract: "One of the secrets relevant to climate change involves how emissions from nature and human activities are changed in the atmosphere to become secondary organic aerosols (SOA).
Now a team of scientists led by Pacific Northwest National Laboratory has discovered an often ignored but very influential process/parameter that can affect not only the air we breathe but the weather and climate. Oligomerization, or molecular bonding, is a process by which smaller molecules combine and form larger molecules, increasing the amount and lifetime of secondary organic aerosols in the atmosphere. These bondings may hold the key to more successful modeling of the particles. Most atmospheric models ignore oligomerization.
"The study's comprehensive sensitivity analysis clearly shows that leaving out secondary organic aerosol oligomerization processes in climate models could severely limit our ability to understand and predict their impacts," noted Dr. Manish Shrivastava, PNNL atmospheric scientist and lead author of the study."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 03, 2016, 01:30:44 AM
The linked reference provides more information on the influence of anthropogenic aerosols:

Pengfei Yu, Daniel M. Murphy, Robert W. Portmann, Owen B. Toon, Karl D. Froyd, Andrew W. Rollins, Ru-Shan Gao & Karen H. Rosenlof (31 August 2016) "Radiative Forcing from Anthropogenic Sulfur and Organic Emissions Reaching the Stratosphere", Geophysical Research Letters, DOI: 10.1002/2016GL070153

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070153/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2016GL070153/abstract)

Abstract: "Stratospheric aerosols cool the Earth by scattering sunlight. Although sulfuric acid dominates the stratospheric aerosol, this study finds that organic material in the lowermost stratosphere contributes 30-40% of the non-volcanic stratospheric aerosol optical depth (sAOD). Simulations indicate that non-volcanic sAOD has increased 77% since 1850. Stratospheric aerosol accounts for 21% of the total direct aerosol radiative forcing (which is negative) and 12% of the total AOD increase from organics and sulfate. There is a larger stratospheric influence on radiative forcing (i.e. 21%) relative to AOD (i.e. 12%) because an increase of tropospheric black carbon warms the planet while stratospheric aerosols (including black carbon) cool the planet. Radiative forcing from non-volcanic stratospheric aerosol mass of anthropogenic origin, including organics, has not been widely considered as a significant influence on the climate system."
Title: Re: The Science of Aerosols
Post by: FishOutofWater on September 03, 2016, 03:23:17 AM
If those organic stratospheric aerosols which cause cooling are primarily in the areas of tropical and subtropical upwelling of air that would amplify the cooling of the tropopause transition layer, leading to the intensification of the strongest hurricanes.

This is important stuff. A cooler stratosphere has profound implications.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 03, 2016, 03:28:07 AM
If those organic stratospheric aerosols which cause cooling are primarily in the areas of tropical and subtropical upwelling of air that would amplify the cooling of the tropopause transition layer, leading to the intensification of the strongest hurricanes.

This is important stuff. A cooler stratosphere has profound implications.

Thanks for the pointer, its never too late to learn something new.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on October 10, 2016, 05:40:36 PM
The linked reference provides new insights into the complex issue of cloud-sensitive aerosol loadings in low level marine clouds:

H. Andersen, J. Cermak, J. Fuchs & K. Schwarz (8 October 2016), "Global Observations of Cloud-Sensitive Aerosol Loadings in Low Level Marine Clouds", JGR: Atmospheres, DOI: 10.1002/2016JD025614


http://onlinelibrary.wiley.com/doi/10.1002/2016JD025614/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2016JD025614/abstract)

Abstract: "Aerosol-cloud interaction is a key component of the Earth's radiative budget and hydrological cycle, but many facets of its mechanisms are not yet fully understood. In this study, global satellite-derived aerosol and cloud products are used to identify at what aerosol loadings cloud droplet size shows the greatest sensitivity to changes in aerosol loading (ACSmax). While on average, cloud droplet size is most sensitive at relatively low aerosol loadings, distinct spatial and temporal patterns exist. Possible determinants for these are identified with reanalysis data. The magnitude of ACSmax is found to be constrained by the total columnar water vapor. Seasonal patterns of water vapor are reflected in the seasonal patterns of ACSmax. Also, situations with enhanced turbulent mixing are connected to higher ACSmax, possibly due to intensified aerosol activation. Of the analyzed aerosol species, dust seems to impact ACSmax the most, as dust particles increase the retrieved aerosol loading without substantially increasing the concentration of cloud condensation nuclei."
Title: Re: The Science of Aerosols
Post by: jai mitchell on November 21, 2016, 07:04:09 PM
This document previously posted shows the impact of dimethyl sulifde on the atmosphere and global cooling impacts from current high-density forest regions.

http://digital.csic.es/bitstream/10261/117629/1/jgrd51980.pdf (http://digital.csic.es/bitstream/10261/117629/1/jgrd51980.pdf)

This study shows the pollen records of previous interglacials showing what primoridal interglacials looked like from a forest biomass perspective.

http://centaur.reading.ac.uk/40025/1/cpd-11-1031-2015.pdf (http://centaur.reading.ac.uk/40025/1/cpd-11-1031-2015.pdf)

This study shows that previous interglacial periods experience significantly increased temperature response to CO2 than the glacial periods.  It is my assertion that the cause of this increased response is due to much higher temperature sensitivities to cloudcover fractions at lower latitudes and more rapid shifts of cloudcover regimes to the further northern latitudes during interglacials with increases in temperature, leading to rapid and significant albedo declines, increased solar absorption and increased temperatures.

http://advances.sciencemag.org/content/2/11/e1501923.full (http://advances.sciencemag.org/content/2/11/e1501923.full)

note that the expected ECS value for this study is closer to 5C.

Also supporting the potential for much higher interglacial ECS values is this study looking at a 2Mya global temperature reconstruction.

http://www.nature.com/nature/journal/v538/n7624/abs/nature19798.html (http://www.nature.com/nature/journal/v538/n7624/abs/nature19798.html)

------------------------

In view of this information, with regard to future potential shifts in our climate.  We are running, while blindfolded, carrying scissors. 

We know that interglacial ECS is very likely at the high end (or higher) than the current IPCC range of 1.5C to 4.5C.  We also know that primordial interglacial forest dimethyl sulfide emissions AT MIDLATITUDES was much higher than our currently (relatively) deforested northern hemisphere can produce.

We know that the largest uncertainty with regard to paleoclimate ECS is the aerosol component.

---------

IF my assertion is correct and this increase is due to increased cloud-cover fraction sensitivity during interglacials.

THEN It is possibly the most critical need of the entire body of science to develop an adequate model of primordial forest dimethyl sulfide emissions in the mid latitudes during previous interglacials

SO THAT we can adequately deduce what how our current anthropogenic impacts on mid-latitude forest densities will induce on our modern cloudcover fraction as temperatures increase.

(reposted to conservative scientists and consequences thread)

Title: Re: The Science of Aerosols
Post by: SteveMDFP on November 21, 2016, 07:27:54 PM
. . .                     
In view of this information, with regard to future potential shifts in our climate.  We are running, while blindfolded, carrying scissors. 
   

Perhaps we should say "running, while blindfolded, juggling chainsaws."
Title: Re: The Science of Aerosols
Post by: jai mitchell on December 11, 2016, 02:22:53 AM
Shmengie posted this question here:

http://forum.arctic-sea-ice.net/index.php/topic,1805.msg96253.html#msg96253 (http://forum.arctic-sea-ice.net/index.php/topic,1805.msg96253.html#msg96253)

Quote
Does moisture content of atmospheric layers (troposphere/stratosphere) change or affect their height at the poles?

Funny, I was just reviewing "Observational Evidence for Aerosols Increasing Upper Tropospheric Humidity" by Riuttanen et al.  see: http://www.atmos-chem-phys.net/16/14331/2016/acp-16-14331-2016.pdf (http://www.atmos-chem-phys.net/16/14331/2016/acp-16-14331-2016.pdf)

I have been analyzing regional impacts of SO2 emission reductions on the tropopause height. A known effect, though the granual regional impacts are not well known, only a global average which is next to useless.

however, seeing the movement of tropical water vapor from the West extratropics all the way to the arctic this year makes me even more confirmed that we are seeing a great shift in the tropopause height, which produces a stronger meridional (North-South) gradient to move tropical water vapor and heat further into the arctic than ever before. (edit note: this appears to be a function of high temperature industrial process Aerosols which move more rapidly into the mid/upper troposphere as opposed to open fire (coal/biomass) aerosols which appear - during Winter especially - to stay predominantly in the lower/mid troposphere)

This paper was a bit of a Surprise to me though, The significant increase in upper tropospheric water vapor (humidity) would seem (at first glance) to cool this region.  I think the real issue here is that the expansion of the tropics is happening at the tropical edge, and the upper tropospheric (humidity) dynamics are limited there, while the boundary layer impacts of reduced AOD and cloud reflectivity levels are impacted more directly with reductions in SO2 emissions.  Not sure though.

So yeah, I would figure that, in the tropics at least, increased humidity at the upper troposphere would lead to a lowering of the tropopause height

--------------
post edit, the effect of increased rainfall in the upper troposphere of the tropics would work to effectively move latent heat from the upper altitudes to the lower altitudes, greatly increasing lower troposphere temperatures and cooling upper troposphere temperatures (in the tropics) this effect has been observed quite clearly in the MSU channel temp analyses. 

By  cooling the upper troposphere this way, the expansion of tropical waves of heat and water vapor in the meridional are reduces since the Coriolis effect is moderated by the lower tropopause heights. 

This is the primary reason that we are currently seeing greater expansions of tropical moisture into the mid latitudes since the last two weeks of 2015 (though it has been evidence since China slowed it's coal consumption growth in early 2013.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on December 14, 2016, 05:14:52 PM
Aerosols can have a large impact on the rate of Arctic Amplification via their impact on clouds, and the linked reference discusses the use of both satellite data and computer models to reduce the uncertainties associated with this important feedback mechanism:

Zamora, L. M., Kahn, R. A., Eckhardt, S., McComiskey, A., Sawamura, P., Moore, R., and Stohl, A.: Arctic aerosol net indirect effects on thin, mid-altitude, liquid-bearing clouds, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1037, in review, 2016.

http://www.atmos-chem-phys-discuss.net/acp-2016-1037/ (http://www.atmos-chem-phys-discuss.net/acp-2016-1037/)

Abstract. Aerosol indirect effects have uncertain, but potentially large, impacts on the Arctic energy budget. Here, we have reduced uncertainty in current-day Arctic net aerosol indirect effects on the surface by better constraining various physical and microphysical characteristics of optically thin, liquid-containing clouds in clean, average and aerosol-impacted conditions using a combination of CALIPSO and CloudSat data and model output. This work provides a foundation for how future observational studies can evaluate previous model estimates of the aerosol indirect effect. Clouds over sea ice and open ocean show large differences in surface and meteorological forcing, including a near doubling of multi-layer cloud presence over the open ocean compared to sea ice. The optically thin cloud subset is susceptible to aerosols, and over sea ice we estimate a regional scale maximum net indirect effect on these clouds during polar night equivalent to ~ 0.6–0.8 W m−2 at the surface. Aerosol presence is related to reduced precipitation, cloud thickness, and radar reflectivity, and may be associated with an increased likelihood of cloud presence in the liquid phase. The observations are consistent with a thermodynamic indirect effect hypothesis and are inconsistent with a glaciation indirect effect.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on January 03, 2017, 08:53:36 PM
The linked reference provides some previously missing field information on Antarctic aerosols:

Giordano, M. R., Kalnajs, L. E., Avery, A., Goetz, J. D., Davis, S. M., and DeCarlo, P. F.: A missing source of aerosols in Antarctica – beyond long-range transport, phytoplankton, and photochemistry, Atmos. Chem. Phys., 17, 1-20, doi:10.5194/acp-17-1-2017, 2017.

http://www.atmos-chem-phys.net/17/1/2017/ (http://www.atmos-chem-phys.net/17/1/2017/)

Abstract. Understanding the sources and evolution of aerosols is crucial for constraining the impacts that aerosols have on a global scale. An unanswered question in atmospheric science is the source and evolution of the Antarctic aerosol population. Previous work over the continent has primarily utilized low temporal resolution aerosol filters to answer questions about the chemical composition of Antarctic aerosols. Bulk aerosol sampling has been useful in identifying seasonal cycles in the aerosol populations, especially in populations that have been attributed to Southern Ocean phytoplankton emissions. However, real-time, high-resolution chemical composition data are necessary to identify the mechanisms and exact timing of changes in the Antarctic aerosol. The recent 2ODIAC (2-Season Ozone Depletion and Interaction with Aerosols Campaign) field campaign saw the first ever deployment of a real-time, high-resolution aerosol mass spectrometer (SP-AMS – soot particle aerosol mass spectrometer – or AMS) to the continent. Data obtained from the AMS, and a suite of other aerosol, gas-phase, and meteorological instruments, are presented here. In particular, this paper focuses on the aerosol population over coastal Antarctica and the evolution of that population in austral spring. Results indicate that there exists a sulfate mode in Antarctica that is externally mixed with a mass mode vacuum aerodynamic diameter of 250 nm. Springtime increases in sulfate aerosol are observed and attributed to biogenic sources, in agreement with previous research identifying phytoplankton activity as the source of the aerosol. Furthermore, the total Antarctic aerosol population is shown to undergo three distinct phases during the winter to summer transition. The first phase is dominated by highly aged sulfate particles comprising the majority of the aerosol mass at low wind speed. The second phase, previously unidentified, is the generation of a sub-250 nm aerosol population of unknown composition. The second phase appears as a transitional phase during the extended polar sunrise. The third phase is marked by an increased importance of biogenically derived sulfate to the total aerosol population (photolysis of dimethyl sulfate and methanesulfonic acid (DMS and MSA)). The increased importance of MSA is identified both through the direct, real-time measurement of aerosol MSA and through the use of positive matrix factorization on the sulfur-containing ions in the high-resolution mass-spectral data. Given the importance of sub-250 nm particles, the aforementioned second phase suggests that early austral spring is the season where new particle formation mechanisms are likely to have the largest contribution to the aerosol population in Antarctica.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 22, 2017, 05:20:59 PM
The linked article is entitled: "Aerosol study to look at great unknown in climate science".  It looks like we still have a lot to learn, and if we were smart we world adopt a precautionary principal approach to climate change.

https://www.theguardian.com/world/2017/feb/22/antarctic-study-examines-impact-of-aerosols-on-climate-change (https://www.theguardian.com/world/2017/feb/22/antarctic-study-examines-impact-of-aerosols-on-climate-change)

Extract: "Australian scientists are studying air pollution and cloud formation in Antarctica in an effort to understand how non-carbon aerosolised particles impact on global temperatures.

It’s the first comprehensive study of the composition and concentration of aerosols in the Antarctic sea ice area, a region that influences cloud formation and weather patterns for much of the southern hemisphere."
Title: Re: The Science of Aerosols
Post by: jai mitchell on March 04, 2017, 11:55:26 PM
linked article shows strong model response to aerosol reductions forcing a widening of the InterTropical Convergence Zone - we are seeing this effect today with expansions of tropical water vapor pulses and atmospheric rivers moving up the pacific and atlantic from geolocation hot spots of pacific warm pool and gulf of mexico.  This will continue to grow in impact and intensity/frequency.

https://www.researchgate.net/profile/Robert_Allen12/publication/303853172_Future_Aerosol_Reductions_and_Widening_of_the_Northern_Tropical_Belt/links/576c5ae508ae9bd709960a4d.pdf (https://www.researchgate.net/profile/Robert_Allen12/publication/303853172_Future_Aerosol_Reductions_and_Widening_of_the_Northern_Tropical_Belt/links/576c5ae508ae9bd709960a4d.pdf)

Future aerosol reductions and widening of the northern tropical belt
Robert J. Allen1 and Osinachi Ajoku1,2

1Department of Earth Sciences, University of California, Riverside, California, USA, 2Scripps Institution of Oceanography,
University of California, San Diego, La Jolla, California, USA

Abstract Observations show that the tropical belt has widened over the past few decades,
a phenomenon associated with poleward migration of subtropical dry zones and large-scale atmospheric circulation. Although part of this signal is related to natural climate variability, studies have identified an externally forced contribution primarily associated with greenhouse gases (GHGs) and stratospheric ozone loss. Here we show that the increase in aerosols over the twentieth century has led to contraction of the northern tropical belt, thereby offsetting part of the widening associated with the increase in GHGs. Over the 21st century, however, when aerosol emissions are projected to decrease, the effects of aerosols and GHGs reinforce one another, both contributing to widening of the northern tropical belt. Models that have larger aerosol forcing, by including aerosol indirect effects on cloud albedo and lifetime, yield significantly larger Northern Hemisphere (NH) tropical widening than models with direct aerosol effects only. More targeted simulations show that future reductions in aerosols can drive NH tropical widening as large as greenhouse gases, and idealized simulations show the importance of NH midlatitude aerosol forcing. Mechanistically, the 21st century reduction in aerosols peaks near 40∘N, which results in a corresponding maximum increase in surface solar radiation, NH midlatitude tropospheric warming amplification, and a poleward shift in the latitude of maximum baroclinicity, implying a corresponding shift in atmospheric circulation. If models with aerosol indirect effects better represent the real world, then future aerosol changes are likely to be an important—if not dominant—driver of NH tropical belt widening.
Title: Re: The Science of Aerosols
Post by: Shared Humanity on March 05, 2017, 03:30:14 PM
A strong case is being made for dumping huge amounts of material into the upper atmosphere in a desperate attempt to keep the planet from burning up. This scares the hell out of me.
Title: Re: The Science of Aerosols
Post by: DrTskoul on March 05, 2017, 03:57:40 PM
A strong case is being made for dumping huge amounts of material into the upper atmosphere in a desperate attempt to keep the planet from burning up. This scares the hell out of me.

It should as we have no effing idea what the unintended consequences would be....
Title: Re: The Science of Aerosols
Post by: jai mitchell on March 21, 2017, 03:29:44 PM
This paper shows that those models in the CMIP ensemble that include full indirect aerosol effects have about 1.5C of additional warming in the arctic over those that do not. (edit: I am estimating that the mean value for non-indirect is close to 3.0C under RCP 4.5 - so indirect Aerosol effects would be +4.5C warming - since we are already at +6C last year, obviously these models are incongruent with reality since they are looking at significantly higher forcing values than the ones we have today)   There are other aerosol effects not adequately modeled within any of these tools, including changes to the lapse rate, tropopause height and larger forcing changes in the tropics, leading to expansions of water vapor to higher latitudes, increased atmospheric rivers >80'N and a semi permanent +IPO.

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0362.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0362.1)

Indirect Aerosol Effect Increases CMIP5 Models’ Projected Arctic Warming

Petr Chylek et al.

Abstract:  Phase 5 of the Coupled Model Intercomparison Project (CMIP5) climate models’ projections of the 2014–2100 Arctic warming under radiative forcing from representative concentration pathway 4.5 (RCP4.5) vary from 0.9° to 6.7°C. Climate models with or without a full indirect aerosol effect are both equally successful in reproducing the observed (1900–2014) Arctic warming and its trends. However, the 2014–2100 Arctic warming and the warming trends projected by models that include a full indirect aerosol effect (denoted here as AA models) are significantly higher (mean projected Arctic warming is about 1.5°C higher) than those projected by models without a full indirect aerosol effect (denoted here as NAA models). The suggestion is that, within models including full indirect aerosol effects, those projecting stronger future changes are not necessarily distinguishable historically because any stronger past warming may have been partially offset by stronger historical aerosol cooling. The CMIP5 models that include a full indirect aerosol effect follow an inverse radiative forcing to equilibrium climate sensitivity relationship, while models without it do not.

Title: Re: The Science of Aerosols
Post by: AbruptSLR on April 16, 2017, 04:50:26 AM
The linked reference discusses the use of machine learn to better evaluate the classification of primary biological aerosols:

Ruske, et. al. 2017, “Evaluation of machine learning algorithms for classification of primary biological aerosol using a new UV-LIF spectrometer”, Atmos. Meas. Tech., 10, 695–708,  doi:10.5194/amt-10-695-2017


http://www.atmos-meas-tech.net/10/695/2017/amt-10-695-2017.pdf (http://www.atmos-meas-tech.net/10/695/2017/amt-10-695-2017.pdf)

Title: Re: The Science of Aerosols
Post by: AbruptSLR on April 18, 2017, 12:27:14 PM
The linked article discusses how CAM5 models open-fire aerosol impacts on direct radiative, cloud and surface-albedo effects:

Yiquan Jiang et. al. (2017), "Impacts of global open-fire aerosols on direct radiative, cloud and surface-albedo effects simulated with CAM5" Atmospheric Chemistry and Physics; 16:14805-14824; DOI: 10.5194/acp-16-14805-2016

http://www.atmos-chem-phys.net/16/14805/2016/acp-16-14805-2016.html (http://www.atmos-chem-phys.net/16/14805/2016/acp-16-14805-2016.html)

Abstract: "Aerosols from open-land fires could significantly perturb the global radiation balance and induce climate change. In this study, Community Atmosphere Model version 5 (CAM5) with prescribed daily fire aerosol emissions is used to investigate the spatial and seasonal characteristics of radiative effects (REs, relative to the case of no fires) of open-fire aerosols including black carbon (BC) and particulate organic matter (POM) from 2003 to 2011. The global annual mean RE from aerosol–radiation interactions (REari) of all fire aerosols is 0.16 ± 0.01 W m−2 (1σ uncertainty), mainly due to the absorption of fire BC (0.25 ± 0.01 W m−2), while fire POM induces a small effect (−0.05 and 0.04 ± 0.01 W m−2 based on two different methods). Strong positive REari is found in the Arctic and in the oceanic regions west of southern Africa and South America as a result of amplified absorption of fire BC above low-level clouds, in general agreement with satellite observations. The global annual mean RE due to aerosol–cloud interactions (REaci) of all fire aerosols is −0.70 ± 0.05 W m−2, resulting mainly from the fire POM effect (−0.59 ± 0.03 W m−2). REari (0.43 ± 0.03 W m−2) and REaci (−1.38 ± 0.23 W m−2) in the Arctic are stronger than in the tropics (0.17 ± 0.02 and −0.82 ± 0.09 W m−2 for REari and REaci), although the fire aerosol burden is higher in the tropics. The large cloud liquid water path over land areas and low solar zenith angle of the Arctic favor the strong fire aerosol REaci (up to −15 W m−2) during the Arctic summer. Significant surface cooling, precipitation reduction and increasing amounts of low-level cloud are also found in the Arctic summer as a result of the fire aerosol REaci based on the atmosphere-only simulations. The global annual mean RE due to surface-albedo changes (REsac) over land areas (0.03 ± 0.10 W m−2) is small and statistically insignificant and is mainly due to the fire BC-in-snow effect (0.02 W m−2) with the maximum albedo effect occurring in spring (0.12 W m−2) when snow starts to melt."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on May 13, 2017, 07:00:37 PM
Xie, X., Zhang, H., Liu, X., Peng, Y., and Liu, Y.: Sensitivity study of cloud parameterizations with relative dispersion in CAM5.1: impacts on aerosol indirect effects, Atmos. Chem. Phys., 17, 5877-5892, doi:10.5194/acp-17-5877-2017, 2017.

http://www.atmos-chem-phys.net/17/5877/2017/ (http://www.atmos-chem-phys.net/17/5877/2017/)

Abstract. Aerosol-induced increase of relative dispersion of cloud droplet size distribution ε exerts a warming effect and partly offsets the cooling of aerosol indirect radiative forcing (AIF) associated with increased droplet concentration by increasing the cloud droplet effective radius (Re) and enhancing the cloud-to-rain autoconversion rate (Au) (labeled as the dispersion effect), which can help reconcile global climate models (GCMs) with the satellite observations. However, the total dispersion effects on both Re and Au are not fully considered in most GCMs, especially in different versions of the Community Atmospheric Model (CAM). In order to accurately evaluate the dispersion effect on AIF, the new complete cloud parameterizations of Re and Au explicitly accounting for ε are implemented into the CAM version 5.1 (CAM5.1), and a suite of sensitivity experiments is conducted with different representations of ε reported in the literature. It is shown that the shortwave cloud radiative forcing is much better simulated with the new cloud parameterizations as compared to the standard scheme in CAM5.1, whereas the influences on longwave cloud radiative forcing and surface precipitation are minimal. Additionally, consideration of the dispersion effect can significantly reduce the changes induced by anthropogenic aerosols in the cloud-top effective radius and the liquid water path, especially in the Northern Hemisphere. The corresponding AIF with the dispersion effect considered can also be reduced substantially by a range of 0.10 to 0.21 W m−2 at the global scale and by a much bigger margin of 0.25 to 0.39 W m−2 for the Northern Hemisphere in comparison with that of fixed relative dispersion, mainly dependent on the change of relative dispersion and droplet concentrations (Δε∕ΔNc).
Title: Re: The Science of Aerosols
Post by: jai mitchell on May 13, 2017, 07:35:31 PM
this is good news to be sure, much more work must be done but this is good.
Title: Re: The Science of Aerosols
Post by: Aporia_filia on June 22, 2017, 01:32:11 PM
I think this might be of relevant interest:

https://www.sciencedaily.com/releases/2017/06/170621133451.htm (https://www.sciencedaily.com/releases/2017/06/170621133451.htm)

"Role aerosols play in climate change unlocked by spectacular Icelandic volcanic eruption"
Title: Re: The Science of Aerosols
Post by: AbruptSLR on June 23, 2017, 03:41:52 PM
If tests on geoengineering are likely to occur, why not set them up so as to determine the aerosol-cloud feedback interaction so that climate model projections can be refined?

