1 00:00:00,050 --> 00:00:10,580 [ music ] 2 00:00:10,600 --> 00:00:13,520 [ crack ] [laughter] 3 00:00:13,540 --> 00:00:16,690 If CO2 is overheating Greenland, why is 4 00:00:16,710 --> 00:00:19,880 the ice still over 10,000 feet thick? 5 00:00:19,900 --> 00:00:24,280 This is a really good question, because it addresses the concept of thickness, 6 00:00:24,300 --> 00:00:27,880 which is extremely important to polar scientists. 7 00:00:27,900 --> 00:00:33,470 It's very easy to see that ice sheets and ice shelves and sea ice are changing 8 00:00:33,490 --> 00:00:37,170 in a sort of spatial sense, but what's even more important 9 00:00:37,190 --> 00:00:40,850 is that they are also thinning. It's very important for sea ice, 10 00:00:40,870 --> 00:00:43,430 but it's also important for the ice sheets. 11 00:00:43,450 --> 00:00:49,610 We know from satellite data and mosaics of that satellite data 12 00:00:49,630 --> 00:00:54,480 that our sea ice extent is decreasing in this sense, the sort of planar sense, 13 00:00:54,500 --> 00:00:59,200 and our ice sheets calve off so we lose mass in that extent as well. 14 00:00:59,220 --> 00:01:02,280 But more importantly, we're getting thinning. 15 00:01:02,300 --> 00:01:04,970 Both in the sea ice and in the ice sheets and you can imagine 16 00:01:04,990 --> 00:01:10,130 that just a little bit of thinning spread over the scale of a continent amounts to a lot of water. 17 00:01:10,150 --> 00:01:14,980 So it's a great question, but I think we just have to fine tune the questioner's expectations. 18 00:01:15,000 --> 00:01:19,030 If I were to walk outside on a really cold day, it would take a little bit of time 19 00:01:19,050 --> 00:01:23,130 for my core body temperature to drop even though I am feeling chilly on the outside. 20 00:01:23,150 --> 00:01:27,320 That's what's happening in Greenland as well. The Greenland ice sheet is really thick. 21 00:01:27,340 --> 00:01:31,830 It's going to take a lot of time to melt all of that ice. 22 00:01:31,850 --> 00:01:37,380 So the Greenland ice sheet is thinning, and it's thinning variably but mostly along the coastlines. 23 00:01:37,400 --> 00:01:44,400 It's thinning beyond our expectations and all of that thinning is taking place upstream of where the ice sheet is grounded. 24 00:01:44,420 --> 00:01:49,570 Therefore that is going right into the ocean and contributing to mean sea level rise. 25 00:01:49,590 --> 00:01:57,200 [ music ] 26 00:01:57,220 --> 00:02:00,033