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Soot emissions much worse than we thought, say scientists

The impact of soot on our climate has been greatly underestimated, according to a new landmark study.

It is the second largest man-made contributor to global warming and its direct warming effect could be about twice previous estimates, the new study by the University of Leeds and the US National Oceanic and Atmospheric Administration (NOAA) suggests.

Tailpipe exhaust of a diesel car, emitting black carbonSoot-also known as black carbon-has a warming effect of about 1.1 watts per square meter (W/m2), approximately two thirds of that of the largest man made contributor to global warming, carbon dioxide, and greater than that of methane.

Huge quantities of man-made soot enter the atmosphere every year, with about 7.5 million tonnes emitted in 2000 alone. These emissions come from a variety of sources. The largest global cause is the burning of forest and savannah grasslands, but diesel engines account for about 70 per cent of emissions from Europe, North America and Latin America.

The results of the study, published in the Journal of Geophysical Research Atmospheres, that there may be a greater potential to curb warming by reducing soot emissions than previously thought.

Health and climate impact

Professor Piers Forster from the University of Leeds’ School of Earth and Environment, who co-led the study, said: “There are exciting opportunities to cool climate by cutting soot emissions, but it is not straightforward. Reducing emissions from diesel engines and domestic wood and coal fires is a no-brainer, as there are tandem health and climate benefits.

Soot is known to exacerbate respiratory conditions. 

“If we did everything we could to reduce these emissions, we could buy ourselves up to half a degree less warming—or a couple of decades of respite,” Professor Forster said.

The 232 page report took four years to complete and is the first comprehensive and quantitative analysis of the role of black carbon in the climate system. Its best estimate is that the effect of soot is about two times that of previous estimates including the estimate from the Intergovernmental Panel on Climate Change (IPCC) Assessment in 2007.

Co-lead author David Fahey from the U.S. National Oceanic and Atmospheric Administration (NOAA) said: “This study confirms and goes beyond other research that suggested black carbon has a strong warming effect on climate, just ahead of methane.”

Reducing black carbon emissions has a major advantage too: the benefit would be seen almost immediately because black carbon’s influence is a continuous short-term process. While carbon dioxide remains in the atmosphere for relatively long periods, existing soot emissions are washed out of the atmosphere in a few weeks.

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Faye Sunderland

Filed under: Global warming, Green credentials

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