Climate change blamed as Superior shrinks

Lake Superior, largest of the Great Lakes and the world's largest freshwater reservoir, has fallen to its lowest level in 81 years, further evidence of the effect that climate change is having on the North American continent.

The lake is a foot and a half below its long-term average. The last time it was this low was in 1926. Falling water levels mean that once-floating boat docks are high and dry, cargo vessels are severely restricted, hydroelectric power is curtailed and lakeshore ecology is changing fast.

Researchers at the University of Minnesota have measured an average temperature rise of 4.5F since 1979. The warmer water is evaporating faster and holding less ice in winter. For the first time in living memory, the ice and snow that usually covers the lake by early December arrived late, allowing water to evaporate.

"It's been a long time since we've been this low, but it has happened," said Tim Calappi of the US Army Corps of Engineers, which is responsible for all large dams and public engineering projects in the US. "We still think this is within range of what's normal, but we have to wait and see."

Others are certain the cause is global warming and in the absence of an official explanation conspiracy theories abound. The effects are dramatic and obvious, however. Boats with keels can no longer operate in many areas, beaches have been left far from the water and large areas of wetlands where wild rice grew have dried out.

Other large bodies of water are also severely depleted. Lake Huron and Lake Michigan are well below average. Thousands of miles away to the south and east, Lake Mead near Las Vegas and Lake Powell on the Utah-Arizona border are only half full. Florida's vast and shallow Lake Okeechobee is at an all-time low.