By Jim Bloch
Thanks to climate change, the Great Lakes region is becoming hotter. The lakes themselves are seeing shrinking ice coverage in the winter, more harmful algal blooms in the summer, vanishing fish populations, most notably whitefish, increased threats of disease from a host of multiplying invasive species, including ticks — and the economic tolls associated with these worsening conditions.
Those are among the conclusions of a recent study from the Chicago-based Environmental Law and Policy Center in which 13 researchers from eight Midwestern universities and the National Oceanic and Atmospheric Administration updated their 2019 study on the effects of climate change on the lakes.
On the bright side, the researchers found that older growth trees sequester more carbon than previously thought, meaning that increased protection for forests may offer one way to slow the consequences of global warming.
Worldwide, the 10 hottest years on records that go back two centuries have occurred in the last 10 years. As the world’s land masses, oceans and atmosphere have overheated, extreme weather has plagued humankind – unprecedented storms, melting polar caps and glaciers, floods from rising seas, droughts and wildfires.
In addition to general warming, climate change has brought specific impacts to the five Great Lakes.
“More than 40 million people rely on Great Lakes for drinking water, fisheries, recreation, commerce, and industry, all of which are impacted by climate change,” according to the report. “The lakes sustain more than 170 species of fish and habitats for over 3,500 species of plants and animals, many of which are rare or found nowhere else.”
The consequences of climate change for the lakes may be condensed into five general areas.
The basin is warming
The Great Lakes Basin is warming – and the pace of warming is quickening.
“Since 1951, annual average air temperatures have increased by 2.9°F in the U.S. Great Lakes region,” according to the report. “Moreover, since the 2019 report, the Midwest
has already warmed another two-thirds as much (1.1°F) as it did in the decades before that (1.6°F), so warming is accelerating.”
Sometimes, the intensity of the heat is immediately dangerous. Cities like Chicago, Detroit and Cleveland act as heat islands as their concrete buildings, sidewalks and asphalt streets cook under the summer sun and retain their heat. According to the EPA, cities are anywhere from one to seven degrees hotter than surrounding areas during the day and two to five degrees hotter at night.
“Urban areas like Chicago may experience over 200 hours above 95°F by the 2030s, up from just 30 hours in recent years,” the report said.
Among other things, such relentless heat endangers vulnerable residents.”
“Lake Superior summer temperatures increased by 4.8°F from 1979 to 2023, the most
of any of the Great Lakes,” the report said. “NOAA observations show that Lakes Michigan, Huron, Erie, and Ontario all experienced record-high average surface temperatures in 2024.” The greatest temperature increases are in the deepest waters of the lakes.
The report suggests that climate change will likely raise the levels of lakes in the coming years, despite great variability year-to-year.
“One modeling study projects that future Great Lakes water levels under climate change could generally increase by mid-century (2040-2049), with Lake Superior rising by 7.48 inches (0.19 meters), Lake Michigan-Huron by 17.32 (0.44 meters), and Lake Erie by 11.02 (0.28 meters), compared to 2010-2019 level,” the report said.
Declining Ice Cover
2024 recorded the lowest average winter ice cover – 4.3 percent — on record for the Great Lakes. 2025 is different, of course. As of Feb. 1, the U.S. National Ice Center reported that nearly 56 percent of the lakes were frozen, above the long-term average, including 95 percent ice coverage on Lake Erie, the smallest and shallowest Great Lake, and 77 percent on Lake Huron.
The St. Clair River at the city of St Clair was packed with ice Feb. 4. Lake St. Clair was frozen over.
Ice cover is important for the protection of certain fish eggs, especially whitefish.
There is significant variability in annual ice coverage of the lakes. But the trend is clear. On average, the extent of ice coverage is 22 percent lower than it was in 1973.
Harmful Algal Blooms Expanding
“Significant rise in industrial agricultural runoff and warming lakes are driving toxic algal blooms—even in typically pristine Lake Superior—threatening human and pets’ health, drinking water, aquatic life, the tourism economy, and recreation,” according to the report.
Harmful algal blooms are caused by cyanobacteria, organisms that occur naturally in the water.
“Despite being bacteria, they’re often called algae, because they get energy from the sun like plants,” according to Michigan Sea Grant. “HABs thrive in warm, shallow, stagnant water with lots of sunshine and extra phosphorus and nitrogen. These nutrients often come from land-based sources, such as leaking septic systems and urban or agricultural run-off carried by rain and melting snow.”
Vanishing Fish Populations
“Whitefish—a staple of the Great Lakes ecosystem and economy—could disappear from parts of Lake Michigan within five years, even if commercial fishing halts,” the report said. “Invasive mussels and warming waters are decimating food sources and spawning conditions.”
Rising river and stream temperatures threaten the habitats of brook trout and brown trout.
Tick and Disease Expansion
“Invasive ticks like the Asian longhorned tick and Lone Star tick are spreading across the Midwest, increasing risks of Lyme disease and other illnesses,” according to the report.
A wetter and warming climate provides breeding grounds for mosquitoes, which can transmit West Nile virus, eastern equine encephalitis, zika and dengue fever, according to the State of Michigan’s website.
Economic Toll
“Reduced snowfall is undermining winter sports industries, while stronger storms and flooding strain infrastructure, impede outdoor industries, and raise insurance and maintenance costs,” according to the report.
The dangerous temperatures in heat islands such as Detroit increase the use of air conditioners, increasing energy costs – not to mention the danger that super high temperatures pose to vulnerable residents.
“Less ice (coverage on the lakes) disrupts ecosystems, worsens shoreline erosion, and hurts tourism and fishing economies,” said the report.
In 2014, officials closed the Toledo drinking water system due to contamination in Western Basin of Lake Erie by harmful algal blooms. The shutdown cost an estimated $65 million. Ongoing HAB control programs add about $100 per year to water bills per households in the Lake Erie watershed.
Forests: Some good news
“A new study of tree ring data from over 9,000 trees in Northern Wisconsin found 16 of the 20 studied species’ growth rates continue to increase, challenging the longtime assumption that tree growth slows down as trees grow older,” the report said.
That’s important because bigger trees hold more carbon.
The longer that cutting trees can be put off, the more carbon they can sequester.
“Uncut forests act as carbon sinks for atmospheric carbon dioxide and thus play a key role in modulating greenhouse warming and climate change,” the report concluded. “Logged forests, in contrast, release large quantities of greenhouse gases which take decades to recoup.”
Jim Bloch is a freelance writer based in St. Clair, Michigan. Contact him at bloch.jim@gmail.com.
