Climate Change Causes Weaker, More Dangerous Lake Ice

Global warming causes temperature swings that leave ice weakened for days, with deadly consequences

A photograph of a frozen lake landscape with trees on the distant horizon
70 percent of drowning deaths in Canada involve lake ice, and these accidents are becoming more common as climate change causes more temperature swings and moderate weather Photo by Lesley Knoll, University of Minnesota

Climate change is warming the Arctic twice as fast as the rest of the world, affecting Arctic wildlife behavior and delaying sea ice refreezing.

Now, new research shows that increasingly warm weather in the North is correlated with a rise in winter drowning deaths. The findings, published on November 18 in the journal PLOS One, take into account more than two decades of data on drownings from ten countries in the northern hemisphere. Most of the drownings occurred on days with air temperatures between 23 and 32 degrees Fahrenheit, Veronica Penney reports for the New York Times. Communities whose livelihoods require extended time on the ice, like Indigenous peoples, saw the sharpest increase in drownings over the past few decades. And often, those who die from drowning are tragically young.

"I started going through this data and I was just like, 'I can't do this.’ It's devastating because the kids are four, five, six years old,” says York University biologist Sapna Sharma, lead author of the new study, to CBC’s Nicole Mortillaro.

The researchers focused on Minnesota, which records data about the age and cause of drownings, as a case study, and found that 44 percent of those who drowned without a vehicle involved were children younger than nine years old.

"They were playing on the ice, tobogganing or ice skating and they just weren't able to recognize when the ice was unsafe,” Sharma tells BBC News’ Mark McGrath. “They may not have recognized that slushy ice or a little open patch of water could be so fatal."

Most of the people who died while using vehicles like snowmobiles were under 24 years old, but adults up to 39 years old were the most vulnerable to winter drowning. Out of all of a country’s drowning deaths, Canada had the highest proportion that involved accidents on lake ice, with a median of 70 percent. Many of these occurred in territories where people cross lake ice for hunting, fishing or transportation, per CBC.

Both both Vermont and Minnesota warn that there’s no such thing as safe ice—lake ice can freeze unpredictably, thin in some areas and thick in others. Parks Canada advises potential ice skaters that clear blue ice is the strongest, while gray ice indicates the presence of water in the ice, which weakens it. Old ice can become rotten, or broken apart from cycles of freezing and thawing, even if it appears thick. And cycles of fluctuating air temperatures are becoming more frequent amid climate change.

“Milder temperatures mean that the ice is not as thick, or not as solid as it would otherwise be,” says Wilfrid Laurier University geographer and environmental scientist Robert McLeman, who was not involved in the new research, to the New York Times. “And so people are going out onto it and not realizing that the ice is rotten.”

As winter arrives amid the Covid-19 pandemic, Sharma is worried that people who are not familiar with ice safety might seek out outdoor activities like lake or pond ice skating without knowing how to recognize risk.

"This is really important especially this year with [Covid-19] and more people spending time outside," Sharma tells CBC. "It might be the first year that they're going out, like exploring nature, because there's nothing else to do."

The new study suggests several ways that localities could advise their communities about ice safety. Germany and Italy, for example, have agencies devoted to monitoring ice conditions and sharing advisories about ice safety, which may have helped reduce the number of drowning deaths. The paper also highlights the value of local knowledge, specifically how Cree hunters track air temperature and precipitation to evaluate inland ice conditions.

“It might be minus 20 Celsius [minus 4 Fahrenheit] today and tomorrow and the weekend, but last week it was 15 Celsius [59 Fahrenheit] ,” Sharma tells the New York Times. “We might have forgotten as individuals that it was warm and sunny last week on a Tuesday, but the ice didn’t forget.”