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Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.00,0:00:13.88,Default,,0000,0000,0000,,{\i1}rc3 prerol music{\i0}
Dialogue: 0,0:00:13.88,0:00:18.07,Default,,0000,0000,0000,,Herald angel: Greeting creatures im\NNeuland. In 2015 governments from around
Dialogue: 0,0:00:18.07,0:00:22.81,Default,,0000,0000,0000,,the world met in Paris and agreed to\Nattempt to limit anthropogenic climate
Dialogue: 0,0:00:22.81,0:00:28.34,Default,,0000,0000,0000,,change to well below two degrees.\NUnfortunately, it seems that since then we
Dialogue: 0,0:00:28.34,0:00:32.76,Default,,0000,0000,0000,,have not done enough and the climate\Ncrisis has only gotten more urgent. Our
Dialogue: 0,0:00:32.76,0:00:38.15,Default,,0000,0000,0000,,next speaker, Stefan Rahmstorf, has more\Naccolades than I have time to tell. He's
Dialogue: 0,0:00:38.15,0:00:42.44,Default,,0000,0000,0000,,published more than 100 papers, including\Nin the journals Nature and Science, co-
Dialogue: 0,0:00:42.44,0:00:46.88,Default,,0000,0000,0000,,authored four books and won the Climate\NCommunication Prize from the American
Dialogue: 0,0:00:46.88,0:00:52.96,Default,,0000,0000,0000,,Geophysical Union, the first European to\Ndo so. Please welcome him. And heed his
Dialogue: 0,0:00:52.96,0:00:55.25,Default,,0000,0000,0000,,advice. Here's Stefan.
Dialogue: 0,0:01:04.62,0:01:10.56,Default,,0000,0000,0000,,Stefan Rahmstorf: Hi, everyone, my name is\NStefan Rahmstorf, and I'm thrilled to be
Dialogue: 0,0:01:10.56,0:01:17.68,Default,,0000,0000,0000,,invited to give a talk at the Chaos\NComputer Club's remote chaos experience
Dialogue: 0,0:01:17.68,0:01:26.72,Default,,0000,0000,0000,,2020. I want to give you an overview of\Nclimate tipping points, a very exciting
Dialogue: 0,0:01:26.72,0:01:34.40,Default,,0000,0000,0000,,subject that I will try to shed some light\Non. But let's first start with some
Dialogue: 0,0:01:34.40,0:01:40.16,Default,,0000,0000,0000,,background on climate change. You probably\Nknow this image. It shows the global
Dialogue: 0,0:01:40.16,0:01:46.72,Default,,0000,0000,0000,,temperature evolution since the year 1880.\NEvery line is one year. This is the more
Dialogue: 0,0:01:46.72,0:01:54.08,Default,,0000,0000,0000,,conventional way of viewing this time\Nseries. And the last seven years have been
Dialogue: 0,0:01:54.08,0:02:04.03,Default,,0000,0000,0000,,the hottest seven years since record\Nkeeping began in the 19th century. We know
Dialogue: 0,0:02:04.03,0:02:08.56,Default,,0000,0000,0000,,the reason for this warming: it's the\Nincrease of carbon dioxide, which you can
Dialogue: 0,0:02:08.56,0:02:13.92,Default,,0000,0000,0000,,see here for the last ten thousand years.\NAnd if you just look at the end of the
Dialogue: 0,0:02:13.92,0:02:21.60,Default,,0000,0000,0000,,curve, how the increase has accelerated in\Never shorter time spans, we have seen an
Dialogue: 0,0:02:21.60,0:02:30.79,Default,,0000,0000,0000,,ever greater increase in the amount of\Ncarbon dioxide in our planet's atmosphere.
Dialogue: 0,0:02:30.79,0:02:37.82,Default,,0000,0000,0000,,This increase causes what we call a\Nradiative forcing that is a kind of
Dialogue: 0,0:02:37.82,0:02:44.68,Default,,0000,0000,0000,,heating in terms of energy release per\Nsquare meter of Earth's surface. And the
Dialogue: 0,0:02:44.68,0:02:51.30,Default,,0000,0000,0000,,increase in CO2 in the atmosphere until\Nnow is causing heating at a rate of two
Dialogue: 0,0:02:51.30,0:02:59.36,Default,,0000,0000,0000,,Watts per square meter surface. We\Nunderstand the energy budget of our planet
Dialogue: 0,0:02:59.36,0:03:04.32,Default,,0000,0000,0000,,pretty well. On the left here in this\Ndiagram, you can see the incoming solar
Dialogue: 0,0:03:04.32,0:03:09.60,Default,,0000,0000,0000,,radiation in yellow. Part of that is\Nreflected already in the atmosphere by the
Dialogue: 0,0:03:09.60,0:03:15.76,Default,,0000,0000,0000,,clouds, for example. Another part is\Nreflected by the bright surfaces, that's
Dialogue: 0,0:03:15.76,0:03:22.96,Default,,0000,0000,0000,,the snow and ice surfaces primarily, and\Nthe rest is absorbed. On the right hand
Dialogue: 0,0:03:22.96,0:03:28.64,Default,,0000,0000,0000,,side, and let's zoom into that, you see in\Norange the long wave radiation, which is
Dialogue: 0,0:03:28.64,0:03:36.08,Default,,0000,0000,0000,,clearly distinct from the incoming short\Nwave solar radiation by its wavelength and
Dialogue: 0,0:03:36.08,0:03:42.24,Default,,0000,0000,0000,,this thick arrow of long wave radiation\Nleaving the Earth's surface basically to a
Dialogue: 0,0:03:42.24,0:03:47.60,Default,,0000,0000,0000,,large extent gets absorbed by the\Natmosphere. And the atmosphere itself
Dialogue: 0,0:03:47.60,0:03:53.84,Default,,0000,0000,0000,,emits like anything, any substance, any\Nmatter depending on its surface
Dialogue: 0,0:03:53.84,0:03:59.60,Default,,0000,0000,0000,,temperature, sorry, depending on its\Ntemperature, emits also infrared
Dialogue: 0,0:03:59.60,0:04:07.92,Default,,0000,0000,0000,,radiation. And one thing that few people\Nrealize is that the back radiation coming
Dialogue: 0,0:04:07.92,0:04:13.68,Default,,0000,0000,0000,,down from the atmosphere through the\Ngreenhouse effect, the greenhouse gases,
Dialogue: 0,0:04:13.68,0:04:20.24,Default,,0000,0000,0000,,is actually twice as large at the Earth's\Nsurface as the absorbed solar radiation.
Dialogue: 0,0:04:20.24,0:04:26.08,Default,,0000,0000,0000,,So heating by the greenhouse effect by the\Nlong wave radiation is twice as big as the
Dialogue: 0,0:04:26.08,0:04:32.24,Default,,0000,0000,0000,,absorbed solar radiation at the Earth's\Nsurface. And so it's little wonder that if
Dialogue: 0,0:04:32.24,0:04:38.80,Default,,0000,0000,0000,,we are increasing this natural greenhouse\Neffect, which actually makes our planet
Dialogue: 0,0:04:38.80,0:04:43.68,Default,,0000,0000,0000,,livable in the first place, if we are\Nincreasing this effect that it is going to
Dialogue: 0,0:04:43.68,0:04:54.00,Default,,0000,0000,0000,,get warmer. We can also quantify this\Neffect. And if you add in not just the CO2
Dialogue: 0,0:04:54.00,0:04:58.64,Default,,0000,0000,0000,,increase, but other human caused\Ngreenhouse gases and also cooling effects
Dialogue: 0,0:04:58.64,0:05:05.04,Default,,0000,0000,0000,,caused by humans, then you see that the\Ntotal human caused warming that we see in
Dialogue: 0,0:05:05.04,0:05:12.88,Default,,0000,0000,0000,,the orange bar is to, within uncertainty,\Nas big as the observed global warming
Dialogue: 0,0:05:12.88,0:05:21.44,Default,,0000,0000,0000,,since the 1950s. And that means that about\N100% of the observed global warming over
Dialogue: 0,0:05:21.44,0:05:28.32,Default,,0000,0000,0000,,the past 70 years is human caused, and the\Nbest estimates of the human caused warming
Dialogue: 0,0:05:28.32,0:05:34.56,Default,,0000,0000,0000,,is actually even slightly more than the\Nobserved warming, which has to do partly
Dialogue: 0,0:05:34.56,0:05:40.80,Default,,0000,0000,0000,,or is consistent with the fact that solar\Nactivity has gone down. So the decrease in
Dialogue: 0,0:05:40.80,0:05:49.84,Default,,0000,0000,0000,,solar activity has compensated a small\Npart of the human caused global warming.
Dialogue: 0,0:05:49.84,0:05:55.84,Default,,0000,0000,0000,,It's also very interesting, and especially\Nto me as a paleoclimatologist who studies
Dialogue: 0,0:05:55.84,0:06:01.84,Default,,0000,0000,0000,,natural climate variations in Earth's\Nhistory and has done so for more than 25
Dialogue: 0,0:06:01.84,0:06:10.72,Default,,0000,0000,0000,,years, how the modern warming compares\Nwith the changes throughout the Holocene,
Dialogue: 0,0:06:10.72,0:06:17.36,Default,,0000,0000,0000,,and before that, since the last Ice Age.\NAnd this is what we see here based on
Dialogue: 0,0:06:17.36,0:06:23.36,Default,,0000,0000,0000,,decades of paleoclimate research,\Ncountless sediment cores taken at the sea
Dialogue: 0,0:06:23.36,0:06:29.68,Default,,0000,0000,0000,,bottom, ice cores on the big ice sheets\Nand so on. We have enough data now to form
Dialogue: 0,0:06:29.68,0:06:35.44,Default,,0000,0000,0000,,meaningful global average temperatures.\NAnd you can see here the warming from the
Dialogue: 0,0:06:35.44,0:06:40.88,Default,,0000,0000,0000,,height of the last ice age into the\NHolocene, the Holocene optimum, the
Dialogue: 0,0:06:40.88,0:06:46.96,Default,,0000,0000,0000,,warmest period about until about five\Nthousand years before present. And since
Dialogue: 0,0:06:46.96,0:06:55.20,Default,,0000,0000,0000,,then, we have seen a very slow cooling\Ntrend, which we have bent around due to
Dialogue: 0,0:06:55.20,0:07:02.72,Default,,0000,0000,0000,,human activities. And we have within 100\Nyears more than undone 5000 years of
Dialogue: 0,0:07:02.72,0:07:08.64,Default,,0000,0000,0000,,natural cooling trend, which normally\Nwould have very slowly continued. These
Dialogue: 0,0:07:08.64,0:07:14.51,Default,,0000,0000,0000,,natural variations, by the way, are due to\Nthe Earth orbital cycles, these so-called
Dialogue: 0,0:07:14.51,0:07:24.32,Default,,0000,0000,0000,,Milankovitch cycles. You can easily read\Nup on those, for example, at Wikipedia.
