Experts spot changing weather patterns affecting Madison lakes

MADISON, Wis. — A four-degree warmup might sound nice to those sitting out on the ice on Madison’s lakes, but for scientists, it’s not comforting at all.

“We’ve had an increase in the temperatures, both the daily high temperatures and the daily low temperatures,” Ed Hopkins, Wisconsin’s assistant state climatologist, said.

For the past two decades, Hopkins has helped tracked the ice on and ice off dates for Lake Mendota. Records go back more than 160 years, making it one of the longest lake ice records on the continent, he pointed out.

But when he looks through the data, a troubling trend appears.

“The times of freeze date is getting later,” he said. “… The interesting thing is that the nighttime temperatures, especially in winter, are becoming higher more rapidly than the daytime.”

The average freeze date for Lake Mendota in 2022 is about five days later than it was in 1971, while the average ice cover duration is down nearly 24 days and the average winter temperature is four degrees warmer.

This year, Lake Mendota froze over officially on Jan. 7.

RELATED: Lake Mendota officially freezes over for winter season

While the statistics may sound like just a crack in the ice, it’s actually a crack in the entire lake’s structure.

“Any time you take part of the circle out of the ecosystem, it will affect the whole ecosystem,” Adam Sodersten, the marketing and communications director for the Clean Lakes Alliance, said.

Cold winter air is almost like a reset button for the lakes. It’s a necessary step that allows certain animals or plants to die off or go dormant. Without the cool period, plants grow longer, blocking out other plants, other fish and introducing the wrong nutrient balance and sunlight in the water.

It’s not just an ecological problem but also an economic one, Sodersten said.

“Outside of all the problems for our ecosystem, this is a big money maker for our area,” he said. “… Maybe you’re not into ice boating, maybe you don’t own one, but it draws people to the lake.’