 We still have time to stop the most catastrophic outcomes. It's not too late. Perhaps the most important economic principle when it comes to the climate crisis is this. There are planetary boundaries and we need to live within them. Because climate change is an existential threat, it requires a different kind of thinking than what conventional economics provides. The backbone of conventional thinking is about trade-offs. The generic economic model is the trade-off between environmental protection and consumption. The more we protect the planet, the less we can consume. This is typically represented in what's called a production possibility frontier, in which more protection comes at the expense of consumption. In the integrated assessment models, the math is more complicated, but it's the same basic logic. There's a trade-off between the costs of mitigation and foregone consumption. Consumption of produced goods and services and consumption of environmental goods like parks, forests, and lakes. But there's a deep flaw in this trade-off model, which is that the failure to protect the natural environment, or more accurately, the tendency to destroy it, undermines the ability to consume. And that means it's also undermining our ability to survive. Notice that in the production possibility frontier, we could engage in zero environmental protection, and it won't affect production. That's because the environment is conceptualized as something that we consume, and that's a fundamental error, because its more important role is the bedrock on which production and life itself depends. In Nordhaus' model, even serious climate change of more than two degrees is assumed to have almost no impact on GDP and by implication consumption. Three degrees of warming only reduces GDP by a little over 2%, and six degrees of warming only reduces it by 8.5%. This is madness. We're only just above one degree now, and we're already experiencing many terrible effects. The heat bulb effect, when temperatures are so high that they can't sweat enough to cool themselves down and will die, suggests that at four and a half degrees, 40% of the earth may be uninhabitable. There's another economic paradigm called ecological economics, which thinks about the problem in a very different and much more relevant way. We're slashing agricultural yields with malnutrition and starvation as the result. We're flooding coastal cities, causing wildfires and widespread property destruction. Disease results. We see evidence already that climate change is pushing certain infections to go to new places. This reality means we need a different understanding of the relationship between humans and the natural world than the one that has dominated conventional economics. Ecological economics begins with the recognition that the human economy exists within a larger planetary system. When human activity is small relative to planetary systems, the assumptions of conventional economics are more reasonable. Ecological economics calls this an empty world. But when human impacts are large, ecological protection is essential to production and we are living in a full world where the value of ecosystems rises tremendously, even exponentially. There are multiple indicators that reveal that we have transitioned from an empty world where ecological impacts can be serious but are local and hence not existentially threatening into a full world in which the human footprint is now unsustainable. This new reality can be seen in a variety of ways. One intuitive metric is called the ecological footprint. This measures the amount of land and shallow seawater necessary to reproduce our standard of living. It also accounts for the excess carbon we're emitting into the atmosphere and it measures that against the capacity of the earth's ecosystems to safely accommodate that production and consumption. Until about 1970, economic activity was below the capacity of the planet. By then, not only had the world filled up, it was now operating above its reproductive or sustainable capacity. That put us into what's called ecological overshoot, wearing down ecosystems or to use economic terms eating into our natural capital. We're deforesting, destroying other species, using up water reserves, and of course destabilizing the climate. We're currently about 60% above planetary capacity. The world is over full with human impacts. Other metrics also show the relentless increasing pressure of humans on the planet. One you're probably already aware of is the amount of carbon and other greenhouse gases that we're emitting. We're now at about 420 parts per million, up from 280 in 1850. A doubling of greenhouse gases in the atmosphere is thought to translate to between 2.6 and 3.9 centigrade degrees of heating. Materials use also shows a growing footprint. Between 1970 and 2017, the total volume of materials used in production around the world, minerals, ores, fossil fuels, and biomass, more than tripled. And while climate change is an existential threat, there's another great ecological collapse underway, what has been called the sixth-grade extinction. More than one million species are now threatened with permanent extinction. The Living Planet Index, a comprehensive measure of biodiversity, finds that since 1970, populations of animal life, including birds, reptiles, mammals, amphibians, and fish, have declined by 68%. The post-1950 period, with its historically unprecedented levels of economic growth, also shows increasing human impact. Termed the Great Acceleration, a wide range of indicators over the last 70 years show exponential increases, whether we're