The Great Lakes that border between the U.S. and Canada, are one of the largest freshwater reserves on the earth constituting about twenty percent of the entire world’s supply. This irreplaceable ecosystem holds as much as six quadrillion gallons of freshwater for the northern portion of the Western Hemisphere. They were created by advancing and retreating glaciers that carved out valleys that, in turn, became lakes when the last ice age ended. For perspective, this would cover the surface of the entire United States with about ten feet of water. The combined surface area of the Great Lakes is greater than ninety-four thousand square miles, or about the size of the UK. The coastline of the combined Great Lakes is longer than either the Atlantic or Pacific coastlines of the contiguous United States.
Fewer icy winters: Traditionally, the culture and economy of the Great Lakes region of the United States has been shaped by icy winters. But global warming has reduced the impact of this driving force bringing with it unwelcome changes and losses. Throughout the world lake ice has long been a bellwether of climate conditions and changes. In Japan, priests at a Shinto temple have measured ice on the nearby lake for six hundred years. In Finland, merchants that use the Tornio River have tracked the dates that the ice breaks up since 1693. It is believed that more than two hundred thousand lakes in the Northern Hemisphere could continue to have ice free winters.
Shortening ice season: Warmer water temperatures reduce the number of days that ice covers the lakes. This stresses native fauna and flora which need to adapt to the temperature fluctuations. The ice season that forms on the Great Lakes is getting shorter each year by an average of about half a day. If the lake water doesn’t cool enough in the winter to form ice, it will warm faster in the spring and summer thereby inhibiting the cooling process for the next winter season. In the winter of 2019/2020, ice covered only 19.5 percent of the Great Lakes, nearly a record low—the long-term average is around 54 percent. Global warming is creating a trend that could shorten the ice season by four to six weeks by the end of the 21st century. That same time frame could mean a rise in the average temperature for the Great Lakes region by six to ten degrees.
Weather’s impact on Great Lakes fragile ecology: Although many miles away from either the Atlantic or Pacific oceans, the Great Lakes’ weather is influenced by both. Weather conditions such as El Nino in the Pacific can influence the weather in the region in any one particular year. The Northeaster that impacts New England and the New York areas also brings an impact. But year on year the area is seeing warmer, shorter ice seasons. Other factors such as the polar vortex of 2013/14 made the winter extra icy cold, bucking the trend, but for only one year. Early snowfalls could inhibit ice from forming early on. An extra warm summer could provide the lake with extra heat in the following winter season. Strong winds can keep the surface of the water churning thereby inhibiting the formation of the ice.
The future is at risk from pollution, warmer waters, and invasive species: Agricultural runoff from extensive fertilizer use by farmland and overflowing sewer systems that find their way into the Great Lakes, create an overabundance of nutrients such as nitrogen and phosphorus in the water. This can lead to toxic algae blooms that rob the water of oxygen and can cause skin blisters for lake users and liver damage for those who drink the water. In 2019, Lake Erie had an algae bloom that covered more than six hundred square miles. Algae blooms were formerly a rare event, but now occur almost every summer. Chicago, the largest of several large cities on the lakes, derives its drinking water from Lake Michigan. But, to do this they had to reverse the flow of the Chicago river which was used for sewage removal. On occasion there are overflows which wind up in the lake. The city is building the Tunnel and Reservoir Plan that, when operational, will reduce or eliminate the discharge of sewage into the lake.
Non-native sea life is threatening the natural ecosystem: Fish and sea life that are not native to the Great Lakes have been introduced either inadvertently or deliberately by shipping or by fishermen. There have been about six thousand shipwrecks in the Great Lakes owing mostly to storms. Many of these wrecks have become homes to sea life introduced by other oceangoing vessels that disrupt or interfere with the lakes’ ecosystems. Such species as Asian carp, sea lampreys, bythotrephes, and alewife fish, all interfere and threaten the natural ecosystems in the lakes. Diatoms, a form of algae, absorb solar energy and release oxygen into the water. They provide food for zooplankton which in turn provide food for fish and other species. If the population of diatoms decreases, it can cause reverberations higher up the food chain. Some diatoms grow on the bottom of thick, snow-covered ice.
Non-agricultural economic impact: Water levels are increasing causing flooding along the lake’s shorelines impacting homes, businesses, and economic activity. Industries such as skiing, snowmobiling, ice fishing, and the accompanying tourist industry are suffering because of the shortened ice season.
Conclusions: Global warming is having an adverse impact on North America’s Great Lakes, which constitute one of the world’s largest reserves of fresh water. The danger to the fragile ecosystems comes mainly from pollution, warmer water, and invasive species. Some effort is being made to protect this great resource, but much more needs to be done. As the population in the area increases so does the demand for fresh water. Nature’s biggest supply must be protected and maintained.
Sources: A Future Less Frozen, by Alejandra Borunda, National Geographic, September, 2020; So Great, So Fragile by Tim Folger, National Geographic, December, 2020.