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#rC3 - The big melt: Tipping points in Greenland and Antarctica

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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
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    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,
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    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.
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    And the reason for this were these
    observations from the Amundson region in
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    West Antarctica. So we're now taking sort
    of a flight into the Amundson Sea region.
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    And what was observed over the recent
    decades is not only that the glaciers here
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    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
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    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,
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    is that the ice sheet is grounded below
    sea level, which is true for many parts of
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    West Antarctica, but also some parts of
    East Antarctica. And also we need to
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    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,
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    then we can show in two dimensions,
    mathematically, we can prove
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    mathematically that an instability occurs
    in this case. The reason is that we have
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    an feedback between the grounding line
    retreat and the ice locks across the
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    grounding line. If the grounding line
    retreats in a case where we have a
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    retrograde sloping bed and the ice is
    ground below sea level, that means that
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    the ice thickness towards the interior is
    larger. And this generally also means that
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    the ice flux across the grounding line is
    larger, leading to further retreat off the
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    grounding line and so on and so on. So
    again, we have a positive feedback
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    mechanism that could drive self-sustained
    ice loss from parts of the West and East
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    Antarctic ice sheet. And the concern is
    now that this marine ice sheet instability
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    is potentially underway in the Amundson
    basin here in West Antarctica. Now, what's
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    unclear is, how fast this change would
    actually occur. So if we have actually
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    triggered the marine ice sheet instability
    in this region, and that means we have a
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    committed ice loss of roughly one meter
    sea level equivalent, then the question is
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    still, how fast does this occur? And for
    this, it really matters how much further
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    global warming continues. So and at which
    rate the temperature will change in the
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    future. So this is what's happening in
    part of the West Antarctic ice sheet. We
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    were also asking ourselves, weather could
    something like this also happen for East
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    Antarctica and how stable are each of the
    different ice basins in Antarctica? So we
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    did something of a stability check on the
    Antarctic ice sheet to assess the risk of
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    long term sea level rise from these
    different regions. What you will see next
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    is an animation where we're increasing the
    global mean temperature, but we're
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    increasing it very, very slowly, at a much
    slower rate than the typical rate of
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    change in the ice sheet to test for the
    stability of these different parts. And
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    what we see is that at roughly 2°C, we are
    losing a large part of the West Antarctic
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    ice sheet. So there's a first tipping
    point around 2°C. And then as the
  • 22:57 - 23:04
    temperature increases, also the surface
    elevation is lowered. And that leads to,
  • 23:04 - 23:11
    potentially then also triggering these
    surface elevation and melt elevation
  • 23:11 - 23:17
    feedbacks in East Antarctica. So around
    6°C to 9°C, there's another major
  • 23:17 - 23:22
    threshold. And after this, large parts of
    the East Antarctic ice sheet could also be
  • 23:22 - 23:31
    committed to long term sea level rise. At
    about 10°C, the Antarctic ice sheet could
  • 23:31 - 23:36
    potentially become ice free on the long
    term. And, this is really important. What
  • 23:36 - 23:41
    we're seeing here are not projections, but
    what we're seeing here is a stability
  • 23:41 - 23:44
    check. So we're not looking at something
    that's happening within the next century
  • 23:44 - 23:49
    or so, but rather we're interested in
    understanding, at which temperatures the
  • 23:49 - 23:55
    Antarctic ice sheet could still survive on
    the long term. We also wanted to see if
  • 23:55 - 24:02
    some of these changes are reversible. And
    what we find is a so-called hysteresis
  • 24:02 - 24:07
    behavior of the Antarctic ice sheet. That
    means, as we're losing the ice and we'll
  • 24:07 - 24:13
    then cool the temperatures back down, the
    ice sheet does not regrow back to its
  • 24:13 - 24:19
    initial state, but it takes much, much
    colder temperatures to regrow the same ice
  • 24:19 - 24:25
    sheet volume that we are currently having
    at present day temperature levels. So
  • 24:25 - 24:31
    there's a significant difference between
    this retreat and the regrowth path. And
  • 24:31 - 24:37
    this can be up to 20 meters of sea level
    equivalent in the difference between these
  • 24:37 - 24:45
    two paths. What this looks like
    regionally, you can see here. So again, we
  • 24:45 - 24:50
    have the retreat and the regrowth path at
    2°C of global warming, and 4°C of global
  • 24:50 - 24:54
    warming. So these are the long term
    effects at these temperature levels. And
  • 24:54 - 25:00
    you can see that, for instance, for 4°C
    large parts of East Antarctic and also of
  • 25:00 - 25:05
    the West Antarctic ice sheet do not regrow
    at the same temperature level. So we
  • 25:05 - 25:10
    clearly observe this hysteresis behavior.
