End Times: A Brief Guide to the End of the World

by Bryan Walsh

  The uncertainty in climate science runs both ways, however. The most likely outcome by the end of the century may be around 5.4 degrees of additional warming—or less if we either get much better at reducing carbon emissions or the climate system turns to be less sensitive than we generally expect.79 But there’s about a 10 percent chance, as Wagner and Martin Weitzman describe in their book Climate Shock, that the uncertainty in those projections could skew in the other direction, and warming might be far worse: as much as 10.8 degrees by 2100 or more, with a 3 percent chance of 18-degree warming.80 That’s the shock in Climate Shock—the shock of a very nasty surprise, one that might be enough to snuff out human life as we know it.

  What Wagner and Weitzman are describing is a “fat-tailed risk.” It’s easy to picture. If you distribute the probability of an event over a line graph, you’ll usually get what’s called a bell curve—close to zero probability at either extreme, and a high probability in the middle, which shows up as a bell shape on the graph. Think of a random day in your own life: you’re highly likely to, say, eat lunch, but very unlikely to win the lottery or get hit by a bus—extremely good or extremely bad events.

  Graph the probability of future global warming, however, and you end up with a curve that has a fat tail at the end, which means the chance of extreme warming—of an extremely negative scenario—is something like 10 percent. How worried should we be about a 10 percent chance of something? It depends on the context. If you get a hit once out of every 10 times you go to the plate in Major League Baseball, let’s just say you’d better be a really good pitcher. But if there were a 10 percent chance that the bridge in front of you would collapse, you wouldn’t cross it. And if you thought there were a 10 percent chance your home would burn down in any given year, you’d pay a lot for insurance—or find somewhere else to live.

  That 10 percent probability is itself an estimate, and as we learn more about the climate, that fat tail may grow fatter or thinner. Ken Caldeira and his colleague Patrick Brown of the Carnegie Institution for Science took the most popular climate models, then examined how well they’ve predicted the amount of warming we’ve seen up to the present. The simple idea is that if a model accurately predicted the past, it’s more likely to accurately predict the future. Unfortunately for us, the models that best predicted the past are also the ones that predict greater levels of warming. Their study finds that the most likely warming is about 1 degree greater than the raw models have suggested—raising the chances that a climate shock could be waiting for us.

  What would that shock feel like? In August 2018, a team of scientists led by Will Steffen of the Australian National University and Johan Rockstrom of the Stockholm Resilience Centre published a grim prophecy for the planet. Even if the world managed to meet the carbon emission reduction goals laid out in the Paris Agreement—which we are very much not on track to do—they calculated that there is a chance that climate change could still continue unimpeded. Instead of a global temperature rise of around 3.6 degrees—terrible but probably endurable—the planet would keep warming, perhaps as high as that 10.8 degrees that Wagner and Weitzman warned us about. Already hot parts of the planet would become uninhabitable. Sea levels could rise 30 to 200 feet above where they are now. “You’re going to eliminate most of the coastal megacities on the planet,” Steffen told me by Skype from his home in Australia, where recent summers have become so hot that fruit has cooked in the trees.81 “We would lose terrestrial biomes, lose rain forests, lose ice.” We would be living in what Steffen and his colleagues called “Hothouse Earth”—assuming we could live there at all.82

  Mainstream climate economics generally treats the global environment as a linear system—so much carbon added to the atmosphere equals so much warming equals so much economic damage. But many scientists believe that the linear system could break down if we pass certain environmental tipping points, creating feedback processes that would make Hothouse Earth inevitable. Steffen pointed to the Arctic sea ice that caps the planet. While it exists, the white ice and snow reflects sunlight, cooling the planet the way a white T-shirt keeps you cooler in the summer, but as it disappears it has been replaced by dark ocean water that absorbs sunlight, further warming the Earth. The hotter the Earth gets, the faster the ice melts, which in turn opens up more dark water, accelerating climate change. And that’s just one tipping point. The Hothouse Earth paper identifies more than a dozen, some of which are connected to each other, so they could fall like dominoes as the climate warmed.

  “The dominant paradigm is that the level of climate change is solely determined by the level of human carbon emissions,” said Steffen. “That’s true at lower levels of emissions. But we are saying that there is a risk that warming as low as minus 2 degrees Celsius [3.6 degrees Fahrenheit] could allow these intrinsic feedbacks to take control of the trajectory of warming.”

  Is the climate system riddled with such tipping points, like land mines on a battlefield? We don’t know for sure—and that’s the biggest climate question of them all.

