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SOURCE: Scientific American

DATE: January 23, 2018

SNIP: Mountain glaciers around the world, from the Himalayas to the Andes, are shrinking in the face of climate change—and that could pose a major threat to water resources for nearby communities.

These mountain glaciers are important resources for human settlements. Glacial runoff, especially during the spring and summer, can provide a critical source of fresh water downstream.

But in a new modeling study of 56 glacier drainage basins worldwide, roughly half the studied sites have already reached a kind of tipping point—after which the amount of fresh water that runs off each year begins to decline.

“As glaciers recede, water is released from long-term glacial storage,” the researchers note in the paper, which was published yesterday in the journal Nature Climate Change. “Thus, annual glacier runoff volume typically increases until a maximum is reached, often referred to as ‘peak water.'” After this point is reached, they note, the amount of annual runoff begins to decline again.

Now, scientists are increasingly aware that mountain glaciers—like mountain snowpack—are growing more vulnerable to the influence of climate change. Yesterday’s study suggests that total glacier volume across all the investigated basins will decrease by about 43 percent by the year 2100, even if the world takes serious steps to mitigate climate change. Under a more severe “business-as-usual” trajectory, in which greenhouse gas emissions continue unabated into the future, these total declines could be as high as 74 percent.