Dialogue: 0,0:07:24.32,0:07:33.02,Default,,0000,0000,0000,,Now let's come to the famous, much feared\Ntipping points in the climate system. What
Dialogue: 0,0:07:33.02,0:07:40.16,Default,,0000,0000,0000,,is a tipping point? That has been\Ndescribed in a seminal paper which I'm
Dialogue: 0,0:07:40.16,0:07:50.34,Default,,0000,0000,0000,,proud of having been a part of from 2008\Nby Tim Lenton and colleagues. And this is
Dialogue: 0,0:07:50.34,0:07:56.01,Default,,0000,0000,0000,,called tipping elements in the Earth's\Nclimate system. And it says that the term
Dialogue: 0,0:07:56.01,0:08:01.50,Default,,0000,0000,0000,,tipping point commonly refers to a\Ncritical threshold at which a tiny
Dialogue: 0,0:08:01.50,0:08:08.72,Default,,0000,0000,0000,,perturbation can qualitatively alter the\Nstate or development of a system and the
Dialogue: 0,0:08:08.72,0:08:13.70,Default,,0000,0000,0000,,different parts of the Earth's system,\Nwhich can undergo such a transition, they
Dialogue: 0,0:08:13.70,0:08:21.12,Default,,0000,0000,0000,,are called the tipping elements. This\Nwhole concept is illustrated in the red
Dialogue: 0,0:08:21.12,0:08:26.37,Default,,0000,0000,0000,,line that's shown here: In the horizontal\Naxis, we see a control parameter and that
Dialogue: 0,0:08:26.37,0:08:32.15,Default,,0000,0000,0000,,could be the greenhouse gas content of our\Natmosphere, it could be the temperature,
Dialogue: 0,0:08:32.15,0:08:37.56,Default,,0000,0000,0000,,it could be, if you talk about natural\Nclimate changes, for example, those
Dialogue: 0,0:08:37.56,0:08:43.69,Default,,0000,0000,0000,,orbital changes, the what we call the\NMilankovitch forcing, which drives
Dialogue: 0,0:08:43.69,0:08:48.89,Default,,0000,0000,0000,,changes. And on the vertical axis, you see\Nthe response. And if you imagine the
Dialogue: 0,0:08:48.89,0:08:54.84,Default,,0000,0000,0000,,control parameter changing from left to\Nright in this diagram, you would march
Dialogue: 0,0:08:54.84,0:09:01.70,Default,,0000,0000,0000,,along that upper part of the red curve\Nhere, the branch, until you come close to
Dialogue: 0,0:09:01.70,0:09:07.28,Default,,0000,0000,0000,,a threshold. And at that threshold, the\Nsystem will undergo a major change and
Dialogue: 0,0:09:07.28,0:09:17.07,Default,,0000,0000,0000,,reach then this lower part of the curve, a\Ndifferent kind of equilibrium state. So
Dialogue: 0,0:09:17.07,0:09:24.49,Default,,0000,0000,0000,,it's basically a small change in the\Ndriver causing a very big systemic
Dialogue: 0,0:09:24.49,0:09:31.34,Default,,0000,0000,0000,,response. That is what defines a tipping\Npoint. If we want to be very accurate
Dialogue: 0,0:09:31.34,0:09:36.42,Default,,0000,0000,0000,,here, we can distinguish two different\Ntypes of tipping points. The first one is
Dialogue: 0,0:09:36.42,0:09:41.56,Default,,0000,0000,0000,,what I just showed you, is repeated here\Non the left side, and it is characterized
Dialogue: 0,0:09:41.56,0:09:49.21,Default,,0000,0000,0000,,by the fact that this red equilibrium line\Nhas one state for every point on the x
Dialogue: 0,0:09:49.21,0:09:55.00,Default,,0000,0000,0000,,axis. So every amount of forcing\Ncorresponds to one particular system
Dialogue: 0,0:09:55.00,0:10:02.13,Default,,0000,0000,0000,,state. And this is some state just makes a\Nmajor transition in a smaller range of the
Dialogue: 0,0:10:02.13,0:10:12.31,Default,,0000,0000,0000,,driving parameter around this threshold.\NNow, a second, even more drastic or non-
Dialogue: 0,0:10:12.31,0:10:18.07,Default,,0000,0000,0000,,linear type of tipping point is shown in\Nthe right hand side, where the equilibrium
Dialogue: 0,0:10:18.07,0:10:24.04,Default,,0000,0000,0000,,states are somewhat more complex than the\Nsingle red line on the left. You can see
Dialogue: 0,0:10:24.04,0:10:30.27,Default,,0000,0000,0000,,here that there is, again, an upper stable\Nbranch and there is also a lower stable
Dialogue: 0,0:10:30.27,0:10:37.42,Default,,0000,0000,0000,,branch, but they overlap. So there is a\Nregion that is shaded here where two
Dialogue: 0,0:10:37.42,0:10:44.96,Default,,0000,0000,0000,,stable equilibria exist. And it depends on\Nthe initial conditions on which of these
Dialogue: 0,0:10:44.96,0:10:55.47,Default,,0000,0000,0000,,branches you are. Now, there is what is\Ncalled a bifurcation structure underlying
Dialogue: 0,0:10:55.47,0:11:03.40,Default,,0000,0000,0000,,this with a bifurcation point. There is an\Nunstable branch which separates the basins
Dialogue: 0,0:11:03.40,0:11:10.05,Default,,0000,0000,0000,,of attraction of the two stable branches.\NSo if you're in the bi-stable regime and
Dialogue: 0,0:11:10.05,0:11:15.39,Default,,0000,0000,0000,,you start kind of away from an equilibrium\Nbut above the dashed line, you will fall
Dialogue: 0,0:11:15.39,0:11:19.89,Default,,0000,0000,0000,,up onto that upper stable branch; if you\Nstart out below the dash line, you will
Dialogue: 0,0:11:19.89,0:11:25.06,Default,,0000,0000,0000,,fall down on the lower branch. That\Nactually is pretty standard non-linear
Dialogue: 0,0:11:25.06,0:11:30.72,Default,,0000,0000,0000,,dynamics. It's a whole branch of physics\Nwhich investigates exactly this type of
Dialogue: 0,0:11:30.72,0:11:37.100,Default,,0000,0000,0000,,behavior in many different physical\Nsystems. So the second type of tipping
Dialogue: 0,0:11:37.100,0:11:43.79,Default,,0000,0000,0000,,point, the right hand side one, is\Ncorresponding to multiple equilibrium
Dialogue: 0,0:11:43.79,0:11:48.30,Default,,0000,0000,0000,,states, in this case two stable\Nequilibria. That's why this error range
Dialogue: 0,0:11:48.30,0:11:54.89,Default,,0000,0000,0000,,here is called bistability, two stable\Nequilibria. It is coming with
Dialogue: 0,0:11:54.89,0:11:59.79,Default,,0000,0000,0000,,irreversibility, so basically, if you\Nmarch to the right here on that upper
Dialogue: 0,0:11:59.79,0:12:06.15,Default,,0000,0000,0000,,stable branch at that bifurcation point,\Nyou fall off down onto the lower stable
Dialogue: 0,0:12:06.15,0:12:11.54,Default,,0000,0000,0000,,branch, but you can't just go back up from\Nthere. You have to go all the way to the
Dialogue: 0,0:12:11.54,0:12:16.70,Default,,0000,0000,0000,,left to that second lower blue point there\Nuntil you can go back onto that stable
Dialogue: 0,0:12:16.70,0:12:24.53,Default,,0000,0000,0000,,branch. The second type is actually as an\Neveryday system that behaves like that it
Dialogue: 0,0:12:24.53,0:12:29.58,Default,,0000,0000,0000,,can be easily compared to a kayak: if\Nyou're sitting in a kayak and you lean a
Dialogue: 0,0:12:29.58,0:12:35.87,Default,,0000,0000,0000,,little bit to one side, then you\Nexperience a counterforce. So the kayak is
Dialogue: 0,0:12:35.87,0:12:41.72,Default,,0000,0000,0000,,trying to upright itself, it's resisting\Nyou tipping it. But if you move further
Dialogue: 0,0:12:41.72,0:12:47.24,Default,,0000,0000,0000,,and further and further, eventually you\Nwill reach a tipping point. This is the
Dialogue: 0,0:12:47.24,0:12:53.82,Default,,0000,0000,0000,,point where the kayak stops resisting your\Nfurther leaning over and instead it starts
Dialogue: 0,0:12:53.82,0:12:59.99,Default,,0000,0000,0000,,tipping over further by itself and then it\Nflips right over until it's upside down
Dialogue: 0,0:12:59.99,0:13:05.94,Default,,0000,0000,0000,,and you're falling out. So I have I have\Ndone this quite a few times. So I have a
Dialogue: 0,0:13:05.94,0:13:11.26,Default,,0000,0000,0000,,kayak that is quite narrow where it easily\Nhappens if you don't take care, that you
Dialogue: 0,0:13:11.26,0:13:18.23,Default,,0000,0000,0000,,flip over. Now, this kayak also has a\Nrange of bistability, so once it's flipped
Dialogue: 0,0:13:18.23,0:13:23.33,Default,,0000,0000,0000,,over, it's also in a stable state and it\Ntakes considerable effort to turn it
Dialogue: 0,0:13:23.33,0:13:28.94,Default,,0000,0000,0000,,upright again into the other stable state\Nwhen it's vertical, upright rather than
Dialogue: 0,0:13:28.94,0:13:37.17,Default,,0000,0000,0000,,upside down. Now, the whole point is that\Nsystems like this exist also in the
Dialogue: 0,0:13:37.17,0:13:45.12,Default,,0000,0000,0000,,climate system. The kind of first type on\Nthe left hand side corresponds, for
Dialogue: 0,0:13:45.12,0:13:51.92,Default,,0000,0000,0000,,example, to sea ice and on the right hand\Nside this type of tipping element compares
Dialogue: 0,0:13:51.92,0:13:58.64,Default,,0000,0000,0000,,to refers to the Greenland ice sheet or\Ncontinental ice sheets, also Antarctica or
Dialogue: 0,0:13:58.64,0:14:06.64,Default,,0000,0000,0000,,the Atlantic Ocean circulation. In terms\Nof the trends in behavior, and that means
Dialogue: 0,0:14:06.64,0:14:12.16,Default,,0000,0000,0000,,if you if you kind of go through a global\Nwarming phase, you're moving from left to
Dialogue: 0,0:14:12.16,0:14:19.44,Default,,0000,0000,0000,,right in these diagrams, then in that\Nsense, they don't differ very much because
Dialogue: 0,0:14:19.44,0:14:26.00,Default,,0000,0000,0000,,in either case, you follow a line like\Nthis green line. So on the left hand side,
Dialogue: 0,0:14:26.00,0:14:32.40,Default,,0000,0000,0000,,the green line more or less follows more\Nor less closely the red equilibrium line
Dialogue: 0,0:14:32.40,0:14:37.28,Default,,0000,0000,0000,,with a certain delay, depending on how\Nsluggish the system responds. So that's
Dialogue: 0,0:14:37.28,0:14:44.88,Default,,0000,0000,0000,,why the green arrows are not exactly on\Ntop of the red line here. And in the
Dialogue: 0,0:14:44.88,0:14:50.56,Default,,0000,0000,0000,,right hand side case, you have a similar\Nthing. You are kind of, in theory, in
Dialogue: 0,0:14:50.56,0:14:56.32,Default,,0000,0000,0000,,equilibrium, you would fall off the cliff\Nat this bifurcation point. But in praxis,
Dialogue: 0,0:14:56.32,0:15:01.44,Default,,0000,0000,0000,,the system has some inertia, it takes some\Ntime. So if you gradually move on the
Dialogue: 0,0:15:01.44,0:15:05.92,Default,,0000,0000,0000,,right towards the right there, you will\Nalso follow a green line, which is very
