WEBVTT 00:01.233 --> 00:04.333 RONALD SMITH: The first question was one of the 00:04.333 --> 00:09.003 most difficult ones on the exam, I believe. 00:09.000 --> 00:18.130 And the point is that you were given, first the Gulf Stream 00:18.133 --> 00:22.703 coming up along the east coast of the United States. 00:22.700 --> 00:29.500 At a particular latitude, 35 degrees North, you are given 00:29.500 --> 00:36.700 information that this is 50 kilometers wide, has a depth 00:36.700 --> 00:46.530 of 1 kilometer, and the pressure difference across it 00:46.533 --> 00:55.803 Delta P, is given by 4000 Pascals. 00:55.800 --> 00:59.230 And you are asked to compute how much water is flowing, the 00:59.233 --> 01:03.733 volumetric flow rate, in the in the Gulf Stream. 01:03.733 --> 01:07.503 So the way I did it was first to use the formula for 01:07.500 --> 01:14.800 geostrophic speed, which is the pressure difference 01:14.800 --> 01:19.600 divided by the length over which the pressure changes. 01:19.600 --> 01:24.170 That's the so called pressure gradient. 01:24.167 --> 01:29.667 And then down below goes 2, the density of water, times 01:29.667 --> 01:32.827 the rotation rate of the earth, times 01:32.833 --> 01:34.303 the sine of the latitude. 01:34.300 --> 01:38.670 That formula is given to you at the top of the second page. 01:38.667 --> 01:44.327 You just need to cancel out the volume and solve for U, 01:44.333 --> 01:48.473 and you'll get that formula for geostrophic flow. 01:48.467 --> 01:56.027 So then what goes into this is a Delta P of 4000 Pascals, a 01:56.033 --> 02:05.973 length of 50 kilometers, 50,000 meters, 2 the density 02:05.967 --> 02:08.597 of seawater is about a 1025. 02:08.600 --> 02:14.670 The rotation rate of the earth is 7.27 x 10 to the minus 5. 02:14.667 --> 02:18.997 And the sine of the latitude, it's going to be the sine of 02:19.000 --> 02:23.000 35 degrees. 02:23.000 --> 02:28.470 When you put in all those numbers, I got 0.9 meters per 02:28.467 --> 02:34.397 second for the speed of flow in the Gulf Stream. 02:36.967 --> 02:43.297 To get the volumetric flow rate, that's going to be the 02:43.300 --> 02:47.670 rate of the product of the area and the flow speed. 02:47.667 --> 02:51.127 The area is given by the product of the 02:51.133 --> 02:53.603 depth and the width. 02:53.600 --> 03:01.900 So it's going to be 50,000 meters times 1000 meters. 03:01.900 --> 03:11.170 So that's going to be 5 times 10 to, what the seventh? 03:11.167 --> 03:15.927 So when you put this value into there and this value into 03:15.933 --> 03:21.903 there, I got about 47 x 10 to the sixth 03:21.900 --> 03:24.430 cubic meters per second. 03:24.433 --> 03:28.703 That's the volume, how many cubic meters of water per 03:28.700 --> 03:32.770 second are passing through some line you draw across the 03:32.767 --> 03:33.327 Gulf Stream. 03:33.333 --> 03:43.603 I asked you to express that I asked you to 03:43.600 --> 03:45.300 express that in sverdrups. 03:45.300 --> 03:49.200 A sverdrup is 1,000,000 cubic meters per second. 03:49.200 --> 03:54.500 So this is 47 sverdrups. 03:54.500 --> 03:56.470 Any questions on that? 03:56.467 --> 03:57.427 Yes. 03:57.433 --> 03:58.833 Student: What is the--why is that the same as the lenght? 03:58.833 --> 04:04.633 PROFESSOR: This is the, well sorry. 04:04.633 --> 04:05.773 So this is a pressure gradient. 04:05.767 --> 04:08.597 So it's how pressure changes with distance. 04:08.600 --> 04:11.500 So I may have messed up my symbols here, but that would 04:11.500 --> 04:12.670 be that distance. 04:12.667 --> 04:13.997 I gave you the pressure difference 04:14.000 --> 04:16.430 across the Gulf Stream. 04:16.433 --> 04:19.333 I gave you the width of the Gulf Stream. 04:19.333 --> 04:22.773 And so the pressure difference divided by that length over 04:22.767 --> 04:26.527 which the pressure changes is the pressure gradient. 04:26.533 --> 04:29.533 That is units of Pascals per meter. 04:29.533 --> 04:34.773 How much does this pressure change per meter as you walk 04:34.767 --> 04:37.897 across or swim across the Gulf Stream? 04:41.300 --> 04:43.330 Questions on that then? 04:43.333 --> 04:46.733 Student: So is the pressure gradient force not pushing the 04:46.733 --> 04:50.373 air in the direction it's moving, it's actually pushing 04:50.367 --> 04:51.097 it across-- 04:51.100 --> 04:52.200 PROFESSOR: That's right. 04:52.200 --> 04:57.630 So presumably there'd be a high pressure over here, low 04:57.633 --> 04:58.673 pressure over there. 04:58.667 --> 05:02.397 So if you were to do a little force balance on a piece of 05:02.400 --> 05:06.800 water in the Gulf Stream, the pressure gradient force would 05:06.800 --> 05:11.400 be off in that direction from high to low. 05:11.400 --> 05:13.170 Because there's higher pressure on that side of the 05:13.167 --> 05:15.267 parcel that on that side. 05:15.267 --> 05:19.627 And that would have to be balanced by a Coriolis force 05:19.633 --> 05:21.003 equal and opposite to that. 05:21.000 --> 05:24.370 And then in order to get that Coriolis force, the fluid 05:24.367 --> 05:27.567 would have to be moving in that direction, that's you, so 05:27.567 --> 05:30.597 we have that right angle relationship between the 05:30.600 --> 05:35.500 velocity of the material and the Coriolis force. 05:38.667 --> 05:43.527 So I didn't ask you about the direction, but it would be off 05:43.533 --> 05:45.703 to the Northeast, the way I've drawn 05:45.700 --> 05:49.900 everything in this diagram. 05:49.900 --> 05:52.500 Other questions on that? 05:52.500 --> 05:54.400 OK, question two. 05:54.400 --> 05:58.270 Now for that you needed this diagram on the next page. 05:58.267 --> 06:02.467 And what I recommended Are you all set? 06:02.467 --> 06:04.927 I'm going to withdraw it because I'm not ready to use 06:04.933 --> 06:05.503 the board yet. 06:05.500 --> 06:06.470 But that's terrific. 06:06.467 --> 06:07.127 Thanks so much. 06:07.133 --> 06:07.433 I appreciate that. 06:07.433 --> 06:08.803 AV Guy fixing projector: I would just blank it at the 06:08.800 --> 06:09.630 moment if it's 06:09.633 --> 06:10.603 PROFESSOR: That's fine. 06:10.600 --> 06:12.370 How do I blank it? 06:12.367 --> 06:12.767 Blank it. 06:12.767 --> 06:13.527 Yes. 06:13.533 --> 06:15.703 Yes, terrific. 06:22.733 --> 06:27.033 So you were given the temperature and salinity for 06:27.033 --> 06:34.503 two water masses and you could plot them on this S-T diagram. 06:34.500 --> 06:37.930 And A plots up here somewhere and B 06:37.933 --> 06:39.633 plots down there somewhere. 