Jul 11 2008
Aerosols, Clouds, and European Warming
Has anyone been able to determine which scientific papers the media will report? It seems like a crap shoot to me. The latest is about aerosols and their effect on surface temperatures. The journal Geophysical Research Letters published a paper titled Aerosol and cloud effects on solar brightening and the recent rapid warming by a group of scientists mostly from Switzerland.
They found that the temperatures in Europe have been increasing faster than expected if greenhouse gases were the only cause. They also calculate that aerosols will cause a surface cooling. This is not news. The “surprising” part (their word) is that the cooling is mostly due to the direct aerosol effect and not the indirect cloud effect.
I’ve included the abstract, just in case anyone was maybe interested in reading the paper.
The rapid temperature increase of 1°C over mainland Europe since 1980 is considerably larger than the temperature rise expected from anthropogenic greenhouse gas increases. Here we present aerosol optical depth measurements from six specific locations and surface irradiance measurements from a large number of radiation sites in Northern Germany and Switzerland. The measurements show a decline in aerosol concentration of up to 60%, which have led to a statistically significant increase of solar irradiance under cloud-free skies since the 1980s. The measurements confirm solar brightening and show that the direct aerosol effect had an approximately five times larger impact on climate forcing than the indirect aerosol and other cloud effects. The overall aerosol and cloud induced surface climate forcing is ~+1 W m^2 dec-1 and has most probably strongly contributed to the recent rapid warming in Europe.
Offhand, I would not expect the aerosol indirect effect (AIE) to be large over the continents. The AIE is a result of clouds being formed where there are insufficient nucleation particles. When more particles are added, there are more cloud drops formed, and this makes the cloud more reflective.
Over the ocean, there are few aerosols - typically in the few hundreds of particles per cubic centimeter. Over the continents, aerosol concentrations are much higher - thousands of particles per cubic centimeter. When forming clouds over the ocean, there will be fewer cloud condensation nuclei for the cloud droplet to form on. This means that the AIE will be larger over the ocean than over the land.
Secondly, the AIE is mostly seen in thin clouds. For thick clouds, the albedo can be more influenced by the actual thickness of the clouds than the cloud drop concentration. So it is not surprising that they did not find a strong AIE signal in their analysis. If they had don’t this over the pristine ocean, then I would expect the AIE to be greater than the direct effect.
But the media reports have been less than clear. For instance, “Aerosol concentrations dropped by up to 60 per cent over the 29-year period, while solar radiation rose by around 1 watt per square metre”. If solar radiation reaching the surface has increased by 1W/m2, and climate sensitivity is around 3 0.8 C/W/m2, shouldn’t the surface temperature have increased by 3 0.8C without the effects of greenhouse gases?
The right-wing blogs got it wrong too. Cart, horse, horse, cart. The horse goes in front. It’s not that the lack of aerosols cause warming, it’s that the aerosols themselves cause cooling. Then when you take them away, it gets warm again. Which is exactly what has happened.
He also confuses aerosols (particulate matter, particulates, solids, etc.) with photochemical smog (volatile organic carbons, nitrogen oxides, ozone, gases, etc.). But that’s just an innocent mistake, right?
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10 Responses to “Aerosols, Clouds, and European Warming”
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Shocker. Newbusters gets it wrong, again. The comments left weren’t that surprising. And who says the right hates science?
If I understand this, then would you expect a lower temperature down wind of the Chinese mainland? I assume there would be increased aerosols in the industrial pollution, or are there too many competing processes to show a clear signal?
Atmoz: In a slightly different abstract for what appears to be the same paper, the authors quantified the contribution. The last sentence reads, “First order estimates indicate that direct and indirect aerosol forcing combined may have produced about 50 percent of the rapid warming since the 1980s.”
http://www.cosis.net/abstracts/EGU2008/03023/EGU2008-A-03023.pdf?PHPSESSID
Yet the AMO is reported to be responsible for a good portion of the high-latitude warming since it started its rise from minimum around 1976. RealClimate, in their Glossary for the AMO, claims the Atlantic Multidecadal Oscillation “is believed to describe some of the observed early 20th century (1920s-1930s) high-latitude Northern Hemisphere warming and some, but not all, of the high-latitude warming observed in the late 20th century.”
http://www.realclimate.org/index.php?p=38
What’s left?
3 C/W/m^2 !!!!!
I sure hope not.
[Reply: Oops. Was thinking 3C for double CO2. Thanks for catching that. Fixed now.]
Natural variation is assumed to be non-existent so the difference between warming expected and warming achieved between 1980 and 1998 must be an aerosol decrease. Uh huh! But Hadley have used that non-existent natural variation to explain a lack of recent warming. And others (eg Ramalamadingdong) use an aerosol increase to explain a lack of recent warming. Three mutually exclusive outcomes and yet you criticize journalists for being confused. This is hand-waving by numbers. Now if scientists could just make that leap to using 3 variables we might be able to take them seriously.
Ok the effects of aerosols is a contested item because it is the “filler” used in climate models to explain certain devaitions from the correlation in the temperature record with GHG concentrations. The problem now is that the actual mechanism of how aerosols cool the planet is being called into question. The end result is we still have a cooling influence, but it may be a larger effect and for a modified order of applicable hypotheses.
If the cooling effect is larger than previously suggested it means that other variables in climate Models would need to be examined to account for the instrument temperature record deviations.
This study is limited spatially and may be the result of a combination of influences regional in nature, I would not look for any changes to climate models anytime soon.
And so science marches on.
JamesG, no one who follows climate science is going to be fooled by your blatant lie.
By “follows climate science” you clearly don’t mean reading the actual papers. Actually it gets worse, the same authors had written:
“Philipona, R., B. Dürr, A. Ohmura, and C. Ruckstuhl (2005), Anthropogenic greenhouse forcing and strong water vapor feedback increase temperature in Europe, Geophys. Res. Lett., 32, L19809, doi:10.1029/2005GL023624.”
About which, Philipona states, “In summary what the paper shows is that the observed temperature increase in Europe is not due to large scale circulation but is driven by radiative effects which increase evapotranspiration at the surface.”
That was before they dug up the aerosol argument of course! I guess that’s science marching on: Always with weasel words in the actual paper but with 100% certainty elsewhere, and we should all just ignore those frequent contradictions and about-faces.
Here are Freeman Dyson’s thoughts..
http://www.nybooks.com/articles/21494
Atmoz,
I have been saying this for months at this site and at RC. I’m glad you posted a paper that supported my hypothesis. All anyone has to do is to look at the satellite-based temperature trend of NH vs SH over the last 30 years (i.e., the divergenge in anomalies). Also, one must recognize that 80% of aerosols are produced in the NH. I have a PhD and have published in peer reviewed journals. I saw this conclusion quite early when diving into the data. I find it surprising that no one at RC supported my hypothesis (in fact, they argues that aerosols are getting worse, not better). What does this say about the capabilities of the so-called scientists at RC? If they can’t get this straight, how can one believe anything they say? Frankly, I was hoping for a more balanced and robust argument for AGW, and honestly, I couldn’t be more disappointed.