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Author Topic: The Science of Aerosols  (Read 21801 times)

AbruptSLR

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Re: The Science of Aerosols
« Reply #50 on: February 23, 2016, 01:16:21 AM »
... their climate model has a total anthropogenic aerosol forcing that is aberrant compared to the scientific consensus.  (More precisely, the contribution from aerosol-radiation interactions in their climate model is in good agreement with the consensus, but the contribution from aerosol-cloud interactions is clearly not.)

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  This paper is an update on old science, so does aberrant mean new/updated and consensus mean old/out-of-date?

Edit: Some of your posts read like AR5 represents "settled-science", which it does not.
« Last Edit: February 23, 2016, 01:26:35 AM by AbruptSLR »
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Theta

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Re: The Science of Aerosols
« Reply #51 on: February 23, 2016, 10:19:05 AM »
It must be here stated that the GHG Radiative Forcing values include the lapse rate and water vapor feedbacks in their calculation.  These associated feedbacks represent about 3/4 of the total forcing produced by a given amount of GHG emissions.

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

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

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

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

Taking this factor alone into consideration means that we shouldn't dismiss it as an outlier because it basically means that there is no way to actually fix the problems that we face with Climate Change because if we stop burning fossil fuels, then Guy McPherson's statements on 4C within weeks, are guaranteed and we'd be dead within months or a few years. So, what we have is a hopeless situation where the best we can do is give up on fighting Climate Change and continue on hoping that by prolonging the lifetime of civilisation, we can find some kind of miracle technology, but even that seems unlikely with civilisation just about to fall off the cliff into oblivion with the economy in shambles.
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Richard Rathbone

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Re: The Science of Aerosols
« Reply #52 on: February 23, 2016, 02:01:08 PM »
What Hoose et al say, is that CNDCmin is effectively a tuning parameter for the indirect effect. So you decide, based on your expert judgement, what the indirect effect should be, and then choose CNDCmin to deliver that value. i.e. aerosol models aren't good enough to tell you what the indirect effect is.

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

AbruptSLR

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Re: The Science of Aerosols
« Reply #53 on: February 23, 2016, 04:30:15 PM »
What Hoose et al say, is that CNDCmin is effectively a tuning parameter for the indirect effect. So you decide, based on your expert judgement, what the indirect effect should be, and then choose CNDCmin to deliver that value. i.e. aerosol models aren't good enough to tell you what the indirect effect is.

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

Outlier, or upper-bound?
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Richard Rathbone

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Re: The Science of Aerosols
« Reply #54 on: February 24, 2016, 01:19:59 PM »
What Hoose et al say, is that CNDCmin is effectively a tuning parameter for the indirect effect. So you decide, based on your expert judgement, what the indirect effect should be, and then choose CNDCmin to deliver that value. i.e. aerosol models aren't good enough to tell you what the indirect effect is.

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

Outlier, or upper-bound?

Outlier.

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

However, its really a demonstration that aerosol models aren't good enough to come up with values for the indirect effect. They need to know what it is in advance and be tuned to give that result and taking the range over which they can be tuned as indicating uncertainty in the indirect effect is the wrong way round. Establishing the range over which its reasonable to tune them from uncertainty in other estimates is the way to establish bounds.

AbruptSLR

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Re: The Science of Aerosols
« Reply #55 on: February 24, 2016, 06:20:24 PM »
The linked (open access) reference points to new development in aerosol-cloud interaction modeling, indicating that some of the older (AR5) models need to be updated:


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


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

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

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

The results show that aerosols that interact with the WDM6 in GRAPES/CUACE obviously increase the total cloud water, liquid water content, and cloud droplet number concentrations, while decreasing the mean diameters of cloud droplets with varying magnitudes of the changes in each case and region. These interactive microphysical properties of clouds improve the calculation of their collection growth rates in some regions and hence the precipitation rate and distributions in the model, showing 24 to 48 % enhancements of threat score for 6 h precipitation in almost all regions. The aerosols that interact with the WDM6 also reduce the regional mean bias of temperature by 3 °C during certain precipitation events, but the monthly means bias is only reduced by about 0.3 °C."
« Last Edit: February 24, 2016, 06:41:55 PM by AbruptSLR »
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AbruptSLR

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Re: The Science of Aerosols
« Reply #56 on: February 24, 2016, 06:38:02 PM »
However, its really a demonstration that aerosol models aren't good enough to come up with values for the indirect effect. They need to know what it is in advance and be tuned to give that result and taking the range over which they can be tuned as indicating uncertainty in the indirect effect is the wrong way round. Establishing the range over which its reasonable to tune them from uncertainty in other estimates is the way to establish bounds.


