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#rC3 - Climate Tipping Points

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    rc3 prerol music
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    Herald angel: Greeting creatures im
    Neuland. In 2015 governments from around
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    the world met in Paris and agreed to
    attempt to limit anthropogenic climate
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    change to well below two degrees.
    Unfortunately, it seems that since then we
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    have not done enough and the climate
    crisis has only gotten more urgent. Our
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    next speaker, Stefan Rahmstorf, has more
    accolades than I have time to tell. He's
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    published more than 100 papers, including
    in the journals Nature and Science, co-
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    authored four books and won the Climate
    Communication Prize from the American
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    Geophysical Union, the first European to
    do so. Please welcome him. And heed his
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    advice. Here's Stefan.
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    Stefan Rahmstorf: Hi, everyone, my name is
    Stefan Rahmstorf, and I'm thrilled to be
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    invited to give a talk at the Chaos
    Computer Club's remote chaos experience
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    2020. I want to give you an overview of
    climate tipping points, a very exciting
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    subject that I will try to shed some light
    on. But let's first start with some
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    background on climate change. You probably
    know this image. It shows the global
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    temperature evolution since the year 1880.
    Every line is one year. This is the more
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    conventional way of viewing this time
    series. And the last seven years have been
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    the hottest seven years since record
    keeping began in the 19th century. We know
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    the reason for this warming: it's the
    increase of carbon dioxide, which you can
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    see here for the last ten thousand years.
    And if you just look at the end of the
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    curve, how the increase has accelerated in
    ever shorter time spans, we have seen an
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    ever greater increase in the amount of
    carbon dioxide in our planet's atmosphere.
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    This increase causes what we call a
    radiative forcing that is a kind of
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    heating in terms of energy release per
    square meter of Earth's surface. And the
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    increase in CO2 in the atmosphere until
    now is causing heating at a rate of two
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    Watts per square meter surface. We
    understand the energy budget of our planet
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    pretty well. On the left here in this
    diagram, you can see the incoming solar
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    radiation in yellow. Part of that is
    reflected already in the atmosphere by the
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    clouds, for example. Another part is
    reflected by the bright surfaces, that's
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    the snow and ice surfaces primarily, and
    the rest is absorbed. On the right hand
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    side, and let's zoom into that, you see in
    orange the long wave radiation, which is
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    clearly distinct from the incoming short
    wave solar radiation by its wavelength and
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    this thick arrow of long wave radiation
    leaving the Earth's surface basically to a
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    large extent gets absorbed by the
    atmosphere. And the atmosphere itself
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    emits like anything, any substance, any
    matter depending on its surface
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    temperature, sorry, depending on its
    temperature, emits also infrared
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    radiation. And one thing that few people
    realize is that the back radiation coming
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    down from the atmosphere through the
    greenhouse effect, the greenhouse gases,
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    is actually twice as large at the Earth's
    surface as the absorbed solar radiation.
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    So heating by the greenhouse effect by the
    long wave radiation is twice as big as the
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    absorbed solar radiation at the Earth's
    surface. And so it's little wonder that if
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    we are increasing this natural greenhouse
    effect, which actually makes our planet
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    livable in the first place, if we are
    increasing this effect that it is going to
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    get warmer. We can also quantify this
    effect. And if you add in not just the CO2
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    increase, but other human caused
    greenhouse gases and also cooling effects
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    caused by humans, then you see that the
    total human caused warming that we see in
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    the orange bar is to, within uncertainty,
    as big as the observed global warming
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    since the 1950s. And that means that about
    100% of the observed global warming over
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    the past 70 years is human caused, and the
    best estimates of the human caused warming
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    is actually even slightly more than the
    observed warming, which has to do partly
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    or is consistent with the fact that solar
    activity has gone down. So the decrease in
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    solar activity has compensated a small
    part of the human caused global warming.
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    It's also very interesting, and especially
    to me as a paleoclimatologist who studies
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    natural climate variations in Earth's
    history and has done so for more than 25
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    years, how the modern warming compares
    with the changes throughout the Holocene,
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    and before that, since the last Ice Age.
    And this is what we see here based on
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    decades of paleoclimate research,
    countless sediment cores taken at the sea
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    bottom, ice cores on the big ice sheets
    and so on. We have enough data now to form
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    meaningful global average temperatures.
    And you can see here the warming from the
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    height of the last ice age into the
    Holocene, the Holocene optimum, the
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    warmest period about until about five
    thousand years before present. And since
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    then, we have seen a very slow cooling
    trend, which we have bent around due to
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    human activities. And we have within 100
    years more than undone 5000 years of
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    natural cooling trend, which normally
    would have very slowly continued. These
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    natural variations, by the way, are due to
    the Earth orbital cycles, these so-called
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    Milankovitch cycles. You can easily read
    up on those, for example, at Wikipedia.
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    Now let's come to the famous, much feared
    tipping points in the climate system. What
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    is a tipping point? That has been
    described in a seminal paper which I'm
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    proud of having been a part of from 2008
    by Tim Lenton and colleagues. And this is
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    called tipping elements in the Earth's
    climate system. And it says that the term
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    tipping point commonly refers to a
    critical threshold at which a tiny
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    perturbation can qualitatively alter the
    state or development of a system and the
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    different parts of the Earth's system,
    which can undergo such a transition, they
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    are called the tipping elements. This
    whole concept is illustrated in the red
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    line that's shown here: In the horizontal
    axis, we see a control parameter and that
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    could be the greenhouse gas content of our
    atmosphere, it could be the temperature,
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    it could be, if you talk about natural
    climate changes, for example, those
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    orbital changes, the what we call the
    Milankovitch forcing, which drives
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    changes. And on the vertical axis, you see
    the response. And if you imagine the
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    control parameter changing from left to
    right in this diagram, you would march
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    along that upper part of the red curve
    here, the branch, until you come close to
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    a threshold. And at that threshold, the
    system will undergo a major change and
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    reach then this lower part of the curve, a
    different kind of equilibrium state. So
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    it's basically a small change in the
    driver causing a very big systemic
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    response. That is what defines a tipping
    point. If we want to be very accurate
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    here, we can distinguish two different
    types of tipping points. The first one is
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    what I just showed you, is repeated here
    on the left side, and it is characterized
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    by the fact that this red equilibrium line
    has one state for every point on the x
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    axis. So every amount of forcing
    corresponds to one particular system
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    state. And this is some state just makes a
    major transition in a smaller range of the
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    driving parameter around this threshold.
