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Black carbon is second largest man-made contributor to global warming, say researchers

An international team of researchers posits that black carbon is the second largest man-made contributor to global warming. Researchers also think that its influence  on climate has been greatly underestimated.

Researchers believe that the direct influence of black carbon, or soot, on climate could be about twice previous estimates. Keeping in mind all the ways it can affect climate, black carbon is thought to have a warming effect of about 1.1 Watts per square meter, which is approximately two thirds of the effect of the largest man-made contributor to global warming, carbon dioxide.

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

The study, which was led by the International Global Atmospheric Chemistry (IGAC) Project, found that the direct influence of black carbon on climate is about a factor of two higher than most previous work on the subject, including the estimates in the 2007 Intergovernmental Panel on Climate Change (IPCC) Assessment.

The study’s findings also reveal that there may be a greater chance of curbing global warming by reducing black carbon emissions than previously thought.

“There are exciting opportunities to cool climate by reducing soot emissions but it is not straightforward,” says co-author Professor Piers Forster from the University of Leeds’s Faculty of Earth and Environment. “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.”

Despite the significance of these findings, researchers warn that people should be careful about jumping to the wrong conclusions about black carbon’s influence on climate, as the role of black carbon in climate change is extremely complex.

“Black carbon influences climate in many ways, both directly and indirectly, and all of these effects must be considered jointly,” says co-lead author Sarah Doherty of the University of Washington.

According to researchers, the dark particles take in solar radiation; they can advance the formation of clouds that can have either a cooling or warming impact; and soot can fall on the surface of snow and ice, assisting with warming and increasing melting. Some sources of black carbon also emit other particle whose effects counteract black carbon, supporting a cooling effect.

The researchers quantified all the complexities of soot and the effects of co-emitted pollutants for different sources, while also considering uncertainties in measurements and calculations. Researchers want public officials to look at all emissions from each source when thinking about ways to curb black carbon emissions for the benefit of the environment and human health.

The study also reveals that black carbon is a significant cause of the rapid warming in the northern hemisphere at mid to high latitudes, including the northern United States. Researchers believe that lowering black carbon emissions might have a significant impact on reducing regional climate change.

“Policy makers, like the Climate and Clean Air Coalition, are talking about ways to slow global warming by reducing black carbon emissions,” says co-lead author Tami Bond from the University of Illinois at Urbana-Champaign. “This study shows that this is a viable option for some black carbon sources and since black carbon is short lived, the impacts would be noticed immediately. Mitigating black carbon is good for curbing short-term climate change, but to really solve the long-term climate problem, carbon dioxide emissions must also be reduced.”

The study, which is considered the first quantitative and comprehensive analysis of this issue, was recently published in the Journal of Geophysical Research-Atmospheres.