"No Longer A Question Of If The West Antarctic Ice Sheet Will Melt, But When"

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The Pine Island Glacier, part of the ice shelf that bounds the West Antarctic Ice Sheet, is one of two glaciers that researchers believe are most likely to undergo rapid retreat, bringing more ice from the interior of the ice sheet to the ocean, where its melting would flood coastlines around the world. A nearly 225-square-mile iceberg broke off from the glacier in 2015, but it wasn’t until Ohio State University researchers were testing some new image-processing software that they noticed something strange in satellite images taken before the event.

In the images, they saw evidence that a rift formed at the very base of the ice shelf nearly 20 miles inland in 2013. The rift propagated upward over two years, until it broke through the ice surface and set the iceberg adrift over 12 days in late July and early August 2015. They report their discovery in the journal Geophysical Research Letters.

“It’s generally accepted that it’s no longer a question of whether the West Antarctic Ice Sheet will melt, it’s a question of when,” said study leader Ian Howat, associate professor of earth sciences at Ohio State. “This kind of rifting behavior provides another mechanism for rapid retreat of these glaciers, adding to the probability that we may see significant collapse of West Antarctica in our lifetimes.”

While this is the first time researchers have witnessed a deep subsurface rift opening within Antarctic ice, they have seen similar breakups in the Greenland Ice Sheet—in spots where ocean water has seeped inland along the bedrock and begun to melt the ice from underneath

EDIT

https://climatecrocks.com/2016/11/29/in-antarctic-summer-signs-of-accelerating-melt/#more-40452

[OKIsItJustMe]

1. No surprise here

https://science.nasa.gov/science-news/science-at-nasa/2014/12may_noturningback

[font face=Serif][font size=5]West Antarctic Glaciers in Irreversible Decline[/font]

[font size=3]May 12, 2014: Over the years, as temperatures around the world have ratcheted upward, climate change researchers have kept a wary eye on one place perhaps more than any other: The West Antarctic Ice Sheet, and particularly the fastest melting part of it, the glaciers that flow into the Amundsen Sea.

In that region, six glaciers hang in a precarious balance, partially supported by land, and partially floating in waters just offshore. There's enough water frozen in the ice sheet that feeds these icy giants to raise global sea levels by 4 feet—if they were to melt. That's troubling because the glaciers are melting. Moreover, a new study finds that their decline appears to be unstoppable.

"We've passed the point of no return," says Eric Rignot, a glaciologist working jointly at NASA's Jet Propulsion Laboratory and the University of California, Irvine. Rignot and colleagues have used 19 years of satellite radar data to map the fast-melting glaciers. In their paper, which has been accepted for publication in Geophysical Research Letters, they conclude that "this sector of West Antarctica is undergoing a marine ice sheet instability that will significantly contribute to sea level rise" in the centuries ahead.

A key concept in the Rignot study is the "grounding line"—the dividing line between land and water underneath a glacier. Because virtually all melting occurs where the glaciers' undersides touch the ocean, pinpointing the grounding line is crucial for estimating melt rates.

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