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


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


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


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

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

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

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

The new paper gives a good start on advancing the science on this topic, but it is far from the end of the story, notes Feingold. "To really quantify the warming and cooling effects of clouds, we will have to apply this approach in different cloud regimes in different places on the globe.""
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Steven

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Re: The Science of Aerosols
« Reply #57 on: February 24, 2016, 11:15:18 PM »
Taking this factor alone into consideration means that we shouldn't dismiss it as an outlier because it basically means that there is no way to actually fix the problems that we face with Climate Change because if we stop burning fossil fuels, then Guy McPherson's statements on 4C within weeks, are guaranteed and we'd be dead within months or a few years.


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

Here is a 2012 scientific paper about this topic:

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

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

That paper suggests that, if we were to abruptly eliminate anthropogenic aerosol and GHG emissions, then the global temperature would increase by a few tenths of a degree (most likely between 0.25 and 0.5 °C) over the decade immediately following zeroed emissions. 

Steven

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Re: The Science of Aerosols
« Reply #58 on: February 24, 2016, 11:26:32 PM »
As this is a peer reviewed paper it will be included in AR6, so what does "aberrant" mean, and what does "scientific consensus" mean?  This paper is an update on old science, so does aberrant mean new/updated and consensus mean old/out-of-date?

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



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

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

AbruptSLR

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Re: The Science of Aerosols
« Reply #59 on: February 24, 2016, 11:46:14 PM »

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


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

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Re: The Science of Aerosols
« Reply #60 on: February 25, 2016, 11:17:17 AM »
For example, Marvel et al (2015) found that the most likely value for TCR is 1.7C (which is above the AR5 most likely value); but the the following Storelvmo et al (2015)research cites a most likely value for TCR of 1.9C (with a 95% CL interval of 1.2C to 2.7C); which again raises the possibility that aerosol negative forcing is stronger than AR5 considers.

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


In reality only one TCR is correct, but due to uncertainty one needs to compare PDFs from different researchers such as the attached image from Marvel et al (2015).  In this regards the Storelvmo et al (2015) range of for TCR of 1.9C (with a 95% CL interval of 1.2C to 2.7C), is much different than the Marvel findings.  Thus when AR6 is published they should have a new & different PDF for TCR than did AR5, due to new findings.
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AbruptSLR

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Re: The Science of Aerosols
« Reply #61 on: February 25, 2016, 11:26:46 AM »

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

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

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

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

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Re: The Science of Aerosols
« Reply #62 on: February 25, 2016, 02:04:23 PM »

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


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

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

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

AbruptSLR

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Re: The Science of Aerosols
« Reply #63 on: February 25, 2016, 04:50:17 PM »

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


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

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

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

Richard,

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

Best regards,
ASLR
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Steven

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Re: The Science of Aerosols
« Reply #64 on: February 25, 2016, 08:28:44 PM »
They are not "lumping together" the forecasts.  The AR5 assessment (and confidence intervals) for aerosol forcing are based on expert judgement, which gives less weight to the older and more primitive models than to the more comprehensive modeling studies.  Moreover, it gives more weight to observationally based (especially satellite) studies.


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

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


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


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



http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter07_FINAL.pdf

AbruptSLR

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Re: The Science of Aerosols
« Reply #65 on: February 25, 2016, 08:53:26 PM »
They are not "lumping together" the forecasts.  The AR5 assessment (and confidence intervals) for aerosol forcing are based on expert judgement, which gives less weight to the older and more primitive models than to the more comprehensive modeling studies.  Moreover, it gives more weight to observationally based (especially satellite) studies.


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

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


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


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

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


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

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

If it is not clear what decadal feedbacks are, they are associated with such phenomena as the PDO/IPO, AMO, etc.  As we have just left a period of negative PDO and are now in a period of positive PDO, we can expect El Ninos to keep driving up estimates of the ECS based on the future satellite record.
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Richard Rathbone

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Re: The Science of Aerosols
« Reply #66 on: February 26, 2016, 01:51:29 PM »

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


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

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

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

Richard,

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

Best regards,
ASLR

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

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

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Re: The Science of Aerosols
« Reply #67 on: February 26, 2016, 05:49:59 PM »
That's the editor's responsibility. The authors submit, the reviewers comment, the authors respond and the editor decides. For all I know, the argument got twisted to meet the comment of a reviewer and the authors aren't exactly happy with it either. Reviewers get to comment on the submission, not the revised version. 

