The largest lake in the world is showing itself to be an extremely sensitive indicator of global warming, said scientists in Duluth, adding that the time to change is now.
DULUTH - Like ice sheets melting in the Arctic, Lake Superior has begun showing some of the world's most tangible evidence of global warming, according to scientists gathered in Duluth this week.
The lake's average winter ice cover is 50 percent smaller than it was 100 years ago, a study found. Since 1980, the water on average in summer has warmed almost 2 degrees Fahrenheit per decade, which is twice as fast as the air has warmed. During that time, wind speeds in the middle of the giant lake also have risen steadily.
"In many ways, you in the Lake Superior basin are the canary in the mine," said David Phillips, senior climatologist at Environment Canada. "Lake Superior is really one of the early victims of climate change."
Worldwide, warmer weather and stronger storms could affect everything from the survival of certain plants and animals to transportation to sewage treatment overflows. But the 400 or so scientists at the "Making a Great Lake Superior Conference" said there's still time to minimize the long-term environmental and economic damage, and to adapt to shorter-term changes that can't be averted.
Individuals, corporations and governments must "mainstream climate change" into their thoughts, plans and projects, said Joel Scheraga of the U.S. Environmental Protection Agency's Global Change Research Program.
Failure to plan could result in more disasters such as the damage done to New Orleans by Hurricane Katrina, he said.
The absence of ice
Prof. Jay Austin said that when he learned that Lake Superior water was warming twice as fast as the air above it, he wondered, "Why is Lake Superior so sensitive to climate change?"
Austin and fellow professor Steve Colman, both of the Large Lakes Observatory at the University of Minnesota Duluth, conducted research to find out.
The answer was ice, or the lack of it, Austin told fellow scientists at the conference Tuesday. Until the last decade or so, harsher winters and cooler average temperatures caused Lake Superior to substantially freeze over in winter. A warming climate has caused ice cover to diminish.
"Ice reflects sunlight back out into space, and it can't be used to heat up the lake," Austin said. "If you take away the ice, you allow the lake to warm up earlier."
Prof. John Magnuson of the University of Wisconsin-Madison showed that the region's inland lakes also are losing days of winter ice cover. Twenty years ago, lakes that lost their ice by April 15 were roughly in the latitude of the Twin Cities. But that "ice-out" line has marched steadily north, until in recent years, lakes 100 miles north of the Twin Cities lost their ice by April 15, his maps showed.
Lake levels affected
Less ice exposes the surface of Superior, the world's largest lake, to more evaporation. The scientists say this undoubtedly played a role in the lake reaching record low monthly levels over the summer, as the region was also in the grip of a drought.
Above-normal rainfall has caused the lake level to rebound since then to near normal levels.
People should be concerned about such trends, but they shouldn't panic or lose hope, said Scheraga, the EPA program director.
Knowing that storms may be stronger is already prompting cities to design sewer systems to handle larger overflows and treat potentially polluted runoff, he said. Similarly, engineers in extreme northern reaches are adjusting building foundation standards and building practices to compensate for dwindling permafrost.
As people work to reduce emissions that are driving the trends, they must also continue to adapt to them because greenhouse gases already in the atmosphere will remain there for a long time, the scientists said.