According to the first comprehensive analysis of the issue, soot, technically known as black carbon, is the second largest man-made contributor to global warming.

The study, co-led by the University of Leeds and published in the Journal of Geophysical Research Atmospheres, has revealed that black carbon has a warming effect of about 1.1 Watts per square meter (W/m2).

This is approximately two-thirds of that of the largest man-made contributor to global warming, carbon dioxide, and greater than that of methane.

The 232-page report, which took four years to complete, suggests that there is greater scope to reduce global warming through reducing black carbon emissions.

University of Leeds’ school of earth & environment’s Professor Piers Forster, 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.

“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.”

Man-made soot is culpable for a large percentage of emissions every year – in 2000 approximately 7.5 million tonnes were emitted alone.

The largest global cause is the burning of forest and savannah grasslands, but diesel engines account for about 70% of emissions from Europe, North America and Latin America.

Black carbon is made up of small dark particle which directly heat up the atmosphere by absorbing incoming and scattered heat from the sun.

It can promote the formation of clouds that can have warming impacts and can also fall on the surface of snow and ice, promoting warming and increasing melting by reducing light reflection.

One major advantage of reducing black carbon emissions is that the effects would be seen almost immediately because, while carbon dioxide remains in the atmosphere for long periods, existing soot emissions are washed out in a few weeks.

Despite this, black carbon reduction is just part of the solution for curbing climate change.

Forster said: “Soot mitigation is an immediate effect but helps for a short time only. We will always need to mitigate CO2 to achieve a long-term cooling.”

Conor McGlone

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