Warmer winters causing more ice-free lakes in Northern Hemisphere, study finds

Climate change is having a widespread effect on lakes across the Northern Hemisphere, a new study has found.

The study, published in the journal Geophysical Research Letters, examined 122 lakes from 1939 to 2016 in North America, Europe and Asia, and found that ice-free years have become more than three times more frequent since 1978.

These ice-free years not only threaten the livelihoods of people who depend on them, but they also have the potential to cause deep ecological impacts.

"Ecologically, ice acts as a reset button," said Sapna Sharma, co-author of the study and an associate professor in the biology department at York University in Toronto.

"In years you don't have ice cover, the water temperatures are warmer in the summer. There's a higher likelihood of algal blooms, some of which may be toxic. And it can really affect spawning times and can affect fish populations under the ice."

There's also concern in the Arctic, where the warming is happening three times faster than anywhere else in the world. And with more warming, there's more permafrost thawing, which can affect water quality in northern communities.

"One impact is on the hydrology of the region," said Claude Duguay, a professor at the University of Waterloo and a university Research Chair in Cryosphere and Hydrosphere from Space who was not involved in the study.

"When you have catastrophic drainage of these lakes, of course, they disappear. And they will not necessarily reform as we get to higher temperature conditions. The impact for communities can be on food security. So you think about trapping, hunting, fishing, as well as water availability for the communities."

Of the millions of lakes in the world, the study suggests that more than 5,000 of them could be ice-free by the end of the century.

Dramatic changes

The authors found that ice-free years were more common in the second half of their study period. While there were only 31 ice-free events before 1978, there were 108 after that year.

One of the oldest records kept of lake ice is that of Lake Suwa near Nagano, Japan, which dates back to 1443, kept by Shinto priests. The study found that rather than freezing annually, it now freezes on average twice every decade.

"Within the next 10 years, it may be the last time that the lake ever freezes again," Sharma said.

These changes to the lakes, the authors say, are likely to continue for decades as the planet warms due to the ongoing release of greenhouse gases into the atmosphere.

The lakes most at risk are those that are deep, as it's more difficult for them to form ice, particularly the Great Lakes, Sharma said.

And it's not just about the quality of the water; it's also about the quantity, she noted. Ice helps reduce the rate of evaporation, so without that essential ice cover, evaporation rates may increase and reduce the amount of available freshwater.

Alex Mills, a professor at York University who studies ice phenology and was not involved in the research, has seen the change himself, particularly on Lake Simcoe in Ontario.

"The overall trend is pretty clear and that is since about 1850, the lake now freezes up about two weeks later than it used to, and it thaws about one week earlier than it used to," he said. "And so if you add those up, there's ice on the lake here about three weeks less per year than there used to be. So that's quite a dramatic change."

Mills said that Barrie, a city that lies on the shores of Lake Simcoe, used to have an annual carnival on Kempenfelt Bay every winter until the 1970s. Then someone fell through "and that was it," he said. "We never have had a carnival on the lake since then."

Though it's likely that more lakes may see more ice-free winters, Sharma said she believes that with more research and solutions, there is still hope.

"I've been to the the [United Nations climate change conference] meetings, and there's just so many young people who care about climate change who are dedicating their work lives to doing something about it. And people have very creative solutions," she said.

"I think in the next 20 or 30 years, if we can get that support to know [the] climate is changing and it's affecting us now and we need to do something about it now — if we get people on board for that, I think we can change things."