Professor Ankur Desai, who led the study, said the rising temperature means more powerful winds on the lake, as well as consequences for currents, pollution and biological cycles.
Since 1985, surface water temperatures measured by lake buoys have climbed 1.2 degrees per decade, Desai said. That's about 15 percent faster than the air above the lake and twice as fast as warming over nearby land.
"The lake's thermal budget is very sensitive to the amount of ice cover over the winter," Desai said. "There is less ice on Lake Superior during the winter, and consequently the water absorbs more heat."
He said wide temperature differential between water and air produces a more stable atmosphere, with calmer winds over the relatively cold water. However, as warming water closes the gap, as in Lake Superior's case, the atmosphere becomes more turbulent.
"We've seen a 5 percent increase per decade in average wind speed since 1985," he said.
Desai, Professor Galen McKinley and graduate research assistant Val Bennington, along with Professor Jay Austin of the University of Minnesota-Duluth, report their findings in the journal Nature Geoscience.