WEBVTT 00:01.933 --> 00:04.003 RONALD SMITH: OK, so we are starting this new subject, 00:04.000 --> 00:06.730 which is a really important one. 00:06.733 --> 00:13.133 And we'll be covering at least these subtopics, starting with 00:13.133 --> 00:16.933 the carbon cycle, then the question of whether we can use 00:16.933 --> 00:21.033 the Holocene as a reference period for judging recent 00:21.033 --> 00:22.473 climate change. 00:22.467 --> 00:26.367 We'll go over the history and the theory of the warming and 00:26.367 --> 00:30.297 cooling we've had over the last hundred years or so, talk 00:30.300 --> 00:35.400 about the IPCC forecasts for the future, and then go back, 00:35.400 --> 00:38.100 in a way, and kind of summarize some of this by 00:38.100 --> 00:41.830 talking about this interesting and useful concept of climate 00:41.833 --> 00:43.233 sensitivity. 00:43.233 --> 00:46.303 So it's quite a lot of material. 00:46.300 --> 00:51.100 The book is chapter 13. 00:51.100 --> 00:54.900 A couple of you have commented that in the earlier editions, 00:54.900 --> 00:57.030 there may not even be such a chapter. 00:57.033 --> 01:00.133 So please check with your classmates that have the 01:00.133 --> 01:05.433 current edition and look at their chapter 13 and see what 01:05.433 --> 01:05.973 the deal is. 01:05.967 --> 01:08.397 If you don't have that chapter, you may want to 01:08.400 --> 01:11.500 borrow someone else's textbook for a few hours while you read 01:11.500 --> 01:14.670 through that chapter. 01:14.667 --> 01:19.567 But a lot of the material, as I'll indicate in a minute, is 01:19.567 --> 01:23.167 coming out of the IPCC reports. 01:23.167 --> 01:24.627 And those are--some are already put online on the 01:24.633 --> 01:29.533 class's server for you, others you can 01:29.533 --> 01:31.273 find very easily online. 01:31.267 --> 01:33.097 Just Google IPCC. 01:33.100 --> 01:34.900 It'll take you to their big website. 01:34.900 --> 01:36.870 There's lots of different reports, you just have to 01:36.867 --> 01:40.697 figure out which ones you're looking for there. 01:40.700 --> 01:43.970 So even if you don't have a chapter 13, you can get a lot 01:43.967 --> 01:48.127 of this from the IPCC reports. 01:48.133 --> 01:52.073 Now I wanted to point out that this subject we're dealing 01:52.067 --> 01:56.427 with now, I think, is one of the four great paradigm shifts 01:56.433 --> 01:59.003 in the earth sciences. 01:59.000 --> 02:03.000 The four, in my mind, being the theory of evolution, that 02:03.000 --> 02:07.330 is, Darwin's idea of the mutability of 02:07.333 --> 02:11.903 species back in the 1860s. 02:11.900 --> 02:14.230 The theory of the Ice Ages, which we've spoken about in 02:14.233 --> 02:15.573 this course. 02:15.567 --> 02:20.097 The idea that just 14,000 years ago, we had a thick 02:20.100 --> 02:24.830 layer of ice covering over much of what is today open, 02:24.833 --> 02:27.233 useful land. 02:27.233 --> 02:31.873 The theory of plate tectonics, which helps us to understand 02:31.867 --> 02:35.397 the layout of the continents, how that has changed through 02:35.400 --> 02:36.470 geologic time. 02:36.467 --> 02:38.497 The difference between continental crust and ocean 02:38.500 --> 02:41.900 crust. It even helps us to understand the shape of the 02:41.900 --> 02:43.570 ocean basins. 02:43.567 --> 02:45.827 And then the theory of global warming, which we'll be 02:45.833 --> 02:46.603 dealing with now. 02:46.600 --> 02:50.400 Now, these each have their own characteristics, but on a 02:50.400 --> 02:55.400 scientific front, they all were true revolutions. 02:55.400 --> 02:59.300 In other words, they changed the very most basic ideas of 02:59.300 --> 03:03.630 how we thought about the different subjects of biology 03:03.633 --> 03:07.403 and climate and geology, and then, not only climate for 03:07.400 --> 03:13.370 global warming, but also the role of humans on the planet. 03:13.367 --> 03:15.427 There are books, interesting books, written on the history 03:15.433 --> 03:18.273 of each of these. 03:18.267 --> 03:19.067 Fascinating reading. 03:19.067 --> 03:22.767 How they were resisted, how they were promoted, what kinds 03:22.767 --> 03:27.167 of evidence finally tipped it over so that the majority of 03:27.167 --> 03:31.227 the scientific community finally accepted these. 03:31.233 --> 03:34.203 Fascinating reading in the history of human thought. 03:34.200 --> 03:36.370 Of course, the theory of evolution was resisted 03:36.367 --> 03:40.367 strongly by the church at that time because it changed the 03:40.367 --> 03:45.667 way we thought about humans and human nature. 03:45.667 --> 03:51.367 Still resisted to this day in some areas. 03:51.367 --> 03:53.767 The theory of the Ice Ages and plate tectonics I don't think 03:53.767 --> 03:59.897 had any kind of resistance or even that much notoriety in 03:59.900 --> 04:01.830 the general public. 04:01.833 --> 04:05.873 So they were mostly battles fought within cadre of 04:05.867 --> 04:07.097 scientists. 04:09.500 --> 04:11.300 So that's a little different. 04:11.300 --> 04:13.370 But then we get to the theory of global warming, and now 04:13.367 --> 04:17.967 we're back in a subject that is of great interest to the 04:17.967 --> 04:22.267 general public as well, and comes straight into politics. 04:25.633 --> 04:27.933 And it has a stake, a current stake. 04:27.933 --> 04:30.503 Now, all of these things were interesting--those first three 04:30.500 --> 04:35.070 were interesting intellectually, but none of 04:35.067 --> 04:39.927 them required that we do much in response to whether the 04:39.933 --> 04:41.973 theory was accepted or not. 04:41.967 --> 04:44.867 Where the theory of global warming is a little different 04:44.867 --> 04:49.367 because it has to do with not only the role of humans on the 04:49.367 --> 04:51.927 planet and the question of whether there are too many 04:51.933 --> 04:55.003 people and our lifestyle is wrong, but also in many 04:55.000 --> 04:58.600 respects it brings in the issue whether we should be 04:58.600 --> 05:02.800 changing our lifestyle or changing the way we do things. 05:02.800 --> 05:03.730 So here we are. 05:03.733 --> 05:07.273 And so you and I are living through this one. 05:07.267 --> 05:10.027 Not only is it a scientific debate, but it has these 05:10.033 --> 05:12.473 political and economic consequences. 05:12.467 --> 05:16.797 It's really a mess, because it's all these fears of 05:16.800 --> 05:21.930 discussion are engaged in the theory of--in the discussions 05:21.933 --> 05:24.003 of the theory of global warming. 05:27.733 --> 05:31.033 Any comments or questions on this? 05:31.033 --> 05:33.233 So, of course, I'm going to try to approach this in the 05:33.233 --> 05:40.103 most boring, scientific way that I can and try to keep to 05:40.100 --> 05:44.430 a large extent out of the politics and these other 05:44.433 --> 05:46.503 discussions. 