Hello AGU,
Vast expanses of seasonal shelf ice are a prominent feature of polar oceans, with enormous consequences for marine food webs and the temperature-ice/snow-albedo feedback on Earth’s climate.
Large temperate lakes, like the Laurentian Great Lakes (~250,000 km2), also experience considerable winter ice cover, which influences shoreline morphology, lake ecology, and regional weather. Shelf ice shields shorelines from storm erosion, provides shelter for fish eggs, affects evaporation, regulates regional weather (e.g., lake-effect snow), and impacts shipping. The annual maximum ice cover (AMIC) on the Great Lakes has fluctuated greatly over the past 52 years, ranging from 12-95% (average AMIC ~43%; https://www.glerl.noaa.gov/data/ice/). While the lakes still experience high ice years (2014, 2015, 2019), there is a concerning trend of a 0.5% yearly decrease in AMIC in synch with warming waters.
This year (2025), ice cover on the Great Lakes appears to be affected by a relatively colder La Niña winter in the Midwest and the southward push of the Arctic Polar Vortex in early January and mid-February. These events lasted several days and led to rapid shelf ice buildup, as shown in this January 29, 2025, image from Grand Haven, MI, along the western shore of Lake Michigan. As of this writing (in late February 2025), ice cover on the Great Lakes is ~50% – exceeding last year’s 16% AMIC, a year marked by near-record low ice during a warm 2024 El Niño winter.
There is an urgent need to understand the complex forces shaping the consequential dynamics of ice on water and the fast-disappearing cryosphere in a warming world.
–Bopi Biddanda, Annis Water Resources Institute, Grand Valley State University, Muskegon, MI (www.gvsu.edu/wri/); and James Kessler, NOAA-Great Lakes Environmental Research Laboratory, Ann Arbor, MI (https://www.glerl.noaa.gov/).