 Yes, indeed, I'm leading the atmospheric chemistry group here at NCAR. Atmospheric chemistry, of course, is a very important topic in this institution. And so this year, we are launching a new initiative, which is the annual Paul Critson lecture. Now, Paul Critson is a Nobel Prize in chemistry, 1996, I believe. He was also the director of ACOM, the director of the Atmospheric Chemistry Division at that time, now a laboratory. Paul Critson is, of course, an excellent scientist, Nobel Prize. He did a lot of work on the ozone layer at a time, in particular, when we didn't know how we could potentially destroy the ozone layer. And he was the first to show that nitrogen oxide, for example, emitted by aircraft, supersonic aircraft, flying in the stratosphere, could reduce the ozone layer by a certain amount. And that would have led, if we had those airplane flying, to an increase in the UV radiation at the surface and leading to a number of problems, health problems, skin cancer, et cetera. So Paul Critson did a lot of work also on the role of fires. He introduced this concept of nuclear winter. If, in particular, a nation would start a nuclear war, the nation that would throw a nuclear bomb somewhere would be penalized just as much as the region where this bomb would explode because of a big layer of particles that would surround the Earth and create a real winter for several years, cooling and a lot of environmental problems. So he got very interested in the future of the Earth. He introduced this concept of geoengineering, in particular, that could be used, perhaps, to counteract against the CO2 warming effect, but he never pushed for it. He just indicated that this would be a way in case we really need to witness large warming effect. And you will hear more about that in a second. And finally, he introduced this concept of the Anthropocene, a new geological period that is really dominated by human activities. So Paul has been here several years and has worked very closely with a group of scientists here. And we felt that we had to honor him. He's still alive. He's 80-plus years, pretty young, isn't it? And he sends his greetings because he's very honored to see that we are organizing every year a lecture in his honor. So today, we try to have an outstanding speaker to be the first speaker in this series. And so we invited Will Steffen. Will Steffen was a professor at Australian National University. He still worked a lot with the Stockholm Resilience Center on basically the fate of the planet, the recognition that the planet is a system and a human can alter a system. But the system can respond in a very dramatic way, much more dramatic than perhaps the climate models are telling us. So we'll hear about that a little bit. Will, he's a good friend of mine. And so I'm really happy that we could invite him for this lecture. We worked together when we were involved in the International Geosphere Biosphere Program, which is really the program that shaped the global change activities internationally in the world. And so Will will tell us a little bit today about what the intropocene is and ask the question, where on earth are we going? Thank you very much, Will, coming from so far away for telling us a bit about our future. Will. Well, thank you very much, Guy. It's an absolute pleasure to be here and to be able to help honor Paul Critzen for his many achievements. But I think in the end, this will be his most important one. So this will be the story of the intropocene. And the first comment I have to make is that Bill almost certainly will be joining a few other of us who are a little bit on in years and having lived in two geological epochs, which no other cohort of human beings will be able to say. So let's start with the story of the intropocene. So the first point I want to make is a very, very simple one, is that our planet operates as a single system. We've heard about the ocean circulation system or the atmospheric system and so on. But in fact, they all work together to generate a single system, just like our bodies, our circulation system, our respiratory system. But we are a single organism with properties that are characteristic of the entire organism. To understand this one, though, we have to start with the very basics. This is a timeline from the beginning of Earth to the present, very complicated, but only two points I want to make. You can distill this out into two major parts, the geosphere, the non-living part of Earth, the rocks, the ice, the sea, the atmosphere, and so on, which every planet has, and the biosphere, which is nearly as old as the whole planet. That's life. And as far as we know, we're the only planet that has life. But the important point is that these arrows that wind through there is how these two are connected. And it's definitely not a one-way street. At major points of Earth's history, the geosphere was fundamentally changed by the biosphere. So life is not just a passenger on a planet that happens to be a Goldilocks planet in the right position. It actually has shaped the planet. And this is very important to remember as we go through and try to understand the Anthropocene. So we can look then at climate. Everyone's interested in climate. And we can start at the top and go through 4 billion years. But as we take closer and closer time slices, we get to the world that we humans have lived in. And this is an interesting