THUNDER BAY — Warming temperatures are leading to shorter periods that people can safely be on and using the Great Lakes’ ice, a new study shows.
“The decrease in the safe period of ice cover will impact how people use the ice recreationally and for other purposes,” said Joshua Culpepper, study co-author and Post-Doctoral Researcher at York University.
“What that means is overall, people will probably have a shorter window of time to use the ice.”
The study, published at York University, compared warmer climate scenarios to the historical condition of the Great Lakes from 1850 to 1880, looking at ice thickness and quality when temperatures are 1°C, 2°C and 4 °C warmer than the average.
In the immediate future, it found that people can expect a range of two to as high as 20 fewer days of safe-ice per year, but in the next few decades, Culpepper said this range will increase to three days and up to 3 weeks.
Culpepper said people can expect upwards of a month less safe-ice time on average across the northern hemisphere toward the end of the century, by their estimates.
Windows of ice-cover will decrease differently at different levels of warming and vary a little from place to place but, on average, they will decrease across the northern hemisphere, likely impacting areas including Lake Superior’s north shore, he added.
“Again, that depends strongly on the ice quality scenario. So, the higher ratio of white ice (to black ice), the shorter that window of safe ice becomes.”
White ice is generally weaker than black ice, especially at temperatures near 0 °C, so as you approach 0 °C, the ice becomes more unsafe if you have primarily white ice cover, said Culpepper.
Culpepper said they found from other studies — which inspired this research — that warmer years tend to have more white ice.
According to the researchers, estimates for 1°C were comparable to contemporary warming, 2°C was similar to a near future within the next few decades and the 4°C warming period was closer to the end of the century.
The study also looked specifically at human weight or periods when people can safely use the ice. They didn't calculate the thicknesses needed for activities that involve snowmobiles or vehicles, but he said you would need much thicker ice cover.
Most of the increase in the amount of time when ice is unsafe, said Culppeper, happens in the earlier parts of its formation period rather than the breakup period – on average for about three weeks during ice formation compared to roughly one week during the melt.
“I think what people should take away from this study is that ice safety is of critical importance. Some of the motivation for this study is ensuring people stay safe on the ice,” said Culpepper.
There are three things, he said, people should consider before going on the ice: the overall thickness of the lake ice, the quality of the lake ice and the conditions leading up to the day people want to go out on the lake.
“You may want to reconsider going out if you have thin ice or a more degraded ice quality, more white ice than black ice and if the temperatures are warmer (near 0 °C). You want to make sure you're practicing really safe practices when you go out on the lake ice,” said Culpepper.
The study has also opened many questions about what people can do on the ice and what is going on underneath, including what ice quality is doing on a finer scale.
“If people wanted to know what was going on in their local lake, that would be something you'd have to look at specifically for that lake,” said Culpepper.
“Other questions are also open about what changes in ice quality and thickness are going to do to under-ice ecosystems because quality and snow can impact the amount of light entering into the water column and we're really interested in what is also going on below the ice.”