WEBVTT 00:01.680 --> 00:04.910 Prof: We're now going to start the block of the course 00:04.911 --> 00:08.831 which is on ecology, and these are the titles of the 00:08.828 --> 00:10.468 upcoming lectures. 00:10.470 --> 00:13.540 You can think of ecology as providing the theater in which 00:13.540 --> 00:16.070 the evolutionary play occurs; that's a metaphor from Evelyn 00:16.065 --> 00:16.415 Hutchinson. 00:16.420 --> 00:20.690 00:20.690 --> 00:27.800 And basically I'm doing a top-down, and then going back; 00:27.800 --> 00:30.650 going from the top down, and then going from the bottom 00:30.645 --> 00:32.805 back up to the top, in going through these 00:32.805 --> 00:33.485 lectures. 00:33.490 --> 00:38.330 So I'm going to start today by taking about climate and the 00:38.326 --> 00:40.886 planet, and how life is distributed on 00:40.890 --> 00:43.480 the planet, and then move from that into 00:43.483 --> 00:44.343 the biology. 00:44.340 --> 00:47.670 So looking at physiological ecology and interactions with 00:47.673 --> 00:50.873 the physical environment, leading from that through 00:50.867 --> 00:52.947 population growth, competition, 00:52.946 --> 00:57.856 predation, parasitism, up to community--so that's sort 00:57.864 --> 01:03.454 of a way of doing a Cartesian bottom up construction of 01:03.445 --> 01:07.585 communities-- and then dealing with some of 01:07.585 --> 01:10.755 the larger scale issues in ecology, 01:10.760 --> 01:13.250 which have to do with islands and meta-populations, 01:13.250 --> 01:18.970 and then systems ecology, energy and matter flow. 01:18.970 --> 01:25.750 And then I'm going to end with a lecture which is both about 01:25.748 --> 01:30.228 the role of biodiversity in ecology, 01:30.230 --> 01:34.600 but also about general takes on the value of biodiversity, 01:34.599 --> 01:38.329 and this last lecture in ecology is going to include some 01:38.334 --> 01:41.474 stuff like an economic take on biodiversity, 01:41.470 --> 01:43.320 an evolutionary take on biodiversity, 01:43.319 --> 01:48.119 as well as the issue of does biodiversity actually help 01:48.123 --> 01:50.973 ecosystems to function better? 01:50.970 --> 01:52.370 So that's what's coming up. 01:52.370 --> 01:55.590 And today we're going to basically look at the climates 01:55.587 --> 01:58.567 of the planet, how the planet can be looked at 01:58.565 --> 02:02.535 as a set of climate machines, and how they generate the 02:02.540 --> 02:04.390 biomes, on the planet. 02:04.390 --> 02:07.890 So at this scale, this stuff I think is probably 02:07.888 --> 02:09.228 pretty familiar. 02:09.229 --> 02:12.819 The world climate is of course cold at the poles and warm at 02:12.823 --> 02:15.933 the tropics, but there's a lot of detail in that. 02:15.930 --> 02:19.020 It tends to be warmer and wetter on the western sides of 02:19.021 --> 02:22.571 the northern continents, and cooler and drier on the 02:22.566 --> 02:25.716 eastern sides of the northern continents. 02:25.720 --> 02:28.060 The influence of the Gulf Stream can be seen pretty 02:28.055 --> 02:31.505 clearly here in Europe, with this large warm area being 02:31.514 --> 02:35.504 sort of pushed up and to the right by the warm water, 02:35.500 --> 02:38.010 which is coming up out of the Gulf of Mexico. 02:38.008 --> 02:41.978 And if you go far east into the huge block of the Eurasian land 02:41.978 --> 02:45.028 mass, you can get so far away from 02:45.032 --> 02:50.122 the effects of the ocean that the coldest temperature, 02:50.120 --> 02:51.340 at least in the Northern Hemisphere, 02:51.340 --> 02:53.280 was recorded right about here. 02:53.280 --> 02:56.860 It was, I think, -127 Fahrenheit; 02:56.860 --> 02:58.060 which, you know, that's nippy. 02:58.060 --> 03:02.390 03:02.389 --> 03:07.329 There are interesting similarities in the climates of 03:07.325 --> 03:08.935 similar places. 03:08.938 --> 03:12.908 So if you look at the western leading edge of North and South 03:12.911 --> 03:16.341 America, and you go about as far south 03:16.343 --> 03:20.343 of the equator as north, basically what you run into is 03:20.336 --> 03:21.586 a temperate rainforest. 03:21.590 --> 03:24.930 There's a temperate rainforest that is stretching from Northern 03:24.925 --> 03:28.025 California up to Alaska, and there's another temperate 03:28.027 --> 03:31.037 rainforest which stretches along the coast of Chile. 03:31.038 --> 03:35.718 And these similarities in climate have created similar 03:35.720 --> 03:39.430 biomes and similar selection pressures, 03:39.430 --> 03:43.520 and have led to convergences in the communities that you see in 03:43.520 --> 03:44.510 these places. 03:44.508 --> 03:47.728 So if you really want to understand why is it that if I 03:47.729 --> 03:51.749 am standing say in Chile, or in part of New Zealand, 03:51.745 --> 03:56.045 or in British Columbia, that they kind of remind me of 03:56.050 --> 03:56.870 each other? 03:56.870 --> 04:00.470 Even though the plants may not be at all related, 04:00.473 --> 04:03.253 they look the same, it feels the same, 04:03.251 --> 04:06.181 the forests have similar structure. 04:06.180 --> 04:11.910 Well you have to go back to why the planet as a whole constructs 04:11.913 --> 04:15.103 similar climates in those places. 04:15.098 --> 04:18.418 Part of it, at a local level, if you're looking say at what's 04:18.415 --> 04:21.615 generating the rainforest in Chile or what's generating the 04:21.620 --> 04:25.360 rainforest in British Columbia, has to do with the way that 04:25.360 --> 04:28.150 mountains are interacting with atmosphere. 04:28.149 --> 04:32.159 So in both, in these situations, you have got clouds 04:32.161 --> 04:36.961 that are coming in off of the ocean, and they are being forced 04:36.961 --> 04:39.401 upward by a mountain range. 04:39.399 --> 04:43.849 And there's some very simple physical chemistry that goes on 04:43.853 --> 04:46.273 when you force a cloud upward. 04:46.269 --> 04:49.749 The rising air is going to be cooling before it condenses. 04:49.750 --> 04:52.750 Then it will condense and form heavy clouds, 04:52.750 --> 04:56.020 and they will rain out, and as the wind is going to 04:56.016 --> 04:59.346 push them up over the top of the mountain range, 04:59.350 --> 05:02.090 basically all the water will leave the cloud. 05:02.088 --> 05:04.798 Well that's what's creating that rainforest. 