05:46.500 --> 05:53.500 But we can't avoid dealing with some of these. 05:53.500 --> 05:57.400 It used to be that, when you went to someone's house or a 05:57.400 --> 06:02.530 cocktail party, your companion would whisper in your ear, now 06:02.533 --> 06:06.333 remember, don't talk about politics or religion. 06:06.333 --> 06:08.673 And now you have to say, don't talk about politics or 06:08.667 --> 06:11.797 religion or global warming, because you get into some 06:11.800 --> 06:15.730 terrible battles quite innocently, making the most 06:15.733 --> 06:16.703 benign remarks. 06:16.700 --> 06:19.470 And suddenly, everybody's in an uproar. 06:19.467 --> 06:21.767 So, particularly hard for someone who works in this 06:21.767 --> 06:30.697 field to avoid that kind of awkward party situation. 06:30.700 --> 06:35.970 So as I've indicated, for a lot of the discussion, then, 06:35.967 --> 06:38.597 that you'll do, and that I will do, and that everybody 06:38.600 --> 06:41.270 else does, your primary reference material are these 06:41.267 --> 06:44.367 very valuable IPCC reports. 06:44.367 --> 06:47.097 There have been a series of IPCC reports, and the most 06:47.100 --> 06:50.530 recent one, called the Fourth Assessment, 06:50.533 --> 06:53.173 was finished in 2007. 06:53.167 --> 06:54.997 And of course, the Intergovernmental Panel on 06:55.000 --> 06:59.100 Climate Change is busily working on the next one. 06:59.100 --> 07:01.870 I don't know when the target date is, but probably within a 07:01.867 --> 07:04.727 year or two, there will be the Fifth 07:04.733 --> 07:08.073 Assessment of climate change. 07:08.067 --> 07:10.427 And some of that material is already being leaked. 07:10.433 --> 07:11.773 You can find it on their website. 07:11.767 --> 07:15.067 But for the most part, we're going to be going back and 07:15.067 --> 07:18.567 focusing most of our attention on the 2007 report. 07:18.567 --> 07:22.467 But there have been other things more recent, such as an 07:22.467 --> 07:27.297 interesting National Academy of Sciences report on, what's 07:27.300 --> 07:29.730 the word they used? 07:29.733 --> 07:32.903 Sudden, they used a different word sudden climate change, 07:32.900 --> 07:35.930 they did a particular study on how fast 07:35.933 --> 07:37.133 climate change will occur. 07:37.133 --> 07:41.573 And I've got that posted on the lab course website. 07:41.567 --> 07:44.427 A special report, also by the National Academy, on high 07:44.433 --> 07:49.273 latitude climate change, and both of those are more recent 07:49.267 --> 07:52.997 than 2007, so those will give you some updated material. 07:53.000 --> 07:55.900 And there is other for example, if you go to this 07:55.900 --> 08:01.700 website, RealClimate.com, which has a reputation for 08:01.700 --> 08:07.900 being a little bit on the liberal side of the issue, but 08:07.900 --> 08:11.700 nevertheless, a lot of scientists post recent results 08:11.700 --> 08:14.630 on RealClimate.com. 08:14.633 --> 08:16.333 And if you're going to do that, though, you should be 08:16.333 --> 08:20.173 evenhanded and go to some of these other anti websites, 08:20.167 --> 08:24.867 like, what are they called, ClimateSkeptic.com 08:24.867 --> 08:25.627 and things like that. 08:25.633 --> 08:28.173 So be sure you, if you're going to bookmark some of 08:28.167 --> 08:31.767 these things, try to get an even number of bookmarks on 08:31.767 --> 08:33.827 the two sides of the issue. 08:33.833 --> 08:36.573 You'll have to decide for yourself, in the end, which 08:36.567 --> 08:41.297 material you accept and which ones you reject. 08:41.300 --> 08:45.470 I'll try to help with that a little bit. 08:45.467 --> 08:48.497 So let's start out by looking at the carbon cycle, which is 08:48.500 --> 08:52.030 really one of the core issues in the debate. 08:52.033 --> 08:55.903 It has to do with what controls the carbon dioxide 08:55.900 --> 08:57.000 level in the atmosphere. 08:57.000 --> 09:01.700 We know the carbon dioxide is a powerful greenhouse gas. 09:01.700 --> 09:07.270 It has a linear molecular structure, but it can flap and 09:07.267 --> 09:11.997 it can vibrate in such a way to absorb and 09:12.000 --> 09:14.800 emit infrared radiation. 09:14.800 --> 09:17.630 So it's a powerful greenhouse gas. 09:17.633 --> 09:22.903 It's in part controlled by anthropogenic processes, so 09:22.900 --> 09:29.200 it's at the center of the whole debate. 09:29.200 --> 09:30.630 You have to know this. 09:30.633 --> 09:35.273 You have to know that when you burn something like coal, the 09:35.267 --> 09:42.227 chemical reaction looks like that, carbon plus oxygen. 09:42.233 --> 09:45.803 You oxidize the carbon to form CO2, and that's a gas that 09:45.800 --> 09:47.870 goes into the atmosphere. 09:47.867 --> 09:50.567 This comes from the atmosphere, and this would be 09:50.567 --> 09:55.267 coming from some buried deposit of coal. 09:55.267 --> 10:01.797 If you're burning methane, which is CH4, you combine that 10:01.800 --> 10:05.870 with oxygen and you get two by-products, water vapor and 10:05.867 --> 10:07.997 carbon dioxide. 10:08.000 --> 10:13.630 The water vapor we pretty much neglect, because it goes into 10:13.633 --> 10:17.833 the atmosphere as water vapor, but then instantly, it becomes 10:17.833 --> 10:20.873 part of the normal hydrologic cycle. 10:20.867 --> 10:23.867 And if you remember early in the course, we computed the 10:23.867 --> 10:27.767 average residence time for water vapor. 10:27.767 --> 10:29.167 Anybody remember what that was? 10:32.000 --> 10:34.030 Nine days, yeah, eight days, nine days. 10:34.033 --> 10:40.073 So in other words, it's cycled back in rain to the earth's 10:40.067 --> 10:43.967 surface or the ocean very, very quickly, and so it really 10:43.967 --> 10:47.197 plays no role in the greenhouse effect. 10:47.200 --> 10:48.200 Let me be careful. 10:48.200 --> 10:51.870 Water vapor is also a very powerful greenhouse gas. 10:51.867 --> 10:55.027 And because there's so much of it, it's actually in a sense 10:55.033 --> 10:57.303 the strongest of all the greenhouse gases. 10:57.300 --> 11:00.870 But it is controlled by the natural system. 11:00.867 --> 11:04.627 It doesn't matter how much we add into it. 11:04.633 --> 11:08.933 The level is not going to change for that reason. 11:08.933 --> 11:12.273 It's going to be controlled by the own, the internal 11:12.267 --> 11:14.127 processes within the atmosphere. 11:14.133 --> 11:16.773 Nothing we can do in adding water vapor is going to have 11:16.767 --> 11:19.927 any influence on changing the amount of water vapor in the 11:19.933 --> 11:21.433 atmosphere. 