1 00:00:00,000 --> 00:00:13,120 *preroll music* 2 00:00:13,120 --> 00:00:19,530 Herald: It's simple when ice gets above 0°, it melts. But is it really that simple 3 00:00:19,530 --> 00:00:23,270 if we are not talking about a small ice cube, but a big sheet of ice covering an 4 00:00:23,270 --> 00:00:28,910 entire continent? Is that really the only factor? And, am I right with my 5 00:00:28,910 --> 00:00:34,090 assessment? I'm looking forward to be enlightened by Professor Doctor Ricarda 6 00:00:34,090 --> 00:00:38,160 Winkelmann. Ricarda Winkelmann is a professor of climate science at the 7 00:00:38,160 --> 00:00:44,190 University of Potsdam, and she's also a researcher for climate impact. She leads 8 00:00:44,190 --> 00:00:48,540 the Ice Dynamics Working Group and Co- leads PIK Future Lab on Earth Resilience 9 00:00:48,540 --> 00:00:52,650 in the Anthropocene. Her research focuses on tipping elements from the Earth system. 10 00:00:52,650 --> 00:00:57,180 And today she'll be talking about the Greenland and Antarctic ice dynamics and 11 00:00:57,180 --> 00:01:03,130 the future sea level rise that are impacted by them. It appears like she's 12 00:01:03,130 --> 00:01:07,110 surely an expert on all things related to ice. So please give a warm hand of 13 00:01:07,110 --> 00:01:11,670 applause for Professor Doctor Ricarda Winkelman with her talk: "The Big Melt: 14 00:01:11,670 --> 00:01:17,710 Tipping Points in Greenland and Antarctica" Have fun! 15 00:01:17,710 --> 00:02:35,650 [no audio] *in between music* 16 00:02:35,650 --> 00:02:39,709 Ricarda Winkelmann: *audio not working* Thanks and welcome. Today, we're going to 17 00:02:39,709 --> 00:02:45,180 take a little excursion to the far north and the far south, to our polar ice sheets 18 00:02:45,180 --> 00:02:51,609 on Greenland and Antarctica. As this year is coming to a close, I thought we'd take 19 00:02:51,609 --> 00:02:58,540 a brief moment to reflect back. 2020 has certainly been an exceptional year for all 20 00:02:58,540 --> 00:03:05,079 of us. It was supposed to be a super year for nature and the environment, as world 21 00:03:05,079 --> 00:03:09,290 leaders put it at the beginning of the year. It's five years after the Paris 22 00:03:09,290 --> 00:03:13,859 climate accord. It's five years after the Sustainable Development Goals have been 23 00:03:13,859 --> 00:03:19,790 announced. However, 2020 turned out to be the year when we've had to face several 24 00:03:19,790 --> 00:03:26,389 global crises, including the ongoing covid-19 pandemic and also the ongoing 25 00:03:26,389 --> 00:03:33,099 climate crisis. What almost got lost in the turmoil is that this year also saw 26 00:03:33,099 --> 00:03:37,939 several weather and climate extremes, which spaned the globe from pole to pole, 27 00:03:37,939 --> 00:03:47,329 with temperatures reaching record highs in the Arctic and Antarctica with +38°C in 28 00:03:47,329 --> 00:03:51,370 the Arctic and in Siberia. That's the highest temperature that was ever recorded 29 00:03:51,370 --> 00:03:55,569 north of the Arctic Circle and it's roughly 18° warmer than the average 30 00:03:55,569 --> 00:04:02,719 maximum daily temperature in June, when this was recorded. And we also saw +18° at 31 00:04:02,719 --> 00:04:07,519 the Antarctic Peninsula, which is, again, the highest temperature ever recorded in 32 00:04:07,519 --> 00:04:15,219 Antarctica. And this was followed by widespread melting on nearby glaciers. 33 00:04:15,219 --> 00:04:21,090 Now, if we're kind of zooming out and taking a look at the bigger picture, we're 34 00:04:21,090 --> 00:04:25,670 also at a very significant point in Earth's history. Here you see the global 35 00:04:25,670 --> 00:04:31,590 mean temperature evolution since the last glacial maximum. So the last ice age until today. 36 00:04:31,590 --> 00:04:35,950 And whenever I look at this graph, I see two things that still strike me to this 37 00:04:35,950 --> 00:04:40,940 day. One is that the Holocene, the interglacial or the warm age, in which 38 00:04:40,940 --> 00:04:45,500 human civilizations have developed and thrived, has been characterized by very 39 00:04:45,500 --> 00:04:50,650 stable climate conditions, by a very stable global mean temperature. And the 40 00:04:50,650 --> 00:04:54,590 other thing is that the difference between an ice age, here, 20 000 years ago 41 00:04:54,590 --> 00:05:00,540 roughly, and a warm age, that's roughly three to four degrees of global average 42 00:05:00,540 --> 00:05:05,690 temperature change. And right now we're on the verge of achieving the same 43 00:05:05,690 --> 00:05:12,700 temperature difference, but at much, much faster rates. So here you see several 44 00:05:12,700 --> 00:05:17,731 future temperature projections from the IPCC. And what you can see is, that in all 45 00:05:17,731 --> 00:05:22,290 of them, the temperature increase, even the lowest one, the temperature increase 46 00:05:22,290 --> 00:05:27,970 is much faster than it was ever recorded before. So I think it's safe to say that 47 00:05:27,970 --> 00:05:32,800 we have truly entered the Anthropocene and that humans have become a geological 48 00:05:32,800 --> 00:05:39,520 force. So in the Anthropocene, humans have become the single most important driver of 49 00:05:39,520 --> 00:05:45,270 global change affecting the entire Earth system, including our ice sheets. But it 50 00:05:45,270 --> 00:05:50,690 was kind of the opposite in the past. Like no other forces on the planet, ice ages 51 00:05:50,690 --> 00:05:55,770 have actually shaped our surroundings and thereby determined our development as 52 00:05:55,770 --> 00:06:01,040 human civilizations. For instance, we owe our fertile soils, to the last ice age, 53 00:06:01,040 --> 00:06:06,060 that also carved our current landscapes that we see all around us, leaving 54 00:06:06,060 --> 00:06:12,900 glaciers behind, rivers and lakes. So even though the ice sheets on Greenland and 55 00:06:12,900 --> 00:06:18,980 Antarctica might seem far away sometimes, they're actually crucial also for us here 56 00:06:18,980 --> 00:06:25,010 today. And today, I want to leave you with an impression why they are so important. 