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Black soot responsible for 25 per cent of global warming

 
Last Updated: Saturday 04 July 2015

Snow covered with black soot a to date, carbon dioxide has been mainly blamed for global warming. But black carbon particles (commonly known as soot) have also done a fair amount of damage, a recent study indicates. As per its findings, black soot, the dusty by-product of the incomplete combustion of fossil fuels, is responsible for about 25 per cent of the observed rise in global temperatures since 1880.

Researchers from the us National Aeronautical and Space Administration (nasa) conducted the study. James Hansen and Larissa Nazarenko examined the soot's effects on snow albedo -- ability of snow/ice to reflect sunlight back into space. They used a computer model to simulate how soot particles affect climate when they darken snow/ice. The model mainly incorporated data from nasa's Terra and Aqua satellites, which monitor the snow cover and its sunlight reflectivity at multiple wavelengths.

The researchers found that fresh snow reflects more than 90 per cent of the sunlight. But the black soot increases the absorption rate, and thus triggers a chain reaction -- the extra absorbed energy melts the snow at a faster rate, and the wet snow absorbs more light than dry snow. The liquefied form of snow (water) absorbs about 90 per cent of the sunlight. "Now we now why glaciers are melting faster than expected. The increased absorption of snow is altering the water cycles, as well as increasing the global temperature," says Hansen. The simulations showed that some of the largest warming effects occurred when there was heavy snow cover and sufficient sunlight. Local soot concentrations in snow vary widely, but the researchers estimate that it reduces light reflection by 1.5 per cent in the Arctic and by three per cent over land in the Northern hemisphere.

Soot's effect on snow albedo has been neglected in previous studies. The Intergovernmental Panel on Climate Change does not include the effects in its evaluations. The findings, published in the Proceedings of the National Academy of Sciences , could be good news for those who want to combat global warming -- soot emissions are easier to reduce than carbon dioxide. Hansen says technology exists to more cleanly burn fossil fuels without releasing large quantities of soot. "But the findings do not change the need to reduce carbon dioxide levels," he cautions.

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