Climate Change in the Great Lakes Region: Temperature Trends, Water Level Variability, and Adaptation

The Great Lakes basin’s climate is changing measurably, with consequences that affect everything from water levels and ice coverage to agricultural productivity and urban infrastructure. Long-term monitoring data from Environment and Climate Change Canada and the National Oceanic and Atmospheric Administration (NOAA) document warming trends, shifting precipitation patterns, and increasingly variable weather that are reshaping life across the region.

Temperature Trends

Mean annual air temperatures across the Great Lakes basin have increased by approximately 1.4 degrees Celsius since 1900, according to the binational State of the Great Lakes report published by the U.S. EPA and Environment Canada. The rate of warming has accelerated since 1980, with the most recent decade (2015-2025) averaging 0.9 degrees Celsius warmer than the 1981-2010 baseline period.

Winter temperatures have increased more rapidly than summer temperatures across the basin. Environment Canada data from weather stations in Thunder Bay, Sault Ste. Marie, and Toronto show that January mean temperatures have risen by 2.1 degrees Celsius since 1950, compared to a 1.0 degree increase for July mean temperatures. This disproportionate winter warming has significant implications for ice formation, seasonal shipping, and winter recreation industries.

Water Levels and Variability

Great Lakes water levels have exhibited increased volatility in recent decades. The period from 2013 to 2020 saw a dramatic swing from record or near-record low levels to record highs across all five lakes. Lake Ontario reached its highest recorded level in May 2017 at 75.88 metres, causing extensive shoreline flooding from Toronto to Kingston.

The International Joint Commission’s Great Lakes-St. Lawrence River Adaptive Management Committee attributes this increased variability to a combination of factors: higher precipitation totals, more intense individual rainfall events, reduced winter ice coverage that increases evaporation, and shifts in the timing and volume of snowmelt. Projections from the Great Lakes Environmental Research Laboratory suggest that this pattern of increased variability will continue, with both high and low water level extremes becoming more likely in coming decades.

Ice Coverage Decline

Great Lakes ice coverage has declined substantially over the past four decades. NOAA’s Great Lakes Environmental Research Laboratory maintains the longest continuous record of Great Lakes ice coverage, dating to 1973. The data shows that maximum annual ice coverage has decreased from an average of approximately 50 percent of total Great Lakes surface area in the 1970s and 1980s to approximately 30 percent in the 2015-2025 period.

The winter of 2023-2024 saw maximum ice coverage reach only 18.7 percent, well below the long-term average. Lake Erie, the shallowest of the Great Lakes and historically the most likely to freeze nearly completely, has experienced several recent winters with maximum ice coverage below 40 percent, compared to its historical average of approximately 80 percent.

Reduced ice coverage has multiple consequences. Open water in winter increases evaporation rates, potentially contributing to lower water levels. It extends the shipping season but also exposes shorelines to winter storm waves that accelerate erosion. Communities along the Lake Huron shoreline, including Goderich, Grand Bend, and Kincardine in Ontario, have reported accelerating bluff erosion in recent winters when ice that would normally protect the shoreline failed to form.

Precipitation Changes

Total annual precipitation across the Great Lakes basin has increased by approximately 10 percent since 1900, according to data compiled by the Midwest Regional Climate Center. More significantly, the intensity of heavy rainfall events has increased. The frequency of events delivering more than 50 millimetres of rain in a 24-hour period has risen by 37 percent across southern Ontario since 1950, based on analysis of Environment Canada precipitation records by the Ontario Climate Consortium.

These more intense rainfall events have implications for urban stormwater management, agricultural erosion control, and flood risk. The City of Burlington, Ontario, experienced catastrophic urban flooding in August 2014 when 191 millimetres of rain fell in approximately 12 hours. Similar intense rainfall events have affected communities across the basin with increasing frequency.

Agricultural Impacts

The agricultural sector in the Great Lakes basin is experiencing both challenges and opportunities from climate change. The growing season in southern Ontario has lengthened by approximately 15 days since 1950, according to Agriculture and Agri-Food Canada data. This extended season has enabled expansion of warm-season crops including soybeans and grain corn into areas of northern Ontario and northern Michigan where they were previously marginal.

However, increased precipitation variability creates challenges for field operations. Spring planting delays due to saturated soils have become more frequent, and intense summer rainfall events can cause crop damage and soil erosion. The Ontario Soil and Crop Improvement Association reports that soil erosion rates on cropland in the Lake Erie watershed have increased by an estimated 15 percent since 2000, contributing to the nutrient loading that drives harmful algal blooms.

Adaptation and Planning

Municipalities across the Great Lakes basin are incorporating climate projections into infrastructure planning and emergency management. The City of Toronto’s climate action strategy, TransformTO, uses downscaled climate projections to plan for increased heat events, more intense rainfall, and higher cooling demand. Hamilton, Guelph, and London have adopted similar climate adaptation frameworks.

The Great Lakes Integrated Sciences and Assessments Center (GLISA), a NOAA-funded regional climate centre based at the University of Michigan, provides decision-support tools and climate data specific to the Great Lakes region. Their resources are available to municipal planners, agricultural operators, and community organizations at glisa.umich.edu.