The depths of Lake Michigan are getting warmer, new study reveals. That could mean more snow and less ice

A new report is offering a look into the effects of climate change on freshwater lakes around the globe, showing the water is getting warmer, even 500 feet below the surface. 

The report was compiled by the National Oceanic and Atmospheric Administration’s Great Lakes Research Laboratory, using data collected every hour over the last 30 years by technology deep within the waters of Lake Michigan, one of the largest freshwater lakes in the world. The peer-reviewed report was published in the Nature Communications journal earlier this month. 

It’s the first sustained look at what happens each year as Lake Michigan’s waters rise and fall, and likely the most detailed measure of temperature below the surface of a freshwater lake available.

The numbers collected over the years show the deeper water warming by about 0.11 degrees Fahrenheit each decade, faster than the ocean or even air temperature. 

While the change doesn’t seem large, the rising temperatures could have impacts on the ice cover on top of the lake each year, as well as the organisms that live in water and depend on the steady changes in temperature, said Eric Anderson, the lead author of the study and a physical scientist with the Great Lakes Research Laboratory. 

It’s evidence that climate change is already having an effect on the Midwest, too. Winter is warmer, on average, as is spring, Anderson said. And summer is lasting longer, stretching into the time where fall usually brings on cooler temperatures.

“What this study does is give us the ground truth to show us what direction we’re heading,” he said. 

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The warmer temperatures deep within the lake are also part of the reason Wisconsin has faced so many issues with erosion along the shorelines. Ice isn’t forming as thick or as early in the season as it once did, keeping the water underneath it. 

Under cold conditions, the ice would act as a buffer, preventing waves from crashing into the shore and washing dirt back out into the lake. Without the ice, little protection is offered during cold, windy stretches, Anderson said. 

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The warming will also affect fish populations within the lake, he said. 

“Certain species are going to be impacted. Coldwater fish like whitefish and yellow perch are going to be impacted,” he said. “With the warmer temperatures and less ice, the ice that used to shelter their eggs near the shore won’t be there, and the eggs are susceptible to the rough shoreline.” 

Warmer water temperatures can also mean fewer eggs, leading to fewer fish successfully hatching into Lake Michigan. 

“Changes in lake conditions can lead to impacts on how abundant fish are,” he said. “And that can change the way things look, change communities and tribes who rely on the lake.”  

The warming of the lake could also result in changes in the amount of snow seen around the lake, said Michael Notaro, the associate director of the Nelson Institute Center for Climate Research at the University of Wisconsin-Madison. 

“The warming lake waters and declining lake ice cover support enhanced lake evaporation and lake-effect precipitation during the cold season. As the lakes warm in the cold season, the temperature difference between the water and overlying air increases, supporting greater turbulent fluxes of heat and moisture from the lake to the atmosphere,” he said in an email. “That favors more vertical atmospheric motion that can support cloud and precipitation formation in the cold season.” 

To understand the data, and why the temperature in Lake Michigan fluctuates, Anderson said it’s important to know that it’s a dimictic lake, meaning it has a full thermal cycle, in tune with the seasons. 

In the summer, the water at the surface of the lake warms up as the air around it warms and the sun beats down. The bottom of the lake, however, remains cool. In the fall, the water begins to cool, along with the air temperature, and the water “turns over,” or mixes with the cooler lower-level water. At that point, the whole lake is the same temperature. 

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In the winter, the surface temperature of the water then drops again, allowing an ice cover to form. But with spring’s warmer temperatures, the ice melts and the warming surface water again mixes with the water at the lower level, Anderson said. 

The turning over of the lake is important to its ecosystem, he said. Many freshwater lakes across the world follow a similar process, meaning that the data gathered in the Lake Michigan research can be extrapolated to other bodies of water. 

“Most freshwater on earth is in these large lakes, the 10 biggest lakes hold over 80% of available freshwater, and more than half of that water is in a lake that acts like Lake Michigan,” he said. “This is a good place to look to understand impacts, it’s a good indicator of what to expect in other lakes around the world.”

Laura Schulte can be reached at leschulte@jrn.com and on Twitter at @SchulteLaura