11:21.433 --> 11:25.733 So it's important to know that water vapor is one product, 11:25.733 --> 11:29.473 but in terms of what that does to climate, that particular 11:29.467 --> 11:32.297 piece is negligible in the sense 11:32.300 --> 11:34.070 that I have just described. 11:36.567 --> 11:39.767 Propane is another form of gas. 11:39.767 --> 11:43.467 It can be burned for heat, and the reaction-- 11:43.467 --> 11:45.267 the stoichiometry is a little bit different. 11:45.267 --> 11:47.097 I've tried to balance those reactions. 11:47.100 --> 11:49.900 I'm not a chemist, so you may want to check me. 11:49.900 --> 11:53.000 Add up the carbons, add up the oxygen, be sure everything 11:53.000 --> 11:57.500 adds up properly, and correct if I've gone wrong here. 11:57.500 --> 12:01.430 But basically water and CO2 again, and 12:01.433 --> 12:03.703 the same thing implies. 12:03.700 --> 12:04.970 The CO2 stays in the 12:04.967 --> 12:09.067 atmosphere, influencing climate. 12:09.067 --> 12:13.097 The water vapor quickly gets cycled into the natural 12:13.100 --> 12:14.470 hydrologic system. 12:14.467 --> 12:17.767 Another thing that's going on, we've talked about calcium 12:17.767 --> 12:22.767 carbonate in this course a couple of times because that 12:22.767 --> 12:25.567 excess calcium that we found in the Quinnipiac River that 12:25.567 --> 12:30.627 wasn't there in ocean water, we argued goes into making 12:30.633 --> 12:33.703 calcium carbonate in the oceans, shells, 12:33.700 --> 12:35.070 limestones, and so on. 12:35.067 --> 12:40.997 There's a lot of that around in the earth's climate system. 12:41.000 --> 12:44.770 If we take a little bit of that and heat it, we can 12:44.767 --> 12:49.397 separate it into the material that's used to make cement, 12:49.400 --> 12:52.570 but that releases CO2 as well. 12:52.567 --> 12:54.927 So there's another source of CO2. 12:54.933 --> 12:56.533 It's not quite as powerful as these. 12:56.533 --> 12:58.503 I'm going to show you some numbers in a minute. 12:58.500 --> 13:04.570 But that is another significant input of CO2, is 13:04.567 --> 13:09.027 the making of cement from natural calcium carbonate that 13:09.033 --> 13:13.633 was precipitated in the oceans by either living 13:13.633 --> 13:17.173 or non-living processes. 13:17.167 --> 13:18.927 Stop me if you have any questions on this. 13:22.400 --> 13:26.470 So when you burn fossil fuels then, you're putting carbon 13:26.467 --> 13:28.167 dioxide in the atmosphere. 13:28.167 --> 13:30.697 And that comes from carbon that's been stored in the 13:30.700 --> 13:35.870 earth, typically for 60 or 100 million years. 13:35.867 --> 13:39.467 Remember in the Cretaceous Period, way back when the 13:39.467 --> 13:43.997 dinosaurs were alive, that's when a lot of forests were 13:44.000 --> 13:47.970 being the earth was very warm during that period of time. 13:47.967 --> 13:50.527 You had tropical forests almost everywhere on the 13:50.533 --> 13:51.673 continents. 13:51.667 --> 13:54.827 Those trees would eventually fall. 13:54.833 --> 13:59.173 And the productivity was so high, instead of their rotting 13:59.167 --> 14:01.967 and putting that CO2 back in the atmosphere, they would be 14:01.967 --> 14:05.997 covered over by another and then another and another. 14:06.000 --> 14:09.770 So you ended up sequestering all of that carbon down in the 14:09.767 --> 14:13.827 crust of the earth where it's been sitting there for 60 or 14:13.833 --> 14:15.733 100 million years. 14:15.733 --> 14:21.473 And now we're suddenly pulling it back out and burning it and 14:21.467 --> 14:24.027 putting it back into the atmosphere. 14:24.033 --> 14:28.803 And in the oceans, too, you had algae growing, 14:28.800 --> 14:32.970 phytoplankton, that would sink to the bottom of the ocean, 14:32.967 --> 14:35.997 and instead of rotting and returning to the ocean system, 14:36.000 --> 14:37.730 they would get covered over. 14:37.733 --> 14:43.103 And today you have all of these oil deposits beneath the 14:43.100 --> 14:46.530 ocean bottom. 14:46.533 --> 14:48.333 And then we dig those up and we burn those, too. 14:48.333 --> 14:54.973 So both on the land and in the oceans, we are removing 14:54.967 --> 14:58.997 ancient, very ancient fossil carbon and burning it to put 14:59.000 --> 15:01.670 it back in the atmosphere. 15:01.667 --> 15:06.467 Now the natural, the modern biosphere is 15:06.467 --> 15:07.697 active in this as well. 15:11.433 --> 15:19.003 For example, trees remove a lot of carbon dioxide during 15:19.000 --> 15:22.200 the summer season when they're growing and use that to build 15:22.200 --> 15:24.200 their woody biomass. 15:24.200 --> 15:28.930 Remember, the trunk of a tree is about 1/5 15:28.933 --> 15:31.503 or one quarter carbon. 15:31.500 --> 15:33.000 Well, where did that carbon come from? 15:33.000 --> 15:34.530 It didn't come from the soil. 15:34.533 --> 15:38.103 From the soil, the tree is getting water and it's getting 15:38.100 --> 15:42.500 nutrients, like nitrogens and phosphorus, but almost all of 15:42.500 --> 15:46.330 the carbon to build a tree trunk is coming from the 15:46.333 --> 15:47.573 atmosphere. 15:49.333 --> 15:54.903 I mentioned in another context that I did a project down on a 15:54.900 --> 15:58.030 small island in the Caribbean last spring. 15:58.033 --> 16:00.673 And we were flying an aircraft around the island. 16:00.667 --> 16:03.327 One of the sensors we had on the airplane was a carbon 16:03.333 --> 16:06.403 dioxide sensor so we could measure how much carbon 16:06.400 --> 16:09.530 dioxide was in the atmosphere upstream of the island, over 16:09.533 --> 16:12.033 the island, and downstream of the island. 16:12.033 --> 16:14.373 The island was forested. 16:14.367 --> 16:16.997 It's the island of Dominica, one of the few Caribbean 16:17.000 --> 16:20.830 islands that still has its original forest. And when we 16:20.833 --> 16:25.273 flew downstream of the island, across the wake of the island, 16:25.267 --> 16:31.497 we found a slight deficit in carbon dioxide. 16:31.500 --> 16:34.530 In other words, the air that had come from upstream and 16:34.533 --> 16:38.533 passed over the island's forests had lost a little bit 16:38.533 --> 16:41.903 of carbon dioxide to those trees, and we found that 16:41.900 --> 16:43.730 deficit downwind. 16:43.733 --> 16:45.733 Now, this has been well known. 16:45.733 --> 16:48.173 You can measure this in lots of other ways. 16:48.167 --> 16:52.897 But this is yet another way to convince yourself that the 16:52.900 --> 16:57.370 forests are actively removing carbon dioxide from the 16:57.367 --> 17:02.097 atmosphere all the time that they're growing. 