According to new research, we can now add the world's freshwater lakes to the ever-growing list of at-risk environmental entities.

A ferry crosses Lake Albert, Uganda, one of the Great Lakes of Africa. (Photo: Wikimedia Commons)

Fill in the blank: "Climate change is the biggest threat to ____" There are so many correct answers to choose from—coral reefs, polar bear survival, national security, or public health not least among them—the remark is starting to sound like a bit of a broken record. And now, according to a new study funded by the National Aeronautics and Space Administration and the National Science Foundation, we can add the world's freshwater lakes to the ever-growing list of at-risk environmental entities.

The study, published in Geophysical Research Letters, examined more than half of the world's freshwater across six continents. The researchers found that, between 1985 and 2009, lake surface water temperatures "rose rapidly," according to satellite temperature data and ground measurements taken from more than 230 lakes worldwide. On average, the world's lakes are warming around 0.61 degrees Fahrenheit, or 0.34 degrees Celsius each decade—rates of warming faster than both the ocean and the atmosphere.

"The widespread warming suggests large changes in Earth's freshwater resources and their processes are not only imminent but already under way."

Warming patterns aren't uniform. Lakes with the highest rates of warming are also experiencing less cloud cover in the summer, including the Great Lakes and lakes throughout Northern Europe, which are warming "significantly faster" than the global average, researchers found. Ice-covered lakes happen to be warming faster than ambient air temperatures, and even the world's deepest ice-covered lakes are warming twice as fast as the air around them.

The consequences of warmer lakes are profound—from threatened water security as water levels evaporate and decline, to economic stress among communities who depend on fisheries for revenue, like the Great Lakes of Africa, which supports Uganda's economy as one of world's largest producers of freshwater fish.

Although lakes in southeastern North America are warming significantly slower than the global average, the most minute of temperature changes can be detrimental on a lake's ecosystem. Scientists predict algae blooms—which can leave lake water devoid of oxygen—will increase by 20 percent thanks to warming waters. Algae blooms, which are toxic to fish and other sea creatures, are projected to increase by five percent. Methane—25 times more powerful than carbon dioxide when studied across 100-year time scales, according to NASA—could increase by four percent throughout the next decade as well.

"The widespread warming reported here suggests that large changes in Earth's freshwater resources and their processes are not only imminent but already under way," the researchers write.

And not a moment too soon to start assessing adaptation and mitigation efforts to save them.

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