2 00:00:09,986 --> 00:00:14,861 One of the simplest positive feedbacks in the climate system is called the ice 3 00:00:14,861 --> 00:00:20,260 albedo feedback. Albedo is a word that 4 00:00:20,260 --> 00:00:25,510 means the fraction of light that gets reflected back out to space. 5 00:00:25,510 --> 00:00:30,680 When visible light comes in and gets reflected back to space, 6 00:00:30,680 --> 00:00:34,590 it doesn't deposit its energy as heat to the planet. 7 00:00:34,590 --> 00:00:35,110 We saw the albedo in the layer model, 8 00:00:35,110 --> 00:00:39,600 the higher the albedo of the planet the colder the planet is 9 00:00:39,600 --> 00:00:44,640 because it doesn't use that energy, that light 10 00:00:44,640 --> 00:00:50,410 to fuel its own thermal energy, it just loses it off the top. 11 00:00:50,410 --> 00:00:57,120 The feedback with ice is that ice and snow are very reflective. 12 00:00:57,120 --> 00:01:01,390 If you have a layer of snow over ground, 13 00:01:01,390 --> 00:01:05,330 it will cause the visible light to 14 00:01:05,330 --> 00:01:08,110 be reflected back out to space; it'll have a high albedo. 15 00:01:08,110 --> 00:01:11,310 And then, you make it warmer, and the light 16 00:01:11,310 --> 00:01:14,100 will hit the darker ground and be absorbed. 17 00:01:14,100 --> 00:01:15,470 This will have a lower albedo. 18 00:01:15,470 --> 00:01:21,000 If you absorb that light, it makes the Earth warmer. 19 00:01:21,000 --> 00:01:26,570 Going from a cold state to a warm state tends to be 20 00:01:26,570 --> 00:01:31,560 amplified by the melting of the ice. And so in this feedback 21 00:01:31,560 --> 00:01:37,070 diagram, the state variable is the temperature, which gets feed back to. 22 00:01:37,070 --> 00:01:42,770 A perturbation to the temperature that makes it a little bit warmer.... 23 00:01:42,770 --> 00:01:46,460 causes ice to melt which makes it warm up even more. 24 00:01:46,460 --> 00:01:48,010 This is an amplifier. 25 00:01:49,560 --> 00:01:51,940 This also works for sea ice because 26 00:01:51,940 --> 00:01:56,190 sea ice is very reflective 27 00:01:56,190 --> 00:02:00,370 and the ocean is some of the lowest albedo material on Earth. 28 00:02:00,370 --> 00:02:03,990 And so if you have sea ice, it's going to reflect the light back to space, 29 00:02:03,990 --> 00:02:07,500 you melt the sea ice, the light will be absorbed in the ocean, it's 31 00:02:07,500 --> 00:02:10,604 suddenly getting added to the Earth's heat budget.