It appears that some scientists somewhere may be considering the possibility of a phenomenological cause for the apparent stall in the rise of global temperatures. As is: Some honest to goodness scientist associated with the United Nations Environment Program may be attributing a cause and effect relationship other than “weather noise” to the stall.
On Thursday, the United Nations Environment Program released a report. The story was picked up the AP; most news articles justifiably focus on the mostly undesirable aspects of the Asian Brown Cloud ( and brown clouds in general.)
However, those who have been wondering about possible causes for the recent flattish trend in GMST would likely note this:
At the same time, the brown clouds have also helped mask the full impact of global warming by helping to cool the earth’s surface and tamp down rising temperatures by between 20 to 80 percent, the study said. That’s because some of the particles that make up the clouds reflect sunlight and cool down the air.
What? The UNEP suggest that brown clouds may be slowing the rate of temperature rise by as much as 20 to 80%? Could that mean that the AR4 best estimate of the warming trend– i.e. “about 2C/century” did not include the impact of the Asian brown cloud? And that it the true underlying trend might be lower? As in “about 0.4 C/century to 1.6 C/century”?
I guess I’ll have to read the report and see if the 80% is relative to the SRES used in the AR4. But, of course, this is what they mean, it appear the consensus may be moving toward the notion that temperatures are not currently rising at a rate of 2C/century as projected in the AR4. 🙂
Reaction at “some blogs”
Interstingly, I first learned of this reading comments at RC. Here’s an a reaction in RC blog comments (bold mine):
Hank Roberts Says:
14 novembre 2008 at 12:23 AMHey, you’ve got friends everywhere — another major source of error in the warming figures just hit the news. I wonder why this is being reported now?
Today’s Wall St. Journal:
Toxic Cloud Masks Warming Effects
By SHAI OSTERBEIJING — A roughly two-mile thick cloud of soot and smog hanging over most of Asia is wrecking havoc on agriculture and health but masking the effects of global warming, a United Nations study found.
The atmospheric brown cloud made of different particles resulting mostly from burning coal is causing hundreds of thousands of deaths in Asia and billions of dollars in economic losses, the study said. But it helps reduce the impact of climate change by between 20% and 80%, said the report released Thursday by the Project Atmospheric Brown Cloud, established by the United Nations Environment Program…..
—————–
Bloomberg.com writes:The pollution makes skies from Beijing to Tehran darker by blocking sunlight as it is absorbed by particles linked with burning fossil fuels. Guangzhou, a city in southern China, has reported a 20 percent drop in sunlight since the 1970s.
The cloud may also be contributing to shifts in weather patterns, including drought in northern China and flooding the southern region of the country as well as affecting the seasonal monsoon, the UN said. At the same time, it may be having a cooling effect on the planet as some soot and biomass material reflects sunlight, the report said. ….
Hank, in answer to your question: the reason the news about brown clouds is being reported now is the United Nations Environment Program released a report Thursday. The UNEP probably initiated this scientific study some time ago.
Other stories
For those of you interested in additional news reports, these both looked interesting Dirty Brown Clouds Impact Glaciers, Agriculture And The Monsoon andExperts say brown clouds not limited To Delhi, mercury not rising.
I suspect we’ll read more about this soon. I’ll be googling to find the UNEP report. If any of you have found it, let me know.
Sigh, I’m glad the “science” is so settled:
Huge haze clouds over the Indian Ocean contribute as much to atmospheric warming as greenhouse gases
BarryW–
I found a 2002 report that suggested that the aerosols warmed. The August 2007 report you limn says
We need a timeline to figure out when scientists believed brown cloud mostly cooled, and when they thought they mostly warmed. We may need several time lines to differentiate between how they were thought to affect Asia vs. the entire planet!
Atmospheric Brown Clouds: Regional Assessment Report with Focus on Asia:
http://www.unep.org/pdf/ABCSummaryFinal.pdf
Thanks Reid!
This is fantastic news! The crisis is averted! We don’t have to choke off our CO2 output, because any warming will be offset by the Asian cloud. Can we dump the cap and trade now? Seriously, under no scenario would China reduce their pollution. In fact, all of these Kyoto treaties and cap and trade regimes would simply shift more production to China, which would further increase pollution.
I’ve been to Shanghai, and the air there is pretty thick. On a good day, I could maybe see 5 miles. Most days I could see less than 1-2 miles. I have another question about their theory, though. Aren’t most of the thermometers used to measure surface temperature for GISS in the US? How much affect could this have? Or do the modelers even look at real thermometers anyway?