    That's another sign that the Antarctic ice
  • 25:10 - 25:16
    sheet is the tipping element in the
    climate system. So both Greenland and
  • 25:16 - 25:22
    Antarctica are tipping elements in the
    climate system. There are a number more
  • 25:22 - 25:27
    candidates for tipping elements, including
    some of the larger biosphere components,
  • 25:27 - 25:32
    for instance, the Amazon rainforest, the
    tropical coral reefs, and also the boreal
  • 25:32 - 25:36
    forests, as well as some of the large
    scale circulations. So, for instance, the
  • 25:36 - 25:41
    Atlantic thermohaline circulation, what we
    often term the Gulf Stream, and the Indian
  • 25:41 - 25:49
    summer monsoon are tipping candidates in
    the climate system. Now, if we go back to
  • 25:49 - 25:54
    our temperature evolution since last
    glacial maximum, and we now insert what we
  • 25:54 - 26:00
    know about the tipping thresholds of these
    different components in the Earth system,
  • 26:00 - 26:05
    then this is what we get. And we see, that
    there are basically three clusters of
  • 26:05 - 26:10
    tipping elements in comparison to the
    global mean temperature here. And you see
  • 26:10 - 26:15
    in these burning ember diagrams that some
    of these tipping elements are at risk of
  • 26:15 - 26:21
    switching into a different state, even
    within the Paris range of 1.5 - 2°C of
  • 26:21 - 26:26
    warming. And among these most vulnerable
    tipping elements are the West Antarctic
  • 26:26 - 26:32
    ice sheet and the Greenland ice sheet and
    in general, the cryosphere elements which
  • 26:32 - 26:38
    seem to react to global warming and
    climate change much faster and therefore
  • 26:38 - 26:44
    belong to the most vulnerable parts of the
    Earth system. So, if there's one thing
  • 26:44 - 26:52
    that I would like you to take away from
    this talk, it is that ice matters. I've
  • 26:52 - 26:57
    presented you with three reasons why.
    First of all, polar ice acts as a climate
  • 26:57 - 27:05
    archive. It also acts as an early warning
    system. Secondly, glaciers and ice sheets
  • 27:05 - 27:09
    are important contributors already to
    current sea level rise, but they will
  • 27:09 - 27:15
    become even more important in the future
    as the global mean temperature keeps
  • 27:15 - 27:20
    rising. And thirdly, both Greenland and
    Antarctica are tipping elements in the
  • 27:20 - 27:25
    Earth system. And one of the next things
    we need to understand is how these tipping
  • 27:25 - 27:28
    elements interact with one another.
    Because we have a very good understanding
  • 27:28 - 27:33
    by now of the different mechanisms behind
    these tipping elements and of the
  • 27:33 - 27:37
    individual temperature thresholds. But one
    of the, I think, most important questions
  • 27:37 - 27:42
    we need to ask ourselves, is how the
    interaction of the tipping elements
  • 27:42 - 27:46
    changes the stability of the Earth system
    as a whole and if there could be something
  • 27:46 - 27:51
    like domino effects in the Earth system.
    And with this, thank you so much for your
  • 27:51 - 27:56
    attention. And I'm very much looking
    forward to questions.
  • 28:07 - 28:28
    Herald: Yeah, OK, fine, good, läuft, könnt
    ihr mich also hör'n, und ihr müsst mir
  • 28:28 - 28:31
    also sagen, wann ich wieder drauf bin.
    Off: Du bist live.
  • 28:31 - 28:36
    H: Hallo, wilkommen zurück! Thanks for
    this awesome talk, Ricarda, and we are now
  • 28:36 - 28:41
    going to have a Q&A. And if you have any
    questions regarding this awesome talk,
  • 28:41 - 28:46
    then please post them to the signal
    angels. They are following on Twitter and
  • 28:46 - 28:54
    the Fediverse here, using the hashtag
    #rc3one, because this is rc1. And you can
  • 28:54 - 28:59
    also post your questions to the IRC. You
    know, I already have a first question. I
  • 28:59 - 29:04
    don't know, Ricarda, if you can hear me,
    but is there anything that this specific the CCC
  • 29:04 - 29:10
    community of nerds and hackers can do more
    than anyone else to help with this issue?
