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Ice cover in North America’s Great Lakes has hit its lowest level for 50 years after an unusually warm start to winter, continuing a decline that is being closely monitored for its links to climate change.
According to data from the Great Lakes Environmental Research Laboratory, just 0.43 per cent of the interconnected lakes was covered with ice on Thursday compared with an average of 10.6 per cent for this time of year over the past half-century.
Low ice cover across the world’s largest group of freshwater lakes by area risks triggering knock-on extreme weather effects across the north-eastern US and southern Canada.
Tony Schumacher, chief meteorologist at the Great Lakes Weather Service, said the record high temperatures in the region at the end of 2023 were partly the result of the naturally occurring El Niño effect, which causes warmer sea-surface temperatures in the Pacific.
Climate change driven by the burning of fossil fuels also played a part, he added. The long-term global average temperature has risen by at least 1.1C since the start of the industrial era.
The US experienced its warmest December on record last year, based on preliminary data from the National Weather Service, with several cities, including Milwaukee, on Lake Michigan, breaking previous records for the month.
The warmer weather prevented the lakes from freezing over as much as is typical for this time of the year. At Lake Erie, the southernmost and shallowest, and the nearby Lake St Clair, adjacent to Detroit and straddling the US-Canadian border, no ice cover was recorded at all.
The anaemic start to winter has resulted in below-average snowfall across much of the US compared to the past 15 years, shrinking the ski season in the north-west and the north-east.
But meteorologists expect more snow in some areas, driven in part by the lack of ice cover. When cold air passes above unfrozen and relatively warmer water, the pressure difference pushes warmer air and water vapour upwards, helping create belts of snow or rain clouds as well as strong winds.
This month’s relatively high water temperatures combined with an anticipated cold snap in mid-January could lead to “pretty significant amounts” of so-called “lake-effect snow” in parts of Michigan, Ohio and New York State, Schumacher said.
“The longer stretch of open water, the greater potential for lake effect snow,” he added.
This phenomenon helped drive heavy snowfall in the central and eastern US at the end of 2022, when a so-called “bomb cyclone” of Arctic wind wreaked havoc on Christmas travel plans.
The long-term downward trend in ice cover across the lakes may have other consequences for society and trade.
Shorter periods every year in which the lakes are frozen could boost key domestic trade routes that criss-cross the lakes, including at a choke point for shipping between Lake Superior, the world’s largest freshwater lake by area, and Lake Huron, according to a paper published in 2022 by University of Wisconsin-Superior academics.
The five lakes in the region hold nearly 20 per cent of the earth’s unfrozen fresh surface water, an area of 94,000 square miles, the paper noted.
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