Great Lakes rise, expected to drop again

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LUDINGTON, Mich. — Great Lakes water levels are rebounding after a decade-long slump that hammered the maritime industry and even fed conspiracy theories about plots to drain the inland seas that make up nearly one-fifth of the world’s fresh surface water.

The three biggest lakes — Superior, Huron and Michigan — have risen steadily since autumn 2007, when for a couple months Superior’s levels were the lowest on record and the others nearly so. Erie, shallowest of the lakes, actually exceeded its long-term average in June. So did Lake Ontario, although its level is determined more by artificial structures than by nature.

The lakes follow cycles, rising and falling over time. Scientists say it’s a natural process with environmental benefits, such as replenishing coastal wetlands. But extreme ups or downs can wreak havoc for people.

During the mid-1980s, levels got so high that houses, businesses and even sections of roads were swept away along Lake Michigan’s southeastern shoreline.

Then a sudden, deep drop-off began in the late 1990s. Cargo ships were forced to substantially lighten their loads. Marina operators were unable to lease slips. Dredging to deepen boat passageways released pollutants that had been buried for years under layers of sediment.

While some waterfront property owners rejoiced over wider beaches, others griped as vegetation — sometimes unsightly and smelly—sprang up.

Scientists attribute the rebound primarily to wetter, colder weather the past couple years. But if grim computer modeling proves accurate, global warming will cause the lakes to recede up to 3 feet this century.

“Climate projections say the lakes will go up and down around a decreasing average,” said Don Scavia, director of the University of Michigan’s Graham Environmental Sustainability Institute. “The lows will be lower than in the past and the highs will be lower than in the past.”

Records extending to the mid-1800s document a series of larger rises and dips at roughly 30-year intervals, said Craig Stow, a scientist with the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Laboratory in Ann Arbor.

So the drop in the 1990s wasn’t unexpected, but its suddenness and severity caught many off guard. Drought and warming temperatures didn’t help as winter ice caps, crucial for limiting evaporation, formed in ever smaller areas.

Since fall 2007, rain and snow have picked up and winters have been colder. The lakes had substantial ice cover during the 2008-09 winter, meteorologists said.

At the end of June, Huron and Michigan — which hydrologically are one lake — were 10 inches higher than the previous year. Erie had risen 5 inches, Superior was near the same level and Ontario was an inch lower. Ontario and Erie were 5 inches above their long-term averages, while the others were within 6 inches of theirs.

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