It’s official! Just as we were waking up from ringing in the New Year, the Wisconsin State Climatology Office declared January 1, 2026 as the date that Lake Mendota officially froze for the 2025/26 winter season. Here at the CFL it’s hard to feel like winter has truly begun until the last of Madison’s lakes freezes over and we know we’re not alone. In Madison, like many, many places on earth, the winter freeze is a big part of our culture and recreation and sense of place – and we have the records to prove it.
You see, thanks largely to the ice block business, folks in Madison have been reliably keeping records of the ice-on and ice-off dates since 1855 and that 170 year old dataset reveals some big changes in winter ice cover.
This year’s freeze is well past the median freeze date of December 20th, but it’s also a far cry from the record late-freeze date of January 30th in 1932. That said, since the start of the current millennium a December ice-on on Lake Mendota has occurred a dozen times – so less than half of the time. By comparison, the 25-year period from 1975-2000 saw 20 December freezes and the 25-year period before that had only three January freeze dates and 22 in December.
Viewed over enough time, a trend emerges that indicates the days of December freezes are moving towards something that’s only talked about in the past tense. As we’ve covered before in this blog, one of the many impacts of climate change on our lakes is that we will eventually live through years where we simply don’t get to declare “ice on” at all.
Around the world, 15,000 lakes currently sit in a climate zone where they experience intermittent lake ice – some years are cold enough where the lakes freeze over and other years are warm enough that they don’t. As annual average temperatures rise, this intermittent ice zone moves north, eventually stranding the current “intermittent” lakes in an ice-free latitude.
Even if the world can somehow get its act together and 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, potentially disrupting the winter experience and traditions of the 394 million people who live within an hour’s drive of their shores. Spoiler alert – we’re probably not stopping at 2 degrees of warming. The most extreme projections for warming would push winter’s ice-covered lake zone out of the United States altogether, well north into Canada.
We’re already seeing this in action. From 1862 through the winter of 1996, southern Wisconsin’s Lake Geneva, which has long been a prime destination for regional ice fishermen, froze over each year. But, since 1997, the lake has now recorded six winters when It hasn’t fully frozen over. Lakes from Alaska to Germany and Japan are experiencing similar trends.
Luckily for anyone who loves ice fishing or skating or simply walking the frozen shoreline of a lake, we’re still living in a world of ice-covered winter lakes. But our lakes are, on average, freezing later and thawing sooner and, as you can see in the graph below, we’re getting less time to enjoy them.
Another issue that our shift in winter freezes and spring thaws has highlighted is the importance of lake ice safety – read our latest post on that here – an issue that is exacerbated by bouncing back and forth between temperatures that are above freezing and below freezing. This week will put that newly formed ice to a test, with rain now weighing it down and highs all the way into the 40s.
Here at the CFL, we’ll be looking forward to the next cold snap and hope our lakes can build up some good ice – thankfully, we’re still living in the part of the Madison lakes timeline where we get to wonder when – not if – the lakes will freeze each year.