    Now, a second, even more drastic or non-
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    linear type of tipping point is shown in
    the right hand side, where the equilibrium
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    states are somewhat more complex than the
    single red line on the left. You can see
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    here that there is, again, an upper stable
    branch and there is also a lower stable
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    branch, but they overlap. So there is a
    region that is shaded here where two
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    stable equilibria exist. And it depends on
    the initial conditions on which of these
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    branches you are. Now, there is what is
    called a bifurcation structure underlying
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    this with a bifurcation point. There is an
    unstable branch which separates the basins
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    of attraction of the two stable branches.
    So if you're in the bi-stable regime and
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    you start kind of away from an equilibrium
    but above the dashed line, you will fall
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    up onto that upper stable branch; if you
    start out below the dash line, you will
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    fall down on the lower branch. That
    actually is pretty standard non-linear
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    dynamics. It's a whole branch of physics
    which investigates exactly this type of
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    behavior in many different physical
    systems. So the second type of tipping
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    point, the right hand side one, is
    corresponding to multiple equilibrium
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    states, in this case two stable
    equilibria. That's why this error range
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    here is called bistability, two stable
    equilibria. It is coming with
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    irreversibility, so basically, if you
    march to the right here on that upper
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    stable branch at that bifurcation point,
    you fall off down onto the lower stable
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    branch, but you can't just go back up from
    there. You have to go all the way to the
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    left to that second lower blue point there
    until you can go back onto that stable
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    branch. The second type is actually as an
    everyday system that behaves like that it
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    can be easily compared to a kayak: if
    you're sitting in a kayak and you lean a
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    little bit to one side, then you
    experience a counterforce. So the kayak is
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    trying to upright itself, it's resisting
    you tipping it. But if you move further
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    and further and further, eventually you
    will reach a tipping point. This is the
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    point where the kayak stops resisting your
    further leaning over and instead it starts
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    tipping over further by itself and then it
    flips right over until it's upside down
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    and you're falling out. So I have I have
    done this quite a few times. So I have a
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    kayak that is quite narrow where it easily
    happens if you don't take care, that you
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    flip over. Now, this kayak also has a
    range of bistability, so once it's flipped
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    over, it's also in a stable state and it
    takes considerable effort to turn it
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    upright again into the other stable state
    when it's vertical, upright rather than
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    upside down. Now, the whole point is that
    systems like this exist also in the
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    climate system. The kind of first type on
    the left hand side corresponds, for
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    example, to sea ice and on the right hand
    side this type of tipping element compares
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    to refers to the Greenland ice sheet or
    continental ice sheets, also Antarctica or
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    the Atlantic Ocean circulation. In terms
    of the trends in behavior, and that means
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    if you if you kind of go through a global
    warming phase, you're moving from left to
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    right in these diagrams, then in that
    sense, they don't differ very much because
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    in either case, you follow a line like
    this green line. So on the left hand side,
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    the green line more or less follows more
    or less closely the red equilibrium line
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    with a certain delay, depending on how
    sluggish the system responds. So that's
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    why the green arrows are not exactly on
    top of the red line here. And in in the
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    right hand side case, you have a similar
    thing. You are kind of, in theory, in
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    equilibrium, you would fall off the cliff
    at this bifurcation point. But in praxis,
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    the system has some inertia, it takes some
    time. So if you gradually move on the
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    right towards the right there, you will
    also follow a green line, which is very
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    similar to the one in the left. So in
    practical terms, if you're not trying to
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    go back, but you just going forward,
    progressive global warming, the difference
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    isn't all that big. And the main
    difference comes from the intrinsic
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    timescale of the system. Obviously, sea
    ice can respond much more quickly to being
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    just a few meters thick compared to
    continental ice sheet like Greenland ice,
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    which is about three thousand meters
    thick. And that just takes a very long
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    time to melt. Now, here's an overview of
    different tipping elements in the climate
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    system. A few examples you can see
    starting on the left here, the boreal
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    forest, that are the kind of northern
    forests, which typically, like ecosystems,
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    do have a tipping point, a point of
    collapse. The whole idea of these tipping
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    points and system collapse is very
    strongly linked actually to ecosystem
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    research and the boreal forests, They have
    a point where they get too dry, that fires
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    and pests are weakening the forest so much
    that in a hot summer like last year in
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    Siberia, they go up in flames lit by
    lightning. Or the Amazon rain forest. This
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    is also a tipping element, has been shown
    in many vegetation dynamics models, which
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    is partly linked to the fact that such a
    forest generates its own rain to an extent
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    by storing water in the soil, keeping it
    there and then bringing it up again
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    through evapotranspiration, as we call it,
    the tree brings up water to the leaves
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    then into the atmosphere again, and then
    it moves with the winds and maybe 50, 100
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    kilometers downwind, it falls again as
    rain. So it's a kind of perpetual rain
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    recycling system which keeps the whole
    forest nice and moist. But if you stress
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    that too far and reduce the first of all,
    you cut down forests, you make it smaller,
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    and also you make it more drought prone by
    warming up the climate, which leads to
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    faster loss of moisture, etc. greater
    moisture requirements by the trees. Then
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    you can stress it up to the point where it
    gets so dry that even the Amazon rain
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    forest can go up in flames. Another
    example of how you see the top right is
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    the permafrost thawing. This is when it
    gets too warm. There is a very simple
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    threshold, namely the freezing point. Of
    course, that is a tipping point in the
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    sense of freezing point of water. When the
    permafrost thaws, then there is methane
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    gas escaping to the atmosphere, which then
    also can enhance the further warming,
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    which then leads to more permafrost
    thawing and so on. Typically, these
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    tipping points are associated with such
    amplifying feedbacks. I will discuss three
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    of these in a little bit more detail. The
    Greenland ice sheet, which is undergoing
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    accelerated ice loss, the Atlantic
    overturning circulation, often called Gulf
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    Stream system. And the third one is the
    coral reefs, which are suffering from
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    large scale die-off, which also as a
    typical ecosystem response, have a
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    critical threshold. These examples are
    discussed in our paper 'Climate tipping
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    points - too risky to bet against' which
    we published in Nature about one year ago.
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    And they are also some of these tipping
    points interact. They're interlinked. And
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    one of our quotes there is that the
    clearest emergency would be if we were
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    approaching a global cascade of tipping
    points. That is a situation where one
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    tipping element is triggering the next one
    in a kind of domino effect. This is what
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    we fear most. Now, let's have a look at
    the Greenland ice sheet. This is a NASA
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    video showing based on GRACE satellite
    data where the ice sheet is losing mass.
