preroll music
Herald: It's simple when ice gets above
0°, it melts. But is it really that simple
if we are not talking about a small ice
cube, but a big sheet of ice covering an
entire continent? Is that really the only
factor? And, am I right with my
assessment? I'm looking forward to be
enlightened by Professor Doctor Ricarda
Winkelmann. Ricarda Winkelmann is a
professor of climate science at the
University of Potsdam, and she's also a
researcher for climate impact. She leads
the Ice Dynamics Working Group and Co-
leads PIK Future Lab on Earth Resilience
in the Anthropocene. Her research focuses
on tipping elements from the Earth system.
And today she'll be talking about the
Greenland and Antarctic ice dynamics and
the future sea level rise that are
impacted by them. It appears like she's
surely an expert on all things related to
ice. So please give a warm hand of
applause for Professor Doctor Ricarda
Winkelman with her talk: "The Big Melt:
Tipping Points in Greenland and
Antarctica" Have fun!
[no audio]
in between music
Ricarda Winkelmann: audio not working
Thanks and welcome. Today, we're going to
take a little excursion to the far north
and the far south, to our polar ice sheets
on Greenland and Antarctica. As this year
is coming to a close, I thought we'd take
a brief moment to reflect back. 2020 has
certainly been an exceptional year for all
of us. It was supposed to be a super year
for nature and the environment, as world
leaders put it at the beginning of the
year. It's five years after the Paris
climate accord. It's five years after the
Sustainable Development Goals have been
announced. However, 2020 turned out to be
the year when we've had to face several
global crises, including the ongoing
covid-19 pandemic and also the ongoing
climate crisis. What almost got lost in
the turmoil is that this year also saw
several weather and climate extremes,
which spaned the globe from pole to pole,
with temperatures reaching record highs in
the Arctic and Antarctica with +38°C in
the Arctic and in Siberia. That's the
highest temperature that was ever recorded
north of the Arctic Circle and it's
roughly 18° warmer than the average
maximum daily temperature in June, when
this was recorded. And we also saw +18° at
the Antarctic Peninsula, which is, again,
the highest temperature ever recorded in
Antarctica. And this was followed by
widespread melting on nearby glaciers.
Now, if we're kind of zooming out and
taking a look at the bigger picture, we're
also at a very significant point in
Earth's history. Here you see the global
mean temperature evolution since the last glacial
maximum. So the last ice age until today.
And whenever I look at this graph, I see
two things that still strike me to this
day. One is that the Holocene, the
interglacial or the warm age, in which
human civilizations have developed and
thrived, has been characterized by very
stable climate conditions, by a very
stable global mean temperature. And the
other thing is that the difference between
an ice age, here, 20 000 years ago
roughly, and a warm age, that's roughly
three to four degrees of global average
temperature change. And right now we're on
the verge of achieving the same
temperature difference, but at much, much
faster rates. So here you see several
future temperature projections from the
IPCC. And what you can see is, that in all
of them, the temperature increase, even
the lowest one, the temperature increase
is much faster than it was ever recorded
before. So I think it's safe to say that
we have truly entered the Anthropocene and
that humans have become a geological
force. So in the Anthropocene, humans have
become the single most important driver of
global change affecting the entire Earth
system, including our ice sheets. But it
was kind of the opposite in the past. Like
no other forces on the planet, ice ages
have actually shaped our surroundings and
thereby determined our development as
human civilizations. For instance, we owe
our fertile soils, to the last ice age,
that also carved our current landscapes
that we see all around us, leaving
glaciers behind, rivers and lakes. So even
though the ice sheets on Greenland and
Antarctica might seem far away sometimes,
they're actually crucial also for us here
today. And today, I want to leave you with
an impression why they are so important.
