Decreased Ice Cover On Great Lakes Likely Factor In Falling Water Levels - WP

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Decreased ice cover on the Great Lakes, probably caused by increasing air and water temperatures and high winds, is a major culprit in lowering water levels, which have hurt the shipping industry, forced lakeside power plants to extend their cooling pipes, frustrated recreational boaters, dried up wetlands and left coastal landowners with docks extending over yards of unsightly muck.

In September, Lake Superior broke its 81-year-old low-water record by 1.6 inches, and last month it was a foot below its seasonal average. It appeared that Lake Michigan and Lake Huron would log record lows for January until storms helped levels stay above the marks set in the 1960s.

The low water has forced freighters that haul iron ore, steel, limestone and other raw materials to lighten their loads and change their routes to avoid running aground in shallow harbors and waterways. "They literally do load these ships by the inch," said Stuart H. Theis, executive director of the U.S. Great Lakes Shipping Association. "To the lowest common denominator, the shallowest point along the way."

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Great Lakes levels have historically fluctuated, with relatively high levels in the 1980s and early 1990s. Scientists say Great Lakes levels are on an overall downward trend, which is likely to continue as a result of reduced ice cover, increased evaporation, and warmer air and water temperatures. "Since the late 1970s, we've seen a slight decline in precipitation and a steeper increase in evaporation," said Cynthia E. Sellinger, a hydrologist with the National Oceanic and Atmospheric Administration. "We've been in a different climactic regime for the last decade with higher air temperatures, which means more evaporation."

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http://www.washingtonpost.com/wp-dyn/content/article/2008/01/26/AR2008012601748.html