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Politics : The Exxon Free Environmental Thread -- Ignore unavailable to you. Want to Upgrade?

To: Wharf Rat who wrote (1478)	11/6/2007 10:29:43 AM
From: Wharf Rat	Read Replies (1) \| Respond to of 49093

Warmth, wind speeds lower Lake Superior Superior suffers with Michigan, Huron, researcher concludes November 3, 2007 BY TINA LAM and ERIC SHARP FREE PRESS STAFF WRITERS TORONTO -- Sharply higher water temperatures and an increase of up to 30% in wind speeds over Lake Superior appear to be coconspirators in the relatively rapid decline in water levels on the world's largest freshwater lake, a scientist told a Great Lakes conference Friday. Water temperatures on Lake Superior, now at near-record low levels, have risen twice as fast as air temperatures in the last 25 years, said Jay Austin, a researcher at the University of Minnesota-Duluth. The same phenomenon has happened on Lakes Michigan and Huron, which are inches above record lows. Austin's findings, first published in a science journal last winter, were the buzz at a two-day meeting of experts focusing on declining lakes in the upper Great Lakes, especially man-made changes including dredging and the installation of shoreline structures to keep sand on beaches. The change in lake temperatures tracks the rise in air temperatures that hundreds of scientists around the world have documented in the second half of the 20th Century, accelerating since 1970. Many of the scientists at the meetings said Austin's work could help them quantify how much water is evaporating from the upper Great Lakes, which has been a difficult question but widely acknowledged as important. In an earlier interview with the Free Press, Austin, trained as an oceanographer and who studies the world's largest lakes such as Superior and Baikal in Russia, said, "What we are finding is completely counterintuitive. You would expect that a bigger lake like (Superior) would react more slowly to global warming." "But just the opposite is happening. It's exhibiting twice as much change as the other lakes" in temperature, Austin said, probably because Superior "has a lot more surface area to absorb heat." Water temperatures in Superior's western basin reached unprecedented levels last summer, he said, a factor in the lake's shrinking ice cover which he estimated is half what it was 25 years ago. Partly because of that, the lake's summer warming has been starting about two weeks sooner than it had before 1980. "That may not sound like much, but it's significant," because the warming season is a few months long, he said Friday. Looking at shoreline temperature data over about 100 years and data from buoys in the middle of Lake Superior since 1980, Austin said sharp increases in air and water temperature began about 25 years ago. Austin said he believes ice cover on the upper Great Lakes has dropped by half in recent decades. He said he doesn't know if his observations are early signs of global warming that will continue. Ice helps prevent evaporation from the lakes in winter and reflects half the sun's heat back into the atmosphere. Without ice, the lake absorbs that heat, kick-starting the warming of the lake in summer, he said. Lake Superior has warmed about 3 degrees centigrade in the last century, mostly in recent decades. Although scientists don't have good measurements to know how much evaporation there has been on the lakes, they know what the factors are that cause it. Austin said higher wind speeds, for example, might retard ice growth and lead to more evaporation. On Lake Erie, where water levels have remained relatively high compared to the past, winter ice cover has been more consistent. While scientists might expect that big lakes, such as Superior, would respond more slowly to higher temperatures, it seems Lake Erie, which is smaller and shallower, is the one that has responded more slowly, he said. Similar changes in wind speed and water temperature might be happening on other shrinking lakes worldwide, possibly because of global warming, but it's harder to study the other lakes, Austin said. The Great Lakes have some of the best data available in the world. Contact TINA LAM at 313-222-6421 or tlam@freepress.com. freep.com