And one reason why they are so important
is because they're an amazing climate
archive. Here you see an ice core taken
from one of the deepest parts of an ice
sheet. And this is basically like counting
tree rings. You can go back to the past
and you can see what the climate was like
in the deep past, ranging several hundreds
of thousands of years back. And you can
see the conditions, for instance, in the
CO2 change, the temperature change over
this really long timescales. So that's one
of the reasons why the ice sheets are so
important. Another one is their so-called
sea level potential. Greenland and
Antarctica are truly sleeping giants. And
to give you an idea of the sheer size of
these two ice sheets, one way of doing
that is to compute their ice volume in the
so-called sea level equivalent. What this
means is, if we were to melt down the
Greenland ice sheet and distribute that
meltwater around the entire globe, then
this would lead to a global sea level rise
of roughly seven meters. For the West
Antarctic ice sheet, it's about five
meters, and for East Antarctica, the
tenfold. So more than sixty five meters in
total of sea level potential that are
stored in these two ice sheets. Now, over
the past decades, the ice sheets have both
been losing mass and they've been losing
mass at an accelerating pace. In fact,
we're currently on track with the worst
case climate change scenario. Here you see
the observations in gray and you also see
several of the projections from the past
for the ice sheets. And as you can see,
we're tracking this upper branch here. So
we're really on track with the worst case
climate change scenario for the ice
sheets. And what this means is even if we
were to stop global warming today, the ice
sheets would still keep losing mass
because of the inertia in the system. So
sea levels would keep rising for decades
or even centuries to come. Why is that?
Well, there are several processes that we
need to understand in order to keep track
of sea level change and also to understand
the ice sheet's evolution in the past and
in the future. Here, you see sort of an
exemplary cut through an ice shelf system,
where the ice sheet is in contact with the
atmosphere. You have a grounded part and
then in many places, you also have these
extensions, these floating extensions, the
so-called ice shelves that surround
particularly Antarctica. The separation
between the two is the so-called grounding
line. Now, generally ice sheets gain mass
through snowfall just on top of the ice
sheet, which then is compressed into ice
and over time, due to the sheer gravity
and the sheer size of the ice sheets, it's
basically pushing its own mass towards the
ocean. And that's one of the reasons why
there's a constant flow of ice. So ice is
really not only a solid, it's also a
fluid. The ice sheets can also lose mass
through surface melting, but also through
melting at the underside of the floating
ice shelves, where they're in contact with
warmer ocean waters. And then there can,
of course, also be ice shelf calving, so
icebergs that break off at the margins of
the ice sheet. Now, what we see here, this
left hand side, that's a typical situation
for the Greenland ice sheet. The Greenland
ice sheet is generally grounded above sea
level in most parts and it's not only much
smaller than Antarctica, but it's also
located further south, so further away
from the pole. And that means it's
generally warmer in Greenland, leading to
more surface melt for the Greenland ice
sheet. Whereas in Antarctica, it's not
only much colder there, but also the ice
sheet is covered and surrounded by
floating ice shelves almost all around the
coastline. And that means that one of the
most important driving processes for mass
loss in Antarctica is this melting
underneath the ice shelves, so the
subshelf melting in contact with the
warmer ocean waters. Just to give you an
impression of the sheer ice thickness, I
brought this picture here. This is my very
first impression of the Antarctic
coastline, the ice shelf margin. This is
close to the German research station
Neumayer III. And I will never forget the
moment that I first saw the ice shelf
edge. It was in the middle of the night,
but we were there in summer, so we had
twenty four hours of daylight. And I woke
up because it suddenly got dark in our
cabin. So I went up to the bridge to see
what was going on and I saw myself in
front of a wall, like really a cliff of
ice. And knowing that these ice shelves
behave like the ice cubes in the water
glass, so only roughly 10 percent are
visible above the sea level, this means
that in this case, we had an ice shelf
edge that was more than 100 meters thick.