world because the climate does some strange things. It seems to oscillate a little bit like a human heartbeat in a very regular pattern. So we're going to try to understand what the last half million years of this pattern looks like because that's the pattern, that's the Earth that we evolved in. And that's the Earth that we know. That's the Earth that we humans are designed to live in. So we'll talk about a little bit more detail in ever-increasing time scales. So here is this jagged pattern in more detail. Well, how do we know what the Earth looks like 400,000 years ago? Well, we do this by drilling deep down into the ice in Antarctica and Greenland and pulling out cores that looked a bit like this. You can see it extruded out there. You can see a model of a core out in the lobby here. And when you look at it carefully layer by layer by layer, we can see the compressed ice that's been laid down over time. And we can pull information out of that. Believe it or not, there are parcels of air from 400,000 years ago before fully modern humans are here, that we can actually extract out of these ice cores. And we can analyze what the Earth was doing. That graph there is temperature. And you can see that it's almost like a human heartbeat. It's very regular, has a limit to the upper and the lower temperature. And we see four of these cycles. We humans have gone through two of them. Fully modern humans evolved somewhere around 200,000 years ago. We've gone through two of these, ice ages, warm periods. And now we're in the Holocene, which has been a good period for humans on Earth because we've been able to develop agriculture and so on. Before that, we were only hunter-gatherers. So that's the last 100,000 years in more detail. You can see why it might have been difficult. It was cold, and it was extremely erratic. So we were certainly around then, but it was hard for us to develop anything like what we enjoy today. So there's the Holocene. It's about 12,000 years old. And for about 10,000 years of that, we have developed agriculture and then settlements and then more complex cities and so on. So this is the precursor for the Anthropocene. Geologists have divided up Earth history all the way back to 4.5 billion years into various time intervals. This long jagged one of ice ages is called the Pleistocene. The Holocene is really special because this is the one where we have really developed as humanity. But what's happened? Well, this is something that Paul Kritsen was involved in because as we finished 10 years of work in the IGBP, the International Geosphere Biosphere Program, we wanted to sort of summarize what we had learned. So we decided that we would actually look at what humans had been doing over the past. Well, we started with only 100 years. But then we decided we should go back to 1750 because that's when before the Industrial Revolution started. There are 12 graphs. And in 12 graphs, we've decided to depict as best we can in only 12 graphs who we are and what we do. So there you see population, economy. Here is energy, urbanization. And then we have resource use, fertilizer, water, paper. And here we have communication, transportation, telecommunications, international tourism, and so on. This is all of us aggregated together. And look what happens. We thought we would see a nice even curve from the Industrial Revolution. We don't. Actually, not much happens until 1950. And then everything exploded. Historians have started to call this the Great Acceleration, completely unique in human history. So we thought, oh, this is fascinating, but this is all humans. And we're sitting here on planet Earth. Have we had any impact at all on planet Earth? And this is where our research in the IGBP came in. So we decided, well, let's do the same thing. Let's pick out 12 indicators of the Earth. And let's start from 1750 and see what they do. And that's what they look like. The top six are the geosphere, the non-living part. You see the famous greenhouse gases up there, carbon dioxide in the upper left. There is climate. There is atmospheric chemistry. And there is ocean chemistry. The bottom six are the biosphere, the living part of the planet. So we look at the ocean, the coast, and the land. We can see the shapes of these curves. They're not quite as clean as the human ones, but they show basically the same shape. And look, at 1950, things started happening to planet Earth. So there's a mass of scientific evidence that stand behind each one of these graphs. And this scientific evidence tells us two things. Number one, all of these curves have gone outside of the Holocene. They're outside of Holocene norms. And the second one, quite critically, is this is not natural variability. There's a massive evidence to say that dominant driver of every single one of these curves is human action. So it was this massive evidence we were presenting at a meeting in Cuernavaca, Mexico in the year 2000. They had just come. We'd just started putting these graphs together. And the paleo people were talking about all the things that had happened before this, and they were referencing the Holocene. And Paul Crutzen was there, and he was getting agitated. And we didn't know why Paul was getting agitated. But he was obviously synthesizing all this information faster than the rest of us could. And finally, after he heard the Holocene for about the 25th time, he blurted out and he