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    You can see increasing blue colors here
    that the Greenland ice sheet is indeed
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    losing mass. You can look up at the NASA
    Vital Signs website, which has very good
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    indicators of various vital signs of our
    planet, including the data on Greenland
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    ice loss, constantly updated. Now, the
    point with the Greenland ice sheet is that
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    it does have a stability diagram like the
    schematic one that I showed you earlier
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    with the bi-stable range. And this is
    shown, I think it was shown for the first
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    time by my colleagues, Calov and
    Ganopolski in 2005 in this article where
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    they used the three dimensional ice sheet
    model coupled inside a global climate
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    model with ocean atmosphere and so on and
    on the x axis is basically increasing
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    amount of heating going on, in this case
    because they were interested in the
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    paleoclimate question, it is this driving
    force by the orbital cycles and
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    Milankovitch cycles. You don't need to
    understand the numbers, but on the
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    vertical axis, you see the response of the
    ice sheet, the size of the ice sheet, in
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    million cubic kilometers. And you can see
    that upper branch in the blue line, we're
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    actually moving towards the right here in
    this model simulation experiment. And you
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    can see you stay on that upper branch
    until you reach this value on the x axis
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    of around about five hundred. And this is
    where the tipping point is there. The ice
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    mass declines, melts away, away very
    quickly. And you then end up at that lower
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    branch with no ice on Greenland. And they
    played this game. They ran the simulation
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    out to more than 550 watts per square
    meter. And the light blue line is what
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    happens when they return, when they turn
    down the heat again. You move towards the
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    left on this diagram, but you don't go
    back up the same way as the dark blue
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    line. You have to go to much lower
    radiation values until the ice sheet
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    starts to grow again and comes back. The
    dots, by the way, are points where this
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    has to has been run for many thousands of
    years really into an equilibrium just to
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    show that there are really for the same
    value on the x axis, two very different
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    equilibrium states with and without
    Greenland ice sheet. And the fact that we
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    now and in the Holocene in the last ten
    thousand years have the Greenland ice
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    sheet and it actually is stable in the
    Holocene climate is only because of the
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    initial condition, because we came out of
    an ice age. If you took away the Greenland
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    ice sheet now, then in the current climate
    or the Holocene or pre-industrial climate,
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    it would never grow back. What is the
    positive feedback? The most positive? We
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    don't mean that it's good. That's actually
    quite bad and positive feedback. We mean
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    and amplifying feedback and the key
    amplifying feedback here is what is called
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    the ice elevation feedback. The Greenland
    ice sheet does not melt because it's very
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    cold at the surface, mostly below
    freezing. And why is it so cold? Because
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    it is very high up in the atmosphere, this
    ice sheet of three thousand meters thick
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    after all. So it's like in a high mountain
    area where it is quite cold. If you took
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    away that ice sheet, though, the surface
    then would be down at sea level or even
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    below if you did this quickly because the
    the bedrock is depressed, but the surface
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    would come up to sea level, but down there
    it's much warmer than up at three thousand
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    meters altitude in the atmosphere. And
    there it is actually too warm to keep any
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    snow on the ground year round, which would
    be required to regrow a new Greenland ice
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    sheet. And that's why you'd have to go
    back to a much colder climate than the
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    Holocene to get the Greenland ice sheet
    back once it were lost. This is a typical
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    example of this amplifying feedback, which
    leads to a self stabilizing system. It can
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    either self stabilize in the upper branch
    here when you start there or it self-
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    stabilizes in the lower branch with no ice
    when you start there. This is what makes
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    it a bi-stable system. To summarize, the
    Greenland ice sheet is melting as another
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    data the great satellites show, but also
    other data sets. It has a tipping point
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    due to the ice elevation feedback. What I
    haven't shown, but it's come out in study
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    with many climate models, simulation
    experiments going through more than two
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    hundred thousand years of simulations from
    the past through the Eemian interglacial
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    period where we know how much the ice
    sheets shrank back. And we could use those
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    data from the past behavior of Greenland
    to calibrate the model. And so we know the
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    tipping point for the complete loss of the
    Greenland ice sheet is somewhere between
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    one degree and three degree global
    warming. We're already at one point two
  • 25:22 - 25:28
    degrees global warming. So we have started
    to enter the danger zone where we crossed
  • 25:28 - 25:34
    that tipping point. It doesn't mean that
    it suddenly starts to melt very fast also
  • 25:34 - 25:39
    because it has its own intrinsic slow
    response time. But what that crossing,
  • 25:39 - 25:44
    that tipping point means is that even
    without further warming, the Greenland ice
  • 25:44 - 25:49
    sheet is doomed and will continue to melt
    until it's gone, and this will lead to
  • 25:49 - 25:56
    seven meters of global sea level rise,
    drowning most of our big coastal cities
  • 25:56 - 26:05
    and to many island nations. Here is a look
    at the future from models, simulations
  • 26:05 - 26:10
    from Ashmont and from NASA. And you can
    see a nice view of what the surface looks
  • 26:10 - 26:15
    like. And here's what the what it looks
    like in the ice sheet model. You can see
  • 26:15 - 26:20
    the ice flowing. You can see it
    retreating. So in purple, that's bedrock
  • 26:20 - 26:27
    that is exposed where the ice sheet has
    withdrawn in this simulation. And so it's
  • 26:27 - 26:33
    as much as ice of ice that you would lose
    in the coming three hundred years, a
  • 26:33 - 26:40
    substantial fraction of the Greenland ice
    sheet. Now, let's look at another kind of
  • 26:40 - 26:47
    tipping element, and that is the Gulf
    Stream system or the North Atlantic
  • 26:47 - 26:52
    current. And I can't really introduce this
    topic is one of my favorite topics, which
  • 26:52 - 26:58
    I have studied since the early 90s,
    without showing a clip from the famous
  • 26:58 - 27:05
    Hollywood blockbuster The Day After
    Tomorrow. What about the North Atlantic
  • 27:05 - 27:11
    current? What about it? The current
    depends upon a delicate balance of salt
  • 27:11 - 27:15
    and fresh water. We all know that, yes.
    But no one is taking into account how much
  • 27:15 - 27:21
    fresh water has been dumped into the ocean
    because of melting polar ice. I think
  • 27:21 - 27:27
    we've hit a critical desalinization point.
