WEBVTT FILE 1 00:00:01.040 --> 00:00:05.040 VO: Using the most advanced Earth observing laser instrument NASA has 2 00:00:05.040 --> 00:00:09.040 ever flown in space, scientists have made precise, detailed measurements of how the elevation 3 00:00:09.040 --> 00:00:13.040 of ice sheets in Greenland and Antarctica have changed over 4 00:00:13.040 --> 00:00:17.040 sixteen years. Smith: We actually see some processes at a scale that’s 5 00:00:17.040 --> 00:00:21.040 almost long enough to tell us about the climate in those two places. VO: Scientists 6 00:00:21.040 --> 00:00:25.040 took ice sheet elevation measurements from 2003, overlaid data 7 00:00:25.040 --> 00:00:29.040 from 2019 and analyzed where the datasets 8 00:00:29.040 --> 00:00:33.040 intersected in order to see where ice was lost or gained. For 9 00:00:33.040 --> 00:00:37.040 example, the study definitively shows that the East Antarctic ice sheet, 10 00:00:37.040 --> 00:00:41.040 the largest of all the ice sheets, is growing. Gardner: But more importantly, 11 00:00:41.040 --> 00:00:45.040 what we find is that growing is more than offset by 12 00:00:45.040 --> 00:00:49.040 increased losses from the West Antarctic ice sheet, which is thinning very 13 00:00:49.040 --> 00:00:53.040 rapidly as it responds to warmer ocean temperatures, specifically in the 14 00:00:53.040 --> 00:00:57.040 Amundsen Embayment area. Fricker: The West Antarctic side, 15 00:00:57.040 --> 00:01:01.040 we’re seeing strong thinning on the ice shelves, which is causing 16 00:01:01.040 --> 00:01:05.040 drawdown on the inland ice, on the grounded ice, upstream. 17 00:01:05.040 --> 00:01:09.040 Most of that is being caused because of changes in ocean 18 00:01:09.040 --> 00:01:13.040 heat flux underneath the ice shelves, which is causing them to thin and then 19 00:01:13.040 --> 00:01:17.040 consequently, the buttressing force is being lost against the grounded 20 00:01:17.040 --> 00:01:21.040 ice, and the grounded ice is then flowing faster into the ocean and causing 21 00:01:21.040 --> 00:01:25.040 sea level rise. In Greenland, we’re seeing 22 00:01:25.040 --> 00:01:29.040 different signatures. Again, in the center of the ice sheet in the plateau, we’re seeing 23 00:01:29.040 --> 00:01:33.040 increased accumulation. So there is a slight increase of mass in the center, 24 00:01:33.040 --> 00:01:37.040 but the overall signal for Greenland is one of thinning, and that is 25 00:01:37.040 --> 00:01:41.040 being caused by ocean and atmospheric signals acting all around 26 00:01:41.040 --> 00:01:45.040 the edges of Greenland. Smith: So we’re seeing 200 gigatonnes per 27 00:01:45.040 --> 00:01:49.040 year of ice flowing into the oceans, which is enough to raise sea 28 00:01:49.040 --> 00:01:53.040 level by about two thirds of a millimeter per year. VO: Combine that with 29 00:01:53.040 --> 00:01:57.040 the almost 118 gigatonnes lost in Antarctica, and sea 30 00:01:57.040 --> 00:02:01.040 level has risen a total of 14 millimeters over the 16 year period due 31 00:02:01.040 --> 00:02:05.040 to ice sheet melt. It may seem small, but the small 32 00:02:05.040 --> 00:02:09.040 changes add up. Gardner: What we expect by the end of the century 33 00:02:09.040 --> 00:02:13.040 is on the order of 2, 3, maybe 4 feet of sea level 34 00:02:13.040 --> 00:02:17.040 rise. And because we have all of our infrastructure that 35 00:02:17.040 --> 00:02:21.040 is built around the coasts, we have a lot of vulnerability 36 00:02:21.040 --> 00:02:25.040 to a meter change in sea level rise. VO: The potential impact 37 00:02:25.040 --> 00:02:29.040 from sea level rise is one critical motivation for the continued study of 38 00:02:29.040 --> 00:02:33.040 the mechanics driving the changes in the ice sheets. Gardner: If we can understand 39 00:02:33.040 --> 00:02:37.040 those mechanisms and how they’ve played out over the last 30 years, well then we 40 00:02:37.040 --> 00:02:41.040 start to look and think about how will those ice sheets respond 41 00:02:41.040 --> 00:02:45.040 to what we project the climate to be into the future. [music] 42 00:02:45.040 --> 00:02:48.380 [music] 43 00:02:48.380 --> 00:02:48.384 [music]