MINNEAPOLIS, March 22 (UPI) -- U.S. scientists have determined Lake Superior's summer surface temperatures have increased by approximately 2.5 degrees Celsius since 1979.
The researchers, led by Jay Austin and Steven Colman of the University of Minnesota, said the increase is about twice the rate of regional atmospheric warming.
Austin and Colman hypothesize declining winter ice cover is causing the lake to absorb more solar radiation than during past years. That increased absorption causes earlier stratification of the lake at a rate of roughly half a day per year.
Large mid-latitude lakes often freeze in winter, mix thoroughly during spring and fall, and stratify in summer due to solar heating. Austin and Colman said the earlier start to Lake Superior's stratified season significantly increases the period during which the lake warms, resulting in higher summer temperatures.
Although little studied, the response of large lakes to climate change will likely have an important regional effect, the scientists said.
The study is detailed in the journal Geophysical Research Letters.
