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Researchers worried about rise in Great Lakes temperatures

"Great Lakes, No Clouds" by NASA Goddard Photo and Video is licensed with CC BY 2.0. To view a copy of this license, visit

The Great Lakes are warming. That’s already brought changes to the coldest and largest of the lakes. Researchers are still sorting out what the future might hold for Lake Superior and the people who live there. And, as the Environment Report finds, a lot of it does not look good.

Lake Superior’s surface temperature has been going up, but in wild fluctuations. The average wind speeds have been increasing by five percent each decade since 1980. And Superior has been pounded by three 500 year to one thousand year storm events in the past eight years.

“If it's not climate change, what is it?”

Peter Annin extensively documented the effects of climate change in his recently revised book Great Lakes Water Wars.

“I mean, that we have the largest lake in the world by surface area is not just seeing one extreme event, it's seeing a series of scientifically documented extreme events that are creating a pattern that is changing the relationship that human beings are having with the Great Lakes that they love,” said Annin.

Right now, people are talking about historically high lake levels. Just a few years ago they were talking about historic lows.

The two most significant things that affect water levels are precipitation and evaporation. In 1998, Lake Superior warmed up about two degrees Celsius. That’s a little over 3.6 degrees Fahrenheit. And, it stayed warm for more than 15 years. That meant high evaporation. Water levels dropped.

Then, things swung in the other direction. Drew Gronewald is hydrologist at the University of Michigan’s School of Environment and Sustainability.

In 2014, there was what we call in the media, the polar vortex and lake temperatures went down by an order of one or two degrees Celsius. And all of a sudden evaporation rates were low. So those changes in temperatures that you're talking about, they are of a big magnitude and they have a huge impact on the hydrology and the physics of the lakes.”

Now, the Great Lakes water levels have always gone up and down, but Peter Annin says this is not the same.

“What's different now is that we're seeing an increase in extremes, an increase in higher highs, lower lows, the speed with which we're rising, the speed with which we're falling. We're breaking records all over the place,” Annin said.

And, lake levels are not the only problem.

Invasive zebra mussels and quagga mussels have covered the bottoms of Lakes Michigan and Huron by the trillions. They filter out a lot of the nutrients from the base of the food web. That’s meant some fish in Huron and Michigan and the shallower parts of Superior where the mussels have invaded have suffered. If Lake Superior warms up, those mussels and other invasives are likely to increase. Already for a couple of decades, whitefish populations have dropped.

“That is our main fish species in Anishinaabe culture. That is the fish species that is most important throughout our creation history.”

That’s Brad Silet. He’s the Lead Fisheries Biologist for the Sault Tribe of Chippewa Indians in Sault Ste. Marie.

He’s worried about invasive species further damaging cold water fish such as whitefish. He’s also concerned about those volatile lake levels we talk about earlier.

“When you start doing these really drastic up and down water levels, you start seeing a lot more of those negative impacts to the hatching of those eggs,” Silet said.

That’s because whitefish spawn in rocky coastal areas. Fluctuations in water levels and ice crashing where it never has before can damage eggs and further reduce whitefish populations

Silet says that’s why Native American fisheries experts are trying to figure out what they can do to save whitefish.

“Right now, Sault Tribe is doing some experimental whitefish rearing," Silet said. "There's another tribe doing it also. We are seeing what it would take to raise white fish to see if we can potentially offset any changes to climate change or invasive species that are happening, at least in our area of the Great Lakes.”

State and federal governments operate fish hatcheries to raise certain sport fish. Government agents are now watching the Native American experiments to see how raising whitefish goes.

It’s pretty clear the Great Lakes will continue to warm over the decades. The thing that has everybody guessing is just how volatilely the lakes will react as that happens.