  • 29:10 - 29:14
    What do you think that
    we can do to help this?
  • 29:14 - 29:17
    R: Yeah, thank you so much. Great
    question. Let me start by saying I'm a
  • 29:17 - 29:24
    nerd and hacker myself. I'm a developer,
    or code developer, of the parallel ice
  • 29:24 - 29:28
    sheet model. That's one of the ice sheet
    models for Greenland and Antarctica that's
  • 29:28 - 29:34
    being used around the globe with many
    different applications. So, yeah, as a
  • 29:34 - 29:40
    fellow nerd and hacker, I can say there's
    lots we can do, in particular towards
  • 29:40 - 29:45
    understanding even better the different
    dynamics of the Greenland and the
  • 29:45 - 29:50
    Antarctic ice sheet, but also beyond that,
    for the Earth system as a whole. I think
  • 29:50 - 29:54
    we're now at a point where we understand
    the individual components of the Earth
  • 29:54 - 29:59
    system better and better. We also have
    better and better observations, satellite
  • 29:59 - 30:06
    observations, but also observations at the
    ground to further understand the different
  • 30:06 - 30:11
    processes. But what we need now is to
    combine this with our knowledge in the
  • 30:11 - 30:17
    modeling community and also with some of
    the approaches from big data, machine
  • 30:17 - 30:22
    learning and so on, to really put this
    together, all the different puzzle pieces
  • 30:22 - 30:26
    to understand what this means for the
    Earth system as a whole. And what I mean
  • 30:26 - 30:31
    by that is, we now understand that there
    are several individual tipping points in
  • 30:31 - 30:36
    the Earth system. And we also know that as
    global warming continues, we're at higher
  • 30:36 - 30:41
    risks of transgressing individual tipping
    points. But what we still need to
  • 30:41 - 30:49
    understand is what does this mean for the
    overall stability of our planet Earth?
  • 30:49 - 30:56
    H: Thank you for this extended answer to
    this question. I have another one. I would
  • 30:56 - 31:01
    like to know, I mean, you showed a slide
    where you showed the browning of the ice
  • 31:01 - 31:08
    surface and then explained that this
    speeds up the process of melting as well.
  • 31:08 - 31:13
    But, can we just paint it white or with a
    reflective paint on it? Has this been
  • 31:13 - 31:16
    simulated? Is this of interest to you
    scientists?
  • 31:16 - 31:20
    R: Yeah, very good question. So basically
    what you're addressing here is the
  • 31:20 - 31:26
    question of the so-called ice albedo
    feedback. We all know this. As we're
  • 31:26 - 31:29
    wearing black clothes in summer, it's
    warmer than when we're wearing white
  • 31:29 - 31:35
    clothes. And the same is basically true
    for our planet as well. So the ice sheets
  • 31:35 - 31:41
    and also the sea ice in the Arctic and
    Antarctica, they contribute considerably
  • 31:41 - 31:49
    to a net cooling still of the planet. So
    if we didn't have these ice landscapes,
  • 31:49 - 31:53
    that would mean that the planet would warm
    even faster and even further than it
  • 31:53 - 31:59
    already is today. So currently, the ice
    albedo feedback is still helping us with
  • 31:59 - 32:05
    keeping the temperatures at lower levels
    than they would be without the ice
  • 32:05 - 32:10
    landscapes. And, yeah, therefore, it is
    definitely of interest to further
  • 32:10 - 32:15
    understand what would this mean for, for
    instance, the global mean temperature, but
  • 32:15 - 32:21
    also regional changes, if we were to lose
    our ice cover completely? And also the
  • 32:21 - 32:25
    reverse question, of course, if we were to
    whiten parts of the planet, then how would
  • 32:25 - 32:34
    this affect temperature? One thing that we
    found out is that if we were to lose the
  • 32:34 - 32:41
    ice sheets and the sea ice in terms of the
    ice albedo feedback alone entirely, then
  • 32:41 - 32:48
    this could already lead to an additional
    global warming of roughly 0.2°C. Now, that
  • 32:48 - 32:53
    may not seem very much, but it certainly
    is important in the grand scheme of
  • 32:53 - 32:59
    things. As we're thinking of, for
    instance, the Paris range of 1.5°C to 2°C
  • 32:59 - 33:03
    of warming, every tenth of a degree
    matters. So, yeah, very interesting
  • 33:03 - 33:08
    question. And this is something that has
    been done with numerical models, just to
  • 33:08 - 33:15
    understand what kind of an effect these
    kind of what-if-scenarios would have also
  • 33:15 - 33:22
    in terms of the albedo.
