2 00:00:02,940 --> 00:00:09,508 The glacial-interglacial cycles 3 00:00:09,508 --> 00:00:17,530 are best captured by this record of the Vostok CO2 concentration through time, 4 00:00:17,530 --> 00:00:23,020 and the global ice volume, and Antarctic temperature, also from that same ice core. 5 00:00:23,020 --> 00:00:28,030 It's got this intensely close correlation between the CO2 concentration 6 00:00:28,030 --> 00:00:31,170 and the Antarctic temperatures. 7 00:00:31,170 --> 00:00:37,750 The way that we think this all works is that the orbit of the Earth around the 8 00:00:37,750 --> 00:00:42,800 Sun affects the intensity of sunlight, as it hits 9 00:00:42,800 --> 00:00:46,240 the Northern Hemisphere of the Earth, in the summertime. 10 00:00:46,240 --> 00:00:49,530 The summertime is important because that's when you 11 00:00:49,530 --> 00:00:53,180 decide whether to melt last winter's snow or whether to keep 12 00:00:53,180 --> 00:00:56,520 it around and continue to accumulate it to make an ice sheet. 13 00:00:56,520 --> 00:00:59,220 And the Northern Hemisphere is important because 14 00:00:59,220 --> 00:01:02,250 that's where the land is, where we can put these ice sheets. 15 00:01:02,250 --> 00:01:05,305 During the glacial time there was 16 00:01:05,305 --> 00:01:11,300 a huge ice sheet in North America called the Laurentide ice sheet, 17 00:01:11,300 --> 00:01:13,960 and in Europe, there was the Fennoscandian ice sheet. 18 00:01:13,960 --> 00:01:15,625 There aren't optional ice sheets 19 00:01:15,625 --> 00:01:17,310 in the Southern hemisphere in the same way. 20 00:01:17,310 --> 00:01:18,515 It's the Northern hemisphere 21 00:01:18,515 --> 00:01:21,980 that's kind of the sweet spot for global climate. 22 00:01:23,700 --> 00:01:28,970 The changes in the ice sheet somehow provoke a 23 00:01:28,970 --> 00:01:31,430 positive feedback in the carbon cycle that 24 00:01:31,430 --> 00:01:36,590 amplifies the climate change and globalizes it. 25 00:01:36,590 --> 00:01:39,725 And it's not very well understood how exactly that happens. 27 00:01:43,180 --> 00:01:50,080 One false conclusion that is often drawn from this record comes from a time 28 00:01:50,080 --> 00:01:56,340 right in here, at the end of ice age, called the deglaciation, 29 00:01:56,340 --> 00:01:59,550 a time when it was just starting to transition 30 00:01:59,550 --> 00:02:04,200 from a full glacial maximum to an interglacial climate. 31 00:02:04,200 --> 00:02:08,420 And if you look in detail at this time the temperature from 32 00:02:08,420 --> 00:02:14,670 Antarctica starts to rise first, before the C02 starts to go up. 33 00:02:14,670 --> 00:02:16,610 It's hard to get this information, 34 00:02:16,610 --> 00:02:18,930 because the temperature comes from 35 00:02:18,930 --> 00:02:23,660 the oxygen 18 which is in the H2O which is in the ice, 36 00:02:23,660 --> 00:02:26,526 and the CO2 is from little bubbles which 37 00:02:26,526 --> 00:02:29,560 don't necessarily have the same age. 38 00:02:29,560 --> 00:02:33,460 In fact its pretty clear that, so you you put snow on 39 00:02:33,460 --> 00:02:37,950 top of snow, until the snow is compressed enough to seal off 40 00:02:37,950 --> 00:02:42,070 and make bubbles, the gases can still exchange with the atmosphere. 41 00:02:42,070 --> 00:02:44,820 There's a difference between the Ice Age and the 42 00:02:44,820 --> 00:02:47,310 Gas Age which make this a little difficult. 43 00:02:47,310 --> 00:02:50,150 But as best we put together, it looks as though the 44 00:02:50,150 --> 00:02:54,900 temperature started warming a little before the CO2 started to rise. 45 00:02:54,900 --> 00:02:59,140 That leads people to conclude erroneously 46 00:02:59,140 --> 00:03:04,810 that since temperature is apparently driving CO2 in this part 47 00:03:04,810 --> 00:03:10,450 here that means that CO2 somehow couldn't drive temperature. 48 00:03:10,450 --> 00:03:14,790 Whereas, you now know that a feedback is simply a loop of cause and effect. 