JamesH–
This wouldn’t avert a crisis. It could mean things are worse than they seem.
After all, developing countries get more prosperous, they are not going to want to breath in lung burning brown smog. So, they would enact clean air law. The CO2 is still there, and then we get double the warming!
There is a reason I’m for NUKES!
I know many of my readers like the comparisons that show IPCC projections appear high compared to observations– but that doesn’t mean there is no warming. It also doesn’t mean there is nothing to worry about. As Roger Pielke Jr. has said: The fact that we may be unable to predict means we do need to be cautious!
I’m reading the UNEP report right now.
Climate researchers seem to be as two minded about the asian brown cloud as they are about regular clouds. Measurements seem to indicate that low clouds at least cause net cooling by reflecting more incoming solar energy than they trap outgoing surface radiation. Yet clouds are reported to have a positive feedback effect in most (all?) climate models. Apparently they can’t make up their minds about smog either.
Nice typo in the Google ad I see above: Climate Change Muths Exposed by…
The particulate matter hanging over China is small potatoes compared to ocean circulation.
Lucia,
I thought Spencer, Svensmark, et. al argue that increased cloudiness [leaving aside for now what causes the increase] represents a negative forcing because of the higher albedo which causes them to reflect sunlight back out. If that is correct, than a brown cloud should ADD to warming because of low albedo and therefore heat retention. Precisely the opposite of what the UN folks are arguing…
tetris (Comment#6744) November 15th, 2008 at 12:00 pm,
But lower albedo than what? The cloud could be lower albedo for incoming visible solar radiation than a water vapor cloud but still higher albedo than the surface. Also, while water vapor clouds have high visible reflectivity, they absorb very well in the near IR. About half or more of incoming solar radiant energy is in the near IR. The thermal IR characteristics are important as well. A water vapor cloud is, to a good approximation, a black body in the thermal IR. Does anyone know the absorptivity, reflectivity and transmittivity characteristics in the 5 to 100 micrometer band of the brown cloud? Even if it does absorb significantly more in the solar spectrum than clear air, it’s absorbing at higher altitude and will also increase thermal emissivity at that altitude so that the heat may radiate back to space at a higher rate than if the energy were absorbed by the surface.
Jacobson et al suggest that aerosols are a positive forcing agent.
Jacobson, M., 2001: Strong radiative heating due to the mixing state of black carbon in atmospheric aerosols, Nature, 409:695-697; Sato, M. et al., 2003: Global atmospheric black carbon inferred from AERONET, Proceedings of the National Academy of Sciences, vol. 100, no. 11: 6319-6324.
Crozier at al says there is a large uncertainity in aerosol forcing, as it relates to GCMs.
“Because of the large uncertainty we have in the radiative forcing of aerosols, there is a corresponding large uncertainty in the degree of radiative forcing overall”, Crozier said. “This introduces a large uncertainty in the degree of warming predicted by climate change models.”
http://news.usti.net/home/news/cn/?/tw.top/2/wed/dg/Uus-climatemodels.RjIW_IaB.html
These authors suggest that aerosol levels were much HIGHER at the end of the 19th century and the beginning of the 20th, than at present. This would indicate that aerosols levels were highest during the warming leading up to 1940.
McConnell et al. Coal burning leaves toxic heavy metal legacy in the Arctic. Proceedings of the National Academy of Sciences, August 2008 DOI: 10.1073/pnas.0803564105
And, oddly, the same author of the UNEP paper, only a year earlier, suggested that aerosols were a net POSITIVE forcing, and contributes to the glacier retreat.
We found that atmospheric brown clouds enhanced lower atmospheric solar heating by about 50 per cent. Our general circulation model simulations, which take into account the recently observed widespread occurrence of vertically extended atmospheric brown clouds over the Indian Ocean and Asia, suggest that atmospheric brown clouds contribute as much as the recent increase in anthropogenic greenhouse gases to regional lower atmospheric warming trends. We propose that the combined warming trend of 0.25 K per decade may be sufficient to account for the observed retreat of the Himalayan glaciers.”
http://www.nature.com/nature/journal/v448/n7153/abs/nature06019.html
My post on this issue:
http://australianclimatemadness.blogspot.com/2008/11/brown-cloud-accelerates-global-warming.html
Cheers,
Simon
Australian Climate Madness
DeWitt Payne: your last point is goes to heart of matter.
