A Word About This Winter: Trends and Variability

CFL grad student, Zach Lawson releases a northern pike back into a well-frozen Lake Mendota. Photo: A. Hinterthuer
CFL grad student, Zach Lawson releases a northern pike back into a well-frozen Lake Mendota. Photo: A. Hinterthuer

Sure it’s been a long winter, but we were surprised when all that lake ice recently got political here in Wisconsin.
In January, State representative Mark Pocan told the legislature that, “Ice fishermen are already noticing fewer days they can be out on our ice covered lakes.” Perhaps because the statement was so counter to current conditions on Madison lakes, it struck some people as a dubious statement. That seemed the case, at least, because the political watchdog website PolitiFact jumped on the claim to test its veracity.
As anyone who’s paid attention to such things can tell you, Pocan was absolutely speaking the truth. In the last 150+ years of recorded data, the number of days our lakes are ice covered has shrunk. Still skeptical? Take a look at the graph below.
Despite all the peaks and valleys, this graph of the number of days Lake Mendota is ice-covered each year is trending down. Courtesy: NTL-LTER
Despite all the peaks and valleys, this graph of the number of days Lake Mendota is ice-covered each year is trending down. Courtesy: NTL-LTER

It’s plain as day, right? So WHY does one particularly cold winter cause so many people to question the reality of our warming world? One reason is the problem of “trend” versus “variability.” Each winter we live through is one variable. A trend only emerges once you can step back and look at A LOT of variables. I could go on, but the video below is just about a perfect explanation. You should watch. Seriously. It’s only a minute long. I’ll wait.

Brilliant. “He could change direction, there’s a lot we don’t know about this guy, but everything we DO know tells us he’s heading in that direction.” That is the trend. The thing we pay most attention to, though, is the dog. It’s so much more active! It’s bouncing around and going places! Like the dog, we’re easily distracted and, honestly, pretty bad at seeing the trends in our observations of past events without charting it all out.
So, yes, this had been the winter of our discontent – of polar vortices, of negative 30+ windchills, of more days stuck inside with toddlers bouncing off the walls than we can count (maybe that one’s just me). But this single winter, no matter how extreme it feels, is just one short dip in the dog’s erratic path. It’s not about to change the trend all on its own.
For all of the ice fishermen out there, I’m sure it’s been more than welcome. But, as they (and an ever growing body of data) can tell you, we’re not getting a lot of winters like this anymore.

Special thanks to the North Temperate Lakes Long-Term Ecological Research team and  their awesome data on Madison lakes. You can find decades of their measurements on ice cover, water temp, fish populations and more with their clickable lake map!

 

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