    Yeah, now that statement about the
  • 27:27 - 27:37
    critical desalination point is a
    completely correct description of the
  • 27:37 - 27:43
    bifurcation point of the Atlantic
    circulation, I'll show it in a minute. And
  • 27:43 - 27:50
    the statement that nobody has taken into
    account the meltwater from the Greenland
  • 27:50 - 27:55
    ice sheet is also was completely correct
    when the movie appeared in 2004. Until
  • 27:55 - 28:01
    then, the typical climate simulations that
    you could see in the IPCC reports,
  • 28:01 - 28:07
    actually until quite a few years later,
    still had not taken account Greenland melt
  • 28:07 - 28:13
    water because basically at that point in
    time, the models, almost all climate
  • 28:13 - 28:18
    models were just ocean-atmosphere models
    plus land surface, but they didn't have
  • 28:18 - 28:24
    continental ice sheet models coupled into
    them. And so in the meantime, of course,
  • 28:24 - 28:30
    we have better models that include
    experiments either with artificially added
  • 28:30 - 28:36
    Greenland meltwater from data estimates or
    fully coupled with ice sheet models. And
  • 28:36 - 28:42
    from that, an example here being that
    nature article by Claus Boening and
  • 28:42 - 28:48
    colleagues. We know that the meltwater
    input from Greenland has a non-negligible
  • 28:48 - 28:54
    effect on the North Atlantic overturning.
    It's probably not the dominant effect, but
  • 28:54 - 29:00
    it adds to various factors that weaken
    this North Atlantic current. And we also
  • 29:00 - 29:09
    know that this system has a well-defined
    tipping point. Actually, I described that
  • 29:09 - 29:17
    in a nature article in 1996 due to a salt
    transport feedback. The basic idea behind
  • 29:17 - 29:24
    that has actually been known since the
    late 1950s or early 60s since work by the
  • 29:24 - 29:30
    famous American oceanographer Henry
    Stommel. But what I showed in my Nature
  • 29:30 - 29:36
    article in 96 is that it actually works
    that way in a complex, three dimensional
  • 29:36 - 29:42
    global ocean circulation model, not just
    in very simplified models. And since then,
  • 29:42 - 29:48
    this has been shown for a whole range of
    different climate models. The sole
  • 29:48 - 29:56
    transportation feedback is also one of
    these amplifying feedbacks, and it's easy
  • 29:56 - 30:02
    to explain. The overturning circulation of
    the Atlantic is called overturning because
  • 30:02 - 30:07
    it's really a vertical overturning where
    water sinks down from the surface to great
  • 30:07 - 30:15
    depth of two to three kilometers in the
    Atlantic because this water is heavy and
  • 30:15 - 30:23
    it spreads thin in the deep ocean until it
    rises up in other parts, mainly around
  • 30:23 - 30:30
    Antarctica in the Antarctic circumpolar
    current area and comes back at the
  • 30:30 - 30:37
    surface. So basically the whole ocean is
    overturned with deep water being renewed
  • 30:37 - 30:45
    and then coming back to the surface on
    very long timescale of about 1000 to 2000
  • 30:45 - 30:54
    years for complete overturning there. Now,
    the whole system is driven by the fact
  • 30:54 - 31:01
    that the water sinks down where it has the
    highest density, and that's in the
  • 31:01 - 31:07
    northern Atlantic and around Antarctica,
    around the Antarctic continent. And it has
  • 31:07 - 31:12
    the highest density there, not only
    because it's very cold, but also quite
  • 31:12 - 31:17
    salty. This is why you don't have deep
    water formation in the North Pacific, in
  • 31:17 - 31:22
    the Northern Hemisphere. You only have
    that in the North Atlantic. And that's
  • 31:22 - 31:28
    because the North Atlantic waters are
    quite salty. And this is because this
  • 31:28 - 31:34
    North Atlantic current exists and brings
    salty water from the subtropics up to the
  • 31:34 - 31:39
    high latitudes, where normally it isn't
    very salty because it gets diluted by
  • 31:39 - 31:45
    excess rainfall, whereas the subtropics
    have excess evaporation and that's why
  • 31:45 - 31:50
    they're salty. And so it's like a chicken
    and an egg situation. The Northern
  • 31:50 - 31:55
    Atlantic is salty because you have this
    overturning circulation and you have this
  • 31:55 - 32:00
    overturning circulation because it's salty
    there. And so you can see the self
  • 32:00 - 32:06
    amplifying feedback there again, which
    means it is a self stabilizing system up
  • 32:06 - 32:11
    to a certain breaking point, a tipping
    point which can be reached if you add too
  • 32:11 - 32:18
    much fresh water, diluting the northern
    Atlantic. And the stability diagram,
  • 32:18 - 32:25
    again, looks like that second one. You've
    seen it for the Greenland ice sheet. As I
  • 32:25 - 32:30
    said, this has been verified in a detailed
    model simulations with many different
  • 32:30 - 32:35
    models that it really works like that in a
    complex 3D situation where you have
  • 32:35 - 32:42
    depending on how much fresh water you add
    into the northern Atlantic, this is the
  • 32:42 - 32:48
    control parameter here, you can move along
    that upper stable branch with the
  • 32:48 - 32:54
    overturning circulation until that Stommel
    bifurcation point. And there this
  • 32:54 - 33:00
    overturning breaks down and you fall down
    onto that lower branch without this
  • 33:00 - 33:07
    overturning. It's labeled here NADW Flow
    that NADW stands for north Atlantic
  • 33:07 - 33:11
    deepwater. It's a, I would say, one of the
    favorite water masses of the
  • 33:11 - 33:21
    oceanographers. Now, let's look at the
    Gulf Stream, the surface circulation in a
  • 33:21 - 33:28
    climate model. This is the CM 2.6 global
    coupled climate model ocean atmosphere by
  • 33:28 - 33:34
    the Geophysical Fluid Dynamics Laboratory
    in Princeton. You can beautifully see the
  • 33:34 - 33:40
    Gulf Stream and dark red here because it's
    warm leaving the coast of the United
  • 33:40 - 33:46
    States at Cape Hatteras there, starting to
    meander, breaking up into these eddies, et
  • 33:46 - 33:53
    cetera. And it actually meets the cold
    waters coming down inshore from the north,
  • 33:53 - 33:59
    which are shown in blue here. And so this
    is what this the surface part of the
  • 33:59 - 34:07
    circulation looks in a global climate
    model. And if you add carbon dioxide to
  • 34:07 - 34:14
    that climate models atmosphere, the
    climate warms, of course, but it does show
  • 34:14 - 34:20
    a peculiar pattern of sea surface
    temperature change, which you see here.