17:02.100 --> 17:04.070 But then, they recycle some of that. 17:04.067 --> 17:08.097 For example, the material in leaves that falls to earth at 17:08.100 --> 17:14.100 this time of year then rots and respires over the winter 17:14.100 --> 17:17.100 season to put that little bit of carbon back in. 17:17.100 --> 17:20.930 Now it still has its woody biomass, which is most of it, 17:20.933 --> 17:25.203 but a little bit goes back into the atmosphere, which 17:25.200 --> 17:28.570 gives that little bit of wiggle in the Keeling curve 17:28.567 --> 17:32.427 that you were studying in your Time Series Lab. 17:32.433 --> 17:37.003 So I want to emphasize that the biosphere is a very active 17:37.000 --> 17:40.300 player in this carbon cycle. 17:40.300 --> 17:45.570 Certainly on the long term, but then on the modern time 17:45.567 --> 17:48.427 scales as well. 17:48.433 --> 17:50.973 Any questions there? 17:50.967 --> 17:51.267 Yeah. 17:51.267 --> 17:54.197 STUDENT: Does the carbon that's sequestered in the 17:54.200 --> 17:57.070 wood, when, like, the wood from the tree rots, is that 17:57.067 --> 17:59.767 also, is that rereleased in the atmosphere? 17:59.767 --> 18:00.297 PROFESSOR: That's right. 18:00.300 --> 18:05.930 So if a tree, if a modern tree today does fall and then you 18:05.933 --> 18:08.473 watch it over some years, it rots and kind of disappears 18:08.467 --> 18:09.167 into the Earth. 18:09.167 --> 18:12.027 That carbon ends up back in the atmosphere. 18:12.033 --> 18:15.733 A little bit may be left in the soil as organic carbon, 18:15.733 --> 18:18.333 but then over a longer period of time, maybe ten or twenty 18:18.333 --> 18:21.073 years, that too will go back to the atmosphere. 18:21.067 --> 18:23.967 So there are few places on earth, however, where you're 18:23.967 --> 18:26.267 getting this sequestration, where you're getting things 18:26.267 --> 18:29.067 falling on top of it faster than it can rot. 18:29.067 --> 18:32.927 But I would say, for example, in most of these New England 18:32.933 --> 18:38.633 forests, most of the ancient tree material is going back 18:38.633 --> 18:39.873 into the atmosphere. 18:44.133 --> 18:47.973 Well, in fact, that's one of the problems with this idea of 18:47.967 --> 18:50.867 solving the global warming problem by 18:50.867 --> 18:53.467 planting lots of trees. 18:53.467 --> 18:57.497 Because what that will do in the short run, indeed, it will 18:57.500 --> 19:00.500 draw extra CO2 from the atmosphere and store it in the 19:00.500 --> 19:02.230 biomass of the tree. 19:02.233 --> 19:06.533 But a typical tree of the species you're familiar with, 19:06.533 --> 19:11.633 both conifers and deciduous, typically have lifetimes of 60 19:11.633 --> 19:14.333 to 80 to 100 years. 19:14.333 --> 19:17.233 And then they will fall and they'll rot and the material 19:17.233 --> 19:17.703 will go back. 19:17.700 --> 19:23.770 So it is a temporary fix, perhaps, to reducing carbon 19:23.767 --> 19:26.667 dioxide buildup in the atmosphere, but by no means is 19:26.667 --> 19:30.167 it permanent because of the short turnover time of trees 19:30.167 --> 19:38.627 in the forest. 19:38.633 --> 19:43.733 So this diagram will summarize some of this. 19:43.733 --> 19:45.973 And there are two types of numbers on here. 19:45.967 --> 19:51.027 There are, for example, storage. 19:51.033 --> 19:53.373 These numbers are in boxes. 19:53.367 --> 19:58.997 And those units would be in gigatons of carbon. 19:59.000 --> 20:03.000 And then the arrows, which are the fluxes, going between 20:03.000 --> 20:05.800 these reservoirs, and those units are in 20:05.800 --> 20:08.800 gigatons per year of carbon. 20:08.800 --> 20:12.100 So for example, in the atmosphere typically and this 20:12.100 --> 20:15.530 is a calculation you could do but we have about 20:15.533 --> 20:19.303 760 gigatons of carbon. 20:19.300 --> 20:22.130 Remember, that's the C in the CO2. 20:22.133 --> 20:26.503 If you want to know what the mass of the carbon dioxide is, 20:26.500 --> 20:30.400 be sure to include the mass of the two oxygens that are on 20:30.400 --> 20:31.030 the carbon dioxide. 20:31.033 --> 20:34.673 This is just the carbon in the carbon dioxide. 20:37.933 --> 20:42.173 For example, let's look at how it interacts with terrestrial 20:42.167 --> 20:45.197 production, the one I've just been talking about, of trees 20:45.200 --> 20:51.600 and other biomass on the continents. 20:51.600 --> 20:57.430 So about 60 gigatons per year is put in and about 62 is 20:57.433 --> 21:01.373 taken out every year. 21:01.367 --> 21:05.167 So it's a very dynamic reservoir. 21:07.800 --> 21:09.970 The difference, however, is rather small. 21:09.967 --> 21:13.327 There's an excess going from the atmosphere into the 21:13.333 --> 21:18.433 biosphere of about two or three gigatons per year. 21:18.433 --> 21:24.573 It's this big exchange, the 60 and the 60 that's responsible 21:24.567 --> 21:29.897 for that wiggle in the Keeling curve. 21:29.900 --> 21:32.830 And it's the annual difference, that two or three 21:32.833 --> 21:37.103 units, that's responsible for that trend 21:37.100 --> 21:37.970 in the Keeling curve. 21:37.967 --> 21:39.967 I'll show you that Keeling curve in a moment. 21:39.967 --> 21:41.827 You've seen it before, but that's a 21:41.833 --> 21:43.933 central part of our argument. 21:43.933 --> 21:46.933 The oceans are somewhat similar, so there's biological 21:46.933 --> 21:49.233 activity taking place in the oceans. 21:49.233 --> 21:51.533 We've talked about that. 21:51.533 --> 21:54.173 We've seen that it's confined to certain parts of the ocean 21:54.167 --> 21:57.127 where you can get nutrients coming up into 21:57.133 --> 21:59.333 the euphotic zone. 21:59.333 --> 22:03.433 The numbers are even bigger than for the terrestrial 22:03.433 --> 22:07.733 biomass, but they too have a similar characteristic. 22:07.733 --> 22:15.433 Large instantaneous cycling, but over a year, only about 22:15.433 --> 22:19.473 two gigatons, and going in the same direction, going from the 22:19.467 --> 22:23.067 atmosphere into the ocean. 22:23.067 --> 22:28.227 There's the cement production, about 6.5. 22:28.233 --> 22:31.803 And there's some other things here. 22:31.800 --> 22:33.530 This is one to look at. 22:33.533 --> 22:37.773 The amount of fossil fuel reserves still in the crust of 22:37.767 --> 22:44.067 the earth is 4,000 units of gigatons. 22:44.067 --> 22:48.667 So you can imagine if you burn the rest of that, what that 22:48.667 --> 22:50.627 would do to that number. 22:50.633 --> 22:56.873 It would be 4,760, unless, you probably should take into 22:56.867 --> 22:58.367 account this removal as well. 22:58.367 --> 23:02.997 But it would be a huge number if one were to burn all of the 23:03.000 --> 23:06.430 fossil fuel reserves and put that carbon dioxide in the 23:06.433 --> 23:08.333 atmosphere. 