57 00:06:25,010 --> 00:06:28,300 And one reason why they are so important is because they're an amazing climate 58 00:06:28,300 --> 00:06:35,260 archive. Here you see an ice core taken from one of the deepest parts of an ice 59 00:06:35,260 --> 00:06:40,610 sheet. And this is basically like counting tree rings. You can go back to the past 60 00:06:40,610 --> 00:06:47,480 and you can see what the climate was like in the deep past, ranging several hundreds 61 00:06:47,480 --> 00:06:52,500 of thousands of years back. And you can see the conditions, for instance, in the 62 00:06:52,500 --> 00:06:58,730 CO2 change, the temperature change over this really long timescales. So that's one 63 00:06:58,730 --> 00:07:04,350 of the reasons why the ice sheets are so important. Another one is their so-called 64 00:07:04,350 --> 00:07:09,940 sea level potential. Greenland and Antarctica are truly sleeping giants. And 65 00:07:09,940 --> 00:07:14,680 to give you an idea of the sheer size of these two ice sheets, one way of doing 66 00:07:14,680 --> 00:07:20,050 that is to compute their ice volume in the so-called sea level equivalent. What this 67 00:07:20,050 --> 00:07:24,510 means is, if we were to melt down the Greenland ice sheet and distribute that 68 00:07:24,510 --> 00:07:29,380 meltwater around the entire globe, then this would lead to a global sea level rise 69 00:07:29,380 --> 00:07:35,090 of roughly seven meters. For the West Antarctic ice sheet, it's about five 70 00:07:35,090 --> 00:07:41,360 meters, and for East Antarctica, the tenfold. So more than sixty five meters in 71 00:07:41,360 --> 00:07:47,740 total of sea level potential that are stored in these two ice sheets. Now, over 72 00:07:47,740 --> 00:07:51,960 the past decades, the ice sheets have both been losing mass and they've been losing 73 00:07:51,960 --> 00:07:57,650 mass at an accelerating pace. In fact, we're currently on track with the worst 74 00:07:57,650 --> 00:08:03,450 case climate change scenario. Here you see the observations in gray and you also see 75 00:08:03,450 --> 00:08:08,060 several of the projections from the past for the ice sheets. And as you can see, 76 00:08:08,060 --> 00:08:12,169 we're tracking this upper branch here. So we're really on track with the worst case 77 00:08:12,169 --> 00:08:17,450 climate change scenario for the ice sheets. And what this means is even if we 78 00:08:17,450 --> 00:08:22,210 were to stop global warming today, the ice sheets would still keep losing mass 79 00:08:22,210 --> 00:08:26,590 because of the inertia in the system. So sea levels would keep rising for decades 80 00:08:26,590 --> 00:08:33,459 or even centuries to come. Why is that? Well, there are several processes that we 81 00:08:33,459 --> 00:08:39,949 need to understand in order to keep track of sea level change and also to understand 82 00:08:39,949 --> 00:08:43,909 the ice sheet's evolution in the past and in the future. Here, you see sort of an 83 00:08:43,909 --> 00:08:50,089 exemplary cut through an ice shelf system, where the ice sheet is in contact with the 84 00:08:50,089 --> 00:08:55,539 atmosphere. You have a grounded part and then in many places, you also have these 85 00:08:55,539 --> 00:09:00,699 extensions, these floating extensions, the so-called ice shelves that surround 86 00:09:00,699 --> 00:09:06,470 particularly Antarctica. The separation between the two is the so-called grounding 87 00:09:06,470 --> 00:09:15,459 line. Now, generally ice sheets gain mass through snowfall just on top of the ice 88 00:09:15,459 --> 00:09:21,930 sheet, which then is compressed into ice and over time, due to the sheer gravity 89 00:09:21,930 --> 00:09:27,129 and the sheer size of the ice sheets, it's basically pushing its own mass towards the 90 00:09:27,129 --> 00:09:32,030 ocean. And that's one of the reasons why there's a constant flow of ice. So ice is 91 00:09:32,030 --> 00:09:37,160 really not only a solid, it's also a fluid. The ice sheets can also lose mass 92 00:09:37,160 --> 00:09:42,470 through surface melting, but also through melting at the underside of the floating 93 00:09:42,470 --> 00:09:48,389 ice shelves, where they're in contact with warmer ocean waters. And then there can, 94 00:09:48,389 --> 00:09:53,879 of course, also be ice shelf calving, so icebergs that break off at the margins of 95 00:09:53,879 --> 00:10:00,480 the ice sheet. Now, what we see here, this left hand side, that's a typical situation 96 00:10:00,480 --> 00:10:06,540 for the Greenland ice sheet. The Greenland ice sheet is generally grounded above sea 97 00:10:06,540 --> 00:10:12,040 level in most parts and it's not only much smaller than Antarctica, but it's also 98 00:10:12,040 --> 00:10:16,509 located further south, so further away from the pole. And that means it's 99 00:10:16,509 --> 00:10:21,939 generally warmer in Greenland, leading to more surface melt for the Greenland ice 100 00:10:21,939 --> 00:10:30,519 sheet. Whereas in Antarctica, it's not only much colder there, but also the ice 101 00:10:30,519 --> 00:10:36,580 sheet is covered and surrounded by floating ice shelves almost all around the 102 00:10:36,580 --> 00:10:40,980 coastline. And that means that one of the most important driving processes for mass 103 00:10:40,980 --> 00:10:45,639 loss in Antarctica is this melting underneath the ice shelves, so the 104 00:10:45,639 --> 00:10:51,860 subshelf melting in contact with the warmer ocean waters. Just to give you an 105 00:10:51,860 --> 00:10:57,819 impression of the sheer ice thickness, I brought this picture here. This is my very 106 00:10:57,819 --> 00:11:03,560 first impression of the Antarctic coastline, the ice shelf margin. This is 107 00:11:03,560 --> 00:11:08,029 close to the German research station Neumayer III. And I will never forget the 108 00:11:08,029 --> 00:11:12,799 moment that I first saw the ice shelf edge. It was in the middle of the night, 109 00:11:12,799 --> 00:11:17,219 but we were there in summer, so we had twenty four hours of daylight. And I woke 110 00:11:17,219 --> 00:11:22,370 up because it suddenly got dark in our cabin. So I went up to the bridge to see 111 00:11:22,370 --> 00:11:27,930 what was going on and I saw myself in front of a wall, like really a cliff of 112 00:11:27,930 --> 00:11:34,180 ice. And knowing that these ice shelves behave like the ice cubes in the water 113 00:11:34,180 --> 00:11:41,209 glass, so only roughly 10 percent are visible above the sea level, this means 114 00:11:41,209 --> 00:11:47,709 that in this case, we had an ice shelf edge that was more than 100 meters thick. 