    H: Very interesting. So should we now
  • 33:22 - 33:24
    start to develop drones
    who can spray paint?
  • 33:24 - 33:29
    R: laughs That's a good question. I
    don't think that's the solution. I think
  • 33:29 - 33:34
    we have a much better solution. And that
    is we know that we need to to mitigate
  • 33:34 - 33:39
    climate change and reduce greenhouse gas
    emissions. And that is one that would work
  • 33:39 - 33:44
    for sure. Whereas these questions of,
    well, should we spray paint all of our
  • 33:44 - 33:50
    buildings at the at the top white? That is
    something that cannot be done at such a
  • 33:50 - 33:56
    large scale as we would need it in order
    to reverse global warming. And another
  • 33:56 - 34:04
    thing to keep in mind is that even if we
    were able to reduce the global signal,
  • 34:04 - 34:10
    this still doesn't mean that we could also
    reverse the regional scale changes. We're
  • 34:10 - 34:16
    already experiencing a large increase in
    extreme weather and climate events. And
  • 34:16 - 34:21
    that is certainly something that I haven't
    seen so far, that this could also be
  • 34:21 - 34:26
    reversed just by reversing the global mean
    temperature change as a whole.
  • 34:26 - 34:31
    H: I have another question. I think that's
    quite interesting. How old is the oldest
  • 34:31 - 34:35
    ice in Antarctica? Are you aware of that?
    And how long would it take a minimum to
  • 34:35 - 34:40
    lose that entirely?
    R: Yeah, very good question. So the oldest
  • 34:40 - 34:45
    ice, there's actually an ongoing search
    for the oldest ice in Antarctica. So to
  • 34:45 - 34:51
    say, we know that Antarctica was ice free
    for the last time, roughly 34 million
  • 34:51 - 34:57
    years ago. So when we're talking about
    these scenarios that eventually Antarctica
  • 34:57 - 35:02
    could become ice free with, of course,
    very strong global warming scenarios of
  • 35:02 - 35:09
    about 10°C of global warming, then we need
    to keep in mind that this was the case for
  • 35:09 - 35:14
    the last time, about 34 million
    years ago. Now, as we're speaking, there
  • 35:14 - 35:21
    is an ongoing project, an international
    collaboration to find and and also drill
  • 35:21 - 35:26
    for the oldest ice so that we can really
    understand our Earth's history better and
  • 35:26 - 35:32
    better. And so this is a very exciting
    project because, as I said, the ice cores
  • 35:32 - 35:36
    are kind of like tree rings and we can
    count back in time and really understand
  • 35:36 - 35:42
    what our global climate was like several,
    hundreds of thousands of years ago. So,
  • 35:42 - 35:48
    yeah, with that being said, I think it's
    important to keep in mind that this is
  • 35:48 - 35:52
    something that humans certainly have never
    experienced and that's therefore
  • 35:52 - 35:58
    unprecedented in our world.
    H: ...for this very elaborate answer to
  • 35:58 - 36:05
    this question, I know it is not the core
    of your research, but someone from the
  • 36:05 - 36:10
    internet asked, if it's possible for old
    viruses and all the bacteria from back
  • 36:10 - 36:16
    when Antarctica was like beginning to
    freeze over or from like
  • 36:16 - 36:20
    millions of years ago, is it possible for
    them to thaw out again? Is that a danger
  • 36:20 - 36:23
    for us?
    R: Oh, that's also a very interesting
  • 36:23 - 36:27
    question. So I'm no expert on this, but I
    could imagine that at the temperatures
  • 36:27 - 36:34
    that we have, Antarctica, especially the
    core ice body, there we have temperatures
  • 36:34 - 36:40
    that go down to, well, I think the coldest
    temperature was something like -90°C that
  • 36:40 - 36:46
    was recorded there. But in any case, it's
    very cold there. So there might be some
  • 36:46 - 36:51
    bacteria that can survive these
    conditions. And I've read about bacteria
  • 36:51 - 36:57
    like that, but I wouldn't know that there
    are many bacterial species or specimen
  • 36:57 - 37:03
    that could survive these kinds of
    conditions. So to be honest, I would have
  • 37:03 - 37:06
    to read up on that. That's a very
    interesting question.