  • 34:20 - 34:25
    And this actually shows the sea surface
    temperature change relative to the global
  • 34:25 - 34:30
    mean. So everything that is blue has
    either warmed less than the global average
  • 34:30 - 34:35
    or even cooled, which is actually the case
    south of Greenland. And everything that is
  • 34:35 - 34:41
    orange or red has warmed substantially
    more than the global average sea surface.
  • 34:43 - 34:50
    And you see a very strong pattern in the
    northern Atlantic with this big cold blob,
  • 34:50 - 34:56
    the blue blob south of Greenland and a
    very warm region inshore of the Gulf
  • 34:56 - 35:02
    Stream along the coast of North America.
    And in the climate model, of course, we
  • 35:02 - 35:07
    are a bit like gods in that sense that we
    have complete information about what's
  • 35:07 - 35:13
    going on there. If we store all the data
    at every point, we know exactly everything
  • 35:13 - 35:18
    that's happening and we can analyze the
    reasons. And the reason for this funny
  • 35:18 - 35:25
    pattern in the northern Atlantic actually
    is a slowdown of the North Atlantic
  • 35:25 - 35:35
    overturning circulation. That means that
    less heat is transported to the subpolar
  • 35:35 - 35:41
    ocean south of Greenland there. That blue
    area, which makes it cool down and the
  • 35:41 - 35:47
    Gulf Stream proper at the surface, moves
    inshore there is complicated dynamical
  • 35:47 - 35:52
    reasons for that. But there is already
    long before this was shown in this model,
  • 35:53 - 35:59
    a theoretical underpinning for this. It
    has to do with the vorticity dynamics on a
  • 35:59 - 36:05
    rotating sphere too technical to go into
    in such a talk. But it's a well understood
  • 36:05 - 36:11
    phenomenon. And so we know that this
    slowdown of the Gulf Stream system is the
  • 36:11 - 36:16
    reason behind this peculiar temperature
    pattern. And this pattern is predicted by
  • 36:16 - 36:23
    this climate model for a global warming
    situation. And my PhD student, Levke
  • 36:23 - 36:29
    Caesar, who was the first author on this
    nature paper from 2018, she looked at all
  • 36:29 - 36:34
    the available measurements of sea surface
    temperatures since the beginning of the
  • 36:34 - 36:40
    20th century. And of course, because we
    have only limited ocean temperature
  • 36:40 - 36:44
    measurements, we have only a fuzzy picture
    here, not a sharp one like in the climate
  • 36:44 - 36:51
    model. But you can see a similar pattern
    in the North Atlantic in the observations
  • 36:51 - 36:56
    compared to what the model predicts in
    response to a slowdown of the overturning
  • 36:56 - 37:01
    circulation. And our conclusion here is
    that we are actually observing this
  • 37:01 - 37:06
    slowdown of the circulation. Why do we
    take indirect evidence for this like this?
  • 37:07 - 37:13
    Because we don't, of course, have
    measurements going back 100 years or more
  • 37:14 - 37:19
    about the strength of that overturning
    circulation. We have actually only started
  • 37:19 - 37:25
    to measure this regularly in 2004 with a
    so-called rapid array, At twenty six
  • 37:25 - 37:32
    degrees north in the Atlantic, and what we
    reconstructed about the evolution of this
  • 37:32 - 37:37
    current for the last period where we do
    have the direct measurements, agrees well
  • 37:38 - 37:46
    with what the direct measurements show. We
    concluded that the overturning circulation
  • 37:46 - 37:54
    has declined since at least the mid 20th
    century by about 15% so far. There are, of
  • 37:54 - 38:01
    course, other indirect types of
    measurements. You can use sediment data of
  • 38:01 - 38:06
    various kinds and with various
    methodologies to reconstruct the strength
  • 38:06 - 38:11
    of this Atlantic overturning and a number
    of different studies compiled here in this
  • 38:11 - 38:17
    diagram. And even though, of course, they
    differ somewhat in the detail, they all
  • 38:17 - 38:24
    tend to agree in this overall picture that
    the Atlantic overturning circulation has
  • 38:24 - 38:29
    been quite stable for the previous
    thousand years or so before the 20th
  • 38:29 - 38:36
    century, but then in the 20th century has
    showed a clear declining signature. And
  • 38:36 - 38:42
    one example of the media coverage of this
    is that Washington Post article here,
  • 38:42 - 38:48
    which if you can see the small print of
    the most read articles there on that, they
  • 38:48 - 38:53
    actually made it to number three or the
    most read Washington Post articles. There
  • 38:53 - 38:59
    is definitely an interest in science and
    climate change science by the readers in
  • 38:59 - 39:10
    the newspapers. So far we've talked about
    a slow down and not so much about where
  • 39:10 - 39:14
    this tipping point is. One reason is we
    don't know really. We know there is this
  • 39:14 - 39:18
    tipping point, that is a robust result of
    many different studies and model
  • 39:18 - 39:24
    experiments and theory, but we don't know
    how far away we are from this. That is
  • 39:24 - 39:28
    very typical for these tipping points
    because they involve highly nonlinear
  • 39:28 - 39:34
    dynamics. That means they can depend very
    sensitively on the exact conditions, for
  • 39:34 - 39:40
    example, in this case, the exact salinity
    distribution in the Atlantic and the exact
  • 39:40 - 39:46
    circulation pattern. And models get these
    things kind of approximately right, but
  • 39:46 - 39:53
    not exactly right. And if you have a
    situation where the question of where the
  • 39:53 - 39:57
    tipping point is is very sensitive to the
    exact conditions, then you have a large
  • 39:57 - 40:03
    uncertainty about where the tipping point
    is. And so there is discussion in the
  • 40:03 - 40:08
    literature. I just point out to one study
    here in science advances that try to
  • 40:08 - 40:17
    correct for the inaccuracies in how we can
    reproduce the salinity in the Atlantic
  • 40:17 - 40:22
    waters and found that if you correct for
    that, the circulation is actually a lot
  • 40:22 - 40:28
    more sensitive than in other models. And
    maybe that model is more correct. And of
  • 40:28 - 40:32
    course, it has other weaknesses as well.
