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Global warming may shrink Great Lakes, report says - Globe and Mail

April 09 2003
Martin Mittelstaedt, Toronto - Enironment Reporter
Globe and Mail

The Great Lakes are poised to become a lot less great because global warming will cause a dramatic plunge in the amount of water they contain, a new report says.

Compiled by a team of scientists from Canada and the United States, the report says the rising temperatures accompanying climate change will cause the lakes to shrink, with water levels in Lake Huron and Lake Michigan likely falling about three metres by 2030.

If concentrations of greenhouse-gas emissions continue to grow unchecked and reach double the level that occurred naturally before industrial times, the drop could be as much as eight metres, or about the height of a two-storey house.

Such declines would cause major ecological changes as shorelines recede, and also harm shipping, cut the supply of electricity from hydro power stations and diminish the grandeur of global fixtures such as Niagara Falls.

The projections were in a report called Confronting Climate Change in the Great Lakes Region.

The water-level forecasts are based on computer models that simulate what would happen to the lakes as the temperature of the air above them warms. Rising temperatures will cause the water in the lakes to heat up and lose more of their moisture to evaporation.

At the same time, the higher temperatures will cause the land around the lakes to become drier, reducing the supply of groundwater feeding streams that flow into the lakes.

"It's the higher temperature which is really driving these future scenarios," said John Magnuson, a limnologist (the scientific study of fresh water) and emeritus professor from the University of Wisconsin. He said "almost every" computer model used by researchers is projecting future declines in the amount of water in the lakes.

The report was jointly released yesterday in major cities around the Great Lakes. It was produced by the Union of Concerned Scientists and the Ecological Society of America, both based in the United States, and the David Suzuki Foundation in Canada.

Lake Huron and Lake Michigan have huge surface areas, making them more vulnerable to evaporation and declining water levels than Lake Superior and Lake Ontario. The report estimated that Lake Superior, the deepest of the lakes, could drop only 0.6 metres by 2030.

The report also projects significant changes to Ontario's climate because of global warming. By the end of the century, if nothing is done to curb greenhouse-gas emissions, average summer temperatures will be four to eight degrees warmer than they are now.

That would mean Ontario would have the hot, humid temperatures that now prevail in the southern United States.

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