Climate Matters•February 7, 2024
Great Lakes Ice
KEY CONCEPTS
The Great Lakes have been unusually ice-free this winter — a scenario that’s likely to occur more often with continued warming.
Despite year-to-year variability, long-term records show a 25% decrease in basin-wide ice cover as well as a trend toward fewer frozen days across the Great Lakes since 1973.
Warmer winters increase the likelihood of ice-free lakes, and the Upper Midwest has experienced some of the nation’s strongest winter warming trends since 1970.
The Great Lakes aren’t alone. Across the Northern Hemisphere, lakes are freezing later in winter and thawing earlier in spring.
Declining lake ice can influence lake water levels and lake-effect snow, and has cascading impacts on cultural heritage, ecosystems, and recreation.
Great Lakes: economic engines
The Great Lakes form the planet’s largest freshwater system. They hold one-fifth of all fresh water on Earth’s surface and supply drinking water for over 30 million people across the eight neighboring U.S. states and the Canadian province of Ontario.
On the U.S. side of the border, businesses that depend on the Great Lakes employ nearly 300,000 people and support an economy worth $17.8 billion — focused around major port cities including Chicago, Cleveland, Detroit, Duluth, and Milwaukee.
The Great Lakes also support diverse ecosystems and are central to regional recreation and cultural traditions.
Important as they are for the economy, drinking water, shipping, fisheries, recreation, and more, the Great Lakes are changing with our warming climate.
Heavier precipitation, warmer waters, less ice
The U.S. Great Lakes region is getting wetter at some of the fastest rates in the country. The Upper Midwest has experienced a significant increase in annual and seasonal precipitation totals, while the heaviest precipitation events in the region have become 45% wetter — among the highest rates nationwide.
The lakes themselves are also warming. In fact, the Great Lakes are among the fastest-warming lakes in the world. Despite lake-to-lake and year-to-year variability, long-term records generally show that summer surface waters are warming — especially in the upper Great Lakes: Superior, Michigan, and Huron.
Along with warming waters, the lakes are also experiencing a decline in winter ice, which has cascading impacts on ecosystems, culture, recreation — and implications for commercial shipping, hydropower generation, and the fishing industry.
Ice decline is observed in both shrinking frozen areas and a shorter duration of ice cover.
Shrinking frozen area
Although the maximum frozen surface area on each lake has high year-to-year variability, all five lakes have experienced a long-term decrease in ice cover with the strongest trend in Lake Superior.
The area-weighted average of all five lakes shows a 25% decrease in ice cover from 1973 to 2023. Detailed ice cover maps show the spatial ice cover patterns each year since 1973.
Fewer frozen days
Lake ice trends are also reflected in the number of frozen days each year (see Methodology). By this measure, ice duration has decreased on all five lakes since 1973, ranging from 15 to 49 fewer frozen days (Lakes Huron and Superior, respectively) now than during the early 1970s. Maps show that ice duration has decreased fastest in shoreline areas.
Natural variability
Year-to-year changes in Great Lakes ice cover are linked to large-scale climate patterns in the Pacific and Atlantic including the El Niño-Southern Oscillation. These patterns affect the location of the westerly jet stream and thereby air temperatures over the Great Lakes — the main factor affecting ice formation.
El Niño winters tend to be warmer and drier across the Great Lakes region. The current El Niño may contribute to the near-record low basinwide ice cover so far in 2024 — at just 7% basin-wide as of February 5.
Warming climate, warming lakes
While these natural climate patterns have a strong influence on year-to-year variations in ice cover, the long-term trends toward warmer waters and decreased ice also reflect the overall warming climate.
Studies have shown that warmer winter air strongly increases the likelihood of ice-free lakes — and the Great Lakes region has experienced some of the largest increases in both winter average temperatures and extremely warm winter days since 1970.
The Great Lakes aren’t alone in these long-term trends in response to climate warming.
Surface waters in hundreds of lakes across the globe have warmed 0.4 to 0.8°F per decade between 1970 and 2010 — more than double recent rates of sea-surface warming.
And across the Northern Hemisphere, on average, the duration of lake ice cover has declined by over two weeks annually as lakes freeze later in winter and thaw earlier in spring. The IPCC assessments indicate that these trends can be attributed to climate change with high confidence.
