WEBVTT FILE 1 00:00:00.160 --> 00:00:04.160 2 00:00:04.160 --> 00:00:08.330 On March 17, the Arctic region reached a milestone 3 00:00:08.330 --> 00:00:12.330 …the second-lowest sea ice maximum extent since satellite measurements began. 4 00:00:12.330 --> 00:00:16.780 The four lowest maximum Arctic extents on record have been in the last four years, 5 00:00:16.780 --> 00:00:21.130 according to analysis from NASA and the National Snow and Ice Data Center. 6 00:00:21.130 --> 00:00:25.130 This year’s maximum extent reached 5.59 million square miles. 7 00:00:25.130 --> 00:00:29.130 But…what does that really mean? 8 00:00:29.130 --> 00:00:33.140 How, and why, do we track sea ice? 9 00:00:33.140 --> 00:00:37.140 We’ve got a good record of extents since the late 1970s. 10 00:00:37.140 --> 00:00:41.640 So by now, the record of the Arctic ice is clearly 11 00:00:41.640 --> 00:00:45.640 one of a decreasing ice cover. 12 00:00:45.640 --> 00:00:50.420 To answer some of my questions, I talked with Dr. Claire Parkinson, 13 00:00:50.420 --> 00:00:54.600 who has been studying sea ice from space for the past four decades. 14 00:00:54.600 --> 00:00:58.730 I got a job at NASA’s Goddard Space Flight Center in July of 1978, 15 00:00:58.730 --> 00:01:02.920 and I’ve been here ever since 16 00:01:02.920 --> 00:01:07.220 and I’ve had the phenomenal opportunity of getting to start 17 00:01:07.220 --> 00:01:12.370 when the satellite data were still fairly new and when, 18 00:01:12.370 --> 00:01:16.370 at Goddard, people were trying to figure out 19 00:01:16.370 --> 00:01:20.550 how to use the satellite data to reveal information about the Earth. 20 00:01:20.550 --> 00:01:24.550 After several years when we started getting a longer record, 21 00:01:24.550 --> 00:01:29.370 then our attention got changed into 22 00:01:29.370 --> 00:01:33.430 “Well what kinds of trends are we seeing in sea ice?” 23 00:01:33.430 --> 00:01:37.730 We’ve maintained this record of sea ice and we recognize now 24 00:01:37.730 --> 00:01:41.730 that it’s very important for climate change, 25 00:01:41.730 --> 00:01:45.890 because sea ice is one of the variables in the Earth system that has been changing 26 00:01:45.890 --> 00:01:49.980 the most dramatically, especially in the Arctic. 27 00:01:49.980 --> 00:01:54.140 But sea ice doesn’t just react to warming global temperatures… 28 00:01:54.140 --> 00:01:59.320 it can actually accelerate the temperature increases. 29 00:01:59.320 --> 00:02:03.450 Now the less sea ice coverage feeds back 30 00:02:03.450 --> 00:02:08.080 into the warming, because if you’ve got less sea ice cover, 31 00:02:08.080 --> 00:02:12.270 that means less of the sun’s radiation that comes down 32 00:02:12.270 --> 00:02:16.280 to the surface will get reflected back. 33 00:02:16.280 --> 00:02:20.490 Sea ice fluctuates with the seasons, growing during the cold, 34 00:02:20.490 --> 00:02:25.930 dark winters until reaching an annual maximum extent 35 00:02:25.930 --> 00:02:30.980 in February or March in the Arctic, and then shrinking through the summer 36 00:02:30.980 --> 00:02:35.030 until reaching a minimum in September. 37 00:02:35.030 --> 00:02:39.040 In the Arctic case, in late summer, it extends over about 5 million square kilometers. 38 00:02:39.040 --> 00:02:43.050 In late winter, it extends way further, over about 39 00:02:43.050 --> 00:02:47.060 15 million square kilometers. which is about one and a half times the area of Canada. 40 00:02:47.060 --> 00:02:51.240 So studying sea ice 41 00:02:51.240 --> 00:02:55.250 includes tracking how it changes seasonally. Rather than just looking 42 00:02:55.250 --> 00:02:59.260 at the annual summer minimum, scientists track how the ice changes throughout the year, 43 00:02:59.260 --> 00:03:03.270 to get a fuller picture of change. 44 00:03:03.270 --> 00:03:07.280 Every month of the year has decreases in the Arctic and it doesn’t mean 45 00:03:07.280 --> 00:03:11.340 every single year has less ice than the year before, 46 00:03:11.340 --> 00:03:22.085 but it means that, overall, the trend is downward.