06:39.633 --> 06:42.673 And from the lines of constant density, which I'm not going 06:42.667 --> 06:43.697 to be able to draw very accurately, you can find that 06:43.700 --> 06:48.570 B is more--so I've got the numbers there. 06:48.567 --> 06:56.697 So the density for B was 1027.5 and the density for A 06:56.700 --> 07:05.900 was 1026.5 units kilograms per cubic meters. 07:05.900 --> 07:09.230 Now I mentioned in class that quite a number of you have 07:09.233 --> 07:13.433 forgotten that you need to put a 10 in front of the numbers 07:13.433 --> 07:13.903 that are given here. 07:13.900 --> 07:20.600 For example these things are written something like 27.5. 07:20.600 --> 07:27.230 You need to make that into 1027.5 in order to have proper 07:27.233 --> 07:30.803 units of kilograms per cubic meter. 07:30.800 --> 07:33.730 To remember that, you could look back at the properties of 07:33.733 --> 07:40.203 water on the front page, where I give a typical density for 07:40.200 --> 07:45.900 seawater as 1025 kilograms per cubic meter. 07:45.900 --> 07:50.230 A number like 27.5 would be ridiculous for water. 07:50.233 --> 07:57.133 That would be a factor of 100 too light. 07:57.133 --> 08:01.703 The other thing is then A turns out to be less than B. 08:01.700 --> 08:05.300 And therefore because density must increase going down, 08:05.300 --> 08:07.970 water mass A must be the higher one 08:07.967 --> 08:09.697 in the water column. 08:09.700 --> 08:12.030 And that was the second part to that question. 08:15.233 --> 08:18.903 Question three, I used the formula, change in salinity is 08:18.900 --> 08:22.770 given by the initial salinity minus d over capital 08:22.767 --> 08:24.667 D plus little d. 08:24.667 --> 08:28.227 And the problem said the heavy rain adds a half meter. 08:28.233 --> 08:33.833 So d is plus 0.5 meters. 08:33.833 --> 08:44.633 And that fresh water is mixed down to a depth of 50 meters. 08:44.633 --> 08:48.973 So the effect of that added fresh water is felt all the 08:48.967 --> 08:50.367 way down to 50 meters. 08:50.367 --> 08:55.667 That means I put in 35 parts per thousand for S0 and then 08:55.667 --> 09:04.197 it's minus 0.5 over 50 plus 0.5 and that comes out to be 09:04.200 --> 09:11.300 minus 0.346 parts per thousand. 09:11.300 --> 09:17.330 And because the original salinity 35, the new salinity 09:17.333 --> 09:21.773 is then 34.65 parts per thousand. 09:21.767 --> 09:24.767 I just subtracted that from the 35 09:24.767 --> 09:29.327 to get the new salinity. 09:29.333 --> 09:31.733 Questions on that? 09:31.733 --> 09:36.103 Question four was about El Nino and in the eastern 09:36.100 --> 09:41.530 tropical Pacific, so in the east there, the SST would be 09:41.533 --> 09:45.133 higher than usual, the air pressure would be lower than 09:45.133 --> 09:49.433 usual, precipitation higher than usual, biological 09:49.433 --> 09:52.773 productivity lower than usual. 09:52.767 --> 09:55.097 And explaining the relationship between A and D, 09:55.100 --> 09:57.000 that would be like this. 09:57.000 --> 10:02.500 So if you have warm water near the surface and cold water 10:02.500 --> 10:08.230 beneath, it's going to be very difficult for nutrient rich 10:08.233 --> 10:13.133 waters to reach the surface because of that stability in 10:13.133 --> 10:14.873 the water column. 10:14.867 --> 10:18.397 If the nutrients can't reach the euphotic zone, then you're 10:18.400 --> 10:20.730 going to have low biological productivity. 10:23.567 --> 10:28.767 Question five was about the last glacial maximum. 10:28.767 --> 10:33.367 CO2 in the atmosphere was low, the isotopes in fresh snow on 10:33.367 --> 10:37.427 Greenland would be lighter than normal, because in that 10:37.433 --> 10:42.333 cold condition there would be more precipitation between 10:42.333 --> 10:45.033 source and Greenland. 10:45.033 --> 10:47.633 More water would have been rained out, the heavier 10:47.633 --> 10:49.473 isotopes rain out, you end up with 10:49.467 --> 10:50.997 lighter ones on Greenland. 10:51.000 --> 10:54.370 The isotopes in deep sea sediments would be heavy 10:54.367 --> 10:58.727 because with ice stored on land, it would be 10:58.733 --> 11:00.403 isotopically light. 11:00.400 --> 11:03.430 The remaining water in the ocean would be isotopically 11:03.433 --> 11:06.273 heavier and the sediments would have picked up and 11:06.267 --> 11:09.527 retained that signal. 11:09.533 --> 11:14.133 Sea level would be low because water is stored on land. 11:14.133 --> 11:18.603 So then the relationship between C and D, oxygen 11:18.600 --> 11:21.430 isotopes in deep sea sediments in sea level, well I've just 11:21.433 --> 11:26.103 said that, so sea level low means that water is being 11:26.100 --> 11:29.830 stored on land in the ice sheets. 11:29.833 --> 11:33.033 And because that is light isotopes, because of the 11:33.033 --> 11:34.933 evaporation process, that's going to 11:34.933 --> 11:38.103 make the oceans heavy. 11:38.100 --> 11:39.370 Questions on that? 11:42.833 --> 11:47.333 In recent centuries we have a perihelion in January. 11:47.333 --> 11:49.003 Explain how the climate would be different if due to 11:49.000 --> 11:50.130 procession-- 11:50.133 --> 11:53.703 All right, so let me put on the board this side review of 11:53.700 --> 11:56.730 the plane of the ecliptic. 11:56.733 --> 12:03.873 The sun will be off center and earth will be here and here. 12:03.867 --> 12:05.467 And this will be today. 12:09.067 --> 12:13.897 But this will be say 10,000 years from now. 12:13.900 --> 12:27.700 And today the perihelion is in January, which means the tilt 12:27.700 --> 12:28.970 of the earth is like that. 12:34.533 --> 12:37.973 If it was going to be in June, then we know that the tilt of 12:37.967 --> 12:41.797 the earth would be like this, because this is northern 12:41.800 --> 12:46.430 hemisphere summer, which is June. 12:46.433 --> 12:49.273 So the tilt is like that. 12:49.267 --> 12:53.067 So then what I wanted you to explain was basically how 12:53.067 --> 12:55.327 these two climates would be different. 12:55.333 --> 13:00.633 And one thing is that in this season the northern-- 13:00.633 --> 13:04.003 in this situation, the northern hemisphere summers, 13:04.000 --> 13:08.130 being perihelion, would be warmer. 13:08.133 --> 13:12.003 The northern hemisphere winters would be colder 13:12.000 --> 13:13.370 because of that distance. 13:13.367 --> 13:15.897 So the northern hemisphere seasons would be stronger. 