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Dialogue: 0,0:00:01.01,0:00:03.01,Default,,0000,0000,0000,,[ music ]
Dialogue: 0,0:00:03.03,0:00:04.08,Default,,0000,0000,0000,,No Turning Back:
Dialogue: 0,0:00:04.10,0:00:06.77,Default,,0000,0000,0000,,West Antarctic Glaciers in Irreversible Decline --
Dialogue: 0,0:00:06.79,0:00:09.14,Default,,0000,0000,0000,,Presented by Science@NASA
Dialogue: 0,0:00:09.16,0:00:10.98,Default,,0000,0000,0000,,Over the years,
Dialogue: 0,0:00:11.00,0:00:13.51,Default,,0000,0000,0000,,as temperatures around the world have ratcheted upward,
Dialogue: 0,0:00:13.53,0:00:16.76,Default,,0000,0000,0000,,climate change researchers have kept a wary eye on one place
Dialogue: 0,0:00:16.78,0:00:18.52,Default,,0000,0000,0000,,perhaps more than any other:
Dialogue: 0,0:00:18.54,0:00:20.19,Default,,0000,0000,0000,,The West Antarctic Ice Sheet,
Dialogue: 0,0:00:20.21,0:00:23.26,Default,,0000,0000,0000,,and particularly the fastest melting part of it,
Dialogue: 0,0:00:23.28,0:00:25.67,Default,,0000,0000,0000,,the glaciers that flow into the Amundsen Sea.
Dialogue: 0,0:00:25.69,0:00:27.36,Default,,0000,0000,0000,,In that region,
Dialogue: 0,0:00:27.38,0:00:29.64,Default,,0000,0000,0000,,six glaciers hang in a precarious balance,
Dialogue: 0,0:00:29.66,0:00:31.90,Default,,0000,0000,0000,,partially supported by land,
Dialogue: 0,0:00:31.92,0:00:34.68,Default,,0000,0000,0000,,and partially floating in waters just offshore.
Dialogue: 0,0:00:34.70,0:00:36.95,Default,,0000,0000,0000,,There's enough water frozen in the ice sheet
Dialogue: 0,0:00:36.97,0:00:38.47,Default,,0000,0000,0000,,that feeds these icy giants
Dialogue: 0,0:00:38.49,0:00:40.95,Default,,0000,0000,0000,,to raise global sea levels by 4 feet-
Dialogue: 0,0:00:40.97,0:00:42.43,Default,,0000,0000,0000,,if they were to melt.
Dialogue: 0,0:00:42.45,0:00:45.32,Default,,0000,0000,0000,,That's troubling because the glaciers are melting.
Dialogue: 0,0:00:45.34,0:00:47.47,Default,,0000,0000,0000,,Moreover, a new study finds that
Dialogue: 0,0:00:47.49,0:00:49.89,Default,,0000,0000,0000,,their decline appears to be irreversible.
Dialogue: 0,0:00:49.91,0:00:51.85,Default,,0000,0000,0000,,'We've passed the point of no return,'
Dialogue: 0,0:00:51.87,0:00:53.36,Default,,0000,0000,0000,,says Eric Rignot,
Dialogue: 0,0:00:53.38,0:00:56.56,Default,,0000,0000,0000,,a glaciologist working jointly at NASA's Jet Propulsion Laboratory
Dialogue: 0,0:00:56.58,0:00:59.37,Default,,0000,0000,0000,,and the University of California, Irvine.
Dialogue: 0,0:00:59.39,0:01:01.19,Default,,0000,0000,0000,,Rignot and colleagues
Dialogue: 0,0:01:01.21,0:01:03.79,Default,,0000,0000,0000,,have used 19 years of satellite radar data
Dialogue: 0,0:01:03.81,0:01:05.40,Default,,0000,0000,0000,,to map the fast-melting glaciers.
