Black Carbon Reduction of Snow Albedo

Kirchstetter, T. W., Lawrence Berkeley National Laboratory

Radiation Processes

Aerosol Life Cycle

Hadley OL and TW Kirchstetter. 2012. "Black-carbon reduction of snow albedo." Nature Climate Change, 2(6), 10.1038/nclimate1433.


Spectrally weighted snow albedo over the 300–2,500 nm solar spectrum: derived from our experiments (dots, 1 standard deviation) and modelled using SNICAR (shaded bands). Upper and lower boundaries of the shaded bands correspond to modelled albedo assuming BC mass absorption cross-sections, at 550 nm, of 7.5 and 15 m2/g, respectively.


Spectrally weighted snow albedo over the 300–2,500 nm solar spectrum: derived from our experiments (dots, 1 standard deviation) and modelled using SNICAR (shaded bands). Upper and lower boundaries of the shaded bands correspond to modelled albedo assuming BC mass absorption cross-sections, at 550 nm, of 7.5 and 15 m2/g, respectively.

Climate models indicate that the reduction of surface albedo caused by black carbon contamination of snow contributes to global warming and near-worldwide melting of ice. However, model predictions of BC-caused snow albedo reduction over a range of BC levels and snow grain sizes have not been verified by measurements. The main reason is that the BC effect is typically masked in natural environments by other variables that influence albedo, such as snow grain size, snow density, snow depth and the interaction of sunlight with the underlying surface, tree cover and solar zenith angle.

In this study, we developed an approach to isolate the effect of BC on snow albedo through laboratory experimentation. We developed processes for making both pristine and BC-laden snow and techniques for measuring the morphology, albedo, and BC content of snow. These methods have allowed us to quantify the snow albedo reduction associated with increasing amounts of BC and as a function of snow grain size.

We verified that black carbon contamination appreciably reduces snow albedo at levels that have been found in natural settings. Increasing the size of snow grains in our experiments decreased snow albedo and amplified the radiative perturbation of black carbon, which justifies the aging-related positive feedbacks that are included in climate models. Moreover, our data provide an extensive verification of the snow, ice, and aerosol radiation model, which will be included in the next assessment of the Intergovernmental Panel on Climate Change.