115 00:11:47,709 --> 00:11:51,439 And that really impressed me. I immediately had to think of this German 116 00:11:51,439 --> 00:11:57,209 expression, "das ewige Eis", the eternal ice. And I really wondered if this is 117 00:11:57,209 --> 00:12:02,240 maybe the right expression because it seemed like it was so static and nothing 118 00:12:02,240 --> 00:12:07,870 was moving. However, that's not true because even in equilibrium, the ice is 119 00:12:07,870 --> 00:12:13,350 constantly moving. It's here just visualized by these little snowflakes and 120 00:12:13,350 --> 00:12:19,100 you can see how the ice is moving from the interior towards the coastlines. And we 121 00:12:19,100 --> 00:12:24,089 have a wide range of velocities at the surface, ranging from almost zero in the 122 00:12:24,089 --> 00:12:29,350 interior of the ice sheet to several kilometers per year in the larger ice 123 00:12:29,350 --> 00:12:34,860 shelves and also the so-called ice streams, the faster flowing ice. If I were 124 00:12:34,860 --> 00:12:42,029 able to take a dive underneath the ice shelves and I could actually take a look 125 00:12:42,029 --> 00:12:47,310 at the grounding line, this would probably be what what I could see. This is the 126 00:12:47,310 --> 00:12:52,480 triple point basically where solid earth, the ice and water all come together. And 127 00:12:52,480 --> 00:12:56,379 this grounding line is a very important role for Antarctic ice dynamics and also 128 00:12:56,379 --> 00:13:04,059 for the future fate of Antarctica. So what makes the dynamics of the ice sheets and 129 00:13:04,059 --> 00:13:10,380 shelves so particularly difficult to understand and also to project the future 130 00:13:10,380 --> 00:13:15,569 evolution is that both ice sheets are subject to several so-called positive, so 131 00:13:15,569 --> 00:13:22,490 self-reinforcing feedback mechanisms. Here are just some examples with some of the 132 00:13:22,490 --> 00:13:28,089 major ones we know very well. One is the ice-albedo-feedback and another one is the 133 00:13:28,089 --> 00:13:33,490 so-called melt-elevation-feedback. As I said, in Greenland we observe a lot of 134 00:13:33,490 --> 00:13:38,330 surface melting. If you've ever flown across the Greenland ice sheet in summer, 135 00:13:38,330 --> 00:13:43,390 you can really see these rivers forming and then even lakes forming at the ice 136 00:13:43,390 --> 00:13:49,889 sheet surface. And over the recent decade, Greenland has been subject to several 137 00:13:49,889 --> 00:13:56,679 extreme melt events, including particularly the year 2010, 2012 and also 138 00:13:56,679 --> 00:14:01,830 last year. And the reason there's this extreme melting at the surface is due to a 139 00:14:01,830 --> 00:14:06,769 combination of factors, it has to do with the duration of the summer, but also even 140 00:14:06,769 --> 00:14:13,259 here in Europe, we observed very warm and dry summers. And that's also something 141 00:14:13,259 --> 00:14:18,639 that was observed for Greenland. So that, for instance, in the year 2019 in August, 142 00:14:18,639 --> 00:14:24,540 almost the entire ice sheet surface was covered with meltwater. Now, why is this 143 00:14:24,540 --> 00:14:29,680 surface melting so important? The reason is that there is also a self-reinforcing 144 00:14:29,680 --> 00:14:33,970 feedback that could be driven by surface melting. And we all know this mechanism 145 00:14:33,970 --> 00:14:38,639 from mountain climbing. If you climb down from the peak of a mountain towards the 146 00:14:38,639 --> 00:14:43,659 valley, it gets warmer around you. And the same is true also for the ice sheets. So 147 00:14:43,659 --> 00:14:48,850 if there's enough melting, it could actually lower the surface to a region 148 00:14:48,850 --> 00:14:53,309 where the temperatures are higher, the surface temperatures are higher, leading 149 00:14:53,309 --> 00:14:57,670 to more melting, which again lowers the surface elevation, leading to higher 150 00:14:57,670 --> 00:15:03,139 temperatures, leading to more melting and so on and so on, so that this can trigger 151 00:15:03,139 --> 00:15:09,809 these self-reinforcing dynamics. And whenever we have such a positive or self- 152 00:15:09,809 --> 00:15:15,450 reinforcing feedback mechanism, we can also have a tipping point. And here is the 153 00:15:15,450 --> 00:15:20,480 depiction of a very simple way of computing, where this tipping point might 154 00:15:20,480 --> 00:15:25,239 be for the Greenland ice sheet, where we've really done this with just 155 00:15:25,239 --> 00:15:31,489 analytical work. So pen and paper, trying to understand where we go from a stable 156 00:15:31,489 --> 00:15:37,449 Greenland ice sheet into unstable regime, which would then lead to a meltdown of the 157 00:15:37,449 --> 00:15:43,249 entire ice sheet until basically no ice is left at the surface. So this is something 158 00:15:43,249 --> 00:15:49,430 that we can understand in theory, but also something that we find in more complex 159 00:15:49,430 --> 00:15:57,339 numerical ice sheet models. And they find that this warming threshold that leads to 160 00:15:57,339 --> 00:16:02,910 basically a decay of the entire ice sheet lies somewhere between 0.8°C and 3.2°C of 161 00:16:02,910 --> 00:16:07,620 warming above pre-industrial levels. And you can see that between these 162 00:16:07,620 --> 00:16:12,619 