    We don't know which of the models is
  • 40:32 - 40:40
    correct, but should we cross this tipping
    point then the North Atlantic circulation
  • 40:40 - 40:44
    system would break down and you get a
    temperature pattern like the one shown
  • 40:44 - 40:49
    here, the cold blob in the Atlantic that
    is now only over the ocean. It exists,
  • 40:49 - 40:53
    right? It's the only part of the world
    that has cooled since the beginning of the
  • 40:53 - 40:58
    20th century, but it hasn't affected any
    land areas. But if the circulation would
  • 40:58 - 41:04
    break down altogether and not only
    weakened by 15%, this cold would expand
  • 41:04 - 41:09
    greatly and affect Great Britain,
    Scandinavia, Iceland, as you can see here,
  • 41:10 - 41:14
    which would then get a much colder
    climate, whereas the rest of the globe
  • 41:14 - 41:20
    continues to have a warmer climate. This
    is really distinct from an ice age. And so
  • 41:20 - 41:24
    this is also really distinct from that
    Hollywood movie The Day After Tomorrow,
  • 41:24 - 41:29
    where the earth goes into a huge ice age,
    an instant freeze. That, of course, is
  • 41:29 - 41:34
    totally unrealistic. And the the
    screenwriter and the director, they knew
  • 41:34 - 41:40
    this. They actually told me that if they
    were in the business of making a movie for
  • 41:41 - 41:46
    a few million viewers, they would stick to
    the laws of physics. But since they make
  • 41:46 - 41:49
    movies for a few hundred million viewers,
    they stick to the laws of Hollywood drama.
  • 41:51 - 41:57
    But you would get a substantial regional
    cooling with a major impact on ecosystems,
  • 41:57 - 42:04
    on human society. Now, let me come to the
    third type of tipping point that I want to
  • 42:04 - 42:10
    discuss today. This is the coral reefs.
    Coral reefs, like many ecosystems, do have
  • 42:10 - 42:17
    critical thresholds. Coral reefs are very
    important, even though they only cover a
  • 42:17 - 42:22
    very small percentage of the Earth's
    surface, they support a quarter of all
  • 42:22 - 42:31
    marine life. 40% coral cover of the world
    has already been lost, 100 countries
  • 42:31 - 42:37
    depend quite substantially on corals.
    There's 800 billion total global assets of
  • 42:37 - 42:44
    coral reefs. So it does have a major
    impact on people. Now, corals, when they
  • 42:44 - 42:52
    are about to die, they bleach. They are
    abandoned by their algae that provides
  • 42:52 - 43:00
    them with nutrition and that's why they
    lose their color. And then after a while,
  • 43:00 - 43:08
    they die. They get covered by other by
    seaweed, non symbiotic algae, and they
  • 43:08 - 43:13
    die. And they do have a temperature
    threshold. It's a critical warming
  • 43:13 - 43:18
    threshold where this bleaching happens.
    But an additional factor, not yet the most
  • 43:18 - 43:25
    important factor, is the acidification of
    water. It's a direct chemical effect of
  • 43:25 - 43:31
    adding carbon dioxide to the atmosphere,
    which then goes partly into the oceans and
  • 43:31 - 43:39
    acidifies the ocean waters. But the main
    effect until now is the marine heatwaves,
  • 43:39 - 43:44
    which cross more and more frequently the
    temperature tolerance threshold of coral
  • 43:44 - 43:50
    reefs. And here you can see that for the
    Great Barrier Reef, a huge, fantastic
  • 43:50 - 43:58
    world wonder that you can see from space.
    And you can see here the bleaching in the
  • 43:58 - 44:05
    year 2016, 2017, 2020, three major
    bleaching events which affect it in each
  • 44:05 - 44:11
    case, the red area here with the most
    severe bleaching, you can see that by now
  • 44:11 - 44:17
    a very large part of the Great Barrier
    Reef has bleached in these three events.
  • 44:17 - 44:24
    And it's very tragic. And you can see
    here, for example, the March, the 2016
  • 44:24 - 44:33
    event in March, the coral was bleached. By
    May, it was already overgrown by seaweed.
  • 44:33 - 44:40
    And just in 2015 and 2016, we actually had
    worldwide coral reef bleaching, not only
  • 44:40 - 44:45
    at the Great Barrier Reef in Australia,
    only the blue ones out of these hundred
  • 44:45 - 44:53
    reefs that were observed in this study,
    only the blue ones escaped bleaching. So
  • 44:53 - 45:01
    we are actually in the midst of a great
    worldwide coral die off event, which is
  • 45:01 - 45:08
    another prediction of climate science
    coming true. If you look at the latest
  • 45:08 - 45:14
    IPCC report, it states that with two
    degrees warming, virtually all coral reefs
  • 45:14 - 45:20
    will be lost, more than 99%. One point
    five degree warming. If we manage to limit
  • 45:20 - 45:27
    the warming to one point five degrees, we
    can save between 10% and 30% of the
  • 45:27 - 45:36
    corals. That is really depressing. Now,
    let me talk briefly about what can we do.
  • 45:36 - 45:42
    A major success is, of course, the Paris
    accord, the biggest failure of which is
  • 45:42 - 45:47
    that it hasn't come 20 years earlier.
    After all, the world community already in
  • 45:47 - 45:55
    1992 decided to stop global warming at the
    Rio Earth Summit. The nations signed the
  • 45:55 - 46:01
    United Nations Framework Convention on
    Climate Change, and it took a full 25
  • 46:01 - 46:09
    years of further negotiations to finally
    reach the Paris accord. Now, you can see
  • 46:09 - 46:17
    here that the goal of this is to hold the
    increase in the global average temperature
  • 46:17 - 46:22
    to well below two degrees above pre-
    industrial level. So it's not two degrees,
  • 46:22 - 46:26
    it's well below two degrees. That's a very
    important point. Many countries would not
  • 46:26 - 46:33
    have signed up if it simply had said two
    degrees, which was an older goal, but it
  • 46:33 - 46:46
    has shown to be insufficient and. And to
    sorry and to pursue efforts to limit the
  • 46:46 - 46:51
    temperature increase to one point five
    degrees above pre-industrial levels. So
  • 46:51 - 46:56
    that is a more stringent Paris goal, but
    at least the nations have committed to
  • 46:56 - 47:02
    pursue efforts. So my view is that every
    person should ask their own government
  • 47:03 - 47:08
    what you are doing here. Is this a
    credible effort to try and limit warming
  • 47:08 - 47:14
    to one point five degrees? We might not
    make it, but at least we should try to
  • 47:14 - 47:19
    limit the warming to one point five to
    avoid the risk of destabilization of the
  • 47:19 - 47:26
    Greenland ice sheet, almost complete coral
    die off and many further risks. So what
  • 47:26 - 47:33
    does this entail? That is an important
    point. If you want to limit global warming
  • 47:33 - 47:39
    to some value, whatever it is, one point
    five, two, three, whatever you choose, it
  • 47:39 - 47:45
    means you can only emit a limited amount
    of carbon dioxide. That is because the
  • 47:45 - 47:53
    amount of global warming is to a good
    extent proportional to the total amount of
  • 47:53 - 47:59
    CO2 that we have ever emitted. So to the
    cumulative emissions, it's like filling a
  • 47:59 - 48:05
    bathtub with water. If you want to draw
    the line at any level and say no further
  • 48:05 - 48:11
    than here, you can only add a limited
    amount of water. And if you want to limit
  • 48:11 - 48:16
    global warming to some value, you can only
    add a limited amount of CO2 to the
  • 48:16 - 48:23
    atmosphere. And this is shown here for two
    different examples, two different amounts.