Les Jonhson: Crozier’s comment on the uncertainty introduced into GCMs by aerosols is telling. If the higher aerosol levels during the late 19th and early 20th centuries are argued to have contributed to the warming observed during the 1920-1940s, what are the implications in terms of the effect of the Asian brown cloud? Is this brown cloud in fact partially masking the forcings responsible for the drop in the various global temperature metrics [land surface, sea surface, deep ocean, lower troposphere, etc.] that we have on record for the better part of the past decade?
I’ll have roll over the pallet for a while “Is this brown cloud in fact partially masking the forcings responsible for the drop in the various global temperature metrics” hmmm can you rephrase that please. Forcings which way e.g.?
Really wonder what those aerosols of mt Pinatubo did, really.
Sekerob,
The argument is that aerosols are supposed to contribute to warming. However, in fact over the past approx 10 years we have an increasingly well documented record of the absence of warming – i.e. cooling -. If the “aerosols contrinute to warming” argument is correct than it follows that the Asian brown cloud must be counteracting/dampening the cooling observed in the various relevant temperature metrics. My point simply is that the UN study contray to its stated conclusions could well mean that we are in fact experiencing more cooling than we realize.
Nothing scientific about these observations.
Over a few decades, I like most Australians, have experienced the effects of the dense smoke layers from some massive bush fires in south eastern Australia.
When the smoke is relatively light, the sun can still shine through and the ground warming from the trapped radiation below the smoke cloud can be quite high.
Conversely when the smoke layer thickens up thereby reducing the solar radiation reaching the ground, there is a cooling effect.
I would suggest that the effects of dust /smog/ brown clouds on the trapping of or reflecting of solar radiation and therefore ground temperatures is far more complex than is currently realised or admitted by the various researchers.
The composition of the industrial / terrestrial origin dust / smog / brown clouds which includes particle size, particle density per cubic metre, type, shapes and composition of the particles and their abilities to absorb and reradiate across the solar spectrum will all have a very significant effect on the heating or cooling aspects of any non water vapour based cloud.
So blanket pronouncements on the heat trapping or cooling effects of industrial / terrestrial origin clouds are probably not worth any consideration until much further work is done on the above aspects of industrial/ terrestrial origin clouds.
Sekerob (Comment#6754) November 15th, 2008 at 3:52 pm ,
Sulfate aerosols injected into the stratosphere by a volcanic eruption are not at all the same as black carbon/smog or even sulfate aerosols in the mid to lower troposphere.
It may help to compare the Asian Brown Cloud with “Global Dimming” from jet contrails etc. See:
Global Dimming: The hidden Climate Change 12 Oct 2007.
Global Dimming BBC
Ramanathan, V (2006) Bjerknes Lecture: Global Dimming and its Masking Effect on Global Warming, Eos Trans. AGU,
87(52), Fall Meet. Suppl., Abstract A23D-01.
Global dimming or local dimming?: Effect of urbanization on sunlight availability
Pinhas Alpert, et al. GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L17802, doi:10.1029/2005GL023320, 2005
On the effect of aerosols containing particulate matter (PM), the sum should be a net positive effect due to dilution. The volume of air is small (relatively speaking) compared to the source when the PM is concentrated. As it dilutes, it becomes very disperse and covers a much broader area. The question becomes does it block more incoming than outgoing at this point. Using the IPCC assumptions of IR radiation, it must trap more than it blocks. Consistancy of assumptions should be used.
What I find more interesting is the stated effect of sulphates. They first cool and then have a slight warming effect per some discussions. They discussed this at RC concerning the value of models one time.
At this point, the “A Depression Would Reduce Carbon Emissions” at Marohasy’s http://jennifermarohasy.com/blog/ might need to be changed to “A Depression Might Cause Global Cooling”.
JohnF Pittman–
The aerosols don’t have to trap more than they block. Unlike GHG’s , aerosols can reflect. Also, if the aerosols are aloft, when warm the re-radiate from above the surface, this tends to have a net cooling effect for the surface.
Lucia, doesn’t the IPCC consider that all the radient energy that hits the surface leave as IR, and in that particles also absorb energy on the space side would indicate that an energy balance using IPCC assumptions would indicate that the particles gain net heat (energy) relative to incoming and outgoing radiation?
This “brown cloud” is interesting. It slows down global warming and “is causing hundreds of thousands of deaths in Asia and billions of dollars in economic losses”. So, if it is removed and global warming resumes it will as a result save hundreds and thousands of lives and billions of dollars. Great!