13:18.967 --> 13:22.027 The southern hemisphere seasons would be weaker, 13:22.033 --> 13:25.503 because in the winter tilted away, you're closer to the 13:25.500 --> 13:30.000 sun, tilted towards, you're further from the sun. 13:30.000 --> 13:35.600 So the proper answer would be that the intensity of the 13:35.600 --> 13:40.170 seasons would be changed, but oppositely early in the 13:40.167 --> 13:41.397 northern and southern hemispheres. 13:43.667 --> 13:46.667 Questions on that? 13:46.667 --> 13:50.497 Sea ice is frozen seawater. 13:50.500 --> 13:53.530 Thickness, let's say 1 to 4 meters. 13:53.533 --> 13:59.233 Salinity, it starts out as seawater. 13:59.233 --> 14:02.933 It loses quite a bit of its salt when it 14:02.933 --> 14:04.173 freezes, but not all. 14:04.167 --> 14:10.197 So a typical salinity for sea ice is between 5 and 20, 14:10.200 --> 14:14.130 somewhere in that range, whereas seawater is 35. 14:14.133 --> 14:17.633 Icebergs on the other hand are compacted snow, an entirely 14:17.633 --> 14:20.833 different origin than sea ice. 14:20.833 --> 14:24.333 And their salinity is essentially zero, since it's 14:24.333 --> 14:31.873 fresh water snow has fallen on the glacier. 14:31.867 --> 14:35.997 Whatever formed the iceberg. 14:36.000 --> 14:36.700 Questions there? 14:36.700 --> 14:39.970 Student: You said that the salinity of sea ice is what? 14:39.967 --> 14:42.467 PROFESSOR: 0. 14:42.467 --> 14:45.697 Now it may be that if it's been floating in seawater for 14:45.700 --> 14:49.000 a while a little bit of seawater has kind of worked 14:49.000 --> 14:50.870 its way into some of the cracks. 14:50.867 --> 14:56.927 But if you find a chunk of pure ice in the iceberg, it'll 14:56.933 --> 15:01.103 have 0 salinity because it came from fallen snow some 15:01.100 --> 15:03.700 years or centuries before. 15:03.700 --> 15:05.330 Student: Sea ice. 15:05.333 --> 15:07.973 PROFESSOR: I'm sorry you asked me about sea ice. 15:07.967 --> 15:08.297 Sorry. 15:08.300 --> 15:09.970 I answered the wrong question. 15:09.967 --> 15:17.097 Sea ice is fresher than ocean water, but has 15:17.100 --> 15:19.400 some salt in it. 15:19.400 --> 15:19.870 Yes? 15:19.867 --> 15:21.767 Student: Can I talk you after class about 15:21.767 --> 15:22.997 PROFESSOR: Of course. 15:27.000 --> 15:27.800 OK. 15:27.800 --> 15:29.070 Now question eight. 15:32.433 --> 15:33.403 What was the question? 15:33.400 --> 15:34.570 OK. 15:34.567 --> 15:35.627 Recent trends in sea ice. 15:35.633 --> 15:40.503 So you may recall that it's conventional to judge both of 15:40.500 --> 15:41.570 these in September. 15:41.567 --> 15:44.527 Now in the northern hemisphere, September is the 15:44.533 --> 15:49.473 minimum in sea ice and in the southern hemisphere that's the 15:49.467 --> 15:50.367 maximum in sea ice. 15:50.367 --> 15:54.497 But that makes sense because in the northern hemisphere the 15:54.500 --> 15:58.900 maximum in sea ice, which occurs say in March or April, 15:58.900 --> 16:01.300 fills the entire basin. 16:01.300 --> 16:07.300 So it's not a question of cold conditions giving us more sea 16:07.300 --> 16:11.230 ice in winter in the Arctic Ocean, it's already coast to 16:11.233 --> 16:14.933 coast. Now a little more may spill out into the Pacific and 16:14.933 --> 16:17.973 the Atlantic, but in terms of the Arctic Basin, it's full. 16:17.967 --> 16:20.967 So that would not be a sensible way to measure 16:20.967 --> 16:24.267 changes in the arctic sea ice. 16:24.267 --> 16:29.267 And for the southern ocean, at the end of the warming season, 16:29.267 --> 16:30.697 there's very little sea ice left. 16:30.700 --> 16:34.830 It retreats mostly right back to the coast. And so that 16:34.833 --> 16:37.333 wouldn't be a sensible way to measure. 16:37.333 --> 16:39.733 Instead we measure it at its maximum in the southern 16:39.733 --> 16:42.673 hemisphere, which is in September. 16:45.233 --> 16:49.633 Anyway in the arctic, sea ice is rapidly decreasing. 16:49.633 --> 16:52.473 In the southern ocean it's approximately constant by the 16:52.467 --> 16:55.827 measure I've just described. 16:55.833 --> 17:01.733 Question nine is computing the mass of salt 17:01.733 --> 17:03.573 in the world ocean. 17:03.567 --> 17:08.727 What I thought you would do there was to estimate the 17:08.733 --> 17:10.703 depth of the ocean at about 5 kilometers. 17:13.400 --> 17:16.270 Estimate the surface area of the ocean as 17:16.267 --> 17:19.297 about 2/3 of the global. 17:19.300 --> 17:24.070 Multiply the two together to get a volume of ocean water. 17:27.167 --> 17:31.497 Multiply that times density to get a mass of ocean water, and 17:31.500 --> 17:35.830 then use the salinity of 35 parts per thousand to 17:35.833 --> 17:37.703 get how much salt. 17:37.700 --> 17:40.370 And I ended up and your number may be slightly different than 17:40.367 --> 17:50.967 mine but I ended up with about 60 x 10 to the 18th 17:50.967 --> 17:53.997 kilograms of salt. 17:54.000 --> 17:55.130 Was the answer I got. 17:55.133 --> 17:55.403 Yes? 17:55.400 --> 17:58.000 Student: When you're converting from volume to mass 17:58.000 --> 18:01.800 are you using density of water or seawater? 18:01.800 --> 18:07.000 PROFESSOR: I think I used sea water, but the 18:07.000 --> 18:09.100 difference is very slight. 18:09.100 --> 18:12.730 It's only 1025 versus 1000. 18:12.733 --> 18:16.573 So your answer would be off by if you chose one versus your 18:16.567 --> 18:20.827 other, the answer would be 2% different, which I don't think 18:20.833 --> 18:23.933 for a rough calculation like this is very significant. 18:29.567 --> 18:30.867 Finally question ten. 18:30.867 --> 18:37.667 The Little Ice Age is the cool period I'm sorry what was 18:37.667 --> 18:40.797 question 10a? 18:40.800 --> 18:42.000 Antarctic bottom water. 18:42.000 --> 18:43.530 Antarctic bottom water is I changed the 18:43.533 --> 18:45.233 exams. It's an old version. 18:45.233 --> 18:51.003 The Antarctic bottom water is that cool, cold water mass in 18:51.000 --> 18:55.830 fact, formed at the bottom of the ocean, formed near the 18:55.833 --> 18:57.073 shores of Antarctica. 18:59.433 --> 19:02.533 A terminal moraine is a pile of rock and soil deposited at 19:02.533 --> 19:04.603 the tip of a moving glacier. 19:04.600 --> 19:07.870 Equatorial upwelling is rising water from the diverging Ekman 19:07.867 --> 19:13.767 Layer, flow at the equator, due to a reversal in the 19:13.767 --> 19:15.827 Coriolis force. 