temperatures, somewhere there's almost a step change. This is now the computed sea 163 00:16:12,619 --> 00:16:17,800 level rise. So up here, this means that Greenland is ice free. So we're going from 164 00:16:17,800 --> 00:16:23,350 an intact Greenland ice sheet to an ice free Greenland somewhere between these 165 00:16:23,350 --> 00:16:29,249 temperatures. What this looks like can be visualized with numerical ice sheet 166 00:16:29,249 --> 00:16:33,829 models. And here you see that once this threshold is exceeded, basically the 167 00:16:33,829 --> 00:16:39,509 eigendynamics lead to a complete meltdown off the ice sheet, until there's almost no 168 00:16:39,509 --> 00:16:44,160 ice left except for in the highest regions here in the east where there are some 169 00:16:44,160 --> 00:16:51,899 small ice caps remaining. Now, something similar, but also different is going on in 170 00:16:51,899 --> 00:16:58,439 Antarctica because, as I said earlier, in Antarctica it's much colder. So we have 171 00:16:58,439 --> 00:17:02,620 very little surface melt at the moment. But at the same time, it's surrounded by 172 00:17:02,620 --> 00:17:07,690 the floating ice shelves and they play the major role in driving sea changes in 173 00:17:07,690 --> 00:17:15,360 Antarctica. Antarctic mass loss has tripled over the recent years, especially 174 00:17:15,360 --> 00:17:19,150 in the so-called Amundson and Bellingshausen Sea regions. So these are 175 00:17:19,150 --> 00:17:24,310 these regions here where you see all these red parts. So this is all ice loss that's 176 00:17:24,310 --> 00:17:32,140 been detected here. And the reason for this is due to the ice shelf ocean 177 00:17:32,140 --> 00:17:37,120 interactions. So here you now see the ocean temperatures surrounding Antarctic 178 00:17:37,120 --> 00:17:42,060 ice shelves. And you can see a stark difference between the temperatures here 179 00:17:42,060 --> 00:17:46,240 around the Amundson and Bellingshausen regions and the temperatures, for 180 00:17:46,240 --> 00:17:50,030 instance, here in the Weddell Sea or in the Ross Sea, the temperature difference 181 00:17:50,030 --> 00:17:55,500 being roughly two degrees. So there's really been a switch from a colder to a 182 00:17:55,500 --> 00:18:01,740 warmer cavity, for instance, here in the Amundson Sea region. And that drives more 183 00:18:01,740 --> 00:18:06,780 sub shelf melting, which in turn leads to a decrease of the so-called buttressing 184 00:18:06,780 --> 00:18:14,360 effect. What this means is, well, first of all, the ice shelves do not contribute to 185 00:18:14,360 --> 00:18:19,200 sea level rise directly, at least not significantly. The reason being that they 186 00:18:19,200 --> 00:18:24,290 are like ice cubes in a water glass. And if that melts down, it also doesn't raise 187 00:18:24,290 --> 00:18:28,780 the water level in the glass. So it's similar with the ice shelves, but at the 188 00:18:28,780 --> 00:18:33,080 same time they are still attached to the grounded part of the sheet. So if the ice 189 00:18:33,080 --> 00:18:39,480 shelves melt or there are larger calving events in the ice shelves, that means that 190 00:18:39,480 --> 00:18:44,760 the flow behind them from the interior of the ice sheet into the ocean accelerates. 191 00:18:44,760 --> 00:18:50,910 It's almost like pulling a plug. And this is what is the so-called buttressing 192 00:18:50,910 --> 00:18:54,610 effects, so the backstress at the grounding line. So if we have enhanced ice 193 00:18:54,610 --> 00:18:59,070 shelf melting, that means that this buttressing effect, this buffering effect 194 00:18:59,070 --> 00:19:04,040 is reduced and therefore we have accelerated outflow into the ocean. Now, 195 00:19:04,040 --> 00:19:09,110 the question is, how does this impact the ice sheet dynamics overall, in particular, 196 00:19:09,110 --> 00:19:15,560 the stability of the West and East Antarctic ice sheets. You may have come 197 00:19:15,560 --> 00:19:21,180 across some of these headlines in recent years. My favorite one is still this one 198 00:19:21,180 --> 00:19:28,150 up here from 2014 where the "Holy Shit Moment of Global Warming" was declared. 199 00:19:28,150 --> 00:19:33,300 And the reason for this were these observations from the Amundson region in 200 00:19:33,300 --> 00:19:38,780 West Antarctica. So we're now taking sort of a flight into the Amundson Sea region. 201 00:19:38,780 --> 00:19:42,860 And what was observed over the recent decades is not only that the glaciers here 202 00:19:42,860 --> 00:19:48,421 have accelerated, so everything that's shown in red is accelerated ice flow, but 203 00:19:48,421 --> 00:19:54,110 at the same time, the glaciers have also retreated into the deeper valleys behind. 204 00:19:54,110 --> 00:19:59,530 So you see this browning at the surface now. So all of these changes where the 205 00:19:59,530 --> 00:20:05,050 glaciers have basically retreated and with this comes another self reinforcing 206 00:20:05,050 --> 00:20:10,140 feedback, the so-called marine ice-sheet instability. For the marine ice sheet 207 00:20:10,140 --> 00:20:16,360 instability to occur, we need two conditions to hold. One, as depicted here, 208 00:20:16,360 --> 00:20:21,170 is that the ice sheet is grounded below sea level, which is true for many parts of 209 00:20:21,170 --> 00:20:26,411 West Antarctica, but also some parts of East Antarctica. And also we need to 210 00:20:26,411 --> 00:20:32,700 generally have a retrograde sloping bed. So that means that the bedrock elevation 211 00:20:32,700 --> 00:20:38,120 decreases towards the interior of the ice sheet. And when these two conditions hold, 212 00:20:38,120 --> 00:20:42,980 then we can show in two dimensions, mathematically, we can prove 213 00:20:42,980 --> 00:20:49,960 mathematically that an instability occurs in this case. The reason is that we have 214 00:20:49,960 --> 00:20:54,980 an feedback between the grounding line retreat and the ice locks across the 215 00:20:54,980 --> 00:20:59,000 grounding line. If the grounding