Are the Great Lakes Getting Warmer?


The Great Lakes, which consist of Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario, comprise one of North America’s national landmarks and treasures.  The Great Lakes account for approximately one-fifth of the world’s surface freshwater.  This makes the Great Lakes the third largest system of surface fresh water in the world behind the polar ice caps and Lake Baikal in Siberia. The Great Lakes alone account for approximately 84% of North America’s surface fresh water and support approximately 6,000 species of wildlife, including numerous species of fish. The Great Lakes are also important sources of drinking water and economic livelihoods. Recreational boating, fishing, hunting, and wildlife viewing account for about $53 billion in revenue for the states surrounding the Great Lakes. However, the Great Lakes and the species the Great Lakes support are under threat due to the effects of climate change.

Lake Superior is currently warming up faster than any other lake in the world. It is the largest lake in the world by surface area, but it is relatively shallow despite its great size. Over the last thirty years, the lake has experienced a 50% decrease in ice cover. Ice cover is essential to keeping the lake cooler because ice reflects solar radiation back into the atmosphere. As the ice cover decreases, the lake absorbs more solar radiation, causing the temperature of the lake to increase. Lake Superior’s water temperature has increased approximately 2.5 °C (4.5 °F) between 1979 and 2006.

Effects of Climate Change

Summer Stratification

As the temperatures of the Great Lakes continue to increase, there is a risk that summer stratification will begin earlier. This means that during the summer, the warm surface layer of water does not mix with the colder bottom water layer. As a result, oxygen from the top of the lake is not transferred to the bottom of the lake. This can be a problem because the decay of dead algae on the lake bottom may deplete oxygen in the cold bottom layer of the lake, leaving organisms in the lower layer oxygen deprived. Lake Superior is already experiencing summer stratification about two weeks earlier than it has in the past thirty years, and some scientists predict that Lake Superior will warm to such an extent that it will be ice-free in the next thirty years.


Climate change provides both a benefit to some fishes and a threat to other fishes. Walleye fish are thriving in the warm waters of Lake Superior, which is bringing more fishing business to the lake. However, invasive species, such as the sea lamprey, also find the warmer waters of Lake Superior inviting. The sea lamprey is a parasite that attaches itself to the side of a fish, particularly the trout, and as a result of its feeding, eventually kills the fish. The sea lampreys thrive in warmer water, and as the population grows, the trout population of Lake Superior may significantly diminish.

Water Level

Scientists have not yet come to a consensus on how climate change affects the water levels of the Great Lakes. Climate change may result in increased water withdrawals from the Great Lakes, thus potentially lowering the water levels. Some research supports the position that the lake system may be sensitive to climate changes with data showing that the Great Lake water levels have been consistently below the long-term average levels since 1997. In 1997, a reduction in the duration of ice cover correlated to a water temperature increase and doubled the evaporation rate. Since 1997, however, the water in the Great Lakes has fluctuated normally, albeit below the average levels.

If the water level is affected by climate change, much of the wildlife living near the lake will be threatened. Wildlife, such as moose, rely on the wetlands surrounding the Great Lakes for food and protection. The reduced water levels exposes and dries out the wetlands around the Great Lakes and threatens the unique ecosystem. Before scientists can definitively determine if climate change has any effect on the water level and thus local wildlife, however, more conclusive data must be produced.

Minimizing the Effects of Climate Change

In order to address the potentially shrinking water levels of the Great Lakes, state and national governments need to adopt and implement programs that focus on encouraging agricultural and urban water conservation. Conservation could be achieved through creating closed systems to recycle used water. Because of the potential risk to the Great Lakes’ wetlands, local governments need to formulate plans to protect the wetlands in order to maintain essential wildlife habitats and the unique ecosystem the wetlands support.

Also, the Great Lakes must not be overrun by invasive species of fish. Invasive species growth in the Great Lakes will need to be monitored and potentially controlled to ensure survival of native fishes.

In response to these suggestions, the Obama administration developed a five-year Great Lakes Action Plan in 2010. The plan seeks to address multiple issues: restoring the wetlands, controlling invasive species, and promoting accountability and education efforts. Estimates to implement this plan are at approximately $2 billion.


The Great Lakes will need to be monitored as global temperatures continue to rise. Fishes who thrive in the warmer waters of the Great Lakes should obtain support, and invasive species must be prevented from spreading throughout the Great Lakes. The local, state, and national governments should emphasize the importance of conservation programs to prevent water levels in the Great Lakes from decreasing further. Plans must be made to maintain wetlands at lower water levels so that the wildlife surrounding the Great Lakes does not lose its natural habitat.  Finally, citizens need to be educated about climate change and how it affects the Great Lakes.


The title picture is a satellite photo of the Great Lakes from the SeaWiFS Project.



Phillip Ross, Climate Change Causing Lake Superior to Warm ‘Faster than any Lake on the Planet’, Int’l Bus. Times (Oct. 15, 2013),

Lisa Borre, Warming Lakes: Climate Change and Variability Drive Low Water Levels on the Great Lakes, Nat’l Geographic (Nov. 20, 2012),

Dina Maron, Lake Superior, a Huge Natural Climate Change Gauge, is Running a Fever, N. Y. Times (July 19, 2010),

Global Warming and the Great Lakes, National Wildlife Federation, (last visited March 12, 2014).

Great Lakes Facts and Figures, Great Lakes Info. Network, (last visited March 12, 2014).

Interview by Cynthia Canti with Tim Kline, PhD student, University of Washington, School of Aquatics and Fisheries (Dec. 4, 2013),

How does Stratification Affect Water Quality?, Great Lakes, (last visited March 12, 2014).