Patty Loew:
Flying south for the winter might appeal to some people but for scientists on Trout Lake it is prime time for key research. What can you learn from a sheet of ice? "In Wisconsin" reporter Art Hackett explains that ice could hold the keys to our environmental future and he shows you why in Vilas County.

Art Hackett:
These two are limnology researchers at the University of Wisconsin’s Trout Lake research station. Limnology is the study of lakes, what's in them and what surrounds them. In October of 2007, Small and Rusak were taking their next to the last samples of the year.

Ann Small:
We have to wait until all the lakes turn over and then that's when we do our final samplings. Cindy monitors that with her temperature and oxygen profile.

Art Hackett:
When a lake turns over in the late fall organic matter from deep in the lake rises to the top. It happens as temperatures drop. Spending four hours in a boat becomes less attractive.

Ann Small:
We're usually raring to go on that last day.

Art Hackett:
Three months later the crew from the UW Trout Lake station isn't in a boat. They are on the ice. Tim Meinke pulse water samples from various depth.

Tim Meinke:
Not too many animals here. The green is from the algae that happened to be in the water.

Art Hackett:
But he's also paying attention to the 15-inch plug of ice pulled from the sampling hole.

Tim Meinke:
The ice grew and motion toward the body of the lake. Since that time we've had snow and rain accumulate on top of the surface. Then we had a warming spell. This white stuff that is not clear like the rest of the ice block is the stuff that has reformed since the original freezing and it contains dirt and air and other particles that make it cloudy like that.

Art Hackett:
The ice creates a record of pollution from the air and runoff from surrounding land. But there is something else about the ice Meinke and other researchers at Trout Lake have noticed.

Tim Meinke:
We are finding ice forming on the lakes much later in the year and the ice is leaving the lakes much earlier in the year.

John Magnuson:
Ice is sort of like a miner's canary for climate change and warming.

Art Hackett:
Dr. John Magnuson is emeritus professor of limnology at the University of Wisconsin. Ice, he says, is a good indicator for several reasons.

John Magnuson:
As you might expect, it is so sensitive to warming. Ice melts quickly and as the environment warms up, it leaves a signal that can be seen very early in the sequence.

Art Hackett:
And the freezing of a lake doesn't just reflect the fact that it is cold on one particular day. It reflects a pattern over time.

John Magnuson:
So in the previous one, two or three months and so it's also an integrated measure.

Art Hackett:
And the duration of ice cover on a given lake measured over a span of years reflects the climate. Climate refers to long-term conditions as opposed to weather, which is what is happening right now. Until scientists started staffing the Trout Lake station year round there were no reliable logs of ice on and ice off dates for Trout Lake and other lakes in the area. The record starts in 1982 and it looks like this.

John Magnuson:
The general trend in all of these lakes is for less ice cover, at about seven days less ice cover on average every ten years for that group of lakes.

Art Hackett:
This is the graph for Trout Lake. Its ice duration has dropped 5.6 days per decade.

Art Hackett:
The limnologists have only been watching the Trout Lake cluster for 25 years. To get really long-term data you have to come to Madison's Lake Mendota, where scientists have been watching the ice come and go for 150 years.

John Magnuson:
We note that it's the freeze and breakup dates are very different from year to year but when you open it up to 150 years, which is about five generations of people, you can see that it used to freeze on average around four months a year and now it's freezing on average at around three months a year. So we've lost about 25% of the ice cover on Mendota.

Art Hackett:
Magnuson says Lake Mendota's ice cover is becoming nine days shorter every decade.

John Magnuson:
We're beginning to have lakes in southern Wisconsin that don't freeze every winter. Now, that hasn't happened to Mendota yet. We came close a few years ago.

Art Hackett:
In the winter of 2000-2001 the ice cover lasted only three weeks. Magnuson won't predict when the first ice-free winter will occur but he offers another prediction involving snowfall.

John Magnuson:
The scenarios for the future are that that will continue. We'll continue to have high levels of snowfall and a lot of precipitation in the winter. That will probably result in more snow on the ice and the ice will be already thinner and so we would expect that we'll have more gray ice relative to clear ice in the future.

Art Hackett:
Limnologists care about the mix of gray ice and clear ice for a reason. More gray ice means less light enters the water. Light levels can alter the populations of microscopic plants and animals living under the ice.

Tim Meinke:
So we have two samples, the greener one comes from up very near the surface. The clearer one comes from a little bit deeper than that and it just is a little bit of a demonstration of how the algae have tended to float towards near the surface where there is more light.

Art Hackett:
Those changes work their way up the food chain affecting what kind of fish live in Wisconsin's lakes and the researchers care about the number of days the ice is covered not just because they plan on ice fishing.

John Magnuson:
The climate is changing quite rapidly at the present time and so you can see the signal of the warming that is occurring in the ice cover data.

Art Hackett:
Magnuson looks at the data for Lake Mendota and sees a disturbing cluster.

John Magnuson:
The red dots are the ten shortest ice cover. All but three are in the most recent years.

Art Hackett:
The ten years when the ice was frozen over the longest, it turns out, were all more than 100 years ago.

Patty Loew:
Several recent scientific papers from the UW continue to document the steep decline in the number of days for ice cover during the last 40 years. Warmer temperatures across North America and other influences, like changes in the ocean currents, can impact weather conditions here in Wisconsin.