05:04.800 --> 05:05.280 Okay? 05:05.276 --> 05:10.806 And the reason for that is that cold air can't hold as much 05:10.807 --> 05:12.807 water as warm air. 05:12.810 --> 05:17.620 And the cooling is going on at a rate of about 6 degrees 05:17.617 --> 05:21.987 Centigrade per kilometer of elevation, going up. 05:21.990 --> 05:25.210 The air which was at 20, coming in off the ocean-- 05:25.209 --> 05:28.209 this is 20 degrees Centigrade--is hitting perhaps 4 05:28.214 --> 05:30.504 degrees at the top of the mountain-- 05:30.500 --> 05:32.780 so you could think of this as the Sierras, 05:32.779 --> 05:38.879 or the top of say the Cascades in Oregon or Washington-- 05:38.879 --> 05:40.439 and then it falls down the other side. 05:40.440 --> 05:43.300 And over here you have dry air falling. 05:43.300 --> 05:46.150 This is wet air rising, and it rains out, 05:46.146 --> 05:48.706 and then you have dry air falling. 05:48.709 --> 05:51.039 And this wet air rising and raining, 05:51.040 --> 05:54.300 and dry air falling and warming, and ending up 4 degrees 05:54.300 --> 05:57.860 warmer at the same elevation on this side than it was on this 05:57.857 --> 05:59.967 side, because of the heat of 05:59.971 --> 06:03.571 condensation that's been released by the rain here. 06:03.569 --> 06:04.809 This is something I want you to remember, 06:04.810 --> 06:07.320 because it actually also applies at the scale of the 06:07.321 --> 06:10.641 whole planet, when you have very large air 06:10.637 --> 06:14.157 cells that are rotating on the planet. 06:14.160 --> 06:17.610 And where there's dry air falling, you're going to get 06:17.605 --> 06:19.835 deserts, and where there is warm air 06:19.839 --> 06:22.149 rising you're going to get rainforests, 06:22.149 --> 06:25.969 whether you have the mountain range there or not. 06:25.970 --> 06:29.230 So we'll see that in a minute, and that's why I wanted to 06:29.233 --> 06:32.093 introduce this level of analysis at this point. 06:32.089 --> 06:32.359 Okay? 06:32.355 --> 06:35.535 So this warm air falling here is called foehn in Switzerland, 06:35.538 --> 06:38.828 and the Swiss always complain that it gives them headaches; 06:38.829 --> 06:41.769 it's called the Santa Ana wind in Los Angeles; 06:41.769 --> 06:45.309 and there's a special wind that blows down the valley behind 06:45.305 --> 06:47.935 Lahaina, Maui, that can hit 140 miles an hour 06:47.942 --> 06:49.862 sometimes, which is similar. 06:49.860 --> 06:53.960 So these local dry hot winds can be very important, 06:53.956 --> 06:58.786 and they're actually what drive the wild fires in Malibu and 06:58.788 --> 07:00.508 things like that. 07:00.509 --> 07:04.439 Okay, now let's take a look at the whole planet. 07:04.439 --> 07:08.429 If the earth was simply a stationary ball, 07:08.430 --> 07:11.610 sitting in space, undisturbed, 07:11.607 --> 07:15.877 but was being heated at the equator, 07:15.879 --> 07:18.619 it would develop basically two convection cells, 07:18.620 --> 07:20.150 one in each hemisphere. 07:20.149 --> 07:24.529 So there would be cold air that was falling on the poles. 07:24.528 --> 07:27.498 It would be falling down to the surface and it would be picking 07:27.502 --> 07:30.002 up moisture and rising, and basically you would get a 07:30.002 --> 07:31.732 belt of rainforest around the equator, 07:31.730 --> 07:35.290 and you would have deserts at the poles and a gradient in 07:35.293 --> 07:35.933 between. 07:35.930 --> 07:40.380 That would be what would happen if the earth were not rotating. 07:40.379 --> 07:44.369 The earth is rotating, and because it's rotating, 07:44.370 --> 07:49.410 on an idealized planet you would get three Hadley cells, 07:49.410 --> 07:52.350 going out from the equator--three in the north and 07:52.350 --> 07:55.950 three in the south-- and at the equator you would 07:55.954 --> 08:00.284 have warm air rising and it would be dropping rain, 08:00.278 --> 08:03.338 because as it rose it cooled, and it would lose capacity to 08:03.341 --> 08:05.191 hold water and it would rain out. 08:10.728 --> 08:11.548 north. 08:11.550 --> 08:13.300 Okay? 08:13.300 --> 08:18.360 There it would be interacting with another similar cell that 08:18.360 --> 08:23.850 would be carrying warm air north and rising at about 60 north. 08:23.850 --> 08:24.210 Okay? 08:24.208 --> 08:28.358 Remember where the rainforests were in Chile and in British 08:28.360 --> 08:32.440 Columbia; they are in this region here 08:32.442 --> 08:35.322 and in this region here. 08:35.320 --> 08:38.950 And this is where the deserts are, around the world; 08:38.950 --> 08:42.490 they're at about 30 North and 30 South. 08:42.490 --> 08:45.280 Now this is an idealized format. 08:45.279 --> 08:49.349 At the boundary, by the way, of where you've got 08:49.350 --> 08:53.940 the polar highs and the northern Hadley cell here, 08:53.940 --> 08:56.830 right at this boundary is where you get a polar front, 08:56.830 --> 09:00.810 and this is where the jet stream goes around the world in 09:00.811 --> 09:04.651 the north and it goes around the world in the south. 09:04.649 --> 09:07.829 So the location of the jet stream that drives most of the 09:07.828 --> 09:11.968 weather that we encounter here, and the idea that it might say 09:11.974 --> 09:16.114 pull in a mass of Canadian- a clipper of Canadian weather 09:16.106 --> 09:19.056 coming in from the polar front here, 09:19.058 --> 09:21.478 is actually generated by this structure, 09:21.480 --> 09:23.340 and it's wobbly. 09:23.340 --> 09:24.180 Okay? 09:24.178 --> 09:27.108 In an idealized world this is all smooth, and these lines are 09:27.105 --> 09:28.075 clean and whatnot. 09:28.080 --> 09:30.370 But, in fact, the surface of the planet has 09:30.371 --> 09:33.411 got stuff on it, like continents and oceans, 09:33.410 --> 09:37.340 and as this stuff moves in its circulation pattern, 09:37.340 --> 09:41.250 both north and south, and west to east, 09:41.250 --> 09:43.740 around the Northern Hemisphere, it wobbles, 09:43.740 --> 09:46.410 because it's been deflected by local perturbations like 09:46.407 --> 09:47.837 mountain ranges and oceans. 09:47.840 --> 09:51.900 09:51.899 --> 09:57.669 So out of this you get patterns of wind that in fact have--well 09:57.666 --> 10:02.406 now but they not only currently generate weather. 10:02.408 --> 10:07.348 You can really only understand say the history of the last 8 or 10:07.346 --> 10:11.326 10,000 years of human civilization on the planet by 10:11.326 --> 10:15.146 realizing that the people who were trading, 10:15.149 --> 10:20.269 and were using boats to move, were relying on the fact that 10:25.822 --> 10:29.032 north you can count on a trade wind; 10:29.028 --> 10:31.268 and that repeats in the Southern Hemisphere. 10:31.269 --> 10:35.489 And this is actually--these trades here, over in the Indian 10:35.493 --> 10:39.793 Ocean, were what drove the trade between India and the Roman 10:39.788 --> 10:41.498 Empire; things like that. 10:41.500 --> 10:44.860 10:44.860 --> 10:48.410 So you should think of the planet as being covered 10:48.413 --> 10:51.463 with--these are really very thin sheets. 