Great Lakes' past may offer clues on climate

From one view of history, the Great Lakes are near record lows, approaching the bottom-scraping frustration of the mid-1960s.

From another, longer view, though, the lakes are nearly as high as they've ever been, just a few feet below the high-water mark reached at the end of the Little Ice Age in the 1850s.

Both pictures are scientifically accurate and are getting more attention from climatologists, lake scientists and environmentalists curious about history's large climate cycles and how they tip the lakes' eons-old balancing act of rainfall and runoff, heating and evaporation.

The fluctuations are raising new questions about whether climate change has begun to alter the depth of the lakes, though the picture is still too complex to yield definitive answers.

"If you look at the record even from 1850 on, at lake levels and precipitation levels, this is not abnormal," said Thomas E. Croley II, research hydrologist at the Great Lakes Environmental Research Laboratory in Ann Arbor, Mich. "But it's always hard to say whether this is the start of something else, and that's where you get so much subjective opinion, so many questions of climate change."

Over the weekend, owners retired the Lake Superior ferry between Minnesota and Isle Royale because the boat was too big to dock in the shallow marina. Deep-lake cargo carriers have left tons of freight at loading docks to cross shallow channels between lakes. Marinas have been dredging more than ever. And still other indicators of lake health seem out of whack.

In the last decade, researchers learned the lakes not only were dropping compared with modern records, but they were also getting warmer -- even faster than temperature increases on land. Lake Superior is 5 degrees Fahrenheit warmer than it was a century ago, "and most of that warming happened recently," within 25 years or so, said Jay Austin, a climatologist at the Large Lakes Observatory at the University of Minnesota in Duluth.

Ice on the lake forms later and melts earlier, he said, and the tipping point when the winter lake begins warming rapidly for the summer has come earlier each year. That in turn has spelled faster evaporation for Lake Superior -- the feeder lake for the lakes system -- which has been steaming away 4.6 millimeters faster every year since 1977.
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