1 00:00:01,010 --> 00:00:03,010 [ music ] 2 00:00:03,030 --> 00:00:04,080 No Turning Back: 3 00:00:04,100 --> 00:00:06,770 West Antarctic Glaciers in Irreversible Decline -- 4 00:00:06,790 --> 00:00:09,140 Presented by Science@NASA 5 00:00:09,160 --> 00:00:10,980 Over the years, 6 00:00:11,000 --> 00:00:13,510 as temperatures around the world have ratcheted upward, 7 00:00:13,530 --> 00:00:16,760 climate change researchers have kept a wary eye on one place 8 00:00:16,780 --> 00:00:18,520 perhaps more than any other: 9 00:00:18,540 --> 00:00:20,190 The West Antarctic Ice Sheet, 10 00:00:20,210 --> 00:00:23,260 and particularly the fastest melting part of it, 11 00:00:23,280 --> 00:00:25,670 the glaciers that flow into the Amundsen Sea. 12 00:00:25,690 --> 00:00:27,360 In that region, 13 00:00:27,380 --> 00:00:29,640 six glaciers hang in a precarious balance, 14 00:00:29,660 --> 00:00:31,900 partially supported by land, 15 00:00:31,920 --> 00:00:34,680 and partially floating in waters just offshore. 16 00:00:34,700 --> 00:00:36,950 There's enough water frozen in the ice sheet 17 00:00:36,970 --> 00:00:38,470 that feeds these icy giants 18 00:00:38,490 --> 00:00:40,950 to raise global sea levels by 4 feet- 19 00:00:40,970 --> 00:00:42,430 if they were to melt. 20 00:00:42,450 --> 00:00:45,320 That's troubling because the glaciers are melting. 21 00:00:45,340 --> 00:00:47,470 Moreover, a new study finds that 22 00:00:47,490 --> 00:00:49,890 their decline appears to be irreversible. 23 00:00:49,910 --> 00:00:51,850 'We've passed the point of no return,' 24 00:00:51,870 --> 00:00:53,360 says Eric Rignot, 25 00:00:53,380 --> 00:00:56,560 a glaciologist working jointly at NASA's Jet Propulsion Laboratory 26 00:00:56,580 --> 00:00:59,370 and the University of California, Irvine. 27 00:00:59,390 --> 00:01:01,190 Rignot and colleagues 28 00:01:01,210 --> 00:01:03,790 have used 19 years of satellite radar data 29 00:01:03,810 --> 00:01:05,400 to map the fast-melting glaciers. 30 00:01:05,420 --> 00:01:07,050 In their paper, 31 00:01:07,070 --> 00:01:08,770 which has been accepted for publication 32 00:01:08,790 --> 00:01:10,410 in Geophysical Research Letters, 33 00:01:10,430 --> 00:01:11,800 they conclude that 34 00:01:11,820 --> 00:01:13,350 'this sector of West Antarctica 35 00:01:13,370 --> 00:01:15,920 is undergoing a marine ice sheet instability 36 00:01:15,940 --> 00:01:18,560 that will significantly contribute to sea level rise' 37 00:01:18,580 --> 00:01:20,590 in the centuries ahead. 38 00:01:20,610 --> 00:01:23,120 A key concept in the Rignot study is the 39 00:01:23,140 --> 00:01:24,570 'grounding line'- 40 00:01:24,590 --> 00:01:26,860 the dividing line between land and water underneath a glacier. 41 00:01:26,880 --> 00:01:29,600 Because virtually all melting occurs 42 00:01:29,620 --> 00:01:31,870 where the glaciers' undersides touch the ocean, 43 00:01:31,890 --> 00:01:34,470 pinpointing the grounding line is crucial 44 00:01:34,490 --> 00:01:36,340 for estimating melt rates. 45 00:01:36,360 --> 00:01:37,330 The problem is, 46 00:01:37,350 --> 00:01:40,930 grounding lines are buried under thousands of feet of glacial ice. 47 00:01:40,950 --> 00:01:43,340 'It's challenging for a human observer 48 00:01:43,360 --> 00:01:45,420 to figure out where they are,' Rignot explains. 