19:15.833 --> 19:21.403 Mid-ocean ridge is the shallow region of water, of shallower 19:21.400 --> 19:25.070 depth in the ocean connected with where ocean crust is 19:25.067 --> 19:29.727 being created by solidifying material from the mantle and 19:29.733 --> 19:36.503 then it's a spreading center for ocean crust. And the Ekman 19:36.500 --> 19:43.400 Layer is the ocean flow driven by wind stress at right angles 19:43.400 --> 19:45.170 to the wind. 19:45.167 --> 19:49.027 You could also have talked about, well the fact--what 19:49.033 --> 19:51.673 kind of a force balance it has, but some kind of a 19:51.667 --> 19:55.667 definition of the Ekman Layer there was needed. 19:55.667 --> 19:57.097 OK. 19:57.100 --> 20:00.330 So that's exam three. 20:27.200 --> 20:29.070 So we're going to finish up the discussion-- 20:29.067 --> 20:29.527 Question. 20:29.533 --> 20:29.973 Julia. 20:29.967 --> 20:31.797 Student: What was the average of the exam? 20:31.800 --> 20:33.130 PROFESSOR: I'm not sure. 20:33.133 --> 20:35.773 Do you guys know what the average is on this? 20:35.767 --> 20:38.497 82. 20:38.500 --> 20:39.730 Better than last time. 20:42.067 --> 20:43.427 Was that the other question too? 20:43.433 --> 20:45.133 Yes. 20:45.133 --> 20:47.573 So we're going to finish up the global warming discussion 20:47.567 --> 20:52.227 today by talking about emission scenarios. 20:52.233 --> 20:53.733 Now again, the primary reference 20:53.733 --> 20:56.103 here is the IPCC reports. 20:56.100 --> 20:58.700 So everything in the diagrams I'm showing are almost 20:58.700 --> 21:02.630 entirely from the IPCC reports which you have, or you can get 21:02.633 --> 21:03.403 very easily. 21:03.400 --> 21:07.630 But there's another report as part of it, SRES. 21:07.633 --> 21:13.573 It also is on the IPCC website which stands for What 21:13.567 --> 21:15.227 does it stand for? 21:15.233 --> 21:21.103 Special Report on Emission Scenarios. 21:21.100 --> 21:22.700 And I'll be talking about that today. 21:22.700 --> 21:24.700 It should have been easy to remember, given the 21:24.700 --> 21:26.930 title of the slide. 21:26.933 --> 21:31.833 So the idea is here that some economists and some industrial 21:31.833 --> 21:36.973 engineers got together to imagine how the emissions of 21:36.967 --> 21:41.167 carbon dioxide in the atmosphere might proceed over 21:41.167 --> 21:44.727 the next 100 years, based on certain population and 21:44.733 --> 21:46.973 economic assumptions. 21:46.967 --> 21:48.627 And they tried quite a variety of different 21:48.633 --> 21:50.733 things, as you will see. 21:50.733 --> 21:53.633 And then for each of those, they handed those off to the 21:53.633 --> 21:55.373 climate modelers. 21:55.367 --> 21:58.927 And the climate modelers ran their climate models with 21:58.933 --> 22:02.733 these different carbon dioxide concentrations. 22:02.733 --> 22:07.403 And the result is a set of projections into the future of 22:07.400 --> 22:11.370 how both CO2 and Earth's climate will change. 22:11.367 --> 22:13.567 And that's what we're going to talk about today. 22:16.467 --> 22:22.827 So here are most of the IPCC emission scenarios. 22:28.300 --> 22:37.300 Time is on the x-axis from 1990 to 2100. 22:37.300 --> 22:41.530 Emission rate is on the y-axis in units of gigatons 22:41.533 --> 22:44.003 of carbon per year. 22:44.000 --> 22:45.630 Gigatons of carbon per year. 22:45.633 --> 22:49.633 Remember that's not the mass of CO2, that's the mass of the 22:49.633 --> 22:50.973 carbon in the CO2. 22:50.967 --> 22:57.897 So if you want to compute the math of carbon dioxide, just 22:57.900 --> 23:02.370 correct for the ratio of the molecular weight of a carbon 23:02.367 --> 23:06.797 dioxide molecule to the carbon by itself. 23:06.800 --> 23:09.730 44/12 would be that ratio, right? 23:09.733 --> 23:12.373 Carbon dioxide is 44, carbon 12. 23:12.367 --> 23:12.727 So yes. 23:12.733 --> 23:16.503 Just multiply these times 44/12. 23:16.500 --> 23:22.630 And the A1 is broken up into some subcategories. 23:22.633 --> 23:28.103 Generally the As have quite a bit of increasing emissions 23:28.100 --> 23:29.700 over the next 100 years. 23:29.700 --> 23:33.070 The two B scenarios are a little more optimistic. 23:33.067 --> 23:38.197 they climb and then declined for B1, or climb and then 23:38.200 --> 23:42.230 increase at a very much slower rate for B2. 23:46.933 --> 23:53.233 These documents were published using data from about 2000 and 23:53.233 --> 23:59.603 projecting it from about 2002 and we have a few years now to 23:59.600 --> 24:03.500 look and see which of these lines we've been on the last 24:03.500 --> 24:04.670 five years. 24:04.667 --> 24:06.297 It's a little bit hard to tell, because they don't 24:06.300 --> 24:09.870 diverge so strongly in the first few years. 24:09.867 --> 24:11.227 They're all pretty similar. 24:11.233 --> 24:15.173 But from the articles I've read recently, it looks like 24:15.167 --> 24:20.367 we're a bit closer to the higher projections than we are 24:20.367 --> 24:23.367 to the lower ones, if you look what's happened over the last 24:23.367 --> 24:24.297 five years. 24:24.300 --> 24:28.700 Now, this may have changed a bit since 2008 when we began 24:28.700 --> 24:32.400 to have these economic difficulties. 24:32.400 --> 24:34.600 So you're going to want to read the literature carefully, 24:34.600 --> 24:40.130 but as of about 2008, 2009, it looks like we were on some of 24:40.133 --> 24:44.203 the more discouraging trajectories, in 24:44.200 --> 24:47.000 terms of CO2 emissions. 24:47.000 --> 24:51.130 Now from these, with a little bit of understanding about how 24:51.133 --> 24:56.103 carbon is put back into the biosphere, you can come up 24:56.100 --> 24:59.330 with total cumulative Well sorry, this is just 24:59.333 --> 25:01.033 summing them up. 25:01.033 --> 25:04.733 Total carbon dioxide cumulative emissions, so just 25:04.733 --> 25:09.233 adding those together to get the different scenarios 25:09.233 --> 25:10.703 expressed in a different way. 25:13.300 --> 25:16.430 From that, with a bit of understanding of how some of 25:16.433 --> 25:19.303 that carbon dioxide will be recycled back into the 25:19.300 --> 25:23.470 biosphere, you can come up with carbon dioxide 25:23.467 --> 25:28.927 concentration projections over the next 100 years. 25:28.933 --> 25:31.573 I don't know why this artist has put the 25:31.567 --> 25:32.697 two up on top there. 25:32.700 --> 25:35.930 That's not a conventional way to write CO2. 25:35.933 --> 25:37.433 So don't be misled by that. 25:37.433 --> 25:40.973 I think this diagram is still accurate in spite of that loss 25:40.967 --> 25:43.867 of credibility given by putting the two 25:43.867 --> 25:46.427 in the wrong place. 