John–
The IPCC AR4 projection appear to be based on the output of AOGCMs. The are physical models with, among other things, multiple layers for the atmosphere.
In principle, aerosols will reflect, absorb or re-radiate from the gridcell in which the aerosols are located in that particular model computation. (I don’t know how the modelers place the aerosols. I haven’t looked into whether they identify a source– like India or China– and then try to track the aerosols as they travel around the globe. My impression is the models used in the AR4 didn’t, but I could easily be wrong on that.)
Anyway, suppose for some odd reason, something with the properties of black carbon were in the stratosphere. It would absorb incoming radiation there. This would tend to warm the stratosphere which re-radiates in all directions. However, since the stratosphere is way up there, and GHG’s are now between the stratosphere and the surface, they absorb in various spectral band. So, now, the GHG’s “blanket” effect tends to prevent the extra heat in the stratosphere from traveling down to the surface. If you like to think of this in terms of electrical resistance, there are now two resisters between the sun and the earth’s surface: The aerosols and the GHG. The net effect would likely be to cool the surface but heat the stratosphere.
On the other hand, if a similar material sits on the surface of snow, it absorbs the radiation at the surface. Now, this heats the ground, re-radiates up (because it can’t really radiate into a solid surface.) The GHGs are now between the ground and the stratosphere, so they act as a partial blanket between the ground and the stratosphere. Compared to the previous example, the net effect is to cool the surface, but heat the stratosphere.
So, it really matters where the aerosols or albedo affecting particles are. As there are all sorts of different aerosols, it matters which aerosols are where!
Yes, that was my point. IIRC, the AR4 indicate a slight overall positive effect of all the aerosols. I just think that a consistantcy of a model’s assumptions is important (even if the assumptions later prove to be wrong) since it makes validating or correcting easier. And what could be more consistant than the IPCC’s use of models describing our earth’s reality. 😉
Lucia,
The report linked by Reid above clearly indicates that these kinds of aerosols would be experted to cause cooling at the surface but warming in the troposphere. This finding suggests that if the aerosols are the source of a recent cooling then there should be a corresponding increase in tropospheric warming. However, we don’t see that which suggests the effect of aerosols is too small to explain the recent trends or that their effect is not understood well enough to draw any conclusions.
I also don’t understand your referenceto the stratosphere since I don’t believe these aerosols get that high. My understanding is only large volcanos have the power to put aerosols into the stratosphere.
All these considerations would be interesting studies for scientists, but really point out in a glaring way that ” the science is not settled”.
Climate scientists are getting funded with billions to settle the science, and until they do, the request that the western societies stifle their economies with carbon taxes and cap and trade is not only premature but completely irresponsible , bordering on the criminal .
Raven–
My the example I discussed was a “counter factual” or analysis of a “what if” scenario. To make the point that where the aerosols are, I exaggerated the sort of “what if” idea and suggested an aerosol with properties “like” black carbon.
Obviously, black carbon is not only in the stratosphere. That’s why I used the term “for some odd reason”.
You are correct that if the aerosols are absorbing significant amounts of heat in the troposphere, then all other things being equal, we expect to see heating where ever they are. As far as I am aware, we have not.
lucia (Comment#6769) November 16th, 2008 at 9:54 am ,
And you can see precisely that effect by looking at the MSU lower stratosphere and lower troposphere records for the effect of the eruptions of El Chichon and Mt. Pinatubo. The LS (t4) temperature spiked up by over 1 C for each eruption and then decayed, apparently to a lower level than before the eruption, although that may be an artifact. The LT temperature dropped by several tenths of a degree and then recovered.
DeWitt– Yep!
The full aerosol problem is thorny. Reading the UNEP document makes that pretty clear. The type and location of aerosols matter, they interact with clouds all sorts of things happen. I skimmed the UNEP document, and I don’t quite know how the aerosol issue happens to relate to the SRES used in the AR4. So, at some point, I’ll read a bit on that.
The SRES specified scenarios. Did it include the ABC? Partially? Not at all? Other aerosols? Etc.? For me, answers to these questions must be deferred in favor of raking leaves.
