SOURCE: Inside Climate News

DATE: May 28, 2020

SNIP: Climate researchers racing to calculate how fast and how high the sea level will rise found new clues on the seafloor around Antarctica. A study released today suggests that some of the continent’s floating ice shelves can, during eras of rapid warming, melt back by six miles per year, far faster than any ice retreat observed by satellites.

As global warming speeds up the Antarctic meltdown, the findings “set a new upper limit for what the worst-case might be,” said lead author Julian Dowdeswell, director of the Scott Polar Research Institute at the University of Cambridge.

The estimate of ice shelf retreat is based on a pattern of ridges discovered on the seafloor near the Larsen Ice Shelf. The spacing and size of the ridges suggest they were created as the floating ice shelves rose and fell with the tides while rapidly shrinking back from the ocean. In findings published today in Science, the researchers estimate that to corrugate the seafloor in this way, the ice would have retreated by more than 150 feet per day for at least 90 days.

Ice shelves float on the ocean but they are fastened to land and act as stoppers that prevent Antarctic ice sheets that are as big as the U.S. and Mexico combined from sliding into the sea. The shelves are frozen to outcrops on the seafloor, but when they melt away from those anchor points, the flow of ice into the ocean speeds up, accelerating sea level rise.

If the rate of retreat estimated by the new study extended across an 18-mile-wide and half-mile-thick ice shelf, as found in the closely watched Pine Island Glacier in West Antarctica, the researchers calculated it would release 138-gigatons of ice per year— three to five times more ice than is currently lost annually from that glacier system.

There’s still no way to know exactly how fast the meltdown will happen with increasing human-caused warming, Fettweis said. But between 12,000 and 15,000 years ago, global sea level rose about 1.5 to 2.3 inches per year for several centuries, raising sea level by 82 feet over a 500-year period.

“The most important message to take home is that the current projections are too conservative. We know it,” he said. “The real drama in all of this is that the faster rates of retreat may turn out to be the most probable in some places, and as of now we do not know where and when.”