Extreme heat. Warmer water. More ticks. Fewer fish. Climate change report brings grim news.
That's according to a new report by the Environmental Law and Policy Center, conducted by researchers around the Great Lakes. The report is an update to a 2019 report examining the effects of climate change on the lakes themselves and surrounding region.
Despite the discouraging tendency these days to see everything through a political prism, the science itself is incontestable and apolitical: Climate change is caused by human activity, primarily the use of fossil fuels, like coal, oil and gas. Fossil fuels account for 75% of greenhouse gas emissions, which trap heat and warm the planet.
A warmer planet incites a ripple effect — and yes, even in the Great Lakes, a place that many consider a climate haven.
Since 1951, annual average air temperatures have increased by nearly 3 degrees Fahrenheit in the U.S Great Lakes region — a stunning change given the massive cooling effect the lakes have on the region.
"Climate is one of the most important issues facing humanity," said Don Wuebbles, lead author on the assessment and emeritus professor at the University of Illinois. "We are driving changes and now we have to figure out together what do we do about it."
Here are eight takeaways from the climate change report.
More: Wisconsin's 2024 climate review: A year of unprecedented weather, and record highs and lows
More dangerous heat waves
The Great Lakes region warmed substantially faster in the six years since the last assessment than it did in decades prior, the report shows.
And with this warming trend, dangerously hot days are happening more often, especially in urban heat islands where surfaces like parking lots, sidewalks and streets absorb and hold onto heat. In Milwaukee, for instance, a mapping campaign by the Wisconsin Department of Natural Resources showed that at night, there can be a 10-degree temperature difference between the hottest and coolest parts of the city.
By the 2030s, urban areas like Chicago could face more than 200 hours of temperatures exceeding 95°F — up sharply from just 30 hours in recent years. This surge in extreme heat drives up energy demand and poses serious health risks to vulnerable populations.
More: Many Milwaukeeans live in a heat island, and 'we can't air condition our way out of this'
In Milwaukee, one of the country's most racially segregated cities, where historical redlining has pushed communities of color into more industrial areas, urban heat islands continue to reinforce longstanding inequities.
The report also shows that the number of cool nights continues to decline, another alarming trend given extreme nighttime heat can actually be deadlier than daytime heat.
More extreme rain events
Since 1951, annual total precipitation has increased by 15% in the U.S. Great Lakes region. With that, the frequency of extreme precipitation events has also continued to increase, the report shows.
Between 2017 and 2024, the number of days with at least 2 inches of precipitation was 6% higher than the 1986-2016 average and 37% higher than what scientists refer to as the baseline period of 1901-1960.
Declining ice cover, rising lake levels
The report confirms growing evidence that winters in the Great Lakes region are being hit hardest by climate change. Winter is the fastest warming season in the region, resulting in the steady decline in ice cover over the past five decades. The decline has also been met with extreme swings from near record highs to near record lows within a few years.
Average ice cover across all five Great Lakes during the 2024 ice season was the lowest on record since scientists began recording it more than 50 years ago.
More: New data shows winters in Great Lakes region shrinking by two or more weeks since 1995
One surprising finding, Wuebbles said, is that while climate change is leading to greater fluctuations in lake levels, they are generally rising overall. A 2022 modeling study projected that by mid-century, Great Lakes water levels could rise upwards of 17.3 inches in Lake Michigan and Huron, and 7.5 inches in Lake Superior.
Warming water temperatures
According to the report, summer lake surface temperatures have increased in recent decades. For instance, Lake Superior summer temperatures increased by nearly 5 degrees Fahrenheit from 1979 to 2023 − the most of any of the Great Lakes. In 2024, Lakes Michigan, Huron, Erie and Ontario all experienced record-high average surface temperatures in 2024.
The report also highlights that the greatest rates of temperature increase continue to be in deeper waters, with smaller increases near shorelines. Winter's influence in deeper waters is also disappearing, with shifts in fall overturn and winter cooling that could impact the lake's ecosystem.
More: In winter, the waters of Lakes Michigan and Huron separate into layers. Not anymore. Why?
Vanishing fish populations
The report highlights that lake whitefish are on the verge of collapse, with stock assessment models showing that in Lake Michigan the prized species may disappear from some locations within five years. And even if commercial fishing for lake whitefish ceases, they could still face local or regional extinction.
Warming winters and reduced ice cover is largely to blame, the report says, as ice cover protects whitefish eggs along the shoreline. However, another reason for the decline is invasive zebra and quagga mussels, which pick off larval whitefish before they reach adulthood.
In Wisconsin, warming summer stream and river temperatures are expected to reduce habitat for brook and brown trout by 68% and 32%, respectively, by mid-century.
More: Invasive mussels drastically altered the Great Lakes. Now, scientists are fighting back.
Ticks are expanding their range
Many kinds of ticks are expanding their range and growing more abundant in the Midwest, presenting an increased risk for disease in humans and wildlife.
For instance, the report highlights warming temperatures have pushed black legged ticks, a primary carrier of Lyme disease, northward. The lone star tick, which is known for causing a life-threatening allergy to red meat, has also expanded its range.
Old growth forests are still helping − for now
The updated assessment also highlighted that old growth forests are still taking in a significant amount of carbon dioxide out of the air
For instance, tree ring data from 9,000 trees in northern Wisconsin show older trees store more carbon than scientists previously thought. The fact that old-growth trees store more carbon underscores why cutting them down is a serious mistake, Wuebbles said.
Delaying tree harvests and protecting older forests enhances carbon sequestration, making untouched forests vital for reducing carbon dioxide and combating climate change.
Rising economic toll
Communities around the region have strong ties to the Great Lakes, and economic impacts of climate change are expected to cross all sectors.
The report notes that the Anishinaabeg, which include the Ojibwe, Ottawa and Potawatomi, are poised to be disproportionately affected by climate change. Impacts to land, water, food and plant and animal species threaten practices as well as cultural sites.
Reductions in lake ice cover are disrupting local economies around the Great Lakes by affecting fishing, winter sports, shipping schedules and biological processes crucial to aquatic ecosystems.
Public health risks are rising due to more frequent heat waves, flooding and the spread of vector-borne diseases like those carried by mosquitoes and ticks.
Industries and transportation systems face challenges from drought, extreme heat and infrastructure damage, while changing lake conditions impact shipping efficiency.
Tourism and fishing are also affected, with shorter winters reducing seasonal activities and warming waters threatening cold-water fish species but benefiting warm-water ones.
More: Great Lakes tribes' knowledge of nature could be key to navigating climate change. Will enough people listen?
This story was updated to add a photo gallery.
Caitlin Looby covers the Great Lakes and the environment for the Milwaukee Journal Sentinel. Reach her at clooby@gannett.com, and follow her on X @caitlooby.
Caitlin's work is supported by the Brico Fund, Fund for Lake Michigan, Barbara K. Frank, and individual contributions. Grants and donations help make this reporting possible. The Journal Sentinel maintains full editorial control.
To learn more about our community-funded journalism initiatives, or to make a tax-deductible donation, visit https://givebutter.com/milwaukee-journal-sentinel. Checks can be addressed to Local Media Foundation with 'JS Environment' in the memo, then mailed to: Local Media Foundation, P.O. Box 85015, Chicago, IL 60689.
This article originally appeared on Milwaukee Journal Sentinel: Report shows ongoing impact of climate change on Great Lakes
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