Dialogue: 0,0:15:05.92,0:15:10.96,Default,,0000,0000,0000,,similar to the one in the left. So in\Npractical terms, if you're not trying to
Dialogue: 0,0:15:10.96,0:15:16.16,Default,,0000,0000,0000,,go back, but you just going forward,\Nprogressive global warming, the difference
Dialogue: 0,0:15:16.16,0:15:20.96,Default,,0000,0000,0000,,isn't all that big. And the main\Ndifference comes from the intrinsic
Dialogue: 0,0:15:20.96,0:15:27.20,Default,,0000,0000,0000,,timescale of the system. Obviously, sea\Nice can respond much more quickly to being
Dialogue: 0,0:15:27.20,0:15:32.32,Default,,0000,0000,0000,,just a few meters thick compared to\Ncontinental ice sheet like Greenland ice,
Dialogue: 0,0:15:32.32,0:15:36.72,Default,,0000,0000,0000,,which is about three thousand meters\Nthick. And that just takes a very long
Dialogue: 0,0:15:36.72,0:15:45.47,Default,,0000,0000,0000,,time to melt. Now, here's an overview of\Ndifferent tipping elements in the climate
Dialogue: 0,0:15:45.47,0:15:55.84,Default,,0000,0000,0000,,system. A few examples you can see\Nstarting on the left here, the boreal
Dialogue: 0,0:15:55.84,0:16:02.08,Default,,0000,0000,0000,,forest, that are the kind of northern\Nforests, which typically, like ecosystems,
Dialogue: 0,0:16:02.08,0:16:10.48,Default,,0000,0000,0000,,do have a tipping point, a point of\Ncollapse. The whole idea of these tipping
Dialogue: 0,0:16:10.48,0:16:15.36,Default,,0000,0000,0000,,points and system collapse is very\Nstrongly linked actually to ecosystem
Dialogue: 0,0:16:15.36,0:16:21.28,Default,,0000,0000,0000,,research and the boreal forests, They have\Na point where they get too dry, that fires
Dialogue: 0,0:16:21.28,0:16:27.04,Default,,0000,0000,0000,,and pests are weakening the forest so much\Nthat in a hot summer like last year in
Dialogue: 0,0:16:27.04,0:16:34.24,Default,,0000,0000,0000,,Siberia, they go up in flames lit by\Nlightning. Or the Amazon rain forest. This
Dialogue: 0,0:16:34.24,0:16:43.76,Default,,0000,0000,0000,,is also a tipping element, has been shown\Nin many vegetation dynamics models, which
Dialogue: 0,0:16:43.76,0:16:51.12,Default,,0000,0000,0000,,is partly linked to the fact that such a\Nforest generates its own rain to an extent
Dialogue: 0,0:16:51.12,0:16:56.48,Default,,0000,0000,0000,,by storing water in the soil, keeping it\Nthere and then bringing it up again
Dialogue: 0,0:16:56.48,0:17:02.64,Default,,0000,0000,0000,,through evapotranspiration, as we call it,\Nthe tree brings up water to the leaves
Dialogue: 0,0:17:02.64,0:17:08.56,Default,,0000,0000,0000,,then into the atmosphere again, and then\Nit moves with the winds and maybe 50, 100
Dialogue: 0,0:17:08.56,0:17:14.72,Default,,0000,0000,0000,,kilometers downwind, it falls again as\Nrain. So it's a kind of perpetual rain
Dialogue: 0,0:17:14.72,0:17:20.88,Default,,0000,0000,0000,,recycling system which keeps the whole\Nforest nice and moist. But if you stress
Dialogue: 0,0:17:20.88,0:17:27.68,Default,,0000,0000,0000,,that too far and reduce the first of all,\Nyou cut down forests, you make it smaller,
Dialogue: 0,0:17:27.68,0:17:34.88,Default,,0000,0000,0000,,and also you make it more drought prone by\Nwarming up the climate, which leads to
Dialogue: 0,0:17:34.88,0:17:40.16,Default,,0000,0000,0000,,faster loss of moisture, etc. greater\Nmoisture requirements by the trees. Then
Dialogue: 0,0:17:40.16,0:17:45.00,Default,,0000,0000,0000,,you can stress it up to the point where it\Ngets so dry that even the Amazon rain
Dialogue: 0,0:17:45.00,0:17:53.44,Default,,0000,0000,0000,,forest can go up in flames. Another\Nexample of how you see the top right is
Dialogue: 0,0:17:53.44,0:17:59.12,Default,,0000,0000,0000,,the permafrost thawing. This is when it\Ngets too warm. There is a very simple
Dialogue: 0,0:17:59.12,0:18:02.96,Default,,0000,0000,0000,,threshold, namely the freezing point. Of\Ncourse, that is a tipping point in the
Dialogue: 0,0:18:02.96,0:18:11.04,Default,,0000,0000,0000,,sense of freezing point of water. When the\Npermafrost thaws, then there is methane
Dialogue: 0,0:18:11.04,0:18:19.36,Default,,0000,0000,0000,,gas escaping to the atmosphere, which then\Nalso can enhance the further warming,
Dialogue: 0,0:18:19.36,0:18:25.20,Default,,0000,0000,0000,,which then leads to more permafrost\Nthawing and so on. Typically, these
Dialogue: 0,0:18:25.20,0:18:34.64,Default,,0000,0000,0000,,tipping points are associated with such\Namplifying feedbacks. I will discuss three
Dialogue: 0,0:18:34.64,0:18:41.04,Default,,0000,0000,0000,,of these in a little bit more detail. The\NGreenland ice sheet, which is undergoing
Dialogue: 0,0:18:41.04,0:18:47.84,Default,,0000,0000,0000,,accelerated ice loss, the Atlantic\Noverturning circulation, often called Gulf
Dialogue: 0,0:18:47.84,0:18:54.48,Default,,0000,0000,0000,,Stream system. And the third one is the\Ncoral reefs, which are suffering from
Dialogue: 0,0:18:54.48,0:18:59.52,Default,,0000,0000,0000,,large scale die-off, which also as a\Ntypical ecosystem response, have a
Dialogue: 0,0:18:59.52,0:19:06.88,Default,,0000,0000,0000,,critical threshold. These examples are\Ndiscussed in our paper 'Climate tipping
Dialogue: 0,0:19:06.88,0:19:12.72,Default,,0000,0000,0000,,points - too risky to bet against' which\Nwe published in Nature about one year ago.
Dialogue: 0,0:19:12.72,0:19:20.08,Default,,0000,0000,0000,,And they are also some of these tipping\Npoints interact, they are interlinked. And
Dialogue: 0,0:19:20.08,0:19:24.96,Default,,0000,0000,0000,,one of our quotes there is that the\Nclearest emergency would be if we were
Dialogue: 0,0:19:24.96,0:19:30.08,Default,,0000,0000,0000,,approaching a global cascade of tipping\Npoints. That is a situation where one
Dialogue: 0,0:19:30.08,0:19:36.40,Default,,0000,0000,0000,,tipping element is triggering the next one\Nin a kind of domino effect. This is what
Dialogue: 0,0:19:36.40,0:19:44.96,Default,,0000,0000,0000,,we fear most. Now, let's have a look at\Nthe Greenland ice sheet. This is a NASA
Dialogue: 0,0:19:44.96,0:19:50.48,Default,,0000,0000,0000,,video showing based on GRACE satellite\Ndata where the ice sheet is losing mass.
Dialogue: 0,0:19:50.48,0:19:56.80,Default,,0000,0000,0000,,You can see increasing blue colors here\Nthat the Greenland ice sheet is indeed
Dialogue: 0,0:19:56.80,0:20:03.28,Default,,0000,0000,0000,,losing mass. You can look up at the NASA\NVital Signs website, which has very good
Dialogue: 0,0:20:03.28,0:20:09.20,Default,,0000,0000,0000,,indicators of various vital signs of our\Nplanet, including the data on Greenland
Dialogue: 0,0:20:09.20,0:20:17.76,Default,,0000,0000,0000,,ice loss, constantly updated. Now, the\Npoint with the Greenland ice sheet is that
Dialogue: 0,0:20:17.76,0:20:24.00,Default,,0000,0000,0000,,it does have a stability diagram like the\Nschematic one that I showed you earlier
Dialogue: 0,0:20:24.00,0:20:29.92,Default,,0000,0000,0000,,with the bi-stable range. And this is\Nshown, I think it was shown for the first
Dialogue: 0,0:20:29.92,0:20:38.72,Default,,0000,0000,0000,,time by my colleagues, Calov and\NGanopolski in 2005 in this article where
Dialogue: 0,0:20:38.72,0:20:43.44,Default,,0000,0000,0000,,they used the three dimensional ice sheet\Nmodel coupled inside a global climate
Dialogue: 0,0:20:43.44,0:20:49.84,Default,,0000,0000,0000,,model with ocean atmosphere and so on and\Non the x axis is basically increasing
Dialogue: 0,0:20:49.84,0:20:54.24,Default,,0000,0000,0000,,amount of heating going on, in this case\Nbecause they were interested in the
Dialogue: 0,0:20:54.24,0:21:01.36,Default,,0000,0000,0000,,paleoclimate question, it is this driving\Nforce by the orbital cycles and
Dialogue: 0,0:21:01.36,0:21:06.64,Default,,0000,0000,0000,,Milankovitch cycles. You don't need to\Nunderstand the numbers, but on the
Dialogue: 0,0:21:06.64,0:21:11.60,Default,,0000,0000,0000,,vertical axis, you see the response of the\Nice sheet, the size of the ice sheet, in
Dialogue: 0,0:21:11.60,0:21:17.84,Default,,0000,0000,0000,,million cubic kilometers. And you can see\Nthat upper branch in the blue line, we're
Dialogue: 0,0:21:17.84,0:21:24.08,Default,,0000,0000,0000,,actually moving towards the right here in\Nthis model simulation experiment. And you
Dialogue: 0,0:21:24.08,0:21:28.72,Default,,0000,0000,0000,,can see you stay on that upper branch\Nuntil you reach this value on the x axis
Dialogue: 0,0:21:28.72,0:21:35.76,Default,,0000,0000,0000,,of around about five hundred. And this is\Nwhere the tipping point is. There the ice
Dialogue: 0,0:21:35.76,0:21:41.28,Default,,0000,0000,0000,,mass declines, melts away, away very\Nquickly. And you then end up at that lower
Dialogue: 0,0:21:41.28,0:21:47.12,Default,,0000,0000,0000,,branch with no ice on Greenland. And they\Nplayed this game. They ran the simulation
Dialogue: 0,0:21:47.12,0:21:52.64,Default,,0000,0000,0000,,out to more than 550 watts per square\Nmeter. And the light blue line is what
Dialogue: 0,0:21:52.64,0:21:58.96,Default,,0000,0000,0000,,happens when they return, when they turn\Ndown the heat again. You move towards the
Dialogue: 0,0:21:58.96,0:22:03.60,Default,,0000,0000,0000,,left on this diagram, but you don't go\Nback up the same way as the dark blue
Dialogue: 0,0:22:03.60,0:22:09.36,Default,,0000,0000,0000,,line. You have to go to much lower\Nradiation values until the ice sheet
Dialogue: 0,0:22:09.36,0:22:15.52,Default,,0000,0000,0000,,starts to grow again and comes back. The\Ndots, by the way, are points where this
Dialogue: 0,0:22:15.52,0:22:21.60,Default,,0000,0000,0000,,has to has been run for many thousands of\Nyears really into an equilibrium just to
Dialogue: 0,0:22:21.60,0:22:27.52,Default,,0000,0000,0000,,show that there are really for the same\Nvalue on the x axis, two very different
Dialogue: 0,0:22:27.52,0:22:34.96,Default,,0000,0000,0000,,equilibrium states with and without\NGreenland ice sheet. And the fact that we
Dialogue: 0,0:22:34.96,0:22:39.60,Default,,0000,0000,0000,,now and in the Holocene in the last ten\Nthousand years have the Greenland ice
