Expeditions to the Russian Arctic to Survey Black Carbon in Snow

Abstract

Snow is the most reflective natural surface on Earth, with an albedo (the ratio of reflected to incident light) typically between 70% and 85%. Because the albedo of snow is so high, it can be reduced by small amounts of dark impurities. Black carbon (BC) in amounts of a few tens of parts per billion (ppb) can reduce the albedo by a few percent depending on the snow grain size [Warren and Wiscombe, 1985; Clarke and Noone, 1985].An albedo reduction of a few percent is not detectable by eye and is below the accuracy of satellite observations. Nonetheless, such a reduction is significant for climate. For a typical incident solar flux of 240 watts per square meter at the snow surface in the Arctic during spring and summer, an albedo change of 1% modifies the absorbed energy flux by an amount comparable to current anthropogenic greenhouse gas forcing. As a result, higher levels of BC could cause the snow to melt sooner in the spring, uncovering darker underlying surfaces (tundra and sea ice) and resulting in a positive feedback on climate [Hansen and Nazarenko, 2004].