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

It is not surprising that denialists have proven very effective at manipulating this process in the past, and I imagine that they will prove successful in manipulating this process to make sure that the input to AR6 can continue to err on the side of least drama.
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AbruptSLR

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Re: The Science of Aerosols
« Reply #68 on: February 26, 2016, 11:48:52 PM »
The linked reference discusses challenges in constraining anthropogenic radiative forcing for aerosol – cloud interaction.  The reference points out that not only do we have a limited understanding of the current interactions, but we also have an even poorer understanding of the preindustrial condition that researchers are trying to use as a baseline.

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


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


Abstract: "A large number of processes are involved in the chain from emissions of aerosol precursor gases and primary particles to impacts on cloud radiative forcing. Those processes are manifest in a number of relationships that can be expressed as factors dlnX/dlnY driving aerosol effects on cloud radiative forcing. These factors include the relationships between cloud condensation nuclei (CCN) concentration and emissions, droplet number and CCN concentration, cloud fraction and droplet number, cloud optical depth and droplet number, and cloud radiative forcing and cloud optical depth. The relationship between cloud optical depth and droplet number can be further decomposed into the sum of two terms involving the relationship of droplet effective radius and cloud liquid water path with droplet number. These relationships can be constrained using observations of recent spatial and temporal variability of these quantities. However, we are most interested in the radiative forcing since the preindustrial era. Because few relevant measurements are available from that era, relationships from recent variability have been assumed to be applicable to the preindustrial to present-day change. Our analysis of Aerosol Comparisons between Observations and Models (AeroCom) model simulations suggests that estimates of relationships from recent variability are poor constraints on relationships from anthropogenic change for some terms, with even the sign of some relationships differing in many regions. Proxies connecting recent spatial/temporal variability to anthropogenic change, or sustained measurements in regions where emissions have changed, are needed to constrain estimates of anthropogenic aerosol impacts on cloud radiative forcing."
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AbruptSLR

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Re: The Science of Aerosols
« Reply #69 on: February 27, 2016, 10:31:10 AM »
Conventional thinking is that reducing BC emissions would help to cool the Earth; however, the linked reference indicates: "… that a reduction in BC emission can lead to an unexpected warming on the Earth's climate system in the future."

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

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

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

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Re: The Science of Aerosols
« Reply #70 on: March 01, 2016, 07:58:53 PM »
The linked website contains numerous links to recorded presentations at the January 2016 Eighth Symposium on Aerosol–Cloud–Climate Interactions in New Orleans.  There are too many presentations to look at, let alone summarize:

https://ams.confex.com/ams/96Annual/webprogram/8AEROSOL.html
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Re: The Science of Aerosols
« Reply #71 on: March 08, 2016, 05:52:35 PM »
The linked reference indicates that Biogenic volatile organic compounds (BVOC) can either create positive, or negative, radiative forcing feedback, and that with continued global warming the Arctic tundra will become a major (as yet unaccounted for) source of BVOC which may be four-time higher than current emission levels.  Therefore, it is important that future state-of-the-art ESM projections include this feedback mechanism:

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

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

Abstract: "Biogenic volatile organic compounds (BVOCs), which are mainly emitted by vegetation, may create either positive or negative climate forcing feedbacks. In the Subarctic, BVOC emissions are highly responsive to temperature, but the effects of climatic warming on BVOC emissions have not been assessed in more extreme arctic ecosystems. The Arctic undergoes rapid climate change, with air temperatures increasing at twice the rate of the global mean. Also, the amount of winter precipitation is projected to increase in large areas of the Arctic, and it is unknown how winter snow depth affects BVOC emissions during summer. Here, we examine the responses of BVOC emissions to experimental summer warming and winter snow addition – each treatment alone and in combination - in an arctic heath during two growing seasons. We observed a three-fold increase relative to ambient in BVOC emissions in response to a 4 °C summer warming. Snow addition had minor effects on growing season BVOC emissions after one winter, but decreased BVOC emissions after the second winter. We also examined differences between canopy and air temperatures, and found that the tundra canopy surface was on average 7.7 °C and maximum 21.6 °C warmer than air. This large difference suggests that the tundra surface temperature is an important driver for emissions of BVOCs, which are temperature-dependent. Our results demonstrate a strong response of BVOC emissions to increasing temperatures in the Arctic, suggesting that emission rates will increase with climate warming and thereby feed back to regional climate change."
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Re: The Science of Aerosols
« Reply #72 on: March 09, 2016, 07:13:12 PM »
The linked article indicates that the direct aerosol-climate feedback (not the radiative forcing) is negative, and that the indirect aerosol-climate feedback is likely even more negative, than previously realized.  This indicates that in order to match the observed Anthropocene GMST history, that other Earth System feedbacks have been more positive than previously assumed.  Thus as people reduce their aerosol emissions in order to control air pollution, the negative aerosol-climate feedback contribution will be reduced while the positive Earth System feedbacks will likely accelerate, thus possibly resulting in a higher rate of global warming than previously assumed:

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


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


Abstract: "Atmospheric aerosols are of significant environmental importance, due to their effects on air quality, as well as their ability to alter the planet’s radiative balance. Recent studies characterizing the effects of climate change on air quality and the broader distribution of aerosols in the atmosphere show significant, but inconsistent results, including the sign of the effect. Using a suite of state-of-the-art climate models, we show that climate change is associated with a negative aerosol–climate feedback of −0.02 to −0.09 W m−2 K−1 for direct radiative effects, with much larger values likely for indirect radiative effects. This is related to an increase in most aerosol species, particularly over the tropics and Northern Hemisphere midlatitudes, largely due to a decrease in wet deposition associated with less large-scale precipitation over land. Although simulation of aerosol processes in global climate models possesses uncertainty, we conclude that climate change may increase aerosol burden and surface concentration, which may have implications for future air quality."
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AbruptSLR

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Re: The Science of Aerosols
« Reply #73 on: March 15, 2016, 11:07:22 PM »
The linked article indicates that Europe's reductions in air pollution since 1980 has added about 0.5C of surface temperature increase to Arctic Amplification.  Just imagine how much greater impact there will be on GMST as Asia continues to reduce its air pollution:

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


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

Abstract: "The Arctic region is warming considerably faster than the rest of the globe, with important consequences for the ecosystems and human exploration of the region. However, the reasons behind this Arctic amplification are not entirely clear. As a result of measures to enhance air quality, anthropogenic emissions of particulate matter and its precursors have drastically decreased in parts of the Northern Hemisphere over the past three decades5. Here we present simulations with an Earth system model with comprehensive aerosol physics and chemistry that show that the sulfate aerosol reductions in Europe since 1980 can potentially explain a significant fraction of Arctic warming over that period. Specifically, the Arctic region receives an additional 0.3 W m−2 of energy, and warms by 0.5 °C on annual average in simulations with declining European sulfur emissions in line with historical observations, compared with a model simulation with fixed European emissions at 1980 levels. Arctic warming is amplified mainly in fall and winter, but the warming is initiated in summer by an increase in incoming solar radiation as well as an enhanced poleward oceanic and atmospheric heat transport. The simulated summertime energy surplus reduces sea-ice cover, which leads to a transfer of heat from the Arctic Ocean to the atmosphere. We conclude that air quality regulations in the Northern Hemisphere, the ocean and atmospheric circulation, and Arctic climate are inherently linked."
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AbruptSLR

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Re: The Science of Aerosols
« Reply #74 on: March 18, 2016, 02:45:24 PM »
According to the IPCC AR5 report: "The transient climate response is likely in the range of 1.0°C to 2.5°C (high confidence) and extremely unlikely greater than 3°C"; however, the linked reference uses only observed data (corrected for aerosol effects) to indicate that TCR is 2.0 +/- 0.8C.


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


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

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


However, I note that Shindell (2014) indicates that it is very unlikely that TCR is less than 1.3C
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140011847.pdf
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AbruptSLR

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Re: The Science of Aerosols
« Reply #75 on: March 18, 2016, 03:20:55 PM »
The linked reference confirms, and quantifies, what we have long known; which is that as China cleans-up its aerosol emissions, GMST will increase due to CO₂ that is already in the atmosphere:

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


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


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


See also (& image):
http://www.carbonbrief.org/21000-2
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Richard Rathbone

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Re: The Science of Aerosols
« Reply #76 on: March 19, 2016, 01:04:08 PM »
Storelvmo et al should be worth the read if you have access to it (I don't). It really needs the range of the constraint halved to bring some reality into the models, but they seem to be gathering the right sort of data to do that eventually.