Dialogue: 0,0:22:39.60,0:22:45.28,Default,,0000,0000,0000,,sheet and it actually is stable in the\NHolocene climate is only because of the
Dialogue: 0,0:22:45.28,0:22:50.40,Default,,0000,0000,0000,,initial condition, because we came out of\Nan ice age. If you took away the Greenland
Dialogue: 0,0:22:50.40,0:22:55.92,Default,,0000,0000,0000,,ice sheet now, then in the current climate\Nor the Holocene or pre-industrial climate,
Dialogue: 0,0:22:55.92,0:23:01.68,Default,,0000,0000,0000,,it would never grow back. What is the\Npositive feedback? The most positive? We
Dialogue: 0,0:23:01.68,0:23:06.56,Default,,0000,0000,0000,,don't mean that it's good. That's actually\Nquite bad and positive feedback. We mean
Dialogue: 0,0:23:06.56,0:23:12.00,Default,,0000,0000,0000,,and amplifying feedback and the key\Namplifying feedback here is what is called
Dialogue: 0,0:23:12.00,0:23:18.48,Default,,0000,0000,0000,,the ice elevation feedback. The Greenland\Nice sheet does not melt because it's very
Dialogue: 0,0:23:18.48,0:23:24.64,Default,,0000,0000,0000,,cold at the surface, mostly below\Nfreezing. And why is it so cold? Because
Dialogue: 0,0:23:24.64,0:23:28.80,Default,,0000,0000,0000,,it is very high up in the atmosphere, this\Nice sheet of three thousand meters thick
Dialogue: 0,0:23:28.80,0:23:35.44,Default,,0000,0000,0000,,after all. So it's like in a high mountain\Narea where it is quite cold. If you took
Dialogue: 0,0:23:35.44,0:23:41.04,Default,,0000,0000,0000,,away that ice sheet, though, the surface\Nthen would be down at sea level or even
Dialogue: 0,0:23:41.04,0:23:46.00,Default,,0000,0000,0000,,below if you did this quickly because the\Nthe bedrock is depressed, but the surface
Dialogue: 0,0:23:46.00,0:23:51.44,Default,,0000,0000,0000,,would come up to sea level, but down there\Nit's much warmer than up at three thousand
Dialogue: 0,0:23:51.44,0:23:57.12,Default,,0000,0000,0000,,meters altitude in the atmosphere. And\Nthere it is actually too warm to keep any
Dialogue: 0,0:23:57.12,0:24:02.64,Default,,0000,0000,0000,,snow on the ground year round, which would\Nbe required to regrow a new Greenland ice
Dialogue: 0,0:24:02.64,0:24:06.80,Default,,0000,0000,0000,,sheet. And that's why you'd have to go\Nback to a much colder climate than the
Dialogue: 0,0:24:06.80,0:24:12.56,Default,,0000,0000,0000,,Holocene to get the Greenland ice sheet\Nback once it were lost. This is a typical
Dialogue: 0,0:24:12.56,0:24:18.40,Default,,0000,0000,0000,,example of this amplifying feedback, which\Nleads to a self stabilizing system. It can
Dialogue: 0,0:24:18.40,0:24:23.60,Default,,0000,0000,0000,,either self stabilize in the upper branch\Nhere when you start there or it self-
Dialogue: 0,0:24:23.60,0:24:28.72,Default,,0000,0000,0000,,stabilizes in the lower branch with no ice\Nwhen you start there. This is what makes
Dialogue: 0,0:24:28.72,0:24:37.36,Default,,0000,0000,0000,,it a bi-stable system. To summarize, the\NGreenland ice sheet is melting as another
Dialogue: 0,0:24:37.36,0:24:43.20,Default,,0000,0000,0000,,data the great satellites show, but also\Nother data sets. It has a tipping point
Dialogue: 0,0:24:43.20,0:24:48.80,Default,,0000,0000,0000,,due to the ice elevation feedback. What I\Nhaven't shown, but it's come out in study
Dialogue: 0,0:24:48.80,0:24:55.60,Default,,0000,0000,0000,,with many climate models, simulation\Nexperiments going through more than two
Dialogue: 0,0:24:55.60,0:25:00.48,Default,,0000,0000,0000,,hundred thousand years of simulations from\Nthe past through the Eemian interglacial
Dialogue: 0,0:25:00.48,0:25:05.60,Default,,0000,0000,0000,,period where we know how much the ice\Nsheets shrank back. And we could use those
Dialogue: 0,0:25:05.60,0:25:13.44,Default,,0000,0000,0000,,data from the past behavior of Greenland\Nto calibrate the model. And so we know the
Dialogue: 0,0:25:13.44,0:25:17.92,Default,,0000,0000,0000,,tipping point for the complete loss of the\NGreenland ice sheet is somewhere between
Dialogue: 0,0:25:17.92,0:25:22.56,Default,,0000,0000,0000,,one degree and three degree global\Nwarming. We're already at one point two
Dialogue: 0,0:25:22.56,0:25:27.51,Default,,0000,0000,0000,,degrees global warming. So we have started\Nto enter the danger zone where we crossed
Dialogue: 0,0:25:27.51,0:25:34.27,Default,,0000,0000,0000,,that tipping point. It doesn't mean that\Nit suddenly starts to melt very fast also
Dialogue: 0,0:25:34.27,0:25:39.24,Default,,0000,0000,0000,,because it has its own intrinsic slow\Nresponse time. But what that crossing,
Dialogue: 0,0:25:39.24,0:25:44.19,Default,,0000,0000,0000,,that tipping point means is that even\Nwithout further warming, the Greenland ice
Dialogue: 0,0:25:44.19,0:25:49.12,Default,,0000,0000,0000,,sheet is doomed and will continue to melt\Nuntil it's gone, and this will lead to
Dialogue: 0,0:25:49.12,0:25:56.17,Default,,0000,0000,0000,,seven meters of global sea level rise,\Ndrowning most of our big coastal cities
Dialogue: 0,0:25:56.17,0:26:04.05,Default,,0000,0000,0000,,and to many island nations. Here is a look\Nat the future from models, simulations
Dialogue: 0,0:26:04.05,0:26:11.51,Default,,0000,0000,0000,,from Ashmont and from NASA. And you can\Nsee a nice view of what the surface looks
Dialogue: 0,0:26:11.51,0:26:15.09,Default,,0000,0000,0000,,like. And here's what the what it looks\Nlike in the ice sheet model. You can see
Dialogue: 0,0:26:15.09,0:26:20.45,Default,,0000,0000,0000,,the ice flowing. You can see it\Nretreating. So in purple, that's bedrock
Dialogue: 0,0:26:20.45,0:26:27.00,Default,,0000,0000,0000,,that is exposed where the ice sheet has\Nwithdrawn in this simulation. And so it's
Dialogue: 0,0:26:27.00,0:26:32.69,Default,,0000,0000,0000,,as much as ice of ice that you would lose\Nin the coming three hundred years, a
Dialogue: 0,0:26:32.69,0:26:43.18,Default,,0000,0000,0000,,substantial fraction of the Greenland ice\Nsheet. Now, let's look at another kind of
Dialogue: 0,0:26:43.18,0:26:46.85,Default,,0000,0000,0000,,tipping element, and that is the Gulf\NStream system or the North Atlantic
Dialogue: 0,0:26:46.85,0:26:52.18,Default,,0000,0000,0000,,current. And I can't really introduce this\Ntopic is one of my favorite topics, which
Dialogue: 0,0:26:52.18,0:26:59.32,Default,,0000,0000,0000,,I have studied since the early 90s,\Nwithout showing a clip from the famous
Dialogue: 0,0:26:59.32,0:27:05.22,Default,,0000,0000,0000,,Hollywood blockbuster The Day After\NTomorrow. What about the North Atlantic
Dialogue: 0,0:27:05.22,0:27:10.68,Default,,0000,0000,0000,,current? What about it? The current\Ndepends upon a delicate balance of salt
Dialogue: 0,0:27:10.68,0:27:16.10,Default,,0000,0000,0000,,and fresh water. We all know that, yes.\NBut no one is taking into account how much
Dialogue: 0,0:27:16.10,0:27:21.14,Default,,0000,0000,0000,,fresh water has been dumped into the ocean\Nbecause of melting polar ice. I think
Dialogue: 0,0:27:21.14,0:27:32.10,Default,,0000,0000,0000,,we've hit a critical desalinization point.\NYeah, now that statement about the
Dialogue: 0,0:27:32.10,0:27:37.03,Default,,0000,0000,0000,,critical desalination point is a\Ncompletely correct description of the
Dialogue: 0,0:27:37.03,0:27:41.92,Default,,0000,0000,0000,,bifurcation point of the Atlantic\Ncirculation, I'll show it in a minute. And
Dialogue: 0,0:27:41.92,0:27:48.91,Default,,0000,0000,0000,,the statement that nobody has taken into\Naccount the meltwater from the Greenland
Dialogue: 0,0:27:48.91,0:27:55.92,Default,,0000,0000,0000,,ice sheet is also was completely correct\Nwhen the movie appeared in 2004. Until
Dialogue: 0,0:27:55.92,0:28:01.67,Default,,0000,0000,0000,,then, the typical climate simulations that\Nyou could see in the IPCC reports,
Dialogue: 0,0:28:01.67,0:28:07.27,Default,,0000,0000,0000,,actually until quite a few years later,\Nstill had not taken account Greenland melt
Dialogue: 0,0:28:07.27,0:28:12.61,Default,,0000,0000,0000,,water because basically at that point in\Ntime, the models, almost all climate
Dialogue: 0,0:28:12.61,0:28:18.03,Default,,0000,0000,0000,,models were just ocean-atmosphere models\Nplus land surface, but they didn't have
Dialogue: 0,0:28:18.03,0:28:24.82,Default,,0000,0000,0000,,continental ice sheet models coupled into\Nthem. And so in the meantime, of course,
Dialogue: 0,0:28:24.82,0:28:30.16,Default,,0000,0000,0000,,we have better models that include\Nexperiments either with artificially added
Dialogue: 0,0:28:30.16,0:28:36.84,Default,,0000,0000,0000,,Greenland meltwater from data estimates or\Nfully coupled with ice sheet models. And
Dialogue: 0,0:28:36.84,0:28:41.17,Default,,0000,0000,0000,,from that, an example here being that\Nnature article by Claus Boening and
Dialogue: 0,0:28:41.17,0:28:48.50,Default,,0000,0000,0000,,colleagues. We know that the meltwater\Ninput from Greenland has a non-negligible
Dialogue: 0,0:28:48.50,0:28:52.99,Default,,0000,0000,0000,,effect on the North Atlantic overturning.\NIt's probably not the dominant effect, but
Dialogue: 0,0:28:52.99,0:29:00.90,Default,,0000,0000,0000,,it adds to various factors that weaken\Nthis North Atlantic current. And we also
Dialogue: 0,0:29:00.90,0:29:07.02,Default,,0000,0000,0000,,know that this system has a well-defined\Ntipping point. Actually, I described that
Dialogue: 0,0:29:07.02,0:29:17.44,Default,,0000,0000,0000,,in a nature article in 1996 due to a salt\Ntransport feedback. The basic idea behind
Dialogue: 0,0:29:17.44,0:29:25.05,Default,,0000,0000,0000,,that has actually been known since the\Nlate 1950s or early 60s since work by the
Dialogue: 0,0:29:25.05,0:29:29.96,Default,,0000,0000,0000,,famous American oceanographer Henry\NStommel. But what I showed in my Nature
Dialogue: 0,0:29:29.96,0:29:35.75,Default,,0000,0000,0000,,article in 96 is that it actually works\Nthat way in a complex, three dimensional
Dialogue: 0,0:29:35.75,0:29:43.04,Default,,0000,0000,0000,,global ocean circulation model, not just\Nin very simplified models. And since then,
