Soot climate forcing via snow and ice albedos

Hansen, James, and Larissa Nazarenko. "Soot Climate Forcing Via Snow and Ice Albedos." Proceedings of the National Academy of Sciences of the United States of America 101.2 (2004): 423-8.

This research study deals with the question if and how soot influences snow and ice albedos and thus serves as a climate forcing, contributing to global warming. The researchers compiled empirical data on fossil fuel black carbon (BC) aerosols amount in snow and compared calculated effects on snow albedo with field data. Main cause for increasing soot is fossil fuels and biomass burning, thus anthropogenic and predominant in the Northern Hemisphere (twice as large as in the Arctic). Soot in snow and ice reduces the visible albedo and increases the absorption of sunlight, measurements in the Alps i.e. show a BC concentration that reduces the albedo by 10 % and doubles the absorption of sunlight. The Soot snow/ice albedo effects contributes to global warming in two ways. First, it raises the global temperature closer to the level of dangerous anthropogenic interference (global warming should be less than 1°C). Second, it leads to ice melting and sea level rise, the meltwater additionally speeds up the process etc. The researchers conclude that the soot climate forcing via snow and ice albedos leads to a rising temperature of +0.3W/m² globally (+ 0.6W/m² in the Northern Hemisphere). Thus the soot effect on snow albedo may be responsible for a quarter of observed global warming. They admit, however, that technology to reduce soot and restore snow albedo to almost original values is within reach, and that cleaner processes are possible or already happen.

Comment: The researchers nevertheless concede that there are several factors which complicate the evaluation of BC amount in snow. Further research is compulsory. Plus this study was accomplished in 2003 (published in 2004), so the data at hand might be outdated.