25:46.433 --> 25:51.973 But again, you see that the B1 scenarios are leveling off, 25:51.967 --> 25:55.497 whereas the A scenarios are climbing very rapidly, 25:55.500 --> 26:02.800 especially the A2 scenario, which has us reaching over 800 26:02.800 --> 26:05.800 parts per million by volume by the year 2100. 26:05.800 --> 26:10.230 Now are you familiar with this organization called 350.org? 26:10.233 --> 26:15.403 So this is what's his name, McKibben's organization. 26:18.133 --> 26:21.803 With some scientific basis, I'm not sure everyone would 26:21.800 --> 26:24.300 agree, but with some scientific thought, they've 26:24.300 --> 26:27.430 decided that 350 should be the limit we should 26:27.433 --> 26:29.473 strive for on CO2. 26:29.467 --> 26:31.367 But remember, we've already passed that. 26:31.367 --> 26:35.197 We're at 397 already. 26:35.200 --> 26:38.230 So but just for record, you could put that on this 26:38.233 --> 26:42.873 diagram, 350.org would have you put the limit right there. 26:42.867 --> 26:47.267 It helps you to understand how far in exceedance of that 26:47.267 --> 26:52.867 number we are and will be in the future. 26:52.867 --> 26:55.297 Any questions on this diagram? 26:55.300 --> 26:55.570 Yes. 26:55.567 --> 27:01.097 Student: What are the different criteria they used 27:01.100 --> 27:05.100 to create different scenarios? 27:05.100 --> 27:06.700 PROFESSOR: I don't have those on 27:06.700 --> 27:08.600 the tip of my tongue. 27:08.600 --> 27:12.270 They have to do with the way certain economic sectors will 27:12.267 --> 27:16.827 develop and that way--which countries will dominate 27:16.833 --> 27:20.573 production of certain items. It's rather detailed, and that 27:20.567 --> 27:22.527 SRES report goes into that. 27:22.533 --> 27:25.003 It makes rather interesting reading. 27:25.000 --> 27:27.800 I apologize for the fact that I don't have those different 27:27.800 --> 27:30.100 economic definitions prepared. 27:30.100 --> 27:31.670 Student: But it's based on the economic growth? 27:31.667 --> 27:34.597 PROFESSOR: Economic growth, economic-- 27:34.600 --> 27:36.470 where production occurs. 27:36.467 --> 27:40.227 Not only a total gross, but in what country production shifts 27:40.233 --> 27:41.273 to and things like that. 27:41.267 --> 27:41.997 Student: So it takes into account shifts to different 27:42.000 --> 27:44.270 forms of energy? 27:44.267 --> 27:44.897 PROFESSOR: Exactly. 27:44.900 --> 27:46.030 Some of that's in there too. 27:46.033 --> 27:46.503 That's right. 27:46.500 --> 27:47.770 That's right. 27:51.500 --> 27:54.800 So now the climate modelers perform their magic. 27:54.800 --> 27:59.000 And as you know, there's about a dozen or so of these climate 27:59.000 --> 28:02.370 models run by different groups around the world that do these 28:02.367 --> 28:02.997 projections. 28:03.000 --> 28:04.330 So you get a lot of different projections. 28:07.067 --> 28:09.967 The number of things gets multiplied because we now have 28:09.967 --> 28:12.067 all these different scenarios, and we have all the different 28:12.067 --> 28:14.367 models running on all the different scenarios. 28:14.367 --> 28:16.297 So you get a lot of different output. 28:16.300 --> 28:18.070 It's a little hard to manage sometimes. 28:18.067 --> 28:21.567 But I want to show you this diagram. 28:21.567 --> 28:24.367 Again, this is from IPCC report. 28:24.367 --> 28:30.627 It shows the surface warming a based on a pre-industrial 28:30.633 --> 28:37.133 reference and versus time, 1985. 28:37.133 --> 28:39.473 This just only goes to 2025. 28:39.467 --> 28:42.627 This is a short time scale here. 28:42.633 --> 28:46.603 It shows something called the commitment curve. 28:46.600 --> 28:51.470 That is code for constant composition. 28:51.467 --> 28:54.267 In other words, that essentially says no further 28:54.267 --> 29:00.127 CO2 emissions starting in the year 2000, essentially. 29:00.133 --> 29:04.273 Now the temperature does continue to climb on that, 29:04.267 --> 29:09.527 because even with constant CO2 emissions, you still have to 29:09.533 --> 29:10.733 warm up the oceans. 29:10.733 --> 29:13.473 Remember the oceans are putting a lag on all of this, 29:13.467 --> 29:16.797 because of their enormous heat capacity. 29:16.800 --> 29:22.500 So this continued rise is due to mostly trying to warm up 29:22.500 --> 29:24.530 the oceans, even though the greenhouse 29:24.533 --> 29:26.473 effect is kind of fixed. 29:26.467 --> 29:27.427 Question, yes. 29:27.433 --> 29:30.333 Student: Is that only anthropogenic on the outside, 29:30.333 --> 29:32.273 or is it all across the outside? 29:32.267 --> 29:34.567 PROFESSOR: Well it's constant atmospheric 29:34.567 --> 29:36.497 composition, is the way it's defined. 29:36.500 --> 29:36.770 [Correction: The assumed carbon dioxide concentration 29:36.767 --> 29:57.067 is about 370ppmv).] 29:57.067 --> 30:00.897 And then these different scenarios follow each other 30:00.900 --> 30:04.270 pretty closely over this time frame. 30:04.267 --> 30:06.897 But if you remember back to the emissions scenarios, or to 30:06.900 --> 30:12.100 the composition one, your past 2025 before they really 30:12.100 --> 30:14.200 diverge very much. 30:14.200 --> 30:16.830 So it's not surprising that even though these scenarios 30:16.833 --> 30:20.903 are wildly different, you don't see much of that up to 30:20.900 --> 30:23.900 the year 2025. 30:23.900 --> 30:25.600 But you do see a lot of rise. 30:25.600 --> 30:31.430 I mean now you're up to a degree or so of warming and 30:31.433 --> 30:35.433 the rate is rather impressive. 30:35.433 --> 30:38.373 Now when you go out to a much longer time scale, that's when 30:38.367 --> 30:39.727 you see the big differences. 30:39.733 --> 30:45.533 So here is up to the present day, this is actual data, and 30:45.533 --> 30:48.533 here's the constant composition commitment curve 30:48.533 --> 30:52.773 that you saw beginning to peel off in the previous one. 30:52.767 --> 30:55.397 While the other ones continued together, but by the time you 30:55.400 --> 30:58.030 get to 2050 now, they're beginning to 30:58.033 --> 30:59.973 diverge quite strongly. 30:59.967 --> 31:05.227 And by 2100 they really are quite different. 31:05.233 --> 31:10.333 I don't want to project how long each of you will live, 31:10.333 --> 31:14.433 but I expect that a lot of you in the classroom will be 31:14.433 --> 31:18.733 around maybe in 2080. 31:18.733 --> 31:25.403 And so that is the world that you will probably live to see, 31:25.400 --> 31:26.870 with some variability. 31:26.867 --> 31:33.227 But I think if the last five years is any guide, probably 31:33.233 --> 31:37.973 you'll be up in this upper range if things continue as 31:37.967 --> 31:38.767 they are going. 