Who Pulled The Plug On Lake Superior?

Why our greatest lake is heating up the climate-change debate

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.


Global warming is not directly to blame, however, for this year’s remarkably low lake level, which is expected to break the record low this fall; scientists agree that recent drought, not a larger climate trend, mostly accounts for the dramatic drop of more than a foot and a half in the past couple of years. But longer-term trends of increased evaporation and less water flowing in from rivers, going back at least 30 years, are certainly a factor. Drought is simply exacerbating a slower downward spiral, likely driven by climate change.

The lake level is arguably of far more interest to the people affected (shippers, boaters, etc.) than the scientists asked to comment on it. The lake as a whole, after all, isn’t in danger of disappearing anytime soon. And the lake itself, as Austin cheekily notes, “doesn’t care if it drops six feet or six inches”—it will go on, forcing us to adapt.

Rather, what Lake Superior researchers are most closely watching is the spring turnover, an annual event in deep, northern, temperate lakes in which the icy surface water heats up and mixes with the rest of the lake, eventually forming a layer of warm water atop a layer of cold water in summer. The spring turnover is happening about 10 to 14 days earlier than it was 25 years ago, scientists say. Lake Superior’s summer season, the period when the water is stratified in warm and cold layers, has been stretched from 130 days to 160—a 25 percent increase. That gives the lake more time to warm up. Last summer, it hit 75 degrees, likely a new record; until recently, it rarely broke 60.

The earlier spring turnover may also be affecting the lake’s nutrient levels and, therefore, what grows in the lake. Urban, for example, has documented a decrease in phosphorous going back 30 to 35 years, which is consistent with theories of climate change and stratification—the longer a lake is stratified, the hypothesis goes, the less phosphorous it contains. Urban was not surprised, then, to also find a decrease in algae over the same period, as phosphorous is the nutrient that algae need to survive. Since algae form the base of the lake’s food chain, this is no small matter. At the same time, as stratification precludes oxygen from circulating into deeper water, a longer summer could spell trouble for bottom-dwelling fish.

The greatest danger of a longer summer may be the red carpet it rolls out to unwelcome invaders. Traditionally, the lake’s famous cold, like that of Minnesota itself, has kept out much of the riff-raff. Warmer water, however, could invite an influx of non-native plants and animals whose lifestyles require more temperate temps. These strangers don’t play by the rules of the existing ecosystem; as sea lampreys have done in Lake Michigan, virtually exterminating the lake trout, these creatures could well do in Lake Superior, upsetting the biological balance.

Already, a potentially havoc-wreaking creature from Ukraine called the Quagga mussel has shown up in the Duluth harbor, according to Lake Superior researcher Sarah Green of Michigan Technological University. It is a cousin of the zebra mussel, an invasive species that has devastated the lower Great Lakes but not Lake Superior, owing to the cold and a lack of calcium needed to make its shell. The Quagga doesn’t need as much calcium, can live in deeper water and on muddy bottoms, and has a broader temperature tolerance—it may be the ultimate invader, just waiting until the time, or the temp, is right.

At the Great Lakes Aquarium in Duluth, hundreds of fish swim in massive tanks approximating their original Lake Superior habitat, unaffected by the changes in the wild. Some are species uniquely adapted to the traditionally cold, nutrient-poor lake. The siscowet, for instance, can only be found in Lake Superior and is the lake’s most abundant predator. Its name is an Ojibwe word for “cooks itself,” as it has an unusual amount of fat to help it survive the cold. Some of these species will probably no longer call the lake home in a hundred years, though it’s too soon to say which will adapt and which will literally, well, cook themselves.

Predicting the effects of climate change involves chemistry, biology, and many more considerations—“It’s like turning all these knobs at the same time,” says Austin. “It’s anyone’s guess whether Lake Superior will turn into a big bass-fishing lake or a big desert.”

Much Superior research is now focused on understanding the lake’s cycles, such as how much carbon—the building blocks of life as well as global warming—is both entering and exiting the lake. Preliminary data shows that the lake is releasing more carbon into the atmosphere than it’s taking in—strange, since the in- and outflows would typically match up. Whether the imbalance truly exists, and what it might mean for the lake and for the regional climate, is still unknown.

A carbon-emitting lake—even a giant one—is unlikely to significantly affect the global carbon cycle (“Though it would help our research funding if we could show that,” jokes Green). However, indications are that the lake is emitting enough carbon to influence measurements taken by scientists of carbon-dioxide storage in the forests of Lake Superior’s watershed. And if we’re to accurately gauge how well these trees are mitigating climate change then it’s important to know the lake’s role in the process. Conversely, the effects of climate change on the region—from added dust in the atmosphere to stronger storms creating more runoff—may be throwing the lake’s carbon cycle off-kilter.

In one long-term scenario, as described in an exhibit at the Great Lakes Aquarium, Lake Superior could become the Great Salt Lake Superior. This would happen if the lake’s water level plummeted far enough—perhaps just over 30 feet—that its sole outlet, at Sault Ste. Marie, would cease to flow, and the lake would become a closed basin filled with salt and other gunk entering from other rivers. Not good for fish or flora; there’s a reason, after all, that the world’s saltiest body of water is called the Dead Sea.

Life within the lake has always been changing. Shorelines have shifted, waters have risen and fallen. Only 2,000 years ago, a forest once stood in Duluth harbor. More recently, when Europeans first settled Lake Superior’s shores, 500-pound sturgeon were abundant—“People would carry them away in wheelbarrows,” says Green. “Legend has it you could practically walk across ponds on their backs.” Now they’re relatively rare, while other fish are plentiful. Change happens. And Austin says the “biggest value judgment” he’s placing on Lake Superior’s warming is to say that it’s “interesting.” Still, today’s unprecedented pace of change is unsettling to others trying to account for the effects.

“The changes that humans are making to the climate are so much faster than the changes before,” says Green. “We’re doing a global experiment, essentially, where we can’t predict the results on an ecological scale and we don’t have a backup. These are the only Great Lakes we have.”

Tim Gihring is senior writer at Minnesota Monthly.