WEBVTT FILE 1 00:00:00.000 --> 00:00:04.480 Greenland and Antarctica are home to most of the world's glacial ice 2 00:00:04.480 --> 00:00:08.680 that accumulates on land– including its only two ice sheets. 3 00:00:08.680 --> 00:00:11.600 That’s why scientists focus their energy here first 4 00:00:11.600 --> 00:00:14.940 when looking for answers about sea level rise. 5 00:00:14.940 --> 00:00:16.850 Here’s a concerning reality: 6 00:00:16.850 --> 00:00:19.990 Combined, the two regions contain enough ice, 7 00:00:19.990 --> 00:00:22.320 that if it were to melt all at once, 8 00:00:22.320 --> 00:00:26.430 sea levels would increase by nearly 215 feet. 9 00:00:26.430 --> 00:00:29.710 10 00:00:29.710 --> 00:00:32.560 Rising Waters: Out-of-Balance Ice Sheets 11 00:00:32.560 --> 00:00:34.940 Now, that isn’t going to happen anytime soon, 12 00:00:34.940 --> 00:00:39.040 but even a few feet of sea level rise (much less 215) 13 00:00:39.040 --> 00:00:42.630 would be disastrous for the planet’s coastal communities. 14 00:00:42.630 --> 00:00:47.320 For most people, these processes are happening so far away 15 00:00:47.320 --> 00:00:51.070 that’s hard to imagine how melting at the poles even occurs. 16 00:00:51.070 --> 00:00:52.750 Let’s lay some groundwork: 17 00:00:52.750 --> 00:00:58.770 A healthy glacier is one that accumulates the same amount of snowfall and it loses. 18 00:00:58.770 --> 00:01:01.100 It’s a system in balance. 19 00:01:01.100 --> 00:01:05.920 Unfortunately, today’s glaciers and ice sheets are not in balance. 20 00:01:05.920 --> 00:01:08.050 Here’s what that actually looks like: 21 00:01:08.050 --> 00:01:12.100 In Greenland, when warm summer air melts the surface of a glacier, 22 00:01:12.100 --> 00:01:15.270 the meltwater drills holes down through the ice. 23 00:01:15.270 --> 00:01:18.080 It makes its way down to the bottom of the glacier 24 00:01:18.080 --> 00:01:20.800 where it runs between the ice and the bedrock, 25 00:01:20.800 --> 00:01:24.290 and eventually shoots out in a plume at the base of the glacier. 26 00:01:24.290 --> 00:01:28.250 The meltwater plume is lighter because it doesn't contain salt 27 00:01:28.250 --> 00:01:30.060 – it’s freshwater. 28 00:01:30.060 --> 00:01:31.890 It rises toward the surface, 29 00:01:31.890 --> 00:01:35.440 mixing warm, salty ocean water upward in the process. 30 00:01:35.440 --> 00:01:38.930 The warm water then rubs up against the bottom of the glacier, 31 00:01:38.930 --> 00:01:41.530 causing even more of the glacier to melt. 32 00:01:41.530 --> 00:01:43.710 This often leads to calving, 33 00:01:43.710 --> 00:01:47.760 where ice cracks and breaks off into large icebergs. 34 00:01:47.760 --> 00:01:49.470 35 00:01:49.470 --> 00:01:53.510 In addition to melting caused by warm air and a warm ocean, 36 00:01:53.510 --> 00:01:57.920 Antarctica faces another challenge: the bedrock itself. 37 00:01:57.920 --> 00:02:03.530 Researches often split Antarctica into two regions: east and west. 38 00:02:03.530 --> 00:02:07.920 Unlike East Antarctica, the bedrock that makes up West Antarctica 39 00:02:07.920 --> 00:02:11.900 is below sea level, which means it’s actually underwater. 40 00:02:11.900 --> 00:02:16.080 Warmer water has an easier time seeping in between the continental shelf 41 00:02:16.080 --> 00:02:18.940 and the ice sheet, melting the ice from below. 42 00:02:18.940 --> 00:02:23.950 This causes the ice shelves to thin and break off into the ocean. 43 00:02:23.950 --> 00:02:25.540 44 00:02:25.540 --> 00:02:30.610 Melting and ice loss have accelerated at both poles in recent years. 45 00:02:30.610 --> 00:02:33.350 The more we learn about this complicated process, 46 00:02:33.350 --> 00:02:38.600 the more accurately we'll be able to predict sea level rise far into the future. 47 00:02:38.600 --> 00:02:51.520