Soot climate forcing via snow and ice albedos James Hansen* †‡ and Larissa Nazarenko* †
Plausible estimates for the effect of soot on snow and ice albedos (1.5% in the Arctic and 3% in Northern Hemisphere land areas) yield a climate forcing of 0.3 Wm2 in the Northern Hemisphere. The ‘‘efﬁcacy’’ of this forcing is 2, i.e., for a given forcing it is twice as effective as CO2 in altering global surface air temperature.
Global Warming. Soot snowice albedo climate forcing is not included in Intergovernmental Panel on Climate Change evaluations. This forcing is unusually effective, causing twice as much global warming as a CO2 forcing of the same magnitude. This high efficacy is a straight-forward consequence of positive albedo feedbacks and atmospheric stability at high latitudes. Our estimate for the mean soot effect on spectrally integrated albedos in the Arctic (1.5%) and Northern Hemisphere land areas (3%) yields a Northern Hemisphere…
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