Who Pulled The Plug On Lake Superior?
Why our greatest lake is heating up the climate-change debate
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SINCE 1906, an employee of the hydroelectric power plant in Sault Ste. Marie, Michigan, has walked down to the thermometer at the water-intake gate every day at precisely 8 a.m. and recorded the temperature of Lake Superior.
It is one of the longest-running records of water temperature in the world. But when Jay Austin, a young scientist at the Large Lakes Observatory in Duluth, crunched this data last year in a routine examination of Lake Superior trends, the recent numbers seemed to be taken from some other planet. A much, much warmer one.
Austin was stumped. The lake, he found, had been heating up slowly until about 30 years ago, when, as he puts it, “It went bananas.” Of the lake’s 6-degree Fahrenheit increase over the past century, about 75 percent of the warming appeared to have occurred since 1980. Austin assumed he had made a mistake. So he and a colleague, Steve Colman, examined temperature data taken from three weather buoys deployed across Lake Superior, focusing on those three mystifying decades. Same result. Stranger still, when Austin and Colman compared Lake Superior’s temperature trend with that of the planet in general, they discovered that the lake was not only heating up fast, it was warming faster than the global average. Nearly twice as fast as the climate around it.
Austin released his findings last spring, and they were soon the subjects of news stories around the world. How could this be happening? Would the continent’s greatest reservoir, containing 10 percent of all the fresh water on Earth, simply evaporate like so much spilled milk? Are other lakes in danger? Austin, who had been happily doing what limnologists do—studying sediment plumes and other unglamorous freshwater phenomena—was suddenly thrust into one of the defining issues of our time: global warming.
When the lake emerged from the meager spring thaw as a shallow shadow of itself, with the lowest water level in 81 years, another round of interviews followed. A CNN crew spent four days with Austin, trying to get to the bottom of Superior’s bottoming out. Meanwhile, leisure-boat docks were abandoned, left high and dry by receding waters. Cargo ships began leaving Duluth with lighter loads, lest they became stranded in port. The Wenonah, a large ferry used to shuttle tourists to Isle Royale, 17 miles offshore, could no longer safely depart from the shallow marina at Grand Portage, and was reassigned to scenic-cruise duty in Grand Marais.
Around the Duluth harbor, conspiracy theorists squawked like seagulls: Cover-up! Corruption! Canadians! Politicians in more powerful places on the lower Great Lakes, according to the leading theory, had struck deals with regulators in the United States and Canada to increase the flow from Superior into their own depleted waters. The scientific evidence, however, points to equally sensational conclusions. Could Lake Superior really become ice-free as soon as 2040, as Austin estimates, with an average winter then looking much like today’s warmest ones?
If Gitchee Gumee has famously never given up its dead, it has also given up few of its secrets—surprisingly little is known about Lake Superior, relative to the oceans or even the other Great Lakes, leaving us unprepared to mitigate the dangers of a warmer lake, whether it’s the loss of wetlands and water quality or thriving exotic species. Austin and his colleagues are just now beginning to learn how Lake Superior is likely to react to a warming world, research that could help us understand not only our own region but the Arctic, the oceans, and anywhere else with a lot of cold water that’s starting to heat up. “Lake Superior is kind of a canary in the coal mine,” Austin says.
In fact, the lake is changing faster than anyone expected, responding more quickly to global warming than any place we know of in the world.
The Large Lakes Observatory is located a couple of miles inland from Lake Superior on the little-used “old campus” of the University of Minnesota–Duluth, where sleepy buildings centered around the ruins of a once-grand Old Main underscore the relative isolation of lakes researchers.
“Lakes aren’t as sexy as oceans,” Austin says, explaining why only a few scientists have bothered to study even the most fundamental principles operating within Lake Superior. There are no whales, sharks, or giant squid in Lake Superior—relatively little biology at all, actually, owing to the water’s extreme cold. Also, because the Great Lakes span state and even international boundaries, no unified political or scientific constituency has taken ownership of the ecosystem, says Noel Urban, an environmental engineering professor and longtime Lake Superior researcher at Michigan Technological University. The lakes’ great size, paradoxically, has marginalized them. Most Lake Superior research so far has focused on localized, pragmatic issues of management and restoration, not pure science.