Robert Wood et. al. (22 June 2017), "Could geoengineering research help answer one of the biggest questions in climate science?", Earth's Future, DOI: 10.1002/2017EF000601

http://onlinelibrary.wiley.com/doi/10.1002/2017EF000601/abstract?utm_content=bufferc1ece&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer (http://onlinelibrary.wiley.com/doi/10.1002/2017EF000601/abstract?utm_content=bufferc1ece&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer)

Extract: "Anthropogenic aerosol impacts on clouds constitute the largest source of uncertainty in quantifying the radiative forcing of climate, and hinders our ability to determine Earth's climate sensitivity to greenhouse gas increases. Representation of aerosol-cloud interactions in global models is particularly challenging because these interactions occur on typically unresolved scales. Observational studies show influences of aerosol on clouds, but correlations between aerosol and clouds are insufficient to constrain aerosol forcing because of the difficulty in separating aerosol and meteorological impacts. In this commentary, we argue that this current impasse may be overcome with the development of approaches to conduct control experiments whereby aerosol particle perturbations can be introduced into patches of marine low clouds in a systematic manner. Such cloud perturbation experiments constitute a fresh approach to climate science and would provide unprecedented data to untangle the effects of aerosol particles on cloud microphysics and the resulting reflection of solar radiation by clouds. The control experiments would provide a critical test of high-resolution models that are used to develop an improved representation aerosol-cloud interactions needed to better constrain aerosol forcing in global climate models."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on July 19, 2017, 05:05:26 PM
The linked reference concludes that: "… aerosol–cloud interactions will play a key role in determining future interhemispheric shifts in climate."

Eui-Seok Chung & Brian J. Soden  (2017), "Hemispheric climate shifts driven by anthropogenic aerosol–cloud interactions", Nature Geoscience, doi:10.1038/ngeo2988

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2988.html?utm_content=buffer4bf23&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer&foxtrotcallback=true (http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2988.html?utm_content=buffer4bf23&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer&foxtrotcallback=true)

Abstract: "The contrasting rainfall between the wet tropics and the dry subtropics largely determines the climate of the tropical zones. A southward shift of these rain belts has been observed throughout the latter half of the twentieth century, with profound societal consequences. Although such large-scale shifts in rainfall have been linked to interhemispheric temperature gradients from anthropogenic aerosols, a complete understanding of this mechanism has been hindered by the lack of explicit information on aerosol radiative effects. Here we quantify the relative contributions of radiative forcing from anthropogenic aerosols to the interhemispheric asymmetry in temperature and precipitation change for climate change simulations. We show that in model simulations the vast majority of the precipitation shift does not result from aerosols directly through their absorption and scattering of radiation, but rather indirectly through their modification of cloud radiative properties. Models with larger cloud responses to aerosol forcing are found to better reproduce the observed interhemispheric temperature changes and tropical rain belt shifts over the twentieth century, suggesting that aerosol–cloud interactions will play a key role in determining future interhemispheric shifts in climate."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on August 02, 2017, 10:17:59 PM
The linked reference studies dynamical cloud response to aerosol forcing and concludes: "The dynamical cloud response is closely linked to the meridional displacement of the Hadley Cell that, in turn, is driven by changes in the cross-equatorial energy transport. In this way, the dynamical cloud changes act as a positive feedback on the meridional displacement of the Hadley Cell, roughly doubling the projected changes in cross-equatorial energy transport compared to that from the microphysical changes alone."

Brian Soden and Eui-Seok Chung (2017), "The Large Scale Dynamical Response of Clouds to Aerosol Forcing" Journal of Climate", https://doi.org/10.1175/JCLI-D-17-0050.1 (https://doi.org/10.1175/JCLI-D-17-0050.1)

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0050.1?utm_content=bufferaa6b0&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0050.1?utm_content=bufferaa6b0&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer)

Abstract: "We use radiative kernels to quantify the instantaneous radiative forcing of aerosols and the aerosol-mediated cloud response in coupled ocean-atmosphere model simulations under both historical and future emission scenarios. The method is evaluated using matching pairs of historical climate change experiments with and without aerosol forcing and accurately captures the spatial pattern and global mean effects of aerosol forcing. We show that aerosol-driven changes in the atmospheric circulation induce additional cloud changes. Thus, the total aerosol-mediated cloud response consists of both local microphysical changes and non-local dynamical changes that are driven by hemispheric asymmetries in aerosol forcing. By comparing coupled and fixed-SST (sea surface temperature) simulations with identical aerosol forcing we isolate the relative contributions of these two components, exploiting the ability of prescribed SSTs to also suppress changes in the atmospheric circulation. The radiative impact of the dynamical cloud changes are found to be comparable in magnitude to that of the microphysical cloud changes, and act to further amplify the inter-hemispheric asymmetry of the aerosol radiative forcing. The dynamical cloud response is closely linked to the meridional displacement of the Hadley Cell that, in turn, is driven by changes in the cross-equatorial energy transport. In this way, the dynamical cloud changes act as a positive feedback on the meridional displacement of the Hadley Cell, roughly doubling the projected changes in cross-equatorial energy transport compared to that from the microphysical changes alone."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on August 05, 2017, 04:25:58 PM
The linked reference finds that the pH dependence of DMS results in a positive feedback for global warming and that the associated warming of Antarctica occurs at twice the rate of the global mean.  This is not good news for WAIS stability:

Schwinger, J., Tjiputra, J., Goris, N., Six, K. D., Kirkevåg, A., Seland, Ø., Heinze, C., and Ilyina, T.: Amplification of global warming through pH dependence of DMS production simulated with a fully coupled Earth system model, Biogeosciences, 14, 3633-3648, https://doi.org/10.5194/bg-14-3633-2017, (https://doi.org/10.5194/bg-14-3633-2017,) 2017.

https://www.biogeosciences.net/14/3633/2017/?utm_content=bufferbbbbb&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer (https://www.biogeosciences.net/14/3633/2017/?utm_content=bufferbbbbb&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer)

Abstract. We estimate the additional transient surface warming ΔTs caused by a potential reduction of marine dimethyl sulfide (DMS) production due to ocean acidification under the high-emission scenario RCP8.5 until the year 2200. Since we use a fully coupled Earth system model, our results include a range of feedbacks, such as the response of marine DMS production to the additional changes in temperature and sea ice cover. Our results are broadly consistent with the findings of a previous study that employed an offline model set-up. Assuming a medium (strong) sensitivity of DMS production to pH, we find an additional transient global warming of 0.30 K (0.47 K) towards the end of the 22nd century when DMS emissions are reduced by 7.3 Tg S yr−1 or 31 % (11.5 Tg S yr−1 or 48 %). The main mechanism behind the additional warming is a reduction of cloud albedo, but a change in shortwave radiative fluxes under clear-sky conditions due to reduced sulfate aerosol load also contributes significantly. We find an approximately linear relationship between reduction of DMS emissions and changes in top of the atmosphere radiative fluxes as well as changes in surface temperature for the range of DMS emissions considered here. For example, global average Ts changes by −0. 041 K per 1 Tg S yr−1 change in sea–air DMS fluxes. The additional warming in our model has a pronounced asymmetry between northern and southern high latitudes. It is largest over the Antarctic continent, where the additional temperature increase of 0.56 K (0.89 K) is almost twice the global average. We find that feedbacks are small on the global scale due to opposing regional contributions. The most pronounced feedback is found for the Southern Ocean, where we estimate that the additional climate change enhances sea–air DMS fluxes by about 9 % (15 %), which counteracts the reduction due to ocean acidification.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on August 25, 2017, 01:54:41 AM
While I do not know that we should be concerned about the fact that the linked reference finds that SOA formation is a non-linear process; nevertheless, I cannot help but to worry that mankind's continued degradation of forests and other related land uses, could result in a non-linear decrease in SOA in the atmosphere, which would result in an associated increase in ECS:

Shrivastava M, Kappa CD, Fan J, et al. (2017), "Recent Advances in Understanding Secondary Organic Aerosol: Implications for global climate forcing", Reviews of Geophysics, DOI: 10.1002/2016RG000540

http://onlinelibrary.wiley.com/doi/10.1002/2016RG000540/full (http://onlinelibrary.wiley.com/doi/10.1002/2016RG000540/full)

Abstract: "Anthropogenic emissions and land-use changes have modified atmospheric aerosol concentrations and size distributions over time. Understanding pre-industrial conditions and changes in organic aerosol due to anthropogenic activities is important because these features 1) influence estimates of aerosol radiative forcing and 2) can confound estimates of the historical response of climate to increases in greenhouse gases. Secondary organic aerosol (SOA), formed in the atmosphere by oxidation of organic gases, represents a major fraction of global submicron-sized atmospheric organic aerosol. Over the past decade, significant advances in understanding SOA properties and formation mechanisms have occurred through measurements, yet current climate models typically do not comprehensively include all important processes. This review summarizes some of the important developments during the past decade in understanding SOA formation. We highlight the importance of some processes that influence the growth of SOA particles to sizes relevant for clouds and radiative forcing, including: formation of extremely low-volatility organics in the gas phase; acid-catalyzed multi-phase chemistry of isoprene epoxydiols (IEPOX); particle-phase oligomerization; and physical properties such as volatility and viscosity. Several SOA processes highlighted in this review are complex and interdependent, and have non-linear effects on the properties, formation and evolution of SOA. Current global models neglect this complexity and non-linearity, and thus are less likely to accurately predict the climate forcing of SOA, and project future climate sensitivity to greenhouse gases. Efforts are also needed to rank the most influential processes and non-linear process-related interactions, so that these processes can be accurately represented in atmospheric chemistry-climate models."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on October 02, 2017, 06:47:10 PM
The linked reference takes a detailed look at the effective radiative forcing, ERF, of aerosols since 1850 and concludes that more research is needed using both models and observational data in order to better constrain ERF for aerosols:

Jan Kretzschmar, Marc Salzmann, Johannes Mülmenstädt, Olivier Boucher, Johannes Quaas (2017), "Comment on “Rethinking the Lower Bound on Aerosol Radiative Forcing”", Journal of Climate, https://doi.org/10.1175/JCLI-D-16-0668.1 (https://doi.org/10.1175/JCLI-D-16-0668.1)

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0668.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0668.1)
http://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-16-0668.1 (http://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-16-0668.1)

Abstract: "In an influential and interesting study, Stevens (2015) suggested that the global and also Northern Hemispheric warming during the early industrial period implies that the effective radiative forcing  by anthropogenic aerosols in the year 2000 compared to 1850 cannot be more negative than −1.0 W m−2. Here results from phase 5 of the Coupled Model Intercomparison Project are analyzed and it is shown that there is little relationship between  and the warming trend in the early industrial period in comprehensive climate models. In particular, some models simulate a warming in the early industrial period despite a strong (very negative)  . The reason for this difference in results is that the global-mean log-linear scaling of   with anthropogenic sulfur dioxide emissions introduced and used by Stevens tends to produce a substantially larger aerosol forcing compared to climate models in the first half of the twentieth century, when SO2 emissions were concentrated over smaller regions. In turn, it shows smaller (less negative)  in the recent period with comparatively more widespread SO2 emissions."
Title: Re: The Science of Aerosols
Post by: sidd on December 19, 2017, 08:24:04 PM
Svensmark et al. after much effort have a paper out on the effects of ions on cloud condensation nucleii. They find that ions help growth of CCN. This supports the link between cosmic rays, solar activity and clouds that he has been proposing for a long time.

open access. Read all aout it:

doi: 10.1038/s41467-017-02082-2

sidd
Title: Re: The Science of Aerosols
Post by: AbruptSLR on December 19, 2017, 08:43:57 PM
Svensmark et al. after much effort have a paper out on the effects of ions on cloud condensation nucleii. They find that ions help growth of CCN. This supports the link between cosmic rays, solar activity and clouds that he has been proposing for a long time.

open access. Read all aout it:

doi: 10.1038/s41467-017-02082-2

sidd

Hausfather has issues with this hypothesis:
Title: Re: The Science of Aerosols
Post by: sidd on December 19, 2017, 09:28:05 PM
The Svensmark paper does not claim that ions are a major influence on climate. The claim is that there is a link between growth rates of CCN and ionization, which is a much weaker statement. I recommend reading the paper.

There are several statements in the paper qualified by "suggests," "speculative" and like phrases. But the actual result does show a growth rate increase in CCN in the experiment. Whether that influences cloud radiative forcing is a different matter, and is not directly claimed in the paper. The do offer a "speculative" hypothesis:

"This suggests that there are vast regions where conditions are such that the proposed mechanism could be important, i.e., where aerosols are nucleated in Inter-Tropical Convergence Zone and moved to regions where relative large variations ionization can be found. Here the aerosols could grow faster under the influence of ion condensation, and the perturbed growth rate will influence the survivability of the aerosols and thereby the resulting CCN density. Finally the aerosols are brought down and entrained into the marine boundary layer, where clouds properties are sensitive to the CCN density [2] .
Although the above is on its own speculative ... "

They then proceed to offer Forbrush events as supporting evidence for the speculation. That i think is legitimate, but not yet convincing.

I am more interested in the evidence that ions increase CCN growth rates. CCNs are poorly understood, and this is one piece of evidence. Whether it will stand up to scrutiny is another matter.


sidd
Title: Re: The Science of Aerosols
Post by: AbruptSLR on December 19, 2017, 09:49:19 PM
There are several statements in the paper qualified by "suggests," "speculative" and like phrases. But the actual result does show a growth rate increase in CCN in the experiment. Whether that influences cloud radiative forcing is a different matter, and is not directly claimed in the paper. The do offer a "speculative" hypothesis:

Gavin is not impressed either, as he notes several missing logic steps in his tweet from several hours ago (see the first attachment):


Edit: Jokimaki seems to be even less impressed than either Hausfather or Schmidt (see the second attachment)
Title: Re: The Science of Aerosols
Post by: sidd on December 20, 2017, 05:34:51 AM
Gavin and Jokimaki seem to be arguing against a claim not made in the paper: that ionization is a significant climate influence.

The paper admits Gavin's criticism that more CCNs will have little effect when there are already CCNs present:

"In regions with a relative high number of CCN the presented effect will be small, in addition the effect on convective clouds and on ice clouds is expected to be negligible. Additional CCNs can even result in fewer clouds [38].

The only place they come close to fantasy is the last bit of Pg 6, which is admittedly reaching quite far; for if a near earth supernova occurs we shall have much more to worry about than more CCNs.

"Finally, if a near-Earth supernova occurs, as may have happened between 2 and 3 million years ago 39 , the ionization can increase 100 to 1000 fold depending on its distance to Earth and time since event. Figure 1b shows that the aerosol growth rate in this case increases by more than 50%. Such large changes should have profound impact on CCN concentrations, the formation of clouds and ultimately climate."

The title of the paper is "Increased ionization supports growth of aerosols into cloud condensation nuclei" so  I do wish people would discuss the meat in the paper rather than a throwaway para at the end. For example I find it interesting that accounting for the effect of the added ion mass has such a strong effect on the growth rate. Another point is that they used sulfuric acid for the experiment, and i wonder what the results would be with other compounds. The experimental results agree with their calculation, so thats good.

sidd


Title: Re: The Science of Aerosols
Post by: AbruptSLR on December 21, 2017, 12:05:41 AM
For example I find it interesting that accounting for the effect of the added ion mass has such a strong effect on the growth rate.

I note that if it is eventually proven that cosmic rays contribute enough CCNs to increase cloud cover enough to contribute to a negative feedback (of any size/magnitude), then as cosmic radiation has been higher than normal for the past several decades (as pointed out by Hausfather) then if cosmic radiation returns to its normal levels in the coming decades, then we will see more warming response (to our anthropogenic radiation forcing) than we have experienced for the past number of decades (at least to the 1960's).
Title: Re: The Science of Aerosols
Post by: sidd on December 21, 2017, 05:34:13 AM
" ...  if it is eventually proven that cosmic rays contribute enough CCNs to increase cloud cover enough to contribute to a negative feedback ..."

I think that is certainly a very interesting question. As the paper says

"Additional CCNs can even result in fewer clouds [38]"

More difficult, they continue:

"Since the ion condensation effect is largest for low SA concentrations and aerosol densities, the impact is believed to be largest in marine stratus clouds."

(SA is sulphuric acid.) But what i want to know is what of cirrus clouds ? That has warming effect. I am also not sure that low clouds universally have cooling effect. That is supposed to work thru increasing shortwave reflection. But on the other hand, arctic/antarctic with winter cloud cover would not cool down as fast.

I think this paper is worth reading, if one ignores, say, the last two paras of page 6.

sidd
Title: Re: The Science of Aerosols
Post by: AbruptSLR on January 26, 2018, 08:28:04 PM
Previous assumptions underestimated the aerosol-cloud interaction associated with ultrafine aerosols:

Jiwen Fan et al (26 Jan 2018), "Substantial convection and precipitation enhancements by ultrafine aerosol particles", Science, Vol. 359, Issue 6374, pp. 411-418, DOI: 10.1126/science.aan8461

http://science.sciencemag.org/content/359/6374/411

Abstract: Aerosol-cloud interactions remain the largest uncertainty in climate projections. Ultrafine aerosol particles smaller than 50 nanometers (UAP<50) can be abundant in the troposphere but are conventionally considered too small to affect cloud formation. Observational evidence and numerical simulations of deep convective clouds (DCCs) over the Amazon show that DCCs forming in a low-aerosol environment can develop very large vapor supersaturation because fast droplet coalescence reduces integrated droplet surface area and subsequent condensation. UAP<50 from pollution plumes that are ingested into such clouds can be activated to form additional cloud droplets on which excess supersaturation condenses and forms additional cloud water and latent heating, thus intensifying convective strength. This mechanism suggests a strong anthropogenic invigoration of DCCs in previously pristine regions of the world.

See also:

Title: "Tiny Particles of Pollution May Strengthen Storms"

https://www.scientificamerican.com/article/tiny-particles-of-pollution-may-strengthen-storms/

Extract: "A study published in the journal Science found that ultra-fine aerosol particles, produced by industrial activity, are helping storms grow bigger and more intense in the Amazon basin. Many scientists had long assumed that these microscopic particles—which can be more than 1,000 times smaller than the width of a human hair—were far too small to have any effect on the weather."
Title: Re: The Science of Aerosols
Post by: jai mitchell on February 02, 2018, 03:55:46 PM
This study indicates that roughly 30% of current Arctic sea ice decline has been offset by non-GHG forcing agents, mostly represented by anthropogenic aerosols.

https://dspace.library.uvic.ca/bitstream/handle/1828/7669/Mueller_Bennit_MSc_2016.pdf?sequence=1&isAllowed=y

I note that they are using Sea Ice Extent.  Had they used volume instead their loss values would be roughly 20% greater (75% vs 63%) and this would increase the amount of volume retention through cooling associated with Aerosols
Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 03, 2018, 06:10:26 PM
The linked reference submitted to the Ringberg 2018 workshop, indicates that the effective radiative forcing for anthropogenic aerosols is not strongly negative:

Title: "Theses on the magnitude of ERFaer"

https://www.mpimet.mpg.de/fileadmin/atmosphaere/WCRP_Grand_Challenge_Workshop/Ringberg_2018/theses/bellouin.pdf

Title: Re: The Science of Aerosols
Post by: AbruptSLR on February 09, 2018, 04:40:49 PM
The linked reference indicates increases in GMSTA of between 0.5 to 1.1C due to expected reductions in anthropogenic aerosols this century.

