The Great Lakes Changed Forever in 1998. Are We Ready for What’s Next?

By M. Davenport, U. of Michigan, Aug. 9, 2025 

https://scitechdaily.com/the-great-lakes-changed-forever-in-1998-are-we-ready-for-whats-next/

 

Heat waves and cold spells have always shaped life around the Great Lakes, but new University of Michigan research reveals these extremes are now occurring far more often than just a few decades ago. Using advanced modeling techniques to reconstruct lake surface temperatures back to 1940, scientists discovered that such events have more than doubled since the late 1990s, coinciding with one of the strongest El Niños on record.
Credit: Shutterstock

Heat waves and cold spells are occurring more frequently around the Great Lakes, according to research from the University of Michigan. These changes have important effects on the region’s weather, economy, and ecosystems.

Heat waves and cold spells have long been a natural feature of life around the Great Lakes. However, recent research from the University of Michigan reveals that these temperature extremes are now occurring in a fundamentally different pattern compared to just three decades ago.

“The appearance of these extreme temperatures is increasing,” said Hazem Abdelhady, a postdoctoral research fellow in the U-M School for Environment and Sustainability, or SEAS. “For most lakes, the appearance is up more than 100% compared with before 1998.” That timing is significant because it coincides with the 1997-1998 El Niño, which is one of the strongest on record, he added.

To uncover this pattern, Abdelhady and his team created an advanced modeling method to track surface temperatures across the Great Lakes. This approach enabled them to analyze the occurrence of heat waves and cold spells as far back as 1940. Surface water temperature strongly influences regional weather, a major consideration for people living in the area, as well as for travelers and shipping operations. However, Abdelhady noted that the rising frequency of extreme temperature events could also have less visible but significant impacts on the ecosystems and economic systems that depend on the lakes.

 

The frequency and intensity of heatwaves and cold spells in the Great Lakes, seen as spikes in these graphs, entered a new regime in the 1990s, according to new research led by the University of Michigan. Using a measurement called degree days that combines the magnitude and duration of a temperature anomaly, the researchers showed the median value more than doubled following a “phase shift” shown as a red line (similar plots are available for all of the Great Lakes). Credit: Adapted with permission from Abdelhady, H.U., et al. Commun Earth Environ, 2025, DOI: 10.1038/s43247-025-02341-x (Used under a CC BY 4.0 license)

“These types of events can have huge impacts on the fishing industry, which is a billion-dollar industry, for example,” Abdelhady said. Tribal, recreational, and commercial fishing in the Great Lakes account for a total value of more than $7 billion annually, according to the Great Lakes Fishery Commission. 

Sudden shifts threaten ecosystems and water quality

According to Abdelhady, fish are generally able to adjust to slow shifts in water temperature by moving to more suitable areas, but they may not be able to escape sudden temperature swings. Fish eggs are especially vulnerable to unexpected spikes or drops.

Extended periods of heat or cold can also interfere with the lakes’ natural processes of mixing and layering, which are crucial for maintaining water quality and supporting aquatic life. These disruptions can affect ecosystems and the water sources that communities depend on for both drinking and recreation.

With the current patterns now identified across all five Great Lakes, the research team is working to expand their model to forecast future extreme temperature events. Abdelhady explained that by exploring how these events relate to larger climate systems, like El Niños and La Niñas, we can become better equipped to manage the risks they pose. 

 

 Red boxes show the intensity of heat waves, while blue boxes show the intensity of cold spells on Lake Superior, the fastest warming of the Great Lakes, since 1940. Black lines indicate “breakpoints” or significant shifts in trends (similar plots are available for all of the Great Lakes). 

Credit: Adapted with permission from Abdelhady, H.U., et al. Commun. Earth Environ., 2025, DOI: 10.1038/s43247-025-02341-x

 

“If we can understand these events, we can start thinking about how to protect against them,” Abdelahdy said.

The study was conducted through the Cooperative Institute for Great Lakes Research, or CIGLR, and published in Communications Earth & Environment, part of the Nature journal family. The work was supported by the National Science Foundation, its Global Centers program, and the National Oceanic and Atmospheric Administration, or NOAA. 

Capturing the greatness of the lakes

A major challenge in this research was the sheer scale of the system being studied. While computer models exist to simulate the behavior of typical lakes worldwide, the Great Lakes present a unique case.

They form a connected system of five distinct lakes, hold over 20% of the planet’s fresh surface water, and have a combined shoreline that rivals the length of the entire U.S. Atlantic coast (including the Gulf of Mexico).

In many regards, the Great Lakes have more in common with coastal oceans than with other lakes, said study coauthor Ayumi Fujisaki-Manome, who is an associate research scientist with SEAS and CIGLR.

“We can’t use the traditional, simpler models for the Great Lakes because they really don’t do well,” Fujisaki-Manome said.

So Abdelhady turned to modeling approaches used to study coastal oceans and tailored them for the Great Lakes. But there was also a data hurdle to overcome in addition to the modeling challenges. 

Filling in historical gaps with data

Satellites have enabled routine direct observations of the Great Lakes starting about 45 years ago, Fujisaki-Manome said. But when talking about climate trends and epochs, researchers need to work with longer time periods.

“The great thing with this study is we were able to extend that historical period by almost double,” Fujisaki-Manome said.

By working with available observational data and trusted data from global climate simulations, Abdelhady could model Great Lakes temperature data and validate it with confidence back to 1940.

“That’s why we use modeling a lot of the time. We want to know about the past or the future or a point in space we can’t necessarily get to,” said coauthor Drew Groneworld, an associate professor in SEAS and a leader of the Global Center for Climate Change and Transboundary Waters. “With the Great Lakes, we have all three of those.”

David Cannon, an assistant research scientist with CIGRL, and Jia Wang, a climatologist and oceanographer with NOAA’s Great Lakes Environmental Research Laboratory, also contributed to the study. The study is a perfect example of how collaborations between universities and government science agencies can create a flow of knowledge that benefits the public and the broader research community, Gronewold said.

The team’s model is now available for other research groups studying the Great Lakes to explore their questions. For the team at U-M, its next steps are using the model to explore spatial differences across smaller areas of the Great Lakes and using the model to look forward in time.

“I’m very curious if we can anticipate the next big shift or the next big tipping point,” Gronewold said. “We didn’t anticipate the last one. Nobody predicted that, in 1997, there was going to be a warm-winter El Niño that changed everything.”

 

 

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