1 00:00:06,760 --> 00:00:09,720 This is Georgie Bites with Oliver Strimpel. 2 00:00:11,520 --> 00:00:14,520 The history of the Earth's climate is archived within the 3 00:00:14,520 --> 00:00:18,520 sedimentary record. That is because there are 4 00:00:18,520 --> 00:00:22,240 certain physical, chemical and biological properties of 5 00:00:22,240 --> 00:00:27,240 sedimentary rocks that can serve as indicators or proxies of the 6 00:00:27,240 --> 00:00:30,200 climate that prevailed when they were deposited. 7 00:00:31,880 --> 00:00:35,000 Over the past few decades, we've discovered more and more 8 00:00:35,000 --> 00:00:38,480 proxies, enabling us to probe more aspects of past 9 00:00:38,480 --> 00:00:41,560 environments such as the temperature and composition of 10 00:00:41,560 --> 00:00:45,960 the atmosphere and of the oceans, sea level, the presence 11 00:00:45,960 --> 00:00:50,240 and extent of ice caps, and even patterns of wind and rainfall. 12 00:00:51,640 --> 00:00:55,160 But now there is a heightened interest in such work, since we 13 00:00:55,160 --> 00:00:58,840 want to understand what the rapid human generated rise in 14 00:00:58,840 --> 00:01:01,120 carbon dioxide means for the planet. 15 00:01:02,560 --> 00:01:06,360 Isabel Montagnez has been reconstructing past global and 16 00:01:06,360 --> 00:01:09,640 regional climates throughout her 30 year research career. 17 00:01:10,640 --> 00:01:13,920 She is a Distinguished Professor of Earth and Planetary Sciences 18 00:01:14,040 --> 00:01:16,800 and Director of the Institute of the Environment at the 19 00:01:16,800 --> 00:01:21,680 University of California, Davis. One climate period in particular 20 00:01:21,680 --> 00:01:25,960 has attracted her attention, the late Paleozoic Ice Age. 21 00:01:26,560 --> 00:01:30,800 That is because in certain key respects, it can serve as an 22 00:01:30,800 --> 00:01:34,760 analogue of the present day. It was the only time in Earth 23 00:01:34,760 --> 00:01:38,840 history when carbon dioxide levels increased abruptly during 24 00:01:38,840 --> 00:01:40,880 a period of recurrent glaciation. 25 00:01:41,560 --> 00:01:45,240 That Ice Age eventually gave way to a much warmer greenhouse, 26 00:01:45,240 --> 00:01:49,960 Earth devoid of ice. Isabel Montanez, welcome to 27 00:01:49,960 --> 00:01:52,040 Geology Bytes. Thank you, Oliver. 28 00:01:52,040 --> 00:01:53,680 It's a pleasure to join you today. 29 00:01:54,360 --> 00:01:57,760 It's impressive that we can reconstruct such apparently 30 00:01:57,760 --> 00:02:02,080 evanescent things as atmospheric temperature and global sea level 31 00:02:02,080 --> 00:02:05,800 through geological time. I said that we use evermore 32 00:02:05,800 --> 00:02:09,400 proxies for this purpose. Can you tell us what these 33 00:02:09,400 --> 00:02:11,800 proxies are? And let's start with the 34 00:02:11,800 --> 00:02:15,200 traditional ones. So some of these proxies that 35 00:02:15,200 --> 00:02:20,040 we've been using for decades now are oxygen isotopes of fossils 36 00:02:20,680 --> 00:02:24,920 of marine shells and corals that formed in the ocean, and equally 37 00:02:24,920 --> 00:02:28,560 as many for minerals that form in ancient soils on land. 38 00:02:29,040 --> 00:02:31,960 And these can give us information like local surface 39 00:02:31,960 --> 00:02:35,800 temperature and the composition of the seawater at the time or 40 00:02:35,800 --> 00:02:39,440 of rainwater in which they formed and the carbon isotopic 41 00:02:39,440 --> 00:02:43,440 composition, which we typically do with the oxygen, sometimes 42 00:02:43,440 --> 00:02:46,800 elemental concentrations of these minerals. 43 00:02:47,200 --> 00:02:50,400 Then when we combine all those together, it provides 44 00:02:50,480 --> 00:02:55,240 information on the local temperatures, humidity, rainfall 45 00:02:55,240 --> 00:02:58,080 patterns. And I think one that is 46 00:02:58,080 --> 00:03:02,960 particularly important is how we reconstruct CO2 in the past. 47 00:03:03,600 --> 00:03:07,080 And there are probably nearly a dozen approaches to 48 00:03:07,080 --> 00:03:12,440 reconstructing CO2 in the past. All of them involve fossils of 49 00:03:12,480 --> 00:03:16,960 living organisms or minerals that are forming in the oceans 50 00:03:17,120 --> 00:03:21,000 or on land. And each of those has their 51 00:03:21,000 --> 00:03:24,200 weaknesses and strengths. So we typically use multiple of 52 00:03:24,200 --> 00:03:28,760 these proxies, like we might use the minerals and soils and the 53 00:03:28,760 --> 00:03:32,320 plants that form in the ecosystems associated with those 54 00:03:32,320 --> 00:03:36,080 soils and they will then together give us pretty good 55 00:03:36,080 --> 00:03:39,800 constraints on what CO2 in the atmosphere was in the past. 56 00:03:40,080 --> 00:03:43,760 Can you pick a few of the most important proxies and explain 57 00:03:43,760 --> 00:03:46,960 the physical mechanisms or chemical mechanisms by which 58 00:03:46,960 --> 00:03:50,720 they managed to record things like CO2 level or temperature? 