And that really impressed me. I
immediately had to think of this German
expression, "das ewige Eis", the eternal
ice. And I really wondered if this is
maybe the right expression because it
seemed like it was so static and nothing
was moving. However, that's not true
because even in equilibrium, the ice is
constantly moving. It's here just
visualized by these little snowflakes and
you can see how the ice is moving from the
interior towards the coastlines. And we
have a wide range of velocities at the
surface, ranging from almost zero in the
interior of the ice sheet to several
kilometers per year in the larger ice
shelves and also the so-called ice
streams, the faster flowing ice. If I were
able to take a dive underneath the ice
shelves and I could actually take a look
at the grounding line, this would probably
be what what I could see. This is the
triple point basically where solid earth,
the ice and water all come together. And
this grounding line is a very important
role for Antarctic ice dynamics and also
for the future fate of Antarctica. So what
makes the dynamics of the ice sheets and
shelves so particularly difficult to
understand and also to project the future
evolution is that both ice sheets are
subject to several so-called positive, so
self-reinforcing feedback mechanisms. Here
are just some examples with some of the
major ones we know very well. One is the
ice-albedo-feedback and another one is the
so-called melt-elevation-feedback. As I
said, in Greenland we observe a lot of
surface melting. If you've ever flown
across the Greenland ice sheet in summer,
you can really see these rivers forming
and then even lakes forming at the ice
sheet surface. And over the recent decade,
Greenland has been subject to several
extreme melt events, including
particularly the year 2010, 2012 and also
last year. And the reason there's this
extreme melting at the surface is due to a
combination of factors, it has to do with
the duration of the summer, but also even
here in Europe, we observed very warm and
dry summers. And that's also something
that was observed for Greenland. So that,
for instance, in the year 2019 in August,
almost the entire ice sheet surface was
covered with meltwater. Now, why is this
surface melting so important? The reason
is that there is also a self-reinforcing
feedback that could be driven by surface
melting. And we all know this mechanism
from mountain climbing. If you climb down
from the peak of a mountain towards the
valley, it gets warmer around you. And the
same is true also for the ice sheets. So
if there's enough melting, it could
actually lower the surface to a region
where the temperatures are higher, the
surface temperatures are higher, leading
to more melting, which again lowers the
surface elevation, leading to higher
temperatures, leading to more melting and
so on and so on, so that this can trigger
these self-reinforcing dynamics. And
whenever we have such a positive or self-
reinforcing feedback mechanism, we can
also have a tipping point. And here is the
depiction of a very simple way of
computing, where this tipping point might
be for the Greenland ice sheet, where
we've really done this with just
analytical work. So pen and paper, trying
to understand where we go from a stable
Greenland ice sheet into unstable regime,
which would then lead to a meltdown of the
entire ice sheet until basically no ice is
left at the surface. So this is something
that we can understand in theory, but also
something that we find in more complex
numerical ice sheet models. And they find
that this warming threshold that leads to
basically a decay of the entire ice sheet
lies somewhere between 0.8°C and 3.2°C of
warming above pre-industrial levels. And
you can see that between these
temperatures, somewhere there's almost a
step change. This is now the computed sea
level rise. So up here, this means that
Greenland is ice free. So we're going from
an intact Greenland ice sheet to an ice
free Greenland somewhere between these
temperatures. What this looks like can be
visualized with numerical ice sheet
models. And here you see that once this
threshold is exceeded, basically the
eigendynamics lead to a complete meltdown
off the ice sheet, until there's almost no
ice left except for in the highest regions
here in the east where there are some
small ice caps remaining. Now, something
similar, but also different is going on in
Antarctica because, as I said earlier, in
Antarctica it's much colder. So we have
very little surface melt at the moment.
