Lake Superior ice sensitive to small climate shifts

Who can forget the dreaded polar vortex winter of 2013 -14? Surely not those of you in Duluth and along Lake Superior's North Shore.

It makes sense that the coldest winter in 35 years would yield the highest ice coverage in decades on the Great Lakes. One brutally cold winter season is weather, not climate. We know the longer term trends show Minnesota is warming fastest in winter.

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What you may not realize is much smaller shifts in winter climate have a huge impact in ice coverage on lakes like Superior.

Here's a note I received today from UMD Professor Jay Austin, with the Large Lakes Observatory in Duluth.

Hi Paul-

Enjoying the series on climate change- nicely done. I thought I would forward you a plot (see attached) that a grad student of mine prepared, showing seasonally averaged Lake Superior ice cover as a function of air temperature, averaged over the winter (Nov-Apr).   Each dot is a different year. (2014 is in the far upper LH corner, showing how wildly anomalous of a year it was).

CC Superior ice and temp
Winter average temperature and ice cover on Lake Superior. I've added blue and red text to enhance clarity. Image: Austin et al. UMD Large Lakes Observatory.

The take home message here is: the difference between a year with basically no open-lake ice and a year with really good ice fishing in Duluth is a function of only 1-2C in average winter air temps. I think one of the really difficult parts of communicating impacts of climate change is that the differences we are talking about (a few C over a century) sound really small. And they are, at least compared to normal diurnal or seasonal variations in temperature that people are familiar with. This graph shows that even small changes in the mean air temp can lead to dramatic differences in how the systems respond. Parts of the system can be very very sensitive to even small changes!

Jay makes a great point, ice cover on big lakes like Superior responds dramatically to relatively small changes in winter temperatures. That's why a couple of degrees warming, with more in winter can produce super-sized changes in Minnesota.

Minnesota is the fastest warming state in the nation in winter since 1970.

Minnesota's northern latitude at the center of North America means we're uniquely positioned to experience some of the most significant climate changes in the US in the coming decades.