interrupted and said, stop saying the Holocene. We're not in the Holocene anymore. And then he had to stop and think a bit because he hadn't thought this through. And he just said, well, we're in the Anthropocene. We're seen being like Pleiocene, Myocene, and Anthropa being human. And that's where the origin of the term, and indeed the concept came from. And it stuck ever since then. So these sets of 12 graphs, previous ones in this, are really the fundamental basis for the Anthropocene. And they still stand after nearly two decades of further research as the most compelling evidence that we have left the Holocene and gone into a new geological epoch. So Paul published this in the year 2000. The meeting was in February. So a couple months later, in the newsletter of the IGBP, Paul published this, The Anthropocene. And being a pretty thorough and also a modest scientist, Paul said, I can't have been the first person to think of this. It's so obvious someone might have thought of this as well. So he scoured the literature and he actually found an obscure paper by a limnologist from the Central USA who'd been studying lakes in the Midwest and was looking at some difference in silicate deposits in the lakes of the Midwest of the US. And so he saw lots of changes in them and he decided he would call this the Anthropocene. But he never followed up on it. And so Paul contacted him and he agreed to be a co-author. But he said, I'm not interested in this anymore. I've gone off and done my own thing. So he sort of handed the baton to Paul to carry on with. So let's start looking now at the geosphere and the biosphere and how they're changing in the Anthropocene. Well, this is what everyone's talking about. This is climate change. So here are direct observations that can go back to about 1880. Going up to 2018 is the last full year we've got. You can see what the trend is. It's really clear in terms of global average surface temperature. It's going up quite strongly. We are already a degree, or a bit more than a degree, warmer than pre-industrial. Now we need to put this on a longer term time for him to understand again what the Anthropocene is like. Not many people have seen this graph. This is fairly modest time back. This is AD0, Roman Empire. So we've gone through 2,000 years. That's natural variability of climate. That's intensively degree. So we have cooled by about 1 tenth of 1 degree over 2,000 years. And the Earth's orbit around the sun tells us that's about what we should be doing. And the variability fits within what we expect from Earth's orbit and solar activity until we see this enormous rapid spike. That's one degree. But that's put on what Earth normally does. Notice how big it is, but notice how fast it is too. And this is why we're seeing so many impacts already at one degree temperature rise way outside the Holocene envelope of variability. These rates of change are quite dramatic. If we look at CO2, which is also going up in a very similar curve that we showed in the upper left of that first set of 12, that is about 100 times faster than the fastest rate we see in the past, which is when the Earth comes out of an ice age. CO2 goes up 100 parts per million very rapidly. But this is 100 times faster. In terms of temperature, the temperature spike is 170 times faster than the background rate over the past 7,000 years of the Holocene. So these are remarkable rates. They're similar to, for example, a huge volcanic eruption, or what we call a Paleocene-Eocene thermal maximum, a big outgassing from ocean sediments about 56 million years ago. It's very, very unusual in Earth history to see rates this fast. That's what's happening to the climate system. But that's half the story. The other half, of course, is human transformation of the biosphere. We tend to forget about this in the climate story. But in fact, we've been changing the biosphere even more dramatically than we've been changing the climate. So much of the Earth's surface, land surface, looks like that. Over half is now fully dominated by human activities. And we can measure this in various ways. This is one of the more intriguing ones done by a Canadian researcher named Voklov Smil. So what he's done is looked at terrestrial vertebrate biomass. Vertebrates are everything that has a backbone. That's us and all other mammals. It's also birds. And it's also reptiles. And it's also amphibians. Four classes. And you add up the weight of every one of these creatures that lives on land. And you get a number. What fraction of that is humans? Well, it's about 30%. Actually, it's a bit more than that now, since we've added more human populations since 2011. About a third of the weight of every creature on Earth is just us, our body weight. But even more dramatic, domesticated animals. Pigs, chickens, chooks, cattle, and so on, they comprise 67%. That leaves 3% for all wild creatures on Earth. Mammals, birds, and so on. This is how dramatically we have changed the land biosphere, even more dramatically than we've changed the climate. This has been assessed by an international body, the Intergovernmental Science Policy Platform, on biodiversity, and so on. And they've just published a report. This is the equivalent of the IPCC for the biosphere. That's all the world's expert looking at what's happening to nature, the living part of planet Earth. It's pretty shocking. Nature is declining globally at rates