Soot, important factor in global warming

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Soot, fossil and biomass burning, as well as from diesel engines, may be responsible for as much as 25 percent of observed global warming over the past century. Soot reducing the ability of snow and ice to reflect sunlight, according to a computer simulation published in a recent paper (Dec. 2003) from Goddard Institute for Space Studies (NASA).

The effects of soot in changing the climate may be forgotten climate factor. Reducing atmospheric soot levels could help to slow global warming relatively simply. Soot is “a more all-around ‘bad actor’ than has been appreciated.

Soot is twice as potent as carbon dioxide in raising surface air temperatures in the Arctic and the Northern Hemisphere.

“We suggest that soot contributes to near worldwide melting of ice that is usually attributed solely to global warming,” National Aeronautics and Space Administration scientists James Hansen and Larissa Nazarenko wrote in a paper published in the Proceedings of the National Academy of Sciences.

Soot, important factor in global warming

Easier than cutting carbon dioxide

The researchers are from the Goddard Institute for Space Studies, part of the US space agency Nasa, and Columbia University Earth Institute. In the report, “Soot Climate Forcing Via Snow And Ice Albedos,” it is suggested that trying to reduce the amount of soot produced would be easier than cutting carbon dioxide and other greenhouse gas emissions.

Soot is defined as “mainly black carbon, the dusty by-product of incomplete combustion of fossil fuels, plants and wood”. Soot is a blackened material formed mainly from carbon particles that are, along with salts and dust, by-products of burning fossil fuels and vegetation.

Its concentrations vary in time and place, but they are often high over China and India, where coal and organic fuels are used domestically, and over Europe and North America, where the main source of fuel is diesel oil.

Soot is suspected of being a major contributor to approximately one million premature deaths globally per year that are blamed on particulate air pollution.

Soot is the aerosol most responsible for reducing atmospheric transparency and visibility, by so much in India and China that agricultural productivity is reduced an estimated 10-20% with additional loss from soot deposited on plant leaves, according to Dr. Hansen.

Soot, important factor in global warming

Soot on snow and ice

The study modelled how soot particles affect climate when they darken snow and ice, causing it to absorb sunlight rather than reflect it.

It was the results of this modelling that indicated that soot is twice as effective as carbon dioxide in raising global surface air temperatures.

The report says high soot emissions may have contributed substantially to global warming over the past century, notably to the growing trend in recent decades for ice, snow and permafrost to melt earlier in the spring.

Soot, important factor in global warming

The authors believe there may be a second effect at work here as well - they suggest soot may cause glaciers, sea ice and ice sheets to melt at lower temperatures than they would otherwise.

This could happen, because the black carbon absorbs more solar energy than clean snow and ice. The study conclude that restoration of snow albedos to something approaching pristine pre-anthropogenic values would have the double benefit of reducing global warming and global ice melt compared to reducing CO2 emissions.

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