Lake Superior Up 4.5 degrees F since 1979

...Something seems amiss with mighty Superior, the deepest and coldest of the Great Lakes, which together hold nearly 20 percent of the world's fresh surface water.

Superior's surface area is roughly the same as South Carolina's, the biggest of any freshwater lake on Earth. It's deep enough to hold all the other Great Lakes plus three additional Lake Eries. Yet over the past year, its level has ebbed to the lowest point in eight decades and will set a record this fall if, as expected, it dips three more inches.

Its average temperature has surged 4.5 degrees Fahrenheit since 1979, significantly above the 2.7-degree rise in the region's air temperature during the same period. That's no small deal for a freshwater sea that was created from glacial melt as the Ice Age ended and remains chilly in all seasons.

A weather buoy on the western side recently recorded an "amazing" 75 degrees, "as warm a surface temperature as we've ever seen in this lake," says Jay Austin, assistant professor at the University of Minnesota at Duluth's Large Lakes Observatory.
Water levels also have receded on the other Great Lakes since the late 1990s. But the suddenness and severity of Superior's changes worry many in the region; it has plunged more than a foot in the past year. Shorelines are dozens of yards wider than usual, giving sunbathers wider beaches but also exposing mucky bottomlands and rotting vegetation.

"C'mon, girls, get out of the mud," Dan Arsenault, 32, calls to his two young daughters at a park near the mouth of the St. Marys River on the southeastern end of Lake Superior. Bree, 5, and 3-year-old Andie are stomping in puddles where water was waist-deep a couple of years ago. The floatation rope that previously designated the swimming area now rests on moist ground.

"This is the lowest I've ever seen it," says Arsenault, a lifelong resident of Sault Ste. Marie in Michigan's Upper Peninsula...

Yet along Superior's shores, boats can't reach many mooring sites and marina operators are begging the U.S. Army Corps of Engineers to dredge shallow harbors. Ferry service between Grand Portage, Minn., and Isle Royale National Park was scaled back because one of the company's boats couldn't dock.

Sally Zabelka has turned away boaters from Chippewa Landing marina in the eastern Upper Peninsula, where not long ago 27-foot vessels easily made their way up the channel from the lake's Brimley Bay. "In essence, our dock is useless this year," she says.

Another worry: As the bay heats up, the perch, walleye and smallmouth bass that have lured anglers to her campground and tackle shop are migrating to cooler waters in the open lake.

Low water has cost the shipping industry millions of dollars. Vessels are carrying lighter loads of iron ore and coal to avoid running aground in shallow channels...

Precipitation has tapered off across the upper Great Lakes since the 1970s and is nearly 6 inches below normal in the Superior watershed the past year. Water evaporation rates are up sharply because mild winters have shrunk the winter ice cap _ just as climate change computer models predict for the next half-century.

Yet those models also envision more precipitation as global warming sets in, says Brent Lofgren, a physical scientist with the Great Lakes Environmental Research Laboratory in Ann Arbor. Instead there's drought, suggesting other causes.
Cynthia Sellinger, the lab's deputy director, suspects residual effects of El Nino, the warming of equatorial Pacific waters that produced warmer winters in the late 1990s, just as the lakes began receding.

Both long-term climate change and short-term meteorological factors may be driving water levels down, says Urban, the Michigan Tech researcher.

But he and Austin are more concerned about effects than causes. There's a big knowledge gap about how food webs and other aquatic systems will respond to warmer temperatures, they say....