unprecedented in human history. We've just saw one example of that. The rate of species extinctions is already accelerating. And they come up with some other conclusions, too, which you can read. But a couple of these, I think, are really important. We are eroding the very foundation of our economy's livelihoods, food security, health, and quality of life around the world. Around 1 million animal and plant species are now threatened with extinction within the next few decades. This would be without a doubt the Earth's sixth great extinction event. So the Anthropocene biosphere is being changed even more rapidly and more dramatically than the Anthropocene climate, although it sort of sits in the background with all the emphasis we put on climate change. The geologists have gotten into the act. And this is a fascinating experience. So I'm one of 35 members, as is Paul Crutzen, of the Anthropocene Working Group. It's convened by Jan Zalasevich from the University of Leicester. What's this all about? Well, a geologist have an extremely careful, thorough, strict way of defining time intervals in Earth history. You've got to go through a really thorough process. As you might imagine, Paul laid down the challenge. Because when he said we're out of the Holocene, he was actually really specific. He said, I think we're in the Anthropocene, and he said a new geological epoch in Earth history. He used the precise term epoch, which has a meaning in geology. He didn't say an era or a period. He said an epoch, which is the same level of the Holocene. And he published that in Nature in 2002. Geologists being geologists, it took them till 2009 to actually form a working group on this. They work pretty slowly, but they're also very thorough. So we've gone through nearly a decade of debating with philosophers, humanity scholars, geologists, engineers about what this Anthropocene is all about. So this is really taking Paul's concept and expanding it to many other disciplines in a very fundamental way. But now we've focused down and said, should this really be formalized in the geological time scale? It goes back to the beginning of Earth. This would be quite a momentous decision. So we finally had a formal vote just last month in the month of May this year. Out of the 35 voting members, Paul doesn't vote. He's not very well these days, so he's a corresponding member of the Anthropocene working group. One other member abstained, but 33 of us voted on two questions, very simple. Should the Anthropocene be formalized in the geological time scale? Should it become a real geological entity ending the Holocene? Which would be actually quite dramatic. And should the base of the Anthropocene, that is the start date, be placed around the mid 20th century? And so there was the vote. Yes, won the formal vote 29 to four. I've never seen such a strong majority in science before. We normally argue in debate and we have differences of opinion. That was remarkable. So that tells you that these conservative geologists are absolutely convinced of the evidence that Paul first put forward. So mid 20th century, those of us who were born before 1950, because it'll be rounder up 1950, may well have lived in two geological epochs, completely unique in human history. And I can probably guarantee Bill will live in two geological epochs, because even if they put it in 1945, he'll probably make it. Anyway, so that's where we stand. Now, it'll be a few years before we actually determine this precisely because the next step is to present a core, a golden spike, a core somewhere down in soil and ocean sediments, or in glacial ice that actually show the start of the Anthropocene. That's gonna be both easy and hard, easy because the evidence is everywhere. When the geologists started drilling, they were astounded. Everything they drilled, they saw changes around the mid 20th century, whether it was plastics, aluminium, oxygen, isotopes, whatever they're looking for, there was a shift, so that it's gonna be hard because they only have to pick one. They want the golden spike, and they will have a whole array to support it. So this will go forward probably in four, five years' time to be formalized by the bodies that sit above our working group. So it's looking pretty positive that within the next five years or so, we will have, I think, quite an interesting announcement to the world that we have indeed as a species extinguished a geological epoch and started a new one. That's some of the evidence we're looking at. So there you see, aluminium, concrete, plastics, synthetic fibers, that's 1950, and that's what they look like. And these are appearing in cores around the world. So the evidence is there. I think we just need to go through the process. All right, I've talked a lot about the climate system and the biosphere, but what about humans and our systems? I mean, Anthropocene puts us front and center of what's happening to planet Earth. So the interesting thing, and this came out in the Anthropocene working group deliberations, is we have to involve the social sciences, the humanities, and so on, because this is front and center about us and our systems and viewing us as objectively as we can about who we are and how we've come to this position. The first criticism was a very strong one by a couple of political scientists from Sweden because Paul and I and lots of other people talked about mankind or humankind