Dialogue: 0,0:29:43.04,0:29:49.78,Default,,0000,0000,0000,,this has been shown for a whole range of\Ndifferent climate models. The sole
Dialogue: 0,0:29:49.78,0:29:54.58,Default,,0000,0000,0000,,transportation feedback is also one of\Nthese amplifying feedbacks, and it's easy
Dialogue: 0,0:29:54.58,0:30:01.74,Default,,0000,0000,0000,,to explain. The overturning circulation of\Nthe Atlantic is called overturning because
Dialogue: 0,0:30:01.74,0:30:08.77,Default,,0000,0000,0000,,it's really a vertical overturning where\Nwater sinks down from the surface to great
Dialogue: 0,0:30:08.77,0:30:16.19,Default,,0000,0000,0000,,depth of two to three kilometers in the\NAtlantic because this water is heavy and
Dialogue: 0,0:30:16.19,0:30:21.18,Default,,0000,0000,0000,,it spreads thin in the deep ocean until it\Nrises up in other parts, mainly around
Dialogue: 0,0:30:21.18,0:30:29.48,Default,,0000,0000,0000,,Antarctica in the Antarctic circumpolar\Ncurrent area and comes back at the
Dialogue: 0,0:30:29.48,0:30:35.73,Default,,0000,0000,0000,,surface. So basically the whole ocean is\Noverturned with deep water being renewed
Dialogue: 0,0:30:35.73,0:30:45.01,Default,,0000,0000,0000,,and then coming back to the surface on\Nvery long timescale of about 1000 to 2000
Dialogue: 0,0:30:45.01,0:30:53.61,Default,,0000,0000,0000,,years for complete overturning there. Now,\Nthe whole system is driven by the fact
Dialogue: 0,0:30:53.61,0:31:00.98,Default,,0000,0000,0000,,that the water sinks down where it has the\Nhighest density, and that's in the
Dialogue: 0,0:31:00.98,0:31:07.38,Default,,0000,0000,0000,,northern Atlantic and around Antarctica,\Naround the Antarctic continent. And it has
Dialogue: 0,0:31:07.38,0:31:12.36,Default,,0000,0000,0000,,the highest density there, not only\Nbecause it's very cold, but also quite
Dialogue: 0,0:31:12.36,0:31:17.93,Default,,0000,0000,0000,,salty. This is why you don't have deep\Nwater formation in the North Pacific, in
Dialogue: 0,0:31:17.93,0:31:22.65,Default,,0000,0000,0000,,the Northern Hemisphere. You only have\Nthat in the North Atlantic. And that's
Dialogue: 0,0:31:22.65,0:31:28.78,Default,,0000,0000,0000,,because the North Atlantic waters are\Nquite salty. And this is because this
Dialogue: 0,0:31:28.78,0:31:34.31,Default,,0000,0000,0000,,North Atlantic current exists and brings\Nsalty water from the subtropics up to the
Dialogue: 0,0:31:34.31,0:31:39.05,Default,,0000,0000,0000,,high latitudes, where normally it isn't\Nvery salty because it gets diluted by
Dialogue: 0,0:31:39.05,0:31:44.16,Default,,0000,0000,0000,,excess rainfall, whereas the subtropics\Nhave excess evaporation and that's why
Dialogue: 0,0:31:44.16,0:31:50.49,Default,,0000,0000,0000,,they're salty. And so it's like a chicken\Nand an egg situation. The Northern
Dialogue: 0,0:31:50.49,0:31:55.05,Default,,0000,0000,0000,,Atlantic is salty because you have this\Noverturning circulation and you have this
Dialogue: 0,0:31:55.05,0:32:00.06,Default,,0000,0000,0000,,overturning circulation because it's salty\Nthere. And so you can see the self
Dialogue: 0,0:32:00.06,0:32:06.42,Default,,0000,0000,0000,,amplifying feedback there again, which\Nmeans it is a self stabilizing system up
Dialogue: 0,0:32:06.42,0:32:11.65,Default,,0000,0000,0000,,to a certain breaking point, a tipping\Npoint which can be reached if you add too
Dialogue: 0,0:32:11.65,0:32:19.34,Default,,0000,0000,0000,,much fresh water, diluting the northern\NAtlantic. And the stability diagram,
Dialogue: 0,0:32:19.34,0:32:24.56,Default,,0000,0000,0000,,again, looks like that second one. You've\Nseen it for the Greenland ice sheet. As I
Dialogue: 0,0:32:24.56,0:32:29.62,Default,,0000,0000,0000,,said, this has been verified in a detailed\Nmodel simulations with many different
Dialogue: 0,0:32:29.62,0:32:36.02,Default,,0000,0000,0000,,models that it really works like that in a\Ncomplex 3D situation where you have
Dialogue: 0,0:32:36.02,0:32:40.63,Default,,0000,0000,0000,,depending on how much fresh water you add\Ninto the northern Atlantic, this is the
Dialogue: 0,0:32:40.63,0:32:46.85,Default,,0000,0000,0000,,control parameter here, you can move along\Nthat upper stable branch with the
Dialogue: 0,0:32:46.85,0:32:54.34,Default,,0000,0000,0000,,overturning circulation until that Stommel\Nbifurcation point. And there this
Dialogue: 0,0:32:54.34,0:33:00.28,Default,,0000,0000,0000,,overturning breaks down and you fall down\Nonto that lower branch without this
Dialogue: 0,0:33:00.28,0:33:06.70,Default,,0000,0000,0000,,overturning. It's labeled here NADW Flow\Nthat NADW stands for north Atlantic
Dialogue: 0,0:33:06.70,0:33:11.40,Default,,0000,0000,0000,,deepwater. It's a, I would say, one of the\Nfavorite water masses of the
Dialogue: 0,0:33:11.40,0:33:21.28,Default,,0000,0000,0000,,oceanographers. Now, let's look at the\NGulf Stream, the surface circulation in a
Dialogue: 0,0:33:21.28,0:33:28.32,Default,,0000,0000,0000,,climate model. This is the CM 2.6 global\Ncoupled climate model ocean atmosphere by
Dialogue: 0,0:33:28.32,0:33:34.32,Default,,0000,0000,0000,,the Geophysical Fluid Dynamics Laboratory\Nin Princeton. You can beautifully see the
Dialogue: 0,0:33:34.32,0:33:40.32,Default,,0000,0000,0000,,Gulf Stream and dark red here because it's\Nwarm leaving the coast of the United
Dialogue: 0,0:33:40.32,0:33:45.41,Default,,0000,0000,0000,,States at Cape Hatteras there, starting to\Nmeander, breaking up into these eddies, et
Dialogue: 0,0:33:45.41,0:33:52.88,Default,,0000,0000,0000,,cetera. And it actually meets the cold\Nwaters coming down inshore from the north,
Dialogue: 0,0:33:52.88,0:33:59.04,Default,,0000,0000,0000,,which are shown in blue here. And so this\Nis what this the surface part of the
Dialogue: 0,0:33:59.04,0:34:07.36,Default,,0000,0000,0000,,circulation looks in a global climate\Nmodel. And if you add carbon dioxide to
Dialogue: 0,0:34:07.36,0:34:13.52,Default,,0000,0000,0000,,that climate models atmosphere, the\Nclimate warms, of course, but it does show
Dialogue: 0,0:34:13.52,0:34:20.00,Default,,0000,0000,0000,,a peculiar pattern of sea surface\Ntemperature change, which you see here.
Dialogue: 0,0:34:20.00,0:34:24.80,Default,,0000,0000,0000,,And this actually shows the sea surface\Ntemperature change relative to the global
Dialogue: 0,0:34:24.80,0:34:29.52,Default,,0000,0000,0000,,mean. So everything that is blue has\Neither warmed less than the global average
Dialogue: 0,0:34:29.52,0:34:34.64,Default,,0000,0000,0000,,or even cooled, which is actually the case\Nsouth of Greenland. And everything that is
Dialogue: 0,0:34:34.64,0:34:42.72,Default,,0000,0000,0000,,orange or red has warmed substantially\Nmore than the global average sea surface.
Dialogue: 0,0:34:42.72,0:34:50.08,Default,,0000,0000,0000,,And you see a very strong pattern in the\Nnorthern Atlantic with this big cold blob,
Dialogue: 0,0:34:50.08,0:34:55.60,Default,,0000,0000,0000,,the blue blob south of Greenland and a\Nvery warm region inshore of the Gulf
Dialogue: 0,0:34:55.60,0:35:02.48,Default,,0000,0000,0000,,Stream along the coast of North America.\NAnd in the climate model, of course, we
Dialogue: 0,0:35:02.48,0:35:07.44,Default,,0000,0000,0000,,are a bit like gods in that sense that we\Nhave complete information about what's
Dialogue: 0,0:35:07.44,0:35:12.72,Default,,0000,0000,0000,,going on there. If we store all the data\Nat every grid point, we know exactly everything
Dialogue: 0,0:35:12.72,0:35:18.16,Default,,0000,0000,0000,,that's happening and we can analyze the\Nreasons. And the reason for this funny
Dialogue: 0,0:35:18.16,0:35:24.96,Default,,0000,0000,0000,,pattern in the northern Atlantic actually\Nis a slowdown of the North Atlantic
Dialogue: 0,0:35:24.96,0:35:34.96,Default,,0000,0000,0000,,overturning circulation. That means that\Nless heat is transported to the subpolar
Dialogue: 0,0:35:34.96,0:35:41.44,Default,,0000,0000,0000,,ocean south of Greenland there. That blue\Narea, which makes it cool down and the
Dialogue: 0,0:35:41.44,0:35:46.96,Default,,0000,0000,0000,,Gulf Stream proper at the surface, moves\Ninshore there is complicated dynamical
Dialogue: 0,0:35:46.96,0:35:52.88,Default,,0000,0000,0000,,reasons for that. But there is already\Nlong before this was shown in this model,
Dialogue: 0,0:35:52.88,0:35:59.36,Default,,0000,0000,0000,,a theoretical underpinning for this. It\Nhas to do with the vorticity dynamics on a
Dialogue: 0,0:35:59.36,0:36:04.88,Default,,0000,0000,0000,,rotating sphere too technical to go into\Nin such a talk. But it's a well understood
Dialogue: 0,0:36:04.88,0:36:10.56,Default,,0000,0000,0000,,phenomenon. And so we know that this\Nslowdown of the Gulf Stream system is the
Dialogue: 0,0:36:10.56,0:36:15.76,Default,,0000,0000,0000,,reason behind this peculiar temperature\Npattern. And this pattern is predicted by
Dialogue: 0,0:36:15.76,0:36:22.64,Default,,0000,0000,0000,,this climate model for a global warming\Nsituation. And my PhD student, Levke
Dialogue: 0,0:36:22.64,0:36:28.88,Default,,0000,0000,0000,,Caesar, who was the first author on this\Nnature paper from 2018, she looked at all
Dialogue: 0,0:36:28.88,0:36:34.32,Default,,0000,0000,0000,,the available measurements of sea surface\Ntemperatures since the beginning of the
Dialogue: 0,0:36:34.32,0:36:39.76,Default,,0000,0000,0000,,20th century. And of course, because we\Nhave only limited ocean temperature
Dialogue: 0,0:36:39.76,0:36:43.84,Default,,0000,0000,0000,,measurements, we have only a fuzzy picture\Nhere, not a sharp one like in the climate
Dialogue: 0,0:36:43.84,0:36:50.56,Default,,0000,0000,0000,,model. But you can see a similar pattern\Nin the North Atlantic in the observations
Dialogue: 0,0:36:50.56,0:36:55.68,Default,,0000,0000,0000,,compared to what the model predicts in\Nresponse to a slowdown of the overturning
Dialogue: 0,0:36:55.68,0:37:01.04,Default,,0000,0000,0000,,circulation. And our conclusion here is\Nthat we are actually observing this
Dialogue: 0,0:37:01.04,0:37:07.04,Default,,0000,0000,0000,,slowdown of the circulation. Why do we\Ntake indirect evidence for this like this?
