TORONTO, Sept. 19, 2024 – Ice may look safe for a game of pick-up hockey on the lake, but as a new study out of York University found, looks can be deceiving. Warming winters are not only affecting ice thickness and timing – when a lake freezes and thaws – but also quality, making it potentially unstable and unsafe.
When lakes and rivers freeze, there are two predominant layers of ice, what's called white ice and black ice. White ice is generally opaque, like snow, and filled with more air bubbles and smaller ice crystals, diminishing its strength and stability, while black ice is clear and dense with few air pockets and larger ice crystals making it a lot stronger.
"Ice quality is important because of its direct implications for load bearing capacity for human safety and also how much light will transmit under ice for life under frozen lakes," says York Professor Sapna Sharma.
The problem, says lead author and York Postdoctoral Fellow Joshua Culpepper, is that the unpredictable and warmer winter weather is creating thinner layers of black ice and sometimes a corresponding thicker layer of white ice, the unstable kind. The two combined can make for treacherous conditions for skaters, hockey players, snowmobilers, ice anglers and ice truckers.
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"We know that in general, lake ice is forming later in the season and breaking up earlier, which implies an overall shorter duration of ice cover, but our study looked at what the ice is doing. How is it changing? You might get periods of time when people are on the ice and they think it's safe, but it really isn't. It's not sufficiently thick enough given the changes in the quality," says Culpepper.
10 cm no longer the golden rule
Thickness alone is no longer a good predictor of safe ice. If there is too much white ice and not enough black ice, the ice it may not be strong enough to hold a person's weight. It's what the researchers are calling a dangerous combination.
"For a human to go out on the ice to skate or play, that requires about 10 centimeters or four inches of black ice…but what we're seeing and what we're predicting is that climate change is contributing to more white ice conditions," says Sharma, who recommends people measure the ice and if there is only a thin layer of black ice to double the usual recommended thickness to at least 20 cm.
"Black ice is clear and there's no slush. You shouldn't be walking over slush," says Sharma, she adds that it's always best to go with someone or a group.
On thin ice
The lack of consideration for quality ice is already leading to a loss of life. In Canada last December, six people, including a couple of teens in Ontario, died within a week plunging through thin ice. Two more died in Ontario this February. In Finland, four people died from falling through weak ice in January and February alone, where the average is said to be 18 people annually. In Sweden, 16 people drowned from falling through the ice in 2014 and at least nine in 2021, for example.
The findings from a 2020 study led by Sharma found widespread drowning across the Northern Hemisphere, but surprisingly, northern Canada, the territories, had the highest drownings per capita even though it was the coldest.
"That is because of the dramatic changes in the Arctic which is warming four times faster than the rest of the globe so it's not just southern regions that are experiencing these changes in ice conditions, but also far north. What you would consider to be like extremely cold icy areas," says Sharma.
"For a transport truck, they require 100 cm or about 42 inches of black ice. So those benchmarks on transportation are no longer viable because there is more white ice, which is approximately less than half the strength of black ice. What we're predicting is a 95 to a 99 per cent loss in winter ice road transportation infrastructure without meaningful adaptations for ice safety."
That could mean remote communities are at risk of not being cut off and unable to access food, supplies, medicine and the like, during the winter.
Unseasonable winter weather
For this study, Culpepper and some of his co-authors had to stop taking ice measurements in mid-February on Lake Simcoe and early March on Paint Lake in the Muskoka region because the ice cover was dangerously thin.
Changes in precipitation from unseasonably warm weather is creating a lot of the unsafe ice conditions and unpredictability. Warmer temperatures, rain and even snow can alter the strength and thickness of lake ice.
Sharma and Culpepper recommend checking the weather reports for the last month.
"Lake ice has a memory," says Sharma. "All of the weather fluctuations are stored in the ice. If the temperature was over 0 C for a period of time, if there was rain or if there were extremely sunny conditions, all of that can affect the safety of the ice for human use. When there are freeze thaw events or temperatures are above 0 C, the ice becomes weaker, and it becomes structurally less stable."
Underneath the ice
The diminishing quality of ice is also affecting life below, the amount of nutrients available for fish and other aquatic life, such as invertebrates, as well as phytoplankton which needs light for photosynthesis, but with more white ice, it's blocking some of that light and compromising the health of the ecosystem.
But as Culpepper says, their study is one of only a few that looks at the quality of lake ice and yet that ice is changing dramatically. "The thing that stuck out to me first is the surprising lack of data that we have on ice quality broadly," he says. "We were diving into what data was available, but trying to find exactly what we could work with in terms of data that's available in the Northern Hemisphere was pretty challenging."
What's needed, he says, is regular measurements of ice quality, including black and white ice thickness, throughout the Northern Hemisphere.
The paper, Lake ice quality in a warming world, was published today in the journal Nature Reviews Earth and Environment.
