Great Lakes ice coverage declined an average of 71 percent over the past 40 years, according to a report from the American Meteorological Society.
The amount of decline varies year to year and lake to lake, according to the report's lead researcher, Jia Wang, an ice research climatologist at the National Oceanic and Atmospheric Administration's Great Lakes Environmental Research Laboratory in Ann Arbor, Mich.
Wang’s report said that based on Coast Guard scanning, satellite photos and other research from 1973 to 2010, ice coverage dropped most on Lake Ontario, 88 percent; the second-largest loss was on Lake Superior, at 79 percent.
The smallest decline, 37 percent, was on Lake St. Clair, a lake between Lakes Erie and Huron that was also included in the study.
The study doesn’t include the current winter, but satellite photos show that only about 5 percent of Great Lakes surface froze over this winter, the Detroit Free Press said. That’s down from years such as 1979, when there was as much as 94 percent ice coverage. On average, about 40 percent of the surfaces freeze over, the newspaper said.
Wang told WBEZ-FM in Chicago that diminished ice coverage speeds wintertime evaporation, reducing the lakes’ water levels, which can spur increased and early algae blooms, damage water quality, and accelerate erosion as more shoreline is exposed to waves.
Wang told the Cleveland Plain Dealer newspaper that natural climatic variables such as El Nino, La Nina play as much a role in the ice decline as a warming global climate.
"We are seeing the impact of global warming here in the Great Lakes -- but the natural variability is at least as large a factor," Wang said.
Wang said global climate change and regional climate patterns are competing over the Great Lakes.
The Great Lakes, scientists say, contain about 20 percent of the world's fresh water supply and cover 94,000 square miles in two countries.
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