Dialogue: 0,0:37:07.04,0:37:13.68,Default,,0000,0000,0000,,Because we don't, of course, have\Nmeasurements going back 100 years or more
Dialogue: 0,0:37:13.68,0:37:18.80,Default,,0000,0000,0000,,about the strength of that overturning\Ncirculation. We have actually only started
Dialogue: 0,0:37:18.80,0:37:24.72,Default,,0000,0000,0000,,to measure this regularly in 2004 with a\Nso-called rapid array, At twenty six
Dialogue: 0,0:37:24.72,0:37:31.60,Default,,0000,0000,0000,,degrees north in the Atlantic, and what we\Nreconstructed about the evolution of this
Dialogue: 0,0:37:31.60,0:37:37.52,Default,,0000,0000,0000,,current for the last period where we do\Nhave the direct measurements, agrees well
Dialogue: 0,0:37:37.52,0:37:46.48,Default,,0000,0000,0000,,with what the direct measurements show. We\Nconcluded that the overturning circulation
Dialogue: 0,0:37:46.48,0:37:56.20,Default,,0000,0000,0000,,has declined since at least the mid 20th\Ncentury by about 15% so far. There are, of
Dialogue: 0,0:37:56.20,0:38:01.22,Default,,0000,0000,0000,,course, other indirect types of\Nmeasurements. You can use sediment data of
Dialogue: 0,0:38:01.22,0:38:05.56,Default,,0000,0000,0000,,various kinds and with various\Nmethodologies to reconstruct the strength
Dialogue: 0,0:38:05.56,0:38:11.32,Default,,0000,0000,0000,,of this Atlantic overturning and a number\Nof different studies compiled here in this
Dialogue: 0,0:38:11.32,0:38:17.36,Default,,0000,0000,0000,,diagram. And even though, of course, they\Ndiffer somewhat in the detail, they all
Dialogue: 0,0:38:17.36,0:38:23.01,Default,,0000,0000,0000,,tend to agree in this overall picture that\Nthe Atlantic overturning circulation has
Dialogue: 0,0:38:23.01,0:38:28.82,Default,,0000,0000,0000,,been quite stable for the previous\Nthousand years or so before the 20th
Dialogue: 0,0:38:28.82,0:38:37.11,Default,,0000,0000,0000,,century, but then in the 20th century has\Nshowed a clear declining signature. And
Dialogue: 0,0:38:37.11,0:38:43.08,Default,,0000,0000,0000,,one example of the media coverage of this\Nis that Washington Post article here,
Dialogue: 0,0:38:43.08,0:38:48.05,Default,,0000,0000,0000,,which if you can see the small print of\Nthe most read articles there on that, they
Dialogue: 0,0:38:48.05,0:38:53.20,Default,,0000,0000,0000,,actually made it to number three or the\Nmost read Washington Post articles. There
Dialogue: 0,0:38:53.20,0:38:59.65,Default,,0000,0000,0000,,is definitely an interest in science and\Nclimate change science by the readers in
Dialogue: 0,0:38:59.65,0:39:09.92,Default,,0000,0000,0000,,the newspapers. So far we've talked about\Na slow down and not so much about where
Dialogue: 0,0:39:09.92,0:39:13.92,Default,,0000,0000,0000,,this tipping point is. One reason is we\Ndon't know really. We know there is this
Dialogue: 0,0:39:13.92,0:39:18.00,Default,,0000,0000,0000,,tipping point, that is a robust result of\Nmany different studies and model
Dialogue: 0,0:39:18.00,0:39:23.76,Default,,0000,0000,0000,,experiments and theory, but we don't know\Nhow far away we are from this. That is
Dialogue: 0,0:39:23.76,0:39:28.00,Default,,0000,0000,0000,,very typical for these tipping points\Nbecause they involve highly nonlinear
Dialogue: 0,0:39:28.00,0:39:34.32,Default,,0000,0000,0000,,dynamics. That means they can depend very\Nsensitively on the exact conditions, for
Dialogue: 0,0:39:34.32,0:39:39.92,Default,,0000,0000,0000,,example, in this case, the exact salinity\Ndistribution in the Atlantic and the exact
Dialogue: 0,0:39:39.92,0:39:46.40,Default,,0000,0000,0000,,circulation pattern. And models get these\Nthings kind of approximately right, but
Dialogue: 0,0:39:46.40,0:39:52.56,Default,,0000,0000,0000,,not exactly right. And if you have a\Nsituation where the question of where the
Dialogue: 0,0:39:52.56,0:39:57.04,Default,,0000,0000,0000,,tipping point is is very sensitive to the\Nexact conditions, then you have a large
Dialogue: 0,0:39:57.04,0:40:03.28,Default,,0000,0000,0000,,uncertainty about where the tipping point\Nis. And so there is discussion in the
Dialogue: 0,0:40:03.28,0:40:08.48,Default,,0000,0000,0000,,literature. I just point out to one study\Nhere in science advances that try to
Dialogue: 0,0:40:08.48,0:40:16.96,Default,,0000,0000,0000,,correct for the inaccuracies in how we can\Nreproduce the salinity in the Atlantic
Dialogue: 0,0:40:16.96,0:40:22.08,Default,,0000,0000,0000,,waters and found that if you correct for\Nthat, the circulation is actually a lot
Dialogue: 0,0:40:22.08,0:40:28.48,Default,,0000,0000,0000,,more sensitive than in other models. And\Nmaybe that model is more correct. And of
Dialogue: 0,0:40:28.48,0:40:32.40,Default,,0000,0000,0000,,course, it has other weaknesses as well.\NWe don't know which of the models is
Dialogue: 0,0:40:32.40,0:40:39.84,Default,,0000,0000,0000,,correct, but should we cross this tipping\Npoint then the North Atlantic circulation
Dialogue: 0,0:40:39.84,0:40:44.16,Default,,0000,0000,0000,,system would break down and you get a\Ntemperature pattern like the one shown
Dialogue: 0,0:40:44.16,0:40:49.20,Default,,0000,0000,0000,,here, the cold blob in the Atlantic that\Nis now only over the ocean. It exists,
Dialogue: 0,0:40:49.20,0:40:53.04,Default,,0000,0000,0000,,right? It's the only part of the world\Nthat has cooled since the beginning of the
Dialogue: 0,0:40:53.04,0:40:58.48,Default,,0000,0000,0000,,20th century, but it hasn't affected any\Nland areas. But if the circulation would
Dialogue: 0,0:40:58.48,0:41:03.92,Default,,0000,0000,0000,,break down altogether and not only\Nweakened by 15%, this cold would expand
Dialogue: 0,0:41:03.92,0:41:09.76,Default,,0000,0000,0000,,greatly and affect Great Britain,\NScandinavia, Iceland, as you can see here,
Dialogue: 0,0:41:09.76,0:41:13.76,Default,,0000,0000,0000,,which would then get a much colder\Nclimate, whereas the rest of the globe
Dialogue: 0,0:41:13.76,0:41:19.60,Default,,0000,0000,0000,,continues to have a warmer climate. This\Nis really distinct from an ice age. And so
Dialogue: 0,0:41:19.60,0:41:23.60,Default,,0000,0000,0000,,this is also really distinct from that\NHollywood movie The Day After Tomorrow,
Dialogue: 0,0:41:23.60,0:41:29.20,Default,,0000,0000,0000,,where the earth goes into a huge ice age,\Nan instant freeze. That, of course, is
Dialogue: 0,0:41:29.20,0:41:33.52,Default,,0000,0000,0000,,totally unrealistic. And the the\Nscreenwriter and the director, they knew
Dialogue: 0,0:41:33.52,0:41:40.72,Default,,0000,0000,0000,,this. They actually told me that if they\Nwere in the business of making a movie for
Dialogue: 0,0:41:40.72,0:41:45.52,Default,,0000,0000,0000,,a few million viewers, they would stick to\Nthe laws of physics. But since they make
Dialogue: 0,0:41:45.52,0:41:50.72,Default,,0000,0000,0000,,movies for a few hundred million viewers,\Nthey stick to the laws of Hollywood drama.
Dialogue: 0,0:41:50.72,0:41:56.88,Default,,0000,0000,0000,,But you would get a substantial regional\Ncooling with a major impact on ecosystems,
Dialogue: 0,0:41:56.88,0:42:03.92,Default,,0000,0000,0000,,on human society. Now, let me come to the\Nthird type of tipping point that I want to
Dialogue: 0,0:42:03.92,0:42:09.60,Default,,0000,0000,0000,,discuss today. This is the coral reefs.\NCoral reefs, like many ecosystems, do have
Dialogue: 0,0:42:09.60,0:42:17.04,Default,,0000,0000,0000,,critical thresholds. Coral reefs are very\Nimportant, even though they only cover a
Dialogue: 0,0:42:17.04,0:42:23.54,Default,,0000,0000,0000,,very small percentage of the Earth's\Nsurface, they support a quarter of all
Dialogue: 0,0:42:23.54,0:42:31.60,Default,,0000,0000,0000,,marine life. 40% coral cover of the world\Nhas already been lost, 100 countries
Dialogue: 0,0:42:31.60,0:42:38.53,Default,,0000,0000,0000,,depend quite substantially on corals.\NThere's 800 billion total global assets of
Dialogue: 0,0:42:38.53,0:42:45.56,Default,,0000,0000,0000,,coral reefs. So it does have a major\Nimpact on people. Now, corals, when they
Dialogue: 0,0:42:45.56,0:42:52.74,Default,,0000,0000,0000,,are about to die, they bleach. They are\Nabandoned by their algae that provides
Dialogue: 0,0:42:52.74,0:43:00.09,Default,,0000,0000,0000,,them with nutrition and that's why they\Nlose their color. And then after a while,
Dialogue: 0,0:43:00.09,0:43:07.17,Default,,0000,0000,0000,,they die. They get covered by other by\Nseaweed, non symbiotic algae, and they
Dialogue: 0,0:43:07.17,0:43:13.35,Default,,0000,0000,0000,,die. And they do have a temperature\Nthreshold. It's a critical warming
Dialogue: 0,0:43:13.35,0:43:19.59,Default,,0000,0000,0000,,threshold where this bleaching happens.\NBut an additional factor, not yet the most
Dialogue: 0,0:43:19.59,0:43:25.47,Default,,0000,0000,0000,,important factor, is the acidification of\Nwater. It's a direct chemical effect of
Dialogue: 0,0:43:25.47,0:43:32.29,Default,,0000,0000,0000,,adding carbon dioxide to the atmosphere,\Nwhich then goes partly into the oceans and
Dialogue: 0,0:43:32.29,0:43:39.35,Default,,0000,0000,0000,,acidifies the ocean waters. But the main\Neffect until now is the marine heatwaves,
Dialogue: 0,0:43:39.35,0:43:44.84,Default,,0000,0000,0000,,which cross more and more frequently the\Ntemperature tolerance threshold of coral
Dialogue: 0,0:43:44.84,0:43:50.09,Default,,0000,0000,0000,,reefs. And here you can see that for the\NGreat Barrier Reef, a huge, fantastic
Dialogue: 0,0:43:50.09,0:43:55.97,Default,,0000,0000,0000,,world wonder that you can see from space.\NAnd you can see here the bleaching in the
Dialogue: 0,0:43:55.97,0:44:05.58,Default,,0000,0000,0000,,year 2016, 2017, 2020, three major\Nbleaching events which affect it in each
Dialogue: 0,0:44:05.58,0:44:11.08,Default,,0000,0000,0000,,case, the red area here with the most\Nsevere bleaching, you can see that by now
Dialogue: 0,0:44:11.08,0:44:17.36,Default,,0000,0000,0000,,a very large part of the Great Barrier\NReef has bleached in these three events.
Dialogue: 0,0:44:17.36,0:44:23.89,Default,,0000,0000,0000,,And it's very tragic. And you can see\Nhere, for example, the March, the 2016
Dialogue: 0,0:44:23.89,0:44:33.04,Default,,0000,0000,0000,,bleaching event in March, the coral was bleached.\NBy May, it was already overgrown by seaweed.
Dialogue: 0,0:44:33.04,0:44:40.21,Default,,0000,0000,0000,,And just in 2015 and 2016, we actually had\Nworldwide coral reef bleaching, not only
Dialogue: 0,0:44:40.21,0:44:45.62,Default,,0000,0000,0000,,at the Great Barrier Reef in Australia,\Nonly the blue ones out of these hundred
Dialogue: 0,0:44:45.62,0:44:53.94,Default,,0000,0000,0000,,reefs that were observed in this study,\Nonly the blue ones escaped bleaching. So
Dialogue: 0,0:44:53.94,0:45:02.25,Default,,0000,0000,0000,,we are actually in the midst of a great\Nworldwide coral die off event, which is
Dialogue: 0,0:45:02.25,0:45:08.02,Default,,0000,0000,0000,,another prediction of climate science\Ncoming true. If you look at the latest
Dialogue: 0,0:45:08.02,0:45:13.92,Default,,0000,0000,0000,,IPCC report, it states that with two\Ndegrees warming, virtually all coral reefs
Dialogue: 0,0:45:13.92,0:45:19.83,Default,,0000,0000,0000,,will be lost, more than 99%. One point\Nfive degree warming. If we manage to limit
Dialogue: 0,0:45:19.83,0:45:26.22,Default,,0000,0000,0000,,the warming to one point five degrees, we\Ncan save between 10% and 30% of the
Dialogue: 0,0:45:26.22,0:45:36.76,Default,,0000,0000,0000,,corals. That is really depressing. Now,\Nlet me talk briefly about what can we do.