10:51.460 --> 10:52.700 When you think, for example, 10:52.701 --> 10:55.231 that we're looking here probably at 3 or 4000 miles, 10:55.230 --> 11:00.050 4 or 5000 kilometers, and the depth of this cell is 11:00.048 --> 11:03.998 actually only about 5 to 10 kilometers. 11:04.000 --> 11:10.000 So it's a very thin cell, which is rotating like that. 11:10.000 --> 11:13.230 Now if there weren't any continents, you'd end up with 11:13.226 --> 11:15.476 something that looked like Jupiter. 11:15.480 --> 11:19.610 Okay, Jupiter has these nice neat bands that go around, 11:19.610 --> 11:24.270 and it is a bit--it's not the perfect, 11:24.269 --> 11:27.149 smooth Hadley cell picture that I was showing you, 11:27.149 --> 11:29.779 but still that's quite a tight band there. 11:29.779 --> 11:31.699 And these are rotating cells. 11:31.700 --> 11:32.830 Jupiter's bigger. 11:32.830 --> 11:36.320 It's got a few more of them than the earth does. 11:36.320 --> 11:40.400 The earth, by the way, sitting on this picture is--oh, 11:40.397 --> 11:42.087 it's about that big. 11:42.090 --> 11:43.380 > 11:43.379 --> 11:44.429 So this is a lot bigger. 11:44.429 --> 11:47.579 11:47.580 --> 11:51.390 Because the earth has the continents and the oceans, 11:51.386 --> 11:55.416 you don't get that smooth picture in a shot from space, 11:55.418 --> 11:57.358 looking at the clouds. 11:57.360 --> 12:01.670 You see a lot of swirls and vortexes that are being caused 12:01.667 --> 12:04.007 by these local perturbations. 12:04.009 --> 12:07.039 Right here you've got the African continent coming down; 12:07.039 --> 12:09.139 you've got Antarctica down here. 12:09.139 --> 12:16.609 This is 40 to 60 south; clear ocean all the way around 12:16.610 --> 12:19.480 the planet; winds blowing in this direction; 12:19.480 --> 12:22.280 they can go all the way around the planet with unobstructed 12:22.277 --> 12:25.267 ocean, just about the whole way, except maybe just from the tip 12:25.267 --> 12:26.277 of South America. 12:26.278 --> 12:30.868 This is where you can get open ocean waves that are up to 100 12:30.870 --> 12:32.630 feet, 30 meters high. 12:32.629 --> 12:34.199 And, of course, this is also where the 12:34.201 --> 12:36.071 Whitbread Round the World race goes down, 12:36.070 --> 12:39.850 so that people can go really fast around the globe and take 12:39.845 --> 12:43.225 their life in their hands in pretty rough weather. 12:43.230 --> 12:47.840 So the earth doesn't really have the idealized model of 12:47.841 --> 12:52.541 climate that I've shown you in the previous pictures. 12:52.538 --> 12:54.918 It's more chaotic, but there's still a pattern 12:54.917 --> 12:57.567 there; and I want to emphasize now 12:57.566 --> 12:59.376 some of the patterns. 12:59.379 --> 13:00.939 So, of course, heat's being moved. 13:00.940 --> 13:04.760 Basically what's going on is that heat's being moved from the 13:04.759 --> 13:06.979 equator, towards the poles, 13:06.975 --> 13:10.085 simply by physical chemical forces, 13:10.090 --> 13:13.250 to try to equalize the heat gradient that's coming in from 13:13.250 --> 13:16.220 the sun, and that's done by wind and by 13:16.219 --> 13:16.769 water. 13:16.769 --> 13:21.729 Now as a packet of air or water moves towards the poles, 13:21.725 --> 13:25.415 it's coming with higher radio velocity. 13:25.418 --> 13:29.508 Just think about the difference in the diameter of the spinning 13:29.509 --> 13:32.149 earth at the equator and at the poles. 13:32.149 --> 13:39.329 At the equator the diameter of the planet is roughly 8000 13:39.332 --> 13:42.592 miles; so the radius is about 4000 13:42.591 --> 13:43.171 miles. 13:43.168 --> 13:47.218 And as you move a packet of air or water up towards the pole, 13:47.221 --> 13:50.801 by the time it gets to the pole, the diameter is 0. 13:50.798 --> 13:51.188 Okay? 13:51.188 --> 13:55.868 So in between--basically it's a trigonometric function that's 13:55.866 --> 14:00.616 telling you what's the diameter of the spinning object as I go 14:00.621 --> 14:01.481 north. 14:01.480 --> 14:04.920 So if I'm coming from the equator, and I'm headed north, 14:04.919 --> 14:08.489 I have more angular momentum than the ground under my feet 14:08.485 --> 14:10.045 that I'm moving onto. 14:10.048 --> 14:13.698 It's moving slower to the east than I am moving. 14:13.700 --> 14:17.490 And if I'm standing at the poles and I start going south, 14:17.490 --> 14:20.950 the ground under my feet is staring to move out from under 14:20.946 --> 14:23.556 me, because I don't have as much 14:23.556 --> 14:24.996 angular momentum. 14:25.000 --> 14:31.030 So what that will do is it will take a packet of air or water 14:31.032 --> 14:35.622 that moves toward the equator, it's coming down with lower 14:35.620 --> 14:39.430 radial velocity, and it will be accelerated to 14:39.428 --> 14:40.448 the west. 14:40.450 --> 14:43.960 That apparent force--and by the way, so going north you'll be 14:43.962 --> 14:46.322 accelerated eastward; coming south you'll be 14:46.323 --> 14:48.633 accelerated westward, in the Northern Hemisphere. 14:48.629 --> 14:50.099 This is an apparent force. 14:50.100 --> 14:50.430 Okay? 14:50.427 --> 14:54.417 It's called the Coriolis force, and it's shaping the direction 14:54.422 --> 14:57.832 of major ocean currents, and it's also shaping things 14:57.827 --> 15:00.617 like the trade winds; and you'll see in a minute that 15:00.620 --> 15:02.030 it shapes the way that hurricanes spin. 15:02.029 --> 15:05.079 15:05.080 --> 15:09.120 So I'd like you to take just--I want to make sure that you get 15:09.115 --> 15:11.695 this, and I'm going to ask, in a minute, 15:11.696 --> 15:13.876 if one of you can explain it. 15:13.879 --> 15:14.149 Okay? 15:14.153 --> 15:17.453 So can you just take a minute and explain it to your partner, 15:17.450 --> 15:20.470 how the Coriolis force works, and what's really going on 15:20.470 --> 15:21.020 here. 15:21.019 --> 15:24.189 It's a piece of three-dimensional geometry, 15:24.190 --> 15:27.670 and basically it's driven by the fact that the earth is 15:27.667 --> 15:31.527 spinning on its axis and things are moving north and south on 15:31.532 --> 15:33.402 the surface of this ball. 15:33.399 --> 15:34.869 Okay? 15:34.870 --> 15:36.120 One or two minutes. 15:36.120 --> 15:49.060 <> 15:49.058 --> 15:52.608 <> 15:52.610 --> 15:54.380 Prof: Do you want to explain it to me? 15:54.379 --> 15:57.619 Student: I need a picture; 15:57.620 --> 16:00.420 I'm not very good with the words here. 16:00.419 --> 16:00.859 Prof: Come on. 16:00.860 --> 16:11.910 16:11.909 --> 16:15.549 So here's a packet moving north. 