Dialogue: 0,0:01:05.42,0:01:07.05,Default,,0000,0000,0000,,In their paper,
Dialogue: 0,0:01:07.07,0:01:08.77,Default,,0000,0000,0000,,which has been accepted for publication
Dialogue: 0,0:01:08.79,0:01:10.41,Default,,0000,0000,0000,,in Geophysical Research Letters,
Dialogue: 0,0:01:10.43,0:01:11.80,Default,,0000,0000,0000,,they conclude that
Dialogue: 0,0:01:11.82,0:01:13.35,Default,,0000,0000,0000,,'this sector of West Antarctica
Dialogue: 0,0:01:13.37,0:01:15.92,Default,,0000,0000,0000,,is undergoing a marine ice sheet instability
Dialogue: 0,0:01:15.94,0:01:18.56,Default,,0000,0000,0000,,that will significantly contribute to sea level rise'
Dialogue: 0,0:01:18.58,0:01:20.59,Default,,0000,0000,0000,,in the centuries ahead.
Dialogue: 0,0:01:20.61,0:01:23.12,Default,,0000,0000,0000,,A key concept in the Rignot study is the
Dialogue: 0,0:01:23.14,0:01:24.57,Default,,0000,0000,0000,,'grounding line'-
Dialogue: 0,0:01:24.59,0:01:26.86,Default,,0000,0000,0000,,the dividing line between land and water underneath a glacier.
Dialogue: 0,0:01:26.88,0:01:29.60,Default,,0000,0000,0000,,Because virtually all melting occurs
Dialogue: 0,0:01:29.62,0:01:31.87,Default,,0000,0000,0000,,where the glaciers' undersides touch the ocean,
Dialogue: 0,0:01:31.89,0:01:34.47,Default,,0000,0000,0000,,pinpointing the grounding line is crucial
Dialogue: 0,0:01:34.49,0:01:36.34,Default,,0000,0000,0000,,for estimating melt rates.
Dialogue: 0,0:01:36.36,0:01:37.33,Default,,0000,0000,0000,,The problem is,
Dialogue: 0,0:01:37.35,0:01:40.93,Default,,0000,0000,0000,,grounding lines are buried under thousands of feet of glacial ice.
Dialogue: 0,0:01:40.95,0:01:43.34,Default,,0000,0000,0000,,'It's challenging for a human observer
Dialogue: 0,0:01:43.36,0:01:45.42,Default,,0000,0000,0000,,to figure out where they are,' Rignot explains.
Dialogue: 0,0:01:45.44,0:01:48.65,Default,,0000,0000,0000,,'There's nothing obvious that sticks out on the surface to say,
Dialogue: 0,0:01:48.67,0:01:50.67,Default,,0000,0000,0000,,'This is where the glacier goes afloat.''
Dialogue: 0,0:01:50.69,0:01:52.99,Default,,0000,0000,0000,,To find the hidden grounding lines,
Dialogue: 0,0:01:53.01,0:01:55.28,Default,,0000,0000,0000,,they examined radar images of the glaciers
Dialogue: 0,0:01:55.30,0:01:58.85,Default,,0000,0000,0000,,made by the European Space Agency's Earth Remote Sensing satellites
Dialogue: 0,0:01:58.87,0:02:01.21,Default,,0000,0000,0000,,from 1992 to 2011.
Dialogue: 0,0:02:01.23,0:02:04.06,Default,,0000,0000,0000,,Glaciers flex in response to tides.
Dialogue: 0,0:02:04.08,0:02:06.15,Default,,0000,0000,0000,,By analyzing the flexing motions,
Dialogue: 0,0:02:06.17,0:02:08.16,Default,,0000,0000,0000,,they were able to trace the grounding lines.
Dialogue: 0,0:02:08.18,0:02:10.29,Default,,0000,0000,0000,,This led to a key discovery.
Dialogue: 0,0:02:10.31,0:02:12.80,Default,,0000,0000,0000,,In all the glaciers they studied,
Dialogue: 0,0:02:12.82,0:02:15.83,Default,,0000,0000,0000,,grounding lines were rapidly retreating away from the sea.
Dialogue: 0,0:02:15.85,0:02:17.42,Default,,0000,0000,0000,,'In this sector,
Dialogue: 0,0:02:17.44,0:02:18.83,Default,,0000,0000,0000,,we are seeing retreat rates
Dialogue: 0,0:02:18.85,0:02:21.31,Default,,0000,0000,0000,,that we don't see anywhere else on Earth,' Rignot says.
