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jai mitchell

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Re: The Science of Aerosols
« Reply #100 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

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

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

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

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

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)

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SteveMDFP

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Re: The Science of Aerosols
« Reply #101 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."

jai mitchell

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Re: The Science of Aerosols
« Reply #102 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

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

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.
« Last Edit: January 04, 2017, 05:18:38 AM by jai mitchell »
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AbruptSLR

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Re: The Science of Aerosols
« Reply #103 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/

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.
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AbruptSLR

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Re: The Science of Aerosols
« Reply #104 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/

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.
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AbruptSLR

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Re: The Science of Aerosols
« Reply #105 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

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."
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jai mitchell

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Re: The Science of Aerosols
« Reply #106 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

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.
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Shared Humanity

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Re: The Science of Aerosols
« Reply #107 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.

DrTskoul

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Re: The Science of Aerosols
« Reply #108 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....
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jai mitchell

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Re: The Science of Aerosols
« Reply #109 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

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.

« Last Edit: March 22, 2017, 04:01:10 PM by jai mitchell »
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AbruptSLR

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Re: The Science of Aerosols
« Reply #110 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

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AbruptSLR

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Re: The Science of Aerosols
« Reply #111 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

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."
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AbruptSLR

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Re: The Science of Aerosols
« Reply #112 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/

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).
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jai mitchell

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Re: The Science of Aerosols
« Reply #113 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.
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Re: The Science of Aerosols
« Reply #114 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

"Role aerosols play in climate change unlocked by spectacular Icelandic volcanic eruption"
« Last Edit: June 22, 2017, 01:38:05 PM by Aporia_filia »

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Re: The Science of Aerosols
« Reply #115 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

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."
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AbruptSLR

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Re: The Science of Aerosols
« Reply #116 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

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."
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AbruptSLR

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Re: The Science of Aerosols
« Reply #117 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

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."
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Re: The Science of Aerosols
« Reply #118 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, 2017.

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.
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AbruptSLR

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Re: The Science of Aerosols
« Reply #119 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

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."
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AbruptSLR

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Re: The Science of Aerosols
« Reply #120 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

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

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."
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sidd

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Re: The Science of Aerosols
« Reply #121 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

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Re: The Science of Aerosols
« Reply #122 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:
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sidd

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Re: The Science of Aerosols
« Reply #123 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
« Last Edit: December 19, 2017, 09:36:33 PM by sidd »

AbruptSLR

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Re: The Science of Aerosols
« Reply #124 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)
« Last Edit: December 19, 2017, 09:56:34 PM by AbruptSLR »
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sidd

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Re: The Science of Aerosols
« Reply #125 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


« Last Edit: December 20, 2017, 05:51:57 AM by sidd »

AbruptSLR

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Re: The Science of Aerosols
« Reply #126 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).
« Last Edit: December 21, 2017, 12:41:38 AM by AbruptSLR »
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sidd

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Re: The Science of Aerosols
« Reply #127 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

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Re: The Science of Aerosols
« Reply #128 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."
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jai mitchell

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Re: The Science of Aerosols
« Reply #129 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
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AbruptSLR

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Re: The Science of Aerosols
« Reply #130 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

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Re: The Science of Aerosols
« Reply #131 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."
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jai mitchell

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Re: The Science of Aerosols
« Reply #132 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/

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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.
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Re: The Science of Aerosols
« Reply #133 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.
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Re: The Science of Aerosols
« Reply #134 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.
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Re: The Science of Aerosols
« Reply #135 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
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Sleepy

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Re: The Science of Aerosols
« Reply #136 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
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/
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. :(
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Re: The Science of Aerosols
« Reply #137 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

Sleepy

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Re: The Science of Aerosols
« Reply #138 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.
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Sleepy

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Re: The Science of Aerosols
« Reply #139 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/
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
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AbruptSLR

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Re: The Science of Aerosols
« Reply #140 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."
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AbruptSLR

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Re: The Science of Aerosols
« Reply #141 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."
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jai mitchell

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Re: The Science of Aerosols
« Reply #142 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

« Last Edit: May 16, 2018, 07:11:32 PM by jai mitchell »
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rboyd

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Re: The Science of Aerosols
« Reply #143 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?

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Re: The Science of Aerosols
« Reply #144 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.
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Ken Feldman

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Re: The Science of Aerosols
« Reply #145 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

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.

jai mitchell

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Re: The Science of Aerosols
« Reply #146 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.

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Ken Feldman

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Re: The Science of Aerosols
« Reply #147 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.

jai mitchell

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Re: The Science of Aerosols
« Reply #148 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


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Ken Feldman

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Re: The Science of Aerosols
« Reply #149 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

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.