Biologist finds lakes not freezing

By ELLEN GOLDBAUM
Contributing Editor

In 30 years of studying the freeze-thaw cycles of lakes throughout New York State, Kenton Stewart, professor emeritus of biological sciences, has never seen some lakes in his lake-ice network stay unfrozen for an entire winter, unless it was an El Nino year.

	Using an ice auger, Kenton Stewart tests the thickness of the ice on Lake LaSalle during a past winter when the lake froze.

Until now.

"The majority of the lakes in the state still froze, but a surprising number that developed ice covers in previous winters had only a partial skim of ice this winter, or did not freeze at all," said Stewart, who studies the freeze-thaw cycles of more than 250 lakes in New York State.

The current season reinforces a hypothesis Stewart and other lake-ice scientists made in a paper published in the journal Science in September 2000: that lake-ice dates are proxy indicators of climate change.

"One surprising thing about this unusually mild winter is that while it was as mild as some of the strong El Nino events that we've seen, it was not associated with an El Nino event in the Pacific Ocean that can have an atmospheric influence," said Stewart. "It also was not foreseen by the Climate Prediction Center of the National Oceanographic and Atmospheric Agency."

In fact, Stewart said, as of last November, the Climate Prediction Center was forecasting a colder-than-normal winter for the Northeast and the Upper Midwest and Great Lakes regions.

"The complete opposite has happened," said Stewart.

"This winter is particularly noteworthy," he continued, "in terms of the number of lakes that did not freeze because many of the lakes that froze during the strong El Nino winter of 1997-1998—which was especially mild—did not freeze this year."

According to Stewart, the amount of solar radiation increases as spring approaches, making it less and less likely that lakes that have not frozen so far will freeze so late in the season.

"Such late freezes have happened, but they are rare for deep lakes, which require many days of sustained, sub-freezing temperatures," he said. "Just two to three cold days won't do it."

Among the lakes in New York State that usually freeze completely but have not done so this winter are Irondequoit Bay in Rochester, Cross Lake west of Syracuse, Onondaga Lake in Syracuse, Hemlock and Canadice lakes south of Rochester, Otisco Lake west of Syracuse, Big Green Lake in Green Lake State Park east of Syracuse and Ashokan and other water-supply reservoirs north of New York City.

The lakes in Stewart's ice network that did freeze this year did so roughly one to three weeks later than usual. Some lakes already have lost their ice, and he expects others to lose their ice about two to three weeks earlier than in most years. He cautioned that because of the temperature gradient across the state, there is no average freeze-up or break-up date that would hold true for the entire state.

Stewart said that the lake-ice data provides additional evidence for the unusual warming this winter because they are independent of air-temperature records.

In September 2000, Stewart and other lake-ice scientists from around the world published a paper in the journal Science in which they drew the first global picture of trends in the formation and dissolution of ice on lakes and rivers in the Northern Hemisphere during the past 150 years.

That paper proved the hypothesis of Stewart and his co-authors that lake-ice dates are proxy indicators of climate change.

"The current season seems to reinforce that point, and it demonstrates how unexpected some freeze-thaw events may be," he said.