16:15.549 --> 16:17.559 Student: Okay. 16:17.558 --> 16:21.448 Prof: Let's take a slice through the equator here, 16:21.450 --> 16:25.620 and what you'd see inside here is a circle, 16:25.620 --> 16:31.860 that has a radius of 4000 miles, and if I do a slice up 16:31.855 --> 16:34.915 here, it has a radius of say 2000 16:34.923 --> 16:35.483 miles. 16:35.480 --> 16:36.640 Student: Right. 16:36.639 --> 16:37.769 Prof: Okay? 16:37.769 --> 16:41.169 So in 24 hours, this thing is spinning very 16:41.169 --> 16:44.039 rapidly; it's got 1000 miles an hour 16:44.043 --> 16:46.263 angular velocity, down here. 16:46.259 --> 16:47.079 Right? 16:47.080 --> 16:53.540 Up here it has--let's see, this is 4 times 3 1/2; 16:53.538 --> 16:57.588 instead of 24,000 miles diameter, this is about 12,000 16:57.590 --> 16:58.890 miles diameter. 16:58.889 --> 17:02.909 So it's only got 500 miles angular velocity, 17:02.905 --> 17:03.835 up here. 17:03.840 --> 17:07.210 So this is coming with 1000 miles angular velocity, 17:07.207 --> 17:10.977 up into an area where the ground under its feet is moving 17:10.979 --> 17:12.999 500 miles per hour slower. 17:13.000 --> 17:15.970 So it's going to go like this. 17:15.970 --> 17:16.960 Student: Ah. 17:16.960 --> 17:18.570 Prof: Got it? 17:18.568 --> 17:19.298 Student: Yeah, it helped. 17:19.298 --> 17:20.488 Prof: Does the picture help? 17:20.490 --> 17:22.840 Student: Yes it does. 17:22.838 --> 17:24.098 <> 17:24.098 --> 17:27.018 Prof: Okay, I just learned that the picture 17:27.016 --> 17:27.786 is helpful. 17:27.788 --> 17:32.088 Okay, I'm going to do the picture again for you. 17:32.088 --> 17:35.558 Actually maybe one of you can come up and help me do it. 17:35.559 --> 17:38.179 Anybody want to help me? 17:38.180 --> 17:41.510 Anybody feeling brave this morning, bold, 17:41.508 --> 17:43.088 life threatening? 17:43.088 --> 17:44.288 Get up at the board with the professor. 17:44.289 --> 17:47.299 17:47.299 --> 17:49.919 Okay, here's the planet. 17:49.920 --> 17:53.000 Here's the north/south axis of the planet. 17:53.000 --> 17:56.330 Here's the equator. 17:56.328 --> 18:01.878 The circumference of the earth at the equator is about 24,000 18:01.876 --> 18:04.056 miles, and the earth is turning around 18:04.057 --> 18:06.957 once per day, which means that a packet of 18:06.962 --> 18:09.622 air or water, which is sitting at the 18:09.617 --> 18:13.017 equator, is moving east at about 1000 miles per hour. 18:13.019 --> 18:16.689 18:16.690 --> 18:18.890 We're going to ship it north. 18:18.890 --> 18:19.540 Okay? 18:19.538 --> 18:21.948 It's going to be carrying heat toward the pole. 18:21.950 --> 18:25.320 18:25.318 --> 18:31.128 We choose a convenient spot to take another slice of the earth 18:31.125 --> 18:36.355 where the circumference of the earth is 12,000 miles. 18:36.358 --> 18:42.518 This chunk of ground is moving at 500 miles per hour. 18:42.519 --> 18:46.129 So as this pack of air goes north, the ground underneath it, 18:46.130 --> 18:49.420 by the time it's gotten up here, is going 500 miles per 18:49.422 --> 18:51.382 hour, towards the east, 18:51.383 --> 18:53.033 slower than it is. 18:53.029 --> 18:58.569 So what it does is it overtakes the ground that's underneath it, 18:58.574 --> 19:00.954 and it bends to the east. 19:00.950 --> 19:02.880 Okay? 19:02.880 --> 19:04.630 And you can just play that back and forth in your head. 19:04.630 --> 19:05.910 You can go from the north to the south. 19:05.910 --> 19:07.590 You can do it in the Southern Hemisphere; 19:07.588 --> 19:10.538 it'll work in the other direction. 19:10.539 --> 19:11.329 Any questions on that? 19:11.329 --> 19:15.529 19:15.528 --> 19:17.728 In order to see it, you actually have to break the 19:17.728 --> 19:19.948 motion of the planet down, in your head, 19:19.952 --> 19:24.002 and put yourself in the shoes of something which is moving 19:24.000 --> 19:27.210 north or south, and essentially what happens is 19:27.210 --> 19:30.450 at the ground you either exceed the speed of the ground 19:30.450 --> 19:32.820 underneath you, or the ground goes out from 19:32.818 --> 19:36.878 under your feet, if you're going south. 19:36.880 --> 19:39.990 So that's basically the Coriolis force. 19:39.990 --> 19:41.880 I once had to explain this in German, 19:41.880 --> 19:46.640 and I was just learning German, and instead of saying "the 19:46.644 --> 19:49.304 earth spins", which is okay in English, 19:49.304 --> 19:51.314 I said, "die Erde spinnt" in German, 19:51.308 --> 19:53.238 which means that the world is crazy. 19:53.240 --> 19:55.810 They loved it. 19:55.808 --> 19:58.998 It was totally wrong, but they loved it. 19:59.000 --> 20:04.560 Okay, the result of this is that if these motions-- 20:04.558 --> 20:07.098 you know, so here you've got the Coriolis Force taking the 20:07.096 --> 20:09.186 Kuroshio Current and bending it to the east, 20:09.190 --> 20:11.470 as it goes north, and then when it comes down the 20:11.470 --> 20:13.370 West Coast as the California Current, 20:13.368 --> 20:17.618 it gets bent to the west, and in each of the hemispheres 20:17.623 --> 20:22.343 you establish a rotation in the ocean that looks like this. 20:22.338 --> 20:25.318 Here in the south you have water which is flowing north; 20:25.319 --> 20:27.439 it's getting bent to the west. 20:27.440 --> 20:30.280 You've got water flowing to the south, it's getting bent to the 20:30.278 --> 20:30.598 east. 20:30.598 --> 20:34.958 So you get counter-clockwise in the Southern Hemisphere and 20:34.958 --> 20:37.888 clockwise in the Northern Hemisphere. 20:37.890 --> 20:40.650 Now on top of this, just as I showed you for the 20:40.650 --> 20:43.640 Hadley cells in the atmosphere, there's an important 20:43.644 --> 20:46.644 three-dimensional cell structure in the oceans. 20:46.640 --> 20:50.790 So north of the Antarctic continent there's a place where 20:50.791 --> 20:54.871 the cold surface water of the Antarctic gets- sinks, 20:54.868 --> 20:57.198 at the Antarctic convergence--it's down about 20:57.204 --> 20:59.514 here-- and it then forms a cell which 20:59.506 --> 21:03.376 creeps along the floors of the major oceans and then comes back 21:03.384 --> 21:03.764 up. 21:03.759 --> 21:07.359 21:07.358 --> 21:11.868 There's a very important spot where water from the Arctic 21:11.874 --> 21:16.154 Ocean, coming down from Greenland, is sinking near the 21:16.146 --> 21:17.836 Gulf Stream here. 21:17.838 --> 21:21.228 And it's one of the real current issues in global warming 21:21.230 --> 21:24.320 as to whether or not this point up here or this-- 21:24.318 --> 21:28.588 actually it's not a point--this whole sheet of sinking water is 21:28.587 --> 21:30.307 going to remain stable. 