Model pinpoints glaciers at risk of collapse due to climate change

As climate change warms the planet, glaciers are melting faster. Many will collapse by the end of the century, drastically raising sea level and inundating coastal cities and island nations.

A University of California, Berkeley, scientist has now created an improved model of glacial movement that could help pinpoint which glaciers in the Arctic and Antarctic are most likely to rapidly slide downhill and fall into the ocean.

The new model, published in the journal The Cryosphere, incorporates the effects of meltwater that percolates to the base of a glacier and lubricates its downhill flow. The model predicts that the most vulnerable glaciers are the thickest ones with a history of faster flow. The research is supported by the U.S. National Science Foundation.

"The model suggests that thick and fast-flowing glaciers are more sensitive to lubrication than thin and slow glaciers," said Whyjay Zheng. "The data from Greenland glaciers support this new finding, indicating that those fast and thick glacier beasts might be more unstable than we thought under global warming."

Zheng built the new model to incorporate a mechanism that has taken on more importance with global warming: meltwater penetrating to the bottoms of glaciers and lubricating their downhill movement over bedrock.

The Arctic and Antarctic have warmed more than the rest of the world -- in March, the Antarctic saw record high temperatures of 70 F above normal, while some parts of the Arctic were more than 60 F warmer than average. The warmer weather causes meltwater lakes to form on many glaciers. The lakes can punch through to the bottom of glaciers by a process called hydrofracture, draining to the bottom of the glaciers through crevasses.

Glaciologists have already seen that the speedup and slowdown of glaciers are related to what's happening at the front of the glaciers, where the ice merges into the ocean and meets warmer water. When the front melts, or calves, into the ocean, the remaining parts tend to speed up.

Basal lubrication by meltwater appears to be creating a feedback loop that accelerates glaciers that have already sped up for other reasons, such as changes at the terminus. "In effect, thicker glaciers are more slippery, which leads to further melting, then more slipping, and so on," said Maria Womack, a program director in NSF's Division of Atmospheric and Geospace Sciences.

Zheng added that "in Greenland, a glacier's speed seems to be mostly controlled by the terminus position. If the terminus is retreating, the glacier will speed up; if the terminus is advancing, the glacier will slow down.

"People think this is probably the primary reason why Greenland glaciers can speed up or slow down. But now, we are starting to think there's another and maybe quicker way to make glaciers slow down or speed up -- basal lubrication."

Zheng wrote and ran his model using the Jupyter Notebook, a web-based interactive computing platform that is available to the public.

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