I remember vividly a winter’s night in 1969 when the sound of a spontaneous room-wide drumming session in the Rathskeller of the UW-Madison Memorial Union became too much input, so I escaped out onto the frozen, silent surface of Lake Mendota. 

The peace on the ice was total. And so soothing that I can conjure up the sensation to this day. 

Back then, I assumed that because it was January, I could safely slip away onto the ice. That’s an assumption I would not make today. 


People ice skate on Lake Mendota on Jan. 16, 2019. The lake froze on Dec. 15, 2018, reopened on Dec. 21, 2018, and then froze again on Jan. 10, 2019. Northern lakes are experiencing fewer frozen days and are likely to experience more ice-free winters as the climate warms. PHOTO BY KELLY APRIL TYRRELL

Many northern latitude lakes are at risk of experiencing ice-free winters in the coming decades, according to a study published January 28 by an international team of researchers, including the UW-Madison. 

In some places, lake ice will disappear altogether

by the end of the century.

The first global estimate of how many lakes are likely to lose winter ice cover as the climate warms is not cheery.

Co-author John Magnuson, emeritus director of the Center for Limnology at the University of Wisconsin-Madison, says the team developed a model to predict which lakes would lose ice first, and how that ice loss would be distributed across different latitudes.

The result is a map that shows the extent of winter lake-ice retreat under different global warming scenarios and highlights what could still be saved if we actually made the effort to reduce global emissions. 

lake map

Currently, 15,000 lakes sit in a climate zone where they experience intermittent lake ice – some years are cold enough that the lakes freeze over and other years are warm enough that they don’t. 

These lakes are a “harbinger of permanent ice loss.” As annual average air temperatures warm, this intermittent ice zone moves north, eventually leaving the lakes south of it looking at an ice-free future. 

These changes are happening now. 

“It’s not one of these climate change predictions where you think, ‘Oh, I have 100 years before this might become my reality,'” says Professor Sapna Sharma of York University.

Even if the world can meet the Paris Agreement’s climate mitigation goals to limit global average temperatures to two degrees Celsius of warming, the study predicts the number of these intermittent ice lakes will increase to 35,300, disrupting the winter experience and traditions of the 394 million people who live within an hour’s drive of their shores.


Lake Mendota thaws in January after an initial freeze in December. Northern lakes are experiencing fewer frozen days and are likely to experience more ice-free winters as the climate warms. PHOTO BY ADAM HINTERTHUER

And under a “worst-case” climate scenario of eight degrees Celsius warming (predicted by some models as the extreme case if the world does not act to reduce its greenhouse gas emissions) the number of intermittent-ice lakes jumps from 35,300 to 230,400, bringing lake ice impacts close to home for 656 million people spread across more than 50 countries. 

The extreme level of warming would push winter’s ice-covered lake zone north of the United States, well into Canada.

From 1862 through the winter of 1996, southern Wisconsin’s Lake Geneva, a prime destination for regional ice fishermen, froze over each year. But, since 1997, the lake has had four ice-free winters. Lakes from Alaska to Germany and Japan are experiencing similar trends. 

The real damage from non-freezing lakes

The drastic changes in Earth’s climate over the last several decades do more than limit human recreation on frozen lakes. 


Graphic example of algal bloom.

Lakes that don’t freeze over are more susceptible to evaporative water loss during the winter, and warm up faster through spring and summer. This can lead to lower water levels, an increase in potentially harmful algal blooms, and reduced oxygen levels in the water, which can be detrimental to fish and other wildlife. It also threatens human use for drinking water, boating and fishing. 

It means millions of people will find themselves awaiting the big winter freeze they have come to depend on and turn to each other to ask: “Winter is coming … right?” 

The study was supported by the Ontario Ministry of Research, Innovation and Science Early Researcher Award, the York University Research Chair program, the Natural Sciences and Engineering Research Council of Canada, the Department of the Interior Northeast Climate Science Center, and the North Temperate Lakes Long-Term Ecological Research program.

What’s been happening with our favorite lake?


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