21:30.308 --> 21:32.758 Because if it doesn't remain stable, 21:32.759 --> 21:36.059 and this moves south, then the Gulf Stream will get 21:36.055 --> 21:39.765 blocked and basically England, France and Spain are going to 21:39.773 --> 21:42.923 end up with a climate which is like that of Northern Canada; 21:42.916 --> 21:43.766 very quickly. 21:43.769 --> 21:48.249 That is something that could happen in a couple of years, 21:48.250 --> 21:49.930 if this thing tips. 21:49.930 --> 21:53.690 So understanding that kind of movement actually has big 21:53.685 --> 21:56.235 implications, for society and for the people 21:56.236 --> 21:58.766 who live in these places, who are in the hundreds of 21:58.771 --> 21:59.251 millions. 21:59.250 --> 22:02.510 22:02.509 --> 22:05.139 Now there are just--I want to show you two things about the 22:05.142 --> 22:05.962 general pattern. 22:05.960 --> 22:09.750 This is just repeating the overall pattern on the planet. 22:09.750 --> 22:13.330 We get hurricanes roughly where there are trade winds, 22:13.329 --> 22:17.049 and we get them both in the Northern and in the Southern 22:17.046 --> 22:18.056 Hemisphere. 22:21.291 --> 22:22.371 in the Pacific. 22:22.368 --> 22:24.618 And I want to show you a little bit about hurricanes and a 22:27.888 --> 22:31.458 sort of large-scale weather patterns that occur on the 22:31.464 --> 22:32.144 planet. 22:32.140 --> 22:34.590 So this question here: Why do cyclones turn 22:34.586 --> 22:37.316 counter-clockwise in the Northern Hemisphere and 22:37.324 --> 22:40.384 clockwise in the Southern, is a bit puzzling, 22:40.380 --> 22:44.620 because I have just shown you that if you take a packet of air 22:44.617 --> 22:48.837 or water and you ship it north, it's going to result in a 22:48.837 --> 22:52.917 clockwise circulation in the north and a counter-clockwise 22:52.915 --> 22:54.915 circulation in the south. 22:54.920 --> 22:57.900 And yet here is a nice photo from space of Hurricane Katrina 22:57.900 --> 23:00.830 starting to go over Florida, before it hits New Orleans; 23:00.828 --> 23:03.798 Cyclone Larry, equally destructive, 23:03.798 --> 23:06.768 plowing into Northern Australia. 23:06.769 --> 23:09.949 And you can see quite clearly that Hurricane Katrina is 23:09.952 --> 23:12.962 counter-clockwise and Cyclone Larry is clockwise. 23:12.960 --> 23:16.620 And that looks puzzling, but here's the answer. 23:16.618 --> 23:19.888 If you take a standard packet of air, 23:19.890 --> 23:21.840 moving south in the Northern Hemisphere, 23:21.838 --> 23:24.438 hitting something like Hurricane Katrina, 23:24.440 --> 23:27.350 it will come down and it will take this low, 23:27.349 --> 23:30.179 and it will spin it. 23:30.180 --> 23:35.040 And if you have this as a set of clockwise forces, 23:35.042 --> 23:38.622 operating on a low, they will spin it 23:38.615 --> 23:40.795 counter-clockwise. 23:40.798 --> 23:44.378 And the same thing operating in the Southern Hemisphere will 23:44.382 --> 23:47.842 spin a cyclone in the Southern Hemisphere into a clockwise 23:47.842 --> 23:48.452 shape. 23:48.450 --> 23:53.220 So really it's an interesting problem of figure and ground, 23:53.220 --> 23:55.340 or just what perspective are you standing in, 23:55.338 --> 23:57.868 when you're trying to figure out why the thing is spinning 23:57.871 --> 23:58.361 that way. 23:58.358 --> 24:04.178 Because basically it is being operated on by external Coriolis 24:04.178 --> 24:09.518 forces that are generating the antagonistic movement, 24:09.519 --> 24:12.479 the unexpected movement in the structure, 24:12.480 --> 24:16.120 but it results in very important consequences for 24:16.123 --> 24:20.073 anybody that's in the path of one of these things. 24:20.068 --> 24:24.128 So that's basically the explanation of why we see a 24:24.133 --> 24:28.443 counter-intuitive kind of spin on these big storms. 24:33.432 --> 24:34.412 neat phenomenon. 24:34.410 --> 24:37.940 It has huge implications, and it drives weather patterns 24:37.943 --> 24:43.473 in fact over much of the planet; not just at the equator. 24:43.470 --> 24:48.420 Under normal conditions basically what's going on is 24:48.417 --> 24:52.327 that you have these, the Kuroshio Current in the 24:52.327 --> 24:54.777 northern Pacific, which is coming down off of 24:54.775 --> 24:58.255 California and Mexico, and then going west along the 24:58.258 --> 24:58.988 equator. 24:58.990 --> 25:01.290 You've got the Humboldt Current in the southern Pacific, 25:01.288 --> 25:03.878 which is coming north, along the coast of Chile and 25:03.884 --> 25:05.964 Peru, and then curving out to the 25:05.957 --> 25:09.267 west, driven in those big clockwise Northern Hemisphere 25:09.270 --> 25:12.770 gyres and counter-clockwise Southern Hemisphere gyres. 25:12.769 --> 25:18.079 And what they're doing--because they have a continent more or 25:18.078 --> 25:22.028 less to the right here-- they are picking up the water 25:22.029 --> 25:25.469 and shoving it offshore, and that's causing the lower 25:25.470 --> 25:29.370 bottom water to well up, and they are shoving the warm 25:29.373 --> 25:31.603 surface water out to the west. 25:31.598 --> 25:35.658 And that causes a big buildup of warm water, 25:35.662 --> 25:39.632 which is out about at Guam in the Marianas, 25:39.631 --> 25:43.601 so--or all the way to the Philippines. 25:43.598 --> 25:47.868 And this pile of warm water is actually about a meter higher 25:47.871 --> 25:50.841 than the water in the eastern Pacific, 25:50.838 --> 25:53.968 and it's being held there by the currents and the winds. 25:53.970 --> 25:56.810 So it's actually, over a distance of about 7 or 25:56.806 --> 25:59.436 8000 miles, it's picking the surface of the 25:59.441 --> 26:02.301 ocean up and it's stacking it up a meter higher, 26:02.299 --> 26:04.629 out to the west, in the Pacific. 26:07.618 --> 26:10.408 what happens is that the currents break down, 26:10.410 --> 26:13.450 and when the currents break down, the force that was holding 26:13.454 --> 26:16.144 the water higher in the western Pacific goes away. 26:16.140 --> 26:17.670 And what does the water do? 26:17.670 --> 26:22.180 It falls downhill, it flows back to the eastern 26:22.182 --> 26:27.972 Pacific, covering the eastern Pacific up with a layer of hot 26:27.969 --> 26:28.949 water. 26:28.950 --> 26:31.360 This has all kinds of consequences. 26:31.358 --> 26:36.828 One of the consequences is that warm water evaporates more than 26:36.833 --> 26:40.273 cold water, and so rainfall increases, 26:40.267 --> 26:44.937 in the eastern Pacific, and cells that carry a lot of 26:44.935 --> 26:50.485 water will then get blown into places like Mexico and Arizona. 