looking at GDP, population, primary energy use, water use, paper, fertilizer, tourism, carbon dioxide, methane, nitrous oxide, fish capture, ocean acidification, tropical forest loss, domesticated land. In 2009, a worldwide group of scientists came together to provide a comprehensive picture of where things stand with respect to human impacts on ecosystems. They called it the planetary boundaries approach. The scientists identified nine planetary boundaries that humans should not breach. They found adverse trends across a number of them, including stratospheric ozone depletion, biodiversity loss, ocean acidification, nitrogen and phosphorus flows into the biosphere, land system change, freshwater consumption, and of course, climate change. While they were unable to quantify all of these trends, the exercise sounded a loud alarm, and a 2015 update found we'd already breached the boundary on biodiversity, chemical flows, land system change, and climate. And we're close on ocean acidification. Now, none of these metrics is perfect. A number of them, such as the ecological footprint and the planetary boundaries framework, have lively literatures pointing out flaws and problems with them. These are important debates which show the need for a lot more work on these kinds of large-scale methods of capturing ecological overshoot. But the flaws of individual measures should not blind us to the fact that they are all giving us one very worrisome message. Humans are destroying ecosystems and killing off species at a dizzying, unsustainable, and accelerating rate. Capitalism is a big part of the problem. Now, capitalism is not the only economic system that has inherent tendencies to degrade the planet, but it is one which does. The pressure to grow, the failure to internalize climate impacts, the lack of democratic accountability over economic outcomes, and extreme concentrations of wealth and power have rendered capitalist economies largely unable to cope with climate destabilization. There are aspects of capitalism, such as its technological dynamism, that work in the opposite direction. But more than a half century after scientists knew what was happening, the global community, and wealthy nations in particular, still haven't mounted an effective response. To do so, we're going to need to rethink the basic structures of the economy to ensure existential safety. Capitalism, with its growth imperative and discourses of neoliberal economics, are destroying the planet. Capitalism is also not yielding the kinds of improvement in human well-being that it should. So what does this all mean for addressing the climate? Well, there's a lot that's not very controversial. We need a shift to an energy system rooted in wind and solar. Massively ramp up energy efficiency. Agricultural reform to sequester carbon and replenish the soil. We need to protect forests. These are big changes. They're all necessary. We need to do them. We need to do them as quickly as possible. There are many people working on the technologies, the financial aspects, the policy, and other dimensions of the energy and agricultural transition. We also need to stop building any new fossil fuel projects and infrastructure now. This is a bit more controversial, but it's actually rather astonishing how quickly this recognition is becoming mainstream. About a decade ago, when the concept of the carbon budget was introduced, the first calculations of the known and monetized reserves of the fossil fuels that we could actually use and stay within warming targets were done. Even then, the vast majority of known reserves were unburnable. That is, they couldn't be used without blowing through the target. That started a movement to hashtag keep it in the ground. The truth of that recognition hadn't penetrated to elite circles. But by 2020, the International Energy Agency, which had traditionally forecast reliance on fossil fuels forever, changed gears and brought its assumptions and prescriptions into alignment with science. It called for an end to building any new coal plants and to any new approvals for oil and gas fields and new coal mines or mine extensions. Unless emissions were fully captured and stored, something that is not yet both technically and economically viable. In effect, this means the International Energy Association is saying no new fossil energy production. But as necessary as these measures may be, they're not sufficient. We need to move beyond the conventional to enacting structural changes using some out-of-the-box approaches. In particular, we need policies that both reduce climate disruption and improve well-being. We're going to have to address some of the sacred cows of capitalism starting with the quest for endless growth. One of the unfortunate truths of climate economics is that GDP and carbon emissions remain linked. The hope of the conventional wisdom is that we can grow green. But throughout nearly a half century of official discussion of climate policy, continued growth has been an unspoken assumption, a sacred cow that hasn't even been a topic of conversation. There are finally cracks in the growth consensus. In fact, the Intergovernmental Panel on Climate Change, the IPCC, in its sixth assessment report created scenarios that give safe pathways which now recognize the need to get off the growth trajectory, at least for growth and energy demand. To understand this conversation, we can turn to a concept that figures centrally in the literature on climate change, which is decoupling or delinking. In this case, we're talking about the coupling of GDP and carbon emissions. I'll talk about carbon, but