Judging from these two sites, dust (and presumably other aerosols) acts somewhat like water vapor, cooling the immediate surface and warming the immediate atmosphere,
but resulting in an overall heating of earth’s atmosphere.
http://www.giss.nasa.gov/research/briefs/miller_01/
http://ams.confex.com/ams/pdfpapers/68739.pdf
– A. McIntire
Lucia, a good measure when approaching this problem is optical thickness of the atmosphere. Here is a link to some observations although it is not the most updated. If you find more and better and post or link it I would be thrilled beyond the doggie who gets hours of hugs everyday.
http://www.esrl.noaa.gov/gmd/publications/annrpt23/chapter3_2.htm
Lucia, my main feeling is that this seems like a red herring. There’s not really enough information to determine if the cloud is affecting the climate, and if so, how much or which way (warmer or cooler). And yet it’s trotted out as a reason that the observations don’t agree with the models. Anytime I hear “global temperatures are being held down by xxxxxxxx, masking the underlying warming trend”, serious doubts arise in my mind.
This also paints us into a corner. If we reduce China’s emmissions, the planet will apparently warm. If the western world funds new, cleaner, power generation, will it help? Perhaps they go nuclear. CO2 output drops, but so do these aerosols, and now the warming that was held back by the aerosols happens anyway!
This also paints us into a corner. If we reduce China’s emmissions, the planet will apparently warm. If the western world funds new, cleaner, power generation, will it help? Perhaps they go nuclear.
It is not “WE” who will reduce China’s emissions .
It will be the Chinese government if they choose so and they will not as far as CO2 is concerned because they cannot .
Not unless they want to return to the middle age and set a spark to a powder barrel of 1.3 billion of people .
China is producing 1.3 billion tons of coal and is about to swing from exporter to importer because they can’t increase the production fast enough . China needs every single ton of it to keep their industry working , their living standards increasing and a billion of people more or less happy with a prospect of being happier .
And that is exactly how the Chinese think when you talk with them (most don’t even know that there is such a thing like “global warming” and when I told them about it , they didn’t care) .
So of course they wil eliminate in the course of time the real hazard for their health (basically SO2 and particules) and they will probably do so much faster than the US and Europeans who needed a century for it .
But their CO2 emission will continue to increase as long as their economy grows and they certainly expect to make it grow FAST (5-10%) for the next 50 years .
I certainly pray that no crazy western politicians come with the idea that WE fund some extremely expensive technologies (like CO2 storage) for the Chinese because with the huge number of their power plants the 500 billions of $ needed to save the US economy would be peanuts compared to what the Chinese would ask from us .
As for thescientific aspect of that question , it really begins to be pathetic and sad for the scientific community .
Clearly the only assessement of the situation could be expressed by
“The science has no clue about the climate and no clue about unknown phenomena that will be discovered in the coming years . every single of those phenomena will have the potential to completely change the long terme projections including their sign . The state of knowledge of the climate science in the present state is about 2 on a scale from 1 (field barely discovered , no theory existent) to 10 (fully formulated consistent theory with verified prediction skills and full integration in the verified scientific knowledge) .”
So nothing is settled and scientists would be well adviced to go back in their laboratories and stop tinkering with economy , energy management and our lives .
MikeC–
The UNEP report above discusses optical depth, which has been monitored in various parts of the globe and linked to industrial and home heating practices in various regions.
TomV–
I suspect you are right about China.
Not only do they plan to grown, but they are one of the countries responding correctly to the current economic crisis: by building infrastructure. So, they probably will grow.
They’ll build more CO2 plants, because no one can stop them. They will fix their SO2 problem because as they prosper, they will want to fix it. (Plus, the technology exists.)
http://www.ens-newswire.com/ens/aug2007/2007-08-01-02.asp
Asian Brown Clouds Intensify Global Warming
Brown clouds of pollution over South Asia have multiplied solar heating of the lower atmosphere by 50 percent, finds new research by scientists at Scripps Institution of Oceanography at the University of California-San Diego.
Then there’s another recent paper suggesting a new ice age is descending upon us. Fear not however, Dr. James Hansen says we can control climatic events.
It’s a good them for them they aren’t held accountable for the all flip flops and sloppy science they’ve been dumping.
The truth is more likely these “scientists” have no idea what’s going on when it gets down to the brass tacks.
As lucia knows light scattering by aerosols is a subject I have some expertise in, the UNEP report gives a very good synopsis to a very complex problem. Rather than the CO2 emissions it’s the ‘Brown-ness’ that’s the problem which can be addressed (retro-fitting emission controls on coal-fired power plants for example)
Yep, a most difficult problem among the many inherently complex physical phenomena and processes that make up the Climate. Radiative energy transport with a gaseous participating medium is hard enough. Adding solid particles makes it almost beyond approach from a fundamental basis. Real world particles seldom fit into those that we might have a chance getting a handle on.