and so on and they quickly said, wait a minute, wait a minute, not everyone on planet Earth is equally responsible for the Anthropocene. They said, this is really the fossil fuel-driven consumption-oriented globalized economy and that wasn't created by mankind in general. In fact, it's only about 20% of us. They said, intra-species inequalities are part of the current ecological crisis and cannot be ignored. So we took that criticism on board. It was pretty harsh criticism. It was published in a journal. And so we went back to our 12 human graphs and we got data for 10 of the 12 that we could split into three groups. We split them into the OECD countries, which are the dark ones. That's the wealthy countries. So it's the European countries, USA, Canada, Japan, and Australia, New Zealand. And then we have the emerging economies, sort of the middle shade there, those so-called BRICS, that's Brazil, Russia, India, China, South Africa, and then the light ones are the poor ones. And all you have to do is look at the first two. Population growth since 1950, very little in OECD, most of it in BRICS and poor countries. But real GDP, look at that. Real GDP correlates with consumption. 75% is still in the wealthy 20%. You don't see much change, even in China and the rest of the world, up until 2010, the latest when we got this data. So that's telling us that indeed, the two gentlemen were correct. There are huge inequalities in terms of numbers of people and who's making the impact on the Earth's system. And you can see other interesting trends through those graphs. So they were right. We've got to look a little bit deeper and then humanity as a whole. So what's happening? Well, actually interestingly, there are some trends that are happening in the wealthy countries, which need to be examined in more detail in terms of the anthropocene. So here we go from 1913, there's about 1950, 1970, and so on. What we're measuring here is income inequality. So we're looking at the fraction of income of a country that's commandeered by the top 1%. So here we have the English-speaking world and here we have Europe and Japan. And what we see is they were very similar back just before the, around the start of the First World War, very unequal. Then we had a World War, a Great Depression, and another World War, and that equalized things in both sets of countries. They looked pretty similar. And then we had a really nice period of coming out of the war, expanding, growing, recovering, with a high level of income equality, and then we see the divergence. The European countries follow an L-shaped curve. They've kept much more income inequality by and large, but the English-speaking world from about 1970 or quickly 1980 has gone the other way. And you can see growing income inequality really sharply. The USA is the worst in terms of income inequality in the English-speaking world, but none of us are very good compared to our European colleagues. So you might say, well, what does this matter? Our standard of living is pretty high, even for poorer people in the Western world. But in fact, there's been some fascinating research coming out of the UK by Richard Wilkinson and Kate Picken. And what they did, they asked the question, are there social implications, well-being implications of income inequality? And their answer is yes. So all these are wealthy countries, right? So there are no poor countries in here. And the correlation here is really simple. These are social problems of wealthy countries. You can read what they are. You've seen a lot of them, obesity, alcohol addiction, teenage births, this sort of stuff. And they correlate an index of these very simply with low income inequality and high income inequality. And the correlation's astounding. They were surprised at how close it is. It doesn't matter what your culture is, whether it's Japan or Norway or Netherlands or whatever. And you can see that as income inequality grows, social problems grow. So they are arguing quite clearly there is a big price to pay for inequality, even if people at the lower end should have a reasonable base income. So what we're starting to see in the Anthropocene is that the human side of things is getting more interesting all the time. But of course, as we generate more and more income, we're generating more and more pressure on the Earth system. But we're actually generating more social problems as inequality grows in many of the Western countries. There are other ways we can do this. These are a couple of colleagues of mine from the ANU in Canberra who did very simple thing. They did GDP, there's GDP growth, and again looking at wealthy countries. And then they have what they call GPI, Genuine Progress Indicator. What did they do? Well, actually it was pretty simple. They subtracted from GDP all the money you spend that actually doesn't contribute to well-being. What is that? You have to make more prisons. Well, that actually generates more GDP, but it doesn't generate any better social outcomes. What about cleaning up from increasing disasters from climate change? Boy, that really boosts your GDP, but it doesn't help your well-being. So when they do this, they find again, about the same time period, this levels off or goes down in wealthy countries. Well, GDP keeps going up. So we're getting more and more indicators here that at the same time, that we're generating climate change, the world's sixth grade extinction, we're actually now beginning to generate social problems within our own societies. And so one of the ways we look at this as a complex system problem is that we're generating system incompatibilities. These things just aren't working together. And you can see it all around the world. You can see it here in terms of denialism, of attacks on science. This, by the way, is a photo I took a few months ago. That's a heat-stressed penguin in West Antarctica. This is when my hometown of Canberra burnt in 2003. 