B. H. Samset, M. Sand, C. J. Smith, S. E. Bauer, P. M. Forster, J. S. Fuglestvedt, S. Osprey & C.-F. Schleussner (24 January 2018), "Climate Impacts From a Removal of Anthropogenic Aerosol Emissions", Geophysical Research Letters, DOI: 10.1002/2017GL076079

http://onlinelibrary.wiley.com/doi/10.1002/2017GL076079/full

Abstract: "Limiting global warming to 1.5 or 2.0°C requires strong mitigation of anthropogenic greenhouse gas (GHG) emissions. Concurrently, emissions of anthropogenic aerosols will decline, due to coemission with GHG, and measures to improve air quality. However, the combined climate effect of GHG and aerosol emissions over the industrial era is poorly constrained. Here we show the climate impacts from removing present-day anthropogenic aerosol emissions and compare them to the impacts from moderate GHG-dominated global warming. Removing aerosols induces a global mean surface heating of 0.5–1.1°C, and precipitation increase of 2.0–4.6%. Extreme weather indices also increase. We find a higher sensitivity of extreme events to aerosol reductions, per degree of surface warming, in particular over the major aerosol emission regions. Under near-term warming, we find that regional climate change will depend strongly on the balance between aerosol and GHG forcing."
Title: Re: The Science of Aerosols
Post by: jai mitchell on February 11, 2018, 12:23:26 AM
Eric Holthaus on the paper linked above.

https://grist.org/article/geoengineering-climate-change-air-pollution-save-planet/

Devil’s Bargain

Quote
According to a new study, we might be locked in this deadly embrace. Research by an international team of scientists recently published in the journal Geophysical Research Letters says that the cooling effect of aerosols is so large that it has masked as much as half of the warming effect from greenhouse gases. So aerosols can’t be wiped out. Take them away and temperatures would soar overnight.
Title: Re: The Science of Aerosols
Post by: gerontocrat on February 11, 2018, 01:03:32 AM
Damned if you do, damned if you don't. A cheerful article on which to end the day.
Title: Re: The Science of Aerosols
Post by: Sleepy on February 11, 2018, 08:14:31 AM
Damned if you do, damned if you don't. A cheerful article on which to end the day.
We have known about the aerosols for a long time. Fig4 was particulary interesting for us on the NH though.
Title: Re: The Science of Aerosols
Post by: gerontocrat on February 11, 2018, 09:35:16 AM
Hullo Sleepy (again),

Yes, I (and many environmentalists) knew about aerosols, but what I did not know was the sheer amount of cooling they currently provide.

Quote
What's clear is that they're cooling us off. If we magically transformed the global economy overnight, and air pollution fell to near zero, we'd get an immediate rise in global temperatures of between 0.5 and 1.1 degrees Celsius, according to the new study.

Getting this into publications like "Rolling Stone" means a lot more people now know.
https://www.rollingstone.com/politics/features/why-aerosols-are-a-deadly-climate-change-threat-w516504
Title: Re: The Science of Aerosols
Post by: Sleepy on February 11, 2018, 11:08:00 AM
Hi gerontocrat, I haven't been following this thread but we've had those higher numbers coming for a while. I remember from my last stint on this forum, think I mentioned Markku Kulmala in some of the earlier posts. After reading about his work in Finland I started to anticipate higher numbers. Highly unscientific, I know, but I'm not a scientist. :)

Here's one of those I remember:
http://science.sciencemag.org/content/339/6122/943 (http://science.sciencemag.org/content/339/6122/943)
Quote
Our findings emphasize the important role of organic compounds in atmospheric aerosol formation, subsequent aerosol growth, radiative forcing and associated feedbacks between biogenic emissions, clouds, and climate.

No simple numbers in that one, but when I saw stuff like this I wasn't really surprised:
https://www.atmos-chem-phys.net/15/12681/2015/ (https://www.atmos-chem-phys.net/15/12681/2015/)
Quote
Regionally and locally, climate impacts can be much larger than the global mean, with a 2.1 K warming projected over China, Japan, and Korea due to the reduced aerosol emissions in RCP8.5

This thread is probably filled with other papers.

Agree that it's good that these things hits regular publications, but we (humanity) have already passed the expiry date and need to drop emissions at 10-15% per year. We should see a war like stand on mitigation now, but too many seems to be on a hunt for another planet instead. :(
Title: Re: The Science of Aerosols
Post by: Hefaistos on February 16, 2018, 08:09:46 AM
An rather shocking article from Science, that transportation is no longer the major source of aerosols. Solvants from household products is now the major source. Transport-derived emissions of volatile organic compounds (VOCs) have decreased owing to stricter controls on air pollution. This means that the relative importance of chemicals in pesticides, coatings, printing inks, adhesives, cleaning agents, and personal care products has increased. McDonald et al. show that these volatile chemical products now contribute fully one-half of emitted VOCs in 33 industrialized cities

"Volatile chemical products emerging as largest petrochemical source of urban organic emissions"

Abstract

A gap in emission inventories of urban VOC sources, which contribute to regional ozone and aerosol burdens, has increased as transportation emissions in the United States and Europe have declined rapidly. A detailed mass balance demonstrates that the use of volatile chemical products (VCPs)—including pesticides, coatings, printing inks, adhesives, cleaning agents, and personal care products—now constitutes half of fossil fuel VOC emissions in industrialized cities. The high fraction of VCP emissions is consistent with observed urban outdoor and indoor air measurements. We show that human exposure to carbonaceous aerosols of fossil origin is transitioning away from transportation-related sources and toward VCPs. Existing U.S. regulations on VCPs emphasize mitigating ozone and air toxics, but they currently exempt many chemicals that lead to secondary organic aerosols.

Full text:
http://science.sciencemag.org/content/359/6377/760.full

http://science.sciencemag.org/content/359/6377/760
Title: Re: The Science of Aerosols
Post by: Sleepy on February 16, 2018, 02:17:36 PM
Thanks Hefaistos.

Adding Fig S2 from the supplementary.
The top row are emissions
at the nation-scale (A) reported by EPA (111), and (B) results from this study.

The bottom row are emissions
for the Los Angeles basin (C) reported by CARB, and (D) results from this study.
Title: Re: The Science of Aerosols
Post by: Sleepy on February 17, 2018, 08:56:26 AM
Don't know if there's a better thread for this in here, so here we go:
Evidence for a continuous decline in lower stratospheric ozone offsetting ozone layer recovery.
https://www.atmos-chem-phys.net/18/1379/2018/ (https://www.atmos-chem-phys.net/18/1379/2018/)
Quote
Abstract. Ozone forms in the Earth's atmosphere from the photodissociation of molecular oxygen, primarily in the tropical stratosphere. It is then transported to the extratropics by the Brewer–Dobson circulation (BDC), forming a protective "ozone layer" around the globe. Human emissions of halogen-containing ozone-depleting substances (hODSs) led to a decline in stratospheric ozone until they were banned by the Montreal Protocol, and since 1998 ozone in the upper stratosphere is rising again, likely the recovery from halogen-induced losses. Total column measurements of ozone between the Earth's surface and the top of the atmosphere indicate that the ozone layer has stopped declining across the globe, but no clear increase has been observed at latitudes between 60° S and 60° N outside the polar regions (60–90°). Here we report evidence from multiple satellite measurements that ozone in the lower stratosphere between 60° S and 60° N has indeed continued to decline since 1998. We find that, even though upper stratospheric ozone is recovering, the continuing downward trend in the lower stratosphere prevails, resulting in a downward trend in stratospheric column ozone between 60° S and 60° N. We find that total column ozone between 60° S and 60° N appears not to have decreased only because of increases in tropospheric column ozone that compensate for the stratospheric decreases. The reasons for the continued reduction of lower stratospheric ozone are not clear; models do not reproduce these trends, and thus the causes now urgently need to be established.

Also an article from Stockholm University with commments from two of the authors:
https://www.su.se/forskning/profilomr%C3%A5den/klimat-hav-och-milj%C3%B6/ozonskiktet-%C3%A5terh%C3%A4mtar-sig-inte-p%C3%A5-v%C3%A5ra-breddgrader-1.370911 (https://www.su.se/forskning/profilomr%C3%A5den/klimat-hav-och-milj%C3%B6/ozonskiktet-%C3%A5terh%C3%A4mtar-sig-inte-p%C3%A5-v%C3%A5ra-breddgrader-1.370911)
Title: Re: The Science of Aerosols
Post by: AbruptSLR on March 28, 2018, 05:28:36 PM
The linked reference discusses both present and future direct radiative forcing contributions from secondary organic aerosols, that have not yet been accounted for in climate models.

Tsigaridis, K. & Kanakidou, M. (2018), "The Present and Future of Secondary Organic Aerosol Direct Forcing on Climate", Curr Clim Change Rep., https://doi.org/10.1007/s40641-018-0092-3

https://rd.springer.com/article/10.1007%2Fs40641-018-0092-3

Abstract: "Secondary organic aerosols (SOA), a subset of organic aerosols that are chemically produced in the atmosphere, are included in climate modeling calculations using very simple parameterizations. Estimates on their shortwave forcing on climate span almost two orders of magnitude, being potentially comparable to sulfate direct forcing. In the longwave, a neglected part of the spectrum when it comes to SOA, the direct SOA forcing could exceed that of sulfate and black carbon, although in absolute values, it is much weaker than the shortwave forcing. Critical for these estimates is the vertical distribution of the climate active agents, pointing to SOA temperature-dependent volatility. Over the last few years, research also revealed the highly oxidized character of organic aerosol and its chemical aging in the atmosphere that partially leads to the formation of brown carbon, an absorbing form of organic aerosol. This review summarizes critical advances in the understanding of SOA behavior and properties relevant to direct climate forcing and puts them in perspective with regard to primary organic aerosol and brown carbon. These findings also demonstrate an emerging dynamic picture of organic aerosol that has not yet been integrated in climate modeling. The challenges for the coming years in order to reduce uncertainties in the direct organic aerosol climate impact are discussed. High priority for future model development should be given to the dynamic link between “white” and “brown” organic aerosol and between primary and secondary organic aerosol. The SOA temperature-dependent volatility parameterizations and wavelength-dependent refractive index should be also included."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on April 09, 2018, 02:29:31 AM
The Arctic is highly sensitive to aerosols:

Q. Coopman  T. J. Garrett  D. P. Finch  J. Riedi (2017), "High Sensitivity of Arctic Liquid Clouds to Long‐Range Anthropogenic Aerosol Transport", Geophysical Research Letters,  https://doi.org/10.1002/2017GL075795

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017GL075795

Abstract: "The rate of warming in the Arctic depends upon the response of low‐level microphysical and radiative cloud properties to aerosols advected from distant anthropogenic and biomass‐burning sources. Cloud droplet cross‐section density increases with higher concentrations of cloud condensation nuclei, leading to an increase of cloud droplet absorption and scattering radiative cross sections. The challenge of assessing the magnitude of the effect has been decoupling the aerosol impacts on clouds from how clouds change solely due to natural meteorological variability. Here we address this issue with large, multi‐year satellite, meteorological, and tracer transport model data sets to show that the response of low‐level clouds in the Arctic to anthropogenic aerosols lies close to a theoretical maximum and is between 2 and 8 times higher than has been observed elsewhere. However, a previously described response of arctic clouds to biomass‐burning plumes appears to be overstated because the interactions are rare and modification of cloud radiative properties appears better explained by coincident changes in temperature, humidity, and atmospheric stability."
Title: Re: The Science of Aerosols
Post by: jai mitchell on May 16, 2018, 05:04:09 PM
Aerosols from human emissions reside mainly in the Troposphere with some small percentage migrating to the Stratosphere.  Aircraft emission of SO2 are included in this tropospheric loading though their impact is much less than that of the fossil fuel (coal mostly) industry.

Typical Tropospheric loading of SO2 only lasts in the atmosphere about 2 weeks since it settles out in precipitation.  Stratospheric volcanoes cause a cooling effect but it lasts much longer since there is barely any water vapor at that altitude. 

Also the cooling effect of stratospheric loading is much more dispersed globally (usually in the respective hemisphere if an upper or lower latitude volcano and globally if a tropical one).  Stratospheric loading only operates on one component of the cooling process where it reflects the incoming solar energy through a fine haze.  Tropospheric loading from human emissions also does this but also has interactions with clouds that, until very recently (and still with much uncertainty!) was not well known.

The interaction with clouds in the troposphere from SO2 causes lower cloud heights, slightly cools the regional troposphere, lowering the effective height of the atmosphere (a cooling effect on the GHG feedback impacting the lapse rate) and leads to shifts in wind and precipitation patterns regionally.  It also causes finer water droplets at cloud tops, making them more white and reflective.

In the Arctic specifically, most models do not include the full impacts of SO2 but the ones that include these cloud interactions recognize quickly that the additional impacts at the very high latitudes are much greater than the global average.  This is due to the lower angle of the sun at high latitudes.

Recent published studies (and historical evidence) indicates that the Arctic will warm between 2C and 4C without coal-produced SO2 emissions.  This warming impact would begin within 2 weeks after the end of emissions and is basically instantaneous. 

The long-term warming impacts could be much higher as these SO2 Tropospheric loading are seen in some studies to have a very strong effect on the prevalence of La Nina events (more SO2 more negative PDO) as well as tropical precipitation (more SO2 more tropical precipitation) as well as observed impacts on the AMO.  These circulation changes are the biggest unknown in the climate models since the regional changes in winds and tropical humidity are expected to produce very large changes in the supremely complicated global atmospheric circulation patterns.

It is quite likely that the end of SO2 will greatly change the rate of upwelling tropical atmosphere, the driver the Hadley Cell, leading to increased expansion of the tropical rain belt from 20' latitude, expanding the 30' dry belt (where most of the global deserts are) and result in greatly increased pulses of water vapor into the upper latitudes and the Arctic.

The observation of these kinds of circulation changes contribute up to 60% of the total sea ice loss observed since 1979:  https://www.atmos.washington.edu/~david/Ding_etal_2017.pdf

FWIW I was documenting the change in circulation and increase in water vapor pulses into the Arctic (as a result of the North East Pacific 'Ridiculously Resilient Ridge' beginning back in 2014: https://forum.arctic-sea-ice.net/index.php/topic,784.0.html

The Hadley Cell has been observed to be already expanding, this will increase significantly with further reductions of aerosols as we end the fossil fuel era: https://www.nature.com/articles/ngeo2091

Title: Re: The Science of Aerosols
Post by: rboyd on May 16, 2018, 09:56:09 PM
One geo-engineering possibility would be to replace the fossil-fuel produced aerosols to keep the overall cooling effect while reducing fossil fuel use. If the geo-engineering is done at the level of the stratosphere that would change the regional distribution though, so could have unforeseen regional effects. Are there any papers on this possibility?
Title: Re: The Science of Aerosols
Post by: Sleepy on May 17, 2018, 06:54:09 AM
Paper attached below.

Earth’s expanding waistline.

Abstract.
Quote
Observations collected over recent decades indicate that the wind and weather patterns flanking the tropics have shifted poleward as the surface of the Earth has warmed. This expansion of the tropics has the potential to affect a large fraction of the world’s population, and its acceleration in recent decades begs the question of whether it is related to human activity. While theory and numerical modeling suggest that increasing greenhouse gas concentrations should widen the tropics, early observation-based studies depict widely varying rates of widening, including many well beyond those simulated in most climate model experiments. In this article, we review the possible causes of tropical widening, including greenhouse gas concentration increases. We find that carefully accounting for methodological differences can reduce the range of observed rates of widening, and that it is too early to detect statistically robust human-caused widening of the entire tropical circulation due to climate change.

Discussion.
Quote
A flurry of studies during the past decade or so has shown compelling evidence for the widening of the Tropics in both observations and model simulations. But recently, more careful analyses indicated that the widening trend since late 1970s may not be as rapid as some metrics have indicated, and may not be happening in all metrics for the TW. By surveying studies based on more reliable tropospheric metrics and contemporary reanalysis datasets, we find that the expansion rate may be dialed down to the neighborhood of 0.2 ◦ per decade in each hemisphere. Individual numerical experiments can reproduce this reduced rate of TW expansion, implying that no ‘hidden forcing’ is needed to explain observed expansion. Accounting for the observed multi-decadal evolution of the SST can fill some of the gap between the modelled and observed trends. The earlier notion that anthropogenic forcings are the predominant cause for the observed expansion seems to arise from a few early studies limited to the use of the problematic tropopause-based and OLR-based TW metrics (gray metrics in Table 1) and early reanalyses, and therefore should be revised. Including recent evidence, it is fair to assert that the natural swings in decadal atmospheric and oceanic variability may have driven at least as much of the observed expansion as human activity. Natural variability thus looms large over TW attribution studies. We may be on the cusp of robust detectability[82], however, and our synthesis reveals several promising paths forward.
Much remains to be done to understand the processes which determine TW. The diverse mechanisms summarized in Box 1 for the eddy-driven HC expansion are incomplete—other factors may cause the tropics to expand independently from the “eddy pump” effect. A mechanistic explanation for seasonal and longitudinal differences is also in order, given the considerable seasonality interhemispheric asymmetry in tropical expansion under GHG concentration increases [83, 81, 84, 18]. More surgically designed numerical experiments are needed to discern which of the hypothesized mechanisms listed above or other novel mechanisms are most relevant to each of the forcings discussed in this review.
Regarding impacts, the climate change that matters is regional. But in addition to informing impacts, the study of regional changes in TW is useful for attribution studies. For instance, stratospheric ozone depletion, GHG concentration increases, aerosols, and natural SST variability may all produce annual and zonal mean changes in TW, but with very different seasonal and regional manifestations. Several recent studies regress regional changes (e.g. the sea level pressure field, precipitation-minus-evaporation) to zonal mean TW in order to identify the spatial fingerprint of the variability of TW, compared to forced regional changes associated with the TW[36, 20, 85, 86]. This approach can be further refined by identifying the seasonal fingerprint of forced change and variability, as well as the spatial fingerprint.
Part of the challenge with measuring the TW is that the most easily observed metrics globally (e.g., tropopause height or OLR) are the least correlated with other measures or with surface impacts, and the most highly correlated (e.g., the overturning stream function) are not always directly observable, but require global, gridded data. In order to produce gridded observational data, reanalyses use forecast models to perform what may be thought of as a physically-based interpolation, but they are no ‘silver bullet’; reanalyses inherit some of the faults of the models on which they’re based, as well as discontinuities in the observations they ingest[87]. Earlier reanalysis produces contain notable spurious trends compared to modern reanalyses and to datasets based on raw observations. Ideally, one would hope for a single metric that is calculable from models, reanalyses, and observational datasets alike, which can in turn be robustly related to the HC edge and other metrics. In the absence of such a metric, an improved understanding of the poor agreement between the observable tropopause-based metrics and other reanalysis-derived metrics is worthy of further study.
Our synthesis shows strong evidence that the tropics have widened a few tenths of a degree per decade since the beginning of the satellite era. The robust detectability of this widening trend is to some extent an artifact of a fortuitous swing in the PDO. Since no one has a crystal ball to tell when the PDO will switch phases (as decadal prediction remains a major challenge to the climate community), it is impossible to predict whether or not the earth’s tropical waistline is going to continue bulging in the coming decade[36]. But the ozone hole is beginning to recover, and judging from the timescale of the PDO, the PDO will likely switch sign in the coming decade or two; indeed, the last few years have seen El Nino-like conditions which may be the harbinger of such a shift. Each of these trends acts to counteract tropical widening. Thus, for the coming few decades, the tropics may contract. At centennial timescales, however, the effect of the uncurbed GHG emissions will begin to dominate, and eventual further widening of the tropics by the end of the century seems all but certain.
Title: Re: The Science of Aerosols
Post by: Ken Feldman on June 01, 2018, 08:11:06 PM
I posted this in one of the Arctic threads, it's also relevant to this discussion.

Article on the role of aerosols in the reduction of Arctic sea ice to date and the expected Arctic warming in the future:

https://journals.ametsoc.org/doi/10.1175/JCLI-D-17-0287.1 (https://journals.ametsoc.org/doi/10.1175/JCLI-D-17-0287.1)

Abstract:

Quote
Observations show that the Arctic sea ice cover has been shrinking at an unprecedented rate since the 1970s. Even though the accumulation of greenhouse gases in the atmosphere has been closely linked with the loss of Arctic sea ice, the role of atmospheric aerosols in past and future Arctic climate change remains elusive. Using a state-of-the-art fully coupled climate model, the authors assess the equilibrium responses of the Arctic sea ice to the different aerosol emission scenarios and investigate the pathways by which aerosols impose their influence in the Arctic. These sensitivity experiments show that the impacts of aerosol perturbations on the pace of sea ice melt effectively modulate the ocean circulation and atmospheric feedbacks. Because of the contrasting evolutions of particulate pollution in the developed and developing countries since the 1970s, the opposite aerosol forcings from different midlatitude regions are nearly canceled out in the Arctic during the boreal summer, resulting in a muted aerosol effect on the recent sea ice changes. Consequently, the greenhouse forcing alone can largely explain the observed Arctic sea ice loss up to the present. In the next few decades, the projected alleviation of particulate pollution in the Northern Hemisphere can contribute up to 20% of the total Arctic sea ice loss and 0.7°C surface warming over the Arctic. The authors’ model simulations further show that aerosol microphysical effects on the Arctic clouds are the major component in the total aerosol radiative forcing over the Arctic. Compared to the aerosol-induced energy imbalance in lower latitudes outside the Arctic, the local radiative forcing by aerosol variations within the Arctic, due to either local emissions or long-range transports, is more efficient in determining the sea ice changes and Arctic climate change.
Title: Re: The Science of Aerosols
Post by: jai mitchell on June 01, 2018, 09:34:16 PM
thanks Ken!

I wonder what level of reductions they are modelling over the next 'few decades'.

an additional 20% decline would also greatly increase albedo absorption in the summer melt season.

Title: Re: The Science of Aerosols
Post by: Ken Feldman on June 01, 2018, 11:39:48 PM
jai,

I don't have access to the full article, so don't know the answers to your questions.

There is another recent study (posted up thread) showing that the total removal of anthropogenic aerosols might increase global temperatures between 0.5 and 1.1 degrees C. Most global climate models have the arctic warming at twice (or a bit more) the global warming.  So if this study is showing only 0.7 degrees C of arctic warming, then maybe the increase from reducing pollution wont be as severe as the other study indicates.
Title: Re: The Science of Aerosols
Post by: jai mitchell on June 03, 2018, 05:27:30 PM
Ken,

since the 0.7C value is projected over only a couple of decades, it is not the full removal of anthropogenic aerosols, only a partial removal.  under the most aggressive mitigation scenarios this value would be approximately half of those aerosols. 

The problem with many studies is that they often rely on a comprehensive suite of different climate models, many of which do not include significant, known impacts of aerosols on the biosphere. 

Of the models that do include these effects, the projected total cooling being provided to the Arctic by anthropogenic aerosols is between 2C and 4C. 

The same study suggested that globally averaged cooling would be 0.7C so this study that you provide, being only a partial removal of those aerosols actually shows a higher level of cooling (and locked-in warming if all were removed) than this one: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076079

However, neither of these studies look at the residual impacts of a rapidly warming arctic on melting permafrost and the increased GHG emissions that would result: so they are both biased low.

image below from crowther et al 2016
https://www.nature.com/articles/nature20150


Title: Re: The Science of Aerosols
Post by: Ken Feldman on June 04, 2018, 08:31:36 PM
Jai,

I'm not finding any studies published in peer-reviewed journals that support a 2 - 4 degree increase in Arctic temperatures from removal of aerosols.  Please post links to your sources.

