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Great Lakes Ice Coverage Down 71 Percent Since 1973

The American Meteorological Society says that the amount of ice covering the Great Lakes has decreased over 71% in the past 40 years. A drop that the author of the report attributes to climate change, El Nino and La Nina. The report published last month said only about 5 percent of the Great Lakes surface froze over this year.

Coast Guard Cutter Katmai Bay

Coast Guard Cutter Katmai Bay breaks ice for freighters navigating through the St. Mary's River in the Great Lakes. During winter, paths must be made in the ice for freighters to continue shipping goods. Photo by Petty Officer 3rd Class William B. Mitchell.

The American Meteorological Society says that the amount of ice covering the Great Lakes has decreased over 71% in the past 40 years. A drop that the author of the report attributes to climate change, El Nino and La Nina. The report published last month said only about 5 percent of the Great Lakes surface froze over this year.

Researchers determined ice coverage by scanning U.S. Coast Guard reports and satellite images taken from 1973 to 2010. They found that ice coverage was down 88 percent on Lake Ontario and fell 79 percent on Lake Superior. However, the ice in Lake St. Clair, which is between Lakes Erie and Huron, diminished just 37 percent.

The study doesn’t include the current winter, but satellite photos show that only about 5 percent of the Great Lakes surface froze over this winter. That’s a steep drop 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 results are consistent with other studies that have found higher surface water temperatures on Lake Superior in recent years.

Jia Wang of the National Oceanic and Atmospheric Administration lab in Ann Arbor, Mi, the lead author of the publication states that  that diminished ice can accelerate wintertime evaporation, causing water levels to fall. The lack of ice could also lead to earlier and increased algae blooms that can damage water quality, and could speed up erosion by exposing more shoreline to waves.

Even Lake Superior’s protected Chequamegon Bay, just north of Ashland, Wis., has been remarkably free of ice. It usually freezes enough for trucks to drive on it, but the ice was never thick enough. That forced the local Madeline Island ferry to operate all season, which has only happened once before.

 

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