500 houses were burnt. And we continue to pour CO2 in. And the students have had enough of it. And they're demonstrating around the world. So we have some serious system incompatibilities that we have to deal with. So here's our problem. Here's what the anthropocene, the trajectory we're on now. Beautiful circulation patterns around the earth. That's the North Pacific circulation patterns. We're stamping our own circulation patterns on top of that, generating an enormous amount of greenhouse gases and other pollutants as we do. We like to think the biosphere looks like this, that we have all these marvelous animals and we can look at nationally geographics and look at all the beautiful photos of African landscapes. But most diverse land looks like this now. It's dominated by humans. And of course, we still have social problems. We have 800 million people who are still in pretty dire poverty. And at the same time, we're rapidly urbanizing and growing inequality in urban areas as well. So this is the world of 2019 that we live in. This is the Anthropocene as it's unfolding up till now. So where are we going? This is the real question we have to ask about the Anthropocene. And just by its name, the Anthropocene tells us that the decisions we make as societies are gonna determine where this planet goes probably for a long, long time in the future. So the final part of my talk is gonna be exploring where we might go with planet earth. So let's go back to this one. This graph I showed you before, this temperature spike that's happened the last century or so. And take that as our starting point. Now let's put this now in an earth system perspective. So what does this mean for the earth system as a whole? So to do that, let's look now into the future. So these are computer climate models that are looking out to 2100. And there are four different scenarios. And they are related to how much we emit. So the blue line at the bottom is low emissions. If we really get our act together, meet the Paris targets. The top one is we just keep emitting, we keep burning fossil fuels and so on. And you see there's a big divergence of from about another one or so degree up to three or four degrees. But the message that's sending everybody, including our politicians, is that where we go with climate is directly related to how much we emit. That's the major driver. But that's not an earth system perspective. That's a fairly linear perspective. So if we put those projections by the way, going back there, if we put those now not from 1900 to 2100, that's only two centuries. Let's put that on 20 centuries and see what it looks like. So there's our graph. Sorry, I've chopped off the top of that. You'll see it in a moment. But here's 1900. That's where that other graph started. There's 2000. So 2100 is about here. There's our time scale intensively degree or temperature scale and that's what it looks like. So when you look at what's happening to the earth system, that's what it looks like. So there you see, this is the low emissions. We're pretty much committed to somewhere between 1.5 and two. That's Paris, Paris targets. But of course, we're pretty much tracking toward the high emission one. So if we move up to that state in only one century, which is definitely possible, according to the climate models, that really is a severe challenge to even the most advanced civilizations with many scholars saying collapse will be the outcome of a four to five degree temperature rise. And of course, some argue, well, two degrees looks pretty hard. Maybe let's keep it 2.5 to three. But of course again, that ignores the fact that we're talking about a well-regulated complex system. So the question we ask ourselves now is, are those intermediate temperatures actually even accessible? Why would they not be accessible? Tipping points in the earth system. Internal processes that once they are triggered will push the temperature even higher. I'll talk a little bit about what those might look like. But the point I want to make here is there is more to the Paris targets than most people think. That there is a risk that if we miss the Paris targets, we're not headed for a 2.5 world, we're headed for a four or five world. So we've done a lot of work in the past decade on what these tipping elements might look like. They come in three types. They're melting of ice, mainly at the poles. They're changes in big patterns of circulation in the ocean and the ocean atmosphere. El Nino's a good example. Also the North Atlantic circulation. And they come in big biomes, big areas of the biosphere that can flip if they're pushed too hard. So already for the Amazon, for example, we see that because climate is shifting, it's getting less rainfall. And so we start to see drought, fires, and we've actually lost 10 years of carbon storage already. And some people think that by two degrees, we'll flip