Climate change has brought more extremes to Great Lakes, study shows

Lake Superior covered in rare ice balls amid freezing temperatures

Video shows Lake Superior covered in a thick layer of icy orbs amid frigid weather conditions.

• A new study reveals the Great Lakes have entered a new climate era marked by more extreme heat waves and cold spells.
• Heat wave intensity tripled in Lake Superior, while cold spell intensity tripled in Lake Erie over the past eight decades.
• These extreme shifts pose challenges for ecosystems, fisheries, navigation and coastal infrastructure.

The Great Lakes has officially entered a new climate era, and the past is no longer a reliable guide for the future.

That’s the landmark finding in a new study by researchers at the University of Michigan, who concluded that in this new era, extremes increasingly will become more extreme.

The study, published in Communications Earth and Environment, showed that by looking at 80 years of extreme heat waves and cold snaps, researchers could pinpoint when each of the five lakes — and the Great Lakes region overall — began shifting to a new reality.

“If we operate based on what we know, it’s not going to be applicable anymore,” said Ayumi Fujisaki Manome, co-author and climate modeler at the Cooperative Institute for Great Lakes Research at the University of Michigan. “That puts us in a very vulnerable situation.”

With stronger climate extremes now the norm, Fujisaki Manome said risks are escalating for ecosystems, fisheries water quality and coastal infrastructure, like power plants and drinking water systems.

Here are six takeaways from the study.

Many changes started after El Niño event in late 1990s

The scientists borrowed computer models typically used for oceans to analyze trends in lake surface temperatures across the Great Lakes over the past eight decades. By studying these trends, they were able to determine when the region — and each individual lake — entered a new climate era.

On average, the shift began in 1998, according to Hazem Abdelhady, co-author and postdoctoral researcher at the University of Michigan. He noted that many of the changes can be traced back to the strong 1997–98 El Niño event, one of the most powerful on record.

Since then, both extreme heat and cold events have grown increasingly intense, Abdelhady said. 

Lake Superior heat waves tripled in intensity, Lake Michigan doubled

Over the past eight decades, the upper Great Lakes — Superior, Huron and Michigan — experienced the largest change in heat wave intensity. Heat waves becoming more intense could mean temperatures rising faster, or high temperatures lasting longer, Abdelhady explained.

The strength of Lake Superior’s heat waves has more than tripled, according to the study. Heat wave intensity in Lakes Huron and Michigan has more than doubled. Abdelhady said Lake Superior likely saw the greatest change because it’s one of the fastest warming lakes in the world, and has seen a dramatic decline in ice cover. 

For all of the lakes, 1996 was the year when things changed significantly, except for Lake Erie, which occurred 1991. 

More: In winter, the waters of Lakes Michigan and Huron separate into layers. Not anymore. Why?

Lake Erie grappling with extreme cold snaps

Cold spells − which would mean a rapid drop in temperature, or abnormally cold weather lasting longer − have more than doubled in intensity across all five lakes, the study found. In Lake Erie, they have nearly tripled. 

Lake Erie has seen the greatest change in cold spells because it’s the shallowest of the Great Lakes and can cool and freeze more quickly, Abdelhady said.

The shift in cold spell intensity happened around 1976 in Lakes Erie and Ontario, 1991 in Lake Michigan and 1996 in Lakes Superior and Huron. 

More: New data shows winters in Great Lakes region shrinking by two or more weeks since 1995

The Great Lakes moderate the region’s climate, weather

Swings in extremes also will be felt outside the Great Lakes because of how the world’s largest surface freshwater system moderates regional climate. 

Water holds onto heat and releases it much more slowly compared with land, which helps cool the summers and warm the winters. 

Areas downwind of the lakes especially will feel the weather impacts of these swings, Fujisaki Manome said. For example, lake-effect snow events will likely become more intense, she said. These events happen in the late fall and early winter when the lakes are ice-free and the water is still warm. And they typically happen on the downwind side of the lakes, which is why cities like Buffalo and Rochester, New York, have recently been hit with such deadly, heavy snowfalls. 

But the study shows that it will be much harder to predict these events, as well as seasonal predictions in general, Fujisaki Manome said. 

Extremes impact supply chains, fisheries, coastal management

The challenge of developing reliable seasonal outlooks may leave many industries unprepared for rapidly changing conditions, Fujisaki Manome said. For instance, cold spells and sudden shifts in ice conditions can disrupt navigation and supply chains, leading to delays and safety risks.

Extreme temperature swings also harm fisheries, as rapid changes prevent fish from adapting quickly enough, Abdelhady noted. 

In Lake Superior, intensifying heat waves could worsen the growing problem of blue-green algae blooms, according to Fujisaki Manome. Though still a relatively new concern for the largest of the Great Lakes, algae blooms have been on the rise since the first major bloom appeared in 2012, which scientists attribute to rising water temperatures from climate change. 

Some algae blooms are toxic, contaminating drinking water. But even if they aren’t toxic, blooms can suck up the oxygen and block sunlight, which impacts the rest of the food web. Algae blooms are also eyesores that can damage coastal economies.

More: Cold, snowy winters are part of Wisconsin’s identity. But are they a thing of the past?

Climate change in the Great Lakes is undeniable

The new study adds to the growing record of how climate change is impacting the Great Lakes region. 

Winter is the fastest-warming season in the Great Lakes region, becoming increasingly warmer and wetter, with less snowfall. The season has shortened by several weeks, and ice cover has steadily declined over the past 50 years.

Changes are even happening to the lakes themselves. For instance, a study published earlier this year found that Lakes Michigan and Huron don’t consistently separate into layers — or stratify — in the winter anymore.

More: Wisconsin’s 2024 climate review: A year of unprecedented weather, and record highs and lows

Caitlin Looby is a Report for America corps member who writes about the environment and the Great Lakes. Reach her at [email protected], follow her on X @caitlooby and learn more about how she approaches her reporting.