Ice cover on North America’s Great Lakes has declined 71% since 1973, says a new study published in the Journal of Climate by researchers at NOAA’s Great Lakes Environmental Research Laboratory.
The biggest loser of ice during the 1973 – 2010 time period was Lake Ontario, which saw an 88% decline in ice cover. During the same time period, Superior lost 79% of its ice, Michigan lost 77%, Huron lost 62%, and Erie lost 50%. The loss of ice is due to warming of the lake waters. Winter air temperatures over the lower Great Lake increased by about 2.7°F (1.5°C) from 1973 – 2010, and by 4 – 5°F (2.3 – 2.7°C) over the northern Lakes, including Lake Superior. Lake Superior’s summer surface water temperature warmed 4.5°F (2.5°C) over the period 1979 – 2006 (Austin and Colman 2007).
During the same period, Lake Michigan warmed by about 3.3°F (1.7°C), Lake Huron by 4.3°F (2.4°C), and Lake Erie showed almost no warming. The amount of warming of the waters in Lakes Superior, Huron, and Michigan is higher than one might expect, because of a process called the ice-albedo feedback: when ice melts, it exposes darker water, which absorbs more sunlight, warming the water, forcing even more ice to melt. This sort of vicious cycle is also responsible for the recent extreme loss of Arctic sea ice.
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