0:00:00.000,0:00:13.120
preroll music
0:00:13.120,0:00:19.530
Herald: It's simple when ice gets above[br]0°, it melts. But is it really that simple
0:00:19.530,0:00:23.270
if we are not talking about a small ice[br]cube, but a big sheet of ice covering an
0:00:23.270,0:00:28.910
entire continent? Is that really the only[br]factor? And, am I right with my
0:00:28.910,0:00:34.090
assessment? I'm looking forward to be[br]enlightened by Professor Doctor Ricarda
0:00:34.090,0:00:38.160
Winkelmann. Ricarda Winkelmann is a[br]professor of climate science at the
0:00:38.160,0:00:44.190
University of Potsdam, and she's also a[br]researcher for climate impact. She leads
0:00:44.190,0:00:48.540
the Ice Dynamics Working Group and Co-[br]leads PIK Future Lab on Earth Resilience
0:00:48.540,0:00:52.650
in the Anthropocene. Her research focuses[br]on tipping elements from the Earth system.
0:00:52.650,0:00:57.180
And today she'll be talking about the[br]Greenland and Antarctic ice dynamics and
0:00:57.180,0:01:03.130
the future sea level rise that are[br]impacted by them. It appears like she's
0:01:03.130,0:01:07.110
surely an expert on all things related to[br]ice. So please give a warm hand of
0:01:07.110,0:01:11.670
applause for Professor Doctor Ricarda[br]Winkelman with her talk: "The Big Melt:
0:01:11.670,0:01:17.710
Tipping Points in Greenland and[br]Antarctica" Have fun!
0:01:17.710,0:02:35.650
[no audio][br]in between music
0:02:35.650,0:02:39.709
Ricarda Winkelmann: audio not working[br]Thanks and welcome. Today, we're going to
0:02:39.709,0:02:45.180
take a little excursion to the far north[br]and the far south, to our polar ice sheets
0:02:45.180,0:02:51.609
on Greenland and Antarctica. As this year[br]is coming to a close, I thought we'd take
0:02:51.609,0:02:58.540
a brief moment to reflect back. 2020 has[br]certainly been an exceptional year for all
0:02:58.540,0:03:05.079
of us. It was supposed to be a super year[br]for nature and the environment, as world
0:03:05.079,0:03:09.290
leaders put it at the beginning of the[br]year. It's five years after the Paris
0:03:09.290,0:03:13.859
climate accord. It's five years after the[br]Sustainable Development Goals have been
0:03:13.859,0:03:19.790
announced. However, 2020 turned out to be[br]the year when we've had to face several
0:03:19.790,0:03:26.389
global crises, including the ongoing[br]covid-19 pandemic and also the ongoing
0:03:26.389,0:03:33.099
climate crisis. What almost got lost in[br]the turmoil is that this year also saw
0:03:33.099,0:03:37.939
several weather and climate extremes,[br]which spaned the globe from pole to pole,
0:03:37.939,0:03:47.329
with temperatures reaching record highs in[br]the Arctic and Antarctica with +38°C in
0:03:47.329,0:03:51.370
the Arctic and in Siberia. That's the[br]highest temperature that was ever recorded
0:03:51.370,0:03:55.569
north of the Arctic Circle and it's[br]roughly 18° warmer than the average
0:03:55.569,0:04:02.719
maximum daily temperature in June, when[br]this was recorded. And we also saw +18° at
0:04:02.719,0:04:07.519
the Antarctic Peninsula, which is, again,[br]the highest temperature ever recorded in
0:04:07.519,0:04:15.219
Antarctica. And this was followed by[br]widespread melting on nearby glaciers.
0:04:15.219,0:04:21.090
Now, if we're kind of zooming out and[br]taking a look at the bigger picture, we're
0:04:21.090,0:04:25.670
also at a very significant point in[br]Earth's history. Here you see the global
0:04:25.670,0:04:31.590
mean temperature evolution since the last glacial[br]maximum. So the last ice age until today.
0:04:31.590,0:04:35.950
And whenever I look at this graph, I see[br]two things that still strike me to this
0:04:35.950,0:04:40.940
day. One is that the Holocene, the[br]interglacial or the warm age, in which
0:04:40.940,0:04:45.500
human civilizations have developed and[br]thrived, has been characterized by very
0:04:45.500,0:04:50.650
stable climate conditions, by a very[br]stable global mean temperature. And the
0:04:50.650,0:04:54.590
other thing is that the difference between[br]an ice age, here, 20 000 years ago
0:04:54.590,0:05:00.540
roughly, and a warm age, that's roughly[br]three to four degrees of global average
0:05:00.540,0:05:05.690
temperature change. And right now we're on[br]the verge of achieving the same
0:05:05.690,0:05:12.700
temperature difference, but at much, much[br]faster rates. So here you see several
0:05:12.700,0:05:17.731
future temperature projections from the[br]IPCC. And what you can see is, that in all
0:05:17.731,0:05:22.290
of them, the temperature increase, even[br]the lowest one, the temperature increase
0:05:22.290,0:05:27.970
is much faster than it was ever recorded[br]before. So I think it's safe to say that
0:05:27.970,0:05:32.800
we have truly entered the Anthropocene and[br]that humans have become a geological
0:05:32.800,0:05:39.520
force. So in the Anthropocene, humans have[br]become the single most important driver of
0:05:39.520,0:05:45.270
global change affecting the entire Earth[br]system, including our ice sheets. But it
0:05:45.270,0:05:50.690
was kind of the opposite in the past. Like[br]no other forces on the planet, ice ages
0:05:50.690,0:05:55.770
have actually shaped our surroundings and[br]thereby determined our development as
0:05:55.770,0:06:01.040
human civilizations. For instance, we owe[br]our fertile soils, to the last ice age,
0:06:01.040,0:06:06.060
that also carved our current landscapes[br]that we see all around us, leaving
0:06:06.060,0:06:12.900
glaciers behind, rivers and lakes. So even[br]though the ice sheets on Greenland and
0:06:12.900,0:06:18.980
Antarctica might seem far away sometimes,[br]they're actually crucial also for us here
0:06:18.980,0:06:25.010
today. And today, I want to leave you with[br]an impression why they are so important.
0:06:25.010,0:06:28.300
And one reason why they are so important[br]is because they're an amazing climate
0:06:28.300,0:06:35.260
archive. Here you see an ice core taken[br]from one of the deepest parts of an ice
0:06:35.260,0:06:40.610
sheet. And this is basically like counting[br]tree rings. You can go back to the past
0:06:40.610,0:06:47.480
and you can see what the climate was like[br]in the deep past, ranging several hundreds
0:06:47.480,0:06:52.500
of thousands of years back. And you can[br]see the conditions, for instance, in the
0:06:52.500,0:06:58.730
CO2 change, the temperature change over[br]this really long timescales. So that's one
0:06:58.730,0:07:04.350
of the reasons why the ice sheets are so[br]important. Another one is their so-called
0:07:04.350,0:07:09.940
sea level potential. Greenland and[br]Antarctica are truly sleeping giants. And
0:07:09.940,0:07:14.680
to give you an idea of the sheer size of[br]these two ice sheets, one way of doing
0:07:14.680,0:07:20.050
that is to compute their ice volume in the[br]so-called sea level equivalent. What this
0:07:20.050,0:07:24.510
means is, if we were to melt down the[br]Greenland ice sheet and distribute that
0:07:24.510,0:07:29.380
meltwater around the entire globe, then[br]this would lead to a global sea level rise
0:07:29.380,0:07:35.090
of roughly seven meters. For the West[br]Antarctic ice sheet, it's about five
0:07:35.090,0:07:41.360
meters, and for East Antarctica, the[br]tenfold. So more than sixty five meters in
0:07:41.360,0:07:47.740
total of sea level potential that are[br]stored in these two ice sheets. Now, over
0:07:47.740,0:07:51.960
the past decades, the ice sheets have both[br]been losing mass and they've been losing
0:07:51.960,0:07:57.650
mass at an accelerating pace. In fact,[br]we're currently on track with the worst
0:07:57.650,0:08:03.450
case climate change scenario. Here you see[br]the observations in gray and you also see
0:08:03.450,0:08:08.060
several of the projections from the past[br]for the ice sheets. And as you can see,
0:08:08.060,0:08:12.169
we're tracking this upper branch here. So[br]we're really on track with the worst case
0:08:12.169,0:08:17.450
climate change scenario for the ice[br]sheets. And what this means is even if we
0:08:17.450,0:08:22.210
were to stop global warming today, the ice[br]sheets would still keep losing mass
0:08:22.210,0:08:26.590
because of the inertia in the system. So[br]sea levels would keep rising for decades
0:08:26.590,0:08:33.459
or even centuries to come. Why is that?[br]Well, there are several processes that we
0:08:33.459,0:08:39.949
need to understand in order to keep track[br]of sea level change and also to understand
0:08:39.949,0:08:43.909
the ice sheet's evolution in the past and[br]in the future. Here, you see sort of an
0:08:43.909,0:08:50.089
exemplary cut through an ice shelf system,[br]where the ice sheet is in contact with the
0:08:50.089,0:08:55.539
atmosphere. You have a grounded part and[br]then in many places, you also have these
0:08:55.539,0:09:00.699
extensions, these floating extensions, the[br]so-called ice shelves that surround
0:09:00.699,0:09:06.470
particularly Antarctica. The separation[br]between the two is the so-called grounding
0:09:06.470,0:09:15.459
line. Now, generally ice sheets gain mass[br]through snowfall just on top of the ice
0:09:15.459,0:09:21.930
sheet, which then is compressed into ice[br]and over time, due to the sheer gravity
0:09:21.930,0:09:27.129
and the sheer size of the ice sheets, it's[br]basically pushing its own mass towards the
0:09:27.129,0:09:32.030
ocean. And that's one of the reasons why[br]there's a constant flow of ice. So ice is
0:09:32.030,0:09:37.160
really not only a solid, it's also a[br]fluid. The ice sheets can also lose mass
0:09:37.160,0:09:42.470
through surface melting, but also through[br]melting at the underside of the floating
0:09:42.470,0:09:48.389
ice shelves, where they're in contact with[br]warmer ocean waters. And then there can,
0:09:48.389,0:09:53.879
of course, also be ice shelf calving, so[br]icebergs that break off at the margins of
0:09:53.879,0:10:00.480
the ice sheet. Now, what we see here, this[br]left hand side, that's a typical situation
0:10:00.480,0:10:06.540
for the Greenland ice sheet. The Greenland[br]ice sheet is generally grounded above sea
0:10:06.540,0:10:12.040
level in most parts and it's not only much[br]smaller than Antarctica, but it's also
0:10:12.040,0:10:16.509
located further south, so further away[br]from the pole. And that means it's
0:10:16.509,0:10:21.939
generally warmer in Greenland, leading to[br]more surface melt for the Greenland ice
0:10:21.939,0:10:30.519
sheet. Whereas in Antarctica, it's not[br]only much colder there, but also the ice
0:10:30.519,0:10:36.580
sheet is covered and surrounded by[br]floating ice shelves almost all around the
0:10:36.580,0:10:40.980
coastline. And that means that one of the[br]most important driving processes for mass
0:10:40.980,0:10:45.639
loss in Antarctica is this melting[br]underneath the ice shelves, so the
0:10:45.639,0:10:51.860
subshelf melting in contact with the[br]warmer ocean waters. Just to give you an
0:10:51.860,0:10:57.819
impression of the sheer ice thickness, I[br]brought this picture here. This is my very
0:10:57.819,0:11:03.560
first impression of the Antarctic[br]coastline, the ice shelf margin. This is
0:11:03.560,0:11:08.029
close to the German research station[br]Neumayer III. And I will never forget the
0:11:08.029,0:11:12.799
moment that I first saw the ice shelf[br]edge. It was in the middle of the night,
0:11:12.799,0:11:17.219
but we were there in summer, so we had[br]twenty four hours of daylight. And I woke
0:11:17.219,0:11:22.370
up because it suddenly got dark in our[br]cabin. So I went up to the bridge to see
0:11:22.370,0:11:27.930
what was going on and I saw myself in[br]front of a wall, like really a cliff of
0:11:27.930,0:11:34.180
ice. And knowing that these ice shelves[br]behave like the ice cubes in the water
0:11:34.180,0:11:41.209
glass, so only roughly 10 percent are[br]visible above the sea level, this means
0:11:41.209,0:11:47.709
that in this case, we had an ice shelf[br]edge that was more than 100 meters thick.
0:11:47.709,0:11:51.439
And that really impressed me. I[br]immediately had to think of this German
0:11:51.439,0:11:57.209
expression, "das ewige Eis", the eternal[br]ice. And I really wondered if this is
0:11:57.209,0:12:02.240
maybe the right expression because it[br]seemed like it was so static and nothing
0:12:02.240,0:12:07.870
was moving. However, that's not true[br]because even in equilibrium, the ice is
0:12:07.870,0:12:13.350
constantly moving. It's here just[br]visualized by these little snowflakes and
0:12:13.350,0:12:19.100
you can see how the ice is moving from the[br]interior towards the coastlines. And we
0:12:19.100,0:12:24.089
have a wide range of velocities at the[br]surface, ranging from almost zero in the
0:12:24.089,0:12:29.350
interior of the ice sheet to several[br]kilometers per year in the larger ice
0:12:29.350,0:12:34.860
shelves and also the so-called ice[br]streams, the faster flowing ice. If I were
0:12:34.860,0:12:42.029
able to take a dive underneath the ice[br]shelves and I could actually take a look
0:12:42.029,0:12:47.310
at the grounding line, this would probably[br]be what what I could see. This is the
0:12:47.310,0:12:52.480
triple point basically where solid earth,[br]the ice and water all come together. And
0:12:52.480,0:12:56.379
this grounding line is a very important[br]role for Antarctic ice dynamics and also
0:12:56.379,0:13:04.059
for the future fate of Antarctica. So what[br]makes the dynamics of the ice sheets and
0:13:04.059,0:13:10.380
shelves so particularly difficult to[br]understand and also to project the future
0:13:10.380,0:13:15.569
evolution is that both ice sheets are[br]subject to several so-called positive, so
0:13:15.569,0:13:22.490
self-reinforcing feedback mechanisms. Here[br]are just some examples with some of the
0:13:22.490,0:13:28.089
major ones we know very well. One is the[br]ice-albedo-feedback and another one is the
0:13:28.089,0:13:33.490
so-called melt-elevation-feedback. As I[br]said, in Greenland we observe a lot of
0:13:33.490,0:13:38.330
surface melting. If you've ever flown[br]across the Greenland ice sheet in summer,
0:13:38.330,0:13:43.390
you can really see these rivers forming[br]and then even lakes forming at the ice
0:13:43.390,0:13:49.889
sheet surface. And over the recent decade,[br]Greenland has been subject to several
0:13:49.889,0:13:56.679
extreme melt events, including[br]particularly the year 2010, 2012 and also
0:13:56.679,0:14:01.830
last year. And the reason there's this[br]extreme melting at the surface is due to a
0:14:01.830,0:14:06.769
combination of factors, it has to do with[br]the duration of the summer, but also even
0:14:06.769,0:14:13.259
here in Europe, we observed very warm and[br]dry summers. And that's also something
0:14:13.259,0:14:18.639
that was observed for Greenland. So that,[br]for instance, in the year 2019 in August,
0:14:18.639,0:14:24.540
almost the entire ice sheet surface was[br]covered with meltwater. Now, why is this
0:14:24.540,0:14:29.680
surface melting so important? The reason[br]is that there is also a self-reinforcing
0:14:29.680,0:14:33.970
feedback that could be driven by surface[br]melting. And we all know this mechanism
0:14:33.970,0:14:38.639
from mountain climbing. If you climb down[br]from the peak of a mountain towards the
0:14:38.639,0:14:43.659
valley, it gets warmer around you. And the[br]same is true also for the ice sheets. So
0:14:43.659,0:14:48.850
if there's enough melting, it could[br]actually lower the surface to a region
0:14:48.850,0:14:53.309
where the temperatures are higher, the[br]surface temperatures are higher, leading
0:14:53.309,0:14:57.670
to more melting, which again lowers the[br]surface elevation, leading to higher
0:14:57.670,0:15:03.139
temperatures, leading to more melting and[br]so on and so on, so that this can trigger
0:15:03.139,0:15:09.809
these self-reinforcing dynamics. And[br]whenever we have such a positive or self-
0:15:09.809,0:15:15.450
reinforcing feedback mechanism, we can[br]also have a tipping point. And here is the
0:15:15.450,0:15:20.480
depiction of a very simple way of[br]computing, where this tipping point might
0:15:20.480,0:15:25.239
be for the Greenland ice sheet, where[br]we've really done this with just
0:15:25.239,0:15:31.489
analytical work. So pen and paper, trying[br]to understand where we go from a stable
0:15:31.489,0:15:37.449
Greenland ice sheet into unstable regime,[br]which would then lead to a meltdown of the
0:15:37.449,0:15:43.249
entire ice sheet until basically no ice is[br]left at the surface. So this is something
0:15:43.249,0:15:49.430
that we can understand in theory, but also[br]something that we find in more complex
0:15:49.430,0:15:57.339
numerical ice sheet models. And they find[br]that this warming threshold that leads to
0:15:57.339,0:16:02.910
basically a decay of the entire ice sheet[br]lies somewhere between 0.8°C and 3.2°C of
0:16:02.910,0:16:07.620
warming above pre-industrial levels. And[br]you can see that between these
0:16:07.620,0:16:12.619
temperatures, somewhere there's almost a[br]step change. This is now the computed sea
0:16:12.619,0:16:17.800
level rise. So up here, this means that[br]Greenland is ice free. So we're going from
0:16:17.800,0:16:23.350
an intact Greenland ice sheet to an ice[br]free Greenland somewhere between these
0:16:23.350,0:16:29.249
temperatures. What this looks like can be[br]visualized with numerical ice sheet
0:16:29.249,0:16:33.829
models. And here you see that once this[br]threshold is exceeded, basically the
0:16:33.829,0:16:39.509
eigendynamics lead to a complete meltdown[br]off the ice sheet, until there's almost no
0:16:39.509,0:16:44.160
ice left except for in the highest regions[br]here in the east where there are some
0:16:44.160,0:16:51.899
small ice caps remaining. Now, something[br]similar, but also different is going on in
0:16:51.899,0:16:58.439
Antarctica because, as I said earlier, in[br]Antarctica it's much colder. So we have
0:16:58.439,0:17:02.620
very little surface melt at the moment.[br]But at the same time, it's surrounded by
0:17:02.620,0:17:07.690
the floating ice shelves and they play the[br]major role in driving sea changes in
0:17:07.690,0:17:15.360
Antarctica. Antarctic mass loss has[br]tripled over the recent years, especially
0:17:15.360,0:17:19.150
in the so-called Amundson and[br]Bellingshausen Sea regions. So these are
0:17:19.150,0:17:24.310
these regions here where you see all these[br]red parts. So this is all ice loss that's
0:17:24.310,0:17:32.140
been detected here. And the reason for[br]this is due to the ice shelf ocean
0:17:32.140,0:17:37.120
interactions. So here you now see the[br]ocean temperatures surrounding Antarctic
0:17:37.120,0:17:42.060
ice shelves. And you can see a stark[br]difference between the temperatures here
0:17:42.060,0:17:46.240
around the Amundson and Bellingshausen[br]regions and the temperatures, for
0:17:46.240,0:17:50.030
instance, here in the Weddell Sea or in[br]the Ross Sea, the temperature difference
0:17:50.030,0:17:55.500
being roughly two degrees. So there's[br]really been a switch from a colder to a
0:17:55.500,0:18:01.740
warmer cavity, for instance, here in the[br]Amundson Sea region. And that drives more
0:18:01.740,0:18:06.780
sub shelf melting, which in turn leads to[br]a decrease of the so-called buttressing
0:18:06.780,0:18:14.360
effect. What this means is, well, first of[br]all, the ice shelves do not contribute to
0:18:14.360,0:18:19.200
sea level rise directly, at least not[br]significantly. The reason being that they
0:18:19.200,0:18:24.290
are like ice cubes in a water glass. And[br]if that melts down, it also doesn't raise
0:18:24.290,0:18:28.780
the water level in the glass. So it's[br]similar with the ice shelves, but at the
0:18:28.780,0:18:33.080
same time they are still attached to the[br]grounded part of the sheet. So if the ice
0:18:33.080,0:18:39.480
shelves melt or there are larger calving[br]events in the ice shelves, that means that
0:18:39.480,0:18:44.760
the flow behind them from the interior of[br]the ice sheet into the ocean accelerates.
0:18:44.760,0:18:50.910
It's almost like pulling a plug. And this[br]is what is the so-called buttressing
0:18:50.910,0:18:54.610
effects, so the backstress at the[br]grounding line. So if we have enhanced ice
0:18:54.610,0:18:59.070
shelf melting, that means that this[br]buttressing effect, this buffering effect
0:18:59.070,0:19:04.040
is reduced and therefore we have[br]accelerated outflow into the ocean. Now,
0:19:04.040,0:19:09.110
the question is, how does this impact the[br]ice sheet dynamics overall, in particular,
0:19:09.110,0:19:15.560
the stability of the West and East[br]Antarctic ice sheets. You may have come
0:19:15.560,0:19:21.180
across some of these headlines in recent[br]years. My favorite one is still this one
0:19:21.180,0:19:28.150
up here from 2014 where the "Holy Shit[br]Moment of Global Warming" was declared.
0:19:28.150,0:19:33.300
And the reason for this were these[br]observations from the Amundson region in
0:19:33.300,0:19:38.780
West Antarctica. So we're now taking sort[br]of a flight into the Amundson Sea region.
0:19:38.780,0:19:42.860
And what was observed over the recent[br]decades is not only that the glaciers here
0:19:42.860,0:19:48.421
have accelerated, so everything that's[br]shown in red is accelerated ice flow, but
0:19:48.421,0:19:54.110
at the same time, the glaciers have also[br]retreated into the deeper valleys behind.
0:19:54.110,0:19:59.530
So you see this browning at the surface[br]now. So all of these changes where the
0:19:59.530,0:20:05.050
glaciers have basically retreated and with[br]this comes another self reinforcing
0:20:05.050,0:20:10.140
feedback, the so-called marine ice-sheet[br]instability. For the marine ice sheet
0:20:10.140,0:20:16.360
instability to occur, we need two[br]conditions to hold. One, as depicted here,
0:20:16.360,0:20:21.170
is that the ice sheet is grounded below[br]sea level, which is true for many parts of
0:20:21.170,0:20:26.411
West Antarctica, but also some parts of[br]East Antarctica. And also we need to
0:20:26.411,0:20:32.700
generally have a retrograde sloping bed.[br]So that means that the bedrock elevation
0:20:32.700,0:20:38.120
decreases towards the interior of the ice[br]sheet. And when these two conditions hold,
0:20:38.120,0:20:42.980
then we can show in two dimensions,[br]mathematically, we can prove
0:20:42.980,0:20:49.960
mathematically that an instability occurs[br]in this case. The reason is that we have
0:20:49.960,0:20:54.980
an feedback between the grounding line[br]retreat and the ice locks across the
0:20:54.980,0:20:59.000
grounding line. If the grounding line[br]retreats in a case where we have a
0:20:59.000,0:21:03.390
retrograde sloping bed and the ice is[br]ground below sea level, that means that
0:21:03.390,0:21:09.750
the ice thickness towards the interior is[br]larger. And this generally also means that
0:21:09.750,0:21:14.450
the ice flux across the grounding line is[br]larger, leading to further retreat off the
0:21:14.450,0:21:18.670
grounding line and so on and so on. So[br]again, we have a positive feedback
0:21:18.670,0:21:23.950
mechanism that could drive self-sustained[br]ice loss from parts of the West and East
0:21:23.950,0:21:29.200
Antarctic ice sheet. And the concern is[br]now that this marine ice sheet instability
0:21:29.200,0:21:35.860
is potentially underway in the Amundson[br]basin here in West Antarctica. Now, what's
0:21:35.860,0:21:42.080
unclear is, how fast this change would[br]actually occur. So if we have actually
0:21:42.080,0:21:46.110
triggered the marine ice sheet instability[br]in this region, and that means we have a
0:21:46.110,0:21:52.830
committed ice loss of roughly one meter[br]sea level equivalent, then the question is
0:21:52.830,0:21:58.080
still, how fast does this occur? And for[br]this, it really matters how much further
0:21:58.080,0:22:02.871
global warming continues. So and at which[br]rate the temperature will change in the
0:22:02.871,0:22:09.924
future. So this is what's happening in[br]part of the West Antarctic ice sheet. We
0:22:09.924,0:22:13.550
were also asking ourselves, weather could[br]something like this also happen for East
0:22:13.550,0:22:19.440
Antarctica and how stable are each of the[br]different ice basins in Antarctica? So we
0:22:19.440,0:22:24.390
did something of a stability check on the[br]Antarctic ice sheet to assess the risk of
0:22:24.390,0:22:28.880
long term sea level rise from these[br]different regions. What you will see next
0:22:28.880,0:22:34.220
is an animation where we're increasing the[br]global mean temperature, but we're
0:22:34.220,0:22:39.570
increasing it very, very slowly, at a much[br]slower rate than the typical rate of
0:22:39.570,0:22:45.330
change in the ice sheet to test for the[br]stability of these different parts. And
0:22:45.330,0:22:52.360
what we see is that at roughly 2°C, we are[br]losing a large part of the West Antarctic
0:22:52.360,0:22:57.050
ice sheet. So there's a first tipping[br]point around 2°C. And then as the
0:22:57.050,0:23:04.430
temperature increases, also the surface[br]elevation is lowered. And that leads to,
0:23:04.430,0:23:10.580
potentially then also triggering these[br]surface elevation and melt elevation
0:23:10.580,0:23:16.870
feedbacks in East Antarctica. So around[br]6°C to 9°C, there's another major
0:23:16.870,0:23:22.230
threshold. And after this, large parts of[br]the East Antarctic ice sheet could also be
0:23:22.230,0:23:30.970
committed to long term sea level rise. At[br]about 10°C, the Antarctic ice sheet could
0:23:30.970,0:23:36.070
potentially become ice free on the long[br]term. And, this is really important. What
0:23:36.070,0:23:40.610
we're seeing here are not projections, but[br]what we're seeing here is a stability
0:23:40.610,0:23:44.210
check. So we're not looking at something[br]that's happening within the next century
0:23:44.210,0:23:48.850
or so, but rather we're interested in[br]understanding, at which temperatures the
0:23:48.850,0:23:55.220
Antarctic ice sheet could still survive on[br]the long term. We also wanted to see if
0:23:55.220,0:24:01.810
some of these changes are reversible. And[br]what we find is a so-called hysteresis
0:24:01.810,0:24:07.390
behavior of the Antarctic ice sheet. That[br]means, as we're losing the ice and we'll
0:24:07.390,0:24:13.480
then cool the temperatures back down, the[br]ice sheet does not regrow back to its
0:24:13.480,0:24:18.990
initial state, but it takes much, much[br]colder temperatures to regrow the same ice
0:24:18.990,0:24:25.270
sheet volume that we are currently having[br]at present day temperature levels. So
0:24:25.270,0:24:31.270
there's a significant difference between[br]this retreat and the regrowth path. And
0:24:31.270,0:24:37.450
this can be up to 20 meters of sea level[br]equivalent in the difference between these
0:24:37.450,0:24:44.650
two paths. What this looks like[br]regionally, you can see here. So again, we
0:24:44.650,0:24:50.130
have the retreat and the regrowth path at[br]2°C of global warming, and 4°C of global
0:24:50.130,0:24:54.200
warming. So these are the long term[br]effects at these temperature levels. And
0:24:54.200,0:25:00.120
you can see that, for instance, for 4°C[br]large parts of East Antarctic and also of
0:25:00.120,0:25:04.710
the West Antarctic ice sheet do not regrow[br]at the same temperature level. So we
0:25:04.710,0:25:10.140
clearly observe this hysteresis behavior.[br]That's another sign that the Antarctic ice
0:25:10.140,0:25:16.250
sheet is the tipping element in the[br]climate system. So both Greenland and
0:25:16.250,0:25:21.780
Antarctica are tipping elements in the[br]climate system. There are a number more
0:25:21.780,0:25:27.230
candidates for tipping elements, including[br]some of the larger biosphere components,
0:25:27.230,0:25:31.750
for instance, the Amazon rainforest, the[br]tropical coral reefs, and also the boreal
0:25:31.750,0:25:36.400
forests, as well as some of the large[br]scale circulations. So, for instance, the
0:25:36.400,0:25:41.450
Atlantic thermohaline circulation, what we[br]often term the Gulf Stream, and the Indian
0:25:41.450,0:25:48.650
summer monsoon are tipping candidates in[br]the climate system. Now, if we go back to
0:25:48.650,0:25:54.340
our temperature evolution since last[br]glacial maximum, and we now insert what we
0:25:54.340,0:25:59.510
know about the tipping thresholds of these[br]different components in the Earth system,
0:25:59.510,0:26:04.610
then this is what we get. And we see, that[br]there are basically three clusters of
0:26:04.610,0:26:09.750
tipping elements in comparison to the[br]global mean temperature here. And you see
0:26:09.750,0:26:14.600
in these burning ember diagrams that some[br]of these tipping elements are at risk of
0:26:14.600,0:26:21.030
switching into a different state, even[br]within the Paris range of 1.5 - 2°C of
0:26:21.030,0:26:26.050
warming. And among these most vulnerable[br]tipping elements are the West Antarctic
0:26:26.050,0:26:32.270
ice sheet and the Greenland ice sheet and[br]in general, the cryosphere elements which
0:26:32.270,0:26:38.040
seem to react to global warming and[br]climate change much faster and therefore
0:26:38.040,0:26:44.450
belong to the most vulnerable parts of the[br]Earth system. So, if there's one thing
0:26:44.450,0:26:51.680
that I would like you to take away from[br]this talk, it is that ice matters. I've
0:26:51.680,0:26:57.210
presented you with three reasons why.[br]First of all, polar ice acts as a climate
0:26:57.210,0:27:05.160
archive. It also acts as an early warning[br]system. Secondly, glaciers and ice sheets
0:27:05.160,0:27:09.460
are important contributors already to[br]current sea level rise, but they will
0:27:09.460,0:27:14.660
become even more important in the future[br]as the global mean temperature keeps
0:27:14.660,0:27:20.481
rising. And thirdly, both Greenland and[br]Antarctica are tipping elements in the
0:27:20.481,0:27:24.770
Earth system. And one of the next things[br]we need to understand is how these tipping
0:27:24.770,0:27:28.350
elements interact with one another.[br]Because we have a very good understanding
0:27:28.350,0:27:32.890
by now of the different mechanisms behind[br]these tipping elements and of the
0:27:32.890,0:27:37.470
individual temperature thresholds. But one[br]of the, I think, most important questions
0:27:37.470,0:27:42.140
we need to ask ourselves, is how the[br]interaction of the tipping elements
0:27:42.140,0:27:46.120
changes the stability of the Earth system[br]as a whole and if there could be something
0:27:46.120,0:27:51.280
like domino effects in the Earth system.[br]And with this, thank you so much for your
0:27:51.280,0:27:56.260
attention. And I'm very much looking[br]forward to questions.
0:28:07.230,0:28:28.060
Herald: Yeah, OK, fine, good, läuft, könnt[br]ihr mich also hör'n, und ihr müsst mir
0:28:28.060,0:28:30.860
also sagen, wann ich wieder drauf bin.[br]Off: Du bist live.
0:28:30.860,0:28:35.970
H: Hallo, wilkommen zurück! Thanks for[br]this awesome talk, Ricarda, and we are now
0:28:35.970,0:28:40.670
going to have a Q&A. And if you have any[br]questions regarding this awesome talk,
0:28:40.670,0:28:46.490
then please post them to the signal[br]angels. They are following on Twitter and
0:28:46.490,0:28:54.140
the Fediverse here, using the hashtag[br]#rc3one, because this is rc1. And you can
0:28:54.140,0:28:58.690
also post your questions to the IRC. You[br]know, I already have a first question. I
0:28:58.690,0:29:03.820
don't know, Ricarda, if you can hear me,[br]but is there anything that this specific the CCC
0:29:03.820,0:29:09.790
community of nerds and hackers can do more[br]than anyone else to help with this issue?
0:29:09.790,0:29:13.570
What do you think that[br]we can do to help this?
0:29:13.570,0:29:17.220
R: Yeah, thank you so much. Great[br]question. Let me start by saying I'm a
0:29:17.220,0:29:23.520
nerd and hacker myself. I'm a developer,[br]or code developer, of the parallel ice
0:29:23.520,0:29:28.240
sheet model. That's one of the ice sheet[br]models for Greenland and Antarctica that's
0:29:28.240,0:29:34.130
being used around the globe with many[br]different applications. So, yeah, as a
0:29:34.130,0:29:39.670
fellow nerd and hacker, I can say there's[br]lots we can do, in particular towards
0:29:39.670,0:29:44.510
understanding even better the different[br]dynamics of the Greenland and the
0:29:44.510,0:29:50.300
Antarctic ice sheet, but also beyond that,[br]for the Earth system as a whole. I think
0:29:50.300,0:29:54.490
we're now at a point where we understand[br]the individual components of the Earth
0:29:54.490,0:29:58.830
system better and better. We also have[br]better and better observations, satellite
0:29:58.830,0:30:05.780
observations, but also observations at the[br]ground to further understand the different
0:30:05.780,0:30:11.070
processes. But what we need now is to[br]combine this with our knowledge in the
0:30:11.070,0:30:16.970
modeling community and also with some of[br]the approaches from big data, machine
0:30:16.970,0:30:21.730
learning and so on, to really put this[br]together, all the different puzzle pieces
0:30:21.730,0:30:26.460
to understand what this means for the[br]Earth system as a whole. And what I mean
0:30:26.460,0:30:30.810
by that is, we now understand that there[br]are several individual tipping points in
0:30:30.810,0:30:35.750
the Earth system. And we also know that as[br]global warming continues, we're at higher
0:30:35.750,0:30:40.580
risks of transgressing individual tipping[br]points. But what we still need to
0:30:40.580,0:30:49.480
understand is what does this mean for the[br]overall stability of our planet Earth?
0:30:49.480,0:30:56.070
H: Thank you for this extended answer to[br]this question. I have another one. I would
0:30:56.070,0:31:01.020
like to know, I mean, you showed a slide[br]where you showed the browning of the ice
0:31:01.020,0:31:07.920
surface and then explained that this[br]speeds up the process of melting as well.
0:31:07.920,0:31:13.210
But, can we just paint it white or with a[br]reflective paint on it? Has this been
0:31:13.210,0:31:16.500
simulated? Is this of interest to you[br]scientists?
0:31:16.500,0:31:20.110
R: Yeah, very good question. So basically[br]what you're addressing here is the
0:31:20.110,0:31:25.920
question of the so-called ice albedo[br]feedback. We all know this. As we're
0:31:25.920,0:31:29.300
wearing black clothes in summer, it's[br]warmer than when we're wearing white
0:31:29.300,0:31:35.370
clothes. And the same is basically true[br]for our planet as well. So the ice sheets
0:31:35.370,0:31:40.920
and also the sea ice in the Arctic and[br]Antarctica, they contribute considerably
0:31:40.920,0:31:48.730
to a net cooling still of the planet. So[br]if we didn't have these ice landscapes,
0:31:48.730,0:31:52.940
that would mean that the planet would warm[br]even faster and even further than it
0:31:52.940,0:31:59.140
already is today. So currently, the ice[br]albedo feedback is still helping us with
0:31:59.140,0:32:04.830
keeping the temperatures at lower levels[br]than they would be without the ice
0:32:04.830,0:32:09.900
landscapes. And, yeah, therefore, it is[br]definitely of interest to further
0:32:09.900,0:32:14.871
understand what would this mean for, for[br]instance, the global mean temperature, but
0:32:14.871,0:32:21.090
also regional changes, if we were to lose[br]our ice cover completely? And also the
0:32:21.090,0:32:25.320
reverse question, of course, if we were to[br]whiten parts of the planet, then how would
0:32:25.320,0:32:33.520
this affect temperature? One thing that we[br]found out is that if we were to lose the
0:32:33.520,0:32:40.650
ice sheets and the sea ice in terms of the[br]ice albedo feedback alone entirely, then
0:32:40.650,0:32:48.420
this could already lead to an additional[br]global warming of roughly 0.2°C. Now, that
0:32:48.420,0:32:53.350
may not seem very much, but it certainly[br]is important in the grand scheme of
0:32:53.350,0:32:58.559
things. As we're thinking of, for[br]instance, the Paris range of 1.5°C to 2°C
0:32:58.559,0:33:03.330
of warming, every tenth of a degree[br]matters. So, yeah, very interesting
0:33:03.330,0:33:08.350
question. And this is something that has[br]been done with numerical models, just to
0:33:08.350,0:33:15.160
understand what kind of an effect these[br]kind of what-if-scenarios would have also
0:33:15.160,0:33:21.650
in terms of the albedo.[br]H: Very interesting. So should we now
0:33:21.650,0:33:24.160
start to develop drones[br]who can spray paint?
0:33:24.160,0:33:28.830
R: laughs That's a good question. I[br]don't think that's the solution. I think
0:33:28.830,0:33:33.590
we have a much better solution. And that[br]is we know that we need to to mitigate
0:33:33.590,0:33:39.200
climate change and reduce greenhouse gas[br]emissions. And that is one that would work
0:33:39.200,0:33:44.090
for sure. Whereas these questions of,[br]well, should we spray paint all of our
0:33:44.090,0:33:50.110
buildings at the at the top white? That is[br]something that cannot be done at such a
0:33:50.110,0:33:56.300
large scale as we would need it in order[br]to reverse global warming. And another
0:33:56.300,0:34:03.510
thing to keep in mind is that even if we[br]were able to reduce the global signal,
0:34:03.510,0:34:09.990
this still doesn't mean that we could also[br]reverse the regional scale changes. We're
0:34:09.990,0:34:16.490
already experiencing a large increase in[br]extreme weather and climate events. And
0:34:16.490,0:34:20.710
that is certainly something that I haven't[br]seen so far, that this could also be
0:34:20.710,0:34:26.030
reversed just by reversing the global mean[br]temperature change as a whole.
0:34:26.030,0:34:30.860
H: I have another question. I think that's[br]quite interesting. How old is the oldest
0:34:30.860,0:34:35.470
ice in Antarctica? Are you aware of that?[br]And how long would it take a minimum to
0:34:35.470,0:34:40.450
lose that entirely?[br]R: Yeah, very good question. So the oldest
0:34:40.450,0:34:45.110
ice, there's actually an ongoing search[br]for the oldest ice in Antarctica. So to
0:34:45.110,0:34:51.310
say, we know that Antarctica was ice free[br]for the last time, roughly 34 million
0:34:51.310,0:34:56.919
years ago. So when we're talking about[br]these scenarios that eventually Antarctica
0:34:56.919,0:35:02.410
could become ice free with, of course,[br]very strong global warming scenarios of
0:35:02.410,0:35:08.530
about 10°C of global warming, then we need[br]to keep in mind that this was the case for
0:35:08.530,0:35:14.010
the last time, about 34 million[br]years ago. Now, as we're speaking, there
0:35:14.010,0:35:20.840
is an ongoing project, an international[br]collaboration to find and and also drill
0:35:20.840,0:35:25.960
for the oldest ice so that we can really[br]understand our Earth's history better and
0:35:25.960,0:35:31.620
better. And so this is a very exciting[br]project because, as I said, the ice cores
0:35:31.620,0:35:35.820
are kind of like tree rings and we can[br]count back in time and really understand
0:35:35.820,0:35:42.250
what our global climate was like several,[br]hundreds of thousands of years ago. So,
0:35:42.250,0:35:47.540
yeah, with that being said, I think it's[br]important to keep in mind that this is
0:35:47.540,0:35:52.010
something that humans certainly have never[br]experienced and that's therefore
0:35:52.010,0:35:58.070
unprecedented in our world.[br]H: ...for this very elaborate answer to
0:35:58.070,0:36:04.731
this question, I know it is not the core[br]of your research, but someone from the
0:36:04.731,0:36:10.361
internet asked, if it's possible for old[br]viruses and all the bacteria from back
0:36:10.361,0:36:16.210
when Antarctica was like beginning to[br]freeze over or from like
0:36:16.210,0:36:19.990
millions of years ago, is it possible for[br]them to thaw out again? Is that a danger
0:36:19.990,0:36:22.520
for us?[br]R: Oh, that's also a very interesting
0:36:22.520,0:36:27.430
question. So I'm no expert on this, but I[br]could imagine that at the temperatures
0:36:27.430,0:36:34.070
that we have, Antarctica, especially the[br]core ice body, there we have temperatures
0:36:34.070,0:36:39.670
that go down to, well, I think the coldest[br]temperature was something like -90°C that
0:36:39.670,0:36:45.540
was recorded there. But in any case, it's[br]very cold there. So there might be some
0:36:45.540,0:36:50.840
bacteria that can survive these[br]conditions. And I've read about bacteria
0:36:50.840,0:36:57.290
like that, but I wouldn't know that there[br]are many bacterial species or specimen
0:36:57.290,0:37:02.640
that could survive these kinds of[br]conditions. So to be honest, I would have
0:37:02.640,0:37:05.920
to read up on that. That's a very[br]interesting question.
0:37:05.920,0:37:11.390
H: Yeah. Thank you for this answer. I[br]remember that you watched, that you showed
0:37:11.390,0:37:17.440
an animation and a graph for a simulated[br]ice decline to find the tipping points in
0:37:17.440,0:37:24.160
Antarctica. And on the x axis of that, I[br]couldn't see a time scale. And now someone
0:37:24.160,0:37:28.010
asked on the internet, what are the[br]timescales between reaching a tipping
0:37:28.010,0:37:32.360
point? And most of the ice being melted?[br]Is that years, decades, centuries,
0:37:32.360,0:37:38.240
millennia? What's kind of the scale there?[br]R: Yes, very important point. So it's
0:37:38.240,0:37:43.130
important to note that we're here showing[br]this over the global mean temperature
0:37:43.130,0:37:47.810
change. And the reason for this is that[br]the way these kind of hysteresis
0:37:47.810,0:37:53.450
experiments are run is that you have a[br]very slow temperature increase. So slow,
0:37:53.450,0:37:59.340
in fact, that it's much slower than the[br]sort of internal time scales of the ice
0:37:59.340,0:38:05.120
itself. And in this case, for instance, we[br]had a temperature increase of
0:38:05.120,0:38:12.910
10^-4°C/year. And the reason for this is[br]because this is the way you're approaching
0:38:12.910,0:38:17.390
the actual hysteresis curve that we were[br]interested in. So this should not be
0:38:17.390,0:38:24.580
mistaken for sea level projections of any[br]sort. So what we find here are the actual,
0:38:24.580,0:38:29.460
so to say, tipping points, the actual[br]critical thresholds, that parts of the
0:38:29.460,0:38:35.550
Antarctic ice sheet cannot survive.[br]Nonetheless, of course, we're also working
0:38:35.550,0:38:39.730
towards sea level projections and trying[br]to understand what kind of sea level
0:38:39.730,0:38:44.700
change we can expect from the ice sheets[br]over the next decades to centuries to
0:38:44.700,0:38:53.360
millennia. And one important thing there[br]is that most of the ice loss that could be
0:38:53.360,0:38:58.350
triggered now, would actually happen after[br]the end of this century. So very often,
0:38:58.350,0:39:03.100
when we see these sea level curves, we're[br]looking until the year 2100. So for the
0:39:03.100,0:39:10.060
next decades, how does the sea level[br]respond to changes in temperature? But
0:39:10.060,0:39:18.450
because we have so much inertia in the[br]system, that means that even if the global
0:39:18.450,0:39:24.140
warming signal was stopped right now, we[br]would still see continued sea level rise
0:39:24.140,0:39:29.949
for several decades to centuries. And that[br]is something important to keep in mind. So
0:39:29.949,0:39:34.690
I think we really need to start thinking[br]of sea level rise in terms of commitment
0:39:34.690,0:39:41.170
rather than these short term predictions.[br]That being said, another important
0:39:41.170,0:39:45.130
question and factor is the rate of sea[br]level change, because this is actually
0:39:45.130,0:39:50.711
what we need to adapt to as civilizations.[br]When we think of building dams, there are
0:39:50.711,0:39:57.350
two questions we need to answer. One is[br]the magnitude of sea level rise and and
0:39:57.350,0:40:03.740
also in its upper scale and upper limit to[br]that. And the other question is the rate
0:40:03.740,0:40:10.359
at which this changes. And what we find is[br]that on the long term, there is something
0:40:10.359,0:40:17.690
like 2.3m/°C of sea level change. So this[br]is sort of a number to keep in mind when
0:40:17.690,0:40:23.080
we think of sea level projections. And[br]yeah, I think it's really important to
0:40:23.080,0:40:29.431
consider longer timescales than the one to[br]the year 2100 when we talk about sea level
0:40:29.431,0:40:35.010
rise.[br]H: Thank you for this answer, very
0:40:35.010,0:40:41.060
interesting and we are out of time now, so[br]thanks for all the questions and thank
0:40:41.060,0:40:45.740
you, Ricarda, for this amazing talk. The[br]next talk on this stage will be about a
0:40:45.740,0:40:51.730
related topic, measuring CO2 indoors, but[br]also in the atmosphere in general. But
0:40:51.730,0:40:55.900
before that, we have a Herald News Show[br]for your prepared. So enjoy!
0:40:55.900,0:41:01.050
Outro music
0:41:01.050,0:41:36.000
Subtitles created by c3subtitles.de[br]in the year 2021. Join, and help us!