Overturning the conventional theory that airborne soot emissions cause regional cooling it has been found that brown clouds of airborne soot can contribute up to a third of atmospheric warming anomalies in the tropics formerly ascribed to CO2 (50 percent of the atmospheric heating caused by CO2 emissions), with its effects ranging as far as the more-temperate American west coast and mountains ranges.
The lead researcher in this study, Prof. V. Ramanathan of the Scripps Institute commented, "The conventional thinking is that brown clouds have masked as much as 50 percent of the global warming .. through ... global dimming ... This study reveals that ... soot particles ... are intensifying the atmospheric warming ... by as much as 50 percent."
Generally speaking the vast Asian Brown Cloud phenomenon has been long suspected as the culprit in disrupting the Indian Ocean monsoon patterns and drought conditions further inland, in Northern China.
Prof. Ramanathan cites the deglaciation of the Himalayas as largely the result of the manifold effects of airborne soot in the region, with both soot-darkened snow melting faster due to lost albedo (reflectivity) and the middle tropospheric warming from airborne soot lying at the same altitude as the beleagured glaciers. Coupled with deforestation that reduces glacial recharge from windborne microclimate precipitation and the associated pall of soot from wood-burning cook fires and the Himalayas are functionally under assault. Ramanathan has also stated that the sooty brown clouds appear to inhibit the formation of low-altitude cumulus clouds that provide a true net cooling benefit in the form of increased cloud-top albedo and surface shading.
Other related studies have found that most airborne soot emissions are from industrial sources - particularly coal-powered industries - with 20-30 percent originating from cook fires and diesel-powered vehicles.
And although this new-found 50 percent heating effect is found only within thicker mid-atmospheric brown cloud, the problem persists - to a lesser degree - throughout the vast Pacific region, where up to 40 percent of the observed warming is caused by the westerly soot borne from Asia. With the Pacific accounting for 30% of the Earth's surface that may account for 12 percent of global warming, worldwide.
With soot being largely responsible for the Arctic melt-off that constitutes 25 percent of the observed global warming of the past century, we might readily account for 33 percent of all human-caused global warming being due to soot.
My comments:
Were another 5 - 10 percent of all global warming found to result from other sources of soot in the industrialized West and in the tropics and subtropics (wood burning, slash & burn agriculture), we might be looking at a net 35 - 40 percent of global warming thus far being due to readily-mitigated soot.
The upside of this is manifold: While these discoveries don't exculpate CO2, it may provide a solution for the short-term and give human civilization a phased approach to dealing with the long-term problem. Soot is not only easily scrubbed from industrial sources, it doesn't persist in the atmosphere for more than a few months at most (if not weeks). We could observe tangible, meaningful results in addressing climate change, with the Arctic and Greenland ice sheets regenerating and the monsoon cycles in Asia resuming their normal patterns.
See also:
http://www.timesonline.co.uk/tol/news/world/asia/article2189190.ece
http://www.sciam.com/article.cfm?id=brown-haze-from-cooking-fires-cooking-earth
What is the composition of those brown clouds in Asia?