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Re: The Science of Aerosols
« Reply #77 on: March 19, 2016, 06:26:01 PM »
Storelvmo et al should be worth the read if you have access to it (I don't).


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

The paper uses:

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


"Figure 1: Radiation measurements from 1,300 surface stations":

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Re: The Science of Aerosols
« Reply #78 on: March 20, 2016, 07:12:42 PM »
That link just takes me to a request to donate. (and some Russian that Google can't translate)

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Re: The Science of Aerosols
« Reply #79 on: March 20, 2016, 08:31:17 PM »
I'm really late to this party, but Hoose et. al 2009 was referenced by the study in question:

Global aerosol-climate models with prognostic treatment of cloud droplet number concentration (CDNC) often prescribe lower bounds for CDNC or aerosol concentrations. Here we demonstrate that this possibly unphysical constraint reduces the simulated aerosol indirect effect by up to 80%, caused by extensively uniform CDNCs. In present-day conditions, the impact of the prescribed lower bound for CDNC is mainly visible over oceans, while with preindustrial emissions, large parts of both land and ocean areas are influenced. We furthermore show that imposing the same constraints on aerosol instead of on CDNC reduces the aerosol indirect effect to a lesser extent.

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Re: The Science of Aerosols
« Reply #80 on: May 02, 2016, 09:23:12 PM »
The linked article indicates that in subtropical regions satellite data indicate strong negative forcing due to aerosols than assumed by most climate models:

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


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

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

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Re: The Science of Aerosols
« Reply #81 on: May 11, 2016, 08:59:10 PM »
The linked "Bits of Science" article indicates that global dimming could be masking 50% of GHG potential warming:

http://www.bitsofscience.org/real-global-temperature-trend-global-dimming-still-masks-50-percent-co2-warming-6990/
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Re: The Science of Aerosols
« Reply #82 on: May 11, 2016, 10:58:28 PM »
The linked "Bits of Science" article indicates that global dimming could be masking 50% of GHG potential warming:

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


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

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Re: The Science of Aerosols
« Reply #83 on: May 11, 2016, 11:10:25 PM »
The linked "Bits of Science" article indicates that global dimming could be masking 50% of GHG potential warming:

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


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


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

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Re: The Science of Aerosols
« Reply #84 on: May 11, 2016, 11:11:53 PM »
The linked "Bits of Science" article indicates that global dimming could be masking 50% of GHG potential warming:

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


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


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


Interesting, I was under the impression that it would be weeks to months.
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AbruptSLR

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Re: The Science of Aerosols
« Reply #85 on: May 11, 2016, 11:23:27 PM »
Interesting, I was under the impression that it would be weeks to months.


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

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

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Re: The Science of Aerosols
« Reply #86 on: May 11, 2016, 11:26:36 PM »
Interesting, I was under the impression that it would be weeks to months.


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

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


Cool, thanks
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Re: The Science of Aerosols
« Reply #87 on: May 19, 2016, 07:10:59 PM »
The linked open access reference indicates that uncertainty on the aerosol indirect effect (AIE) is greater in local regions than it is globally, which points to a need to better understand AIE for specific different conditions:

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

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

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

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AbruptSLR

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Re: The Science of Aerosols
« Reply #88 on: May 26, 2016, 05:09:54 PM »
I have frequently cited research on secondary aerosol particles, and while the linked reference concludes that cloud formation associated with such secondary aerosol particles will slightly reduce climate sensitivity; another way of looking at this research is that if/when the source of such secondary aerosol particles is reduced/degraded (such as by deforestation and wildfires), then near future climate sensitivity values will actually be higher that what AR5 reported/assumes.

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


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

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


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

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

This is where it gets tricky. Up until now, scientists believed that sulfuric acid, which is mainly produced from fossil-fuel emissions — cars, factories, etc. — were necessary for the formation of secondary aerosols. But in this new study, a group of scientists shows that Earth can actually produce these particles without any help from humans.
Instead, it gets made from a mix of tree vapors and highly energetic particles that bombard our atmosphere from outer space called cosmic rays."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: The Science of Aerosols
« Reply #89 on: May 26, 2016, 05:10:30 PM »
The linked reference indicates that aerosols in the Arctic have a “profound” impact on the global climate system. Climate models often underestimate the extent to which aerosols from industrial air pollution (especially those containing black carbon) warm the atmosphere because they assume Arctic air is cleaner than it actually is:

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

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

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

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

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

Extract: "Aerosols from the production of heavy oil is a growing climate and pollution concern because new tar sands developments are on the drawing board in Venezuela, Utah and elsewhere, the study says. Today, heavy oil accounts for 10 percent of global crude oil production worldwide, mostly in Canada, which produced about 1.1 billion barrels of oil in 2014.
“The results indicate that the environmental impacts of Canadian tar sands are much larger than previously recognized,” said Allen Robinson, a mechanical engineering professor at Carnegie Mellon University who is unaffiliated with the study. “What is so novel about this paper is that tar sands were not on anybody’s radar as a major source of aerosol.”"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: The Science of Aerosols
« Reply #90 on: June 21, 2016, 05:25:50 PM »
The linked reference concludes with regards to the faux hiatus and implications of aerosol reductions in the future that: "Our results suggest that a slowdown in GMST trends could have been predicted in advance, and that future reduction of anthropogenic aerosol emissions, particularly from China, would promote a positive PDO and increased GMST trends over the coming years."

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

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

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

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

Extract: "Human-caused aerosols are, therefore, at least another factor to add to the list of those that have contributed to the global surface warming slowdown …"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: The Science of Aerosols
« Reply #91 on: August 03, 2016, 06:24:15 PM »
The linked reference indicates that emissions twenty-first century of SO2, BC, and OC are expected to decrease much more rapidly than GHG emissions; which should result in a net increase in positive radiative forcing for realistic emission pathways:

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

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

Abstract: "This paper compares projections over the twenty-first century of SO2, BC, and OC emissions from three technologically detailed, long-term integrated assessment models. The character of the projections and the response of emissions due to a comprehensive climate policy are discussed focusing on the sectoral level. In a continuation of historical experience, aerosol and precursor emissions are increasingly decoupled from carbon dioxide emissions over the twenty-first century due to a combination of emission controls and technology shifts over time. Implementation of a comprehensive climate policy further reduces emissions, although there is significant variation in this response by sector and by model: the response has many similarities between models for the energy transformation and transportation sectors, with more diversity in the response for the building and industrial sectors. Much of these differences can be traced to specific characteristics of reference case end-use and supply-side technology deployment and emissions control assumptions, which are detailed by sector."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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sidd

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Re: The Science of Aerosols
« Reply #92 on: August 03, 2016, 09:24:33 PM »
That Smith paper on aerosols disappoints. Two yers since Cowtan and Way debunked the hiatus, and we see aguments  made on the basis of the non existent hiatus ...

Referees are slacking at that journal.

AbruptSLR

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Re: The Science of Aerosols
« Reply #93 on: August 05, 2016, 04:50:23 PM »
The linked reference indicates that aerosol forcing plays a significant role in modeled climate-cloud feedback variance & reducing the uncertainties associated with aerosol interactions would help to narrow the large range of climate sensitivity recognized by the IPCC:

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

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

Abstract: "Aerosols can influence cloud radiative effects, and thus may alter interpretation of how the earth’s radiative budget responds to climate forcing. Three different ensemble experiments from the same climate model with different greenhouse gas and aerosol scenarios are used to analyze the role of aerosols in climate feedbacks and their spread across initial condition ensembles of transient climate simulations. The standard deviation of global feedback parameters across ensemble members is low, typically 0.02 Wm−2 K−1. Feedbacks from high (8.5 Wm−2) and moderate (4.5 Wm−2) year 2100 forcing cases are nearly identical. An aerosol kernel is introduced to remove effects of aerosol cloud interactions that alias into cloud feedbacks. Adjusted cloud feedbacks indicate an ‘aerosol feedback’ resulting from changes to climate that increase sea-salt emissions, mostly in the S. Ocean. Ensemble simulations also indicate higher tropical cloud feedbacks with higher aerosol loading. These effects contribute to a difference in cloud feedbacks of nearly 50% between ensembles of the same model. These two effects are also seen in aquaplanet simulations with varying fixed drop number. Thus aerosols can be a significant modifier of cloud feedbacks, and different representations of aerosols and their interactions with clouds may contribute to multi-model spread in climate feedbacks and climate sensitivity in multi model archives."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: The Science of Aerosols
« Reply #94 on: August 06, 2016, 05:14:40 PM »
The linked reference states: "The model with the strongest response (HadGEM3-GA4) compares best with observations of AOD regionally, …". This indicates that as scientists improve their CMIP6 models to better match observations, we can expect to see more projections of accelerating global warming beyond the CMIP5 projections due to the continuing reductions of sulfur dioxide emissions from China:

