How is it that – for a settled science – all these new “cooling” mechanisms are suddenly being found? Could it have something to do with trying to rescue climate models which have failed to predict the slowdown in global warming? “Climate science” is now hunting for previously unidentified cooling effects to explain the warming that has not happened.
This time it is the brightness of clouds! Apparently manmade pollution in the form of organics can enhance the formation of clouds which happen to be brighter from above and which reflect more of the suns radiation. Voilà! An as yet unidentified cooling effect.
But this conclusion comes not from measurements but from yet another model!
From the University of Machester (via Alpha Galileo):
Organic vapours affect clouds leading to previously unidentified climate cooling
University of Manchester scientists, writing in the journal Nature Geoscience, have shown that natural emissions and manmade pollutants can both have an unexpected cooling effect on the world’s climate by making clouds brighter.
Clouds are made of water droplets, condensed on to tiny particles suspended in the air. When the air is humid enough, the particles swell into cloud droplets. It has been known for some decades that the number of these particles and their size control how bright the clouds appear from the top, controlling the efficiency with which clouds scatter sunlight back into space. A major challenge for climate science is to understand and quantify these effects which have a major impact in polluted regions.
The tiny seed particles can either be natural (for example, sea spray or dust) or manmade pollutants (from vehicle exhausts or industrial activity). These particles often contain a large amount of organic material and these compounds are quite volatile, so in warm conditions exist as a vapour (in much the same way as a perfume is liquid but gives off an aroma when it evaporates on warm skin).
The researchers found that the effect acts in reverse in the atmosphere as volatile organic compounds from pollution or from the biosphere evaporate and give off characteristic aromas, such as the pine smells from forest, but under moist cooler conditions where clouds form, the molecules prefer to be liquid and make larger particles that are more effective seeds for cloud droplets.
“We discovered that organic compounds such as those formed from forest emissions or from vehicle exhaust, affect the number of droplets in a cloud and hence its brightness, so affecting climate,” said study author Professor Gordon McFiggans, from the University of Manchester’s School of Earth, Atmospheric and Environmental Sciences.
“We developed a model and made predictions of a substantially enhanced number of cloud droplets from an atmospherically reasonable amount of organic gases.
“More cloud droplets lead to brighter cloud when viewed from above, reflecting more incoming sunlight. We did some calculations of the effects on climate and found that the cooling effect on global climate of the increase in cloud seed effectiveness is at least as great as the previously found entire uncertainty in the effect of pollution on clouds.”
- ‘Cloud droplet number enhanced by co-condensation of organic papers,’ by Gordon McFiggans et al, will be published in Nature Geoscience on Sunday 5 May 2013.
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