But at the same time, it's surrounded by
the floating ice shelves and they play the
major role in driving sea changes in
Antarctica. Antarctic mass loss has
tripled over the recent years, especially
in the so-called Amundson and
Bellingshausen Sea regions. So these are
these regions here where you see all these
red parts. So this is all ice loss that's
been detected here. And the reason for
this is due to the ice shelf ocean
interactions. So here you now see the
ocean temperatures surrounding Antarctic
ice shelves. And you can see a stark
difference between the temperatures here
around the Amundson and Bellingshausen
regions and the temperatures, for
instance, here in the Weddell Sea or in
the Ross Sea, the temperature difference
being roughly two degrees. So there's
really been a switch from a colder to a
warmer cavity, for instance, here in the
Amundson Sea region. And that drives more
sub shelf melting, which in turn leads to
a decrease of the so-called buttressing
effect. What this means is, well, first of
all, the ice shelves do not contribute to
sea level rise directly, at least not
significantly. The reason being that they
are like ice cubes in a water glass. And
if that melts down, it also doesn't raise
the water level in the glass. So it's
similar with the ice shelves, but at the
same time they are still attached to the
grounded part of the sheet. So if the ice
shelves melt or there are larger calving
events in the ice shelves, that means that
the flow behind them from the interior of
the ice sheet into the ocean accelerates.
It's almost like pulling a plug. And this
is what is the so-called buttressing
effects, so the backstress at the
grounding line. So if we have enhanced ice
shelf melting, that means that this
buttressing effect, this buffering effect
is reduced and therefore we have
accelerated outflow into the ocean. Now,
the question is, how does this impact the
ice sheet dynamics overall, in particular,
the stability of the West and East
Antarctic ice sheets. You may have come
across some of these headlines in recent
years. My favorite one is still this one
up here from 2014 where the "Holy Shit
Moment of Global Warming" was declared.
And the reason for this were these
observations from the Amundson region in
West Antarctica. So we're now taking sort
of a flight into the Amundson Sea region.
And what was observed over the recent
decades is not only that the glaciers here
have accelerated, so everything that's
shown in red is accelerated ice flow, but
at the same time, the glaciers have also
retreated into the deeper valleys behind.
So you see this browning at the surface
now. So all of these changes where the
glaciers have basically retreated and with
this comes another self reinforcing
feedback, the so-called marine ice-sheet
instability. For the marine ice sheet
instability to occur, we need two
conditions to hold. One, as depicted here,
is that the ice sheet is grounded below
sea level, which is true for many parts of
West Antarctica, but also some parts of
East Antarctica. And also we need to
generally have a retrograde sloping bed.
So that means that the bedrock elevation
decreases towards the interior of the ice
sheet. And when these two conditions hold,
then we can show in two dimensions,
mathematically, we can prove
mathematically that an instability occurs
in this case. The reason is that we have
an feedback between the grounding line
retreat and the ice locks across the
grounding line. If the grounding line
retreats in a case where we have a
retrograde sloping bed and the ice is
ground below sea level, that means that
the ice thickness towards the interior is
larger. And this generally also means that
the ice flux across the grounding line is
larger, leading to further retreat off the
grounding line and so on and so on. So
again, we have a positive feedback
mechanism that could drive self-sustained
ice loss from parts of the West and East
Antarctic ice sheet. And the concern is
now that this marine ice sheet instability
is potentially underway in the Amundson
basin here in West Antarctica. Now, what's
unclear is, how fast this change would
actually occur. So if we have actually
triggered the marine ice sheet instability
in this region, and that means we have a
committed ice loss of roughly one meter
sea level equivalent, then the question is
still, how fast does this occur? And for
this, it really matters how much further
global warming continues. So and at which
rate the temperature will change in the
future. So this is what's happening in
part of the West Antarctic ice sheet. We
were also asking ourselves, weather could
something like this also happen for East
Antarctica and how stable are each of the
different ice basins in Antarctica? So we
did something of a stability check on the
Antarctic ice sheet to assess the risk of
long term sea level rise from these
different regions. What you will see next
is an animation where we're increasing the
global mean temperature, but we're
increasing it very, very slowly, at a much
slower rate than the typical rate of
change in the ice sheet to test for the
stability of these different parts. And
what we see is that at roughly 2°C, we are
