Infrastructure protectionBlack carbon’s contribution to climate change underestimated

Published 22 January 2013

Black carbon is the second largest man-made contributor to global warming and its influence on climate has been greatly underestimated, according to the first quantitative and comprehensive analysis of this issue; black carbon is believed to have a warming effect of about 1.1 Watts per square meter (W/m²), approximately two thirds of the effect of the largest man made contributor to global warming, carbon dioxide.

Black carbon exhaust from ashalt production // Source: bigstock.com

Black carbon is the second largest man-made contributor to global warming and its influence on climate has been greatly underestimated, according to the first quantitative and comprehensive analysis of this issue.

The landmark study, published Saturday in the Journal of Geophysical Research-Atmospheres, a journal of the American Geophysical Union, says the direct influence of black carbon, or soot, on warming the climate could be about twice previous estimates. 

An International Geosphere-Biosphere Program release reports that accounting for all of the ways it can affect climate, black carbon is believed to have a warming effect of about 1.1 Watts per square meter (W/m²), approximately two thirds of the effect of the largest man made contributor to global warming, carbon dioxide.

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.” The study, a four-year, 232-page effort, led by the International Global Atmospheric Chemistry (IGAC) Project, is likely to guide research efforts, climate modeling, and policy for years to come.

The report’s best estimate of direct climate influence by black carbon is about a factor of two higher than most previous work, including the estimates in the last Intergovernmental Panel on Climate Change (IPCC) Assessment released in 2007, which were based on the best available evidence and analysis at that time.

Scientists have spent the years since the last IPCC assessment improving estimates, but the new assessment notes that emissions in some regions are probably higher than estimated. This is consistent with other research that also hinted at significant under-estimates in some regions’ black carbon emissions. 

The results indicate that there may be a greater potential to curb 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. 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,” says co-author Professor Piers Forster from the University of Leeds’s School of Earth and Environment.

The international team urges caution because the role of black carbon in climate change is complex.  “Black