The Great Lakes of North America, the planet’s largest concentration of fresh water, are thawing earlier each spring, according to an analysis of ice break-ups dating back to 1846.
Barbara Benson of the University of Wisconsin-Madison, and colleagues studied the timing of ice break-up on 61 lakes in Minnesota, Wisconsin, Michigan, New York and Ontario between 1975 and 2004, during which time the average global air temperature rose by 0.4 °C. The team gathered the dates from government databases, lake associations, newspapers and local residents.
On 56 of the lakes the spring thaw showed an earlier trend, occurring two days…
