Last week, John Magnuson, director emeritus of the Center for Limnology, spoke at our weekly Wednesday seminar about lake ice trends in our warming world. In short, the onset and duration of lake ice cover in the northern hemisphere looks a lot like the infamous “hockey stick” showing the average rise in global temperature, except the lake ice trend is heading in reverse.
We are losing 1.8 days of ice cover every decade.
It may not sound like much, but it means that, one hundred years ago, anyone who loved to skate, ski, ice fish or (yes) sail on our frozen lakes had, on average, a full month longer to enjoy those pursuits.
So what’s that mean this year? With local organizations holding their annual “ice on pools,” can we hazard a guess as to when Lake Mendota might freeze? Well, yes, but not much of one. We can look at the ten-day forecast and see that a freeze isn’t likely by mid-December. (For reference, Lake Mendota went “ice-on” on December 16th last year). And climate scientists are predicting an El Nino event is likely this winter. Historically, says Magnuson, winters featuring an El Nino have shorter ice-cover durations.
But that’s about as far as we can get on the prediction front. Magnuson presented new research trying to pick apart the numerous variables that can affect lake ice cover. Things like weather patterns, climate cycles like the El Nino-Southern Oscillation, and even sunspots all play a role. But, while researchers can say that a variable like climate oscillations impacts winter lake ice more than something like sunspots, it’s still impossible to predict what, exactly, is running the show.
The talk reminded me of a blog post from the winter of 2011/2012. Fishermen were still out (in boats, no less!) on Lake Monona on January 5th and Lake Mendota didn’t freeze until January 14th. That year, the ice was off by March 11th, giving us only 57 days of a frozen surface (compare that to the median duration of 105 days). Still, only two years later, we were introduced to the polar vortex and longest stretch of ice cover (117 days) in twenty years.
Years like that, however, are getting fewer and further between. It seems much more likely that this winter will be a milder one than the last and add another data point to our 150 years of observation showing a decline in the number of days Madison lakes spend “on ice.” While some folks may welcome that change, something Magnuson told me in 2012 gives me pause – we’re losing a lot more than just lake ice:
“Human beings have a strong sense of place,” says Magnuson. “And in Wisconsin, our sense of place includes the four seasons and that includes winter. And in our area, that sense of place includes lakes. And these are important to us. This sense of place affects how we see ourselves and what we do in their lives and what we hope our children will get to do in their lives.”
“Historically [in the mid-1800’s] Lake Mendota had about 4 months of ice. And right now we’re averaging about three.”
Maybe the ecological or economic impacts of that change aren’t catastrophic, but “on the other hand, I’m unhappy. I’m actually sad that we’re losing winter as we knew it.”