  • 48:23 - 48:30
    This is actually, the numbers here are
    emissions from the year 2016. So it's
  • 48:31 - 48:37
    don't take these numbers from now. We have
    already had four more years of emissions.
  • 48:39 - 48:50
    The solid lines throw show three scenarios
    with six hundred billion tons of CO2 and
  • 48:50 - 48:56
    they all have the same amount of emission.
    So they're all three solid lines, get the
  • 48:56 - 49:01
    same amount of warming. This is about
    actually these lines correspond to about a
  • 49:01 - 49:08
    50 percent chance of ending up at one
    point five degrees. And so they will get
  • 49:08 - 49:16
    you the same amount of warming, but with
    different times of when the peak emissions
  • 49:16 - 49:23
    are reached. So 2016 went past without us
    getting over the peak of the emissions.
  • 49:23 - 49:30
    2020, maybe we still have a chance.
    Emissions have dropped a bit in 2020, but
  • 49:30 - 49:34
    not for structural change and mostly, but
    due to Corona. But we still we have a
  • 49:34 - 49:39
    chance that maybe next year they are lower
    still. And what this shows is that the
  • 49:39 - 49:46
    longer you wait, the steeper your
    reductions have to be, not only because
  • 49:46 - 49:51
    you're starting later, but also because
    you have to reach zero earlier at the end.
  • 49:51 - 49:56
    Notice how all these three lines, the
    later you start with reducing, the earlier
  • 49:56 - 50:02
    you have to reach zero emissions, because
    the surface area under these curves is
  • 50:02 - 50:09
    what counts for the climate goal. The
    dashed lines a more generous goal, which
  • 50:09 - 50:15
    would end at about 1.75 degrees or so,
    best estimate. this is kind of the weaker
  • 50:15 - 50:21
    Paris goal of well below two degrees,
    which would allow us to gradually reduce
  • 50:21 - 50:28
    emissions to zero by 2050. This is not
    counting in any negative emissions
  • 50:28 - 50:34
    afterwards, by the way. This is the net
    emissions, if you like. So we have to
  • 50:34 - 50:40
    reach net zero emissions in 2050. But of
    course, if we wait five more years until
  • 50:40 - 50:45
    the emissions start to decline, then
    they'll have to be at zero five years
  • 50:45 - 50:51
    earlier. So this is why it's so important
    to start now. This, by the way, so from an
  • 50:51 - 50:59
    article by Christiana Figueres et al. in
    Nature, published 2017, where I was a
  • 50:59 - 51:06
    coauthor as well. Now, a final point. Can
    tipping points maybe help us? And I'm
  • 51:06 - 51:11
    talking here about societal tipping
    points. And there are also some
  • 51:11 - 51:17
    interesting studies on that. The basic
    idea is that shown in the top right here,
  • 51:17 - 51:25
    we are in a kind of stable equilibrium
    where the red ball is now and we are stuck
  • 51:25 - 51:31
    there. It's hard to get out of this, but
    there is a better equilibrium, a more
  • 51:31 - 51:36
    stable one further off to the right. And
    the question is, how do we get over the
  • 51:36 - 51:43
    hill into that beneficial equilibrium of a
    sustainable global economy, a sustainable
  • 51:43 - 51:49
    energy system, a stable climate and so on?
    Complete decarbonization, that means no
  • 51:49 - 51:56
    more fossil fuel use. And these this green
    addition there that is added there, this
  • 51:56 - 52:02
    is just some examples of how we can make
    this transition earlier, easier and the
  • 52:02 - 52:08
    hill that we have to get over smaller, so
    we can make this current status quo that
  • 52:08 - 52:15
    we're in a little bit less comfortable by
    putting a price on carbon. We can make the
  • 52:15 - 52:23
    transition easier by subsidizing renewable
    energies. There are there is a greening of
  • 52:23 - 52:28
    values. There is a tipping point in
    thinking, in society. There are many co
  • 52:28 - 52:34
    benefits of this transformation in terms
    of avoided air pollution. For example,
  • 52:34 - 52:40
    millions of people die every year from
    outdoor air pollution, which would which
  • 52:40 - 52:45
    to a large extent go away if we stop
    fossil fuel use. And we have seen a
  • 52:45 - 52:51
    massive movement by the young people
    Fridays for future. He is Greta Thunberg
  • 52:51 - 52:57
    talking to me at our institute. She came
    last year to visit us here, here is a
  • 52:57 - 53:03
    Fridays demonstration in Berlin where I
    took this photo. This is really changing
  • 53:03 - 53:09
    the societies values and it's changing
    election results and it could be a tipping
  • 53:09 - 53:16
    point towards a sustainable global
    society. And with that hopeful message, I
  • 53:16 - 53:22
    want to end and I thank you very much for
    your attention. If you want to read more,
  • 53:22 - 53:27
    there's a couple of books of mine that
    have also come out in English. You can
  • 53:27 - 53:33
    follow me on the blogs and of course, in
    social media, preferably Twitter, but also
  • 53:33 - 53:38
    the scientist for future logo there,
    because many thousands of scientists are
  • 53:38 - 53:44
    engaged there to try and stop the climate
    crisis. This is really a matter of
  • 53:44 - 53:50
    survival of civilization. Thank you very
    much for listening. Stick to science and
  • 53:50 - 53:54
    leave policy to us. Well, we tried that
    approach. You didn't want to hear about
  • 53:54 - 53:57
    the science when it could have made a
    difference.
  • 53:57 - 54:04
    Herald: Thank you so much Stefan for your
    talk. Now we have some questions from the
  • 54:04 - 54:10
    Internets. Let's see the first question
    Question: Which additional tipping points
  • 54:10 - 54:15
    will be triggered at two degrees, three
    degrees and so on?
  • 54:15 - 54:22
    Answer: That is actually a difficult
    question to answer because of the
  • 54:22 - 54:28
    uncertainty that I mentioned in my talk
    about where these tipping points are.
