Soot Causes Early Snow Melting

A number of global studies have suggested that soot from fossil-fuel combustion forms a blanket on Earth’s snow and ice, which hampers solar reflectivity and causes unnatural warming and melting. A new report focuses on the snow pack in the Rocky, Cascade, and Sierra Nevada mountain ranges in the western U.S., predicting that the soot settling there causes the snow to melt up to a month earlier in the year than normal (J. Geophys. Res., DOI: 10.1029/2008JD011039). Computer models from the lab of atmospheric scientist Yun Qian and colleagues at Pacific Northwest National Laboratory find that the extra heat from soot-absorbed sunlight boosts temperatures of the snow and surrounding air by up to 1.2 °F. The unique models combine the simulation of small sections of landscape, rather than the global landscape, with a simulation of the chemistry of aerosols in the atmosphere, allowing the researchers to predict the amount of soot that would fall in the mountain regions. The researchers note that receding snow also exposes darker terrain, causing further warming and melting. “The snow-melt time change can affect the water supply, aggravating winter flooding and summer droughts,” Qian says.