A while back I advanced the hypothesis that soot was a major driver of sea ice melting in the Arctic. Black carbon deposits on ice and snow tend to force them to melt much faster by reducing their albedo. I hypothesized that this might explain why there were record low summer sea ice coverages of late in Arctic sea ice but relatively average winter sea ice extents — black carbon can’t build up in the fall and winter because they are constantly covered with new snow and ice while soot that falls in the summer stays on the surface.
By the way, this would be good news – an anthropogenic effect due to soot is MUCH easier to correct than one due to CO2, as we know how to have a prosperous fossil fuel powered economy without soot but we don’t know how to have one without CO2.
Kevin Lawton has a post correlating past warming with areas that are susceptible to thaws, concluding that black carbon may have a role in past warming. I have to think about his argument more, but he has some good links to recent work on black carbon and warming.