  • 54:28 - 54:34
    There is one in Antarctica, the Wilkes
    basin, that is a part of the Antarctic ice
  • 54:34 - 54:41
    sheet that that could be triggered, say,
    below three degrees. There are others like
  • 54:41 - 54:46
    the ocean circulation where you probably
    at least we hope you have to go beyond
  • 54:46 - 54:51
    three degrees to really trigger a collapse
    of the Gulf Stream system. But the truth
  • 54:51 - 54:57
    is that they are very large uncertainty
    ranges. And the main fact is that with
  • 54:57 - 55:05
    every bit of extra warming, we increase
    the risk of crossing more tipping points.
  • 55:05 - 55:11
    Q: And are there some of these tipping
    points that are interrelated or
  • 55:11 - 55:16
    correlated? For instance, could we save
    some tipping points if we are able to save
  • 55:16 - 55:20
    others, for instance, the collapse of the
    Gulf Stream?
  • 55:20 - 55:25
    A: Yes, there are these interconnections.
    For example, if the Gulf Stream system
  • 55:25 - 55:32
    collapses, it will affect the atmospheric
    circulation. The monsoon systems then can
  • 55:32 - 55:37
    shift the tropical rainfall balance. This
    is not just theoretical. We see that in
  • 55:37 - 55:41
    paleoclimate where we have seen these
    collapses of the North Atlantic
  • 55:41 - 55:48
    circulation and the paleo climatic proxy
    data show that it comes with shifts in the
  • 55:48 - 55:54
    tropical rainfall belts that could then in
    this way trigger a major drought in the
  • 55:54 - 56:00
    Amazon region if the Gulf Stream system
    collapses. And so it would be very wise to
  • 56:00 - 56:05
    prevent these tipping points, especially
    when it comes to the ocean circulation or
  • 56:05 - 56:10
    atmospheric circulation, because it's
    really going to mess up the weather
  • 56:10 - 56:17
    patterns in a major way.
    Q: How long have we known about human
  • 56:17 - 56:22
    caused climate change?
    A: Well, in principle, in the 19th
  • 56:22 - 56:30
    century, Alexander von Humboldt, actually,
    wrote in 1843, if I remember correctly,
  • 56:30 - 56:36
    that humans are changing the climate by
    cutting down forests and emitting large
  • 56:36 - 56:41
    amounts of gases at the centers of
    industry. That's almost a little literal
  • 56:41 - 56:46
    quote by Alexander von Humboldt. We've
    known about how sensitive the climate is
  • 56:46 - 56:52
    to a change in CO2 since the Swedish Nobel
    laureate Svante Arrhenius, remotely
  • 56:52 - 56:59
    related to Greta Thunberg by the way, in
    India studied the effect of CO2 doubling.
  • 56:59 - 57:06
    He wasn't worried by that because he
    thought global warming would be great.
  • 57:06 - 57:13
    Bring it on. It just died, now it's back.
    You can see my picture so?
  • 57:13 - 57:19
    Herald: yeah
    A: and so he suggested, you know, burning
  • 57:19 - 57:26
    a lot of coal to enhance global warming. I
    guess he came from Sweden and thought cold
  • 57:26 - 57:31
    is bad without thinking it through
    properly. But the first real expert
  • 57:31 - 57:37
    reports warning the US government, Lyndon
    B. Johnson, of the coming global warming
  • 57:37 - 57:44
    due to fossil fuel use was a rebel report
    in nineteen sixty five, exactly 50 years,
  • 57:44 - 57:49
    half a century before finally the Paris
    agreement was reached.
  • 57:49 - 57:53
    Q: Will you be publishing your slides from
    the talk?
  • 57:53 - 58:00
    A: Yes, I will. Uploading the slides.
    Q: What is or what should be the ultimate
  • 58:00 - 58:05
    goal of the climate change mitigation? For
    instance, is it saving lives, saving other
  • 58:05 - 58:10
    species?
    A: Well, I think the the ultimate goal is,
  • 58:10 - 58:16
    of course, preserving human civilization,
    as we know it, but because I think if we
  • 58:16 - 58:25
    let this run, we will not only destroy a
    lot of ecosystems and biodiversity, but we
  • 58:25 - 58:32
    will probably cause major hunger crisis,
    which with big droughts like the one in
  • 58:32 - 58:39
    Syria before the unrest in Syria started
    in two 2011, the country went through the
  • 58:39 - 58:44
    biggest drought in history. And according
    to settlement data from the eastern
  • 58:44 - 58:51
    Mediterranean, it was the worst drought in
    at least nine hundred years. And then I
  • 58:51 - 58:58
    think especially in some unstable,
    conflicted countries, this can really turn
  • 58:58 - 59:04
    them into failed states. That is what
    happened in Syria. And it's what a German
  • 59:05 - 59:12
    report for the German government actually
    warned in 2009. It was called climate
  • 59:12 - 59:16
    change as a security risk, I was actually
    one of the coauthors of that report
  • 59:16 - 59:20
    because I was in the German government's
    advisory panel on global change at the
  • 59:20 - 59:27
    time. And I think we will see increasing
    hunger crisis, failed states and all the
  • 59:27 - 59:33
    effects that that has on international
    politics if we cannot keep global warming
  • 59:33 - 59:40
    below two degrees.
    Q: And finally, is there a specific call
  • 59:40 - 59:44
    to action for the chaos community? Is
    there anything that we can do with our
  • 59:44 - 59:51
    mindset and our skills?
    A: That's a good question that I haven't
  • 59:51 - 59:57
    thought about, but maybe you can know
    yourself the best thing, what you can do,
  • 59:58 - 60:04
    I think the key is really to keep up the
    pressure on the political world, like
  • 60:04 - 60:11
    Fridays for future has been doing: Go on
    the streets, protest, vote with climate as
  • 60:11 - 60:16
    a priority. I think these are the key
    things that everyone should be doing and
  • 60:16 - 60:21
    specifically in whatever profession they
    are. They will see some ways of how you
  • 60:21 - 60:27
    can help to reduce emissions in your
    company, put sustainability at the top of
  • 60:27 - 60:31
    the agenda and so on.
    Herald: Stefan, thanks so much for taking
  • 60:31 - 60:37
    the time to join us today.
    Stefan: It's a great pleasure and honor.
  • 60:37 - 60:43
    Herald: Always welcome. And now the news.
  • 60:43 - 61:22
    Subtitles created by c3subtitles.de
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Title:
#rC3 - Climate Tipping Points
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Video Language:
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Duration:
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