Mention global warming, and most people picture expanding deserts, melting glaciers, and seas slowly submerging the shore. But now, near the Great Lakes of North America, scientists may have found an unexpected indicator of global warming: more snowfall.
The Great Lakes region already gets a lot of snow. It's brought there by storms and cold, dry winds from Canada that suck moisture and warmth from the lake surface. The winds carry clouds eastward to drop snow within a couple of hundred kilometers of the lake shore. The colder the air and the warmer the water, the more snow deposited downwind. Previous work suggested that lake-effect snowfall has grown more abundant over the last half-century, but the cause wasn't clear.
To investigate, a team of scientists led by geographer Adam Burnett of Colgate University in Hamilton, New York, compared historical records of snowfall at 15 weather stations within the lake-effect snowfall region with 10 stations outside the region. In the 1 November issue of the Journal of Climate, the team reports a marked increase in lake-derived snowfall since the 1930s and '50s.
Backing that conclusion is an analysis of sediments from three small lakes inside the lake-effect region. Isotopes in these sediments suggest that over the last century ever more precipitation has been coming from the Great Lakes. (Stations outside the region, however, showed no trend at all, ruling out large-scale shifts of northeast weather.) The team points out that the Great Lakes seem to be warming. This would create a larger gap between water temperature and air temperatures in winter, and an increase in snowfall, Burnett suggests.
Evaluating historical snowfall records is notoriously difficult, says David Kristovich, a meteorologist at the Illinois State Water Survey and the University of Illinois, Urbana-Champaign. But the team's use of multiple lines of evidence makes the case intriguing, he says. And he adds that because of the strong influences of the Great Lakes on local weather, that region is particularly well-suited for looking at regional responses to changes in global climate.