Here's another recent study that shows the impact of aerosols is much lower than previously reported:

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017JD027298 (https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017JD027298)

Here's the abstract:

Quote
Source attribution of Arctic sulfate and its radiative forcing due to aerosol‐radiation interactions (RFari) for 2010–2014 are quantified in this study using the Community Earth System Model equipped with an explicit sulfur source‐tagging technique. The model roughly reproduces the seasonal pattern of sulfate but has biases in simulating the magnitude of near‐surface concentrations and vertical distribution. Regions that have high emissions and/or are near/within the Arctic present relatively large contributions to Arctic sulfate burden, with the largest contribution from sources in East Asia (27%). Seasonal variations of the contribution to Arctic sulfate burden from remote sources are strongly influenced by meteorology. The mean RFari of anthropogenic sulfate offsets one third of the positive top of the atmosphere (TOA) RFari from black carbon. A 20% global reduction in anthropogenic SO2 emissions leads to a net Arctic TOA forcing increase of +0.019 W m−2. These results indicate that a joint reduction in BC and SO2 emissions could prevent at least some of the Arctic warming from any future SO2 emission reductions. Sulfate RFari efficiency calculations suggest that source regions with short transport pathways and meteorology favoring longer lifetimes are more efficient in influencing the Arctic sulfate RFari. Based on Arctic climate sensitivity factors, about −0.19 K of the Arctic surface temperature cooling is attributed to anthropogenic sulfate, with −0.05 K of that from sources in East Asia, relative to preindustrial conditions.
Title: Re: The Science of Aerosols
Post by: Ken Feldman on June 04, 2018, 08:58:30 PM
Here's a 2015 study that shows the responses of three climate models to an idealized removal of all aerosols:

https://www.atmos-chem-phys.net/15/8201/2015/acp-15-8201-2015.pdf (https://www.atmos-chem-phys.net/15/8201/2015/acp-15-8201-2015.pdf)

Table 2 on page 8207 of that journal summarizes the results.  The formatting of the table doesn't translate, so here's an excerpt:

Emissions  Model           Temp Change (C)
SO2          HadGEM            0.838
SO2          ECHAM-HAM      0.831
SO2          NorESM             0.396
SO2          Mean                0.688

The effects for Organic Carbon was less warming (mean of 0.132) and for Black Carbon was slight cooling (mean of -0.044).

This is for the instantaneous removal of all anthropogenic aerosols, which won't happen (less than half of aerosols are now coming from utilities and industries).  And it doesn't include the responses from natural aerosols which may increase as a result of climate change.

So while the reduction of anthropogenic aerosols due to a decrease in fossil fuel burning may result in a slight increase in temperature, it probably will be far less than the 2 to 4 degrees I keep seeing people post in the ASI forums.
Title: Re: The Science of Aerosols
Post by: jai mitchell on June 06, 2018, 06:41:09 AM
the 2 to 4 degrees is in the Arctic only which experiences much greater impacts
Title: Re: The Science of Aerosols
Post by: Ken Feldman on June 06, 2018, 07:15:43 PM
the 2 to 4 degrees is in the Arctic only which experiences much greater impacts

The recent studies I posted about  upthread show much smaller impacts, less than 1 degree C.  Are you confusing the overall warming impacts (including polar amplification due to warm water transport to the Arctic and changing air currents) from increased greenhouse gas concentrations with the increase due to reduced aerosols?  If so, you're double counting the impacts, as these studies are using GCMs that take into account these effects.
Title: Re: The Science of Aerosols
Post by: jai mitchell on June 07, 2018, 07:05:43 PM
Earlier papers that project aerosol forcing have real problems since many (most!) of the ESM models did not include key (known) atmospheric and atmospheric chemistry interactions with aerosols.  These models underestimate the aerosol effect.  This has been well known even before the publication of AR5 as satellite observations indicated much greater effects than were being modeled.

This total indirect effect is comprised of First (FIE) and Second (SIE) indirect effects, both are negative (cooling). 

The lack of these mechanisms in some models and the poor representation (compared to direct observations in others) led to the great uncertainty bars in the AR4 and AR5 (image below) for this effect.  The total indirect effect here is labeled "Cloud Adjustments due to Aerosols" with a median value of about 0.56 Watts/m^2.

Recent observations from the Satellite record indicate that the FIE component itself is underestimated by approximately 23% which has a cascading local effect based on relative humidity of several watts per meter squared.  See: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL077679

Quote
One‐unit enhancement in aerosol scattering coefficient by swelling effect is found to lead to a systematic underestimation of the first indirect effect (FIE) by about 23% that can result in an underestimation in the FIE‐related radiative forcing by several W/m2 depending on aerosol properties and relative humidity.

Recent observations from the satellite record performed by a different team of scientists shows that the FIE effect is approximately double the total effect shown in the graphic below (and cited as the median value of aerosol cloud impacts in AR5) See : http://www-k12.atmos.washington.edu/~dennis/McCoy-2017-Theglobalaerosol-cloud.pdf

Quote
Using preindustrial emissions models, the change in Nd between preindustrial and present day is estimated. Nd is inferred to have more than tripled in some regions. Cloud properties from Moderate Resolution Imaging Spectroradiometer (MODIS) are used to estimate the radiative forcing due to this change in Nd. The Twomey (FIE) effect operating in isolation is estimated to create a radiative forcing of -0.97 ± 0.23 W m^2 relative to the preindustrial era.

The problem (and this will be cross posted in the "Conservative Scientists" thread) is that these more recent papers that rely on models specifically tuned to include the total effects of aerosols show much higher cooling impacts, especially in the  Arctic than your examples.  see: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076079

Quote
We note that in two models, Arctic warming due to aerosol reductions reaches 4°C in some locations (Figures S2–S5). The four‐model mean increase for the 60°N–90°N region is 2.8°C.

note:  Even the four models used in this paper severely underestimate the FIE as shown in the first papers (23%) cited which was published only 1 month ago

Image of average model (4 model) response to aerosols removal found here: https://wol-prod-cdn.literatumonline.com/cms/attachment/46814f2f-f617-4dea-83ce-0ab4c61244bf/grl56865-fig-0002-m.jpg

You can download the Supplementary information with the individual model results of aerosol removal on temperatures (figures S2-S5) here:
https://agupubs.onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1002%2F2017GL076079&attachmentId=2186427861

It is strongly urged that you limit your research for best accuracy to papers less than 2 years old since the modeling capabilities have increased significantly since 2015.  I understand that this has produced a lot of confusion in the discussion since the understanding of these aerosol impacts are changing very rapidly.

(postscript)  I note that the Wang paper that you cited on the previous page was published only last January and holds a much lower (by an order of magnitude!) cooling effect from Sulfates.  I was confused about the CESM use of tracers for SO2 and did some background research.  The CESM version 1.2.0 was released in 2013 and subsequent releases have only been for technical glitches (apparently)  the Aerosol component (CAM5) included new organic coupling.  However, the indication is that the CESM model does not include more recent developments in aerosol-cloud interactions.  The use of synthetic tracers is apparently an attempt to adjust the discrepancy between modeled and observed sulfate loading see lecture notes here: http://www.cesm.ucar.edu/events/tutorials/2016/lecture5-tilmes.pdf

AHA!! yes indeed, this recent paper shows that the CESM model projects the total indirect effect about 1/2 the observed effect produced from only the FIE!  So the CESM severely underestimates this cloud effect.  https://www.osti.gov/pages/servlets/purl/1375377
Title: Re: The Science of Aerosols
Post by: jai mitchell on June 08, 2018, 07:57:21 PM
WRT CESM as a model for aerosol response.

The long awaited release of CESM2 has occurred today.  This means that the previous papers using this model will likely have very different results since the process took over 4 years to produce the new version, using much greater computing capacity and much more detailed modules.  Here is the ins and outs of the new CESM2

http://www.cesm.ucar.edu/models/cesm2/whatsnew.html
Title: Re: The Science of Aerosols
Post by: Ken Feldman on June 10, 2018, 12:55:10 AM
Jai,

Those are all good papers, based on recent modelling.  There are other good papers based on recent modelling that show the aerosol -cloud interactions may be over estimated.

For example, this 2017 paper that used observations of increased aerosol loading from a volcanic eruption:

https://www.nature.com/articles/nature22974 (https://www.nature.com/articles/nature22974)

Quote
Aerosols have a potentially large effect on climate, particularly through their interactions with clouds, but the magnitude of this effect is highly uncertain. Large volcanic eruptions produce sulfur dioxide, which in turn produces aerosols; these eruptions thus represent a natural experiment through which to quantify aerosol–cloud interactions. Here we show that the massive 2014–2015 fissure eruption in Holuhraun, Iceland, reduced the size of liquid cloud droplets—consistent with expectations—but had no discernible effect on other cloud properties. The reduction in droplet size led to cloud brightening and global-mean radiative forcing of around −0.2 watts per square metre for September to October 2014. Changes in cloud amount or cloud liquid water path, however, were undetectable, indicating that these indirect effects, and cloud systems in general, are well buffered against aerosol changes. This result will reduce uncertainties in future climate projections, because we are now able to reject results from climate models with an excessive liquid-water-path response.
Title: Re: The Science of Aerosols
Post by: jai mitchell on June 11, 2018, 02:58:37 AM
Ken,

Excellent paper, however it does support a higher sensitivity for FIE than the current AR5.  See below:

https://ora.ox.ac.uk/objects/uuid:a63e1dbb-1671-4ed7-b19d-3fc7fdca5eff/download_file?file_format=application/pdf&safe_filename=MAIN_TEXT_affiliation_and_aknowledgement_changes_accepted.pdf&type_of_work=Journal%20article

Quote
Despite such massive emissions and large anomalies in reff, we estimate a moderate globalmean radiative forcing of -0.21 ± 0.08 W.m-2 (1 standard deviation, Supplementary S15) for
September-October which equates to a global annual mean effective radiative forcing of -0.035 ± 0.013 W.m-2 (1 standard deviation) assuming that a forcing only occurs in September and October 2014. Global emissions of anthropogenic SO2 currently total around 100 TgSO2/year and the Intergovernmental Panel on Climate Change17,47 suggests a best estimate for the aerosol forcing of -0.9 W.m-2 , yielding a forcing efficiency of -0.009 W.m-2 318 /TgSO2. The emissions for September and October 2014 total approximately 4 TgSO2, thus the global annual mean radiative forcing efficiency for the 2014-15 eruption at  Holuhraun yields a forcing efficiency of -0.0088 ± 0.0024 W.m-2 320 /TgSO2 (1 standard deviation). The similarity is remarkable, but may be by chance given the modelled sensitivity to emission location and time (Supplementary S12).

So the values measured are slightly below the global mean AR5 value, but:

Quote
The global ERF from HadGEM3 over the September-October 2014 period is estimated at -0.21 W.m-2 . . . .We also investigate whether a fissure eruption of this magnitude could have a more significant radiative impact if the timing/location of the eruptions were different (Supplementary S12). Our simulations suggest that for contrasting scenarios the global ERF would i) strengthen to -0.29 W.m-2 (+40%) if the eruption commenced at the beginning of  June, ii) strengthen to -0.49 W.m-2 (+140%) if the fissure eruption had occurred in an area of South America where it could affect clouds in a stratocumulus-dominated regime

In other words, the constraint fits if it involves a far nothern hemisphere loading and the fall period, the effect is greatly exacerbated during both summer and in regions with higher relative humidity (i.e. the tropics). 

cheers!
Title: Re: The Science of Aerosols
Post by: Ken Feldman on June 11, 2018, 07:06:43 PM
Jai,

The point of the volcanic study was that it shows that aerosol impacts on cloud properties from other studies may be overestimated.  From the paper:

Quote
Changes in cloud amount or cloud liquid water path, however, were undetectable, indicating that these indirect effects, and cloud systems in general, are well buffered against aerosol changes. This result will reduce uncertainties in future climate projections, because we are now able to reject results from climate models with an excessive liquid-water-path response.

This may be because the cloud impacts are much lower than the direct impacts of increased reflection of sunlight.  Here's a 2018 paper that reviews the current science related to aerosols:

https://link.springer.com/article/10.1007/s40641-018-0089-y (https://link.springer.com/article/10.1007/s40641-018-0089-y)

Quote
The first scale is energetic: the ERFaci is approximately two orders of magnitude smaller than the shortwave cloud radiative effect (e.g., [153]). The path to a 1% effect goes partly through large perturbations that occur rarely, or over limited areas (shiptracks, closing of open cells; [47]), and small perturbations that occur frequently, posing challenges for observability. For example, [122] indicate that shiptracks, the most eminently observable manifestation of ACI, exert a paltry 0.5 mW m−2 of forcing globally. The challenge is therefore to determine the meteorological conditions under which aerosol perturbations manifest as energetically significant, along with their geographical coverage and frequency of occurrence.

The second set of scales is spatiotemporal: the scales relevant for ACI range from the microscale through cloud-process scales for cloud-top turbulent entrainment and cloud updrafts. However, the aerosol perturbations at cloud-scale affect the regional and global circulation, and these regional- through global scale changes feed back as meteorological influences on cloud processes [112, 133, 150, 151]. This means that constraining ERFaci requires understanding the microscale, the cloud process scale, and the global scale, as well as the interactions between scales.

And improvements in comparing model outputs to observations are leading to lower estimates of forcing for aerosol-cloud impacts:

Quote
As discussed in “Why Are ERFaci Estimates so Challenging?”, progress is being made on understanding the discrepancy between GCM and observational estimates of ERFaci, which was large in AR5 (ERFari+aci = −0.93 to−0.45~W~m −2 
 to−0.45~W~m−2
 with a median of −0.85 W m−2 for studies using the satellite record, compared against − 1.68to−0.81~W~m −2 
to−0.81~W~m−2
 with a median value of − 1.38 W m−2 for GCM studies; [18]). Gryspeerdt et al. [52] show that the choice of N a  proxy can significantly reduce the discrepancy; their best estimate of RFaci based on a GCM-observation combination is −0.4 W m−2. Christensen et al. [28] and Neubauer et al. [102] take a different approach, investigating the effects of reducing near-cloud biases in satellite aerosol observations consistently between observations and modeling. This simplification of ACI, where the effect of clouds on aerosols is reduced, succeeds at bringing the GCM and observations into agreement and leads to a reduction in the intrinsic ERFaci to −0.28 ± 0.26 W m−2 from −0.49 ± 0.18 W m−2 when no removal of near-cloud aerosol observations is performed. However, the distant aerosol field can also be expected to have less causal connection with the aerosol that perturbed the cloud; the resulting forcing estimate should probably be considered an upper (i.e., least negative) bound.
Title: Re: The Science of Aerosols
Post by: jai mitchell on June 11, 2018, 07:53:59 PM
Ken,

Thanks for those papers, they are very good and provide great news, if their constraints prove to be true,  I remain somewhat skeptical of the overall results, knowing that the disentanglement of aerosol impacts on regional preciptitation, cloud height and reflectivity is very difficult to disengage and the larger effects of global atmospheric circulation patterns (and the potential for increased Relative Humidity) that would result from a complete removal of aerosols produces another massive amount of uncertainty.

I enjoyed reading the reference document from your paper above.  it is found here.  https://www.atmos-chem-phys.net/17/13151/2017/acp-17-13151-2017.pdf
Title: Re: The Science of Aerosols
Post by: Ken Feldman on June 11, 2018, 09:27:34 PM
Ken,

Thanks for those papers, they are very good and provide great news, if their constraints prove to be true,  I remain somewhat skeptical of the overall results, knowing that the disentanglement of aerosol impacts on regional preciptitation, cloud height and reflectivity is very difficult to disengage and the larger effects of global atmospheric circulation patterns (and the potential for increased Relative Humidity) that would result from a complete removal of aerosols produces another massive amount of uncertainty.

I enjoyed reading the reference document from your paper above.  it is found here.  https://www.atmos-chem-phys.net/17/13151/2017/acp-17-13151-2017.pdf

For those who don't have time to follow the link Jai posted, here is the key takeaway from the study:

Quote
These new estimates suggest that
aerosol effects on the radiative properties of clouds are even
smaller than previously demonstrated from satellite-based
studies. This new methodology therefore further widens the
gap between the satellite and the very strong forcing estimates
derived using most GCMs.
Title: Re: The Science of Aerosols
Post by: Csnavywx on June 12, 2018, 06:43:35 AM
I am inherently more interested in their effects in convection-prone areas. From a meteorologist's perspective and anecdotal experience, they seem to have significant effects on deep convection (often as an enhancement -- especially in oceanic environments where boundary layer moisture restriction is less of an issue).
Title: Re: The Science of Aerosols
Post by: jai mitchell on June 12, 2018, 10:29:16 PM
And it doesn't include the responses from natural aerosols which may increase as a result of climate change

Ocean acidification and tropical forest loss is projected to decline Dimethyl Sulfide emissions by a significant amount
Title: Re: The Science of Aerosols
Post by: Ken Feldman on June 13, 2018, 12:30:45 AM
Here's a good overview of some of the possible changes to natural aerosol emissions due to climate change:

https://link.springer.com/article/10.1007/s40641-018-0086-1 (https://link.springer.com/article/10.1007/s40641-018-0086-1)

It's a long paper, as it goes through each time of natural aerosol and discuss the current understanding of how they are impacted by changes in temperature, wind speed and precipitation or moisture content.  Here is the abstract:

Quote
Purpose of Review

Climate factors may considerably impact on natural aerosol emissions and atmospheric distributions. The interdependencies of processes within the aerosol-climate system may thus cause climate feedbacks that need to be understood. Recent findings on various major climate impacts on aerosol distributions are summarized in this review.

Recent Findings

While generally atmospheric aerosol distributions are influenced by changes in precipitation, atmospheric mixing, and ventilation due to circulation changes, emissions from natural aerosol sources strongly depend on climate factors like wind speed, temperature, and vegetation. Aerosol sources affected by climate are desert sources of mineral dust, marine aerosol sources, and vegetation sources of biomass burning aerosol and biogenic volatile organic gases that are precursors for secondary aerosol formation. Different climate impacts on aerosol distributions may offset each other.

Summary

In regions where anthropogenic aerosol loads decrease, the impacts of climate on natural aerosol variabilities will increase. Detailed knowledge of processes controlling aerosol concentrations is required for credible future projections of aerosol distributions.
Title: Re: The Science of Aerosols
Post by: jai mitchell on June 15, 2018, 03:25:57 AM
Ocean acidification and warming impacts on global DMS production

https://www.mpimet.mpg.de/fileadmin/staff/ilyinatatiana/SixAllNatureCC2013.pdf

Global warming amplified by reduced sulphur fluxes as a result of ocean acidification

Quote
Marine  DMS  emissions  are  the  largest  natural source of atmospheric sulphur and changes in their strength have the potential to alter the Earth’s radiation budget.  Here we  establish  observational-based  relationships  between  pH changes and DMS concentrations to estimate changes in future DMS emissions with Earth system model  climate simulations. Global  DMS  emissions  decrease  by  about  18(± 3)%  in  2100 compared with pre-industrial times as a result of the combined effects of ocean acidification and climate change. The reduced DMS   emissions   induce   a   significant   additional   radiative forcing, of which 83% is attributed to the impact of ocean acidification, tantamount to an equilibrium temperature response between  0.23  and  0.48 K.  Our  results  indicate  that  ocean acidification  has  the  potential  to  exacerbate  anthropogenic warming through a mechanism that is not considered at present in projections of future climate change
Title: Re: The Science of Aerosols
Post by: gerontocrat on July 09, 2018, 09:34:54 AM
As anthropogenic aerosol emissions decrease, relative importance of Northern Oceans heat uptake increases. Important for Arctic Sea Ice, methinks?

https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-18-0170.1

Evolving Relative Importance of the Southern Ocean and North Atlantic in Anthropogenic Ocean Heat Uptake

Jia-Rui Shi*, Shang-Ping Xie, and Lynne D. Talley
Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA

https://doi.org/10.1175/JCLI-D-18-0170.1

Quote
Abstract
Ocean uptake of anthropogenic heat over the past 15 years has mostly occurred in the Southern Ocean, based on Argo float observations. This agrees with historical simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5), where the Southern Ocean (south of 30±S) accounts for 72%±28% of global heat uptake, while the contribution from the North Atlantic north of 30±N is only 6%. Aerosols preferentially cool the Northern Hemisphere, and the effect on surface heat flux over the subpolar North Atlantic opposes the greenhouse gas (GHG) effect in nearly equal magnitude. This heat uptake compensation is associated with weakening (strengthening) of the Atlantic Meridional Overturning Circulation (AMOC) in response to GHG (aerosol) radiative forcing. Aerosols are projected to decline in the near future, reinforcing the greenhouse effect on the North Atlantic heat uptake. As a result, the Southern Ocean, which will continue to take up anthropogenic heat largely through the mean upwelling of water from depth, will be joined by increased relative contribution from the North Atlantic due to substantial AMOC slowdown in the 21st century. In the RCP8.5 scenario, the percentage contribution to global uptake is projected to decrease to 48%±8% in the Southern Ocean and increase to 26%±6% in the northern North Atlantic. Despite the large uncertainty in the magnitude of projected aerosol forcing, our results suggest that anthropogenic aerosols, given their geographic distributions and temporal trajectories, strongly influence the high latitude ocean heat uptake and interhemispheric asymmetry through AMOC change.
Title: Re: The Science of Aerosols
Post by: jai mitchell on July 10, 2018, 05:55:48 PM
We looked at the results of Durack et. al. (2014) here. 

The results of the paper in ASLR's post above (Aerosol impact in the NH OHC) was discussed at that time.

https://forum.arctic-sea-ice.net/index.php/topic,1011.msg38424.html#msg38424

Quote
3.  The basic model of understanding appears to be severely underestimating northern hemisphere aerosol effects.
Title: Re: The Science of Aerosols
Post by: rboyd on July 22, 2018, 10:56:00 PM
When we burn coal, the aerosol effect is pretty immediate and then stabilizes due to the low transit time of the aerosols in the atmosphere. The CO2 effect is cumulative, given the long transit time of CO2 in the atmosphere.

Therefore, even if we just stabilize the level of coal burning then rate of climate change should increase (no increases in aerosols to offset the cumulative increases in CO2). The impact of aerosol (SO2) scrubbers is even worse, as we continue with CO2 but greatly reduce the aerosols. If China goes this way to clean up their air we will rapidly find out how much climate dimming is produced by aerosols. Probably not a good outcome for global climate change, nor for regional weather patterns.
With the new maritime SO2 emission standards, this is already being put into practice for maritime traffic globally.