  What’s true for climate change is true for all the existential risks surveyed in this book, only more so. We’re forced to grapple with uncertainty in a contest where the price of getting it wrong, of failing to do enough to forestall catastrophe, may be infinite. And the human brain does not do well with uncertainty, especially the kind of fat-tailed uncertainty presented by climate change. As Weitzman told me, “there is a human tendency to say that the probability is effectively one, or the probability is effectively zero.” Instead of treating that 10 percent probability of catastrophically high warming as if it has a one-in-ten chance of actually coming true—which would demand that we do much, much more—we act as if it’s impossible. “With these worst-case scenarios, it’s as if we can’t seem to afford to act on them,” said Weitzman.

  Part of what holds us back is the distributed, globalized causes of man-made climate change. A ton of carbon emissions emitted at any one place in the world has a warming effect on the entire world. To prevent nuclear war we have to focus our efforts on just a few nuclear-capable nations, but every country contributes to climate change, as indeed almost every individual does through their use of energy. Ever have a dispute at work where no one will take responsibility because everyone is implicated? That’s climate change times 7.7 billion—the ultimate collective action problem.

  While the causes of climate change are distributed around the world, the effects of warming are primarily distributed in the future. There is a time lag built into the machinery of climate change. Even if we somehow halted all man-made greenhouse gas emissions today—no more coal, no more oil, no more gasoline—the climate would continue to warm by an additional 0.5 degrees simply because of the greenhouse gases emitted in the past, going all the way back to the Industrial Revolution.83

  The real victims every time we turn the ignition on our cars or switch on the air-conditioning are not us, the people of the present generation, but our children, our grandchildren, and their descendants. With every other existential risk—a nuclear war, a bioengineered pandemic, even hostile aliens—the people of today would be the first victims, even if the greater tragedy is the loss of the far larger number of human beings who would have lived in the future. But the worst consequences of climate change, those that might truly qualify as existential, won’t hit home until many or most of us are long gone. That raises a vital question: what do we actually owe the people of tomorrow?

  When you think about yourself—at least while doing so inside the narrow metal tube of a machine that uses functional magnetic resonance imaging (fMRI)—a certain part of your brain, called the medial prefrontal cortex, or MPFC, will light up like Times Square on New Year’s Eve. If you think about a family member, the MPFC will still light up, though less robustly. And if you think about other people whom you feel you have no connection to—like, say, the inhabitants of the South Asian island nation of the Maldives, which will likely one day be erased by climate-change-driven
sea level rise—the MPFC will light up even less.

  You don’t need a $3 million MRI machine to know that human beings are self-centered creatures.84 But as Jane McGonigal, the research director of the Institute for the Future, noted in a 2017 article for Slate, what’s strange is that if you think about your own self in the future, you’ll see less activation in the MPFC than when you imagine your present self. The further out in time you imagine that self, the weaker the activation is.85 As McGonigal writes: “Your brain acts as if your future self is someone you don’t know very well and, frankly, someone you don’t care about.”86 And if we view our own selves in the future as virtual strangers, how much less do we care about the lives of generations yet to be born?

  There are sound economic reasons for privileging the present over the future—the foremost being that, whatever the actuarial tables might say, the future isn’t guaranteed to anyone. The question is how much we should value the present over the future. Economists have a figure for this—the “social discount rate,” which quantifies how much present-day value declines as we move into the future. It’s essentially the inverse of an interest rate, which calculates how much an investment will grow in the future. An array of factors go into determining the social discount rate, like how much interest banks charge on loans and the expected rate of return from investments. The Obama administration, for instance, used a discount rate of 5 percent for its analysis of the social cost of CO2 emissions—how much economic damage each ton of carbon dioxide is estimated to cause.87

  Economists also discount the future in part because they expect it to be richer—much richer—than the present. The temporary dip of economic crashes notwithstanding, that’s been the case historically, especially in the modern era. Global GDP increased from about $1 trillion in 1900 to over $40 trillion in 2000—and then more than doubled over the next eighteen years.88 We invent new technologies and we become more productive, and for mainstream economists, there’s no reason to think that the engine of growth will run out of fuel anytime soon. And so economists on the whole tend to be less worried about problems like climate change that will mostly be felt in the future. At the current rate of growth, the global economy will be twice as large in about twenty years—and a world that is twice as rich should be able to handle disasters that are twice as severe. Or at least that’s the hope.

  Discounting makes sense over relatively short time horizons, like the decision of a business to take out a loan. But when we begin to look into the further future—future on the scale of climate change, many decades and even centuries from now—discounting can spit back results that seem confounding. The philosopher Derek Parfit, whom we met back in the introduction, wrote that “at a discount rate of five percent, one death next year counts for more than a billion deaths in 500 years.”89 What that means is that the economic reasoning of discounting concludes that it would be more worthwhile to save one life next year, rather than save more than a billion lives five centuries from now. To put that in monetary terms, with a 5 percent discount rate, it would only be worth spending about $2,200 today in order to prevent $87 trillion in damages—the size of the total world economy now—in 500 years. Make it 700 years and it would only be worth spending 13 cents today. That’s how much we discount the far future.

