AGU: Geophysical Research Letters

 

Editors' Highlight

Lake Superior summer water temperatures are increasing more rapidly than regional air temperatures

Though little studied, the response of large lakes to climate change will likely have an important regional effect. Large midlatitude lakes, which often freeze over in winter, thoroughly mix during spring and fall, and stratify in summer due to solar heating, provide a relatively closed environment to study interannual relationships between ice cover, lake response, and long-term warming. Focusing on Lake Superior, Austin and Colman (2007) analyzed data from buoys, weather stations on and near the lake, and historical ice records, and found that summer surface water temperatures have increased approximately 2.5°C since 1979, roughly twice the rate of regional atmospheric warming. They hypothesize that this discrepancy is caused by declining winter ice cover, which increases the ability of the lake to absorb solar radiation. This causes the onset of the stratified warm layer to occur earlier at a rate of roughly half a day per year. The earlier start to the stratified season significantly increases the period over which the lake absorbs heat and warms during the summer months, resulting in higher summer temperatures.

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