23:08.333 --> 23:12.273 Questions on this busy diagram here? 23:15.267 --> 23:18.927 I'm going to use these numbers to do something we did early 23:18.933 --> 23:20.803 in the course. 23:20.800 --> 23:25.170 I want to compute residence times, because sometimes 23:25.167 --> 23:28.097 that's helpful to get a physical feeling for the way 23:28.100 --> 23:29.770 these reservoirs work. 23:29.767 --> 23:33.627 So I'm going to be using the atmosphere as the reservoir, 23:33.633 --> 23:36.303 and then either these large monthly-- 23:36.300 --> 23:42.500 month by month fluxes or the smaller annual total fluxes to 23:42.500 --> 23:46.430 compute the residence time. 23:46.433 --> 23:48.373 So residence time is for CO2. 23:48.367 --> 23:51.997 On the month by month, on the seasonal basis, I'll take that 23:52.000 --> 23:57.630 760 gigatons and divide it here I'm just using the 23:57.633 --> 23:59.733 atmospheric number. 23:59.733 --> 24:03.003 I probably should have summed up the atmosphere and the 24:03.000 --> 24:06.130 ocean number, but I'm just using the atmospheric number. 24:06.133 --> 24:11.673 And when I do that, I get a pretty short time, 13 years. 24:11.667 --> 24:15.367 I get even a shorter time if I use, if I put the ocean 24:15.367 --> 24:17.197 numbers in there as well. 24:17.200 --> 24:20.030 So there's this rapid cycling that's taking place. 24:20.033 --> 24:23.473 But in a way it's kind of irrelevant because it cancels 24:23.467 --> 24:25.897 itself out at the end of the year. 24:25.900 --> 24:27.570 So I'm not going to put a great deal of 24:27.567 --> 24:29.867 stock in this number. 24:29.867 --> 24:31.227 It is a residence time. 24:31.233 --> 24:34.833 It is computed in the proper way, but the fluxes we're 24:34.833 --> 24:38.773 using are balanced over the course of a year. 24:38.767 --> 24:41.797 And so, the numbers is not of great use. 24:41.800 --> 24:46.500 On the longer term, I'll take 760 and divide it by one of 24:46.500 --> 24:47.670 those imbalances. 24:47.667 --> 24:51.497 Now again, I've used the imbalance for just the 24:51.500 --> 24:52.570 terrestrial biomass. 24:52.567 --> 24:55.797 Maybe I could have changed that to four by adding up two 24:55.800 --> 24:58.130 here and two there. 24:58.133 --> 24:59.433 But you can see what that will do to the 24:59.433 --> 25:01.903 numbers pretty easily. 25:01.900 --> 25:04.230 I've just used two gigatons per year here. 25:04.233 --> 25:05.573 And I got 380 years. 25:05.567 --> 25:07.927 Now this is a more useful number because this is 25:07.933 --> 25:12.003 actually how long a carbon dioxide molecule is likely to 25:12.000 --> 25:20.030 stay in the atmosphere before it's returned into one of the 25:20.033 --> 25:22.473 biosphere sinks. 25:22.467 --> 25:25.527 So when we're trying to predict the future of carbon 25:25.533 --> 25:29.673 dioxide concentrations in the atmosphere, we have to realize 25:29.667 --> 25:32.897 that it stays there for quite a long period of time in spite 25:32.900 --> 25:35.600 of these fluxes back and forth between the 25:35.600 --> 25:40.130 atmosphere and the biosphere. 25:40.133 --> 25:43.003 Questions there? 25:43.000 --> 25:49.930 So from economic data, we can get a pretty good handle on 25:49.933 --> 25:52.003 the carbon dioxide emissions that have taken 25:52.000 --> 25:55.600 place in past years. 25:55.600 --> 25:57.600 And here you see various curves. 25:57.600 --> 26:00.370 The black is the total, where all the others 26:00.367 --> 26:03.297 have been summed up. 26:03.300 --> 26:07.570 The two largest independent sources have been coal, in the 26:07.567 --> 26:12.227 green, and petroleum, in the dark blue. 26:12.233 --> 26:17.473 Each of those is about six billion metric tons 26:17.467 --> 26:19.327 of carbon per year. 26:19.333 --> 26:20.503 So this is not accumulated. 26:20.500 --> 26:23.930 This is what's emitted each year. 26:23.933 --> 26:26.673 And of course, that number has been growing since the 26:26.667 --> 26:30.797 beginning of the Industrial Revolution, where we began to 26:30.800 --> 26:33.800 use fossil fuels for steam engines and then for 26:33.800 --> 26:38.400 electricity generation and transportation and so on. 26:38.400 --> 26:41.270 Natural gas is growing rapidly now. 26:41.267 --> 26:44.797 Cement production is lower but still growing. 26:44.800 --> 26:48.600 And a small amount is the gas flaring that you see in some 26:48.600 --> 26:52.030 of these oils fields and gas fields, just burning off 26:52.033 --> 26:56.473 excess gas. 27:00.733 --> 27:02.173 So it's rising very rapidly. 27:02.167 --> 27:06.127 No sign at all of any decrease in this. 27:06.133 --> 27:10.233 There have been some temporary for example, in the 1970s 27:10.233 --> 27:13.373 there was a kind of an oil crisis, and you see a tiny 27:13.367 --> 27:14.597 little bit of a dip there. 27:14.600 --> 27:16.970 But generally it's just a curve that's 27:16.967 --> 27:19.027 rising very, very steeply. 27:19.033 --> 27:22.773 And this is the rate at which we are putting CO2 into the 27:22.767 --> 27:23.027 atmosphere. 27:23.033 --> 27:26.803 This is not the accumulated amount. 27:26.800 --> 27:28.070 Questions there? 27:31.367 --> 27:37.167 So we've been monitoring carbon dioxide concentration. 27:37.167 --> 27:40.467 The first measurement started on the Mauna Loa Observatory, 27:40.467 --> 27:44.197 up on the Big Island of Hawaii, up on top of the high 27:44.200 --> 27:45.500 volcanic peak there. 27:45.500 --> 27:48.670 There's a picture of the laboratory. 27:48.667 --> 27:50.967 And I know you've seen this before, and now I know that 27:50.967 --> 27:53.227 you're familiar with it because you're working with it 27:53.233 --> 27:54.533 in your lab. 27:54.533 --> 27:58.333 This is exactly the same data set that I gave you to work on 27:58.333 --> 28:01.133 in Lab Number Four. 28:01.133 --> 28:06.203 And the features here, of course, plotting the units are 28:06.200 --> 28:09.570 in parts per million by volume, not by mass. 28:09.567 --> 28:10.997 So it's by molecule. 28:11.000 --> 28:17.000 It's a ratio, for every for every million molecules of 28:17.000 --> 28:20.470 air, there are 320-- 28:20.467 --> 28:22.167 molecules of carbon dioxide. 28:22.167 --> 28:27.097 That's the way you would read that number. 28:27.100 --> 28:30.670 There's an annual oscillation that has to do with the mostly 28:30.667 --> 28:34.527 the Northern Hemisphere biomass drawing carbon dioxide 28:34.533 --> 28:39.503 in the summer and releasing it in the winter. 28:39.500 --> 28:42.970 And then on top of that, you've got a trend, which you 28:42.967 --> 28:45.597 can see from the smoothed line here. 28:45.600 --> 28:48.870 And that slope has been increasing. 28:48.867 --> 28:54.767 And of course, the increase in that slope is because of this, 28:54.767 --> 28:57.527 the rate at which we've been putting CO2 into the 28:57.533 --> 28:58.773 atmosphere has been increasing. 