losing a large part of the West Antarctic
ice sheet. So there's a first tipping
point around 2°C. And then as the
temperature increases, also the surface
elevation is lowered. And that leads to,
potentially then also triggering these
surface elevation and melt elevation
feedbacks in East Antarctica. So around
6°C to 9°C, there's another major
threshold. And after this, large parts of
the East Antarctic ice sheet could also be
committed to long term sea level rise. At
about 10°C, the Antarctic ice sheet could
potentially become ice free on the long
term. And, this is really important. What
we're seeing here are not projections, but
what we're seeing here is a stability
check. So we're not looking at something
that's happening within the next century
or so, but rather we're interested in
understanding, at which temperatures the
Antarctic ice sheet could still survive on
the long term. We also wanted to see if
some of these changes are reversible. And
what we find is a so-called hysteresis
behavior of the Antarctic ice sheet. That
means, as we're losing the ice and we'll
then cool the temperatures back down, the
ice sheet does not regrow back to its
initial state, but it takes much, much
colder temperatures to regrow the same ice
sheet volume that we are currently having
at present day temperature levels. So
there's a significant difference between
this retreat and the regrowth path. And
this can be up to 20 meters of sea level
equivalent in the difference between these
two paths. What this looks like
regionally, you can see here. So again, we
have the retreat and the regrowth path at
2°C of global warming, and 4°C of global
warming. So these are the long term
effects at these temperature levels. And
you can see that, for instance, for 4°C
large parts of East Antarctic and also of
the West Antarctic ice sheet do not regrow
at the same temperature level. So we
clearly observe this hysteresis behavior.
That's another sign that the Antarctic ice
sheet is the tipping element in the
climate system. So both Greenland and
Antarctica are tipping elements in the
climate system. There are a number more
candidates for tipping elements, including
some of the larger biosphere components,
for instance, the Amazon rainforest, the
tropical coral reefs, and also the boreal
forests, as well as some of the large
scale circulations. So, for instance, the
Atlantic thermohaline circulation, what we
often term the Gulf Stream, and the Indian
summer monsoon are tipping candidates in
the climate system. Now, if we go back to
our temperature evolution since last
glacial maximum, and we now insert what we
know about the tipping thresholds of these
different components in the Earth system,
then this is what we get. And we see, that
there are basically three clusters of
tipping elements in comparison to the
global mean temperature here. And you see
in these burning ember diagrams that some
of these tipping elements are at risk of
switching into a different state, even
within the Paris range of 1.5 - 2°C of
warming. And among these most vulnerable
tipping elements are the West Antarctic
ice sheet and the Greenland ice sheet and
in general, the cryosphere elements which
seem to react to global warming and
climate change much faster and therefore
belong to the most vulnerable parts of the
Earth system. So, if there's one thing
that I would like you to take away from
this talk, it is that ice matters. I've
presented you with three reasons why.
First of all, polar ice acts as a climate
archive. It also acts as an early warning
system. Secondly, glaciers and ice sheets
are important contributors already to
current sea level rise, but they will
become even more important in the future
as the global mean temperature keeps
rising. And thirdly, both Greenland and
Antarctica are tipping elements in the
Earth system. And one of the next things
we need to understand is how these tipping
elements interact with one another.
Because we have a very good understanding
by now of the different mechanisms behind
these tipping elements and of the
individual temperature thresholds. But one
of the, I think, most important questions
we need to ask ourselves, is how the
interaction of the tipping elements
changes the stability of the Earth system
as a whole and if there could be something
like domino effects in the Earth system.
And with this, thank you so much for your
attention. And I'm very much looking
forward to questions.
Herald: Yeah, OK, fine, good, läuft, könnt
ihr mich also hör'n, und ihr müsst mir
also sagen, wann ich wieder drauf bin.
Off: Du bist live.
H: Hallo, wilkommen zurück! Thanks for
this awesome talk, Ricarda, and we are now
going to have a Q&A. And if you have any
questions regarding this awesome talk,
then please post them to the signal
angels. They are following on Twitter and
the Fediverse here, using the hashtag
#rc3one, because this is rc1. And you can
also post your questions to the IRC. You
know, I already have a first question. I
don't know, Ricarda, if you can hear me,
but is there anything that this specific the CCC
community of nerds and hackers can do more
than anyone else to help with this issue?
What do you think that
we can do to help this?