26:53.571 --> 26:56.051 heavier rainfall in the American West, 26:56.048 --> 26:58.758 and all the way through to the Mississippi Valley, 26:58.759 --> 27:01.959 than you will during normal conditions. 27:01.960 --> 27:04.910 But another very important thing happens. 27:04.910 --> 27:07.560 This covers up the upwelling. 27:07.558 --> 27:09.658 It covers up the cold water that was coming up from the 27:09.655 --> 27:12.195 bottom of the ocean, and that cold water that was 27:12.201 --> 27:15.801 coming up from the bottom of the ocean is carrying with it all 27:15.801 --> 27:17.161 kinds of fertilizer. 27:17.160 --> 27:20.230 Basically the bottom of the ocean has been receiving the 27:20.227 --> 27:23.287 dead bodies of algae and zooplankton and everything else 27:23.294 --> 27:24.414 for a long time. 27:24.410 --> 27:27.600 There's been a lot of nitrogen and phosphate building up down 27:27.596 --> 27:30.456 there, and under normal conditions that's being carried 27:30.464 --> 27:31.744 up by the upwelling. 27:34.832 --> 27:37.232 turns off the fertilization process. 27:37.230 --> 27:40.640 The alga production goes down, zooplankton production goes 27:40.636 --> 27:43.916 down, the fish don't have so much to eat and the fishery 27:43.923 --> 27:45.123 stocks collapse. 27:45.118 --> 27:48.118 So once every ten or eleven years, 27:48.118 --> 27:52.518 when this happens, the great fisheries of the 27:52.519 --> 27:56.859 Eastern Pacific collapse, and that means that thousands 27:56.858 --> 28:01.398 of fishermen go out of work; it means that sea birds starve. 28:01.400 --> 28:05.640 And you should think of the whole Pacific Ocean as kind of 28:05.641 --> 28:10.181 ringing like a bell on about a ten or eleven year interval. 28:10.180 --> 28:13.380 And since the Pacific Ocean occupies roughly half the 28:13.383 --> 28:15.713 planet, that means there are signatures 28:15.711 --> 28:18.861 of this that reverberate all the way around the planet, 28:18.859 --> 28:22.139 on about a ten year interval. 28:22.140 --> 28:23.640 When I was doing my Ph.D. 28:23.635 --> 28:26.385 on the evolution of mosquito fish in Hawaii, 28:26.390 --> 28:30.650 I had sixty years of records of the level of sugar plantation 28:30.653 --> 28:33.863 reservoirs in Hawaii, and I did a time series 28:33.862 --> 28:37.652 analysis on it and I picked up two very dominant signals. 28:37.650 --> 28:40.020 There was a short frequency signal, which was the 28:40.021 --> 28:42.841 weekends--that's when people went home on the weekends; 28:42.838 --> 28:45.778 so the reservoirs didn't fluctuate on the weekends. 28:48.874 --> 28:51.764 and it was the biggest, strongest signal in the data. 28:51.759 --> 28:53.689 So up in Hawaii, which is really quite a ways 28:53.689 --> 28:54.579 away-- on this map, 28:54.580 --> 28:58.190 Hawaii would be up off the map, up here somewhere--this is 28:58.192 --> 29:02.602 making a big impact on the ten-year rainfall record, 29:02.598 --> 29:06.458 and it's doing so in Arizona and New Mexico and Texas, 29:06.460 --> 29:09.390 and California as well. 29:11.210 --> 29:12.870 And to see what it looks like. 29:12.868 --> 29:17.368 This is a NOA picture of the temperature of the Pacific, 29:17.365 --> 29:22.265 going from the eastern Pacific out to the western Pacific. 29:22.269 --> 29:23.519 And these are different years. 29:23.519 --> 29:27.469 So this is starting in 1986 and going up to 2001, 29:27.470 --> 29:30.320 and this year, right here, where you see a big 29:33.535 --> 29:38.615 pushing all the way back in to the eastern Pacific is 1997; 29:41.130 --> 29:42.610 And, in fact, there is right now, 29:45.509 --> 29:46.469 Yes, Myra? 29:46.470 --> 29:50.710 Student: > 29:50.710 --> 29:54.480 Prof: There appears to have been this kind of cyclicity 29:54.482 --> 29:58.382 in the Pacific for as long back as we can see in the records. 29:58.380 --> 30:01.580 I think that the things that would probably make it break 30:01.582 --> 30:03.472 down are plate tectonic events. 30:06.632 --> 30:09.072 of Panama formed about ten million years ago. 30:09.068 --> 30:09.868 I suspect it would've been different. 30:09.869 --> 30:14.429 30:14.430 --> 30:17.590 And this is just that--this is the actual temperature, 30:17.588 --> 30:20.508 and then this is the deviation from the normal. 30:20.509 --> 30:23.209 And, by the way, they call a year that's sort of 30:28.073 --> 30:28.673 down here. 30:33.509 --> 30:45.939 water in the eastern Pacific, with all of its consequences. 30:49.390 --> 30:52.990 and of course that would be happening basically right along 30:52.993 --> 30:53.433 here. 30:53.430 --> 30:56.940 But upwelling is normal in much of the planet, 30:56.943 --> 30:59.993 and it happens along coastal margins. 30:59.990 --> 31:04.530 So the areas here that are indicated in red is where cold, 31:04.528 --> 31:08.448 deep water is being moved to the surface by various forces, 31:08.450 --> 31:11.480 and in the process is fertilizing the surface layer, 31:11.480 --> 31:14.160 and that's driving the productivity of the world's 31:14.157 --> 31:14.647 oceans. 31:14.650 --> 31:18.680 So people, of course, have discovered this; 31:18.680 --> 31:21.470 I mean, one could have made a theoretical argument, 31:21.474 --> 31:24.444 but in fact the world's fishermen discovered this long 31:24.436 --> 31:26.726 before there was any climatic theory. 31:26.730 --> 31:30.490 And the greatest productivity in the world's oceans are in 31:30.490 --> 31:33.590 places like the North Sea, the Benguela Current, 31:33.592 --> 31:37.702 and the West Coast of Africa; the coast of Peru with its 31:37.700 --> 31:41.310 gigantic anchovy fishery; West Coast of North America 31:41.306 --> 31:44.096 with tuna and sardines and things like that; 31:44.098 --> 31:48.238 and you can see a few other spots around the world that are 31:48.236 --> 31:49.516 very productive. 31:49.519 --> 31:50.719 Fishing is mighty good in New Zealand. 31:50.720 --> 31:54.070 31:54.068 --> 31:57.558 The way this works is through a combination of offshore winds 31:57.557 --> 31:59.007 and the Coriolis force. 