The Science of Aerosols

[Sciguy]

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

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.

[jai mitchell]

the 2 to 4 degrees is in the Arctic only which experiences much greater impacts

[Sciguy]

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.

[jai mitchell]

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

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

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

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

[jai mitchell]

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

[Sciguy]

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

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.

[jai mitchell]

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

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:

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!

[Sciguy]

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:

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

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:

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.

[jai mitchell]

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

[Sciguy]

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:

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.

[Csnavywx]

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).

[jai mitchell]

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

[Sciguy]

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

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:

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.

[jai mitchell]

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

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

[gerontocrat]

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

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.

[jai mitchell]

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

3.  The basic model of understanding appears to be severely underestimating northern hemisphere aerosol effects.

[rboyd]

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.

[gerontocrat]

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

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.

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.

[Rob Dekker]

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 :

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) :

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.

[AbruptSLR]

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."

[diablobanquisa]

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!

[AbruptSLR]

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."

[Rob Dekker]

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 !

[vox_mundi]

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



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."

[AbruptSLR]

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.

[jai mitchell]

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

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.

[b_lumenkraft]

Daniel Rosenfeld et al (DOI: 10.1126/science.aav0566)

Abstract

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

[wdmn]

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

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?

[sidd]

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

[jai mitchell]

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.

[GeoffBeacon]

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 Later he wrote in the Huffington Post

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 says of Rosenfeld et al.

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 by Unger et al. Figure 2 shows the progression of cooling/warming from different activities



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

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

"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?


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.

[Richard Rathbone]

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.

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.

[GeoffBeacon]

Whether or not this paper is alarmist about aerosols my question remains (perhaps with slightly less urgency):

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.

[jai mitchell]

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.

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. . .)

[rboyd]

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.

[jai mitchell]

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.   

[Sciguy]

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/

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.

[vox_mundi]

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



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.



"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."

[Tom_Mazanec]

Aerosols twice as cooling as thought:
https://m.phys.org/news/2019-01-cooling-effect-aerosols-cumulus-msc.html

[b_lumenkraft]

From Toms link:

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. 

[be cause]

get burning that coal ? b.c.

[b_lumenkraft]

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!

[KiwiGriff]

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.


 


 

[jai mitchell]

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

[jai mitchell]

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.

[morganism]

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."

[Sciguy]

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

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

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.

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).

[vox_mundi]

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, 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.

[petm]

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:

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.

[Tom_Mazanec]

More on the recent "good news"
https://phys.org/news/2019-08-pollution-wont-global-spike.html