line retreats in a case where we have a 216 00:20:59,000 --> 00:21:03,390 retrograde sloping bed and the ice is ground below sea level, that means that 217 00:21:03,390 --> 00:21:09,750 the ice thickness towards the interior is larger. And this generally also means that 218 00:21:09,750 --> 00:21:14,450 the ice flux across the grounding line is larger, leading to further retreat off the 219 00:21:14,450 --> 00:21:18,670 grounding line and so on and so on. So again, we have a positive feedback 220 00:21:18,670 --> 00:21:23,950 mechanism that could drive self-sustained ice loss from parts of the West and East 221 00:21:23,950 --> 00:21:29,200 Antarctic ice sheet. And the concern is now that this marine ice sheet instability 222 00:21:29,200 --> 00:21:35,860 is potentially underway in the Amundson basin here in West Antarctica. Now, what's 223 00:21:35,860 --> 00:21:42,080 unclear is, how fast this change would actually occur. So if we have actually 224 00:21:42,080 --> 00:21:46,110 triggered the marine ice sheet instability in this region, and that means we have a 225 00:21:46,110 --> 00:21:52,830 committed ice loss of roughly one meter sea level equivalent, then the question is 226 00:21:52,830 --> 00:21:58,080 still, how fast does this occur? And for this, it really matters how much further 227 00:21:58,080 --> 00:22:02,871 global warming continues. So and at which rate the temperature will change in the 228 00:22:02,871 --> 00:22:09,924 future. So this is what's happening in part of the West Antarctic ice sheet. We 229 00:22:09,924 --> 00:22:13,550 were also asking ourselves, weather could something like this also happen for East 230 00:22:13,550 --> 00:22:19,440 Antarctica and how stable are each of the different ice basins in Antarctica? So we 231 00:22:19,440 --> 00:22:24,390 did something of a stability check on the Antarctic ice sheet to assess the risk of 232 00:22:24,390 --> 00:22:28,880 long term sea level rise from these different regions. What you will see next 233 00:22:28,880 --> 00:22:34,220 is an animation where we're increasing the global mean temperature, but we're 234 00:22:34,220 --> 00:22:39,570 increasing it very, very slowly, at a much slower rate than the typical rate of 235 00:22:39,570 --> 00:22:45,330 change in the ice sheet to test for the stability of these different parts. And 236 00:22:45,330 --> 00:22:52,360 what we see is that at roughly 2°C, we are losing a large part of the West Antarctic 237 00:22:52,360 --> 00:22:57,050 ice sheet. So there's a first tipping point around 2°C. And then as the 238 00:22:57,050 --> 00:23:04,430 temperature increases, also the surface elevation is lowered. And that leads to, 239 00:23:04,430 --> 00:23:10,580 potentially then also triggering these surface elevation and melt elevation 240 00:23:10,580 --> 00:23:16,870 feedbacks in East Antarctica. So around 6°C to 9°C, there's another major 241 00:23:16,870 --> 00:23:22,230 threshold. And after this, large parts of the East Antarctic ice sheet could also be 242 00:23:22,230 --> 00:23:30,970 committed to long term sea level rise. At about 10°C, the Antarctic ice sheet could 243 00:23:30,970 --> 00:23:36,070 potentially become ice free on the long term. And, this is really important. What 244 00:23:36,070 --> 00:23:40,610 we're seeing here are not projections, but what we're seeing here is a stability 245 00:23:40,610 --> 00:23:44,210 check. So we're not looking at something that's happening within the next century 246 00:23:44,210 --> 00:23:48,850 or so, but rather we're interested in understanding, at which temperatures the 247 00:23:48,850 --> 00:23:55,220 Antarctic ice sheet could still survive on the long term. We also wanted to see if 248 00:23:55,220 --> 00:24:01,810 some of these changes are reversible. And what we find is a so-called hysteresis 249 00:24:01,810 --> 00:24:07,390 behavior of the Antarctic ice sheet. That means, as we're losing the ice and we'll 250 00:24:07,390 --> 00:24:13,480 then cool the temperatures back down, the ice sheet does not regrow back to its 251 00:24:13,480 --> 00:24:18,990 initial state, but it takes much, much colder temperatures to regrow the same ice 252 00:24:18,990 --> 00:24:25,270 sheet volume that we are currently having at present day temperature levels. So 253 00:24:25,270 --> 00:24:31,270 there's a significant difference between this retreat and the regrowth path. And 254 00:24:31,270 --> 00:24:37,450 this can be up to 20 meters of sea level equivalent in the difference between these 255 00:24:37,450 --> 00:24:44,650 two paths. What this looks like regionally, you can see here. So again, we 256 00:24:44,650 --> 00:24:50,130 have the retreat and the regrowth path at 2°C of global warming, and 4°C of global 257 00:24:50,130 --> 00:24:54,200 warming. So these are the long term effects at these temperature levels. And 258 00:24:54,200 --> 00:25:00,120 you can see that, for instance, for 4°C large parts of East Antarctic and also of 259 00:25:00,120 --> 00:25:04,710 the West Antarctic ice sheet do not regrow at the same temperature level. So we 260 00:25:04,710 --> 00:25:10,140 clearly observe this hysteresis behavior. That's another sign that the Antarctic ice 261 00:25:10,140 --> 00:25:16,250 sheet is the tipping element in the climate system. So both Greenland and 262 00:25:16,250 --> 00:25:21,780 Antarctica are tipping elements in the climate system. There are a number more 263 00:25:21,780 --> 00:25:27,230 candidates for tipping elements, including some of the larger biosphere components, 264 00:25:27,230 --> 00:25:31,750 for instance, the Amazon rainforest, the tropical coral reefs, and also the boreal 265 00:25:31,750 --> 00:25:36,400 forests, as well as some of the large scale circulations. So, for instance, the 266 00:25:36,400 --> 00:25:41,450 Atlantic thermohaline circulation, what we often term the Gulf Stream, and the Indian 267 00:25:41,450 --> 00:25:48,650 summer monsoon are tipping candidates in the climate system. Now, if we go back to 268 00:25:48,650 --> 00:25:54,340 our temperature