Ice coverage for the North American Great Lakes reached a record low for February, according to NOAA’s Great Lakes Environmental Research Laboratory (GLERL).
Only 7% of the five freshwater lakes were covered in ice on February 13, 2023, which is significantly below the 35-40% ice cover expected for the time of year. Ice extent across the basin briefly jumped to 21% in early February in response to a cold snap but then declined. Maximum ice cover typically occurs between the middle of February and early March. NOAA has been keeping records on the Great Lakes ice extent since 1973.
Air temperatures are the main factor affecting ice cover on the Great Lakes, and a warmer-than-average January contributed to the lack of ice. According to the US National Ice Center, each of the five lakes experienced warmer-than-average air temperatures in January. In addition, it was a particularly warm January across the contiguous US, with an average temperature of 35.2°F (5.1° above average) according to NOAA (January 2023 was Earth’s seventh-warmest January on record).
Although there is year-to-year variability in the ice cover of the lakes, NOAA research has found that in recent years ice cover has been in a downward trend. Analysis led by Jia Wang, an ice climatologist at NOAA’s GLERL, found significant declines in the average ice cover of the Great Lakes between 1973 and 2017. During the winter period of those 44 years, which runs from December 1 to April 30, average ice cover on the Great Lakes declined by around 70%.
Ice cover protects the shoreline of lakes. Without it, high waves can scour the coastline and cause severe flooding. Ayumi Fujisaki-Manome, a researcher at NOAA’s Cooperative Institute for Great Lakes Research at the University of Michigan, said, “The moisture and heat from the lake surface water are absorbed into the atmosphere by storm systems, and then fall back to the ground as snow in the winter. When ice is not present, we can end up with big snowstorms like those that hit Buffalo, New York in December.”
Although human-induced warming plays a role in this decline, other key factors contributing to reduced ice loss are long-term patterns of climate variability over the Pacific and Atlantic oceans. Four patterns of climate variability are contributing to ice cover changes: the North Atlantic Oscillation, the Atlantic Multidecadal Oscillation, the Pacific Decadal Oscillation and the El Niño-Southern Oscillation.
“Each year, we have to look at these four patterns to model ice cover,” said Wang. “Right now, the Pacific Decadal Oscillation together with the North Atlantic Oscillation are causing warming in the Great Lakes.”
GLERL will continue to monitor the ice levels and will announce the end-of-season ice extent later this year.