59 00:03:51,120 --> 00:03:54,240 Yeah. In the oceans, the proxies of 60 00:03:54,240 --> 00:03:59,160 CO2 typically involve the isotopic composition of marine 61 00:03:59,160 --> 00:04:01,480 shells. And why do they do that? 62 00:04:01,480 --> 00:04:05,360 Because these isotopic compositions are very sensitive 63 00:04:05,720 --> 00:04:11,200 to the pH of the sea water. And in turn, the pH is a good 64 00:04:11,600 --> 00:04:15,640 recorder of how much CO2 the ocean is dissolving. 65 00:04:15,960 --> 00:04:18,920 You know, the ocean is like a big sponge and it is always 66 00:04:18,920 --> 00:04:22,720 absorbing CO2. It is limited by how much it can 67 00:04:22,720 --> 00:04:26,440 take by the other carbon of chemicals in the ocean. 68 00:04:26,800 --> 00:04:30,680 So pH is a good indicator of what the balance of those other 69 00:04:30,680 --> 00:04:35,880 carbon molecules are. If we can reconstruct pH and we 70 00:04:35,880 --> 00:04:40,080 can reconstruct another component of the ocean, like how 71 00:04:40,080 --> 00:04:43,280 much one of these dissolved carbon molecules were in there, 72 00:04:43,520 --> 00:04:46,240 then we can reconstruct CO2 in the atmosphere. 73 00:04:46,640 --> 00:04:50,760 And what's really exciting is we've done this mostly on using 74 00:04:50,760 --> 00:04:54,760 these micro fossils called foraminifera and it's worked 75 00:04:54,760 --> 00:04:57,240 very, very well. Some of the best estimates of 76 00:04:57,240 --> 00:05:01,960 CO2 in the past, unfortunately those former menifer have only 77 00:05:01,960 --> 00:05:06,560 existed the last at best couple 100 million years and that means 78 00:05:06,560 --> 00:05:08,400 we have this big void prior to that. 79 00:05:08,880 --> 00:05:13,200 And just literally if a month ago someone has shown how well 80 00:05:13,200 --> 00:05:16,040 this works on fossil brachiopods. 81 00:05:16,360 --> 00:05:20,880 So that has really now expanded our ability to use that type of 82 00:05:20,880 --> 00:05:26,800 CO2 proxy way back to 500 million years on land. 83 00:05:26,800 --> 00:05:30,040 There are several different approaches, but two of the best 84 00:05:30,040 --> 00:05:34,600 are those carbonate minerals, we call them pedogenic or soil 85 00:05:34,600 --> 00:05:40,160 formed carbonates in soils and they are in any soils that 86 00:05:40,160 --> 00:05:42,680 formed in relatively drier conditions. 87 00:05:43,040 --> 00:05:46,840 So the southwest of the US would be a good example, Africa, 88 00:05:47,080 --> 00:05:50,600 Brazil. And these form around roots 89 00:05:50,960 --> 00:05:56,200 because roots respires CO2 at night and that CO2 gets 90 00:05:56,200 --> 00:06:00,080 dissolved in the poor waters of the soil and they get 91 00:06:00,080 --> 00:06:04,960 oversaturated and that comes out as a new mineral carbonate. 92 00:06:05,840 --> 00:06:10,200 The very cool thing about soils is that there is a balance of 93 00:06:10,200 --> 00:06:15,520 how much of the CO2 in the soil is from those roots respiring or 94 00:06:15,520 --> 00:06:19,880 microbes respiring in the soil, and how much is actually 95 00:06:19,880 --> 00:06:24,360 infiltrated from the atmosphere. And the balance of the 96 00:06:24,360 --> 00:06:28,520 atmospheric CO2 versus the soil form CO2 is recorded in the 97 00:06:28,520 --> 00:06:33,160 carbon isotopes of the carbonate mineral as well as the organic 98 00:06:33,160 --> 00:06:36,640 matter in the soil. And that can be then used to 99 00:06:36,640 --> 00:06:39,040 reconstruct CO2 in the atmosphere. 100 00:06:40,280 --> 00:06:43,520 And then the other one that I think it's just so elegant, but 101 00:06:43,720 --> 00:06:48,760 very straightforward and that is that all plants, vascular plants 102 00:06:48,760 --> 00:06:54,040 that have formed since you've 440 million years ago or so, 103 00:06:54,840 --> 00:06:59,640 have breathing pores on their leaves or on their stems, what 104 00:06:59,640 --> 00:07:03,480 we call stomata. They are little holes where 105 00:07:04,080 --> 00:07:07,720 water comes out because plants transpire water, but it's also 106 00:07:07,720 --> 00:07:12,080 where they take in CO2 from the atmosphere to photosynthesize. 