The Great Lakes contain 20 percent of the world’s freshwater (McBean 2008) and are already facing the impacts of anthropogenic climate change. The Greats Lakes have seen a 10 to 25 percent increase in precipitation from 1981 to 2010 (NOAA, 2019) due to increased evaporation. The amount of precipitation is predicted to increase by 12.5 percent by 2080 (Wang 2016). Increased rainfall has led to increased nutrients washed out of soils, as found in two studied watersheds (Wang 2018). In one watershed the amount of phosphorus washed out, due to soil erosion, could increase by 108 percent by 2099 (Ibid). These additional nutrients can result in nutrient loading and therefore algae booms and eutrophication in the Great Lakes.
One reason for the increased precipitation is the reduction in ice cover, which results in more evaporation. Ice cover has decreased by 71 percent on the Great Lakes from 1973 to 2010 (Collingsworth, 2017). Many commercially important fish species allow their eggs to overwinter below the ice, with reduced ice cover their eggs are more susceptible to wave action damage (Ibid). Models to predict how much ice coverage will be reduced vary widely but they all agree that the coverage will reduce by 2050. One initial benefit of reduced ice cover is that it will reduce the number of winter kills as there will be more circulation of oxygen.
There has been a reduction in the amount of ice cover, as the surface water temperatures of the Great Lakes has increased. In 2019, all the Great Lakes were at or below the ten-year average surface water temperature (NOAA, 2019). By 2100, water temperatures are expected to have increased by 2 to 7 degrees Celsius from their current levels (Collingsworth, 2017). This will reduce the quality of fish habitat and could change the benthic macroinvertebrate communities (Ibid). One in ten Americans and one in four Canadians utilizes the fisheries of the Great Lakes (Hayes 1999). The impact of invasive species will also be amplified. One study found increased mortality of lake trout (Salvelinus namaycush) due to sea lampreys (Petromyzon marinus) increased with temperatures. Climate change will only continue to impact these species that so many people rely on.
Warmer waters have created heavy rain events which have increased 35 percent from 1951 to 2017 (NOAA 2019). In the Lake Michigan area, it only takes 2.5 inches of rain in a day to overflow the sewers (Patz, 2008). The number of the incidents of overflow is expected to rise 50 to 125 percent by 2100 (Ibid). Lake Michigan provides drinking water to 40 million people. On the flipside, snow fall in most areas has decreased; however, lake affect snow in the southern and eastern parts of the Great Lakes has increased due to less ice cover generating more snow (Hayhoe, 2010). This is forecasted to be a temporary pattern, while increased precipitation may lead to an initial increase in snowfall in some areas, this will transition to mostly rain by 2050. Overall, snowfall will decrease in the Great Lakes region by 30 to 60 percent (Ibid). Increased precipitation, reduced ice cover, warmer surface waters and extreme weather events are only a fraction of the current and future impacts of climate change on the Great Lakes.
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