31:38.767 --> 31:44.297 So that's a warming of about again this is based on this 31:44.300 --> 31:50.030 reference, not pre-industrial but that's a warming of about 31:50.033 --> 31:54.703 3 degrees Celsius from the current day. 31:54.700 --> 31:56.270 Then they begin to level out. 31:56.267 --> 32:00.197 All of these scenarios begin to level out, except for A2 32:00.200 --> 32:02.800 perhaps, because of the assumptions 32:02.800 --> 32:04.000 that have been made. 32:04.000 --> 32:10.030 And in fact by the time we are removing fossil fuels at a 32:10.033 --> 32:14.603 high rate for the next 100 years, we will have depleted a 32:14.600 --> 32:17.100 fairly significant fraction of the fossil fuel. 32:17.100 --> 32:23.370 So this turning over is not all our choice. 32:23.367 --> 32:26.267 Some of this will turn over simply because the remaining 32:26.267 --> 32:28.497 amount of fossil fuels to be burned is 32:28.500 --> 32:31.870 getting to be so small. 32:31.867 --> 32:33.097 Questions on this? 32:35.300 --> 32:39.730 Again, you'll find this in the IPCC report. 32:39.733 --> 32:45.133 Now when you plot the same data on a larger time frame, 32:45.133 --> 32:49.403 going back 1000 years, so here we are today. 32:49.400 --> 32:52.470 So what they've done is taken that historic proxy data that 32:52.467 --> 32:56.897 I've shown you before, with a little bit of a hint of a 32:56.900 --> 33:00.570 medieval warming, and a little bit of a hint of a little ice 33:00.567 --> 33:04.297 age in here, and then our current kind of two phased 33:04.300 --> 33:09.200 warming in the 20th century, and then put these IPCC 33:09.200 --> 33:13.400 scenarios tacked on to that, it helps you to put in 33:13.400 --> 33:16.900 perspective as to how the changes relate to what we've 33:16.900 --> 33:20.870 seen over the last part of the Holocene period. 33:20.867 --> 33:23.727 It's quite a steep and dramatic rise compared to the 33:23.733 --> 33:25.833 flat climate we've had recently. 33:28.400 --> 33:29.600 Any questions on that? 33:29.600 --> 33:30.030 Yes. 33:30.033 --> 33:33.303 Student: How about relative to periods significantly prior to 33:33.300 --> 33:34.070 PROFESSOR: Yes. 33:34.067 --> 33:34.997 So that's important. 33:35.000 --> 33:35.570 Now. 33:35.567 --> 33:37.627 I don't have the diagram here, but they're loaded in the 33:37.633 --> 33:40.703 previous presentations. 33:40.700 --> 33:42.300 You can go back and see that. 33:42.300 --> 33:45.570 And of course what will happen is when you get 10,000 years 33:45.567 --> 33:49.667 back so here's 1000 years back when you go 10 times more, 33:49.667 --> 33:54.927 then you're back into the Pleistocene, the LGM, the Last 33:54.933 --> 33:57.003 Glacial Maximum, and then this temperature 33:57.000 --> 33:58.770 drops about 5 degrees. 33:58.767 --> 34:04.467 So take that distance and put it down here and that'll give 34:04.467 --> 34:05.497 you a different sense. 34:05.500 --> 34:05.970 Right? 34:05.967 --> 34:08.597 That'll give you a sense of well, OK, this is higher than 34:08.600 --> 34:12.970 any of that, but as an absolute change it is 34:12.967 --> 34:15.697 comparable to what we had going in and 34:15.700 --> 34:16.700 out of the ice ages. 34:16.700 --> 34:19.630 It was all down here however, so this is unique in its 34:19.633 --> 34:24.633 warmth, but not unique in its magnitude of the fluctuating. 34:24.633 --> 34:25.973 That's a good point to keep in mind. 34:25.967 --> 34:30.767 So you can be fooled by just what period of geologic 34:30.767 --> 34:36.227 history you've used here to form a basis for comparison. 34:36.233 --> 34:37.473 Other questions on this? 34:40.433 --> 34:43.633 And of course it won't be uniform, the warming. 34:43.633 --> 34:48.273 Here's the warmth they anticipate under three of the 34:48.267 --> 34:56.767 scenarios, B1, A1, B and A2 up from 20 to 29, most of the 34:56.767 --> 34:58.727 warmth is in the northern hemisphere. 34:58.733 --> 35:01.933 Up to the end of the century then, much more warming, but 35:01.933 --> 35:05.233 again concentrated in the northern 35:05.233 --> 35:07.903 hemisphere, high latitudes. 35:07.900 --> 35:11.970 Values as high as 7 degrees Celsius. 35:11.967 --> 35:15.497 My god, that's a lot of warming. 35:15.500 --> 35:19.400 That's an amazing amount of warming. 35:19.400 --> 35:21.200 Certainly there would be no arctic ice. 35:21.200 --> 35:23.730 Certainly there'd be no glaciers in the northern 35:23.733 --> 35:27.473 hemisphere, mountain glaciers, under that climate. 35:32.200 --> 35:37.530 OK, any questions on these IPCC projections? 35:37.533 --> 35:37.833 Yes. 35:37.833 --> 35:40.473 Student: What about in comparison to the Pliocene, 35:40.467 --> 35:42.297 the period that we said was comparable-- 35:42.300 --> 35:43.470 PROFESSOR: The Pliocene, right. 35:43.467 --> 35:47.297 So that would then be comparable the Pliocene also 35:47.300 --> 35:51.570 seemed to have much higher temperatures at the high 35:51.567 --> 35:53.197 latitudes than we have today. 35:53.200 --> 35:57.900 So this kind of scenario is one of the reasons why there 35:57.900 --> 36:00.830 is a lot of research on the Pliocene, because they need 36:00.833 --> 36:04.903 too had this kind of warmth in the northern high latitudes. 36:04.900 --> 36:07.900 And we don't understand why that is exactly, but it may 36:07.900 --> 36:11.030 well be something similar to this. 36:11.033 --> 36:13.673 Except that it didn't seem that the CO2 values were as 36:13.667 --> 36:17.727 high back then during the Pliocene. 36:17.733 --> 36:20.403 But it'd be worth reading a couple papers on the Pliocene 36:20.400 --> 36:25.430 to see to what extent they if you just Google Pliocene 36:25.433 --> 36:32.203 climate, you can quickly just use a 36:32.200 --> 36:34.070 Google Scholar for example. 36:34.067 --> 36:38.067 If you want to get the peer reviewed literature, go into 36:38.067 --> 36:41.367 Google Scholar and search for Pliocene climate and you'll 36:41.367 --> 36:43.767 find a lot of recent papers that are trying to deal with 36:43.767 --> 36:45.027 just this issue. 36:48.300 --> 36:54.130 So a lot of problems then we perceive could be connected 36:54.133 --> 36:55.233 with this global warming. 36:55.233 --> 36:56.873 And these are all pretty obvious. 36:56.867 --> 36:58.927 I just list them here. 36:58.933 --> 37:01.773 And it may not be complete. 37:01.767 --> 37:04.997 We expect increasing drought, which will-- 37:05.000 --> 37:09.100 and some human populations as well as animal populations 37:09.100 --> 37:10.370 will be forced to migrate. 