49 00:03:14,790 --> 00:03:18,410 There's no reason why cause and effect has to be a one-way street. 50 00:03:18,410 --> 00:03:24,880 And it took much longer than 800 years for the full CO2 and 51 00:03:24,880 --> 00:03:27,380 temperature responses to develop. 52 00:03:27,380 --> 00:03:30,440 The fact that the temperature in 53 00:03:30,440 --> 00:03:33,130 Antarcita might have provoked the CO2 to start rising 54 00:03:33,130 --> 00:03:35,590 does not mean that the temperature rose all the way 55 00:03:35,590 --> 00:03:38,700 without any help from the rising CO2. 56 00:03:38,700 --> 00:03:43,110 A feedback loop allows these things to go in that direction. 57 00:03:47,550 --> 00:03:50,570 The temperature changes during the ice age cycles 58 00:03:50,570 --> 00:03:54,750 are about five to six degrees Centigrade, 59 00:03:54,750 --> 00:03:57,100 which is a remarkably small temperature change 60 00:03:57,100 --> 00:03:59,970 when you consider that the whole world looked different. 61 00:03:59,970 --> 00:04:01,920 Sea level was 120 meters lower. 62 00:04:01,920 --> 00:04:06,590 You could have walked from England to France or Russia to Alaska. 63 00:04:07,910 --> 00:04:12,420 and that was only with a five or six degree C temperature change. 64 00:04:12,420 --> 00:04:16,940 For a comparison, the temperature change predicted for the year 2100 65 00:04:16,940 --> 00:04:22,200 under business as usual, is about something like that. 66 00:04:22,200 --> 00:04:24,330 That same order of magnitude. 67 00:04:24,330 --> 00:04:28,350 The temperature changes of the last 1000 68 00:04:28,350 --> 00:04:30,700 years are comparable to what we've 69 00:04:30,700 --> 00:04:33,450 seen so far and that's really small potatoes 70 00:04:33,450 --> 00:04:36,420 compared to what is forcast for the future. 71 00:04:36,420 --> 00:04:37,740 About half 72 00:04:37,740 --> 00:04:43,160 of the warming on the deglaciation or, in other words, half the reason 73 00:04:43,160 --> 00:04:47,080 why it was colder during the ice age, is due to the lower CO2. 74 00:04:47,080 --> 00:04:50,560 The other half is due to the shininess, 75 00:04:50,560 --> 00:04:53,816 the albedo, of those ice sheets. 76 00:04:53,816 --> 00:04:58,820 They can put together an analysis 77 00:04:58,820 --> 00:05:03,600 of the glacial climate and try to derive 78 00:05:03,600 --> 00:05:08,040 value for the climate sensitivity. Delta T(2x), 79 00:05:08,040 --> 00:05:10,260 how much you expect the earth to change 80 00:05:10,260 --> 00:05:15,380 its temperature, in equilibrium from doubling the CO2 concentration. 81 00:05:15,380 --> 00:05:21,240 And the values they come up with for the climate sensitivity are 82 00:05:21,240 --> 00:05:27,200 completely consistent with those from diagnosing the instrumental record period. 83 00:05:27,200 --> 00:05:28,690 And they're also what the climate 84 00:05:28,690 --> 00:05:34,720 models are tending to produce. If CO2 were not a greenhouse 85 00:05:34,720 --> 00:05:40,170 gas, we wouldn't be able to explain even why the earth isn't in a deep freeze. 86 00:05:40,170 --> 00:05:47,370 And then if CO2 didn't have about the impact on climate that we think it does, 87 00:05:47,370 --> 00:05:52,150 we wouldn't be able to explain all these past temperature changes. 89 00:05:52,150 --> 00:05:53,767 The fact that we 90 00:05:53,767 --> 00:05:57,925 can only explain the instrumental temperature record with 91 00:05:57,925 --> 00:06:01,236 climate models using the greenhouse effect and the 92 00:06:01,236 --> 00:06:04,470 rising CO2 concentrations is the smoking 93 00:06:04,470 --> 00:06:06,857 gun for climate change, but we know the 94 00:06:06,857 --> 00:06:12,016 gun works because, if things didn't work the way we 95 00:06:12,016 --> 00:06:14,326 think they do, we wouldn't be able to 96 00:06:14,326 --> 00:06:18,340 explain anything about the climates of the past either.