Overall, everything (increasing CO2 emissions, fugitive methane, SO2 reductions) seems to be pointing to an acceleration in climate change. Add another El Nino and the next decade could become the "climate shock" decade.
Title: Re: The Science of Aerosols
Post by: gerontocrat on August 04, 2018, 10:18:52 AM
Neven is in danger of becoming (in)famous.

https://www.theguardian.com/environment/climate-consensus-97-per-cent/2018/aug/03/pollution-is-slowing-the-melting-of-arctic-sea-ice-for-now

Pollution is slowing the melting of Arctic sea ice, for now
Human carbon pollution is melting the Arctic, but aerosol pollution is slowing it down


Quote
I asked Arctic writer Neven Curlin what his thoughts were. He maintains the go-to site for updated news on the Arctic and its ice. He told me,

Arctic sea ice loss is already bad news, and this research comes on top of it. It’s amazing to think that the loss could’ve been even faster, if it hadn’t been for this dampening effect. If reducing the emissions of aerosols leads to an even faster warming of the Arctic, this will only further decrease the temperature gradient between the pole and the equator, likely adding to the destabilisation of Northern Hemisphere weather patterns. Never mind the longer term risks tied to sea level rise, methane release and changes to ocean currents. Not reducing aerosols isn’t an option, either, and so we find ourselves in quite a predicament. Hopefully future research will show that the number is actually lower.

He also reiterated the importance of this topic. He told me that we need more young minds to study the cryosphere; we need more data to help us understand the long-term trends. To gather that data, we need more and better equipment. This is a great example of how a small investment now can pay huge dividends in the future.

I plonked this into the comments thing of the article as the link was just to Neven.typepad.

Quote
The link in the article  is to Neven's blog. The mass of data and comment on all things environmental are to be found on  https://forum.arctic-sea-ice.net/index.php  "The Arctic Sea Ice Forum" founded by Neven and open to all.

Title: Re: The Science of Aerosols
Post by: Rob Dekker on August 12, 2018, 08:44:46 AM
Neven published this post in the ASIB :

http://neven1.typepad.com/blog/2018/08/aerosols-and-arctic-sea-ice-loss.html

which is essentially a summary of an article in the Guardian, it which he was quoted :

https://www.theguardian.com/environment/climate-consensus-97-per-cent/2018/aug/03/pollution-is-slowing-the-melting-of-arctic-sea-ice-for-now

The interesting claim from that article is this one :

Quote
So how much of an effect do aerosols have? It turns out 23% of the warming caused by greenhouse gases was offset by the cooling from aerosols.

I always like to check the science on such claims, and after Michael Sweet in the ASIB comment section found a free copy of the paper (Mueller et al 2018), I decided to review it :

https://dspace.library.uvic.ca/bitstream/handle/1828/7669/Mueller_Bennit_MSc_2016.pdf?sequence=1

I admit that I know very little about aerosols, and have not been following the literature about it.
So it may very well be that the better informed people on this fine forum find all of the following rather boring. But for me, it was pretty exciting and educative.

What I really wanted to know was how they determined that aerosols had a significant impact on Arctic Sea Ice decline.

Overall, I find the paper extremely thorough, and well argued.
I especially like their careful and formal handling of uncertainty in the data, and I learned a lot just reading the methods they use.

At the core, their method is pretty straightforward : They use CMIP5 GCM simulations of ALL, GHG only and NAT only forcings and use (multi-variable) linear regression to tease out these signals from the observed SIE over the 1953-2012 period. Something like this :

  SIEobs. = βoant*SIEoant + βnat*SIEnat + βghg*SIEghg

where SIEnat is the CMIP5 simulation of SIE (Sea Ice Exent) with Natural forcings only, SIEghg is the CMIP5 simulation of SIE with well mixed GHGs only, and SIEoant is the CMIP5 simulation of SIE with "everything else" (which is mostly aerosols).
In CMIP5, there is no "OANT" simulation, so they use OANT = ALL - GHG - NAT. Which makes sense. Just remember that OANT is basically "everything else" that is not GHG or Natural driven. That's mostly aerosols, but not exclusively.

SIEobs is the observed Arctic Sea Ice extent in September.

For SIEobs, they use three different SIE data sets : HadISST2 (which is a bit dated), Walsh and Chapman (WC) which is a great dataset, which we extensively discussed in the comment section here :
http://neven1.typepad.com/blog/2016/01/september-arctic-sea-ice-extent-1935-2014.html
and a new dataset by Piron and Pasalodos (PP) which I did not know about before and will certainly take a look at, especially since they date back to 1933.
PP and WC are apparently very similar for the 1953-2012 period that Mueller et al used.

The β's are scaling factors.

Here it gets interesting.
If a β factor is close to unity (1), that suggests that the simulation is very consistent with the actual observed SIE. If a β factor is much different from 1, there may be something fishy going on. For example, if a β factor is close to 0, the signal is not detected at all. That would mean the simulated signal is not detectable in real live observations. If the β factor is much bigger than 1, there may be more causes for the signal in the observed data set than the simulations suggest.
Now just keep that in mind for a moment, because I will get back to that.

In my opinion, the real impressive part (the awe factor) in this paper is the way in which they deal with uncertainties. They have truly set up a Detection and Attribution mechanism, where the calculate formally how the uncertainties in the estimations propagate through the system. And there are many uncertainties to deal with : uncertainties in the GHG / aerosol / NAT forcings, uncertainties in the modeling of their effect on Arctic SIE, the uncertainties in the SIE record etc etc.

There are several formal statistical methods they use (like regularized optimal fingerprinting (ROF), and the residual consistency test (RCT)) that I can learn from, and could apply to my own method of predicting SIE in September based on earlier (June) data :
https://forum.arctic-sea-ice.net/index.php/topic,103.msg162418.html#msg162418

When they apply these methods, the signals for GHG increases, Natural forcing and OANT (mostly aerosols) clearly are present in all 3 SIE data sets. They all come out of the noise, with a 90% certainty. That's impressive.

So overall, I really like this paper.

The only question I have is regarding the β factor they obtain for OANT (everything else but GHG and NAT forcings). I attached the results, from Figure 3.3 in the paper.

This suggests that the OANT signal has a β factor of about 1.7 or 1.8. That means that the OANT (aerosols mostly) signal shows up 1.7 to 1.8 stronger in the actual SIE record than the simulations suggest. So either aerosols have a much stronger effect on SIE than simulations suggest, or there is another signal present in reality (maybe something like land snow-cover or so) which is similar to the aerosol, which is there in reality, but is not properly taken into account by the GCM CMIP5 simulations.

Also, I don't see the 23% number from the Guardian anywhere in the paper.
All I see is a 30% number (from the conclusions) :
Quote
OANT has offset about 30% of the decline that would have been
expected in the absence of OANT forcing due to the combined climate response from
GHG and NAT forcing.
I suspect that the difference (23% versus 30%) is caused by the fact that aerosols do not fully cover the OANT (everything except for GHG and NATural) forcings.

So, overall a great paper, with the notion that maybe they overestimated the influence of aerosols on Arctic Sea Ice extent by a factor of 1.7 - 1.8.
Title: Re: The Science of Aerosols
Post by: AbruptSLR on August 20, 2018, 07:08:10 PM
The linked reference indicates that climate models need to account for the geographic distribution of anthropogenic aerosol emissions in order to correctly simulate the associated radiative forcing impacts on global warming:

Geeta G. Persad & Ken Caldeira (2018), "Divergent global-scale temperature effects from identical aerosols emitted in different regions", Nature Communications, volume 9, Article number: 3289, DOI: https://doi.org/10.1038/s41467-018-05838-6

https://www.nature.com/articles/s41467-018-05838-6

Abstract: "The distribution of anthropogenic aerosols’ climate effects depends on the geographic distribution of the aerosols themselves. Yet many scientific and policy discussions ignore the role of emission location when evaluating aerosols’ climate impacts. Here, we present new climate model results demonstrating divergent climate responses to a fixed amount and composition of aerosol—emulating China’s present-day emissions—emitted from 8 key geopolitical regions. The aerosols’ global-mean cooling effect is fourteen times greater when emitted from the highest impact emitting region (Western Europe) than from the lowest (India). Further, radiative forcing, a widely used climate response proxy, fails as an effective predictor of global-mean cooling for national-scale aerosol emissions in our simulations; global-mean forcing-to-cooling efficacy differs fivefold depending on emitting region. This suggests that climate accounting should differentiate between aerosols emitted from different countries and that aerosol emissions’ evolving geographic distribution will impact the global-scale magnitude and spatial distribution of climate change."
Title: Re: The Science of Aerosols
Post by: diablobanquisa on September 07, 2018, 11:14:36 AM


For SIEobs, they use three different SIE data sets : HadISST2 (which is a bit dated), Walsh and Chapman (WC) which is a great dataset, which we extensively discussed in the comment section here :
http://neven1.typepad.com/blog/2016/01/september-arctic-sea-ice-extent-1935-2014.html
and a new dataset by Piron and Pasalodos (PP) which I did not know about before and will certainly take a look at, especially since they date back to 1933.
PP and WC are apparently very similar for the 1953-2012 period that Mueller et al used.



Hi Rob,

Just to point out that the Piron and Pasalodos (PP) dataset is our time series, the one that we discussed nicely and extensively here: http://neven1.typepad.com/blog/2016/01/september-arctic-sea-ice-extent-1935-2014.html

(Journal article: https://doi.org/10.5281/zenodo.44756 , NetCDF file with the gridded data: https://doi.org/10.5281/zenodo.44757 , CSV file with the extent values: https://doi.org/10.5281/zenodo.44758)

Glad to see that our data are useful!

Title: Re: The Science of Aerosols
Post by: AbruptSLR on September 11, 2018, 07:32:08 PM
The linked reference provides evidence that CMIP5 model projections 'have underestimated the cooling effect that aerosol particles have had on climate in recent decades"; which 'suggests that the models are not sensitive enough to increasing greenhouse gas concentrations in the atmosphere'.  In other words, this reference finds that the CMIP5 models (as a group) underestimate both TCR & ECS:


Trude Storelvmo et al. (29 August 2018), "Lethargic response to aerosol emissions in current climate models", Geophysical Research Letters, https://doi.org/10.1029/2018GL078298

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL078298

"Abstract
The global temperature trend observed over the last century is largely the result of two opposing effects – cooling from aerosol particles and greenhouse gas (GHG) warming. While the effect of increasing GHG concentrations on Earth's radiation budget is well‐constrained, that due to anthropogenic aerosols is not, partly due to a lack of observations. However, long‐term surface measurements of changes in downward solar radiation (SDSR), an often‐used proxy for aerosol radiative impact, are available worldwide over the last half‐century. We compare SDSR changes from ∼1,400 stations to those from the CMIP5 global climate simulations over the period 1961‐2005. The observed SDSR shows a strong early downward trend followed by a weaker trend‐reversal, broadly consistent with historical aerosol emissions. However, despite considerable changes to known aerosol emissions over time, the models show negligible SDSR trends, revealing a lethargic response to aerosol emissions, and casting doubt on the accuracy of their future climate projections.

Plain Language Summary
Observations of incoming solar radiation, as measured at approximately 1400 surface stations worldwide, show a strong downward trend from the 1960s to the 1980s, followed by a weaker trend reversal thereafter. These trends are thought to be due to changes in the amount of aerosol particles in the atmosphere, and we find support for that here in the temporal evolution of anthropogenic aerosol emissions. This is expected because aerosol particles reflect and/or absorb sunlight back to space, and have a net cooling effect on Earth's climate. However, we find that the current generation of climate models simulate negligible solar radiation trends over the last half‐century, suggesting that they have underestimated the cooling effect that aerosol particles have had on climate in recent decades. Despite this, climate models tend to reproduce surface air temperature over the time period in question reasonably well. This, in turn, suggests that the models are not sensitive enough to increasing greenhouse gas concentrations in the atmosphere, with important implications for their ability to simulate future climate."
Title: Re: The Science of Aerosols
Post by: Rob Dekker on September 30, 2018, 01:37:27 AM


For SIEobs, they use three different SIE data sets : HadISST2 (which is a bit dated), Walsh and Chapman (WC) which is a great dataset, which we extensively discussed in the comment section here :
http://neven1.typepad.com/blog/2016/01/september-arctic-sea-ice-extent-1935-2014.html
and a new dataset by Piron and Pasalodos (PP) which I did not know about before and will certainly take a look at, especially since they date back to 1933.
PP and WC are apparently very similar for the 1953-2012 period that Mueller et al used.



Hi Rob,

Just to point out that the Piron and Pasalodos (PP) dataset is our time series, the one that we discussed nicely and extensively here: http://neven1.typepad.com/blog/2016/01/september-arctic-sea-ice-extent-1935-2014.html

(Journal article: https://doi.org/10.5281/zenodo.44756 , NetCDF file with the gridded data: https://doi.org/10.5281/zenodo.44757 , CSV file with the extent values: https://doi.org/10.5281/zenodo.44758)

Glad to see that our data are useful!

I did not realize that. That is so cool diablo ! Congratulations !
Title: Re: The Science of Aerosols
Post by: vox_mundi on October 24, 2018, 06:37:52 PM
Copernicus Sentinel-5P Reveals New Atmospheric Nasties (http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-5P/Copernicus_Sentinel-5P_reveals_new_nasties)
http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-5P/Copernicus_Sentinel-5P_reveals_new_nasties

(https://3c1703fe8d.site.internapcdn.net/newman/csz/news/800/2018/7-copernicusse.jpg)

Streams of data on carbon monoxide, nitrogen dioxide, ozone, along with information on aerosols and clouds have been available since July. On 17 October, sulphur dioxide and formaldehyde joined the list of air pollutants routinely available for services such as air-quality forecasting and volcanic ash monitoring.

Sulphur dioxide affects air quality badly and can lead to breathing problems. While it is released into the atmosphere mainly through industrial processes, it is also present in volcanic plumes.

Monitoring the spread of volcanic plumes is critical for aircraft safety.

Nicolas Theys from the Royal Belgian Institute for Space Aeronomy said, "Copernicus Sentinel-5P's near-realtime data on sulphur dioxide and aerosols are being used in the Support to Aviation Control Service and in the European Natural Disaster Coordination Information System for Aviation.

"The unprecedented level of details offered by the mission allows Volcanic Ash Advisory Centre users to better track and forecast the dispersion of volcanic plumes."
Title: Re: The Science of Aerosols
Post by: AbruptSLR on October 27, 2018, 01:06:44 AM
China is the source of the ozone-depleting carbon tetrachloride emissions:

M. F. Lunt et al. (28 September 2018), "Continued Emissions of the Ozone‐Depleting Substance Carbon Tetrachloride From Eastern Asia", Geophysical Research Letters, https://doi.org/10.1029/2018GL079500

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL079500

Abstract
Carbon tetrachloride (CCl4) is an ozone‐depleting substance, accounting for about 10% of the chlorine in the troposphere. Under the terms of the Montreal Protocol, its production for dispersive uses was banned from 2010. In this work we show that, despite the controls on production being introduced, CCl4 emissions from the eastern part of China did not decline between 2009 and 2016. This finding is in contrast to a recent bottom‐up estimate, which predicted a significant decrease in emissions after the introduction of production controls. We find eastern Asian emissions of CCl4 to be 16 (9–24) Gg/year on average between 2009 and 2016, with the primary source regions being in eastern China. The spatial distribution of emissions that we derive suggests that the source distribution of CCl4 in China changed during the 8‐year study period, indicating a new source or sources of emissions from China's Shandong province after 2012.

Plain Language Summary
Carbon tetrachloride is one of several man‐made gases that contribute to the depletion of the ozone layer high in the atmosphere. Because of this, restrictions were introduced on the use of this ozone‐depleting substance, with the expectation that production should by now be close to 0. However, the slower than expected rate of decline of carbon tetrachloride in the atmosphere shows this is not the case, and a large portion of global emissions are unaccounted for. In this study we use atmospheric measurements of carbon tetrachloride from a site in East Asia to identify the magnitude and location of emissions from this region between 2009 and 2016. We find that there are significant ongoing emissions from eastern China and that these account for a large part of the missing emissions from global estimates. The presence of continued sources of this important ozone‐depleting substance indicates that more could be done to speed up the recovery of the ozone layer.
Title: Re: The Science of Aerosols
Post by: jai mitchell on January 23, 2019, 04:02:28 AM
https://www.sciencedaily.com/releases/2019/01/190122104611.htm

We need to rethink everything we know about global warming
New calculations show scientists have grossly underestimated the effects of air pollution

Quote
Rosenfeld and his colleague Yannian Zhu from the Meteorological Institute of Shaanxi Province in China developed a new method that uses satellite images to separately calculate the effect of vertical winds and aerosol cloud droplet numbers. They applied this methodology to low-lying cloud cover above the world's oceans between the Equator and 40S. With this new method, Rosenfeld and his colleagues were able to more accurately calculate aerosols' cooling effects on the Earth's energy budget. And, they discovered that aerosols' cooling effect is nearly twice higher than previously thought.

Compare the AR5 value of Faero of -0.9 W/m^2 with Mauritsen & Pincus 2017 display of current locked in warming based on Transient Climate Response (only through 2100) as derived from the fact that aerosol forcing has been suppressing warming.

Title: Re: The Science of Aerosols
Post by: b_lumenkraft on January 23, 2019, 04:28:52 AM
Daniel Rosenfeld et al (DOI: 10.1126/science.aav0566)

Abstract

Quote
Lack of reliable estimates of cloud condensation nuclei (CCN) aerosols over oceans has severely limited our ability to quantify their effects on cloud properties and extent of cooling by reflecting solar radiation – a key uncertainty in anthropogenic climate forcing. Here we introduce a methodology for ascribing cloud properties to CCN and isolating the aerosol effects from meteorological effects. Its application showed that, for a given meteorology, CCN explains 3/4 of the variability in clouds radiative cooling effect, mainly through affecting shallow cloud cover and water path. This reveals a much greater sensitivity of cloud radiative forcing to CCN than previously reported, which means too much cooling if incorporated in present climate models. This hints to yet unknown compensating aerosol warming effects, possibly through deep clouds.

Link >> https://www.researchgate.net/publication/330478810_Aerosol-driven_droplet_concentrations_dominate_coverage_and_water_of_oceanic_low_level_clouds
Title: Re: The Science of Aerosols
Post by: wdmn on January 23, 2019, 07:10:25 AM
https://www.sciencedaily.com/releases/2019/01/190122104611.htm

We need to rethink everything we know about global warming
New calculations show scientists have grossly underestimated the effects of air pollution

Quote
Rosenfeld and his colleague Yannian Zhu from the Meteorological Institute of Shaanxi Province in China developed a new method that uses satellite images to separately calculate the effect of vertical winds and aerosol cloud droplet numbers. They applied this methodology to low-lying cloud cover above the world's oceans between the Equator and 40S. With this new method, Rosenfeld and his colleagues were able to more accurately calculate aerosols' cooling effects on the Earth's energy budget. And, they discovered that aerosols' cooling effect is nearly twice higher than previously thought.

Compare the AR5 value of Faero of -0.9 W/m^2 with Mauritsen & Pincus 2017 display of current locked in warming based on Transient Climate Response (only through 2100) as derived from the fact that aerosol forcing has been suppressing warming.

I'm trying to make sense of the graph you posted. Is the locked in warming in addition to the warming that's already occurred? Does it assume that aerosols go to zero during this century? What is the "with carbon uptake" scenario?
Title: Re: The Science of Aerosols
Post by: sidd on January 23, 2019, 07:53:30 AM
The difficulty is that if aerosols were twice as  effective at cooling than previously thought, then the models must have been wrong in the other direction on efficacy of warming agents in matching historical data ...

sidd
Title: Re: The Science of Aerosols
Post by: jai mitchell on January 23, 2019, 04:08:00 PM
I'm trying to make sense of the graph you posted. Is the locked in warming in addition to the warming that's already occurred? Does it assume that aerosols go to zero during this century? What is the "with carbon uptake" scenario?

No it is total warming from Pre-industrial by 2100 (See definition of Transient Climate Response), I am not sure now if it means zero aerosol emissions at 2100.  I used to think that it did but now I fear that the models are being tweaked in every way possible to project less warming than should be expected.


The difficulty is that if aerosols were twice as  effective at cooling than previously thought, then the models must have been wrong in the other direction on efficacy of warming agents in matching historical data ...

sidd

The range of aerosol cooling effects within the paper is well within the projected uncertainty of the study.  Remember, the models include uncertainty in their projected ranges, though they usually only show the median values of projections.

Title: Re: The Science of Aerosols
Post by: GeoffBeacon on January 25, 2019, 01:19:15 AM
I'd describe myself as an activist. Rarely successful but I keep trying. Climate change is clearly most important but on this I am a voice amongst many but I try to pass on what I discover to like minds and to decision makers (politicians & related) that I seek out.

(I hope that wasn't to self centred but it might help any response.)

I have an uncomfortable feeling now that decision makers haven't much of a clue (or any sort of a clue) as to the current state of the climate - even those honest and clear minded enough to put aside the "I don't like it so I don't believe it" effect. I also have some problem with the climate science community (OK, that's another thread) and this paper by Rosenfeld et al. causes me some angst.  Partly because it suggests Hansen's Faustian bargain may be much worse. Hansen raised this issue in 1990 in  Sun and dust versus greenhouse gases: an assessment of their relative roles in global climate change, Nature 346 713–9 (https://www.nature.com/articles/346713a0) Later he wrote in the Huffington Post (https://www.huffingtonpost.com/dr-james-hansen/doubling-down-on-our-faustian-bargain_b_2989535.html)

Quote
The principal implication of our present analysis probably relates to the Faustian bargain. Increased short-term masking of greenhouse gas warming by fossil fuel particulate and nitrogen pollution represents a 'doubling down' of the Faustian bargain, an increase in the stakes. The more we allow the Faustian debt to build, the more unmanageable the eventual consequences will be. Yet globally there are plans to build more than 1000 coal-fired power plants (Yang and Cui 2012) and plans to develop some of the dirtiest oil sources on the planet (EIA 2011). These plans should be vigorously resisted. We are already in a deep hole—it is time to stop digging.

A  report in Science Daily (https://www.sciencedaily.com/releases/2019/01/190122104611.htm) says of Rosenfeld et al.

Quote
For a while now, the scientific community has known that global warming is caused by human made emissions in the form of greenhouse gases and global cooling by air pollution in the form of aerosols.

However, new research published in Science by Hebrew University of Jerusalem Professor Daniel Rosenfeld shows that the degree to which aerosols cool the earth has been grossly underestimated, necessitating a recalculation of climate change models to more accurately predict the pace of global warming

Question 1: Does this mean that Hansen's Faustian bargain has just got much worse.

Question 2: Why has it taken 30 years to find this out?

