A pair of researchers from the NASA Goddard Institute for Space (GISS) and Columbia University have found that black carbon is responsible for 50%, or almost 1 °C of the total 1.9 °C increased Arctic warming from 1890 to 2007. The paper by Drew Shindell and Greg Faluvegi of Columbia, published in Nature Geoscience, also notes that most of the Arctic warming—1.48 °C of the 1.9 °C—occurred from 1976 to 2007.
The study is the first to quantify the Arctic’s sensitivity to black carbon emissions from various latitudes, and concludes that the Arctic responds strongly to black carbon emissions from the Northern Hemisphere mid-latitudes, where the emissions and the forcing are greatest.
Black carbon is an aerosol produced from the incomplete combustion of fossil fuels and biomass and is estimated to be the second or third largest contributor to climate change. Its emissions cause damage in two ways: while in the atmosphere, the dark particulates absorb sunlight and emit it as heat; when it falls back to earth it can darken snow and ice, reducing their reflectivity and accelerating melting.
Arctic warming is more than twice the observed global average surface warming of 0.78 °C above pre-industrial levels. According to another study published by Lenton, et al. in the Proceedings of the National Academy of Sciences last year (earlier post), this increased warming may soon lead to the disappearance of the Arctic summer ice, which would in turn accelerate Arctic warming by exposing darker heat-absorbing water now covered by heat reflecting ice. This would also increase the risk of releasing methane and other greenhouse gases from permafrost and from methane hydrates in the ocean, which could lead to a runaway feedback process.
Because black carbon only remains in the atmosphere for several days to weeks, reducing it can bring about almost immediate mitigation of warming, whereas decreases in temperature lag reductions in CO2 by 1,000 years or more (earlier post).
Drew Shindell and Greg Faluvegi (2009) Climate response to regional radiative forcing during the twentieth century. Nature Geoscience 2, 294 - 300 doi: 10.1038/ngeo473