R: Yeah, thank you so much. Great
question. Let me start by saying I'm a
nerd and hacker myself. I'm a developer,
or code developer, of the parallel ice
sheet model. That's one of the ice sheet
models for Greenland and Antarctica that's
being used around the globe with many
different applications. So, yeah, as a
fellow nerd and hacker, I can say there's
lots we can do, in particular towards
understanding even better the different
dynamics of the Greenland and the
Antarctic ice sheet, but also beyond that,
for the Earth system as a whole. I think
we're now at a point where we understand
the individual components of the Earth
system better and better. We also have
better and better observations, satellite
observations, but also observations at the
ground to further understand the different
processes. But what we need now is to
combine this with our knowledge in the
modeling community and also with some of
the approaches from big data, machine
learning and so on, to really put this
together, all the different puzzle pieces
to understand what this means for the
Earth system as a whole. And what I mean
by that is, we now understand that there
are several individual tipping points in
the Earth system. And we also know that as
global warming continues, we're at higher
risks of transgressing individual tipping
points. But what we still need to
understand is what does this mean for the
overall stability of our planet Earth?
H: Thank you for this extended answer to
this question. I have another one. I would
like to know, I mean, you showed a slide
where you showed the browning of the ice
surface and then explained that this
speeds up the process of melting as well.
But, can we just paint it white or with a
reflective paint on it? Has this been
simulated? Is this of interest to you
scientists?
R: Yeah, very good question. So basically
what you're addressing here is the
question of the so-called ice albedo
feedback. We all know this. As we're
wearing black clothes in summer, it's
warmer than when we're wearing white
clothes. And the same is basically true
for our planet as well. So the ice sheets
and also the sea ice in the Arctic and
Antarctica, they contribute considerably
to a net cooling still of the planet. So
if we didn't have these ice landscapes,
that would mean that the planet would warm
even faster and even further than it
already is today. So currently, the ice
albedo feedback is still helping us with
keeping the temperatures at lower levels
than they would be without the ice
landscapes. And, yeah, therefore, it is
definitely of interest to further
understand what would this mean for, for
instance, the global mean temperature, but
also regional changes, if we were to lose
our ice cover completely? And also the
reverse question, of course, if we were to
whiten parts of the planet, then how would
this affect temperature? One thing that we
found out is that if we were to lose the
ice sheets and the sea ice in terms of the
ice albedo feedback alone entirely, then
this could already lead to an additional
global warming of roughly 0.2°C. Now, that
may not seem very much, but it certainly
is important in the grand scheme of
things. As we're thinking of, for
instance, the Paris range of 1.5°C to 2°C
of warming, every tenth of a degree
matters. So, yeah, very interesting
question. And this is something that has
been done with numerical models, just to
understand what kind of an effect these
kind of what-if-scenarios would have also
in terms of the albedo.
H: Very interesting. So should we now
start to develop drones
who can spray paint?
R: laughs That's a good question. I
don't think that's the solution. I think
we have a much better solution. And that
is we know that we need to to mitigate
climate change and reduce greenhouse gas
emissions. And that is one that would work
for sure. Whereas these questions of,
well, should we spray paint all of our
buildings at the at the top white? That is
something that cannot be done at such a
large scale as we would need it in order
to reverse global warming. And another
thing to keep in mind is that even if we
were able to reduce the global signal,
this still doesn't mean that we could also
reverse the regional scale changes. We're
already experiencing a large increase in
extreme weather and climate events. And
that is certainly something that I haven't
seen so far, that this could also be
reversed just by reversing the global mean
temperature change as a whole.
H: I have another question. I think that's
quite interesting. How old is the oldest
ice in Antarctica? Are you aware of that?
And how long would it take a minimum to
lose that entirely?
