Why is the Great Lakes so cold?

The Great Lakes, a collection of five freshwater lakes located in North America, are known for their cold temperatures, particularly during the winter months. This is primarily due to the region’s low weather temperatures, which cause the lake’s water to become cold.

Sometimes the water near the surface gets so cold, it freezes. During winter, nearly the whole water column (the depth from surface to bottom) becomes uniformly cold and near freezing. Lake temperatures are largely driven by interactions with the atmosphere, so colder air temperatures lead to colder lake temperatures.

For instance, colder-than-normal air temperatures set in over Lake Superior in January and chilled the lake surface. The sun begins to warm the cold water near a lake’s surface, but this process takes time and depends on the intensity and duration of sunlight.

In recent years, however, there have been changes in the winter conditions of the Great Lakes. The long-term average for ice coverage on all five lakes—Superior, Michigan, Erie, Huron, and Ontario—is 54 percent. But last winter, ice covered only 19.5 percent of the lakes’ surfaces—a near-record low. Some lakes in the region didn’t freeze at all. Others saw only faint traces of ice around their edges, or froze briefly.

These changes in ice cover and water temperature play a key role in the life cycles of fish, plants, and microorganisms in the lakes. As climate change continues to impact weather patterns, scientists are increasingly interested in better understanding winter’s role in the Great Lakes, how global warming is changing life beneath the ice, and what, if anything, humans can do to adjust.

In conclusion, the Great Lakes are cold due to the region’s low weather temperatures and their interaction with the atmosphere. However, changes in these conditions due to climate change are leading to less ice cover and warmer water temperatures, which could have significant impacts on the ecosystems within the lakes.