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

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

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

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: The Science of Aerosols
« Reply #95 on: August 15, 2016, 09:57:53 PM »
Per the linked reference current climate change models do not adequately account for the influence of secondary organic aerosols, SOAs (including those from trees). Thus we may well all be in for an unpleasant surprise as increasing wildfires, drought, pests, and heat/seasonal stress reduce the current negative forcing associated with such SOAs:

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


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

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

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

Extract: "One of the secrets relevant to climate change involves how emissions from nature and human activities are changed in the atmosphere to become secondary organic aerosols (SOA).
Now a team of scientists led by Pacific Northwest National Laboratory has discovered an often ignored but very influential process/parameter that can affect not only the air we breathe but the weather and climate. Oligomerization, or molecular bonding, is a process by which smaller molecules combine and form larger molecules, increasing the amount and lifetime of secondary organic aerosols in the atmosphere. These bondings may hold the key to more successful modeling of the particles. Most atmospheric models ignore oligomerization.
"The study's comprehensive sensitivity analysis clearly shows that leaving out secondary organic aerosol oligomerization processes in climate models could severely limit our ability to understand and predict their impacts," noted Dr. Manish Shrivastava, PNNL atmospheric scientist and lead author of the study."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: The Science of Aerosols
« Reply #96 on: September 03, 2016, 01:30:44 AM »
The linked reference provides more information on the influence of anthropogenic aerosols:

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

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

Abstract: "Stratospheric aerosols cool the Earth by scattering sunlight. Although sulfuric acid dominates the stratospheric aerosol, this study finds that organic material in the lowermost stratosphere contributes 30-40% of the non-volcanic stratospheric aerosol optical depth (sAOD). Simulations indicate that non-volcanic sAOD has increased 77% since 1850. Stratospheric aerosol accounts for 21% of the total direct aerosol radiative forcing (which is negative) and 12% of the total AOD increase from organics and sulfate. There is a larger stratospheric influence on radiative forcing (i.e. 21%) relative to AOD (i.e. 12%) because an increase of tropospheric black carbon warms the planet while stratospheric aerosols (including black carbon) cool the planet. Radiative forcing from non-volcanic stratospheric aerosol mass of anthropogenic origin, including organics, has not been widely considered as a significant influence on the climate system."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

FishOutofWater

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Re: The Science of Aerosols
« Reply #97 on: September 03, 2016, 03:23:17 AM »
If those organic stratospheric aerosols which cause cooling are primarily in the areas of tropical and subtropical upwelling of air that would amplify the cooling of the tropopause transition layer, leading to the intensification of the strongest hurricanes.

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

AbruptSLR

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Re: The Science of Aerosols
« Reply #98 on: September 03, 2016, 03:28:07 AM »
If those organic stratospheric aerosols which cause cooling are primarily in the areas of tropical and subtropical upwelling of air that would amplify the cooling of the tropopause transition layer, leading to the intensification of the strongest hurricanes.

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

Thanks for the pointer, its never too late to learn something new.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: The Science of Aerosols
« Reply #99 on: October 10, 2016, 05:40:36 PM »
The linked reference provides new insights into the complex issue of cloud-sensitive aerosol loadings in low level marine clouds:

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


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

Abstract: "Aerosol-cloud interaction is a key component of the Earth's radiative budget and hydrological cycle, but many facets of its mechanisms are not yet fully understood. In this study, global satellite-derived aerosol and cloud products are used to identify at what aerosol loadings cloud droplet size shows the greatest sensitivity to changes in aerosol loading (ACSmax). While on average, cloud droplet size is most sensitive at relatively low aerosol loadings, distinct spatial and temporal patterns exist. Possible determinants for these are identified with reanalysis data. The magnitude of ACSmax is found to be constrained by the total columnar water vapor. Seasonal patterns of water vapor are reflected in the seasonal patterns of ACSmax. Also, situations with enhanced turbulent mixing are connected to higher ACSmax, possibly due to intensified aerosol activation. Of the analyzed aerosol species, dust seems to impact ACSmax the most, as dust particles increase the retrieved aerosol loading without substantially increasing the concentration of cloud condensation nuclei."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson