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]