Dialogue: 0,0:02:21.33,0:02:23.78,Default,,0000,0000,0000,,Smith Glacier's line moved the fastest,
Dialogue: 0,0:02:23.80,0:02:25.92,Default,,0000,0000,0000,,retreating 22 miles upstream.
Dialogue: 0,0:02:25.94,0:02:29.19,Default,,0000,0000,0000,,The other lines retreated from 6 to 19 miles.
Dialogue: 0,0:02:29.21,0:02:31.98,Default,,0000,0000,0000,,As the glaciers melt and lose weight,
Dialogue: 0,0:02:32.00,0:02:34.13,Default,,0000,0000,0000,,they float off the land where they used to sit.
Dialogue: 0,0:02:34.15,0:02:36.42,Default,,0000,0000,0000,,Water gets underneath the glacier
Dialogue: 0,0:02:36.44,0:02:38.36,Default,,0000,0000,0000,,and pushes the grounding line inland.
Dialogue: 0,0:02:38.38,0:02:39.76,Default,,0000,0000,0000,,This, in turn,
Dialogue: 0,0:02:39.78,0:02:42.10,Default,,0000,0000,0000,,reduces friction between the glacier and its bed.
Dialogue: 0,0:02:42.12,0:02:43.56,Default,,0000,0000,0000,,The glacier speeds up,
Dialogue: 0,0:02:43.58,0:02:45.64,Default,,0000,0000,0000,,stretches out and thins,
Dialogue: 0,0:02:45.66,0:02:48.21,Default,,0000,0000,0000,,which drives the grounding line to retreat farther inland.
Dialogue: 0,0:02:48.23,0:02:50.63,Default,,0000,0000,0000,,This is a positive feedback loop
Dialogue: 0,0:02:50.65,0:02:52.58,Default,,0000,0000,0000,,that leads to out of control melting.
Dialogue: 0,0:02:52.60,0:02:56.55,Default,,0000,0000,0000,,The only natural factor that can slow or stop this process
Dialogue: 0,0:02:56.57,0:02:58.47,Default,,0000,0000,0000,,is a 'pinning point' in the bedrock --
Dialogue: 0,0:02:58.49,0:03:01.69,Default,,0000,0000,0000,,a bump or projection that snags the glacier from underneath
Dialogue: 0,0:03:01.71,0:03:03.72,Default,,0000,0000,0000,,and keeps it from sliding toward the sea.
Dialogue: 0,0:03:03.74,0:03:06.02,Default,,0000,0000,0000,,To investigate this possibility,
Dialogue: 0,0:03:06.04,0:03:09.10,Default,,0000,0000,0000,,the researchers made a novel map of the bed beneath the glaciers
Dialogue: 0,0:03:09.12,0:03:11.56,Default,,0000,0000,0000,,using radar and other data from satellites
Dialogue: 0,0:03:11.58,0:03:13.44,Default,,0000,0000,0000,,and NASA's airborne IceBridge mission.
Dialogue: 0,0:03:13.46,0:03:17.07,Default,,0000,0000,0000,,The map revealed that the glaciers had already floated off
Dialogue: 0,0:03:17.09,0:03:19.40,Default,,0000,0000,0000,,many of their small pinning points.
Dialogue: 0,0:03:19.42,0:03:21.91,Default,,0000,0000,0000,,In short, there seems to be no turning back.
Dialogue: 0,0:03:21.93,0:03:24.24,Default,,0000,0000,0000,,'At current melt rates,' concludes Rignot,
Dialogue: 0,0:03:24.26,0:03:27.67,Default,,0000,0000,0000,,'these glaciers will be 'history' within a few hundred years.'
Dialogue: 0,0:03:27.69,0:03:30.99,Default,,0000,0000,0000,,For more news about climate change and other hot topics,
Dialogue: 0,0:03:31.01,0:03:34.41,Default,,0000,0000,0000,,stay tuned to Science.nasa.gov.