1 June 2007Detroit Free Press / Chicago TribuneJames Janega
From one view of history, the Great Lakes are near record lows, approaching the bottom-scraping frustration of the mid-1960s.
But from another, longer view, the lakes are nearly as high as they've ever been, just a few feet below the high-water mark reached in the 1850s.
Both pictures are scientifically accurate and are getting increased 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 posing 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. "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."
Recently, owners retired the Lake Superior ferry between Minnesota and Isle Royale because its draft was too deep to dock. 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, they also were getting warmer.
Lake Superior is 5 degrees 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 and earlier each year. That, in turn, has spelled faster evaporation for Lake Superior, which has been steaming away .18 inches faster every year since 1977.
"Lake Superior is sort of this canary in the coal mine," Austin said. "It responds very quickly to climate change."
And that realization has prompted a wider look at the lakes' past.
For years, depth markings of falling water levels and satellite views of shrinking ice sheets have told a bleak tale of drought and dwindling waters in the Great Lakes, particularly Lakes Superior, Michigan and Huron.
But in the last decade, climate researchers, pollen experts and specialists in prehistoric forests also have added their expertise, uncovering more evidence below the lakes' diminishing waters.
The evidence suggests water levels have risen and fallen by several yards over the centuries, often tied to cycles of warming and cooling.
"The evidence is pretty strong it was once much drier around here than at the present time," said Thomas Johnson, a geologist at the Large Lakes Observatory, citing evidence from long-ago beach ridges and drowned swamps not quite at the shores of the modern Great Lakes.
Piecing together those clues, climate detectives suspect Lakes Superior, Michigan and Huron may have been lower than 20th-Century historical averages in the 13th and 17th centuries -- and much higher in the 16th Century as well as over the last 50 years.
The renewed look at the lakes' far past is hoped to yield insight for the future, said Cynthia Sellinger, who tracks lake levels for the Great Lakes research lab, part of the National Oceanic and Atmospheric Administration.
Still, modern climate measurements go only so far, she said.
"If you take a certain slice in someone's lifetime, they could say, 'Oh, this is a catastrophe,' " Sellinger said of modern low levels. "But in their grandfather's lifetime, they would say 'Oh, well, we've been here before.' In most people's lifetime, they don't see that range."