107 00:07:13,040 --> 00:07:18,680 And so there is a very simple inverse relationship by how much 108 00:07:18,680 --> 00:07:22,560 CO2 is in the atmosphere and how many of those pores they have on 109 00:07:22,560 --> 00:07:25,720 their leaves or stems. If there isn't a lot of CO2 in 110 00:07:25,720 --> 00:07:29,240 the atmosphere, they need lots of those pores to be sure that 111 00:07:29,240 --> 00:07:33,760 they get enough CO2. And vice versa, if there's a lot 112 00:07:33,760 --> 00:07:36,360 of CO2 in the atmosphere, they don't need as many of them. 113 00:07:36,800 --> 00:07:40,240 And it's to their advantage to not have too many because as I 114 00:07:40,240 --> 00:07:43,640 mentioned, they lose water through these pores and they 115 00:07:43,640 --> 00:07:46,160 don't want to lose water, especially if it's getting drier 116 00:07:46,160 --> 00:07:50,400 in seasonally or with time. And it's a very tight connection 117 00:07:50,440 --> 00:07:54,000 between the amount of CO2 in the atmosphere in those pores that 118 00:07:54,000 --> 00:07:57,720 develop. And we simply use how many pores 119 00:07:57,720 --> 00:08:04,600 per square millimeter on a leaf. We're not talking about proxies 120 00:08:04,600 --> 00:08:08,240 based on isotopes. Why should they be sensitive to 121 00:08:08,240 --> 00:08:11,120 these environmental parameters? Is it something to do with the 122 00:08:11,120 --> 00:08:14,480 reaction kinetics of the different weight of the 123 00:08:14,480 --> 00:08:17,560 different carbons in the carbon dioxide from the different 124 00:08:17,560 --> 00:08:19,520 isotopes? Absolutely. 125 00:08:19,600 --> 00:08:25,040 The proportion of the heavier versus the lighter isotope into 126 00:08:25,040 --> 00:08:28,560 the mineral, for instance, will have a lot to do with 127 00:08:28,560 --> 00:08:31,000 temperature. And if there are other 128 00:08:31,000 --> 00:08:34,679 parameters in the soil or in the water that are affecting the 129 00:08:34,679 --> 00:08:39,640 rate at which those atoms are being brought in, yes, that will 130 00:08:39,640 --> 00:08:43,280 also affect it. It's a lot easier to move or 131 00:08:43,280 --> 00:08:47,400 incorporate the lighter isotope than it is a heavier mass. 132 00:08:47,920 --> 00:08:52,200 For plants, it's a bit more complicated in that it has to do 133 00:08:52,200 --> 00:08:54,800 with their physiological functioning. 134 00:08:54,800 --> 00:09:00,440 How well are they taking in CO2 or photosynthesizing and 135 00:09:00,440 --> 00:09:03,640 processing it? Does any of the material you 136 00:09:03,640 --> 00:09:07,720 analyze for these proxies include the actual original 137 00:09:07,720 --> 00:09:11,880 organic matter from these skeletons, or from these leaves 138 00:09:11,880 --> 00:09:14,880 that survives, or the soil? Or are you just talking about 139 00:09:14,880 --> 00:09:18,160 the replaced material that generally forms a fossil? 140 00:09:18,800 --> 00:09:22,040 Great question. Minerals in soils, very, very 141 00:09:22,040 --> 00:09:28,000 small minerals will often form effectively cages around this 142 00:09:28,000 --> 00:09:32,080 organic matter and we call it mineral associated organic 143 00:09:32,080 --> 00:09:35,120 matter. Now millions of years ago, sure 144 00:09:35,240 --> 00:09:37,800 it's not preserving it perfectly, but it is pretty 145 00:09:37,800 --> 00:09:41,080 impressive how most of the molecular structure that it can 146 00:09:41,080 --> 00:09:43,640 preserve. And another way is these 147 00:09:43,640 --> 00:09:48,760 carbonates that form in the soil actually entomb the organic 148 00:09:48,760 --> 00:09:53,200 matter that was in the soil as they were precipitating for 149 00:09:53,200 --> 00:09:56,160 plants. It isn't in fact, the actual 150 00:09:56,240 --> 00:09:59,440 cellulose or lipids of the actual leaf. 151 00:10:00,080 --> 00:10:04,520 It's that waxy layer, a cuticular layer that protects 152 00:10:04,520 --> 00:10:06,360 the leaf. And there's a layer on the 153 00:10:06,360 --> 00:10:08,920 bottom of the leaf and there's a layer on the top of the leaf. 154 00:10:09,400 --> 00:10:13,400 So effectively, those breathing pores that we measure their 155 00:10:13,400 --> 00:10:16,520 sizes, their depths, and the number of them on the leaf. 156 00:10:17,040 --> 00:10:22,320 They're casts in that waxy cuticular layer and that is 157 00:10:22,320 --> 00:10:25,640 preserved beautifully. I can show you images from a 158 00:10:25,640 --> 00:10:29,960 microscope of something 300 million years old and a ginkgo 159 00:10:29,960 --> 00:10:33,440 from 100 million years and a modern one, and you'd be hard 160 00:10:33,440 --> 00:10:36,960 pressed to know the difference. Wow, that's amazing. 161 00:10:36,960 --> 00:10:39,160 The actual original wax material. 162 00:10:39,320 --> 00:10:43,320 It is and we have even extracted from them some of those lipids, 163 00:10:43,320 --> 00:10:46,560 so you do get things stuck on there that are preserved. 164 00:10:47,080 --> 00:10:49,840 Can you tell us about some of the more recently developed 165 00:10:50,080 --> 00:10:53,560 nontraditional proxies? The turn of the Millennium has 166 00:10:53,560 --> 00:10:58,160 been an explosion of development of new proxies. 167 00:10:58,520 --> 00:11:01,440 I think we can attribute a lot of that to the technology, the 168 00:11:01,440 --> 00:11:05,720 machines that give us the possibility to do isotopes 169 00:11:05,760 --> 00:11:08,400 across the periodic table. It's just amazing. 170 00:11:08,400 --> 00:11:11,360 It's something that 40 years ago we couldn't have even imagined. 