evolution since last glacial maximum, and we now insert what we 269 00:25:54,340 --> 00:25:59,510 know about the tipping thresholds of these different components in the Earth system, 270 00:25:59,510 --> 00:26:04,610 then this is what we get. And we see, that there are basically three clusters of 271 00:26:04,610 --> 00:26:09,750 tipping elements in comparison to the global mean temperature here. And you see 272 00:26:09,750 --> 00:26:14,600 in these burning ember diagrams that some of these tipping elements are at risk of 273 00:26:14,600 --> 00:26:21,030 switching into a different state, even within the Paris range of 1.5 - 2°C of 274 00:26:21,030 --> 00:26:26,050 warming. And among these most vulnerable tipping elements are the West Antarctic 275 00:26:26,050 --> 00:26:32,270 ice sheet and the Greenland ice sheet and in general, the cryosphere elements which 276 00:26:32,270 --> 00:26:38,040 seem to react to global warming and climate change much faster and therefore 277 00:26:38,040 --> 00:26:44,450 belong to the most vulnerable parts of the Earth system. So, if there's one thing 278 00:26:44,450 --> 00:26:51,680 that I would like you to take away from this talk, it is that ice matters. I've 279 00:26:51,680 --> 00:26:57,210 presented you with three reasons why. First of all, polar ice acts as a climate 280 00:26:57,210 --> 00:27:05,160 archive. It also acts as an early warning system. Secondly, glaciers and ice sheets 281 00:27:05,160 --> 00:27:09,460 are important contributors already to current sea level rise, but they will 282 00:27:09,460 --> 00:27:14,660 become even more important in the future as the global mean temperature keeps 283 00:27:14,660 --> 00:27:20,481 rising. And thirdly, both Greenland and Antarctica are tipping elements in the 284 00:27:20,481 --> 00:27:24,770 Earth system. And one of the next things we need to understand is how these tipping 285 00:27:24,770 --> 00:27:28,350 elements interact with one another. Because we have a very good understanding 286 00:27:28,350 --> 00:27:32,890 by now of the different mechanisms behind these tipping elements and of the 287 00:27:32,890 --> 00:27:37,470 individual temperature thresholds. But one of the, I think, most important questions 288 00:27:37,470 --> 00:27:42,140 we need to ask ourselves, is how the interaction of the tipping elements 289 00:27:42,140 --> 00:27:46,120 changes the stability of the Earth system as a whole and if there could be something 290 00:27:46,120 --> 00:27:51,280 like domino effects in the Earth system. And with this, thank you so much for your 291 00:27:51,280 --> 00:27:56,260 attention. And I'm very much looking forward to questions. 292 00:28:07,230 --> 00:28:28,060 Herald: Yeah, OK, fine, good, läuft, könnt ihr mich also hör'n, und ihr müsst mir 293 00:28:28,060 --> 00:28:30,860 also sagen, wann ich wieder drauf bin. Off: Du bist live. 294 00:28:30,860 --> 00:28:35,970 H: Hallo, wilkommen zurück! Thanks for this awesome talk, Ricarda, and we are now 295 00:28:35,970 --> 00:28:40,670 going to have a Q&A. And if you have any questions regarding this awesome talk, 296 00:28:40,670 --> 00:28:46,490 then please post them to the signal angels. They are following on Twitter and 297 00:28:46,490 --> 00:28:54,140 the Fediverse here, using the hashtag #rc3one, because this is rc1. And you can 298 00:28:54,140 --> 00:28:58,690 also post your questions to the IRC. You know, I already have a first question. I 299 00:28:58,690 --> 00:29:03,820 don't know, Ricarda, if you can hear me, but is there anything that this specific the CCC 300 00:29:03,820 --> 00:29:09,790 community of nerds and hackers can do more than anyone else to help with this issue? 301 00:29:09,790 --> 00:29:13,570 What do you think that we can do to help this? 302 00:29:13,570 --> 00:29:17,220 R: Yeah, thank you so much. Great question. Let me start by saying I'm a 303 00:29:17,220 --> 00:29:23,520 nerd and hacker myself. I'm a developer, or code developer, of the parallel ice 304 00:29:23,520 --> 00:29:28,240 sheet model. That's one of the ice sheet models for Greenland and Antarctica that's 305 00:29:28,240 --> 00:29:34,130 being used around the globe with many different applications. So, yeah, as a 306 00:29:34,130 --> 00:29:39,670 fellow nerd and hacker, I can say there's lots we can do, in particular towards 307 00:29:39,670 --> 00:29:44,510 understanding even better the different dynamics of the Greenland and the 308 00:29:44,510 --> 00:29:50,300 Antarctic ice sheet, but also beyond that, for the Earth system as a whole. I think 309 00:29:50,300 --> 00:29:54,490 we're now at a point where we understand the individual components of the Earth 310 00:29:54,490 --> 00:29:58,830 system better and better. We also have better and better observations, satellite 311 00:29:58,830 --> 00:30:05,780 observations, but also observations at the ground to further understand the different 312 00:30:05,780 --> 00:30:11,070 processes. But what we need now is to combine this with our knowledge in the 313 00:30:11,070 --> 00:30:16,970 modeling community and also with some of the approaches from big data, machine 314 00:30:16,970 --> 00:30:21,730 learning and so on, to really put this together, all the different puzzle pieces 315 00:30:21,730 --> 00:30:26,460 to understand what this means for the Earth system as a whole. And what I mean 316 00:30:26,460 --> 00:30:30,810 by that is, we now understand that there are several individual tipping points in 317 00:30:30,810 --> 00:30:35,750 the Earth system. And we also know that as global warming continues, we're at higher 318 00:30:35,750 --> 00:30:40,580 risks of transgressing individual tipping points. But what we still need to 319 00:30:40,580 --> 00:30:49,480 understand is what does this mean for the overall stability of our planet Earth? 320 00:30:49,480 --> 00:30:56,070 H: Thank you for this extended answer to this question. I have another one. I would 321 00:30:56,070 --> 00:31:01,020 like to know, I mean, you showed a slide where you showed the browning of the ice 322 00:31:01,020 --> 00:31:07,920 surface and then explained that this speeds up the process of melting as well. 323 00:31:07,920 --> 00:31:13,210 But, can we just paint it white or with a reflective paint on it? Has this been 324 00:31:13,210 --> 00:31:16,500 simulated? Is this of interest to you scientists? 325 00:31:16,500 --> 00:31:20,110 R: Yeah, very good question. So basically what you're addressing here is the 326 00:31:20,110 --> 00:31:25,920 question of the so-called ice albedo feedback. We all know this. As we're 327 00:31:25,920 --> 00:31:29,300 wearing black clothes in summer, it's warmer than when we're wearing white 328 00:31:29,300 --> 00:31:35,370 clothes. And the same is basically true for our planet as well. So the ice sheets 329 00:31:35,370 --> 00:31:40,920 and also the sea ice in the Arctic and Antarctica, they contribute considerably 330 00:31:40,920 --> 00:31:48,730 to a net cooling still of the planet. So if we didn't have these ice landscapes, 331 00:31:48,730 --> 00:31:52,940 that would mean that the planet would warm even faster and even further than it 332 00:31:52,940 --> 00:31:59,140 already is today. So currently, the ice albedo feedback is still helping us with 333 00:31:59,140 --> 00:32:04,830 keeping the temperatures at lower levels than they would be without the ice 334 00:32:04,830 --> 00:32:09,900 landscapes. And, yeah, therefore, it is definitely of interest to further 335 00:32:09,900 --> 00:32:14,871 understand what would this mean for, for instance, the global mean temperature, but 336 00:32:14,871 --> 00:32:21,090 also regional changes, if we were to lose our ice cover completely? And also the 337 00:32:21,090 --> 00:32:25,320 reverse question, of course, if we were to whiten parts of the planet, then how would 338 00:32:25,320 --> 00:32:33,520 this affect temperature? One thing that we found out is that if we were to lose the 339 00:32:33,520 --> 00:32:40,650 ice sheets and the sea ice in terms of the ice albedo feedback alone entirely, then 340 00:32:40,650 --> 00:32:48,420 this could already lead to an additional global warming of roughly 0.2°C. Now, that 341 00:32:48,420 --> 00:32:53,350 may not seem very much, but it certainly is important in the grand scheme of 342 00:32:53,350 --> 00:32:58,559 things. As we're thinking of, for instance, the Paris range of 1.5°C to 2°C 343 00:32:58,559 --> 00:33:03,330 of warming, every tenth of a degree matters. So, yeah, very interesting 344 00:33:03,330 --> 00:33:08,350 question. And this is something that has been done with numerical models, just to 345 00:33:08,350 --> 00:33:15,160 understand what kind of an effect these kind of what-if-scenarios would have also 346 00:33:15,160 --> 00:33:21,650 in terms of the albedo. H: Very interesting. So should we now 347 00:33:21,650 --> 00:33:24,160 start to develop drones who can spray paint? 348 00:33:24,160 --> 00:33:28,830 R: *laughs* That's a good question. I don't think that's the solution. I think 349 00:33:28,830 --> 00:33:33,590 we have a much better solution. And that is we know that we need to to mitigate 350 00:33:33,590 --> 00:33:39,200 climate change and reduce greenhouse gas emissions. And that is one that would work 351 00:33:39,200 --> 00:33:44,090 for sure. Whereas these questions of, well, should we spray paint all of our 352 00:33:44,090 --> 00:33:50,110 buildings at the at the top white? That is something that cannot be done at such a 353 00:33:50,110 --> 00:33:56,300 large scale as we would need it in order to reverse global warming. And another 354 00:33:56,300 --> 00:34:03,510 thing to keep in mind is that even if we were able to reduce the global signal, 355 00:34:03,510 --> 00:34:09,990 this still doesn't mean that we could also reverse the regional scale changes. We're 356 00:34:09,990 --> 00:34:16,490 already experiencing a large increase in extreme weather and climate events. And 357 00:34:16,490 --> 00:34:20,710 that is certainly something that I haven't seen so far, that this could also be 358 00:34:20,710 --> 00:34:26,030 reversed just by reversing the global mean temperature change as a whole. 359 00:34:26,030 --> 00:34:30,860 H: I have another question. I think that's quite interesting. How old is the oldest 360 00:34:30,860 --> 00:34:35,470 ice in Antarctica? Are you aware of that? And how long would it take a minimum to 361 00:34:35,470 --> 00:34:40,450 lose that entirely? R: Yeah, very good question. So the oldest 362 00:34:40,450 --> 00:34:45,110 ice, there's actually an ongoing search for the oldest ice in Antarctica. So to 363 00:34:45,110 --> 00:34:51,310 say, we know that Antarctica was ice free for the last time, roughly 34 million 364 00:34:51,310 --> 00:34:56,919 years ago. So when we're talking about these scenarios that eventually Antarctica 365 00:34:56,919 --> 00:35:02,410 could become ice free with, of course, very strong global warming scenarios of 366 00:35:02,410 --> 00:35:08,530 about 10°C of global warming, then we need to keep in mind that this was the case for 367 00:35:08,530 --> 00:35:14,010 the last time, about 34 million years ago. Now, as we're speaking, there 368 00:35:14,010 --> 00:35:20,840 is an ongoing project, an international collaboration to find and and also drill 369 00:35:20,840 --> 00:35:25,960 for the oldest ice so that we can really understand our Earth's history better and 370 00:35:25,960 --> 00:35:31,620 better. And so this is a very exciting project because, as I said, the ice cores 371 00:35:31,620 --> 00:35:35,820 are kind of like tree rings and we can count back in time and really understand 372 00:35:35,820 --> 00:35:42,250 what our global climate was like several, hundreds of thousands of years ago. So, 373 00:35:42,250 --> 00:35:47,540 yeah, with that being said, I think it's important to keep in mind that this is 374 00:35:47,540 --> 00:35:52,010 something that humans certainly have never experienced and that's therefore 375 00:35:52,010 --> 00:35:58,070 unprecedented in our world. H: ...for this very elaborate answer to 376 00:35:58,070 --> 