  • 37:06 - 37:11
    H: Yeah. Thank you for this answer. I
    remember that you watched, that you showed
  • 37:11 - 37:17
    an animation and a graph for a simulated
    ice decline to find the tipping points in
  • 37:17 - 37:24
    Antarctica. And on the x axis of that, I
    couldn't see a time scale. And now someone
  • 37:24 - 37:28
    asked on the internet, what are the
    timescales between reaching a tipping
  • 37:28 - 37:32
    point? And most of the ice being melted?
    Is that years, decades, centuries,
  • 37:32 - 37:38
    millennia? What's kind of the scale there?
    R: Yes, very important point. So it's
  • 37:38 - 37:43
    important to note that we're here showing
    this over the global mean temperature
  • 37:43 - 37:48
    change. And the reason for this is that
    the way these kind of hysteresis
  • 37:48 - 37:53
    experiments are run is that you have a
    very slow temperature increase. So slow,
  • 37:53 - 37:59
    in fact, that it's much slower than the
    sort of internal time scales of the ice
  • 37:59 - 38:05
    itself. And in this case, for instance, we
    had a temperature increase of
  • 38:05 - 38:13
    10^-4°C/year. And the reason for this is
    because this is the way you're approaching
  • 38:13 - 38:17
    the actual hysteresis curve that we were
    interested in. So this should not be
  • 38:17 - 38:25
    mistaken for sea level projections of any
    sort. So what we find here are the actual,
  • 38:25 - 38:29
    so to say, tipping points, the actual
    critical thresholds, that parts of the
  • 38:29 - 38:36
    Antarctic ice sheet cannot survive.
    Nonetheless, of course, we're also working
  • 38:36 - 38:40
    towards sea level projections and trying
    to understand what kind of sea level
  • 38:40 - 38:45
    change we can expect from the ice sheets
    over the next decades to centuries to
  • 38:45 - 38:53
    millennia. And one important thing there
    is that most of the ice loss that could be
  • 38:53 - 38:58
    triggered now, would actually happen after
    the end of this century. So very often,
  • 38:58 - 39:03
    when we see these sea level curves, we're
    looking until the year 2100. So for the
  • 39:03 - 39:10
    next decades, how does the sea level
    respond to changes in temperature? But
  • 39:10 - 39:18
    because we have so much inertia in the
    system, that means that even if the global
  • 39:18 - 39:24
    warming signal was stopped right now, we
    would still see continued sea level rise
  • 39:24 - 39:30
    for several decades to centuries. And that
    is something important to keep in mind. So
  • 39:30 - 39:35
    I think we really need to start thinking
    of sea level rise in terms of commitment
  • 39:35 - 39:41
    rather than these short term predictions.
    That being said, another important
  • 39:41 - 39:45
    question and factor is the rate of sea
    level change, because this is actually
  • 39:45 - 39:51
    what we need to adapt to as civilizations.
    When we think of building dams, there are
  • 39:51 - 39:57
    two questions we need to answer. One is
    the magnitude of sea level rise and and
  • 39:57 - 40:04
    also in its upper scale and upper limit to
    that. And the other question is the rate
  • 40:04 - 40:10
    at which this changes. And what we find is
    that on the long term, there is something
  • 40:10 - 40:18
    like 2.3m/°C of sea level change. So this
    is sort of a number to keep in mind when
  • 40:18 - 40:23
    we think of sea level projections. And
    yeah, I think it's really important to
  • 40:23 - 40:29
    consider longer timescales than the one to
    the year 2100 when we talk about sea level
  • 40:29 - 40:35
    rise.
    H: Thank you for this answer, very
  • 40:35 - 40:41
    interesting and we are out of time now, so
    thanks for all the questions and thank
  • 40:41 - 40:46
    you, Ricarda, for this amazing talk. The
    next talk on this stage will be about a
  • 40:46 - 40:52
    related topic, measuring CO2 indoors, but
    also in the atmosphere in general. But
  • 40:52 - 40:56
    before that, we have a Herald News Show
    for your prepared. So enjoy!
  • 40:56 - 41:01
    Outro music
  • 41:01 - 41:36
    Subtitles created by c3subtitles.de
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Title:
#rC3 - The big melt: Tipping points in Greenland and Antarctica
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Duration:
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