Role of black carbon in the Arctic’s new normal

In “The Arctic shifts to a new normal” (Physics Today, October 2013, page 35 ), Martin Jeffries, James Overland, and Don Perovich state, without citing a reference, that “the warming might be further enhanced by the rise in atmospheric concentrations of carbon aerosols… . Black carbon deposition might be reducing the albedo and thus accelerating the melting of sea ice and of snow and ice on land.”

Actually, the atmospheric concentrations of black carbon have been declining, as shown at all three of the atmospheric observatories making continuous measurements on the coast of the Arctic Ocean: Alert, Canada; Barrow, Alaska; and Ny Ålesund, Svalbard, Norway. ¹ Alert has the longest record; the wintertime peaks there for 2006–8 were one-third of their average for 1989–91. The decline of Arctic black carbon has been attributed to the dissolution of the Soviet Union, which resulted in the closing of emission sources in Russia and Eastern Europe and depopulation of the Russian Arctic. ² Correspondingly, the black carbon content of Arctic snow is now no higher than it was 30 years ago. ³ The dramatic loss of Arctic sea ice must therefore be attributed to other causes.