Clouds (various phases of water) fall into the same category and are related, of course.
What’s unfortunate, in my opinion, is that the GCMs are tuned using these fuzziest of fuzzy numbers; the radiative transport characteristics of real-world particles.
It would be much better if controlling phenomena corresponded to something well-understood in addition to being powerful. Then we could make less wishy-washy statements.
Phil definitely has expertise in this area.
The reasons I think this will be addressed are a) the technology exists to do this and b) poor air quality is something that bothers people on the ground. So, as the Asian economies improve, they will retrofit emission controls on their power plants.
If the net effect of the brown cloud is cooling, and that’s effect is not correctly accounted for either in the SRES or the models used by the IPCC when writing the AR4, then the ABC might explain the divergence between IPCC projections and the observations.
That said… the implications are not at all good. I wish the narratives weren’t saying “masking warming”. I wish they were saying “masking th warming action of GHG’s”. No net warming is not “masking warming”– it’s not currently warming. But if the reason for that is a combination of negative and positive forcing, we’ll see loads of heating when the ABC is cleaned up. (Which it will be.)
Brownie clouds? I think I shall go to Asia…
Lucia,
I wrote a paper awhile back on the general aerosol issue and the effect of the expected reductions this century (ala Kuznets). I have a briefer non-technical version up at http://www.yaleclimatemediaforum.org/2008/06/common-climate-misconceptions-why-reducing-sulfate-aerosol-emissions-complicates-efforts-to-moderate-climate-change/ but the general gist is that a ~50% projected reduction by century’s end yields a warming of around 0.36 C, though frankly the uncertainty in aerosol forcing is so huge its anyone’s bet what we’d actually end up with.
The relevant future scenarios from the AR4 are here:
Thanks Zeke–
Interesting post over at the yale forum.
Out of curiosity, do you know if the total SO2 emissions actually dropped from 1990 to 2000 as suggested in the figure? (I know there is a big uncertainty interval at 1990 and I’m going by the “dot” marking the center.
The estimates of SO2 dictate forcings in the input to models. So, I’m wondering about that. Thanks, Lucia
Lucia,
I’m having trouble finding handy data (since I have no journal access at work), but http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VF0-43B2JRM-5&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=b7a85c289067c0ef7ba98fac92b0c8b7 might have what you are looking for.
The wikipedia article on global dimming has this:
Referenced to http://www.nasa.gov/centers/goddard/news/topstory/2007/aerosol_dimming.html
Zeke–
That graph is consistent with what I’ve seen before. What’s puzzling me is how these sorts of figures interact with the newer UNEP report. (I’ll get those articles you suggested. Just a bit busy today though.)
Lucia,
Isn’t the area most affected by this cloud showing higher anomalies?
MikeBryant: Evidently, the areas affected by the cloud are mostly showing high anomalies.
The UNEP reports seems to have mostly qualitative discussions (which is fine.) to some extent, the much of the text seems to translate to “this may or may not be the effects of aerosols, we aren’t sure.” ( Given some people’s tendencies to assume something must be criticism– I don’t think expressing uncertainty is a bad thing. It’s a good thing.)
Zeke has the salient point on aerosols. We really don’t know whether to give them a positive or negative sign. So, they “may” do just about anything, which is true of any unknown. It is well known, though, that black soot helps the melting of ice — including Arctic ice. So the brown cloud may be both cooling the Earth and melting the Arctic, which might warm the Earth. Does the possible warming and the possible cooling cancel out? Maybe. Or maybe not. But, the science is settled. Correct?
Darwin–
Evidently, the science is not settled. . . and there is a “spectrum of confidence.” (Does confidence come in colors? Can my level of confidence be said to be “green” or “yellow”?)
Science is never settled. That’s one of it’s features.
But, lucia, does that mean science is in denial?
Darwin,
I don’t think science is in denial. I think “some” bloggers hate the idea that the projections in the AR4 might be off that they are trying to inflate all sorts of estimates of “weather noise”.
Ehmm, sorry for being stupid, but brown clouds are over areas that has warmed a lot. Saying that brown clouds reduced warming by 80% is the same as suggesting that the already high warming of these areas would have been five times greater. That would have created an extreme hotspot, which I don’t find very plausible, and certainly not due to a well mixed green house gas whose main impact is over the poles. Also, the brown particles reside in the atmosphere where they absorb sunlight. Thus the atmosphere should have warmed much more than the surface layer. Which have not happended…
It seems to be an order-of-magnitude problem with this assessment.