R: Yeah, very good question. So the oldest
ice, there's actually an ongoing search
for the oldest ice in Antarctica. So to
say, we know that Antarctica was ice free
for the last time, roughly 34 million
years ago. So when we're talking about
these scenarios that eventually Antarctica
could become ice free with, of course,
very strong global warming scenarios of
about 10°C of global warming, then we need
to keep in mind that this was the case for
the last time, about 34 million
years ago. Now, as we're speaking, there
is an ongoing project, an international
collaboration to find and and also drill
for the oldest ice so that we can really
understand our Earth's history better and
better. And so this is a very exciting
project because, as I said, the ice cores
are kind of like tree rings and we can
count back in time and really understand
what our global climate was like several,
hundreds of thousands of years ago. So,
yeah, with that being said, I think it's
important to keep in mind that this is
something that humans certainly have never
experienced and that's therefore
unprecedented in our world.
H: ...for this very elaborate answer to
this question, I know it is not the core
of your research, but someone from the
internet asked, if it's possible for old
viruses and all the bacteria from back
when Antarctica was like beginning to
freeze over or from like
millions of years ago, is it possible for
them to thaw out again? Is that a danger
for us?
R: Oh, that's also a very interesting
question. So I'm no expert on this, but I
could imagine that at the temperatures
that we have, Antarctica, especially the
core ice body, there we have temperatures
that go down to, well, I think the coldest
temperature was something like -90°C that
was recorded there. But in any case, it's
very cold there. So there might be some
bacteria that can survive these
conditions. And I've read about bacteria
like that, but I wouldn't know that there
are many bacterial species or specimen
that could survive these kinds of
conditions. So to be honest, I would have
to read up on that. That's a very
interesting question.
H: Yeah. Thank you for this answer. I
remember that you watched, that you showed
an animation and a graph for a simulated
ice decline to find the tipping points in
Antarctica. And on the x axis of that, I
couldn't see a time scale. And now someone
asked on the internet, what are the
timescales between reaching a tipping
point? And most of the ice being melted?
Is that years, decades, centuries,
millennia? What's kind of the scale there?
R: Yes, very important point. So it's
important to note that we're here showing
this over the global mean temperature
change. And the reason for this is that
the way these kind of hysteresis
experiments are run is that you have a
very slow temperature increase. So slow,
in fact, that it's much slower than the
sort of internal time scales of the ice
itself. And in this case, for instance, we
had a temperature increase of
10^-4°C/year. And the reason for this is
because this is the way you're approaching
the actual hysteresis curve that we were
interested in. So this should not be
mistaken for sea level projections of any
sort. So what we find here are the actual,
so to say, tipping points, the actual
critical thresholds, that parts of the
Antarctic ice sheet cannot survive.
Nonetheless, of course, we're also working
towards sea level projections and trying
to understand what kind of sea level
change we can expect from the ice sheets
over the next decades to centuries to
millennia. And one important thing there
is that most of the ice loss that could be
triggered now, would actually happen after
the end of this century. So very often,
when we see these sea level curves, we're
looking until the year 2100. So for the
next decades, how does the sea level
respond to changes in temperature? But
because we have so much inertia in the
system, that means that even if the global
warming signal was stopped right now, we
would still see continued sea level rise
for several decades to centuries. And that
is something important to keep in mind. So
I think we really need to start thinking
of sea level rise in terms of commitment
rather than these short term predictions.
That being said, another important
question and factor is the rate of sea
level change, because this is actually
what we need to adapt to as civilizations.
When we think of building dams, there are
two questions we need to answer. One is
the magnitude of sea level rise and and
also in its upper scale and upper limit to
that. And the other question is the rate
at which this changes. And what we find is
that on the long term, there is something
like 2.3m/°C of sea level change. So this
is sort of a number to keep in mind when
we think of sea level projections. And
yeah, I think it's really important to
consider longer timescales than the one to
the year 2100 when we talk about sea level
rise.
H: Thank you for this answer, very
interesting and we are out of time now, so
thanks for all the questions and thank
you, Ricarda, for this amazing talk. The
next talk on this stage will be about a
related topic, measuring CO2 indoors, but
also in the atmosphere in general. But
before that, we have a Herald News Show
for your prepared. So enjoy!
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