﻿1 00:00:00,000 --> 00:00:04,040 Picture a simple theoretical planet. Simpler. 2 00:00:04,059 --> 00:00:08,070 Simpler. Keep, keep going, keep--nope that's 3 00:00:08,090 --> 00:00:12,110 too far. That is just a dot. Not even trying. Ok, 4 00:00:12,130 --> 00:00:16,130 there. This is DaisyWorld, a place where only two things 5 00:00:16,149 --> 00:00:20,150 live: black daisies and white daisies. 6 00:00:20,170 --> 00:00:24,170 In the early days, the atmosphere of DaisyWorld 7 00:00:24,190 --> 00:00:28,190 is cooler and black daisies thrive in these cooler temperatures. 8 00:00:28,210 --> 00:00:32,200 The black daisy population does so well in fact 9 00:00:32,220 --> 00:00:36,250 that it absorbs more energy and begins the warm the little planet. 10 00:00:36,270 --> 00:00:40,290 But now it's too warm for black daisies, but it's just right for the white 11 00:00:40,310 --> 00:00:44,390 daisies to blossom and expand. And while the planet is covered with 12 00:00:44,410 --> 00:00:48,429 more and more white daisies, they begin to reflect more energy back 13 00:00:48,450 --> 00:00:52,460 into space. We call this amount of reflectance albedo. The more reflective 14 00:00:52,480 --> 00:00:56,480 the surface of the planet, the higher its albedo. We can think of it 15 00:00:56,500 --> 00:01:00,519 as a percentage of how much energy is coming in and then bouncing back out 16 00:01:00,540 --> 00:01:04,539 into space. For instance, the albedo of a perfect mirror would 17 00:01:04,560 --> 00:01:08,570 be one hundred percent. If we had a completely 18 00:01:08,590 --> 00:01:12,680 black surface the albedo would be zero percent. 19 00:01:12,700 --> 00:01:16,720 20 00:01:16,740 --> 00:01:20,759 Or a waterworld, that could be twenty percent. 21 00:01:20,780 --> 00:01:24,800 Now the white daisies cool the planet again, 22 00:01:24,820 --> 00:01:28,839 and that makes it more favorable for black daisies to thrive once again. 23 00:01:28,860 --> 00:01:32,900 Now we're back to where we started. The black daisies have taken over 24 00:01:32,920 --> 00:01:36,950 but they'll warm up the planet, and then they'll die and the white daisies will grow 25 00:01:36,970 --> 00:01:41,000 but then they'll reflect more heat back out and then they'll die and on and on and on and back 26 00:01:41,020 --> 00:01:45,020 and forth. 27 00:01:45,040 --> 00:01:49,050 And over time, within a narrowly defined temperature range, 28 00:01:49,070 --> 00:01:53,070 DaisyWorld stays resilient and makes it possible for daisies to exist 29 00:01:53,090 --> 00:01:57,090 at all. Of course, this is a theoretical planet; there are no 30 00:01:57,110 --> 00:02:01,110 variables, like rotation, seasons, 31 00:02:01,130 --> 00:02:05,119 diseases, 32 00:02:05,140 --> 00:02:09,169 geography, or even humans. 33 00:02:09,190 --> 00:02:13,210 It does illustrate how a change in one environmental condition 34 00:02:13,230 --> 00:02:17,250 can cause a change in a second condition, which in turn, can change the first condition 35 00:02:17,270 --> 00:02:21,280 again. We call this a feedback loop. 36 00:02:21,300 --> 00:02:25,310 The DaisyWorld model is an example of a negative feedback 37 00:02:25,330 --> 00:02:29,340 loop because the initial changes to the climate are muted by the combination 38 00:02:29,360 --> 00:02:33,370 of black and white daisies. On Earth 39 00:02:33,390 --> 00:02:37,390 we can see this kind of negative feedback loop with clouds. Let's say 40 00:02:37,410 --> 00:02:41,400 increasing temperatures cause more surface evaporation, which cause more 41 00:02:41,420 --> 00:02:45,459 cloud formation, and clouds, much like our white daisies, have a 42 00:02:45,480 --> 00:02:49,510 higher albedo than the Earth's surface. Then the clouds will 43 00:02:49,530 --> 00:02:53,540 reflect more heat and cool the planet. When we look at snow 44 00:02:53,560 --> 00:02:57,570 and ice at the poles, which have a high albedo, we can see a positive 45 00:02:57,590 --> 00:03:01,610 feedback loop. When temperatures rise, the snow and ice 46 00:03:01,630 --> 00:03:05,630 melt, and so even more energy is absorbed by the water, and this 47 00:03:05,650 --> 00:03:09,640 continues to melt the snow and ice even further. With increasing climate change 48 00:03:09,660 --> 00:03:13,660 the natural reflectance of our icy poles dramatically declines. 49 00:03:13,680 --> 00:03:17,670 DaisyWorld is a much simpler place than our own planet, 50 00:03:17,690 --> 00:03:21,730 but it shows us that maintaining a population on Earth requires a 51 00:03:21,750 --> 00:03:25,780 delicate balance with the right organisms and the right range of 52 00:03:25,800 --> 00:03:29,800 environmental conditions. 53 00:03:29,820 --> 00:03:33,820 54 00:03:33,840 --> 00:03:37,850 Beep, beep. 55 00:03:37,870 --> 00:03:41,880 56 00:03:41,900 --> 00:03:46,340