49 00:01:45,440 --> 00:01:48,650 'There's nothing obvious that sticks out on the surface to say, 50 00:01:48,670 --> 00:01:50,670 'This is where the glacier goes afloat.'' 51 00:01:50,690 --> 00:01:52,990 To find the hidden grounding lines, 52 00:01:53,010 --> 00:01:55,280 they examined radar images of the glaciers 53 00:01:55,300 --> 00:01:58,850 made by the European Space Agency's Earth Remote Sensing satellites 54 00:01:58,870 --> 00:02:01,210 from 1992 to 2011. 55 00:02:01,230 --> 00:02:04,060 Glaciers flex in response to tides. 56 00:02:04,080 --> 00:02:06,150 By analyzing the flexing motions, 57 00:02:06,170 --> 00:02:08,160 they were able to trace the grounding lines. 58 00:02:08,180 --> 00:02:10,289 This led to a key discovery. 59 00:02:10,310 --> 00:02:12,800 In all the glaciers they studied, 60 00:02:12,820 --> 00:02:15,830 grounding lines were rapidly retreating away from the sea. 61 00:02:15,850 --> 00:02:17,420 'In this sector, 62 00:02:17,440 --> 00:02:18,830 we are seeing retreat rates 63 00:02:18,850 --> 00:02:21,310 that we don't see anywhere else on Earth,' Rignot says. 64 00:02:21,330 --> 00:02:23,780 Smith Glacier's line moved the fastest, 65 00:02:23,800 --> 00:02:25,920 retreating 22 miles upstream. 66 00:02:25,940 --> 00:02:29,190 The other lines retreated from 6 to 19 miles. 67 00:02:29,210 --> 00:02:31,980 As the glaciers melt and lose weight, 68 00:02:32,000 --> 00:02:34,130 they float off the land where they used to sit. 69 00:02:34,150 --> 00:02:36,420 Water gets underneath the glacier 70 00:02:36,440 --> 00:02:38,360 and pushes the grounding line inland. 71 00:02:38,380 --> 00:02:39,760 This, in turn, 72 00:02:39,780 --> 00:02:42,100 reduces friction between the glacier and its bed. 73 00:02:42,120 --> 00:02:43,560 The glacier speeds up, 74 00:02:43,580 --> 00:02:45,640 stretches out and thins, 75 00:02:45,660 --> 00:02:48,210 which drives the grounding line to retreat farther inland. 76 00:02:48,230 --> 00:02:50,630 This is a positive feedback loop 77 00:02:50,650 --> 00:02:52,580 that leads to out of control melting. 78 00:02:52,600 --> 00:02:56,550 The only natural factor that can slow or stop this process 79 00:02:56,570 --> 00:02:58,470 is a 'pinning point' in the bedrock -- 80 00:02:58,490 --> 00:03:01,690 a bump or projection that snags the glacier from underneath 81 00:03:01,710 --> 00:03:03,720 and keeps it from sliding toward the sea. 82 00:03:03,740 --> 00:03:06,020 To investigate this possibility, 83 00:03:06,040 --> 00:03:09,100 the researchers made a novel map of the bed beneath the glaciers 84 00:03:09,120 --> 00:03:11,560 using radar and other data from satellites 85 00:03:11,580 --> 00:03:13,440 and NASA's airborne IceBridge mission. 86 00:03:13,460 --> 00:03:17,070 The map revealed that the glaciers had already floated off 87 00:03:17,090 --> 00:03:19,400 many of their small pinning points. 88 00:03:19,420 --> 00:03:21,910 In short, there seems to be no turning back. 89 00:03:21,930 --> 00:03:24,240 'At current melt rates,' concludes Rignot, 90 00:03:24,260 --> 00:03:27,670 'these glaciers will be 'history' within a few hundred years.' 91 00:03:27,690 --> 00:03:30,990 For more news about climate change and other hot topics, 92 00:03:31,010 --> 00:03:34,414 stay tuned to Science.nasa.gov.