171 00:11:12,080 --> 00:11:14,400 I'll give you a couple of examples. 172 00:11:14,520 --> 00:11:19,680 Uranium isotopes in carbonates that form in the ocean, and even 173 00:11:19,880 --> 00:11:21,400 some people are trying this in lakes. 174 00:11:21,880 --> 00:11:26,480 These are now allowing us to look at the oxygenation levels 175 00:11:26,560 --> 00:11:30,360 on the ocean floor where a lot of these shells and life might 176 00:11:30,360 --> 00:11:31,920 be living. Today. 177 00:11:32,160 --> 00:11:35,840 Our deep ocean is quite oxygenated, but it turns out 178 00:11:35,840 --> 00:11:38,720 that when you have global warming, that changes 179 00:11:38,720 --> 00:11:41,880 considerably. So these uranium isotopes that 180 00:11:41,880 --> 00:11:45,160 are now measurable in these shells or even just disseminated 181 00:11:45,160 --> 00:11:51,240 carbonates in old sediments, allow us to see how the 182 00:11:51,240 --> 00:11:56,000 oxygenation is changed, whether anoxic conditions are forming 183 00:11:56,320 --> 00:11:59,480 anywhere on the sea floor, whether it's off a coast or deep 184 00:11:59,480 --> 00:12:02,480 in the ocean. And in turn, it tells us about 185 00:12:02,480 --> 00:12:05,680 how changes in the ocean circulation were happening. 186 00:12:06,120 --> 00:12:09,880 And the very cool thing about uranium isotopes is you can do 187 00:12:09,880 --> 00:12:13,360 those in one location on Earth and it's representative of the 188 00:12:13,360 --> 00:12:17,640 whole ocean because of the well mixed nature and the residence 189 00:12:17,640 --> 00:12:22,240 time of uranium in the oceans. Another example, going back to 190 00:12:22,240 --> 00:12:27,800 the periodic table, we now do the stable isotopic compositions 191 00:12:27,800 --> 00:12:33,560 of strontium, calcium, magnesium, lithium, potassium, 192 00:12:34,160 --> 00:12:40,320 mercury, and these allow us to look at degrees of weathering on 193 00:12:40,320 --> 00:12:43,880 land, which is really important because weathering on land is 194 00:12:43,880 --> 00:12:47,920 tightly coupled to CO2 in the atmosphere and to temperature. 195 00:12:48,320 --> 00:12:53,200 So this gives us an opportunity to again, track what's happening 196 00:12:53,200 --> 00:12:56,800 in changes in greenhouse gases that we're getting from other 197 00:12:56,800 --> 00:12:59,800 proxies and how is the landscape responding. 198 00:13:00,080 --> 00:13:04,000 And that's important because those responses in turn remove 199 00:13:04,040 --> 00:13:07,160 CO2 from the atmosphere. In fact, it's one of the ways 200 00:13:07,160 --> 00:13:10,880 that the Earth has maintained its temperatures through 201 00:13:10,880 --> 00:13:15,080 maintaining its greenhouse gases in these balances of these 202 00:13:15,080 --> 00:13:19,800 processes, Mercury isotopes, fingerprints of passive volcanic 203 00:13:19,800 --> 00:13:24,440 episodes, so we can now tie them directly to the other isotopes. 204 00:13:24,840 --> 00:13:29,120 Was the increase in CO2 or methane in the atmosphere driven 205 00:13:29,120 --> 00:13:32,520 by volcanism? These same isotopes are telling 206 00:13:32,520 --> 00:13:36,880 us something about aridity and seasonality on land in different 207 00:13:36,880 --> 00:13:40,640 places, and they can even tell us about other sources of 208 00:13:40,640 --> 00:13:44,960 greenhouse gases that aren't volcanoes, like melting methane 209 00:13:45,240 --> 00:13:48,000 out of the oceans. So it really opens up a whole 210 00:13:48,000 --> 00:13:53,240 new world for us beyond just temperatures, effective moisture 211 00:13:53,440 --> 00:13:56,360 and maybe seawater and precipitation composition. 212 00:13:57,320 --> 00:14:00,480 And then lastly, I'd be remiss if I didn't say they're all of 213 00:14:00,480 --> 00:14:03,600 these biologic proxies, primarily what we call 214 00:14:03,600 --> 00:14:06,640 biomarkers. Those are biomolecules. 215 00:14:06,840 --> 00:14:11,080 So rather than looking at the organic matter that we extract 216 00:14:11,360 --> 00:14:16,000 as a bulk form, we can actually extract specific biomolecules 217 00:14:16,000 --> 00:14:18,720 like lipids, hope pains and others. 218 00:14:19,120 --> 00:14:21,440 And each of them have their own function. 219 00:14:21,680 --> 00:14:25,480 So we can look at things like the physiological functioning of 220 00:14:25,480 --> 00:14:29,880 the plants, how did they respond to drought, Were they very 221 00:14:29,880 --> 00:14:33,480 resilient to deep freezes. But we can also look at 222 00:14:33,480 --> 00:14:37,600 microbial interactions with all of these other environmental 223 00:14:37,600 --> 00:14:40,360 conditions and their role and temperatures. 224 00:14:40,760 --> 00:14:43,920 They're another independent source of temperatures as well. 225 00:14:44,360 --> 00:14:48,680 So all of this tool bag, no one group will do all of them, but 226 00:14:49,120 --> 00:14:53,360 for any given time period there are just enormous amounts of 227 00:14:53,360 --> 00:14:56,280 information that is being developed. 