Less Ice Cover, Earlier Blooms

By Lee Bergquist and Thomas Content of the Journal Sentinel

(originally published March 25 2007)

Following the example of her pioneering father, Nina Leopold Bradley has documented our warming planet’s effects on our state. The trend has us heading toward a new climate. Right now we’re at the brink.

But perhaps the hardest evidence of global warming is the dwindling ice cover on our lakes.

The duration of ice on Lake Mendota in Dane County has slipped from an average of four months between 1850 and 1870 to nearly three months for the 20 years ending in 2005, according to research at the University of Wisconsin-Madison.

John Magnuson, a lake researcher at UW, said less ice cover could harm the health of some lakes.

For shallow lakes, less ice means more evaporation, which could reduce water levels.

The water in deeper lakes is divided by different temperature zones. If lakes stay warmer for a longer period, they could lose their ability to recirculate water and deprive bottom-dwelling fish of oxygen.

Outside his office in January, waves on Lake Mendota licked the shoreline. The lake didn’t freeze until Jan. 20 – the second latest date in 152 years.

Scientists found similar results on other Wisconsin lakes, across Canada and as far away as Lake Baikal in Russia.


“The studies from other places made it clear that this was not just a local phenomenon,” Magnuson said. “You didn’t need a theory. You didn’t need a computer model. You didn’t even need a thermometer.”

Other changes documented in Wisconsin include the earlier bloom of the pussy willow – a tree with silky buds and favored by many nature lovers as an early sign of spring.

Mark D. Schwartz of UW-Milwaukee found that the plant and a flowering herb called scilla bloomed nearly three weeks earlier in southwestern Wisconsin in 1998 than in 1965. Other regions of the state showed less change, but the trend “sticks out like a branch,” Schwartz said.

“It’s the sort of thing where you look at an alternative explanation, but given the amount of change we are seeing, the balance of evidence points to human events as a key factor,” he said.

Some insects also appear to be affected by higher temperatures and are moving northward.

Eggs of the praying mantis – a non-native species introduced as a predator to other insects – have begun to make it through Wisconsin winters in the past five years and are hatching on their own, according to entomologist Phil Pellitteri of UW-Madison.

“I see this as the tip of the iceberg,” observed botanist Don Waller of UW-Madison, who has studied the effects of climate change for 25 years.

“I never thought I would see definitive biological and physical evidence of global warming just a few years after most of us woke up to it.”

One concern, he said, is that plants and cold-blooded animals, in particular, “can’t just turn up the thermostat like we can” and adapt quickly to changes.

The original article can be found here.

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