00:36:04,731 this question, I know it is not the core of your research, but someone from the 377 00:36:04,731 --> 00:36:10,361 internet asked, if it's possible for old viruses and all the bacteria from back 378 00:36:10,361 --> 00:36:16,210 when Antarctica was like beginning to freeze over or from like 379 00:36:16,210 --> 00:36:19,990 millions of years ago, is it possible for them to thaw out again? Is that a danger 380 00:36:19,990 --> 00:36:22,520 for us? R: Oh, that's also a very interesting 381 00:36:22,520 --> 00:36:27,430 question. So I'm no expert on this, but I could imagine that at the temperatures 382 00:36:27,430 --> 00:36:34,070 that we have, Antarctica, especially the core ice body, there we have temperatures 383 00:36:34,070 --> 00:36:39,670 that go down to, well, I think the coldest temperature was something like -90°C that 384 00:36:39,670 --> 00:36:45,540 was recorded there. But in any case, it's very cold there. So there might be some 385 00:36:45,540 --> 00:36:50,840 bacteria that can survive these conditions. And I've read about bacteria 386 00:36:50,840 --> 00:36:57,290 like that, but I wouldn't know that there are many bacterial species or specimen 387 00:36:57,290 --> 00:37:02,640 that could survive these kinds of conditions. So to be honest, I would have 388 00:37:02,640 --> 00:37:05,920 to read up on that. That's a very interesting question. 389 00:37:05,920 --> 00:37:11,390 H: Yeah. Thank you for this answer. I remember that you watched, that you showed 390 00:37:11,390 --> 00:37:17,440 an animation and a graph for a simulated ice decline to find the tipping points in 391 00:37:17,440 --> 00:37:24,160 Antarctica. And on the x axis of that, I couldn't see a time scale. And now someone 392 00:37:24,160 --> 00:37:28,010 asked on the internet, what are the timescales between reaching a tipping 393 00:37:28,010 --> 00:37:32,360 point? And most of the ice being melted? Is that years, decades, centuries, 394 00:37:32,360 --> 00:37:38,240 millennia? What's kind of the scale there? R: Yes, very important point. So it's 395 00:37:38,240 --> 00:37:43,130 important to note that we're here showing this over the global mean temperature 396 00:37:43,130 --> 00:37:47,810 change. And the reason for this is that the way these kind of hysteresis 397 00:37:47,810 --> 00:37:53,450 experiments are run is that you have a very slow temperature increase. So slow, 398 00:37:53,450 --> 00:37:59,340 in fact, that it's much slower than the sort of internal time scales of the ice 399 00:37:59,340 --> 00:38:05,120 itself. And in this case, for instance, we had a temperature increase of 400 00:38:05,120 --> 00:38:12,910 10^-4°C/year. And the reason for this is because this is the way you're approaching 401 00:38:12,910 --> 00:38:17,390 the actual hysteresis curve that we were interested in. So this should not be 402 00:38:17,390 --> 00:38:24,580 mistaken for sea level projections of any sort. So what we find here are the actual, 403 00:38:24,580 --> 00:38:29,460 so to say, tipping points, the actual critical thresholds, that parts of the 404 00:38:29,460 --> 00:38:35,550 Antarctic ice sheet cannot survive. Nonetheless, of course, we're also working 405 00:38:35,550 --> 00:38:39,730 towards sea level projections and trying to understand what kind of sea level 406 00:38:39,730 --> 00:38:44,700 change we can expect from the ice sheets over the next decades to centuries to 407 00:38:44,700 --> 00:38:53,360 millennia. And one important thing there is that most of the ice loss that could be 408 00:38:53,360 --> 00:38:58,350 triggered now, would actually happen after the end of this century. So very often, 409 00:38:58,350 --> 00:39:03,100 when we see these sea level curves, we're looking until the year 2100. So for the 410 00:39:03,100 --> 00:39:10,060 next decades, how does the sea level respond to changes in temperature? But 411 00:39:10,060 --> 00:39:18,450 because we have so much inertia in the system, that means that even if the global 412 00:39:18,450 --> 00:39:24,140 warming signal was stopped right now, we would still see continued sea level rise 413 00:39:24,140 --> 00:39:29,949 for several decades to centuries. And that is something important to keep in mind. So 414 00:39:29,949 --> 00:39:34,690 I think we really need to start thinking of sea level rise in terms of commitment 415 00:39:34,690 --> 00:39:41,170 rather than these short term predictions. That being said, another important 416 00:39:41,170 --> 00:39:45,130 question and factor is the rate of sea level change, because this is actually 417 00:39:45,130 --> 00:39:50,711 what we need to adapt to as civilizations. When we think of building dams, there are 418 00:39:50,711 --> 00:39:57,350 two questions we need to answer. One is the magnitude of sea level rise and and 419 00:39:57,350 --> 00:40:03,740 also in its upper scale and upper limit to that. And the other question is the rate 420 00:40:03,740 --> 00:40:10,359 at which this changes. And what we find is that on the long term, there is something 421 00:40:10,359 --> 00:40:17,690 like 2.3m/°C of sea level change. So this is sort of a number to keep in mind when 422 00:40:17,690 --> 00:40:23,080 we think of sea level projections. And yeah, I think it's really important to 423 00:40:23,080 --> 00:40:29,431 consider longer timescales than the one to the year 2100 when we talk about sea level 424 00:40:29,431 --> 00:40:35,010 rise. H: Thank you for this answer, very 425 00:40:35,010 --> 00:40:41,060 interesting and we are out of time now, so thanks for all the questions and thank 426 00:40:41,060 --> 00:40:45,740 you, Ricarda, for this amazing talk. The next talk on this stage will be about a 427 00:40:45,740 --> 00:40:51,730 related topic, measuring CO2 indoors, but also in the atmosphere in general. But 428 00:40:51,730 --> 00:40:55,900 before that, we have a Herald News Show for your prepared. So enjoy! 429 00:40:55,900 --> 00:41:01,050 *Outro music* 430 00:41:01,050 --> 00:41:36,000 Subtitles created by c3subtitles.de in the year 2021. Join, and help us!