Soot almost as bad as CO 2 for global warming

Aharply reducing the amount of "black carbon" - commonly known as soot - in the atmosphere could help slow global warming and buy precious time in the fight against climate change, new research says.

Soot produced by burning coal, diesel, wood and dung causes significantly more damage to the environment than previously thought, two US researchers have found. Black carbon could cause up to 60 per cent of the current warming effect of carbon dioxide, making it an important target for efforts to slow global warming.

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. These deaths are mainly among women and children.

Greg Carmichael, of the University of Iowa, one of the authors of the study, published in Nature Geoscience, said: "Trying to develop strategies that really go after black carbon is a very good short-term strategy and a win-win strategy [from] both climate and air pollution perspectives."

Professor Carmichael and Veerabhadran 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, higher than the estimate of 0.2 to 0.4 watts in last year's report from the Intergovernmental Panel on Climate Change.

The 8 million tonnes of soot released into the atmosphere every year have also created a number of "hot spots" around the world, contributing to rising temperatures.

The plains of south Asia along the Ganges River and continental east Asia are both such hot spots, in part because up to 35 per cent of global black carbon output comes from China and India.

Fine black soot settling on snow and ice - and thus trapping more of the sun's radiative force - have also accelerated the melting of glaciers in the Himalayas and ice cover in the Arctic, two regions that have been hit especially hard by climate change in recent decades.

"A major focus on decreasing black carbon emissions offers an opportunity to mitigate the effects of global warming trends in the short term," the authors conclude.

Most particulates in the atmosphere reduce the warming effect from greenhouse gases by bouncing radiation back into space - so-called global dimming. But black carbon has the opposite effect and professors Ramanathan and Carmichael argue that its contribution to global warming has been underestimated.

The researchers say programs to replace wood-burning stoves with clean technology in developing countries should be pursued to reduce the number of deaths caused by inhaling the smoke.

The authors stress that these measures are not a magic bullet for climate change.

"It is important to emphasise that black carbon reduction can only help delay and not prevent unprecedented climate changes due to CO2 emissions,"