Question 3: Will any of this get through to policy makers?
(Internet search of BBC and UK: nothing on Rosenfeld. Similarly WAPO & NYT)

As an activist I'm interested in what the policy implications are. I've been campaigning against
cars, planes, high buildings and beef&lamb for climate reasons - for many years now. An naturally have campaigned for renewable energy. I've been campaigning for trees and the use of wood.

However, for some time I have had in the back of my mind Attribution of climate forcing to economic sectors (https://www.pnas.org/content/107/8/3382) by Unger et al. Figure 2 shows the progression of cooling/warming from different activities

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fbrusselsblog.co.uk%2Fimg%2FUnger_Fig2.jpg&hash=81dfcb70973d8b1a5f031aa062f66480)

As far as I can see, this shows on road transport (mostly cars), household biofuel, animal husbandry (beef & lamb particularly?) warm the Earth early on but industry (inc cement and steel manufacture?), biomass burning, agricultural waste burning and shipping have medium to long term cooling effects before warming starts.

Additionally, Unger has criticised policies for planting trees to slow climate change. From the Nature Blog (https://blog.nature.org/science/2014/09/24/forest-nadine-unger-plant-trees-climate/)

Quote
According to Unger’s latest findings, the volatile organic compounds (VOCs) emitted by trees heat our climate. It’s controversial because it’s a new idea, modeled by Unger, and there are lots of ways to run a model.

Unger has also expressed the view that aviation is much less of a problem than many think and has a significant cooling effect before it turns to warming. I haven't the reference to hand (a saved link broken) but found this

Quote
"From the point of view of the general public, there's been a level of anxiety that people feel recently about their carbon footprint when they go to airports," Unger said. "We should be feeling that way when we turn on our car ignitions."

"Attribution of climate forcing.." is now almost a decade old and the latest findings from Rosenfeld seem to have substantially increased estimates of the cooling before the warming starts. As we have short term as well as long term problems, this is worrying

But do we now have? :

1.Cars - very, very, bad from the start.

2.Beef & lamb -  very bad from the start.

3.Fossil fuel power - very bad but we worry about losing the initial cooling.

4.High buildings - bad but the embodied CO2 comes from "industry" so some initial cooling.

5.Planes - not so bad but we worry about losing the initial cooling.

6. Trees - where can they be planted to avoid the aerosol warming effects?
 (http://1.Cars - very, very, bad from the start.

2.Beef & lamb -  very bad from the start.

3.Fossil fuel power - very bad but we worry about losing the initial cooling.

4.High buildings - bad but the embodied CO2 comes from "industry" so some initial cooling.

5.Planes - not so bad but we worry about losing the initial cooling.

6. Trees - where can they be planted to avoid the aerosol warming effects?)

Sadly the "I don't like it so I don't believe it" effect kicks in." and there is
a reluctance to accept that stopping mass car ownership is a priority (http://www.brusselsblog.co.uk/ministry-of-housing-no-homes-for-motorists/).

Title: Re: The Science of Aerosols
Post by: Richard Rathbone on January 25, 2019, 03:11:09 AM
There's nothing to back up this alarmism in the abstract of the Rosenfeld paper. (the paper is paywalled so I can't check that) Looks like a journalist misunderstanding what the implications are to me. All it says it that if models incorporate the findings without recalibrating the rest of their aerosol models, they'll get it badly wrong and that aerosols may have heating effects too.

Quote
Lack of reliable estimates of cloud condensation nuclei (CCN) aerosols over oceans has severely limited our ability to quantify their effects on cloud properties and extent of cooling by reflecting solar radiation – a key uncertainty in anthropogenic climate forcing. Here we introduce a methodology for ascribing cloud properties to CCN and isolating the aerosol effects from meteorological effects. Its application showed that, for a given meteorology, CCN explains 3/4 of the variability in clouds radiative cooling effect, mainly through affecting shallow cloud cover and water path. This reveals a much greater sensitivity of cloud radiative forcing to CCN than previously reported, which means too much cooling if incorporated in present climate models. This hints to yet unknown compensating aerosol warming effects, possibly through deep clouds.
Title: Re: The Science of Aerosols
Post by: GeoffBeacon on January 26, 2019, 12:09:35 AM
Whether or not this paper is alarmist about aerosols my question remains (perhaps with slightly less urgency):

Quote
But do we now have? :

1.Cars - very, very, bad from the start.

2.Beef & lamb -  very bad from the start.

3.Fossil fuel power - very bad but we worry about losing the initial cooling.

4.High buildings - bad but the embodied CO2 comes from "industry" so some initial cooling.

5.Planes - not so bad but we worry about losing the initial cooling.

6. Trees - where can they be planted to avoid the aerosol warming effects?


Point 6 is relevant to BECCS.
Title: Re: The Science of Aerosols
Post by: jai mitchell on January 29, 2019, 07:58:35 PM
There's nothing to back up this alarmism in the abstract of the Rosenfeld paper. (the paper is paywalled so I can't check that) Looks like a journalist misunderstanding what the implications are to me. All it says it that if models incorporate the findings without recalibrating the rest of their aerosol models, they'll get it badly wrong and that aerosols may have heating effects too.

Quote
Lack of reliable estimates of cloud condensation nuclei (CCN) aerosols over oceans has severely limited our ability to quantify their effects on cloud properties and extent of cooling by reflecting solar radiation – a key uncertainty in anthropogenic climate forcing. Here we introduce a methodology for ascribing cloud properties to CCN and isolating the aerosol effects from meteorological effects. Its application showed that, for a given meteorology, CCN explains 3/4 of the variability in clouds radiative cooling effect, mainly through affecting shallow cloud cover and water path. This reveals a much greater sensitivity of cloud radiative forcing to CCN than previously reported, which means too much cooling if incorporated in present climate models. This hints to yet unknown compensating aerosol warming effects, possibly through deep clouds.

The author said that the cloud effects of aerosols from his study, which is considered robust, produces a much greater cooling effect than currently understood and that there is likely an additional heating mechanism that makes the models still perform within the range.  He hypthesized an additional heating mechanism from deeper clouds to do this. 

It is my understanding that the models are still to simplistic to address the regional variations accross the globe and that they do not yet include the effects on GHG forcing and aerosols on larger variability patterns (IPO, MJO, AO etc. . .)
Title: Re: The Science of Aerosols
Post by: rboyd on February 11, 2019, 09:02:44 PM
The author said that the cloud effects of aerosols from his study, which is considered robust, produces a much greater cooling effect than currently understood and that there is likely an additional heating mechanism that makes the models still perform within the range.  He hypthesized an additional heating mechanism from deeper clouds to do this. 

It is my understanding that the models are still to simplistic to address the regional variations accross the globe and that they do not yet include the effects on GHG forcing and aerosols on larger variability patterns (IPO, MJO, AO etc. . .)

After reading the paper my take is that it does identify a significantly greater cooling effect from aerosols than currently assumed. To align this with the actual increase in global temperatures there must be a greater source of warming. If that warming is another side effect of aerosols it will diminish with the aerosols. If the source of the extra heating is not from aerosols (perhaps climate sensitivity much closer to Hansen's estimates) then the removal of aerosols will greatly accelerate global warming.
Title: Re: The Science of Aerosols
Post by: jai mitchell on March 26, 2019, 06:31:01 PM
Question 1: Does this mean that Hansen's Faustian bargain has just got much worse.

Yes, it indicates that total committed warming is much higher now than we had previously thought, that we have committed warming (with frozen soil feedbacks) that are approaching 2.5C)

Question 2: Why has it taken 30 years to find this out?

There was an orbital aerosol polarimetry sensor attached to the GLORY satellite that would have been used to determine total cloud forcing parameters globally and the exact chemical makeup of these aerosols.  However, even after a prior mission had failed due to fairing malfunction and the fairing release mechanism was replaced with the military preferred Taurus satellite delivery mechanism, the GLORY satellite suffered catastrophic failure due to fairing malfunction.

Rosenfeld used recent satellite data as a patchwork from multiple sources to produce this result which is considered quite robust.

Question 3: Will any of this get through to policy makers?
(Internet search of BBC and UK: nothing on Rosenfeld. Similarly WAPO & NYT)

No.  If they have any interest at all they are latched into the IPCC 1.5SR report that states we have almost double the current level of emissions before we lock in 1.5C of warming (even though 2017 was 1.2C.   :'(
Title: Re: The Science of Aerosols
Post by: Ken Feldman on April 16, 2019, 09:24:47 PM
A link to this study showing an increase in natural aerosols in the absence of anthropogenic aerosols and also a negative feedback at higher temperatures and CO2 was posted by AbruptSLR in the Antarctica forum:

https://www.atmos-chem-phys.net/19/4763/2019/ (https://www.atmos-chem-phys.net/19/4763/2019/)

Quote
Abstract
 
Both higher temperatures and increased CO2 concentrations are (separately) expected to increase the emissions of biogenic volatile organic compounds (BVOCs). This has been proposed to initiate negative climate feedback mechanisms through increased formation of secondary organic aerosol (SOA). More SOA can make the clouds more reflective, which can provide a cooling. Furthermore, the increase in SOA formation has also been proposed to lead to increased aerosol scattering, resulting in an increase in diffuse radiation. This could boost gross primary production (GPP) and further increase BVOC emissions. In this study, we have used the Norwegian Earth System Model (NorESM) to investigate both these feedback mechanisms. Three sets of experiments were set up to quantify the feedback with respect to (1) doubling the CO2, (2) increasing temperatures corresponding to a doubling of CO2 and (3) the combined effect of both doubling CO2 and a warmer climate. For each of these experiments, we ran two simulations, with identical setups, except for the BVOC emissions. One simulation was run with interactive BVOC emissions, allowing the BVOC emissions to respond to changes in CO2 and/or climate. In the other simulation, the BVOC emissions were fixed at present-day conditions, essentially turning the feedback off. The comparison of these two simulations enables us to investigate each step along the feedback as well as estimate their overall relevance for the future climate.

We find that the BVOC feedback can have a significant impact on the climate. The annual global BVOC emissions are up to 63 % higher when the feedback is turned on compared to when the feedback is turned off, with the largest response when both CO2 and climate are changed. The higher BVOC levels lead to the formation of more SOA mass (max 53 %) and result in more particles through increased new particle formation as well as larger particles through increased condensation. The corresponding changes in the cloud properties lead to a −0.43 W m−2 stronger net cloud forcing. This effect becomes about 50 % stronger when the model is run with reduced anthropogenic aerosol emissions, indicating that the feedback will become even more important as we decrease aerosol and precursor emissions. We do not find a boost in GPP due to increased aerosol scattering on a global scale. Instead, the fate of the GPP seems to be controlled by the BVOC effects on the clouds. However, the higher aerosol scattering associated with the higher BVOC emissions is found to also contribute with a potentially important enhanced negative direct forcing (−0.06 W m−2). The global total aerosol forcing associated with the feedback is −0.49 W m−2, indicating that it has the potential to offset about 13 % of the forcing associated with a doubling of CO2.

Title: Re: The Science of Aerosols
Post by: vox_mundi on June 20, 2019, 09:08:08 PM
Connecting the Dots: Nitrogen Dioxide Over Siberian Pipelines
http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-5P/Connecting_the_dots_nitrogen_dioxide_over_Siberian_pipelines

(https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2019/06/nitrogen_dioxide_over_siberian_pipelines/19452167-1-eng-GB/Nitrogen_dioxide_over_Siberian_pipelines_large.gif)

New maps that use information from the Copernicus Sentinel-5P satellite reveal emissions of nitrogen dioxide along a Siberian natural gas pipeline that connects the Urengoy gas field—the second-largest gas field in the world—with Europe.

The Urengoy–Pomary–Uzhhorod pipeline is one of Russia's main natural gas export pipelines. In order to maintain the pressure and flow over long distances, a series of compressor stations are strategically placed to help push the gas along.

Compressor stations typically run on gas-powered turbines, and their high-temperature combustion usually leads to small quantities of nitrogen dioxide emissions being lost to the atmosphere.

Until now, it has proved difficult to measure trace-gas concentrations over snow-covered regions such as Siberia, northern Europe and Canada, as it has been very difficult to distinguish clouds from snow and ice in the data retrieval algorithms—considering snow and clouds appear equally bright and cold.

Using data from the Copernicus Sentinel-5P's Tropomi instrument, scientists from the Royal Netherlands Meteorological Institute (KNMI) have now solved this problem.

https://youtu.be/h7M-Cfta9Q0

"We estimate the nitrogen dioxide emissions are typically 10—30 tonne(N)/month, a small amount. These results show what the high-spatial resolution of Tropomi combined with new and innovative detection methods, can do," adds Ronald van der A also from KNMI.

"For most locations, there is no nitrogen dioxide information during the snow season, but with this new method, nitrogen dioxide can be observed despite the snow." ... "We think, that these new results will offer new exciting possibilities for detecting smaller-scale emissions, that we did not even know existed today. This will be another example that will lead to a better understanding of air quality."
Title: Re: The Science of Aerosols
Post by: Tom_Mazanec on June 24, 2019, 07:01:34 PM
Aerosols twice as cooling as thought:
https://m.phys.org/news/2019-01-cooling-effect-aerosols-cumulus-msc.html
Title: Re: The Science of Aerosols
Post by: b_lumenkraft on June 24, 2019, 07:06:05 PM
From Toms link:

Quote
The researchers found that clouds containing more aerosols reflected more heat than prior estimates had suggested—more than twice as much. More specifically, they found that approximately three-quarters of the amount of heat reflected was due to aerosols. They suggest that such a large percentage shows that the radiative cooling capacity of clouds is much more sensitive to the presence of aerosols than has been thought. They note that this is important because climate change models take into account the amount of heat that clouds reflect back into space. It also shows that the heating effect of greenhouse gases is higher than has been thought because it has been mitigated by the impact of aerosols in clouds.

Oh. My. Gosh.  :-\
Title: Re: The Science of Aerosols
Post by: be cause on June 24, 2019, 07:23:47 PM
get burning that coal ? b.c.
Title: Re: The Science of Aerosols
Post by: b_lumenkraft on June 24, 2019, 07:56:55 PM
And who foreshadowed it long time ago, and was ridiculed for saying it, to a point when you can't even mention their name anymore?

Yeah, that's right, Sam Carana!
Title: Re: The Science of Aerosols
Post by: KiwiGriff on June 24, 2019, 09:54:35 PM
This paper .
K. Haustein, F.E. Otto, V. Venema, P. Jacobs, K. Cwtan, Z. Hausfather, R.G. Way, B. White, A. Subramanian, and A.P. Schurer, "A limited role for unforced internal variability in 20th century warming.", Journal of Climate, 2019. http://dx.doi.org/10.1175/JCLI-D-18-0555.1
Recently discussed at both carbon brief and real climate.
http://www.realclimate.org/index.php/archives/2019/06/unforced-variations-vs-forced-responses/#ITEM-22424-0
https://www.carbonbrief.org/guest-post-why-natural-cycles-only-play-small-role-in-rate-of-global-warming

Gives a value for aerosol cooling as 0.4C presently as can be seen in the third figure at carbon brief.

Sorry for not linking directly to the figure it is interactive and above my pay scale to work out how to paste it here or explain the paper better than both links do.
 
Anyone with more than a passing interest should read both links and the comments at real climate.


 


 
Title: Re: The Science of Aerosols
Post by: jai mitchell on June 26, 2019, 06:07:04 PM
The cooling effect from 1950-1980 is limited and may imply a weaker negative cooling effect from Aerosols, however, if you plot SO2 vs Northern Hemisphere temps (which experiences most of the effects from SO2 and is not moderated by the large southern ocean) the forcing signal becomes more clear.  The resultant warming after 1976 shows that there was much greater warming (positive forcing) in the bin than the global temperature response indicates.

Therefore the negative forcing from SOx is greater and the TCR is greater.

NH temperature data through 2012 - GISStemp
SO2 data - Anthropogenic Sulfur Dioxide Emissions 1850-2005,  Smith, S.J. et al
Title: Re: The Science of Aerosols
Post by: jai mitchell on June 26, 2019, 06:21:34 PM
The impact of northern hemisphere cooling effects of SOx vs. the Southern hemisphere.  Temperature data from NASA GISStemps and SO2 data from Smith et. al as above.

The amount of warming incurred after the northern hemisphere clean air acts which only slightly reduced SO2 emissions from their 1930 levels indicates a higher degree of forcing and cooling effect from SO2.  This is shown a bit more clearly when the southern hemisphere warming is shown to be about 1/2 of the amount produced in the northern hemisphere, as well as the gradual increase in Southern Hemisphere SO2 that starts to moderate SH warming in the 1990s.
Title: Re: The Science of Aerosols
Post by: morganism on June 29, 2019, 11:07:43 PM
Hot off the new EarthArXiv

Large uncertainty in volcanic aerosol radiative forcing derived from ice cores

https://eartharxiv.org/mbtg8/

"Currently, reconstructions of pre-20th century volcanic forcing are derived from sulfate concentrations measured in polar ice cores, predominantly using a relationship between average ice sheet sulfate deposition and stratospheric sulfate aerosol based on a single explosive eruption - the 1991 eruption of Mt. Pinatubo. Here we derive volcanic radiative forcing from ice-core-records using a perturbed parameter ensemble of aerosol-climate model simulations of explosive eruptions, which enables the uncertainty to be estimated. We find that a very wide range of eruptions with different sulfur dioxide emissions, eruption latitudes, emission altitudes and in different seasons produce ice-sheet sulfate deposition consistent with ice-core-derived values for eruptions during the last 2500 years. Consequently, we find a large uncertainty in the volcanic forcing, suggesting uncertainties on the global mean temperature response of more than 1C for several past explosive eruptions, which has not been previously accounted for."
Title: Re: The Science of Aerosols
Post by: Ken Feldman on July 16, 2019, 07:31:46 PM
China has reduced sulfur dioxide significantly over the past ten years as the following two papers demonstrate.

https://www.nature.com/articles/s41598-017-14639-8 (https://www.nature.com/articles/s41598-017-14639-8)

Quote
Li, Can & Mclinden, Chris & Fioletov, Vitali & Krotkov, Nickolay & Carn, Simon & Joanna, Joiner & Streets, David & He, Hao & Ren, Xinrong & Li, Zhanqing & Dickerson, Russell. (2017).

India Is Overtaking China as the World’s Largest Emitter of Anthropogenic Sulfur Dioxide.

Scientific Reports. 7. 10.1038/s41598-017-14639-8.

Severe haze is a major public health concern in China and India. Both countries rely heavily on coal for energy, and sulfur dioxide (SO2) emitted from coal-fired power plants and industry is a major pollutant contributing to their air quality problems. Timely, accurate information on SO2 sources is a required input to air quality models for pollution prediction and mitigation. However, such information has been difficult to obtain for these two countries, as fast-paced changes in economy and environmental regulations have often led to unforeseen emission changes. Here we use satellite observations to show that China and India are on opposite trajectories for sulfurous pollution. Since 2007, emissions in China have declined by 75% while those in India have increased by 50%. With these changes, India is now surpassing China as the world’s largest emitter of anthropogenic SO2. This finding, not predicted by emission scenarios, suggests effective SO2 control in China and lack thereof in India. Despite this, haze remains severe in China, indicating the importance of reducing emissions of other pollutants. In India, ~33 million people now live in areas with substantial SO2 pollution. Continued growth in emissions will adversely affect more people and further exacerbate morbidity and mortality.

(https://media.springernature.com/lw900/springer-static/image/art%3A10.1038%2Fs41598-017-14639-8/MediaObjects/41598_2017_14639_Fig2_HTML.jpg)

https://www.atmos-chem-phys-discuss.net/acp-2019-407/acp-2019-407.pdf (https://www.atmos-chem-phys-discuss.net/acp-2019-407/acp-2019-407.pdf)

Quote
Significant reduction of PM2.5 in eastern China due to regional-scale emission control: Evidences
from the SORPES station, 2011-2018

Aijun Ding1,2, Xin Huang1,2, Wei Nie1,2, Xuguang Chi1,2, Zheng Xu1,2, Longfei Zheng1,2,5       Zhengning Xu1,2, Yuning Xie1,2,†, Ximeng Qi1,2, Yicheng Shen1,2, Peng Sun1,2, Jiaping
Wang1,2, Lei Wang1,2, Jiannin Sun1,2, Xiu-Qun Yang1,2, Wei Qin3, Xiangzhi Zhang3,4, Wei Cheng3,Weijing Liu5, Liangbao Pan4, and Congbin Fu1,2

Abstract. Haze pollution caused by PM2.5  is the largest air quality concern in China in
recent years. Long-term measurements of PM2.5  and the precursors and chemical speciation is
crucially important for evaluating the efficiency of emission control, understanding formation and
transport of PM2.5  associated with the change of meteorology and for accessing the impact of human activities to regional climate change. Here we reported long-term continuous     measurements of PM2.5, chemical components, and their precursors at a regional background
station, the Station for Observing Regional Processes of the Earth System (SORPES), in Nanjing
eastern China since 2011. We found that PM2.5  at the station has experienced a substantial
decrease (-9.1%/yr), accompanied with even much significant reduction of SO2 (-16.7%/yr), since the national “Ten measures” for air took action in 2013. Control of open biomass burning and fossil-fuel combustion are the two dominant factors that influence the PM2.5 
reduction in early summer and winter, respectively. In cold season (November-January), increased nitrate fraction was observed with more NH3  available from a substantial reduction of sulfate, and the change of year-to-year meteorology contributed to 24% of the PM2.5  decrease since 2013. This study highlights several important implications on air pollution control policy in China.