  An easier way to understand the queasy moral math of discounting is to turn the tables and imagine ourselves not as the people of the present, looking into the future, but as the future of the past. I’m indebted to Nick Beckstead, a program officer at the Open Philanthropy Project—a Silicon Valley–based nonprofit that supports evidence-based charities—for the following analogy. Let’s say the ancient Romans had been told by their ancient Roman scientists that an act that seemed to benefit their society in the short term—like burning cheap but polluting coal, for instance—could expose generations two thousand years in the future to existential risk? From our perspective in the present, it would have been insane for the Romans to do something that would risk our quality of life and even our existence, even if it seemed to benefit them in their time. Yet if the Romans employed the same discounting analysis mainstream economists employ for climate change, the math would tell them to go ahead—the value of even all of human civilization a couple thousand years into their future would be practically nil to them, just as the value of humans hundreds of years into our future is nil to us—at least with a 5 percent discount rate.

  But that 5 percent discount rate wasn’t chiseled on a stone tablet and handed down by Adam Smith. We can choose our own discount rate, and that choice is a rough reflection of how much we value the future, which is another way of saying how much we care about climate change. “If you want to trivialize climate change, you want a high discount rate, which will legitimately trivialize it,” said Weitzman. “And if you want climate change to matter and to get people to do something about it, you’re going to have to have a story that presumes a low discount rate.”

  You’ll recall that the 2006 Stern Review on climate change predicted much greater economic costs from warming than most other models. A main reason is that Stern chose an unusually low discount rate: just 1.4 percent. This was in part because Stern was more pessimistic than the average economist about how much wealthier future generations would be, and in part because he took an ethical stand that we, the people of the present, should value our distant descendants almost as much as we value ourselves. Stern used that discount rate to argue that it made economic sense to spend as much as 1 percent of global GDP now to avert dangerous climate change in the future—a figure he later raised to 2 percent of GDP,90 which today would amount to well north of a trillion dollars a year.

  We can let the economists argue over the validity of Stern’s choices—and they certainly did. Weitzman, for one, was critical of where Stern set the discount rate in his models, but he also acknowledges that conventional discounting fails in the face of the fat-tailed risk of catastrophic climate change. If one degree of warming equals the loss of 1 percent of GDP growth, and two degrees equals 2 percent, then we could probably count on future economic growth more than compensating for whatever global warming throws at us, however bumpy the ride may be. But if there are hidden tipping points, if the relationship between temperature rise and economic damage is not linear but rather exponential, then we have a very different story.91

  How we choose to value future generations will help decide what we should do now about climate change. And that should worry us. We know from neuroscience and psychology that we don’t instinctually care about the future, and we know from economics that it doesn’t seem to pay to care about the future. But ethically, what should our relationship to our future descendants be, those great-great-great grandchildren whose quality of life, perhaps their very life, will depend in part on what we do today? It’s a question that directly matters for climate change, but it applies to every existential risk threatening the loss of that future. So we need to speak not just to the economists but to the ethicists.

  Most ethicists would say that it is wrong to automatically value the life of someone close to you in space over the life of someone far away. We often do that in practice—we tend to care more about our countrymen and neighbors than we do about foreigners—but that doesn’t justify our chauvinism. In fact, the growth of internationally focused charities like the Gates Foundation and the general increase in foreign aid over time92 show that as humanity has matured, we have taken a larger interest in the well-being of those separated from us by space, in part because global media allows us to witness their lives. So why don’t we take a greater interest in the well-being of future generations separated from us by time?

  We do, to a certain extent. I love my son more than I thought was possible, and my wife and I will sacrifice some of our present enjoyment for his future well-being. (It began with sleep.) We all love our children—in the particular. But while the children may be our future, they’re not a very useful stand-in for the farther future that matters for climat
e change and other existential risks. A better question would be: was I ready to sacrifice for my son when he was just a possibility? Will we sacrifice for our hypothetical children and grandchildren and great-grandchildren, whom we may never know and who may never know us?

  For most of us, our revealed preferences indicate that the answer is no, as the collective lack of sufficient action on climate change demonstrates. The problem is that, as the Yale futurist and sociologist Wendell Bell has written, “a present sacrifice for the welfare of the future appears to be a one-way street.”93 We experience the sacrifice in the here and now, and people we will never meet enjoy the benefit. So instead the present is essentially “colonizing the future,” in the words of the social philosopher Roman Krznaric, treating it “as a distant colonial outpost where we dump ecological degradation, nuclear waste, public debt and technological risk.”94

  Because they don’t exist yet, these people of the future have no voice, no way to lobby for their needs. The United Nations exists in part to give representation to everyone living on Earth now, no matter where they are, but as the New York University ethicist Samuel Scheffler told me, “There is no trans-temporal United Nations. The only way we’re going to work for the future is if we are motivated to act on their behalf.”