28:58.767 --> 29:04.497 So that rate of change of carbon dioxide concentration 29:04.500 --> 29:06.300 has been increasing as well. 29:12.500 --> 29:14.870 So any questions on the it's called the Keeling curve 29:14.867 --> 29:18.167 because the scientist that got this started back in the '50s 29:18.167 --> 29:19.797 was Charles Keeling. 29:19.800 --> 29:21.930 He passed away a couple of years ago, but he's one of the 29:21.933 --> 29:24.073 great heroes in climate science. 29:24.067 --> 29:28.827 To have the forethought to get an accurate measurement of 29:28.833 --> 29:34.203 this type going early enough, so by the time we got to the 29:34.200 --> 29:39.600 year 2000, we had a good record and the beginning of a 29:39.600 --> 29:42.530 clear understanding of what's causing this rise. 29:47.133 --> 29:51.803 Now here's another diagram from the IPCC report that's a 29:51.800 --> 29:54.370 really important one. 29:54.367 --> 29:56.527 You can read through the legend, but I put these little 29:56.533 --> 29:58.573 labels up here as well. 29:58.567 --> 30:04.467 This is the annual change in carbon dioxide concentration 30:04.467 --> 30:07.467 in parts per million by volume. 30:07.467 --> 30:12.997 And the bars are the actual annual change. 30:13.000 --> 30:16.100 And if that curve looks familiar, if those bar graph 30:16.100 --> 30:19.970 looks familiar, it's because you computed that very same 30:19.967 --> 30:22.197 quantity in your lab exercise. 30:22.200 --> 30:25.670 So you're familiar with how to do this. 30:25.667 --> 30:30.497 And the increase started out at about 0.5 parts per million 30:30.500 --> 30:36.170 change per year and is now about three times that amount 30:36.167 --> 30:38.867 of increase per year. 30:38.867 --> 30:44.797 Up above is the expected change from emissions if all 30:44.800 --> 30:50.600 the CO2 we're putting in, namely that, remained in the 30:50.600 --> 30:56.800 atmosphere, and it's about twice what we're actually 30:56.800 --> 31:00.230 finding as the increase every year in the atmosphere. 31:00.233 --> 31:02.233 So here's what we've learned from this. 31:02.233 --> 31:09.233 The biomass is taking in about half of that extra that we are 31:09.233 --> 31:11.503 emitting into the atmosphere. 31:11.500 --> 31:13.670 That's rather remarkable. 31:13.667 --> 31:18.967 The reason seems to be that carbon dioxide is in many 31:18.967 --> 31:25.067 places around the earth and the ocean a limiting quantity 31:25.067 --> 31:29.567 for photosynthesis. 31:29.567 --> 31:33.467 So that when you increase the concentration of CO2, you 31:33.467 --> 31:35.967 increase the rate at which plants grow. 31:35.967 --> 31:39.727 It's called CO2 fertilization. 31:39.733 --> 31:44.533 So as CO2 has increased, the plants have tried to take some 31:44.533 --> 31:47.473 of that excess back out. 31:47.467 --> 31:49.227 They take about half of it out. 31:49.233 --> 31:52.273 There's some speculation about whether they will continue to 31:52.267 --> 31:54.927 be able to take out half, because they need other 31:54.933 --> 31:55.773 nutrients as well. 31:55.767 --> 31:58.997 They need phosphorus and nitrogen, they need water, if 31:59.000 --> 32:00.900 they're plants growing on land. 32:00.900 --> 32:04.070 And it might be that as these other ingredients become 32:04.067 --> 32:09.497 limiting, the biosphere will no longer be able to do this 32:09.500 --> 32:12.170 for us, and these numbers could creep up. 32:12.167 --> 32:15.397 As this one increases, these might actually creep up 32:15.400 --> 32:19.430 eventually to become more equal to the amount that we're 32:19.433 --> 32:23.103 putting in every year. 32:23.100 --> 32:24.330 Questions on that? 32:27.467 --> 32:30.527 So it's interesting to look at this from a historical 32:30.533 --> 32:32.573 perspective because what we're doing now is so 32:32.567 --> 32:35.027 unusual and so rapid. 32:35.033 --> 32:37.173 So if we go back 10,000 years, this 32:37.167 --> 32:38.927 roughly covers the Holocene. 32:41.800 --> 32:44.330 Here is carbon dioxide concentration in parts per 32:44.333 --> 32:45.833 million by volume. 32:45.833 --> 32:49.703 And of course, the Keeling curve is the little red part 32:49.700 --> 32:51.500 here, it's just that little part. 32:51.500 --> 32:55.100 Before that time, we get that data from the ice cores, the 32:55.100 --> 32:59.730 little vesicles, the little bubbles in the ice cores give 32:59.733 --> 33:01.233 us the data prior to that time. 33:01.233 --> 33:05.703 But it was pretty flat through the Holocene, with a value of 33:05.700 --> 33:11.770 about 270 or 280 or 290 parts per million. 33:11.767 --> 33:15.067 And then in the Industrial Revolution, on this time 33:15.067 --> 33:18.127 scale, it shoots up almost vertically. 33:18.133 --> 33:21.203 If you blow that up, blow that time scale up, and show it 33:21.200 --> 33:25.270 here going back to 1800, it was slow at first and then has 33:25.267 --> 33:29.027 become more and more rapid, as we discussed in the previous 33:29.033 --> 33:34.073 couple of diagrams because the rate of carbon dioxide 33:34.067 --> 33:35.497 emissions has increased so strongly. 33:38.633 --> 33:41.333 We can go back even further in geologic time. 33:44.267 --> 33:46.697 And you've seen this kind of thing before. 33:46.700 --> 33:55.100 This is an ice core showing carbon dioxide concentrations. 33:55.100 --> 34:01.100 Here we are in the Holocene, right about here, with 34:01.100 --> 34:05.870 preindustrial levels around 270 or 280. 34:05.867 --> 34:09.067 But just prior to that, 15,000, 20,000 years ago at 34:09.067 --> 34:11.667 the end of last Ice Age, the values were down about 200 34:11.667 --> 34:15.897 hundred, and then oscillated around those lower levels for 34:15.900 --> 34:18.800 at least 400,000 years. 34:18.800 --> 34:21.730 It's hard to put this recent data even on the same scale 34:21.733 --> 34:25.773 because it plots as almost a vertical line. 34:25.767 --> 34:28.327 So the rate at which we're putting CO2 in and changing 34:28.333 --> 34:33.033 atmospheric composition is far higher than anything one could 34:33.033 --> 34:36.603 diagnose from previous geologic eras. 34:40.267 --> 34:44.467 There's another piece to this argument that I find kind of 34:44.467 --> 34:45.827 interesting. 34:45.833 --> 34:48.973 It has to do with the isotopes of carbon. 34:48.967 --> 34:54.067 Carbon, like hydrogen and oxygen that we spoke about 34:54.067 --> 34:59.327 earlier in the week, come as a primary element and then 34:59.333 --> 35:02.433 various heavier isotopes. 35:02.433 --> 35:05.203 And most carbon is Carbon 12, but there's a 35:05.200 --> 35:06.570 Carbon 13 as well. 35:06.567 --> 35:09.397 It's a stable isotope of carbon. 