37:14.400 --> 37:17.400 They'll be some extinctions probably. 37:17.400 --> 37:22.630 The one that's most talked about will be the polar bears. 37:22.633 --> 37:29.333 My strategy for global warming is that if I just buy a house 37:29.333 --> 37:35.233 300 miles north of New Haven, that'll pretty much account 37:35.233 --> 37:38.703 for the global warming that'll take place in my lifetime. 37:38.700 --> 37:40.030 Pretty clever, right? 37:40.033 --> 37:41.673 A lot of deep thought went into that. 37:44.100 --> 37:45.700 But imagine the polar bears, right? 37:45.700 --> 37:47.200 They live in this arctic environment. 37:47.200 --> 37:47.930 It's going to warm up. 37:47.933 --> 37:50.303 They're going to lose the sea ice very quickly 37:50.300 --> 37:52.270 from which they hunt. 37:52.267 --> 37:53.597 They aren't going to mind the warm so much. 37:53.600 --> 37:57.230 They can probably handle that, but they normally do their 37:57.233 --> 38:00.133 hunting off the sea ice. 38:00.133 --> 38:02.673 Without sea ice, they won't to have a way to eat. 38:02.667 --> 38:06.027 And therefore we're probably going to lose the polar bear 38:06.033 --> 38:08.503 pretty quickly. 38:08.500 --> 38:10.000 That ecosystem will be gone. 38:10.000 --> 38:11.770 There will be frequenct heat waves. 38:11.767 --> 38:16.667 For example, a few years ago we had a heat wave in Europe. 38:16.667 --> 38:19.897 I believe that was in 2003 that killed some tens of 38:19.900 --> 38:22.270 thousands of people. 38:22.267 --> 38:27.627 And we had one just a year and a half ago in eastern Europe. 38:27.633 --> 38:30.573 And the projections are that these will occur very 38:30.567 --> 38:34.997 frequently as we get towards the middle and the end of the 38:35.000 --> 38:36.870 current century. 38:36.867 --> 38:39.367 And of course, if you're living up north that's not too 38:39.367 --> 38:41.297 bad, or if you have air conditioning. 38:41.300 --> 38:43.170 But air conditioning is a problem because that uses 38:43.167 --> 38:48.027 energy which may require fossil fuel burning, which 38:48.033 --> 38:49.703 would put more CO2 in the atmosphere. 38:49.700 --> 38:51.500 So that's kind of a downward spiral. 38:54.500 --> 38:56.830 The ice on land will melt. 38:56.833 --> 38:59.833 The mountain glaciers we spoke about, and the ice sheets of 38:59.833 --> 39:02.773 Greenland and Antarctica we talked about. 39:02.767 --> 39:07.697 And because that, ice on land is supported by the land, when 39:07.700 --> 39:09.430 it melts, that lifts sea level. 39:09.433 --> 39:12.773 Remember if ice is already floating in the ocean and you 39:12.767 --> 39:15.467 melt it, that doesn't change sea level. 39:15.467 --> 39:19.667 But if ice is supported by the land, as a mountain glacier 39:19.667 --> 39:23.597 would be, or a large ice sheet would be, that will cause sea 39:23.600 --> 39:25.370 level to rise. 39:25.367 --> 39:29.167 And it could be the order of several meters, which would 39:29.167 --> 39:32.767 have a big impact on coastal development. 39:35.633 --> 39:43.933 Today many rivers flow all summer because they get for 39:43.933 --> 39:46.003 example, in California the rivers that come down out of 39:46.000 --> 39:50.230 the Sierra Nevada range, they do decrease their flow in 39:50.233 --> 39:51.873 summertime because there's not much rain. 39:51.867 --> 39:54.827 But they keep it going because there's enough glacial ice 39:54.833 --> 39:57.903 melting through the summer to provide those rivers with 39:57.900 --> 40:00.570 water even in July and August. Well, that 40:00.567 --> 40:01.627 will certainly change. 40:01.633 --> 40:03.373 And there's all these rivers coming 40:03.367 --> 40:04.667 down out of the mountains. 40:04.667 --> 40:09.397 If there's not rain in that season, those rivers will 40:09.400 --> 40:10.770 certainly go dry. 40:10.767 --> 40:14.527 Because without the ice and snow to store water at high 40:14.533 --> 40:19.533 altitudes and this will be a big difference between today. 40:19.533 --> 40:23.633 Many, many rivers around the world are flowing in summer 40:23.633 --> 40:28.473 only because of snow pack melting, that stores that 40:28.467 --> 40:31.297 water until late summer. 40:31.300 --> 40:33.600 Tropical diseases will move forward. 40:33.600 --> 40:36.670 And I hesitated to put this in there but I did, because it's 40:36.667 --> 40:39.967 not likely that would happen, but it's constantly discussed 40:39.967 --> 40:42.727 in the literature, in the scientific literature, as a 40:42.733 --> 40:43.503 possibility. 40:43.500 --> 40:49.500 That is, if you look at the planet Venus with its 40:49.500 --> 40:55.070 unusually warm climate surface temperature for Venus is 460 40:55.067 --> 41:00.597 in Celsius, 735 in Kelvin it has the solar system's 41:00.600 --> 41:04.530 strongest greenhouse effect, has a rather high albedo, it 41:04.533 --> 41:05.733 reflects a lot of sunlight. 41:05.733 --> 41:09.903 But nevertheless it as a very high surface temperature 41:09.900 --> 41:13.630 because of its high greenhouse effect. 41:13.633 --> 41:17.803 And the idea is that it probably wasn't always like 41:17.800 --> 41:22.970 this, but some kind of process amplified itself. 41:22.967 --> 41:27.427 Probably it started to warm up, that for some of this 41:27.433 --> 41:32.033 carbon that was in the surface of the planet to come off the 41:32.033 --> 41:34.473 planet and form carbon dioxide which 41:34.467 --> 41:36.727 warmed the planet further. 41:36.733 --> 41:39.633 Water may have played a role too, but now most of 41:39.633 --> 41:41.203 the water is gone. 41:41.200 --> 41:44.530 Water may have played a role in getting Venus to its hot 41:44.533 --> 41:46.933 state, but most of that's gone now. 41:46.933 --> 41:52.403 Anyway, either a water vapor feedback or a CO2 feedback 41:52.400 --> 41:57.200 probably took Venus from an earth-like state to its 41:57.200 --> 41:58.630 current state. 41:58.633 --> 42:02.803 And so there is some worry that this 42:02.800 --> 42:03.770 could happen to earth. 42:03.767 --> 42:06.827 We could get to some point where suddenly these two 42:06.833 --> 42:11.703 feedbacks, carbon dioxide and water vapor feedbacks, might 42:11.700 --> 42:15.970 then take control of the climate and run away and give 42:15.967 --> 42:19.967 us something that's much, much higher than any of these IPCC 42:19.967 --> 42:20.797 projections. 42:20.800 --> 42:25.100 It's not likely, but you can read about it in the 42:25.100 --> 42:26.370 literature. 42:29.433 --> 42:32.133 There are advantages however. 