the discussion is also relevant for all greenhouse gases. To grow green, the two need to be decoupled. That is, we need to be able to expand GDP without raising emissions. A good deal of the debate is about whether that can be done. Now, there are two major types of decoupling. One is called relative, and it means less emissions per unit of GDP. We can also think of this as the carbon intensity of GDP. How much carbon do we have to emit to get a dollar of GDP? Now, absolute decoupling is what really matters. It means that emissions actually fall as GDP rises. Unfortunately, too much of the focus has been on relative decoupling and not enough on actually reducing emissions. Growth and emissions have historically been tightly linked, and for the most part, they remain so. Looking over the last few decades of the GDP emissions relationship, two points stand out. First, while there has been some weakening of the linkage for wealthy countries, there's still a significant positive relationship. When rich countries grow, they put more greenhouse gases into the atmosphere. That is, these countries haven't decoupled in absolute terms. Second, the link between carbon and GDP is actually getting stronger among global South countries. So we're going to have to get a handle on this basic carbon fact to meet the stringent decarbonization targets set out by the IPCC to cut emissions in half by 2030 and to get to net zero by 2050. What does that mean for wealthy countries? In broad strokes, it requires emissions reductions of more than 10% a year. That's far beyond any experience we've had, which is why we need those structural changes. Assuming that we can continue with the basic arrangements of capitalism, allowing private investors so much leeway over what they do, aiming for maximal growth just won't work. A better review of studies of decoupling, looking at 835 peer-reviewed articles concluded large absolute reductions of resource use and greenhouse gas emissions cannot be achieved through observed decoupling rates. Hence, decoupling needs to be complemented by sufficiency-oriented strategies and strict enforcement of absolute reduction targets. To put that more plainly, the authors are saying we can't grow our way to emissions targets. Sufficiency-oriented strategies is just academic language for getting off the growth trajectory and meeting needs that is producing what's sufficient rather than maximizing output. An even stronger conclusion comes from economist Enno Schroeder and Servos Storm, who have calculated that for even an 85% emissions reduction target by 2050, per capita global GDP growth must be negative. Now, these are the conclusions for modeling. We come to a similar point of view by looking at the last few decades of experience. First, consider relative decoupling, that is reducing emissions per unit of GDP, even if overall emissions are rising. Considering a sample of 15 high-emitting countries from 1990 to 2008 when the financial collapse occurred, all but Brazil and India achieved some degree of relative decoupling. However, far fewer were able to absolutely decouple, that is, actually reduce emissions. We can see that Germany is the only country to achieve meaningful declines. The UK reduced, but by just a bit. Here we also see a clear positive relation between growth and emissions. The countries that reduced didn't grow by much. In contrast, those that grew a lot, such as China, India and Brazil, also polluted a lot. Since 2008, more countries have had success with absolute decoupling. We can add the US, Switzerland, Italy, Japan and the Netherlands to the list. Although I must say, with the US, it's a bit of a mirage because reductions in carbon emission were mostly wiped out by soaring methane emissions. That point aside, the interesting thing about the experiences of the absolute decoupling countries is that only the US and Switzerland experienced growth in GDP. France, Germany, Italy, the Netherlands and just slightly the UK have actually shrunk in real terms. Which means there's still a contradiction between growing and achieving emissions targets. Green growth remains a mirage. As it happens, the measures I've been showing you typically overstate the extent of emissions reductions because they only count emissions that occur within the country or what are called territorial emissions. There are also emissions that are associated with trade. If the European Union imports a lot of goods from China where dirty coal is used to produce those goods, those emissions should count against the EU. And the carbon embodied in the products that the EU exports should count against the countries those items are going to. As it happens, wealthy countries have exported or outsourced a lot of their carbon emissions to the global south, which is one cause of more rapidly growing emissions there and reductions in the global north. Some researchers have called this ecologically unequal exchange. If we look at trade adjusted, that is these consumption emissions over this period, the US, Switzerland and the Netherlands are no longer in the category of absolute reducers because their success is due to exporting their pollution. And remember, those countries that did achieve absolute declines also had negative GDP growth over the last decade. Now the point of this exercise has been to show that neither from modeling nor historical experience can we conclude that wealthy countries can equitably grow their way to carbon or greenhouse gas sustainability. But if growth isn't feasible for reaching emissions targets, what can we do? Are we doomed or is there another way forward?