35:09.400 --> 35:15.500 And the buried fossil fuel happens to be depleted in 35:15.500 --> 35:20.630 Carbon 13 relative to the normal Carbon 12. 35:20.633 --> 35:27.273 So when we dig up this fossil fuel and burn it, we're now 35:27.267 --> 35:32.667 putting a lot of the dominantly we're putting in 35:32.667 --> 35:37.727 the Carbon 12 into the atmosphere, which takes 35:37.733 --> 35:42.403 whatever fraction we started with, Carbon 13 to Carbon 12 35:42.400 --> 35:47.370 in the atmosphere, and making the overall carbon in the 35:47.367 --> 35:50.427 atmosphere lighter, because we're mixing in more of the 35:50.433 --> 35:54.833 light carbon from the fossil fuel burning. 35:54.833 --> 36:01.003 And indeed, if you plot Delta Carbon 13, using the same kind 36:01.000 --> 36:06.570 of Delta notation we used before, from 1977 to 2002, 36:06.567 --> 36:08.027 it's a decreasing number. 36:08.033 --> 36:10.133 This is data from the South Pole. 36:10.133 --> 36:13.303 Here's some data from Mauna Loa. 36:13.300 --> 36:17.200 And it shows also a decreasing trend. 36:17.200 --> 36:21.870 So some would argue, how do we know that new carbon dioxide 36:21.867 --> 36:24.027 in the atmosphere is coming from the 36:24.033 --> 36:26.873 burning of fossil fuels? 36:26.867 --> 36:29.497 Well, one argument would have been, well we're putting twice 36:29.500 --> 36:31.500 that much in the atmosphere. 36:31.500 --> 36:33.000 It makes sense that at least half of 36:33.000 --> 36:34.900 that would stick around. 36:34.900 --> 36:36.330 It's a pretty powerful argument. 36:36.333 --> 36:38.673 But maybe this is even a more powerful argument, because 36:38.667 --> 36:40.727 that carbon we're putting it has a 36:40.733 --> 36:43.403 certain isotopic signature. 36:43.400 --> 36:46.770 And now we see that signature showing up in 36:46.767 --> 36:49.297 the atmospheric carbon. 36:49.300 --> 36:55.200 So it's another argument for the case that the burning of 36:55.200 --> 36:58.600 fossil fuels is what's leading to that increase in carbon 36:58.600 --> 37:01.630 dioxide in the atmosphere. 37:01.633 --> 37:02.303 Questions on that. 37:02.300 --> 37:02.630 Yes? 37:02.633 --> 37:05.473 STUDENT: Do we know why it's depleted 37:05.467 --> 37:07.367 in the heavier isotope? 37:07.367 --> 37:09.797 PROFESSOR: Yeah, it has to do with the plants that 37:09.800 --> 37:12.430 originally took in that carbon. 37:12.433 --> 37:16.673 So when a plant grows, as I mentioned, it takes carbon in 37:16.667 --> 37:19.097 from the atmosphere to build its biomass. 37:19.100 --> 37:23.200 It actually prefers the light isotope 37:23.200 --> 37:25.200 over the heavy isotope. 37:25.200 --> 37:28.630 So when those plants, way back, 100 million years ago, 37:28.633 --> 37:30.733 were growing their biomass, they were doing it 37:30.733 --> 37:33.233 preferentially out of Carbon 12. 37:33.233 --> 37:36.933 And then when they got buried, that left behind a lot of the 37:36.933 --> 37:38.973 Carbon 13 in the atmosphere. 37:38.967 --> 37:40.467 They buried a lot of the Carbon 12. 37:40.467 --> 37:43.467 Now we're reversing that, putting the Carbon 12 back in 37:43.467 --> 37:44.027 the atmosphere. 37:44.033 --> 37:48.903 So it has to do it how plants draw in CO2 into their leaves 37:48.900 --> 37:51.070 and then use that to build their biomass. 37:54.233 --> 37:55.473 Good question. 37:57.533 --> 38:01.473 So let's conclude, then, our brief discussion 38:01.467 --> 38:02.767 of the carbon cycle. 38:02.767 --> 38:05.967 Fossil fuel burning is quickly returning to the atmosphere 38:05.967 --> 38:09.797 carbon stored for millions of years in crustal reservoirs. 38:14.000 --> 38:17.730 About half of the emitted CO2 stays in the atmosphere, and 38:17.733 --> 38:20.303 we estimate it'll stay there for at least a few hundred 38:20.300 --> 38:25.230 years, given the cycling rate between the biosphere and the 38:25.233 --> 38:26.303 atmosphere. 38:26.300 --> 38:31.500 The CO2 emission rate has increased with time since the 38:31.500 --> 38:33.300 beginning of the Industrial Revolution. 38:36.133 --> 38:39.373 And the current CO2 concentration, which is 38:39.367 --> 38:43.067 approximately 395 parts per million by volume, is the 38:43.067 --> 38:44.597 highest in several million years. 38:44.600 --> 38:47.270 Let me be careful of what I say here. 38:47.267 --> 38:50.467 If I go back to this diagram, which shows the last 400,000 38:50.467 --> 38:55.797 years, clearly, now that we're up at 390 or 395, that's way 38:55.800 --> 38:59.530 higher than anything we've had during the Ice Ages. 38:59.533 --> 39:05.073 Yet if you go back way earlier, say 50, 60, 100 39:05.067 --> 39:08.627 million years ago, you'll find periods in the earth's history 39:08.633 --> 39:10.873 where the carbon dioxide concentration in the 39:10.867 --> 39:15.127 atmosphere was actually much higher than it is even today. 39:15.133 --> 39:17.833 So I don't want to make a blanket statement saying that 39:17.833 --> 39:20.403 it's as high as it's ever been. 39:20.400 --> 39:26.500 So instead I have said, it is the highest it's been in 39:26.500 --> 39:30.000 several million years. 39:30.000 --> 39:35.070 But again, this is the kind of an argument that arises. 39:35.067 --> 39:38.867 Someone will say, well, yes, we're putting a lot of CO2 in 39:38.867 --> 39:44.027 the atmosphere, but it hasn't by any means reached an 39:44.033 --> 39:45.473 unprecedented level. 39:45.467 --> 39:49.497 There have been periods in the ancient earth history where 39:49.500 --> 39:51.270 carbon dioxide concentrations have been 39:51.267 --> 39:53.767 much higher than this. 39:53.767 --> 39:57.627 So it all depends on what you want to use for your reference 39:57.633 --> 40:02.573 timeframe as to what kind of a statement you 40:02.567 --> 40:03.467 make in this regard. 40:03.467 --> 40:08.927 So be very careful about that not to overstate the 40:08.933 --> 40:15.003 uniqueness of the current carbon dioxide concentration. 40:15.000 --> 40:17.270 It's probably safe to say there's never been a time in 40:17.267 --> 40:21.967 Earth's history where the CO2 is increasing as rapidly as it 40:21.967 --> 40:25.767 is today, where the rate has been as large. 40:25.767 --> 40:28.797 But in terms of the absolute amount, the record we're 40:28.800 --> 40:32.800 setting now is only the record for the last few million 40:32.800 --> 40:36.430 years, not for--certainly not for all of Earth's history. 40:41.733 --> 40:45.473 So we've got a couple minutes to begin the next section, 40:45.467 --> 40:50.197 which is the Holocene as a reference time period. 40:50.200 --> 40:53.770 And I wanted you to be aware of these particular often 40:53.767 --> 40:55.997 discussed dates. 40:58.667 --> 41:04.627 The retreat of the last large ice sheets was occurring 41:04.633 --> 41:09.433 around 11,000 years before present. 