228 00:14:56,760 --> 00:15:01,280 So how do you try and make sense of all the paleoclimate data 229 00:15:01,280 --> 00:15:04,120 you've been able to reconstruct from all these proxies? 230 00:15:04,400 --> 00:15:08,960 So our approach is to contextualize that data by using 231 00:15:09,040 --> 00:15:13,360 an Earth system model. This model, which was produced 232 00:15:13,360 --> 00:15:17,320 by the National Center for Atmospheric Research, or NCAR, 233 00:15:17,440 --> 00:15:25,200 is our US model for the IPCC's work, but also for predicting 234 00:15:25,200 --> 00:15:27,240 the climate over the next 10 days. 235 00:15:27,440 --> 00:15:32,560 They are the most comprehensive, all inclusive of every process 236 00:15:32,600 --> 00:15:37,520 that is in the ocean, the atmosphere on land that we know 237 00:15:37,520 --> 00:15:41,680 of that influences climate. Climate is effectively the 238 00:15:41,680 --> 00:15:44,040 interaction of the ocean and the atmosphere. 239 00:15:44,640 --> 00:15:49,240 So these models not only allow the ocean and the atmosphere to 240 00:15:49,520 --> 00:15:55,080 interact and be fully in equilibrium, it allows for cloud 241 00:15:55,440 --> 00:15:58,680 differences and development. It allows for aerosols. 242 00:15:59,080 --> 00:16:02,960 It models all of the changes in the circulation of the ocean, 243 00:16:03,440 --> 00:16:08,960 the effects of sea ice on that circulation, continental ice 244 00:16:08,960 --> 00:16:12,600 sheets, how do they influence the temperatures, the air 245 00:16:12,600 --> 00:16:17,680 humidity, sea ice response, and turn back to the ocean? 246 00:16:17,960 --> 00:16:22,200 It has vegetation. Vegetation interacts with the 247 00:16:22,200 --> 00:16:26,760 atmosphere and the soils in terms of moving carbon and 248 00:16:26,760 --> 00:16:29,840 water. So it influences once again the 249 00:16:29,840 --> 00:16:34,240 atmosphere and the ocean and it just iterates so that these 250 00:16:34,240 --> 00:16:39,840 processes are fully interacting and feeding back on one another. 251 00:16:40,560 --> 00:16:44,160 And the proof that these models are really comprehensive and 252 00:16:44,160 --> 00:16:48,560 correct is that they are calibrated to the modern where 253 00:16:48,560 --> 00:16:52,600 we have 100 plus years of excellent data from around the 254 00:16:52,600 --> 00:16:57,720 world and they can reproduce those very, very accurately. 255 00:16:58,680 --> 00:17:00,880 OK, so you've managed to build this model. 256 00:17:02,040 --> 00:17:05,160 How do you make use of it? What kind of questions can you 257 00:17:05,480 --> 00:17:08,480 interrogate it with? So you start out with the 258 00:17:08,480 --> 00:17:10,920 boundary conditions, those baseline boundary conditions, 259 00:17:10,920 --> 00:17:15,520 and then they are run to evaluate the climate processes 260 00:17:15,520 --> 00:17:19,920 and the ecosystem functioning. What is their sensitivity to 261 00:17:19,920 --> 00:17:23,800 this changing CO2 and ice sheet distribution? 262 00:17:24,280 --> 00:17:26,480 You don't usually change much else because you're not 263 00:17:26,480 --> 00:17:29,320 interested in whether mountains are building or weathering down 264 00:17:29,320 --> 00:17:32,600 or whether the ocean basins are changing in configuration. 265 00:17:32,800 --> 00:17:34,840 Those are millions a year time scale things. 266 00:17:35,160 --> 00:17:38,040 But you are interested in what happens if you lose tropical 267 00:17:38,040 --> 00:17:41,800 forests or whether temperatures are changing and rainfall 268 00:17:41,800 --> 00:17:43,840 patterns are changing. So that's what we're after. 269 00:17:43,840 --> 00:17:47,640 We're interested in seeing what is the sensitivity of these. 270 00:17:48,120 --> 00:17:52,120 We're also interested in are there thresholds, are there CO2 271 00:17:52,120 --> 00:17:55,280 thresholds where things just plummet or where the changes 272 00:17:55,280 --> 00:17:58,520 start accelerating? And are there tipping points 273 00:17:58,760 --> 00:18:02,920 where those forests disappear, or where their ice collapses, or 274 00:18:02,920 --> 00:18:05,840 where the monsoon system effectively collapses or 275 00:18:05,840 --> 00:18:08,760 intensifies? I said in my introduction that 276 00:18:08,760 --> 00:18:12,240 you've been especially interested in the late Paleozoic 277 00:18:12,240 --> 00:18:17,120 Ice Age because it can serve as an analogue to the present day. 278 00:18:17,480 --> 00:18:21,840 How far does the similarity go? I want to stress that it is the 279 00:18:21,840 --> 00:18:25,600 process scale we're after here. Continental configuration was 280 00:18:25,600 --> 00:18:27,960 quite different. In fact, it was the opposite of 281 00:18:27,960 --> 00:18:29,720 today. It was a supercontinent. 