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A warmer than usual start to winter has driven ice cover to its lowest level for 50 years in North America’s Great Lakes, after decades of dwindling ice cover which is being closely monitored for its links to climate change.
Just 0.43 per cent of the interconnected lakes was covered with ice on Thursday compared to a long-term average of 10.6 per cent for this time of year over the last half century, data from the Great Lakes Environmental Research Laboratory showed.
Low ice cover across the world’s largest group of freshwater lakes by area can trigger knock-on extreme weather effects across the north-eastern US and southern Canada.
The naturally occurring El Niño effect, which causes warmer sea-surface temperatures in the Pacific, contributed to record high temperatures in the region at the end of 2023, said Tony Schumacher, chief meteorologist at the Great Lakes Weather Service.
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 based on preliminary data from the National Weather Service, with several cities breaking previous records for the month including Milwaukee, on Lake Michigan.
Warmer weather prevented the lakes from freezing over as much as they usually would at 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 meant 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 more snow is expected in some areas, driven in part by the lack of ice cover, some meteorologists expect.
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.”
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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