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Over the last four decades, the area covered by lakes globally has grown by close to 18,000 square miles, an expanse nearly twice the size of Lake Erie.

Scientists used satellite imagery and artificial intelligence to map 3.4 million lakes around the world between 1984 and 2019, finding that lake area grew as reservoirs expanded and rising temperatures melted glaciers and permafrost, particularly in Greenland, the Rocky Mountains, and the Tibetan Plateau. Growth in these regions offset losses in central Asia, northern China, southern Australia, and the more arid parts of the U.S. West, where drought and water drawdowns sapped lakes. The findings were published in Nature Communications.

The growth in small lakes, in particular, poses a threat to the climate. Bacteria and fungi feed on dead plants and animals, producing carbon dioxide and other heat-trapping gases as a byproduct. This phenomenon is more pronounced in small lakes, which typically accumulate more organic matter than large lakes, according to Jing Tang, a biologist at the University of Copenhagen and coauthor of the study. And because small lakes are often shallow, “this makes it easier for gases to reach the surface and up into the atmosphere,” she said.

As a result of their recent growth, the world’s lakes now produce an additional 4.8 million metric tons of carbon dioxide yearly, scientists estimate, more than the yearly emissions of Albania. “There have been major and rapid changes with lakes in recent decades that affect greenhouse gas accounts,” Tang said. “Among other things, our newfound knowledge of the extent and dynamics of lakes allows us to better calculate their potential carbon emissions.”


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