In late October, the National Oceanic and Atmospheric Administration (NOAA) reported that Lake Superior water temperatures were nearly three degrees Celsius higher than the historical average. On October 20, the typical temperature for Lake Superior is 8.8 degrees Celsius, but this year, it reached 11.6 degrees Celsius, marking the second-highest temperature ever recorded on that date. The warmest October 20 temperature on record was registered in 2021.
Unusually warm autumn weather this year transformed October into a summer-like month in northwestern Ontario, breaking numerous daytime temperature records by up to nine degrees Celsius. While the immediate effects of the warm autumn may not be readily apparent, it appears to be contributing to maintaining Lake Superior’s relatively warm temperatures for this period, continuing a trend that impacts underwater ecosystems and coastal weather patterns.
Researchers, such as Jay Austin, a physical oceanography PhD and a professor at the University of Minnesota Duluth, have been monitoring seasonal temperature variations over the years. According to Austin, the warmer air temperatures significantly influence Lake Superior. He noted that warm air temperatures result in a slower cooling rate for the lake, which can be predicted reliably based on air temperature alone.
Over the past 40 years, data from instruments and satellite readings have shown a gradual rise in water temperatures across the Great Lakes, with Lake Superior experiencing above-average temperatures. Austin emphasized that elevated water temperatures can affect ecosystems, potentially fostering the growth of algae blooms due to the extended duration of warm surface water, which is biologically more productive.
Lake Superior is identified as one of the fastest-warming lakes globally by the Great Lakes Integrated Sciences and Assessment (GLISA). The research group attributes this trend partly to earlier spring ice melt, leading to longer periods of lake stratification and increased exposure to solar radiation. GLISA data indicates that summer surface temperatures on Lake Superior surged by an average of 2.5°C between 1979 and 2006.
Margueritte Xenopoulos, a professor at Trent University and Canada Research Chair in Global Change of Freshwater Ecosystems, along with her colleagues, advocates for increased winter research on the Great Lakes to anticipate future developments. Xenopoulos highlighted the potential rise in nutrient runoff into the Great Lakes due to warmer weather and emphasized the importance of monitoring for ensuring safe drinking water for the millions of people residing around the Great Lakes.
Enhancing understanding of the evolving changes in these regions can aid in preparing for climate change impacts and devising strategies to mitigate potential adverse consequences, especially around Lake Superior.