Dialogue: 0,0:45:36.76,0:45:42.31,Default,,0000,0000,0000,,A major success is, of course, the Paris\Naccord, the biggest failure of which is
Dialogue: 0,0:45:42.31,0:45:47.54,Default,,0000,0000,0000,,that it hasn't come 20 years earlier.\NAfter all, the world community already in
Dialogue: 0,0:45:47.54,0:45:54.65,Default,,0000,0000,0000,,1992 decided to stop global warming at the\NRio Earth Summit. The nations signed the
Dialogue: 0,0:45:54.65,0:46:01.82,Default,,0000,0000,0000,,United Nations Framework Convention on\NClimate Change, and it took a full 25
Dialogue: 0,0:46:01.82,0:46:12.24,Default,,0000,0000,0000,,years of further negotiations to finally\Nreach the Paris accord. Now, you can see
Dialogue: 0,0:46:12.24,0:46:17.19,Default,,0000,0000,0000,,here that the goal of this is to hold the\Nincrease in the global average temperature
Dialogue: 0,0:46:17.19,0:46:21.68,Default,,0000,0000,0000,,to well below two degrees above pre-\Nindustrial level. So it's not two degrees,
Dialogue: 0,0:46:21.68,0:46:26.47,Default,,0000,0000,0000,,it's well below two degrees. That's a very\Nimportant point. Many countries would not
Dialogue: 0,0:46:26.47,0:46:32.92,Default,,0000,0000,0000,,have signed up if it simply had said two\Ndegrees, which was an older goal, but it
Dialogue: 0,0:46:32.92,0:46:45.52,Default,,0000,0000,0000,,has shown to be insufficient and. And to\Nsorry and to pursue efforts to limit the
Dialogue: 0,0:46:45.52,0:46:50.64,Default,,0000,0000,0000,,temperature increase to one point five\Ndegrees above pre-industrial levels. So
Dialogue: 0,0:46:50.64,0:46:56.08,Default,,0000,0000,0000,,that is a more stringent Paris goal, but\Nat least the nations have committed to
Dialogue: 0,0:46:56.08,0:47:03.20,Default,,0000,0000,0000,,pursue efforts. So my view is that every\Nperson should ask their own government
Dialogue: 0,0:47:03.20,0:47:08.40,Default,,0000,0000,0000,,what you are doing here. Is this a\Ncredible effort to try and limit warming
Dialogue: 0,0:47:08.40,0:47:13.84,Default,,0000,0000,0000,,to one point five degrees? We might not\Nmake it, but at least we should try to
Dialogue: 0,0:47:13.84,0:47:18.56,Default,,0000,0000,0000,,limit the warming to one point five to\Navoid the risk of destabilization of the
Dialogue: 0,0:47:18.56,0:47:26.08,Default,,0000,0000,0000,,Greenland ice sheet, almost complete coral\Ndie off and many further risks. So what
Dialogue: 0,0:47:26.08,0:47:32.96,Default,,0000,0000,0000,,does this entail? That is an important\Npoint. If you want to limit global warming
Dialogue: 0,0:47:32.96,0:47:38.88,Default,,0000,0000,0000,,to some value, whatever it is, one point\Nfive, two, three, whatever you choose, it
Dialogue: 0,0:47:38.88,0:47:45.04,Default,,0000,0000,0000,,means you can only emit a limited amount\Nof carbon dioxide. That is because the
Dialogue: 0,0:47:45.04,0:47:53.12,Default,,0000,0000,0000,,amount of global warming is to a good\Nextent proportional to the total amount of
Dialogue: 0,0:47:53.12,0:47:59.20,Default,,0000,0000,0000,,CO2 that we have ever emitted. So to the\Ncumulative emissions, it's like filling a
Dialogue: 0,0:47:59.20,0:48:05.04,Default,,0000,0000,0000,,bathtub with water. If you want to draw\Nthe line at any level and say no further
Dialogue: 0,0:48:05.04,0:48:10.72,Default,,0000,0000,0000,,than here, you can only add a limited\Namount of water. And if you want to limit
Dialogue: 0,0:48:10.72,0:48:15.84,Default,,0000,0000,0000,,global warming to some value, you can only\Nadd a limited amount of CO2 to the
Dialogue: 0,0:48:15.84,0:48:23.36,Default,,0000,0000,0000,,atmosphere. And this is shown here for two\Ndifferent examples, two different amounts.
Dialogue: 0,0:48:23.36,0:48:30.56,Default,,0000,0000,0000,,This is actually, the numbers here are\Nemissions from the year 2016. So it's
Dialogue: 0,0:48:30.56,0:48:39.44,Default,,0000,0000,0000,,don't take these numbers from now. We have\Nalready had four more years of emissions.
Dialogue: 0,0:48:39.44,0:48:50.48,Default,,0000,0000,0000,,The solid lines throw show three scenarios\Nwith six hundred billion tons of CO2 and
Dialogue: 0,0:48:50.48,0:48:56.16,Default,,0000,0000,0000,,they all have the same amount of emission.\NSo they're all three solid lines, get the
Dialogue: 0,0:48:56.16,0:49:01.28,Default,,0000,0000,0000,,same amount of warming. This is about\Nactually these lines correspond to about a
Dialogue: 0,0:49:01.28,0:49:08.16,Default,,0000,0000,0000,,50 percent chance of ending up at one\Npoint five degrees. And so they will get
Dialogue: 0,0:49:08.16,0:49:16.16,Default,,0000,0000,0000,,you the same amount of warming, but with\Ndifferent times of when the peak emissions
Dialogue: 0,0:49:16.16,0:49:23.44,Default,,0000,0000,0000,,are reached. So 2016 went past without us\Ngetting over the peak of the emissions.
Dialogue: 0,0:49:23.44,0:49:29.52,Default,,0000,0000,0000,,2020, maybe we still have a chance.\NEmissions have dropped a bit in 2020, but
Dialogue: 0,0:49:29.52,0:49:34.24,Default,,0000,0000,0000,,not for structural change and mostly, but\Ndue to Corona. But we still we have a
Dialogue: 0,0:49:34.24,0:49:41.41,Default,,0000,0000,0000,,chance that maybe next year they are lower\Nstill. And what this shows is that the
Dialogue: 0,0:49:41.41,0:49:46.16,Default,,0000,0000,0000,,longer you wait, the steeper your\Nreductions have to be, not only because
Dialogue: 0,0:49:46.16,0:49:51.19,Default,,0000,0000,0000,,you're starting later, but also because\Nyou have to reach zero earlier at the end.
Dialogue: 0,0:49:51.19,0:49:57.15,Default,,0000,0000,0000,,Notice how all these three lines, the\Nlater you start with reducing, the earlier
Dialogue: 0,0:49:57.15,0:50:01.84,Default,,0000,0000,0000,,you have to reach zero emissions, because\Nthe surface area under these curves is
Dialogue: 0,0:50:01.84,0:50:07.32,Default,,0000,0000,0000,,what counts for the climate goal. The\Ndashed lines a more generous goal, which
Dialogue: 0,0:50:07.32,0:50:15.73,Default,,0000,0000,0000,,would end at about 1.75 degrees or so,\Nbest estimate. this is kind of the weaker
Dialogue: 0,0:50:15.73,0:50:21.45,Default,,0000,0000,0000,,Paris goal of well below two degrees,\Nwhich would allow us to gradually reduce
Dialogue: 0,0:50:21.45,0:50:28.05,Default,,0000,0000,0000,,emissions to zero by 2050. This is not\Ncounting in any negative emissions
Dialogue: 0,0:50:28.05,0:50:34.01,Default,,0000,0000,0000,,afterwards, by the way. This is the net\Nemissions, if you like. So we have to
Dialogue: 0,0:50:34.01,0:50:40.32,Default,,0000,0000,0000,,reach net zero emissions in 2050. But of\Ncourse, if we wait five more years until
Dialogue: 0,0:50:40.32,0:50:44.45,Default,,0000,0000,0000,,the emissions start to decline, then\Nthey'll have to be at zero five years
Dialogue: 0,0:50:44.45,0:50:50.68,Default,,0000,0000,0000,,earlier. So this is why it's so important\Nto start now. This, by the way, so from an
Dialogue: 0,0:50:50.68,0:50:58.40,Default,,0000,0000,0000,,article by Christiana Figueres et al. in\NNature, published 2017, where I was a
Dialogue: 0,0:50:58.40,0:51:06.38,Default,,0000,0000,0000,,coauthor as well. Now, a final point. Can\Ntipping points maybe help us? And I'm
Dialogue: 0,0:51:06.38,0:51:10.33,Default,,0000,0000,0000,,talking here about societal tipping\Npoints. And there are also some
Dialogue: 0,0:51:10.33,0:51:17.47,Default,,0000,0000,0000,,interesting studies on that. The basic\Nidea is that shown in the top right here,
Dialogue: 0,0:51:17.47,0:51:24.54,Default,,0000,0000,0000,,we are in a kind of stable equilibrium\Nwhere the red ball is now and we are stuck
Dialogue: 0,0:51:24.54,0:51:31.19,Default,,0000,0000,0000,,there. It's hard to get out of this, but\Nthere is a better equilibrium, a more
Dialogue: 0,0:51:31.19,0:51:36.21,Default,,0000,0000,0000,,stable one further off to the right. And\Nthe question is, how do we get over the
Dialogue: 0,0:51:36.21,0:51:43.07,Default,,0000,0000,0000,,hill into that beneficial equilibrium of a\Nsustainable global economy, a sustainable
Dialogue: 0,0:51:43.07,0:51:49.04,Default,,0000,0000,0000,,energy system, a stable climate and so on?\NComplete decarbonization, that means no
Dialogue: 0,0:51:49.04,0:51:55.72,Default,,0000,0000,0000,,more fossil fuel use. And these this green\Naddition there that is added there, this
Dialogue: 0,0:51:55.72,0:52:02.30,Default,,0000,0000,0000,,is just some examples of how we can make\Nthis transition earlier, easier and the
Dialogue: 0,0:52:02.30,0:52:08.16,Default,,0000,0000,0000,,hill that we have to get over smaller, so\Nwe can make this current status quo that
Dialogue: 0,0:52:08.16,0:52:15.16,Default,,0000,0000,0000,,we're in a little bit less comfortable by\Nputting a price on carbon. We can make the
Dialogue: 0,0:52:15.16,0:52:23.28,Default,,0000,0000,0000,,transition easier by subsidizing renewable\Nenergies. There are there is a greening of
Dialogue: 0,0:52:23.28,0:52:28.90,Default,,0000,0000,0000,,values. There is a tipping point in\Nthinking, in society. There are many co
Dialogue: 0,0:52:28.90,0:52:34.08,Default,,0000,0000,0000,,benefits of this transformation in terms\Nof avoided air pollution. For example,
Dialogue: 0,0:52:34.08,0:52:39.53,Default,,0000,0000,0000,,millions of people die every year from\Noutdoor air pollution, which would which
Dialogue: 0,0:52:39.53,0:52:45.80,Default,,0000,0000,0000,,to a large extent go away if we stop\Nfossil fuel use. And we have seen a
Dialogue: 0,0:52:45.80,0:52:51.94,Default,,0000,0000,0000,,massive movement by the young people\NFridays for future. He is Greta Thunberg
Dialogue: 0,0:52:51.94,0:52:56.89,Default,,0000,0000,0000,,talking to me at our institute. She came\Nlast year to visit us here, here is a
Dialogue: 0,0:52:56.89,0:53:02.60,Default,,0000,0000,0000,,Fridays demonstration in Berlin where I\Ntook this photo. This is really changing
Dialogue: 0,0:53:02.60,0:53:08.55,Default,,0000,0000,0000,,the societies values and it's changing\Nelection results and it could be a tipping
Dialogue: 0,0:53:08.55,0:53:16.40,Default,,0000,0000,0000,,point towards a sustainable global\Nsociety. And with that hopeful message, I
Dialogue: 0,0:53:16.40,0:53:21.99,Default,,0000,0000,0000,,want to end and I thank you very much for\Nyour attention. If you want to read more,
Dialogue: 0,0:53:21.99,0:53:27.48,Default,,0000,0000,0000,,there's a couple of books of mine that\Nhave also come out in English. You can
Dialogue: 0,0:53:27.48,0:53:32.95,Default,,0000,0000,0000,,follow me on the blogs and of course, in\Nsocial media, preferably Twitter, but also
Dialogue: 0,0:53:32.95,0:53:38.20,Default,,0000,0000,0000,,the scientist for future logo there,\Nbecause many thousands of scientists are
Dialogue: 0,0:53:38.20,0:53:44.63,Default,,0000,0000,0000,,engaged there to try and stop the climate\Ncrisis. This is really a matter of
Dialogue: 0,0:53:44.63,0:53:50.70,Default,,0000,0000,0000,,survival of civilization. Thank you very\Nmuch for listening. Stick to science and
Dialogue: 0,0:53:50.70,0:53:54.40,Default,,0000,0000,0000,,leave policy to us. Well, we tried that\Napproach. You didn't want to hear about
Dialogue: 0,0:53:54.40,0:53:59.85,Default,,0000,0000,0000,,the science when it could\Nhave made a difference.
