Crumbling Antarctic ice sheets could speed sea level rise

Fifty feet in 500 years?

Mountains of the Antarctic Sound.
New climate modeling suggests more significant melting of the Antarctic ice sheets and ice shelves driven by atmospheric warming. @bberwyn photo.

Staff Report

The edges of Antarctic ice sheets may crumble and collapse much faster than most existing climate models suggest, potentially raising global sea level by as much as 50 feet in the next 500 years, according to researchers from Penn State and University of Massachusetts, Amherst.

The scientists added new, previously underestimated processes to their projection after studying the role of Antarctic ice melting during the warm Pliocene era, about 3 million years ago when sea level rose by as much as 30 to 60 feet.

Currently, warm ocean waters are the primary driver of Antarctic melting, but in the new calculations, atmospheric warming will become the dominant driver of ice loss, and prolonged ocean warming will delay recovery for thousands of years, the scientists said, reporting their findings in the March 31 issue of Nature.

The new research confirms earlier findings that only parts of Antarctica will melt, even in a worst-case global warming scenario, but the melting suggested by the latest modeling would be enough to double the 100-year sea level rise estimates included in the most recent assessments by the Intergovernmental Panel on Climate Change.

Explaining the findings in a press release, researcher David Pollard, with the Penn State Earth and Environmental Systems Institute, said existing climate models, based on warm-water erosion of floating ice shelves, couldn’t explain the big rise in sea levels documented from the Pliocene.

So the researchers looked at other mechanisms that could cause additional melting.

Fracturing and deepening of crevasses on the low-lying floating ice shelves by pooling of surface meltwater, and rainfall caused by warming air temperatures. If emissions continue unabated, this process will begin to dominate ocean warming within 100 years. It already caused the disintegration of the Larsen B Ice Shelf in 2002.

And once the floating ice shelves are gone, huge walls at the edge of the ice sheet could start collapsing under their own weight, eroding the ice sheets farther inland.

The new model combines these mechanisms with various greenhouse gas emissions scenarios and tests the data against ice sheet retreat during the Pliocene and from the last interglacial period around 125,000 years ago.

“Although the future sea-level contribution in our model is greater than previously thought, it is based on credible mechanisms and is consistent with geologic evidence of past sea-level rise,” said Pollard. “We regard the results as worst-case envelopes of possible future behavior, and the mechanisms should be considered seriously in future work.

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