BUFFALO, N.Y. -- In his 30 years of studying freeze-thaw cycles of lakes in New York State, Kenton Stewart, Ph.D., has never seen some lakes in his lake-ice network stay unfrozen for an entire winter unless it was an El Nino year.Until the winter that officially ended on Wednesday.
"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, professor emeritus of biological sciences at the University at Buffalo. Stewart, who studies the freeze-thaw cycles of more than 250 lakes in New York State, said lakes that did not freeze this winter include some that did so during an El Nino year.
Those that froze did so 1-3 weeks later than usual. Some lakes have already thawed and Stewart expects others to lose their ice about 2-3 weeks earlier than normal. 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.
"One surprising thing about the 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 predicting a colder than normal winter for the Northeast and the Upper Midwest and Great Lakes areas. "The complete opposite has happened," said Stewart.
"This winter was 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 1997-98, 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 as spring progresses. "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 did not do so this winter were:
o Irondequoit Bay in Rochester
o Hemlock and Canadice lakes located south of Rochester
o Cross Lake located west of Syracuseo Onondaga Lake in Syracuse
o Otisco Lake located west of Syracuse
o Big Green Lake in Green Lake State Park located east of Syracuse
o Ashokan and other water supply reservoirs north of New York City
Conesus Lake located south of Rochester froze only partially this winter.
Stewart said that the lake-ice data provide 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. Stewart contacts the hundreds of lakeside observers in his loyal ad hoc network multiple times during each winter. He is able to evaluate the general trustworthiness of the lake-ice dates he gets by comparing them with what he knows about the depth and surface area of a lake, data from other observers in the area and the extent of detail provided by the observer.
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