Dialogue: 0,0:53:59.85,0:54:03.79,Default,,0000,0000,0000,,Herald: Thank you so much Stefan for your\Ntalk. Now we have some questions from the
Dialogue: 0,0:54:03.79,0:54:10.11,Default,,0000,0000,0000,,Internets. Let's see the first question\NQuestion: Which additional tipping points
Dialogue: 0,0:54:10.11,0:54:17.70,Default,,0000,0000,0000,,will be triggered at two degrees, three\Ndegrees and so on?
Dialogue: 0,0:54:17.70,0:54:22.78,Default,,0000,0000,0000,,Stefan: That is actually a difficult\Nquestion to answer because of the
Dialogue: 0,0:54:22.78,0:54:29.26,Default,,0000,0000,0000,,uncertainty that I mentioned in my talk\Nabout where these tipping points are.
Dialogue: 0,0:54:29.26,0:54:33.74,Default,,0000,0000,0000,,There is one in Antarctica, the Wilkes\Nbasin, that is a part of the Antarctic ice
Dialogue: 0,0:54:33.74,0:54:40.57,Default,,0000,0000,0000,,sheet that that could be triggered, say,\Nbelow three degrees. There are others like
Dialogue: 0,0:54:40.57,0:54:46.44,Default,,0000,0000,0000,,the ocean circulation where you probably\Nat least we hope you have to go beyond
Dialogue: 0,0:54:46.44,0:54:51.88,Default,,0000,0000,0000,,three degrees to really trigger a collapse\Nof the Gulf Stream system. But the truth
Dialogue: 0,0:54:51.88,0:54:57.94,Default,,0000,0000,0000,,is that they are very large uncertainty\Nranges. And the main fact is that with
Dialogue: 0,0:54:57.94,0:55:06.50,Default,,0000,0000,0000,,every bit of extra warming, we increase\Nthe risk of crossing more tipping points.
Dialogue: 0,0:55:06.50,0:55:10.33,Default,,0000,0000,0000,,Herald: And are there some of these\Ntipping points that are interrelated or
Dialogue: 0,0:55:10.33,0:55:16.01,Default,,0000,0000,0000,,correlated? For instance, could we save\Nsome tipping points if we are able to save
Dialogue: 0,0:55:16.01,0:55:19.71,Default,,0000,0000,0000,,others, for instance, the collapse of the\NGulf Stream?
Dialogue: 0,0:55:19.71,0:55:24.88,Default,,0000,0000,0000,,S: Yes, there are these interconnections.\NFor example, if the Gulf Stream system
Dialogue: 0,0:55:24.88,0:55:32.16,Default,,0000,0000,0000,,collapses, it will affect the atmospheric\Ncirculation. The monsoon systems then can
Dialogue: 0,0:55:32.16,0:55:37.12,Default,,0000,0000,0000,,shift the tropical rainfall balance. This\Nis not just theoretical. We see that in
Dialogue: 0,0:55:37.12,0:55:41.44,Default,,0000,0000,0000,,paleoclimate where we have seen these\Ncollapses of the North Atlantic
Dialogue: 0,0:55:41.44,0:55:48.48,Default,,0000,0000,0000,,circulation and the paleo climatic proxy\Ndata show that it comes with shifts in the
Dialogue: 0,0:55:48.48,0:55:54.08,Default,,0000,0000,0000,,tropical rainfall belts that could then in\Nthis way trigger a major drought in the
Dialogue: 0,0:55:54.08,0:56:00.48,Default,,0000,0000,0000,,Amazon region if the Gulf Stream system\Ncollapses. And so it would be very wise to
Dialogue: 0,0:56:00.48,0:56:05.04,Default,,0000,0000,0000,,prevent these tipping points, especially\Nwhen it comes to the ocean circulation or
Dialogue: 0,0:56:05.04,0:56:10.24,Default,,0000,0000,0000,,atmospheric circulation, because it's\Nreally going to mess up the weather
Dialogue: 0,0:56:10.24,0:56:17.20,Default,,0000,0000,0000,,patterns in a major way.\NHerald: How long have we known about
Dialogue: 0,0:56:17.20,0:56:23.42,Default,,0000,0000,0000,,human caused climate change?\NS: Well, in principle, in the 19th
Dialogue: 0,0:56:23.42,0:56:30.07,Default,,0000,0000,0000,,century, Alexander von Humboldt, actually,\Nwrote in 1843, if I remember correctly,
Dialogue: 0,0:56:30.07,0:56:36.65,Default,,0000,0000,0000,,that humans are changing the climate by\Ncutting down forests and emitting large
Dialogue: 0,0:56:36.65,0:56:40.70,Default,,0000,0000,0000,,amounts of gases at the centers of\Nindustry. That's almost a little literal
Dialogue: 0,0:56:40.70,0:56:46.48,Default,,0000,0000,0000,,quote by Alexander von Humboldt. We've\Nknown about how sensitive the climate is
Dialogue: 0,0:56:46.48,0:56:52.29,Default,,0000,0000,0000,,to a change in CO2 since the Swedish Nobel\Nlaureate Svante Arrhenius, remotely
Dialogue: 0,0:56:52.29,0:56:59.91,Default,,0000,0000,0000,,related to Greta Thunberg by the way, in\NIndia studied the effect of CO2 doubling.
Dialogue: 0,0:56:59.91,0:57:04.54,Default,,0000,0000,0000,,He wasn't worried by that because he\Nthought global warming would be great.
Dialogue: 0,0:57:04.54,0:57:13.57,Default,,0000,0000,0000,,Bring it on. It just died, now it's back.\NYou can see my picture so?
Dialogue: 0,0:57:13.57,0:57:20.08,Default,,0000,0000,0000,,Herald: yeah\NA: and so he suggested, you know, burning
Dialogue: 0,0:57:20.08,0:57:25.77,Default,,0000,0000,0000,,a lot of coal to enhance global warming. I\Nguess he came from Sweden and thought cold
Dialogue: 0,0:57:25.77,0:57:31.03,Default,,0000,0000,0000,,is bad without thinking it through\Nproperly. But the first real expert
Dialogue: 0,0:57:31.03,0:57:37.61,Default,,0000,0000,0000,,reports warning the US government, Lyndon\NB. Johnson, of the coming global warming
Dialogue: 0,0:57:37.61,0:57:44.29,Default,,0000,0000,0000,,due to fossil fuel use was a rebel report\Nin nineteen sixty five, exactly 50 years,
Dialogue: 0,0:57:44.29,0:57:50.10,Default,,0000,0000,0000,,half a century before finally the Paris\Nagreement was reached.
Dialogue: 0,0:57:50.10,0:57:53.38,Default,,0000,0000,0000,,Herald: Will you be publishing your\Nslides from the talk?
Dialogue: 0,0:57:53.38,0:58:00.20,Default,,0000,0000,0000,,S: Yes, I will. Uploading the slides.\NHerald: What is or what should be the
Dialogue: 0,0:58:00.20,0:58:04.19,Default,,0000,0000,0000,,ultimate goal of the climate change\Nmitigation? For instance, is it saving
Dialogue: 0,0:58:04.19,0:58:10.24,Default,,0000,0000,0000,,lives, saving other species?\NS: Well, I think the the ultimate goal is,
Dialogue: 0,0:58:10.24,0:58:15.92,Default,,0000,0000,0000,,of course, preserving human civilization,\Nas we know it, but because I think if we
Dialogue: 0,0:58:15.92,0:58:24.64,Default,,0000,0000,0000,,let this run, we will not only destroy a\Nlot of ecosystems and biodiversity, but we
Dialogue: 0,0:58:24.64,0:58:32.00,Default,,0000,0000,0000,,will probably cause major hunger crisis,\Nwhich with big droughts like the one in
Dialogue: 0,0:58:32.00,0:58:39.44,Default,,0000,0000,0000,,Syria before the unrest in Syria started\Nin 2011, the country went through the
Dialogue: 0,0:58:39.44,0:58:44.08,Default,,0000,0000,0000,,biggest drought in history. And according\Nto settlement data from the eastern
Dialogue: 0,0:58:44.08,0:58:51.44,Default,,0000,0000,0000,,Mediterranean, it was the worst drought in\Nat least nine hundred years. And then I
Dialogue: 0,0:58:51.44,0:58:58.32,Default,,0000,0000,0000,,think especially in some unstable,\Nconflicted countries, this can really turn
Dialogue: 0,0:58:58.32,0:59:04.64,Default,,0000,0000,0000,,them into failed states. That is what\Nhappened in Syria. And it's what a German
Dialogue: 0,0:59:04.64,0:59:11.52,Default,,0000,0000,0000,,report for the German government actually\Nwarned in 2009. It was called climate
Dialogue: 0,0:59:11.52,0:59:15.52,Default,,0000,0000,0000,,change as a security risk, I was actually\None of the coauthors of that report
Dialogue: 0,0:59:15.52,0:59:19.76,Default,,0000,0000,0000,,because I was in the German government's\Nadvisory panel on global change at the
Dialogue: 0,0:59:19.76,0:59:26.64,Default,,0000,0000,0000,,time. And I think we will see increasing\Nhunger crisis, failed states and all the
Dialogue: 0,0:59:26.64,0:59:32.56,Default,,0000,0000,0000,,effects that that has on international\Npolitics if we cannot keep global warming
Dialogue: 0,0:59:32.56,0:59:39.76,Default,,0000,0000,0000,,below two degrees.\NHerald: And finally, is there a specific
Dialogue: 0,0:59:39.76,0:59:44.16,Default,,0000,0000,0000,,call to action for the chaos community? Is\Nthere anything that we can do with our
Dialogue: 0,0:59:44.16,0:59:50.64,Default,,0000,0000,0000,,mindset and our skills?\NS: That's a good question that I haven't
Dialogue: 0,0:59:50.64,0:59:58.08,Default,,0000,0000,0000,,thought about, but maybe you can know\Nyourself the best thing, what you can do,
Dialogue: 0,0:59:58.08,1:00:03.84,Default,,0000,0000,0000,,I think the key is really to keep up the\Npressure on the political world, like
Dialogue: 0,1:00:03.84,1:00:11.44,Default,,0000,0000,0000,,Fridays for future has been doing: Go on\Nthe streets, protest, vote with climate as
Dialogue: 0,1:00:11.44,1:00:16.08,Default,,0000,0000,0000,,a priority. I think these are the key\Nthings that everyone should be doing and
Dialogue: 0,1:00:16.08,1:00:21.20,Default,,0000,0000,0000,,specifically in whatever profession they\Nare. They will see some ways of how you
Dialogue: 0,1:00:21.20,1:00:26.64,Default,,0000,0000,0000,,can help to reduce emissions in your\Ncompany, put sustainability at the top of
Dialogue: 0,1:00:26.64,1:00:31.33,Default,,0000,0000,0000,,the agenda and so on.\NHerald: Stefan, thanks so much for taking
Dialogue: 0,1:00:31.33,1:00:36.25,Default,,0000,0000,0000,,the time to join us today.\NStefan: It's a great pleasure and honor.
Dialogue: 0,1:00:36.25,1:00:42.72,Default,,0000,0000,0000,,Herald: Always welcome. And now the news.
Dialogue: 0,1:00:42.72,1:01:22.09,Default,,0000,0000,0000,,Subtitles created by c3subtitles.de\Nin the year 2021. Join, and help us!