282 00:18:30,000 --> 00:18:33,640 Today we have our continents at their maximum distribution away 283 00:18:33,640 --> 00:18:36,760 from one another on the globe. Many things are different. 284 00:18:37,400 --> 00:18:41,600 That said, the processes in the Earth system, whether it's in 285 00:18:41,600 --> 00:18:45,880 the climate system, the ecosystems on land and how they 286 00:18:45,880 --> 00:18:48,360 interact with the environmental parameters. 287 00:18:48,600 --> 00:18:53,320 So the atmosphere, the oceans, land, life, these processes have 288 00:18:53,480 --> 00:18:57,160 existed and fundamentally functioned as they do today 289 00:18:57,240 --> 00:19:01,600 since we've had ecosystems in terms of general structure and 290 00:19:01,600 --> 00:19:04,200 configuration similar to what we have today. 291 00:19:04,280 --> 00:19:08,760 So 400 million years or so, certainly the last 300 million 292 00:19:08,760 --> 00:19:12,400 years. So inferring how climate may 293 00:19:12,400 --> 00:19:16,640 change in the future in one particular region from looking 294 00:19:16,640 --> 00:19:19,600 at the deep time, we can't do that because of the continental 295 00:19:19,600 --> 00:19:22,400 configuration differences and other things like that. 296 00:19:23,120 --> 00:19:28,040 But evaluating how these processes in the climate system, 297 00:19:28,120 --> 00:19:34,720 in the ecosystems, ice response, ocean response, evaluating how 298 00:19:34,720 --> 00:19:40,320 they respond to increases in CO2 or vice versa, decreases and the 299 00:19:40,320 --> 00:19:44,480 consequent warming or cooling that goes with that on a global 300 00:19:44,480 --> 00:19:50,200 scale and how those responses interact with one another and 301 00:19:50,200 --> 00:19:55,480 how they may even feedback on the initial warming or cooling, 302 00:19:55,680 --> 00:19:59,960 that is fundamental information that we can glean from looking 303 00:19:59,960 --> 00:20:04,080 at past periods. The main thing that makes a time 304 00:20:04,080 --> 00:20:07,760 period relevant or not is whether the atmospheric CO2 305 00:20:07,760 --> 00:20:12,800 concentrations were within the range of what we are seeing 306 00:20:13,040 --> 00:20:16,800 since we started burning fossil fuels and what we project into 307 00:20:16,800 --> 00:20:21,480 our fairly near future. And that is the case for the 308 00:20:21,480 --> 00:20:26,080 late paleozoric ice house. In fact it's the only time when 309 00:20:26,080 --> 00:20:32,280 CO2 was in the range of what we see since the pre industrial and 310 00:20:32,280 --> 00:20:37,000 what we're going into except for a transient period in the last 311 00:20:37,000 --> 00:20:40,240 several million years. But isn't the fact that there 312 00:20:40,240 --> 00:20:44,160 was ice or recurrent ice on the poles something that also 313 00:20:44,160 --> 00:20:46,080 distinguished that period from others? 314 00:20:46,160 --> 00:20:50,440 Of course this is the last time other than the last 34 million 315 00:20:50,440 --> 00:20:54,480 years where there has been continental scale ice on Earth 316 00:20:55,000 --> 00:20:57,040 all the time. In between there may have been 317 00:20:57,240 --> 00:21:01,360 ephemeral, short lived, maybe small Alpine, maybe continental 318 00:21:01,360 --> 00:21:05,080 glaciers, but nothing that we can find in the rock record nor 319 00:21:05,080 --> 00:21:08,640 do we produce in climate models. So this is it. 320 00:21:08,640 --> 00:21:13,880 This is the last time that we see the ice house as it came on 321 00:21:13,880 --> 00:21:19,680 the onset and its response to short lived warming, essentially 322 00:21:19,680 --> 00:21:23,120 the experiment we're doing now and ultimately it's terminal 323 00:21:23,120 --> 00:21:25,760 demise as it turned into a greenhouse. 324 00:21:26,240 --> 00:21:29,200 I want to come back to the boundary conditions that you 325 00:21:29,200 --> 00:21:31,680 mentioned. So when the configuration of the 326 00:21:31,680 --> 00:21:34,960 continents was completely different and presumably ocean 327 00:21:34,960 --> 00:21:38,280 circulation as a result was completely different, how come 328 00:21:38,520 --> 00:21:43,400 we believe that the sensitivities on a global scale 329 00:21:43,480 --> 00:21:47,000 would still be relevant to the situation we find ourselves in 330 00:21:47,000 --> 00:21:48,560 today? So I'm going to give you an 331 00:21:48,560 --> 00:21:53,480 example of our modeling that gives us detailed seasonal 332 00:21:53,520 --> 00:21:57,680 response to the CO2 changes within that range of the pre 333 00:21:57,680 --> 00:22:00,360 industrial to what we anticipate in the future. 334 00:22:01,040 --> 00:22:05,560 And then how we can say that we have confidence in that modeling 335 00:22:05,560 --> 00:22:07,800 based on the proxies that we've developed. 