A new study puts more scientific teeth behind everything from having white Christmases to how long ski hills stay open: Winters on the Great Lakes are shrinking.
Since 1995, winter has shortened by about 14 days — and in some spots close to three weeks, according to the recent study published in Environmental Research Letters. The study adds to mounting evidence that winter is the most rapidly changing season in the Great Lakes region, growing warmer and wetter with less snow.
Most prior research has been done on land. When it comes to what is going on in the lakes themselves, “winter is quite the blind spot” for scientists, said Craig Stow, researcher at the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Lab and co-author on the study. That’s because so far, most scientific research has occurred after ice off, when the last bit of ice melts and research vessels can get out on the water, he said.
The study adds another piece to the puzzle, contributing to the ever-evolving understanding of what occurs in lakes during the winter months, Stow said.
Here are four takeaways about the importance of this new study, and how winter out on the lakes doesn’t look the same as it used to.
When lake water ‘mixes’ is key to understanding seasons
Most of the information scientists have gathered during the winter has been on changes in ice cover, showing a steady overall decline over the past half century, accompanied by extreme swings between years with extensive and minimal ice cover.
But ice cover is just one aspect of measuring winter changes on the world’s largest surface freshwater system. Scientists also needed to look at when the water in the lakes “mixes.”
In general, water in the lakes mixes during the spring and fall. That’s the point at which the water temperature is about the same from top to bottom. In the summer and winter the lakes are stratified, forming distinct layers based on temperature. In the summer, the surface is warmer than the bottom. In the winter it’s the opposite: the surface is colder than the bottom.
The lakes mix when the surface temperature hits a magic number: 4 degrees Celsius or roughly 39 degrees Fahrenheit. That’s when water is at its most dense — so dense that it will sink to the bottom, allowing the water column to turnover, or mix. To measure this, the scientists looked at surface water temperatures from satellite data.
Understanding how climate change is impacting winter conditions across the entire region has remained elusive because just one lake consistently freezes over — Lake Erie — while the four others regularly see ice cover only on their nearshore areas.
In other words, winter looks a lot different in Lake Erie than in Lake Superior.
Nevertheless, the scientists found that winter is shrinking by about two weeks per decade on average across all five lakes.
A steeper decline is seen in some locations, like the bay of Green Bay
The biggest drop in winter days occurred in Lakes Superior and Erie, which has lost close to three weeks of winter, according to co-author on the study Eric Anderson, a researcher at the Colorado School of Mines, in Golden, Colorado.
The scientists also saw trends in different spots within each of the lakes. For instance, in Lakes Michigan and Ontario, the loss of winter days was mostly within shallow areas, like the shoreline and bays. Anderson also noted a steep decline in ice cover days within Lake Michigan’s bay of Green Bay.
However, in Lakes Superior, Huron and Erie, winter days were lost across the entire area of each lake, including both shallow and offshore areas.
According to the study, the Great Lakes also have lost an average of about 1.5 days of ice cover per year since 1995.
Lake Superior gains fall days, Lake Michigan gains spring days
There was a split between losing winter days to fall or spring, Anderson said. For instance, Lake Superior is losing its winter days to fall, while Lakes Michigan and Huron are losing winter days to spring.
However, it’s not yet clear why this split is occurring. Much more research will be needed to uncover the underlying reasons, Anderson said.
Projections are hard because so much is going on simultaneously
While it’s clear that winter isn’t the same in the Great Lakes as it once was, Stow said it’s hard to make projections about what the impacts will be because “everything is changing.”
With climate change “there is too much going on at once,” Stow said, but a shrinking winter will likely have cascading effects throughout the rest of the year.
A lack of ice and change in the timing of lake mixing can impact the food web, which in turn can affect fisheries, a $7 billion dollar industry in the region.
For example, a change in timing and warmer waters can cause phytoplankton to bloom before zooplankton, which feed on them. Without zooplankton, the entire food chain, especially fish that rely on them, can be disrupted.
Ice helps protect fish populations that spawn in the fall in nearshore areas by calming winds and waves. This prevents sediment from being stirred up, ensuring higher hatchling survival in the spring.
The shrinking season may also spell radical changes for recreation and business. It could take years, even decades, for that to fully shake out.
Caitlin Looby is a Report for America corps member who writes about the environment and the Great Lakes. Reach her at clooby@gannett.com, follow her on X @caitlooby and learn more about her reporting.
(This story was republished on Feb. 24,2026, to make it free for all readers.)
This article originally appeared on Milwaukee Journal Sentinel: New data shows winters in Great Lakes region shrinking by two or more weeks since 1995
Reporting by Caitlin Looby, Milwaukee Journal Sentinel / Milwaukee Journal Sentinel
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