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Sci Tech
The effect of soot on climate
JAMES RANDERSON
Soot produced by burning coal, diesel, wood and dung causes significantly more damage to the environment than previously thought, according to research published recently. So-called ‘black carbon’ could cause up to 60 per cent of the current warming effect of carbon dioxide, according to the U.S. researchers, making it an important target for efforts to slow global warming.
Number of deaths
Around 400,000 people are estimated to die each year due to inhaling soot particles, particularly because of indoor cooking on wood and dung stoves in developing countries. Professor Greg Carmichael and Professor V. Ramanathan, at Scripps Institution of Oceanography in San Diego, put together data from satellites, aircraft and surface instruments on the warming effect from black carbon. They conclude that its effect in the atmosphere is around 0.9 watts per square metre.
Most particulates in the atmosphere reduce the warming effect from greenhouse gases by bouncing radiation back into space — so-called global dimming.
Opposite effect
But black carbon has the opposite effect and Ramanathan and Carmichael argue that its contribution to global warming has been underestimated. “The aerosols in aggregate are either acting to, you could say, cool the atmosphere or mask the effect of CO{-2},” said Carmichael, “[Black carbon] is the only component of this aerosol mix that in and of itself is a heating element.”
Previous estimates had not taken into account the fact that it has a larger impact at high altitude in the atmosphere and that it interacts with other particulates.
Guardian Newspapers Limited 2008
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