that into a dry ecosystem. And the problem is, as you start getting more fires and the forest shrinks, the rainfall recycling diminishes, it gets drier, and so that's what the tipping point looks like. And we could look at other ones. Permafrost, frozen soil up in the Siberian region, that's 50 to 250. GT means billions of tons of carbon. Could be lost by 2100. By comparison, our emissions are 10 billion tons a year. So that's five to 25 years of human emissions locked up in that permafrost. Arctic sea ice, that graph just shows it's dropping decade by decade as the Arctic warms. Coral reefs, we've probably crossed the tipping point. We've lost a bit of the Great Barrier Reef already. The next heat wave will probably take out even more of it. Greenland, losing ice at an increasing rate, same with West Antarctica. Those are the two most vulnerable parts of polar ice. And again, most people think tipping points could be as low as two degrees for both of those, perhaps even lower for West Antarctica. But these things are not independent. They're part of one interacting system. That's the point I want to keep making. This is one system. And the challenge to us in science is to put these pieces together in a complex system framework. And when we do that, we start to see two things. One is these things can tip at different temperature ranges, one to three, three to five, and five or above. So you can see that color coded. But these arrows indicate they're linked. The simple way to think of it is much more complex than this in reality. But the simple way to think is a row of dominoes. When you start tipping the first ones that tips another one, it tips another one, it tips another one. It's a bit more complicated in the Earth's system, but that's not a bad analogy. That if we start tipping enough of these at two degrees or a bit above, the dominoes aren't going to stop. They're going to keep tipping until you tip the row of dominoes. Which puts you up into first the three to five and the five degree range. So this is our challenge in science over the next few years is to really pin down how this system operates. We tried to do a cartoon-like picture showing the Earth between ice ages, the valley here, and the Holocene, that little valley at the top. And the fact that instead of sitting nicely in that little valley, which we could do or should do for another 10,000 years, we've shoved it out here into the Anthropocene. So that's Paul's insight is that we left that nice valley of stability, and we're out here in this landscape that's a bit strange, it's harder, we don't know quite what it looks like. But our argument here is we got two pathways. We can either get control of our actions, get our emissions down, protect the biosphere, perhaps even learn how to pull carbon out of the atmosphere, or we can keep going on the same pathway of more emissions and more degradation of the biosphere at which point we think we could go over a cliff and down into a deep hot valley called Hothouse Earth. The Earth would be very stable, probably for millions of years, but it would not be good for large mammals like humans. So this is our ice core of oscillating between ice ages and warm periods. There's our temperature spike, we're here, we've gone out of the Holocene, and there is our dominoes, which may drive us over the cliff. So this is a cartoon, a sort of stability landscape, as we call it in the business, of where the Earth might be going. Can we inhabit Hothouse Earth? Well, probably not. Most of the tropics and subtropics will be inhabitable. Big changes in temperature and rainfall, 20 to 40 meters of sea level rise eventually. And some have actually made a carrying capacity estimate of around one million humans, not the 7.5 or so that we've got. So it's not a nice, nice world. It's going to be really difficult for us and a lot of other creatures as well. How plausible is this? People say, well, this is pretty wild science, isn't it? Well, one thing we know for sure is that Earth does behave as a complex system in the lake returnary. We see that in the ice cores, no doubt about that. Hothouse Earth conditions are accessible with projected CO2 concentration and temperature. The climate models can give you a five or six degree world if forced hard enough. Some of those feedback processes are the same ones we see in the glacial-interglacial cycling. So we know they're real. The Earth has actually done this. And we observe instabilities in some tipping elements even at one degree. So this isn't fanciful. We have more work to do. So the best way when people challenge me on this, I say, look, this is a risk analysis. And any reasonable human when they would see this sort of data would say, yeah, you can't say for sure that that tipping cascade is gonna take off, but there's a very credible and big risk that it will. Carbon cycle feedbacks, we can calculate. We're starting to calculate how big they are. Here are three of them, 25 billion tons from the Amazon, 30 from the Great Northern Force, 40 from permafrost thawing. That's at two degrees. We estimate this already by 2100. So the question is, how does that stack up against what we need to do to get emissions down? Well, you don't need to convince the students about that. You've seen this young lady, Greta Thunberry, from Stockholm in Sweden, and she doesn't mince any words. Our civilization is being sacrificed for the