42:32.133 --> 42:35.433 There are vast regions in the northern hemisphere, 42:35.433 --> 42:39.773 especially Canada and northern Asia, where agriculture is 42:39.767 --> 42:44.867 mostly limited by lack of summer warmth. 42:44.867 --> 42:49.067 And so you would find greatly increased agricultural 42:49.067 --> 42:53.867 productivity in Canada and Asia under these IPCC global 42:53.867 --> 42:57.267 warming scenarios. 42:57.267 --> 43:01.067 Also at the present time, many more people die from cold 43:01.067 --> 43:04.767 every year than from warmth. 43:04.767 --> 43:07.597 And of course, my heating bill will be less, 43:07.600 --> 43:11.000 so I'd enjoy that. 43:11.000 --> 43:14.970 And it's now known and well documented in the literature 43:14.967 --> 43:22.297 that when CO2 concentrations rise, plants grow more quickly 43:22.300 --> 43:25.600 because it of what's called CO2 fertilization. 43:25.600 --> 43:29.630 And so crops will grow generally more quickly. 43:29.633 --> 43:33.603 Some would argue that the crop--the nature of the plant 43:33.600 --> 43:38.470 structure however changes and makes that plant material less 43:38.467 --> 43:40.227 nutritious. 43:40.233 --> 43:41.103 So be careful. 43:41.100 --> 43:44.430 It's not only the mass of the plant that you grow, but 43:44.433 --> 43:46.373 weather--if you're going to eat it, whether or not it's 43:46.367 --> 43:47.597 nutritious for humans. 43:47.600 --> 43:49.230 So be a little bit careful on that one. 43:49.233 --> 43:53.633 But there's no doubt that CO2 fertilization is already being 43:53.633 --> 43:56.773 seen in forests and in agriculture. 43:56.767 --> 43:59.627 So that's a real factor, a real positive factor. 44:03.833 --> 44:07.333 So these again are pretty obvious. 44:07.333 --> 44:10.573 If we wanted to reduce global warming what would we do? 44:10.567 --> 44:12.227 Well none of these are easy. 44:12.233 --> 44:14.203 Many of these are impossible. 44:14.200 --> 44:19.900 But I list them anyway, being the eternal optimist. Reduce 44:19.900 --> 44:25.570 human populations, reduce per capita use of energy. 44:25.567 --> 44:29.467 One way to do that would be to increase energy costs so that 44:29.467 --> 44:32.797 each of us would work harder to reduce our per 44:32.800 --> 44:36.430 capita use of energy. 44:36.433 --> 44:40.203 Reforest the continents, because when you grow a tree, 44:40.200 --> 44:43.330 you sequester a certain amount of carbon dioxide. 44:43.333 --> 44:45.273 There are a couple of problems with that. 44:45.267 --> 44:47.467 I've mentioned one of them already. 44:47.467 --> 44:52.697 A tree typically only lives 60 or 100 years and then it will 44:52.700 --> 44:57.130 die and that carbon dioxide will be returned. 44:57.133 --> 45:00.203 Within 20 years, it'll be back in the atmosphere. 45:00.200 --> 45:04.630 So it's not a permanent way to store carbon dioxide. 45:04.633 --> 45:07.603 And also recently in the literature, it's been pointed 45:07.600 --> 45:10.470 out, and it's really quite obvious when you think about 45:10.467 --> 45:15.197 it, forests are very dark in their coloration. 45:15.200 --> 45:17.800 Their albedo is very low. 45:17.800 --> 45:22.470 And so if you add more forest, you decrease the average 45:22.467 --> 45:26.797 albedo of the planet, which would warm the planet. 45:26.800 --> 45:29.130 So be careful about that trade off. 45:32.867 --> 45:35.167 Fertilize the oceans. 45:35.167 --> 45:38.967 For a while we were talking about putting iron into the 45:38.967 --> 45:41.997 oceans, because that turned out to be a limiting nutrient 45:42.000 --> 45:45.370 for phytoplankton growth. 45:45.367 --> 45:50.497 And phytoplankton draw in CO2 just like plants on land do. 45:50.500 --> 45:52.470 The question once again though, how long would it stay 45:52.467 --> 45:53.697 in the oceans? 45:53.700 --> 45:56.500 Would it fall to the bottom to be covered over, or would it 45:56.500 --> 46:01.000 just return back into the atmosphere. 46:01.000 --> 46:03.830 Stop third world economic growth. 46:03.833 --> 46:07.473 Well that's kind of a joke, because how in the world would 46:07.467 --> 46:08.997 you do that? 46:09.000 --> 46:11.400 Of course in the first world we use much more carbon 46:11.400 --> 46:16.000 dioxide, we emit much more carbon dioxide per capita than 46:16.000 --> 46:19.500 the third world does. 46:19.500 --> 46:21.770 And that's because we have a higher standard of living and 46:21.767 --> 46:27.097 the third world aspire to have the same standard of living 46:27.100 --> 46:28.500 that we do. 46:28.500 --> 46:31.370 And so that's going to be where a lot of the increasing 46:31.367 --> 46:34.227 CO2 emissions will come from. 46:34.233 --> 46:35.473 Shift to nuclear energy. 46:35.467 --> 46:39.097 Nuclear energy does not emit any carbon dioxide. 46:39.100 --> 46:42.700 Shift to renewable energies of various types, wind, solar, 46:42.700 --> 46:43.470 geothermal. 46:43.467 --> 46:45.897 I'm going to be talking about these, by the way, in the last 46:45.900 --> 46:46.800 week of the course. 46:46.800 --> 46:50.670 We're going to talk a bit about renewable energy. 46:50.667 --> 46:53.767 The big thing that's talked about these days is CCS, 46:53.767 --> 46:55.327 Carbon Capture and Storage. 46:55.333 --> 46:59.273 It's removing carbon dioxide from the atmosphere and 46:59.267 --> 47:04.497 burying it down deep in the crust of the earth. 47:04.500 --> 47:07.600 A lot of research is being funded, including a big grant 47:07.600 --> 47:10.870 here in the geology department at Yale to work on some 47:10.867 --> 47:14.627 aspects of this. 47:14.633 --> 47:16.833 The question is-- of the questions is would it stay 47:16.833 --> 47:17.503 down there? 47:17.500 --> 47:20.870 I mean it's light material. 47:20.867 --> 47:23.567 You'd like to combine it or condense it in some way that 47:23.567 --> 47:27.067 it's stable and would stay down where you put it. 47:27.067 --> 47:29.767 But after all, it is a material that would like to 47:29.767 --> 47:32.997 gasify and come back out. 47:33.000 --> 47:37.330 And so there again I would worry about how long it would 47:37.333 --> 47:38.803 stay buried down there. 47:38.800 --> 47:42.770 And then various geoengineering hypotheses have 47:42.767 --> 47:45.827 been made, such as constructing some kind of a 47:45.833 --> 47:52.633 shade over the earth to prevent some of the sunlight 47:52.633 --> 47:54.133 from reaching the earth. 47:54.133 --> 47:56.203 We're out of time. 47:56.200 --> 47:58.770 I've got a few more comments about this for next Monday, 47:58.767 --> 48:00.067 but enjoy your weekend.