41:09.433 --> 41:11.173 That's right when the ice was in the 41:11.167 --> 41:13.797 process of melting back. 41:17.367 --> 41:20.527 There was a warm period that followed that called the 41:20.533 --> 41:25.033 Holocene Optimum about seven to eight thousand years ago. 41:28.867 --> 41:32.067 That comes into the argument when one is trying to find out 41:32.067 --> 41:36.397 whether the current warm climate is 41:36.400 --> 41:38.700 unique even in the Holocene. 41:38.700 --> 41:42.730 In other words, is our current climate cooler or warmer than 41:42.733 --> 41:46.733 this so-called Holocene Optimum. 41:46.733 --> 41:50.703 Much more recently, the Medieval Warm Period, which 41:50.700 --> 41:55.570 was roughly 1000 A.D., is another 41:55.567 --> 41:56.627 important reference point. 41:56.633 --> 41:59.503 This, by the way, is the period when the Vikings 41:59.500 --> 42:01.500 colonized Greenland. 42:01.500 --> 42:07.470 There was a warm period when they could grow crops in the 42:07.467 --> 42:09.727 coastal regions of Greenland. 42:09.733 --> 42:15.433 Then came the Little Ice Age from 1400 to 1800 A.D. I'll 42:15.433 --> 42:19.173 say a bit more about that. 42:19.167 --> 42:20.997 And then we get into this period, as you're seeing in 42:21.000 --> 42:26.030 your data analysis in the lab, of a more rapid climate change 42:26.033 --> 42:28.333 over the last hundred years or so. 42:28.333 --> 42:30.873 So at the very minimum, be aware of these. 42:30.867 --> 42:34.867 And I'll point these out to you as we look at various 42:34.867 --> 42:37.797 historical reconstructions of temperature. 42:37.800 --> 42:45.570 For example, this one goes back 12,000 years, so that's 42:45.567 --> 42:47.797 covering most of the Holocene. 42:47.800 --> 42:50.630 And there's lots of different data sets represented. 42:50.633 --> 42:53.603 The black curve is an average from a number of different 42:53.600 --> 42:54.900 proxy data sets. 42:54.900 --> 42:57.900 A proxy data set is where you haven't measured temperature 42:57.900 --> 43:01.670 directly with a thermometer, but you're keeping track of 43:01.667 --> 43:04.827 something that you think depends on temperature. 43:04.833 --> 43:06.003 Maybe it's lake levels. 43:06.000 --> 43:07.330 Maybe it's isotopes. 43:07.333 --> 43:10.703 Maybe it's there's a lot of different things you can use. 43:10.700 --> 43:15.470 They're all called climate proxies, and they show a lot 43:15.467 --> 43:18.067 of variability when you average them together they 43:18.067 --> 43:20.467 show some trend. 43:20.467 --> 43:22.997 You see a rapid warming coming out of the last Ice Age. 43:23.000 --> 43:25.170 Then you see this climatic optimum, what I called the 43:25.167 --> 43:27.067 Holocene Optimum, right here. 43:27.067 --> 43:28.667 And then it cooled off a little bit. 43:28.667 --> 43:30.827 And then there's some wiggles near the end that we'll talk 43:30.833 --> 43:34.673 about in just a minute. 43:34.667 --> 43:37.497 And again these are plotted as temperature anomalies. 43:37.500 --> 43:41.500 They've chosen some period of time as a reference to compute 43:41.500 --> 43:43.170 the temperature anomaly. 43:45.867 --> 43:48.567 This shows the last thousand years or so. 43:48.567 --> 43:51.597 So we're looking at a more recent period of time. 43:51.600 --> 43:56.470 And this is from the IPCC report, I think. 43:56.467 --> 43:58.067 Now I've forgotten which is which. 43:58.067 --> 44:03.927 Anyways, these are two different authors' graphs 44:03.933 --> 44:08.173 describing the Northern Hemisphere temperature 44:08.167 --> 44:10.997 reconstructions for the last thousand years. 44:11.000 --> 44:13.500 And they look a lot alike, but I wanted to point out some 44:13.500 --> 44:16.930 differences, because it's on these differences that many 44:16.933 --> 44:19.673 arguments will be built. 44:19.667 --> 44:22.467 For example, this author has shown a lot of 44:22.467 --> 44:25.867 the different proxies. 44:25.867 --> 44:28.867 And if you average those together, you'd probably get 44:28.867 --> 44:31.897 something that rose a little bit in this period of time, 44:31.900 --> 44:33.730 then sank a little bit more. 44:33.733 --> 44:36.873 Here's the Little Ice Age, a little cooler in this period 44:36.867 --> 44:41.897 of time, and then you get the rapid rise and rise again. 44:41.900 --> 44:47.800 This author has suppressed all the different proxies and 44:47.800 --> 44:50.870 instead just shown the standard 44:50.867 --> 44:54.197 deviation in the data. 44:54.200 --> 44:57.570 I think it's like the two sigma and the one sigma. 44:57.567 --> 45:00.697 And while he does show a little bit of a rise, the way 45:00.700 --> 45:03.400 he's plotted it gives you the idea that this is more of a 45:03.400 --> 45:08.030 straight line, maybe slightly decreasing, and then rising 45:08.033 --> 45:08.803 rapidly at the end. 45:08.800 --> 45:15.270 By the way, this is the famous hockey stick diagram. 45:15.267 --> 45:20.967 Because that shape looks a bit like a hockey stick. 45:20.967 --> 45:23.927 It used to be, twenty years ago, when you Google hockey 45:23.933 --> 45:30.503 stick, all you would get would be websites about hockey. 45:30.500 --> 45:32.900 Now when you Google hockey stick, you get hockey and you 45:32.900 --> 45:36.800 get climate change because of all the controversy over this. 45:36.800 --> 45:40.230 The author this original diagram, Mike Mann, was a PhD 45:40.233 --> 45:41.003 from our department. 45:41.000 --> 45:42.870 In fact, I sat on his committee. 45:42.867 --> 45:44.967 This wasn't in his thesis, it was in following work. 45:44.967 --> 45:48.227 But I've tried to follow the arguments. 45:48.233 --> 45:53.333 The poor guy has been badgered by the right wing anti-global 45:53.333 --> 45:55.473 warming crowd incessantly. 45:55.467 --> 45:58.527 Because the implication of this diagram is that what's 45:58.533 --> 46:03.703 happened in the past hundred years is unique in regards to 46:03.700 --> 46:05.900 what's happened over the last thousand years. 46:05.900 --> 46:08.270 But it seems to me you'd get that impression from this 46:08.267 --> 46:11.227 curve as well, even though they've given you more of a 46:11.233 --> 46:15.873 warming period in here, in Medieval Warm Period. 46:15.867 --> 46:18.927 Still, what's happening today in steepness and in height 46:18.933 --> 46:20.033 seems to be unique. 46:20.033 --> 46:26.173 So all the arguments and the dispute over the details of 46:26.167 --> 46:29.567 how this diagram were constructed seem to be kind of 46:29.567 --> 46:32.767 moot now because we see such a rapid rise the 46:32.767 --> 46:36.727 last 20 or 30 years. 46:36.733 --> 46:39.933 So, we're out of time today, but we'll be 46:39.933 --> 46:41.833 continuing this on Monday.