Letters

A climate tipping point In Janet Raloff’s article “Forest invades tundra” (SN: 7/5/08, p. 26), there seems to be a paradox. Raloff says that the albedo from normal snow coverage of the tundra “helps maintain the region’s chilly temperatures,” implying that the coverage also preserves the mats of plant matter. A little later in the article, Ken Tape explains how the arrival of tiny shrubs traps snow, insulating and warming the soil beneath and stimulating the growth of bacteria.