The world's lakes are warming faster than both the oceans and the air around them, creating blooms of algae that are toxic to fish and rob water of oxygen.
The warming lakes threaten freshwater supplies and ecosystems across the planet, according to a study spanning six continents.
Henry Gholz, program director in the Division of Environmental Biology at the National Science Foundation, said that the knowledge of how lakes are responding to global change has been lacking, which has made forecasting the future of lakes and the life and livelihoods they support very challenging.
Gholz noted that these newly reported trends are a wake-up call to scientists and citizens, including water resource managers and those who depend on freshwater fisheries.
The study found that lakes are warming an average of 0.61 degrees Fahrenheit each decade. That's greater than the warming rate of the oceans or the atmosphere, and it can have profound effects, the scientists say.
At the current rate, algal blooms, which ultimately rob water of oxygen, should increase by 20 percent over the next century. Some 5 percent of the blooms will be toxic to fish and animals.
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Emissions of methane, a greenhouse gas 20 times more powerful than carbon dioxide, will increase 4 percent over the next decade.
Co-author Stephanie Hampton of Washington State University said that warm-water lakes have experienced less dramatic temperature increases, but their waters may have already nearly reached the highest temperatures fish can tolerate.
The study is published in the journal Geophysical Research Letters.