A new analysis of data from buoys, weather stations, and historical ice records indicates that summer surface temperatures of Lake Superior have increased approximately 2.5°C since 1979, roughly twice the rate of regional atmospheric warming.
Austin and Colman hypothesize that declining winter ice cover is causing the lake to absorb more solar radiation than it did in past years. The increased absorption, in turn, causes earlier stratification of the lake at a rate of roughly half a day per year.
Large mid-latitude lakes often freeze over in winter, mix thoroughly during spring and fall, and stratify in summer due to solar heating. The earlier start to Lake Superior's stratified season significantly increases the period over which the lake warms during the summer months, resulting in higher summer temperatures. Though little-studied, the response of large lakes to climate change will likely have an important regional effect.
Title: Lake Superior summer water temperatures are increasing more rapidly than regional air temperatures: a positive ice-albedo feedback
Authors: Jay A. Austin: Large Lakes Observatory and Department of Physics, University of Minnesota, Duluth; Steven M. Colman: Large Lakes Observatory and Department of Geology, University of Minnesota, Duluth.
Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL029021, 2007
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