opportunity of a very small number of people to continue making enormous sums of money. That's pretty direct. She says what polite adults don't say, but would need to be said. And she says, you are stealing children's future in front of their very eyes. And it's triggered similar demonstrations of students around the world. These two gentlemen have written one of the most interesting books I've read called The Systems View of Life. And so they start with the origins of life four billion years ago. All the way up to humans, homo sapiens. It's a brilliant book of how we came about how single-celled organisms came about and how unique Earth is and life on Earth is. But they make some strong statements at the end about what's happening to life on Earth. And this is the best one. Our world today is dominated by a global economic system with disastrous social and environmental impacts. They call it predatory capitalism. And they note that we are the only species on Earth who destroy our own habitat. We can't find any other species that actually destroys its own habitat. And of course we're threatening countless other species with extinction in the process. So here's the problem. This is the famous triple bottom line of environment, social equity, economy. But in fact, this is the way it operates today and continues to operate. That these two are secondary compared to this. So what do we do about it? Well, actually there are a lot of really good thinkers out in the social sciences and humanities who actually have good solutions. One of the best I've seen is Kate Rayworth at Oxford University. She has the donut, her donut economics. She says, look, here's what we should do with our economic systems. We need a social floor so that everyone has a reasonable level of well-being, not just wealth, well-being. So we need social equity, gender equity, health. You can read this, the sort of things that social scientists talk about. But the point is you can't forget the fact that there is a ceiling that planet Earth sets for us. It has its limits. And one of the ways Earth system scientists have tried to define this is by nine processes for which we've developed so-called planetary boundaries. You see climate changes up there, biodiversity loss, but there are other things. Ozone is here because it's important for the chemistry of the atmosphere. We have chemical pollutants, plastics, chemicals that are poured into the environment and so on. And we started to quantify where this ceiling lies. So here's where the economy needs to operate. But we don't yet have the legal and political framework in place to ensure that the economy operates in that space. Kate puts forward seven things to move from the present predatory economy to this one. There are three that, in my view, stuck out. One is systems thinking. Our economy today does not think of systems. It's simple cause and effect. And it's optimization of one parameter, basically. Income, wealth, profit. But in fact, that's not the way the Earth operates. That's not how human social systems operate. So Kate argues, we actually need to redesign the economy so it delivers equity by design so that governments don't have to redistribute income after the economy distorts it. That the economy itself distributes it by design. And very importantly, we need to regenerate the biosphere by design. When companies approach me and say, look, I've looked at the planetary boundaries. How much more can I go before I had a big boundary? I said, you've already crossed it. Start regenerating and stop using resources at an ever-increasing rate. So the economy needs to be regenerative by design. In other words, you don't make money unless you regenerate the biosphere. Philosophers have jumped in too. Very simple. This guy, the past Jack Robotti from University of Chicago, he really nails it. He says, our society is based on human-centric, but the Anthropocene demands a zoe or life-centric approach. Says it beautifully. Right now, we're departmental thinking. We split things up, separate them, think of a university, departments. Says we need epochal consciousness, going back to the new epoch of the Anthropocene. The final comment I wanna make comes from Australia. From the oldest continuous living culture on planet Earth. At least 65,000 years, as far as we can tell. And there's some real wisdom that they say, and they understand really what we should be doing. We're only here for a short amount of time to do what we've been put here to do, which is to look after country. That's our role. Notice we're only a tool in the cycle of things. They understood systems and have understood systems for tens of thousands of years. We go out into the world and help keep the balance of nature. Again, balance systems, feedbacks, and so on. It's a big cycle of living with the land and then eventually going back to it. That's what we humans need to do. So, Paul Critson asked one of the most important questions I think that humanity faces when he at Crenovaca sifted through all that scientific data that was coming out and just said, wait a minute, stop. We're not in the Holocene. We're in the Anthropocene. So what Paul was really saying is, where on earth are we going? And that's the question we have to deal with and deal with very quickly and decisively. So thanks very much for your attention. I hope we have some time now for some questions and discussion. Thank you.