An unstable future
With continued heat-trapping emissions and resulting warming, the Great Lakes are projected to experience further warming of surface waters and reductions in ice duration over this century, with greater ice loss in scenarios with higher carbon pollution.
And a recent study estimates that, under 2°C of global warming, the number of lakes across the Northern Hemisphere that experience only intermittent ice cover would increase 2.4-fold to 35,300 lakes, impacting up to 394 million people globally.
Impacts of declining lake ice
Declining ice cover has cascading impacts on winter cultural heritage across the Great Lakes region as it limits access for recreational (ice skating), subsistence (ice fishing), ceremonial (sacred sites), and educational (citizen science) activities.
Unpredictable, unstable lake ice is also a safety hazard. In recent decades, the highest rates of winter drownings have occurred at times when air temperatures were near freezing, and in communities that rely on lake ice access for livelihoods and Indigenous traditions.
Reduced lake ice can also impact ecosystem health. Declining lake ice and warming surface waters could also lead to increased competition between cool- and warm-water fish species. The regional rise in rainfall extremes can also increase nutrient runoff, creating conditions that promote harmful algal blooms that have cascading ecological effects.
Although less lake ice can potentially extend shipping seasons, ice-free lake surfaces can also enhance evaporation and lead to lower water levels which can in turn restrict shipping.
Larger, longer ice-free lake surfaces also have the potential to increase lake-effect snow, which occurs when cold air flowing over relatively warm, large areas of open water generates intense, localized snowfall downwind of the Great Lakes. Warmer waters and declining ice has likely contributed to the observed increase in snowfall in northern lake-effect zones of Lake Michigan and Lake Superior.
LOCAL STORY ANGLES
Monitor current conditions and seasonal outlooks for each lake:
NOAA GLERL provides seasonal temperature and precipitation forecasts as well as a dashboard to track water levels for each of the Great Lakes. The U.S. National Ice Center provides 30-day forecasts and seasonal outlooks for Great Lakes ice. The Midwestern Regional Climate Center also has a range of Great Lakes monitoring data and science assessments.
How is the region adapting to a warmer climate?
GLISA, a Climate Adaptation Partnership supported by NOAA, provides detailed retrospective and prospective reports for each of the Great Lakes along with resources and climate scenarios to guide adaptation planning in Great Lakes cities.
CONTACT EXPERTS
Sapna Sharma, PhD
Professor
York University
Related expertise: lake warming, ice loss, water quality, climate change, freshwater fisheries
Contact: sharma11@yorku.ca
Ayumi Fujisaki-Manome, PhD (she/her/hers)
Associate Research Scientist
University of Michigan
Related expertise: lake ice, lake-effect snow, polar oceanography
Contact: ayumif@umich.edu
Alison Gillespie
Public Affairs Specialist
Related expertise: NOAA
Contact: alison.gillespie@noaa.gov
Melissa Widhalm, MS
Regional Climatologist, Associate Director
Midwestern Regional Climate Center, Purdue University
Related expertise: Climate change impacts in the Midwest
Contact: mwidhalm@purdue.edu
FIND EXPERTS
Submit a request to SciLine from the American Association for the Advancement of Science or to the Climate Data Concierge from Columbia University. These free services rapidly connect journalists to relevant scientific experts.
Browse maps of climate experts and services at regional NOAA, USDA, and Department of the Interior offices.
Explore databases such as 500 Women Scientists, BIPOC Climate and Energy Justice PhDs, and Diverse Sources to find and amplify diverse expert voices.
Reach out to your State Climate Office or the nearest Land-Grant University to connect with scientists, educators, and extension staff in your local area.
METHODOLOGY
Ice cover and duration data for each of the Great Lakes were obtained from NOAA’s Great Lakes Environmental Research Laboratory (GLERL). Maximum annual ice cover is presented as the maximum daily percent of each lake’s total surface area that was frozen each year. Ice duration is defined as the total number of days each year with at least 5% of the lake surface frozen. This indicator spans each calendar year (winter through spring); the calendar year assigned corresponds to the end of each annual period (e.g., data for 2023 run from December 2022 through May 2023).