31:59.009 --> 32:01.479 So let's first do the offshore wind. 32:01.480 --> 32:05.790 If you have any body of land, and you have wind blowing 32:05.790 --> 32:08.780 offshore, it pushes the surface water 32:08.782 --> 32:13.152 off, and just in order for gravity to equilibrate the water 32:13.151 --> 32:16.791 pressure, it's going to therefore pull up 32:16.787 --> 32:19.357 deep water at the shore line. 32:19.358 --> 32:24.388 And if any of you live on the West Coast, 32:24.390 --> 32:26.650 I think you know this perfectly well, 32:26.650 --> 32:31.520 because you know that very often the water on the shoreline 32:31.517 --> 32:35.207 of the West Coast is colder than the air, 32:35.210 --> 32:37.980 and it is going to produce fog. 32:37.980 --> 32:41.600 And all the way from roughly Santa Barbara up to Juneau, 32:41.598 --> 32:44.818 you have fog banks, which is because you have cold 32:44.823 --> 32:48.383 water hitting warm air; it's that cold upwelling water 32:48.378 --> 32:50.868 hitting the warm air that makes the fog, 32:50.868 --> 32:55.028 which is so characteristic of the West Coast of the United 32:55.029 --> 32:56.949 States, and is also characteristic, 32:56.953 --> 33:00.943 by the way, of the West Coast of Namibia. 33:00.940 --> 33:03.900 There are even some beetles that live in the desert of 33:03.901 --> 33:07.591 Namibia that are specialized for catching the fog on their feet. 33:07.588 --> 33:10.968 They stand on their heads and they put their feet up and they 33:10.974 --> 33:14.024 catch water with their feet, because it doesn't rain in 33:14.021 --> 33:14.701 Namibia. 33:14.700 --> 33:19.270 Now if we were to look at say the coast of Oregon, 33:19.273 --> 33:24.133 and we have wind or current which is coming south; 33:24.130 --> 33:27.440 we're in the Northern Hemisphere, we're going south. 33:27.440 --> 33:30.900 The Coriolis force is working, and because we're coming south 33:30.898 --> 33:33.708 we're going to be-- we have less angular momentum 33:33.707 --> 33:36.957 than the earth under our feet, and therefore it's going to be 33:36.959 --> 33:38.249 diverted out to the west. 33:38.250 --> 33:41.590 That means that there's going to be a tendency for the 33:41.588 --> 33:44.108 Coriolis force to suck water offshore. 33:44.108 --> 33:46.868 And the wind or the current could be coming south, 33:46.868 --> 33:51.088 but the net vector of movement of surface water will be 33:51.093 --> 33:55.013 deflected off to the right, by the Coriolis force, 33:55.009 --> 33:58.159 and pulled offshore, and so you're going to get cold 33:58.163 --> 34:01.463 bottom water, welling up to the surface and 34:01.462 --> 34:03.212 fertilizing things. 34:03.210 --> 34:08.240 Okay, that's a little bit about how the climate machine is 34:08.239 --> 34:10.269 working in the ocean. 34:10.268 --> 34:14.318 Now let's take a minute to look at what it's doing to the biomes 34:14.320 --> 34:18.110 on the surface of the planet, on the terrestrial part of the 34:18.112 --> 34:18.822 planet. 34:18.820 --> 34:23.280 Ecologists have broken the planet down into areas that 34:23.284 --> 34:28.344 basically look similar from the structure of their ecological 34:28.338 --> 34:31.538 communities, and are thought to be similar 34:31.539 --> 34:35.019 in terms of the general control of ecological processes. 34:35.018 --> 34:37.528 So you've got ice sheets, of course. 34:37.530 --> 34:39.650 Then you've got tundra. 34:39.650 --> 34:43.470 In tundra you normally don't see plants that are taller than, 34:43.469 --> 34:45.189 oh, 10 or 20 centimeters. 34:45.190 --> 34:49.530 You have things like dwarf birch, lots of moss, 34:49.527 --> 34:51.317 things like that. 34:51.320 --> 34:55.050 Often tundra is overlying permafrost. 34:55.050 --> 34:59.550 Then you've got the taiga or the northern coniferous forests, 34:59.552 --> 35:03.532 which stretch across much of the high latitudes in the 35:03.528 --> 35:05.328 Northern Hemisphere. 35:05.329 --> 35:08.729 You can't really get to these places in the Southern 35:08.731 --> 35:09.601 Hemisphere. 35:09.599 --> 35:10.249 Okay? 35:10.250 --> 35:13.570 Antarctica is too cold, and Africa and Australia don't 35:13.572 --> 35:15.392 really go far enough south. 35:15.389 --> 35:18.589 There's a little bit of replication of this in South 35:18.592 --> 35:22.112 America, but it's mostly a question there of altitude. 35:22.110 --> 35:27.670 Then you get some forests that are extremely similar in Eastern 35:27.673 --> 35:30.773 North America, across Western Europe and into 35:30.773 --> 35:33.933 Central Asia, and in China and Manchuria, 35:33.929 --> 35:37.179 which is temperate broadleaf forest. 35:37.179 --> 35:41.019 You get similarities in the rainforests of the Amazon and 35:41.023 --> 35:45.073 the Congo, and in Southeast Asia, and in Northern Australia, 35:45.072 --> 35:46.242 and so forth. 35:46.239 --> 35:50.029 There are, in other words, these large biomes around the 35:50.032 --> 35:53.002 planet that are mainly shaped by climate. 35:53.000 --> 35:57.200 And I'm just going to touch quickly on two of them. 35:57.199 --> 35:59.799 One of them is the desert biome. 35:59.800 --> 36:05.470 And one tends to find deserts at about 30 North and about 30 36:05.471 --> 36:06.241 South. 36:06.239 --> 36:10.259 So, of course, the Sahara and the Arabian 36:10.257 --> 36:12.767 Desert are at 30 North. 36:12.768 --> 36:18.438 The deserts of Mexico and Arizona are at about 30 North. 36:18.440 --> 36:22.080 The Chilean and Peruvian deserts, the Atacama Desert, 36:22.079 --> 36:23.759 are at about 30 South. 36:23.760 --> 36:27.870 The Kalahari and the Namib are at about 30 South, 36:27.869 --> 36:33.179 and the Great Central Desert of Australia is about 30 South. 36:33.179 --> 36:36.929 And remember, this is where you have cold air 36:36.927 --> 36:37.777 falling. 36:37.780 --> 36:39.720 At the equator you have warm air rising, 36:39.719 --> 36:42.779 and where you have the deserts you have cold air falling, 36:42.780 --> 36:45.170 and there's very little water in that cold, 36:45.170 --> 36:47.230 dry air that's falling. 36:47.230 --> 36:49.940 It's quite hot during the day and it's cold at night. 36:49.940 --> 36:54.370 So, for example, if you're in the hot desert of 36:54.367 --> 36:57.687 Central Australia, and it's nightfall, 36:57.693 --> 37:00.993 on a nice clear night the temperature will go, 37:00.989 --> 37:04.419 say in Fahrenheit, from 80 or 90 degrees, 37:04.420 --> 37:09.280 down to freezing, in about two or three hours. 37:09.280 --> 37:12.200 And so Aborigines learn to do things like all sleep together 37:12.197 --> 37:13.037 in a big bunch. 37:13.039 --> 37:16.999 37:17.000 --> 37:20.480 The wet tropical forests are about at the equator, 37:20.476 --> 37:25.056 where you have warm air rising; warm, moisture-laden air is 37:25.063 --> 37:25.733 rising. 37:25.730 --> 37:27.250 There are some interesting twists on that. 37:27.250 --> 37:29.560 For example, if you take a packet of air off 37:29.559 --> 37:32.459 the south Atlantic and you blow it into the Amazon, 37:32.460 --> 37:37.300 the Amazon actually will transpire the moisture in that 37:37.302 --> 37:39.432 air; the trees in the Amazon will 37:39.434 --> 37:42.904 transpire it, so that by the time a packet of 37:42.900 --> 37:44.840 rain, that started here in the south 37:44.842 --> 37:46.392 Atlantic, hits the Andes, 37:46.389 --> 37:48.769 it's been rained out three times. 