336 00:22:08,520 --> 00:22:11,760 We have the CO2 proxies, we have the temperature proxies for the 337 00:22:11,760 --> 00:22:14,760 late Pilozoic Ice Age. And now we had these uranium 338 00:22:14,760 --> 00:22:17,840 isotopes and the uranium isotopes were telling us that up 339 00:22:17,840 --> 00:22:22,400 to 25% of the sea floor was going anoxic globe. 340 00:22:23,000 --> 00:22:25,760 Yes, different continental configuration, so clearly 341 00:22:25,760 --> 00:22:30,800 different ocean circulation and with ice sheets and we said this 342 00:22:30,800 --> 00:22:36,200 is during ice house where we have big ice where we are 343 00:22:36,240 --> 00:22:38,520 generally cool. In fact, other studies we've 344 00:22:38,520 --> 00:22:40,960 done have shown that this is the only other time that global 345 00:22:40,960 --> 00:22:43,800 temperatures on in line with what we're humans have been 346 00:22:43,800 --> 00:22:45,920 seeing since they've evolved in today. 347 00:22:46,720 --> 00:22:50,040 Why are we going 25% anoxic of the sea floor? 348 00:22:50,040 --> 00:22:53,040 That's phenomenal. That has huge implications for 349 00:22:53,040 --> 00:22:56,280 the future if correct. So the climate models, we use 350 00:22:56,280 --> 00:23:01,080 them with the right boundary conditions to evaluate how the 351 00:23:01,080 --> 00:23:05,480 presence of ice and sea ice included would change the ocean 352 00:23:05,480 --> 00:23:08,440 circulation. Despite the fact that again we 353 00:23:08,440 --> 00:23:11,400 are looking at very different continental configurations and 354 00:23:11,400 --> 00:23:15,480 ice only in the Southern Hemisphere with the doubling of 355 00:23:15,480 --> 00:23:20,240 CO2 or even 50% increase essentially where we are today 356 00:23:20,600 --> 00:23:24,600 from pre industrial, we can see changes for instance in the 357 00:23:24,600 --> 00:23:28,680 Northern hemisphere polar region, major changes in sea ice 358 00:23:28,720 --> 00:23:33,120 formation, but more importantly in circulation at the mid depth 359 00:23:33,400 --> 00:23:38,080 of the ocean, we can see where deep water formation is forming. 360 00:23:38,760 --> 00:23:42,680 So during the times of low CO2, we have deep water formation at 361 00:23:42,680 --> 00:23:45,880 both poles, very similar to today, even though the 362 00:23:45,880 --> 00:23:49,920 continents in their very different configuration, we take 363 00:23:49,920 --> 00:23:53,480 the CO2, we double it and we lose the Northern hemisphere 364 00:23:53,480 --> 00:23:55,920 deep water formation, very different world. 365 00:23:55,920 --> 00:23:59,040 And we see that then in the climate on land and we see in 366 00:23:59,040 --> 00:24:03,680 the sea surface temperatures, we do a 50% increase in CO2 to make 367 00:24:03,680 --> 00:24:07,040 it more like today, 400 PPM. And what do we discover? 368 00:24:07,240 --> 00:24:11,200 It's a threshold because under that we're not seeing much 369 00:24:11,200 --> 00:24:14,280 change. At 400, all of a sudden we see 370 00:24:14,280 --> 00:24:16,880 these major changes and not much more. 371 00:24:17,000 --> 00:24:20,720 Even when we double go 50% more, and it fits our proxies 372 00:24:20,720 --> 00:24:25,040 beautifully, it tells us that about 18 to 25% of the sea floor 373 00:24:25,040 --> 00:24:27,640 would go anoxic because of this change. 374 00:24:28,600 --> 00:24:31,840 So again, different boundary conditions in terms of 375 00:24:31,840 --> 00:24:36,480 continental configuration has to be different ocean circulation 376 00:24:36,480 --> 00:24:40,120 because you have one huge ocean called Panthelasa and then a 377 00:24:40,120 --> 00:24:43,720 more huge Mediterranean. That's the other part of the 378 00:24:43,720 --> 00:24:47,640 ocean, open to the other one, but still very different. 379 00:24:48,360 --> 00:24:52,680 But what have we learned? It doesn't matter the ocean, it 380 00:24:52,680 --> 00:24:56,040 circulates and it still couples with the atmosphere, and it is 381 00:24:56,040 --> 00:24:59,480 still equally sensitive to changes in CO2. 382 00:24:59,760 --> 00:25:03,800 Where the water may go down deep to circulate in our conveyor 383 00:25:03,800 --> 00:25:07,840 belt may be different, but it's not about where those continents 384 00:25:07,840 --> 00:25:09,960 are. It's about the CO2 and the 385 00:25:09,960 --> 00:25:14,560 warming effect on the ocean and the ice and sea ice behaviour 386 00:25:15,160 --> 00:25:18,720 that seems to be robust regardless of that boundary 387 00:25:18,720 --> 00:25:21,720 conditions of the continent. Wow, That's a pretty dramatic 388 00:25:21,760 --> 00:25:27,040 conclusion then, that it just so happens based on your model that 389 00:25:27,120 --> 00:25:28,840 we've gotten to the tipping point. 390 00:25:29,440 --> 00:25:33,040 You can imagine we put that out there and the default response 391 00:25:33,040 --> 00:25:35,880 by scientists is, oh, come on, it's so different back then. 392 00:25:35,920 --> 00:25:41,400 And our response back is yes, but step back and ask yourself 393 00:25:41,400 --> 00:25:44,520 why the responses are not that different. 