That’s a shame, Urban says, because the lakes are big enough that they affect the weather in the region around them, from snowfall to rainfall, and we presently don’t understand how warming waters will affect the area’s climate in the long term. “It would certainly be nice,” he says, “to be able to predict those changes ahead of time rather than be surprised by them.” Scientists could also be using Lake Superior, given its size and frigidity, as a more accessible substitute for research in the Arctic, where global warming stands to significantly alter the planet.
Even the technology available to Lake Superior researchers has been meager compared to the sophisticated arsenal at oceanographers’ disposal. Some 140 years ago, a Harvard scientist named Louis Agassiz (who would later be the first to postulate an Ice Age) became obsessed with Lake Superior, discovering new species of fish with little more than a net and a magnifying glass. Austin has considerably more tools in his lab today, including a carbon-dioxide detector; temperature gauges that clamp to buoys; and a Webb Electric Glider, a missile-like robot that can cruise in the lake for up to 30 days, measuring everything from temperature to turbidity to oxygen levels. But this equipment is relatively new—until recently, most Lake Superior data came from simple instruments attached to widely scattered government buoys.
Admittedly, Austin’s first scientific interest was not Lake Superior but the sea. He researched the Oregon and Carolina coasts before landing in Duluth two years ago. A California native, he has the lanky, laid-back demeanor of someone unused to shivering through winter in a parka, and on a recent afternoon in the lab, he wore a Hawaiian shirt and shorts, as though longing for island beaches. But he and his wife (a scientist who, like Austin, works at the Large Lakes Observatory and UMD) have grown fond of Lake Superior, even strolling across the ice in winter.
Large lakes and oceans, despite their obvious differences, operate similarly—Lake Superior, Austin says, is basically an inland ocean. So he and the other scientists and research assistants at the Large Lakes Observatory use oceanographic techniques to study not only the Great Lakes but enormous lakes the world over, from Lake Tanganyika in Africa to Lake Baikal in Siberia. “There is amazing, weird stuff going on in Lake Superior,” Austin says, from the Deep Chlorophyll Maximum (a sort of Bermuda Triangle for algae, where the organisms appear to become trapped and die) to the so-called “three sisters” (an occasional series of increasingly powerful waves that some suspect helped founder the Edmund Fitzgerald). It’s just that few people have paid attention, until now.
What Austin and Colman concluded last spring is that water temperatures in Lake Superior have increased 4.5 degrees since 1979—twice as fast as the slower, steadier warming of the air. Austin was shocked; he had expected to find both air and water temps increasing at the same pace. But he now believes he has found the culprit: ice cover, or rather, lack of it.
It’s no coincidence, Austin believes, that the steep incline in average lake temperatures that began around 1980 closely corresponds with a steep decline in annual ice cover over the same period. The ice, he theorizes, was preventing the lake from rapid warming—ice, because of its light color, reflects sunlight back into space, keeping the water cool underneath. But now that the average annual ice cover is shrinking, the lake is warming with a vengeance. Open water is extremely good at absorbing heat. And so the lake is now likely caught in a feedback system: Warmer temperatures mean less ice, and vice versa. As Austin puts it, “It’s a double whammy.”
One effect of less ice cover and warmer temps is increased evaporation, lake water dissipating into the atmosphere. There is always some evaporation on the lake, but lately there has been more “evap,” as scientists shorthand it, than rainfall replacing it. Evaporation is especially easy on Lake Superior in winter, when cold, dry winds can whip water from the surface like sand from a beach, pulling droplets up and away into the air. Ice cover was acting as a cap on evap, Austin believes. And now the cap is loosening, such that the lake has been steaming away 4.6 millimeters faster every year for the past three decades.