37:48.768 --> 37:50.788 It's gone back up into the atmosphere, made a cloud; 37:50.789 --> 37:52.759 gone down into the ground; gone up into the atmosphere; 37:52.760 --> 37:53.860 rained out, made a cloud. 37:53.860 --> 37:55.640 And it's done that about, on the average, 37:55.639 --> 37:57.599 three times by the time it hits the Andes. 37:57.599 --> 38:01.049 So there's some interesting local stuff going on. 38:01.050 --> 38:04.930 But roughly speaking, you find the world's greatest 38:04.932 --> 38:09.052 biodiversity near the equator in these rainforests. 38:09.050 --> 38:11.880 And so if we just take a look at one of them, 38:11.876 --> 38:14.506 the Corcovado Rainforest in Costa Rica; 38:14.510 --> 38:18.480 and all of you are eligible to go on an OTS course to Costa 38:18.478 --> 38:22.718 Rica, and as part of it you'll probably go to the Corcovado. 38:22.719 --> 38:26.759 Or, if you were lucky enough to be in Rick Prum's class this 38:26.757 --> 38:29.107 semester, you got taken by Rick, 38:29.108 --> 38:33.128 over spring break, to Ecuador, where they logged 38:33.132 --> 38:36.222 450 species of birds in ten days. 38:36.219 --> 38:40.659 And in that kind of habitat you are going to run into extremely 38:40.657 --> 38:44.727 high species diversity, and you're going to see all 38:44.731 --> 38:49.571 kinds of stuff that you just never run into in the temperate 38:49.565 --> 38:50.625 latitudes. 38:50.630 --> 38:54.780 So I strongly recommend a visit to one of these places, 38:54.779 --> 38:56.469 if you possibly can. 38:56.469 --> 38:58.979 For a biologist it's pretty much--this, 38:58.980 --> 39:04.170 and say going over a coral reef, especially at night, 39:04.170 --> 39:06.500 it's kind of like Christmas, because every time you turn 39:06.498 --> 39:08.868 around the corner there's another surprise under the tree 39:08.869 --> 39:09.969 > 39:09.969 --> 39:13.159 and there's something beautiful and strange that you've never 39:13.155 --> 39:13.895 seen before. 39:13.900 --> 39:20.580 So this is the biological consequence of a long period of 39:20.576 --> 39:24.176 fairly stable warm, moist conditions, 39:24.175 --> 39:27.215 which are the ecological theater that has allowed this 39:27.219 --> 39:29.689 kind of evolutionary play to take place. 39:29.690 --> 39:32.600 39:32.599 --> 39:36.879 If we look back in time, there are a couple of things 39:36.878 --> 39:40.578 about say the last-- this is roughly the last 39:40.583 --> 39:44.353 fifty-million years, from the Eocene up to the 39:44.347 --> 39:47.307 Holocene-- there are a couple of fairly 39:47.311 --> 39:51.751 neat things that have happened in terms of the global pattern 39:51.753 --> 39:52.793 of climate. 39:52.789 --> 39:55.709 One of them is that if you go back to Eocene, 39:55.710 --> 39:59.550 when it was really quite warm, and you had temperate forests 39:59.547 --> 40:02.277 that went right up to the Arctic Ocean, 40:02.280 --> 40:05.320 you can demonstrate that there were large trees growing in 40:05.324 --> 40:09.064 Northern Greenland, at a latitude where it was dark 40:09.056 --> 40:14.476 for nearly six months a year; it was warm but it was dark. 40:14.480 --> 40:17.450 And that really is a rather interesting comment on what 40:17.445 --> 40:20.575 trees are capable of; that you could make a tree that 40:20.583 --> 40:24.063 would live in complete darkness, not doing anything for six 40:24.059 --> 40:27.389 months, and then turn back on and become actually quite a tall 40:27.393 --> 40:29.503 forest; these trees are a meter, 40:29.501 --> 40:32.561 two meters in diameter, in Northern Greenland. 40:32.559 --> 40:35.759 So that's one kind of thing that the historical look at 40:35.757 --> 40:37.177 ecology will give you. 40:37.179 --> 40:38.779 But there's another one, which is really, 40:38.780 --> 40:42.560 I think, important for everyone on the planet now, 40:42.559 --> 40:46.169 and that is that the Eocene, Oligocene and Miocene were all 40:46.168 --> 40:48.808 pretty warm; in fact, they were much warmer 40:48.813 --> 40:50.533 than the earth currently is. 40:50.530 --> 40:54.140 And when you look say at the distribution of tropical 40:54.135 --> 40:57.115 forests-- which is in green--you can see 40:57.117 --> 41:01.337 that tropical forests covered really most of the earth for 41:01.335 --> 41:04.955 tens of millions of years; and compare that to their 41:04.961 --> 41:06.031 distribution now. 41:06.030 --> 41:09.470 We're essentially in an interglacial in the Pleistocene 41:09.465 --> 41:10.225 right now. 41:10.230 --> 41:13.410 The planet is really much colder than it has been, 41:13.407 --> 41:14.247 on average. 41:14.250 --> 41:17.520 And you can see those sorts of trends written in the 41:17.523 --> 41:20.543 distribution of the biomes across the planet. 41:20.539 --> 41:26.399 And it would be terribly neat to have a slow motion videotape, 41:26.400 --> 41:30.910 taken from a distant satellite, over the last 65 million years, 41:30.909 --> 41:33.209 to see this kind of thing going on. 41:33.210 --> 41:36.360 One would have to be, of course, a bit patient. 41:36.360 --> 41:39.930 So here are the things I want you to remember about climate; 41:39.929 --> 41:44.609 organisms and the climate machine of the planet. 41:44.610 --> 41:46.850 If all you know is the seasonal pattern of temperatures, 41:46.849 --> 41:48.599 daylight and water availability, 41:48.603 --> 41:51.723 you can predict a lot about what you're going to find in 41:51.715 --> 41:54.765 terms of biomass, in terms of biome; 41:54.769 --> 41:56.639 all that kind of stuff. 41:56.639 --> 42:01.409 I would like you to remember, out of this lecture and out of 42:01.405 --> 42:04.795 your reading, how mountains create rain and 42:04.797 --> 42:08.187 rain shadows and hot down-slope winds. 42:08.190 --> 42:11.790 I'd like you to remember the pattern of winds and currents, 42:11.786 --> 42:13.766 from the equator to the poles. 42:13.768 --> 42:18.378 I'd like you to remember how the so-called Coriolis force 42:20.393 --> 42:23.703 this wonderful thing of piling up a meter high mountain of hot 42:23.697 --> 42:25.697 water, in the Western Pacific, 42:25.697 --> 42:27.977 and then letting it fall back down; 42:27.980 --> 42:30.480 how ocean currents drive upwelling; 42:30.480 --> 42:34.060 and why cold, nutrient-rich water will well 42:34.063 --> 42:37.993 up at the edge of a continent, or an island; 42:37.989 --> 42:42.659 and how the climate structures the biomes on the planet. 42:42.659 --> 42:43.999 Okay. 42:44.000 --> 42:49.000