394 00:25:45,120 --> 00:25:49,840 It's because there are physics in the system that don't care 395 00:25:49,840 --> 00:25:53,640 where the continents are. They care about the ocean as a 396 00:25:53,640 --> 00:25:57,560 whole and how it's operating. It's always a conveyor belt. 397 00:25:57,800 --> 00:26:01,640 It may slow down, it may accelerate, but it's still a 398 00:26:01,680 --> 00:26:06,720 conveyor belt that is strongly governed by how much sea ice is 399 00:26:06,800 --> 00:26:10,320 in the polar regions, how much continental ice is there, how 400 00:26:10,320 --> 00:26:15,520 warm the ocean is in that region, how stratified it is. 401 00:26:16,160 --> 00:26:19,640 So nuanced differences, yes, hugely. 402 00:26:19,800 --> 00:26:23,160 But as a global system, it's still operating as the systems 403 00:26:23,320 --> 00:26:27,840 as we know it. What can we learn then from your 404 00:26:27,840 --> 00:26:33,480 late Paleozoic Ice Age or ice house model with regard to our 405 00:26:33,480 --> 00:26:38,160 climate future and I presume one of the differences that even 406 00:26:38,160 --> 00:26:43,400 though CO2 was rising rapidly than it was not rising on 407 00:26:43,520 --> 00:26:47,360 anything like the rate that has happened since pre industrial 408 00:26:47,360 --> 00:26:49,680 times? You hit the nail on the head. 409 00:26:49,720 --> 00:26:53,960 I would say two key findings. Just by changing the climate 410 00:26:53,960 --> 00:26:59,720 initially, and if the ecosystem in a given location is changed, 411 00:27:00,000 --> 00:27:04,120 we can actually change other parameters in the Earth system 412 00:27:04,320 --> 00:27:08,160 substantially. For example, we've modeled that 413 00:27:08,160 --> 00:27:13,520 if we changed the ecosystem in the tropics, the wet tropics at 414 00:27:13,520 --> 00:27:18,520 that time, by moving one type of ecosystem and replacing it with 415 00:27:18,520 --> 00:27:22,400 another, based on the fossil record that these shifts really 416 00:27:22,400 --> 00:27:28,080 happened, we could change the outflow from the Amazon basin by 417 00:27:28,080 --> 00:27:35,600 fourfold or decrease it by half. So changing the ecosystem in a 418 00:27:35,600 --> 00:27:38,840 given location can change our runoff. 419 00:27:39,360 --> 00:27:43,960 So flooding it can change the coastal environment because it 420 00:27:43,960 --> 00:27:46,880 can bring a lot of nutrients to coastal waters. 421 00:27:46,880 --> 00:27:50,000 That is not a good thing. It causes eutrophication. 422 00:27:50,280 --> 00:27:54,360 It can change the atmosphere's water because it can put less in 423 00:27:54,360 --> 00:27:57,480 the atmosphere and more in the ground to run off. 424 00:27:58,080 --> 00:28:01,920 So that's a big finding. We're looking at a time period 425 00:28:02,440 --> 00:28:06,800 similar to Dave in terms of ice sheets, where CO2 was at its low 426 00:28:06,800 --> 00:28:11,240 point, precisely in the range of the lows of the last glacials 427 00:28:11,240 --> 00:28:13,720 during the Pleistocene, the last million years. 428 00:28:14,160 --> 00:28:18,480 And it rose within these glacial interglacial cycles, similarly 429 00:28:18,480 --> 00:28:20,840 doubling. But there were also these 430 00:28:20,840 --> 00:28:26,080 intervals of rapid rises in CO2 that were driven by volcanism 431 00:28:26,120 --> 00:28:29,280 and maybe even changes in ocean circulation. 432 00:28:30,000 --> 00:28:34,480 The important thing here is that we are seeing enormous changes 433 00:28:34,640 --> 00:28:38,280 in the climate system, influences on the ecosystems and 434 00:28:38,280 --> 00:28:41,960 land in the ocean, changes in the oxygenation state of the 435 00:28:42,040 --> 00:28:47,880 oceans, changes in ice sheet stability, all in response to 436 00:28:47,880 --> 00:28:52,560 these changes in CO2 within the range of our pre industrial 437 00:28:52,840 --> 00:28:56,600 Pleistocene to our future. And as you said, at rates 438 00:28:56,600 --> 00:28:59,520 minimally an order of magnitude slower. 439 00:28:59,880 --> 00:29:04,080 And that should be eye opening that our Earth system is capable 440 00:29:04,560 --> 00:29:09,840 of responding to changes in CO2 analogous to our world and 441 00:29:09,840 --> 00:29:13,600 future at all. Because we should be thinking, 442 00:29:13,600 --> 00:29:17,800 why would it not be now? Isabel Montanez, thank you very 443 00:29:17,800 --> 00:29:19,560 much. It's very much my pleasure. 444 00:29:20,800 --> 00:29:23,480 To see pictures and illustrations that support this 445 00:29:23,480 --> 00:29:28,720 podcast, go to geologybytescom where you'll also find a subject 446 00:29:28,720 --> 00:29:30,640 matter index of all the episodes. 447 00:29:31,080 --> 00:29:34,600 There you can also give me feedback which I welcome as well 448 00:29:34,600 --> 00:29:37,440 as sign U to get my emails about new episodes.