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Lake Warming Above 1.5°C Means Less Winter Ice, More Summer Algae

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The number of lakes throughout the Northern Hemisphere likely to remain ice-free in winter, and correspondingly clogged with algal blooms in summer, would more than double at 2.0°C average global warming and quadruple at 3.0°C, according to a recent study published in the journal Nature Climate Change.

To assess the threat of ice loss, a study team led by York University lake biologist Dr. Sapna Sharma “built a model using records for more than 500 lakes across the Northern Hemisphere going back to 875 AD,” reports the Globe and Mail. The model, which “correctly predicted a lake’s susceptibility to loss of winter ice cover 95% of the time,” was then “applied to a wider database of 1.4 million lakes to determine which ones would maintain annual ice cover, assuming steadily rising global temperatures.”

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Researchers discovered that in a 2.0°C scenario, 35,300 lakes in the Northern Hemisphere could be reduced to intermittent winter ice cover—up nearly 140% from the 14,800 lakes across North America, Europe, and Asia that today can no longer be depended upon to ice over as the days shorten. At 3.0°C, 57,600 historically icebound northern lakes, or 4.6% of the total, would often be open water. And “with little or no action to avert the worst effects of climate change,” the number of lakes experiencing intermittent ice loss could hit 215,600.

This shift in seasonal patterns for inland waters would have “major implications for anywhere from 394 million to 656 million people in more than 50 countries and shows that impacts from climate change are not a distant threat,” Sharma said, as winter ice cover has for millennia been central to maintaining healthy aquatic ecosystems.

“Years of reduced ice cover tend to coincide with warmer water temperatures and lower oxygen concentrations that can kill fish and increase the prevalence of toxic algal blooms,” the Globe explains.

And Sharma said it was unlikely her study fully captured the escalating peril to northern waters. The recent results “are likely conservative,” reports the Globe, in part because the data used covered just a small subset of the some 117 million of the Earth’s lakes, more than 50 million of which still freeze. Moreover, Sharma said the temperature data used in the study’s modelling did not “reflect the fact that northern regions are warming more quickly than global averages, meaning those regions could lose ice cover at a faster clip.”