Quote
3 Results and Discussion

Based on continuous measurement at the SORPES station, Fig. 2 shows the trends of PM2.5  mass concentration and the two key precursors (SO2  and NO2) since 2011, and the main PM2.5
chemical components (BC, SO 2- and NO -) since 2013. Considering the difference in the observation duration and the specific emission control in east China associated with the national
“Ten Measures” for air since 2013 (Sheehan et al., 2014; Wang et al., 2017; Liu et al., 2018), we
conducted linear regression for the two periods: August 2011-July 2018 and August 2013- July 2018, respectively. It can be found that PM2.5  concentration and the mixing ratio of two  precursors show an overall decreasing trend during the past seven years (-6.4%/yr, -12.1%/yr, and -4.6%/yr for PM2.5, SO2  and NO2, respectively), but more remarkable decreasing
trends (- 9.1%/yr, -16.7%/yr, and -5.2%/yr for PM2.5, SO2 and NO2, respectively) since 2013. Among the two precursors, SO2  showed an even more significant reduction with an annual decrease about 17%/yr, which means almost 80% of SO2  was reduced in the past five years. It demonstrates  that the YRD region, as one of the main industry bases with a huge consumption of coal, achieved a very big success of air pollution prevention from desulfurization in power plants and factories in recent years. In fact, a national wide significant reduction of SO2  in the past few years has been also reported by ground and satellite measurements and emission estimations (C. Li et al., 2017; Liu et al., 2018; Zheng et al., 2018).
Title: Re: The Science of Aerosols
Post by: vox_mundi on August 02, 2019, 12:06:43 AM
Aerosol Emissions May Not Cool the Planet as Much as We Thought
https://arstechnica.com/science/2019/08/aerosol-emissions-may-not-cool-the-planet-as-much-as-we-thought/

... The result means that there's a "constraint on the overall cooling effect of aerosol emissions"

Velle Toll, et.al. Weak average liquid-cloud-water response to anthropogenic aerosols (https://www.nature.com/articles/s41586-019-1423-9), Nature volume 572, pages51–55 (2019)

Abstract

The cooling of the Earth’s climate through the effects of anthropogenic aerosols on clouds offsets an unknown fraction of greenhouse gas warming. An increase in the amount of water inside liquid-phase clouds induced by aerosols, through the suppression of rain formation, has been postulated to lead to substantial cooling, which would imply that the Earth’s surface temperature is highly sensitive to anthropogenic forcing. Here we provide direct observational evidence that, instead of a strong increase, aerosols cause a relatively weak average decrease in the amount of water in liquid-phase clouds compared with unpolluted clouds. Measurements of polluted clouds downwind of various anthropogenic sources—such as oil refineries, smelters, coal-fired power plants, cities, wildfires and ships—reveal that aerosol-induced cloud-water increases, caused by suppressed rain formation, and decreases, caused by enhanced evaporation of cloud water, partially cancel each other out. We estimate that the observed decrease in cloud water offsets 23% of the global climate-cooling effect caused by aerosol-induced increases in the concentration of cloud droplets. These findings invalidate the hypothesis that increases in cloud water cause a substantial climate cooling effect and translate into reduced uncertainty in projections of future climate.

(https://media.springernature.com/lw685/springer-static/image/art%3A10.1038%2Fs41586-019-1423-9/MediaObjects/41586_2019_1423_Fig6_HTML.png)
Title: Re: The Science of Aerosols
Post by: petm on August 02, 2019, 12:39:16 AM
Weak average liquid-cloud-water response to anthropogenic aerosols

Thanks, important article. Lame that they didn't pay for open access though. There's an editorial on it here: https://www.nature.com/articles/d41586-019-02287-z


Last paragraph of the conclusion:
Quote
The cancellations between increases and decreases in LWP that we have observed in liquid clouds downwind of different aerosol sources under a wide range of meteorological conditions is in stark contrast to the unidirectional aerosol-induced increases in the LWP simulated by 45 GCMs . Although in multiple GCMs an increase in the LWP enhances the Twomey effect by more than 100%45, our analysis of pollution tracks show that decreases in the LWP in fact offset 23% of the Twomey effect. The compensation between increases and decreases in the LWP in pol- lution tracks agrees with the bidirectional LWP responses found in idealized process-level model simulations15–17 and in global satellite observations of maritime clouds19,20. Now, our analysis of pollution tracks shows with unprecedented confidence that the global average LWP response to anthropogenic aerosols is weak. We expect this con- straint on the LWP response based on observations of pollution tracks to lead to improved aerosol-cloud parameterizations in GCMs and to translate into reduced uncertainty in aerosol forcing calculations and more reliable projections of future climate.

Hope they're on the right track. The number of assumptions and limitations is frightening.
Title: Re: The Science of Aerosols
Post by: Tom_Mazanec on August 03, 2019, 09:55:04 PM
More on the recent "good news"
https://phys.org/news/2019-08-pollution-wont-global-spike.html
Title: Re: The Science of Aerosols
Post by: DrTskoul on August 03, 2019, 09:59:32 PM
Weak average liquid-cloud-water response to anthropogenic aerosols

Thanks, important article. Lame that they didn't pay for open access though. There's an editorial on it here: https://www.nature.com/articles/d41586-019-02287-z


Last paragraph of the conclusion:
Quote
The cancellations between increases and decreases in LWP that we have observed in liquid clouds downwind of different aerosol sources under a wide range of meteorological conditions is in stark contrast to the unidirectional aerosol-induced increases in the LWP simulated by 45 GCMs . Although in multiple GCMs an increase in the LWP enhances the Twomey effect by more than 100%45, our analysis of pollution tracks show that decreases in the LWP in fact offset 23% of the Twomey effect. The compensation between increases and decreases in the LWP in pol- lution tracks agrees with the bidirectional LWP responses found in idealized process-level model simulations15–17 and in global satellite observations of maritime clouds19,20. Now, our analysis of pollution tracks shows with unprecedented confidence that the global average LWP response to anthropogenic aerosols is weak. We expect this con- straint on the LWP response based on observations of pollution tracks to lead to improved aerosol-cloud parameterizations in GCMs and to translate into reduced uncertainty in aerosol forcing calculations and more reliable projections of future climate.

Hope they're on the right track. The number of assumptions and limitations is frightening.

Lame indeed, should have been open access...
Title: Re: The Science of Aerosols
Post by: Reginald on August 04, 2019, 03:28:22 AM
Speaking of Aerosols, but not inside clouds.

Harvard creates advisory panel to oversee solar geoengineering project
https://www.nature.com/articles/d41586-019-02331-y

Nature, July 2019

Scientists will inject particles of calcium carbonate into the atmosphere and study their effects on incoming sunlight.

Plans to test a technique that would cool the planet by blocking sunlight are one step closer to reality. Harvard University in Cambridge, Massachusetts, has created an external advisory panel to examine the potential ethical, environmental and geopolitical impacts of this geoengineering project, which has been developed by the university’s researchers.

Known as the Stratospheric Controlled Perturbation Experiment (SCoPEx), the project would involve the release of calcium carbonate particles from a steerable balloon some 20 kilometres above the southwestern United States.

Louise Bedsworth, executive director of the California Strategic Growth Council, a state agency that promotes sustainability and economic prosperity, will lead the Harvard advisory panel, the university said on 29 July. The other seven members include Earth-science researchers and specialists in environmental and climate law and policy.

Title: Re: The Science of Aerosols
Post by: DrTskoul on August 04, 2019, 02:35:51 PM
And somehow I shudder to the idea...
Title: Re: The Science of Aerosols
Post by: TerryM on August 04, 2019, 09:03:08 PM
And somehow I shudder  to the idea...


While I'm sure that Harvard has been given a thumbs up by all of the worlds various political bodies, I can't but feel the pain this will cause to the installed base of PV and Solar Thermal facilities.


Will the diurnal winds that spin so many turbines be effectively muted in the dim days ahead, and what will become of the marginal northern farms that are limited today not by temperature, but by the seasonal lack of solar radiation. At one time these farms were seen by some as the answer to failing agriculture in more southern climes.


Just because we've made some minor errors - Australian Cane Toads, The Grand Banks Fisheries and  Mono Culture Forestry spring to mind - is no indication that this time won't be, almost uniquely, successful.


Harvard itself has an unblemished reputation - ask any Slav, but even the brightest and the best have been known to err on the side of hubris.
Terry
Title: Re: The Science of Aerosols
Post by: jai mitchell on August 05, 2019, 08:20:50 PM
More on the recent "good news"
https://phys.org/news/2019-08-pollution-wont-global-spike.html

Quote
meaning pollution is unlikely to offset more than half of greenhouse gas warming.

our current top of atmosphere energy imbalance as measured by the ocean heat content increases (SEE NODC OHC) is 0.6 Watts per meter squared.  The total forcing from GHGs is about 2.4 Watts per meter squared.  This means that some large portion of the total forcing is being offset by aerosols.  if less than half we still have the 0.6 Watts per meter squared being experienced PLUS the (estimate) 1.0 Watts per meter squared from aerosols.  to reach equilibrium)  Since methane is about 20% of the current forcing and other short lived climate pollutants balancing each other out,

even this 'good news' study indicates that we still have about 1.6 Watts per meter squared of globally averaged annual forcing to be worked through the system before reaching temperature equilibrium.

This does not include the longer term climate warming feedbacks due to carbon cycle emissions as the earth warms from the 1.6 Watts per meter equilibrium warming.
Title: Re: The Science of Aerosols
Post by: Oscillidous on August 19, 2019, 10:20:57 PM
Regarding this recent paper, I don't know of many other papers exploring the idea that reduced droplet formation in clouds is what is responsible for greater cooling, it's the reflective of the particulates themselves, no? Seems to me the equivalent of saying "good news, fire doesn't cause as much frostbite as previously thought" when obviously no one was even considering the possibility.

The paper in Nature recording localized temperature change over North America 3 days after 9/11 is an example of observed warming as a result from absence of some anthropocentric aerosols, which at least to my laymen understanding seems to be a better analogue for what to expect as a result of reduced industrial output.
Title: Re: The Science of Aerosols
Post by: Ktb on August 26, 2019, 01:12:38 PM
Got to hear Dr. Jim Haywood from Exeter University and the Met Office speak today about Aerosol masking, clouds, and possible future geoengineering. He agreed to provide me his powerpoint presentation. I will try to upload it here when I obtain it.

Edit: Jim** Haywood
Title: Re: The Science of Aerosols
Post by: TerryM on August 26, 2019, 01:30:59 PM
Got to hear Dr. James Haywood from Exeter University and the Met Office speak today about Aerosol masking, clouds, and possible future geoengineering. He agreed to provide me his powerpoint presentation. I will try to upload it here when I obtain it.
Looking forward to it.
Terry
Title: Re: The Science of Aerosols
Post by: Ktb on September 04, 2019, 04:44:28 PM
Having a million difficulties trying to upload the presentation as a PDF.

I tried to take detailed notes, and stuck around for the Q&A. I may be able to answer some basic questions if anybody has any.
Title: Re: The Science of Aerosols
Post by: blumenkraft on September 04, 2019, 04:59:15 PM
Having a million difficulties trying to upload the presentation as a PDF.


The download works well. Thank you!
Title: Re: The Science of Aerosols
Post by: Ken Feldman on September 04, 2019, 11:15:55 PM
Having a million difficulties trying to upload the presentation as a PDF.

I tried to take detailed notes, and stuck around for the Q&A. I may be able to answer some basic questions if anybody has any.

Did the question about a possible spike in warming from reduced aerosols with the reduction in fossil fuel burning come up?  If so, what was the answer?
Title: Re: The Science of Aerosols
Post by: Ktb on September 05, 2019, 01:31:42 AM

Did the question about a possible spike in warming from reduced aerosols with the reduction in fossil fuel burning come up?  If so, what was the answer?

Yes, I actually asked about Hansen et al.'s 2013 paper on aerosol masking, and the effect that immediately stopping production of sulfates via oil/coal/etc. Dr. Haywood said he respected Dr. Hansen, but believed that the warming effect would not be as great or as rapid as Hansen described. Additionally, Dr. Haywood said that sulfates would be replaced with other aerosols that occur naturally, the names of which escape me.
Title: Re: The Science of Aerosols
Post by: Ken Feldman on September 05, 2019, 08:02:49 PM
Thanks.  Here's a paper that discusses variability of natural aerosols.

https://www.nature.com/articles/nature12674 (https://www.nature.com/articles/nature12674)

Quote
Large contribution of natural aerosols to uncertainty in indirect forcing
K. S. Carslaw, L. A. Lee, C. L. Reddington, K. J. Pringle, A. Rap, P. M. Forster, G. W. Mann, D. V. Spracklen, M. T. Woodhouse, L. A. Regayre & J. R. Pierce

Nature volume 503, pages 67–71 (07 November 2013)

Abstract

The effect of anthropogenic aerosols on cloud droplet concentrations and radiative properties is the source of one of the largest uncertainties in the radiative forcing of climate over the industrial period. This uncertainty affects our ability to estimate how sensitive the climate is to greenhouse gas emissions. Here we perform a sensitivity analysis on a global model to quantify the uncertainty in cloud radiative forcing over the industrial period caused by uncertainties in aerosol emissions and processes. Our results show that 45 per cent of the variance of aerosol forcing since about 1750 arises from uncertainties in natural emissions of volcanic sulphur dioxide, marine dimethylsulphide, biogenic volatile organic carbon, biomass burning and sea spray. Only 34 per cent of the variance is associated with anthropogenic emissions. The results point to the importance of understanding pristine pre-industrial-like environments, with natural aerosols only, and suggest that improved measurements and evaluation of simulated aerosols in polluted present-day conditions will not necessarily result in commensurate reductions in the uncertainty of forcing estimates.
Title: Re: The Science of Aerosols
Post by: jai mitchell on September 09, 2019, 09:38:39 PM
Having a million difficulties trying to upload the presentation as a PDF.

I tried to take detailed notes, and stuck around for the Q&A. I may be able to answer some basic questions if anybody has any.

interesting to see what happened to arctic sea ice and the development of "the blob" in the north east pacific ocean after the 2014 eruption in iceland.
Title: Re: The Science of Aerosols
Post by: morganism on September 19, 2019, 03:22:48 AM
Dust from a giant asteroid crash caused an ancient ice age

http://www.fieldmuseum.org/about/press/dust-giant-asteroid-crash-caused-ancient-ice-age

“Our hypothesis is that the large amounts of extraterrestrial dust over a timeframe of at least two million years played an important role in changing the climate on Earth, contributing to cooling,” says Heck.

“Our results show for the first time that such dust, at times, has cooled Earth dramatically,”

Title: Re: The Science of Aerosols
Post by: Richard Rathbone on September 19, 2019, 11:59:25 PM
Having a million difficulties trying to upload the presentation as a PDF.

I tried to take detailed notes, and stuck around for the Q&A. I may be able to answer some basic questions if anybody has any.

That looks quite promising for the next generation of climate models. Its seems we finally have enough measurements of aerosols to be able to have robust arguments about what sort of modelling approach makes sense rather than crossing fingers and praying that we haven't overfitted too badly.
Title: Re: The Science of Aerosols
Post by: Ktb on September 21, 2019, 02:36:00 PM
Glad everybody enjoyed the read. The presentation was fantastic. Excellent speaker.
Title: Re: The Science of Aerosols
Post by: jai mitchell on September 27, 2019, 01:45:22 AM
Study on the aerosol impact of the 2014-2015 eruption of Bárðarbunga in Iceland


https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015GL067070

Observations of a substantial cloud-aerosol indirect effect
during the 2014–2015 Bárðarbunga-Veiðivötn
fissure eruption in Iceland
Daniel T. McCoy1 and Dennis L. Hartmann

Quote
The estimated changes in upwelling SW and cloud albedo over the first 2 months of the eruption due to anomalies in re are shown in Figure 4. Cloud albedo was estimated to increase by up to 3% in the Norwegian Sea and Greenland Sea (Figure 4b). Local increases in upwelling SW exceeded 2 W/m^2. The zonal mean upwelling SW across the 60°N–70°N latitude band was estimated to increase by 1 W /m*2, and the cloud albedo was estimated to increase by 1.5% (Figure 4

Title: Re: The Science of Aerosols
Post by: wdmn on January 07, 2020, 09:22:39 PM
New study on the negative forcing of aerosols:

Ensembles of Global Climate Model Variants Designed for the Quantification and Constraint of Uncertainty in Aerosols and Their Radiative Forcing

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019MS001628

Abstract
Tropospheric aerosol radiative forcing has persisted for many years as one of the major causes of uncertainty in global climate model simulations. To sample the range of plausible aerosol and atmospheric states and perform robust statistical analyses of the radiative forcing, it is important to account for the combined effects of many sources of model uncertainty, which is rarely done due to the high computational cost. This paper describes the designs of two ensembles of the Met Office Hadley Centre Global Environment Model‐U.K. Chemistry and Aerosol global climate model and provides the first analyses of the uncertainties in aerosol radiative forcing and their causes. The first ensemble was designed to comprehensively sample uncertainty in the aerosol state, while the other samples additional uncertainties in the physical model related to clouds, humidity, and radiation, thereby allowing an analysis of uncertainty in the aerosol effective radiative forcing. Each ensemble consists of around 200 simulations of the preindustrial and present‐day atmospheres. The uncertainty in aerosol radiative forcing in our ensembles is comparable to the range of estimates from multimodel intercomparison projects. The mean aerosol effective radiative forcing is −1.45 W/m2 (credible interval of −2.07 to −0.81 W/m2), which encompasses but is more negative than the −1.17 W/m2 in the 2013 Atmospheric Chemistry and Climate Model Intercomparison Project and −0.90 W/m2 in the Intergovernmental Panel on Climate Change Fifth Assessment Report. The ensembles can be used to reduce aerosol radiative forcing uncertainty by challenging them with multiple measurements as well as to isolate potential causes of multimodel differences.


According to Eric Holthous:

"This study implies that there's an additional 1°C or so of warming baked in to aerosol pollution worldwide.

This study means we've warmed the planet more than we thought, it's just been hidden."

https://twitter.com/EricHolthaus/status/1214575877410971649


So we're at ~2.2C now, (plus emissions of last decade)... ambitious is now 3C it would seem.
Title: Re: The Science of Aerosols
Post by: TerryM on January 08, 2020, 10:16:13 PM
^^
IIRC +1.5 - +2.0C is where the runaway greenhouse effects were supposed to kick in. When albedo changes and permafrost melt take over from AGW & push temperature and sea level rise into high gear. A gear that speeds us to civilizational collapse.


I don't think anyone has claimed that we can sustain 3C, so if short term aerosols are all that's keeping the lid on we may be facing a short journey.


The Excitement Builds
Terry
Title: Re: The Science of Aerosols
Post by: wdmn on January 13, 2020, 12:21:33 AM
^^^
In regards to the paper posted above, I should note that it's unclear as to whether this study treats aerosols in the same way as AR5, i.e. this study includes "natural" aerosols such as sand and salt, whereas AR5 seems to only include anthropogenic aerosols in its -0.9 w/m2 forcing.

However, counterintuitively, the discussion from the paper suggests that including these natural aerosols actually reduces the forcing:

"The global mean 1850–2008 aerosol RFs are −2.12 (credible interval −2.76, −1.47) W/m2 (RF) based on the AER PPE and −1.45 (−2.07, −0.81) W/m2 (ERF) based on the AER‐ATM PPE. There are several factors that contribute to the weaker forcing in AER‐ATM. First, more natural aerosols (sea spray, DMS, and dust) are typically emitted in AER‐ATM than in AER... Larger natural aerosol emissions in both 1850 and 2008 reduce the magnitude of the aerosol‐cloud interaction (Carslaw, Lee, Reddington, Pringle, et al., 2013)."

In other words, when fewer natural aerosols were included, the mean forcing went up to -2.12 w/m2.

It should also be noted that these were the aerosol estimates for 2008. So, it is quite possible they have gone down now as China has made an effort to clean up their pollution. James Hansen seems to think that's the reason for the accelerated warming in the last 5 years.
Title: Re: The Science of Aerosols
Post by: TerryM on January 14, 2020, 12:26:47 AM
Ya But, ya but - Hansen thinks? - Holy Shit!
Terry ???
Title: Re: The Science of Aerosols
Post by: jai mitchell on January 14, 2020, 02:59:05 AM
^^^
In regards to the paper posted above, I should note that it's unclear as to whether this study treats aerosols in the same way as AR5, i.e. this study includes "natural" aerosols such as sand and salt, whereas AR5 seems to only include anthropogenic aerosols in its -0.9 w/m2 forcing.


The AR5 forcing parameters can be found here:  http://www.pik-potsdam.de/~mmalte/rcps/  The direct aerosol forcing includes anthropogenic and natural aerosols (like mineral dust) and they include the indirect forcing in the total cloud effect forcing parameter which combined comes out to about -0.9 W/m^2. 
Title: Re: The Science of Aerosols
Post by: wdmn on January 14, 2020, 04:22:42 AM
Thanks JM.
Title: Re: The Science of Aerosols
Post by: Wherestheice on January 14, 2020, 06:12:19 AM
Can someone explain to me what -0.9 W/m^2 means in regards to temperature?
Title: Re: The Science of Aerosols
Post by: wdmn on January 14, 2020, 06:37:13 AM
James Hansen gives the number of  0.75 ± 0.25°C per W/m2.

So the -0.9 W/m2 number from AR5 would give ~0.68 degrees C of warming masked by aerosols.

Using the -1.45 W/m2 number from the new paper linked above we get ~1.1 degrees C.

Either way you've got to believe we're well over 1.5C of warming already (plus additional warming from last 10 years of emissions). I'd say (and no one has shown how to get another answer from the math) realistically we're approaching ~2.5C of warming locked in. That means we're desperately scrambling (or we should be) to avoid hitting 3C based on our emissions over the next 2 decades.

Source with Hansen's number:
http://www.columbia.edu/~jeh1/mailings/2018/20181206_Nutshell.pdf
Title: Re: The Science of Aerosols
Post by: Wherestheice on January 14, 2020, 07:03:59 AM
James Hansen gives the number of  0.75 ± 0.25°C per W/m2.

So the -0.9 W/m2 number from AR5 would give ~0.68 degrees C of warming masked by aerosols.

Using the -1.45 W/m2 number from the new paper linked above we get ~1.1 degrees C.

Either way you've got to believe we're well over 1.5C of warming already (plus additional warming from last 10 years of emissions). I'd say (and no one has shown how to get another answer from the math) realistically we're approaching ~2.5C of warming locked in. That means we're desperately scrambling (or we should be) to avoid hitting 3C based on our emissions over the next 2 decades.

Source with Hansen's number:
http://www.columbia.edu/~jeh1/mailings/2018/20181206_Nutshell.pdf

Ah okay, I see. Thank you for explaining. Yeah I don't see us staying below 2 C at this point.The new target needs to be avoiding 3 C.

In that paper that you linked that had the -1.45 W/m2 figure, do we know how much the natural aerosols are blocking? Vs how much the human related aerosols are blocking? I think the latter part of that question is the most important part of this whole discussion.
Title: Re: The Science of Aerosols
Post by: nanning on January 14, 2020, 07:09:41 AM
A metaphor:

Noun

runaway (plural runaways)

   2. A vehicle (especially, a train) that is out of control.


That seems to describe civilisation to me.
'We' think we still have control but nobody is steering our train.
The tracks ahead are bending down because of increasing natural GHG sources, moving our train onto a increasingly declined track... 'Falling'
Title: Re: The Science of Aerosols
Post by: wdmn on January 14, 2020, 07:57:52 AM
@wherestheice
All I can say with certainty is that they created two models, and one included fewer natural aerosols. The one with fewer natural aerosols had a stronger negative forcing of -2.12 W/m^2; so the natural aerosols have a warming effect via cloud feedbacks (apparently).

A RF of -2.12 W/m^2 for anthro aerosols would be equivalent to ~1.6C of masked warming. But I am not sure that this is a fair extrapolation to make... It would certainly be a much higher number than anyone has previously suggested. (It would mean we would have to reconsider things like ECS and TCR).

The ~1.45 number fits with the estimated RFs from CO2 and other GHGs given by Hansen, with the combined total being roughly 3 W/m^2. If -1.45 W/m2 is masked by aerosols it means we should have recorded around 1.16 degrees of warming over the 280ppm earth (which is right about where we are).

