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