Wish I could say more; I've found it difficult to get straight answers on this when I have asked, and I don't understand enough about the modelling.
Title: Re: The Science of Aerosols
Post by: Hefaistos on January 14, 2020, 04:01:32 PM

Did the question about a possible spike in warming from reduced aerosols with the reduction in fossil fuel burning come up?  If so, what was the answer?

Yes, I actually asked about Hansen et al.'s 2013 paper on aerosol masking, and the effect that immediately stopping production of sulfates via oil/coal/etc. Dr. Haywood said he respected Dr. Hansen, but believed that the warming effect would not be as great or as rapid as Hansen described. Additionally, Dr. Haywood said that sulfates would be replaced with other aerosols that occur naturally, the names of which escape me.

The reduction of anthropogenic aerosols won't happen that fast.
Yes, the world is getting off the coal, but we have another two decades of oil burning on the same levels as today.
My hypothesis: the reduction in aerosols (+ve effect) will be matched by a reduction in FF emissions (-ve effect) so that the net warming effect from GHG will remain on the same level.
Title: Re: The Science of Aerosols
Post by: Tom_Mazanec on January 14, 2020, 04:05:53 PM

Did the question about a possible spike in warming from reduced aerosols with the reduction in fossil fuel burning come up?  If so, what was the answer?

Yes, I actually asked about Hansen et al.'s 2013 paper on aerosol masking, and the effect that immediately stopping production of sulfates via oil/coal/etc. Dr. Haywood said he respected Dr. Hansen, but believed that the warming effect would not be as great or as rapid as Hansen described. Additionally, Dr. Haywood said that sulfates would be replaced with other aerosols that occur naturally, the names of which escape me.

The reduction of anthropogenic aerosols won't happen that fast.
Yes, the world is getting off the coal, but we have another two decades of oil burning on the same levels as today.
My hypothesis: the reduction in aerosols (+ve effect) will be matched by a reduction in FF emissions (-ve effect) so that the net warming effect from GHG will remain on the same level.
GHGs remain in the atmosphere decades to millennia.
Aerosols remain in the atmosphere days to months.
Title: Re: The Science of Aerosols
Post by: nanning on January 14, 2020, 06:30:53 PM
Thanks for giving the voice of reason Tom :).
Title: Re: The Science of Aerosols
Post by: Hefaistos on January 14, 2020, 09:46:31 PM

Did the question about a possible spike in warming from reduced aerosols with the reduction in fossil fuel burning come up?  If so, what was the answer?

Yes, I actually asked about Hansen et al.'s 2013 paper on aerosol masking, and the effect that immediately stopping production of sulfates via oil/coal/etc. Dr. Haywood said he respected Dr. Hansen, but believed that the warming effect would not be as great or as rapid as Hansen described. Additionally, Dr. Haywood said that sulfates would be replaced with other aerosols that occur naturally, the names of which escape me.

The reduction of anthropogenic aerosols won't happen that fast.
Yes, the world is getting off the coal, but we have another two decades of oil burning on the same levels as today.
My hypothesis: the reduction in aerosols (+ve effect) will be matched by a reduction in FF emissions (-ve effect) so that the net warming effect from GHG will remain on the same level.
GHGs remain in the atmosphere decades to millennia.
Aerosols remain in the atmosphere days to months.

My point was that the reduction of aerosols will take considerable time, on a scale of multiple decades. And a lot will happen with GHG emissions during that time, which is a counterbalancing effect.

Another point is that aerosols have mostly a local or regional effect, whereas GHG have a global effect. Aerosols are estimated to increase for some years to come in e.g. SE Asia.

The main GHG is water vapor, and it remains in the atm. for a few days only during the hydrological cycle. The theory says that when aerosols are reduced, we get less cloudiness, thus less water vapor. And less cooling effect.

However this is theory, in practice we have seen examples of the opposite effects. As in this research:
"Response of the atmospheric hydrological cycle over the tropical Asian monsoon regions to anthropogenic aerosols and its seasonality" by Takahashi et al, 2018, show that:
"The results show that, as a whole, the Asian monsoon precipitation is reduced by the increase in aerosol loading during boreal summer and winter. This decrease in precipitation corresponds to a decrease in precipitable water due to the cooling in surface air temperature (SAT), mainly over adjacent oceans. The cooling is explained by the sum of the direct and indirect effects of aerosols. A modulation of the Walker circulation occurs, which can be explained by the east-west horizontal SAT gradient over the tropics due to the spatially heterogeneous increase in aerosols. "

https://progearthplanetsci.springeropen.com/articles/10.1186/s40645-018-0197-2


Title: Re: The Science of Aerosols
Post by: wdmn on January 14, 2020, 10:50:04 PM
Hefaistos,

While it might take a while to clean up our aerosols, ~1.1C of masked warming still means ~1.1C of masked warming. It means that -- best case scenario -- if we went to zero emissions tomorrow we'd still approach 2.5C of warming since preindustrial.

So, while you suggest that the longer it takes us to reduce our emissions (and so to clean up aerosols) the more time we buy ourselves, in fact, the opposite is true. The longer it takes, the more screwed we are, since that ~1.1C is already there, waiting, even if the rate of temp. rise from emissions goes down (it won't for sometime based on the last 10 years, and what's likely over the next 10) we are unlikely to avoid catastrophic levels of warming. We need to reach zero emissions as soon as possible. No matter how quickly or slowly we do that, we will find ourselves in a much warmer world.

Finally, the paper in question accounts for warming from cloud feedbacks from aerosols, but these tend to be from non-anthro sources, as already discussed in this thread.
Title: Re: The Science of Aerosols
Post by: jai mitchell on January 14, 2020, 11:02:19 PM
Hefaistos,

While it might take a while to clean up our aerosols, ~1.1C of masked warming still means ~1.1C of masked warming. It means that -- best case scenario -- if we went to zero emissions tomorrow we'd still approach 2.5C of warming since preindustrial.

So, while you suggest that the longer it takes us to reduce our emissions (and so to clean up aerosols) the more time we buy ourselves, in fact, the opposite is true. The longer it takes, the more screwed we are, since that ~1.1C is already there, waiting, even if the rate of temp. rise from emissions goes down (it won't for sometime based on the last 10 years, and what's likely over the next 10) we are unlikely to avoid catastrophic levels of warming. We need to reach zero emissions as soon as possible. No matter how quickly or slowly we do that, we will find ourselves in a much warmer world.

Finally, the paper in question accounts for warming from cloud feedbacks from aerosols, but these tend to be from non-anthro sources, as already discussed in this thread.

much of those emissions are organic carbon which are primarily produced through biomass burning.  so they won't all go away.

Much will go away and of these, over time, it is projected that ch4 levels will also go down that will help reduce the overall burden.  Of course the uncertainty and (VERY LIKELY IN MY OPINION) rapid increase in carbon cycle emissions from warming soils will provide more than this uncertainty in future committed warming.

edit:

but we still have to accept that the current top of atmosphere energy imbalance is between 0.8 and 1.2 Watts per meter squared (even with the aerosol masking!).
Title: Re: The Science of Aerosols
Post by: wdmn on January 15, 2020, 12:32:43 AM
JM,

Thanks for the clarification.

Do you have a source for that energy imbalance? Hansen says, "Increasing the amount of CO2 from its pre-industrial level (280 ppm) to the 2018 amount (407 ppm) causes a climate forcing of ~2.1 W/m2," and, "Non-CO2 GHGs cause a climate forcing today [in 2018], relative to preindustrial conditions of more than 1 W/m2."

So that would put us at more than 3.1 W/m^2 in 2018. How much of the 0.8-1.2 you mentioned included in that?

Right now we're in the situation that aerosols seem to have declined (due to Chinese clean coal, etc), but methane growth in the atmosphere is accelerating... I agree that this is unlikely to continue, though more recent science does suggest that we are closer to frozen soil feedbacks being a problem than has previously been assumed.

Title: Re: The Science of Aerosols
Post by: Wherestheice on January 15, 2020, 01:05:57 AM
Maybe this paper can help straighten things out a bit?

Their conclusion is that a 35-80% reduction in human emissions would cause a 1 C rise in temp.

And it looks like they don't include BB in their calculations.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/jgrd.50192

Title: Re: The Science of Aerosols
Post by: Wherestheice on January 15, 2020, 01:09:50 AM
Also this.... "the climate and extreme event responses to a removal of anthropogenic aerosols, from a world with around 1.5°C GHG‐dominated warming. Global surface temperature is predicted to increase by 0.7°C (multimodel mean, model range is 0.5–1.1°C), while the land surface warms by 1.0°C (model range 0.7–1.6). As sulfate is the dominant aerosol surface temperature driver for present‐day emissions"

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076079
Title: Re: The Science of Aerosols
Post by: jai mitchell on January 15, 2020, 01:21:58 AM
this is a good and recent one, the values quoted are slightly lower than what I cited but they are based on 15 year period averages and are ocean heat content not EEI  I thought there was some recent work showing higher EEI values but don't see it at the moment.

https://www.frontiersin.org/articles/10.3389/fmars.2019.00432/full
Title: Re: The Science of Aerosols
Post by: nanning on January 15, 2020, 05:51:25 AM
Thanks Wherestheice.
-

Are airborne microplastics considered as aerosols?

The billions of rolling car tyres around the world keep on shedding them (emitting) for the foreseeable future.
Title: Re: The Science of Aerosols
Post by: Wherestheice on January 15, 2020, 06:29:36 AM
Thanks Wherestheice.
-

Are airborne microplastics considered as aerosols?

The billions of rolling car tyres around the world keep on shedding them (emitting) for the foreseeable future.

Seems like they could be, see here... https://earther.gizmodo.com/microplastics-are-airborne-polluted-arctic-snow-reveal-1837239022

"There’s even a chance that the microplastic bits could end up acting like other tiny particles known as aerosols. "
Title: Re: The Science of Aerosols
Post by: nanning on January 15, 2020, 10:53:47 AM
Thanks for the link. I could've made that search myself, sorry for being lazy there.

I think it is high time that scientists investigate this all pervasive and permanent microplastic pollution. Not just its effects on lifeforms and foodchains/endocrine systems.
Title: Re: The Science of Aerosols
Post by: jai mitchell on February 12, 2020, 08:27:19 PM
I bet that there is a discernible strong northern hemisphere GMST signal that occurred between Jan 21st 2020 and through February 15th (and possibly longer) due to China coronavirus quarantine and lunar new year extension.

January was the warmest on record, perhaps February will be also?
Title: Re: The Science of Aerosols
Post by: mitch on February 12, 2020, 10:50:59 PM
On the brighter side, some scientists have found that minor changes in altitude of jets would get rid of much of the warming contrail cover:
https://www.sciencedaily.com/releases/2020/02/200212121959.htm

 
Title: Re: The Science of Aerosols
Post by: jai mitchell on February 17, 2020, 06:37:40 PM
https://carnegiescience.edu/news/do-climate-effects-air-pollution-impact-global-economy

Do The Climate Effects Of Air Pollution Impact The Global Economy?

Quote
Estimates indicate that aerosol pollution emitted by humans is offsetting about 0.7 degrees Celsius, or about 1.3 degrees Fahrenheit, of the warming due to greenhouse gas emissions,” said lead author Zheng. “This translates to a 40-year delay in the effects of climate change. Without cooling caused by aerosol emissions, we would have achieved 2010-level global mean temperatures in 1970.”

Previous research has shown that climate change provides some economic benefits to countries in cool regions—which would be warmed to temperatures that are ideal for agricultural productivity and human labor—and economic harm to countries in already hot regions.
Title: Re: The Science of Aerosols
Post by: VeliAlbertKallio on March 21, 2020, 03:42:00 AM
S E A   R E S E A R C H   S O C I E T Y ' S   A P P E A L   T O
T H E  G O V E R N M E N T S  W O R L D - W I D E  :

WORLD GOVERNMENTS MUST LEARN FROM CORONAVIRUS EMISSIONS SHUTDOWN AS MUCH AS POSSIBLE

Global Circulation Models (GCMs) are computer models of the world's atmosphere based on observations and assumptions if there are no direct information available. World emissions shutdowns are a novel opportunity to learn about how climate system responds under different circumstances that cannot be normally experimentally checked. It is vitally important for the world's governments not to shut down meteorological measurements. Indeed, efforts must increase to use opportunity to test and search regional responses of the highly unusual situation. World Meteorological Organisation (WMO) and national meteorological organisations must quickly come up with new research proposals to gain every possible bit of information as this helps to understand how world's climate will respond as the world moves towards ZERO emissions. It is a tremendous tragedy if this unique opportunity to find more about how our atmosphere operates is lost. We do not foresee many situations like this rising when large world regions turn their lights off one after another. Modelling SO2, N2O, O3, CFC, CO2, CH4, CO shut downs.

Sponsors, please look at serious proposals to make research offers right now!
Let's make something positive happen out of this coronavirus calamity.

Veli Albert Kallio
Vice President, Sea Research Society
Environmental Affairs Department
https://en.wikipedia.org/wiki/Sea_Research_Society
Title: Re: The Science of Aerosols
Post by: TerryM on March 21, 2020, 10:20:07 AM
^^
Ramen!!
Terry
Title: Re: The Science of Aerosols
Post by: Pmt111500 on March 21, 2020, 11:36:21 AM
Yes, let's keep recording the weather no matter what. F.e. the North Pacific record after China shut down will be of exceptional interest.
Title: Re: The Science of Aerosols
Post by: Tom_Mazanec on April 13, 2020, 01:27:34 AM
Now that much industry has been shut down for weeks, can we detect any heating from aerosol reduction?
Title: Re: The Science of Aerosols
Post by: kassy on April 16, 2020, 03:58:06 PM
Earth is way dustier than we thought. That may be a problem for climate forecasts.

...

Dust in the upper atmosphere interacts with clouds, oceans and even radiation, or heat, from the sun. It can affect weather, precipitation and even has an impact on climate change. In a new study, scientists from the University of California Los Angeles (UCLA) found that there is four times as much coarse dust in our planet's atmosphere than has previously be seen in climate models.

There is more than one type of dust. In Earth's atmosphere, there is fine dust that is easily picked up by winds in dry areas, as well as coarser dust made of larger grains often from desert regions_ that can actually contribute to global warming in a similar way to greenhouse gases, according to a statement from UCLA. These large, coarse particles absorb radiation coming in from the sun and leaving the Earth, trapping that radiation on our planet. So, it's important for researchers to understand how much dust, especially course dust, is floating around in the atmosphere.

...

This team analyzed dozens of dust observations made by aircraft and compared them to how much dust current climate models predict should be in the atmosphere. And, while climate models predict only about 4 million metric tons, the team found that there is closer to 17 metric tons of coarse dust in our atmosphere.

"When we compared our results with what is predicted by current climate models, we found a drastic difference," study co-author Jasper Koka, a UCLA associate professor of atmospheric and oceanic sciences, said in the statement.

he team also found that dust particles also stay in the air longer than expected. This could mean that, since they're in the atmosphere for longer, they fall back to Earth much farther from the location where they were first picked up by the wind. So dust from a desert could affect ocean ecosystems and even increase how much carbon dioxide oceans absorb, according to the statement.

https://www.space.com/earth-atmosphere-dustier-thought-climate-models.html

Climate models miss most of the coarse dust in the atmosphere
https://advances.sciencemag.org/content/6/15/eaaz9507/
Title: Re: The Science of Aerosols
Post by: interstitial on April 16, 2020, 10:15:24 PM
<snip>
This team analyzed dozens of dust observations made by aircraft and compared them to how much dust current climate models predict should be in the atmosphere. And, while climate models predict only about 4 million metric tons, the team found that there is closer to 17 metric tons of coarse dust in our atmosphere.
<snip>
I assume that is 17 million metric tons
Title: Re: The Science of Aerosols
Post by: kassy on April 16, 2020, 11:39:18 PM
I just autocompleted that.  ;)

Quote
Abstract
Coarse mineral dust (diameter, ≥5 μm) is an important component of the Earth system that affects clouds, ocean ecosystems, and climate. Despite their significance, climate models consistently underestimate the amount of coarse dust in the atmosphere when compared to measurements. Here, we estimate the global load of coarse dust using a framework that leverages dozens of measurements of atmospheric dust size distributions. We find that the atmosphere contains 17 Tg of coarse dust, which is four times more than current climate models simulate. Our findings indicate that models deposit coarse dust out of the atmosphere too quickly. Accounting for this missing coarse dust adds a warming effect of 0.15 W·m−2 and increases the likelihood that dust net warms the climate system. We conclude that to properly represent the impact of dust on the Earth system, climate models must include an accurate treatment of coarse dust in the atmosphere.
Title: Re: The Science of Aerosols
Post by: kassy on June 22, 2020, 10:44:12 AM
The study into Southern Ocean clouds is in.

Scientists just sampled the most pristine air on Earth. Here's what they found.

...

But due to how remote the Southern Ocean is, there have been very few actual studies of the clouds there. Because of this lack of data, computer models that simulate present and future climates overpredict how much sunlight reaches the ocean surface compared to what satellites actually observe. The main reason for this inaccuracy is due to how the models simulate clouds, but nobody knew exactly why the clouds were off. For the models to run correctly, researchers needed to understand how the clouds were being formed.

To discover what is actually happening in clouds over the Southern Ocean, a small army of atmospheric scientists, including us, went to find out how and when clouds form in this remote part of the world. What we found was surprising — unlike the Northern Hemisphere oceans, the air we sampled over the Southern Ocean contained almost no particles from land. This means the clouds might be different from those above other oceans, and we can use this knowledge to help improve the climate models.

Ice clouds and liquid clouds
Clouds are made of tiny water droplets or ice crystals, or often a mixture of the two. These form on small particles in the air. The type of particle plays a big role in determining whether a liquid droplet or ice crystal forms. These particles can be natural — like sea spray, pollen, dust or even bacteria — or from human sources like cars, stoves, power plants and so on.

To the untrained eye, an ice cloud and a liquid cloud look much the same, but they have very different properties. Ice clouds reflect less sunlight, precipitate more and don't last as long as liquid clouds. It matters to the weather — and to climate models — what kinds of clouds are around.

...

This was the mystery: Why are there more liquid clouds than the models think there are? To solve it, we needed to know what kinds of particles are floating around in the atmosphere around Antarctica.

Before we went down there, we had a few clues.


Previous modeling studies have suggested that the ice–forming particles found over the Southern Ocean may be very different from those found in the Northern Hemisphere. Dust is a great ice cloud seeder, but due to the lack of dusty land sources in the Southern Hemisphere, some scientists have hypothesized that other types of particles might be driving ice cloud formation over the Southern Ocean.

...

Bacterial maps

...

The atmosphere is full of microorganisms that are carried hundreds to thousands of kilometers on air currents before returning to Earth. These bacteria are like airborne license plates, they are unique and tell you where the car — or air — came from. Since scientists know where most bacteria live, it's possible to look at the microbes in an air sample and determine where that air came from. And once you know that, you can predict where the particles in the air came from as well - the same place the bacteria usually live.

...

Ocean bacteria alone
In most ocean regions around the world, especially in the Northern Hemisphere where there is a lot of land, the air contains both marine and terrestrial particles. That's what we expected to find down south.

With the frozen filters safely back at our lab in Colorado, we extracted DNA from the bacteria and sequenced it to determine what species we had caught. Much to our surprise, the bacteria were essentially all marine species that live in the Southern Ocean. We found almost no land-based bacteria.

If the bacteria were from the ocean, then so were the cloud-forming particles. This was the answer we were looking for.

https://www.livescience.com/most-pristine-air-on-earth-bacteria.html

Airborne bacteria confirm the pristine nature of the Southern Ocean boundary layer

We found that the summer airborne bacterial community in the marine boundary layer over the Southern Ocean directly south of Australia is dominated by marine bacteria emitted in sea spray, originating primarily from the west in a zonal band at the latitude of collection. We found that airborne communities were more diverse to the north, and much less so toward Antarctica. These results imply that sea spray sources largely control the number concentrations of nuclei for liquid cloud droplets and limit ice nucleating particle concentrations to the low values expected in nascent sea spray. In the sampled region, the sources of summer cloud-active particles therefore are unlikely to have changed in direct response to perturbations in continental anthropogenic emissions.

https://www.pnas.org/content/117/24/13275
Title: Re: The Science of Aerosols
Post by: kassy on November 05, 2020, 04:33:18 PM
Soot particles influence global warming more than assumed

...

Burning wood, petroleum products or other organic materials releases soot particles into the atmosphere that consist mainly of carbon. This soot is considered the second most important anthropogenic climate forcing agent after carbon dioxide. In the atmosphere or as deposits on snow and ice surfaces, soot particles absorb the short-​wave radiation of the sun and thus contribute to global warming.

In the atmosphere, soot particles also have an indirect effect on the climate by altering the formation, development and properties of clouds. A research team led by Ulrike Lohmann, professor at the Institute for Atmosphere and Climate at ETH Zurich, has now for the first time investigated how two specific types of soot particles influence clouds and, in turn, the climate: on the one hand, soot aerosols that age due to ozone and, on the other, those that age due to sulfuric acid.

Soot chemistry changes cloud formation

"Until now, it was assumed that these two types of soot ageing had little effect on cloud formation and climate," says David Neubauer, scientific programmer in Lohmann's research group. However, the results of the simulations now carried out on the CSCS supercomputer "Piz Daint" paint a different picture.

...

Simulations of ozone-​aged soot show that when the carbon dioxide content of the atmosphere doubles compared to the pre-​industrial era, fewer low clouds form. Considerably more cloud droplets are initially formed by ozone ageing of soot. However, their high concentration leads to more cloud top cooling causing more dry air being mixed in from above.  "These clouds then evaporate more quickly, especially in a warmer climate," explains Lohmann. "In a warmer climate, the air mixed in also has a lower relative humidity". Due to the faster evaporation, less low-​lying clouds remain, and more short-​wave radiation reaches the earth and warms it.

The soot particles aged by sulfuric acid, on the other hand, cause more ice crystals to form and make cirrus clouds optically thicker, i.e. they are less permeable to radiation. They extend as far as the tropopause, which is located at an altitude of 10-​18 kilometres, and also linger longer in higher regions of the atmosphere. As a result, cirrus clouds absorb more of the long-​wave thermal radiation emitted by the Earth and allow less of it to escape into space. The warming effect of cirrus clouds increases and exacerbates global warming: When the carbon dioxide content of the atmosphere doubles compared to pre-​industrial times, both types of soot ageing together lead to a 0.4 to 0.5 ºC increase in global warming. As a result, the water cycle will further accelerate and global precipitation will further increase, the researchers write.

..

https://ethz.ch/en/news-and-events/eth-news/news/2020/11/soot-particles-influence-global-warming.html