The claim seems both far-fetched and intuitive, since, on the one hand, you don’t imagine a few ticks of temperature would turn entire economies into zombie markets, and since, on the other, you yourself have surely labored at work on a hot day with the air-conditioning out and understand how hard that can be. The bigger-picture perspective is harder to swallow, at least at first. It may sound like geographic determinism, but Hsiang, Burke, and Miguel have identified an optimal annual average temperature for economic productivity: 13 degrees Celsius, which just so happens to be the historical median for the United States and several other of the world’s biggest economies. Today, the U.S. climate hovers around 13.4 degrees, which translates into less than 1 percent of GDP loss—though, like compound interest, the effects grow over time. Of course, as the country has warmed over the last decades, particular regions have seen their temperatures rise, some of them from suboptimal levels to something closer to an ideal setting, climate-wise. The greater San Francisco Bay Area, for instance, is sitting pretty right now, at exactly 13 degrees.
This is what it means to suggest that climate change is an enveloping crisis, one that touches every aspect of the way we live on the planet today. But the world’s suffering will be distributed as unequally as its profits, with great divergences both between countries and within them. Already-hot countries like India and Pakistan will be hurt the most; within the United States, the costs will be shouldered largely in the South and Midwest, where some regions could lose up to 20 percent of county income.
Overall, though it will be hit hard by climate impacts, the United States is among the most well-positioned to endure—its wealth and geography are reasons that America has only begun to register effects of climate change that already plague warmer and poorer parts of the world. But in part because it has so much to lose, and in part because it so aggressively developed its very long coastlines, the U.S. is more vulnerable to climate impacts than any country in the world but India, and its economic illness won’t be quarantined at the border. In a globalized world, there is what Zhengtao Zhang and others call an “economic ripple effect.” They’ve also quantified it, and found that the impact grows along with warming. At one degree Celsius, with a decline in American GDP of 0.88 percent, global GDP would fall by 0.12 percent, the American losses cascading through the world system. At two degrees, the economic ripple effect triples, though here, too, the effects play out differently in different parts of the world; compared to the impact of American losses at one degree, at two degrees the economic ripple effect in China would be 4.5 times larger. The radiating shock waves issuing out from other countries are smaller because their economies are smaller, but the waves will be coming from nearly every country in the world, like radio signals beamed out from a whole global forest of towers, each transmitting economic suffering.
For better or for worse, in the countries of the wealthy West we have settled on economic growth as the single best metric, however imperfect, of the health of our societies. Of course, using that metric, climate change registers—with its wildfires and droughts and famines, it registers seismically. The costs are astronomical already, with single hurricanes now delivering damage in the hundreds of billions of dollars. Should the planet warm 3.7 degrees, one assessment suggests, climate change damages could total $551 trillion—nearly twice as much wealth as exists in the world today. We are on track for more warming still.
Over the last several decades, policy consensus has cautioned that the world would only tolerate responses to climate change if they were free—or, even better, if they could be presented as avenues of economic opportunity. That market logic was probably always shortsighted, but over the last several years, as the cost of adaptation in the form of green energy has fallen so dramatically, the equation has entirely flipped: we now know that it will be much, much more expensive to not act on climate than to take even the most aggressive action today. If you don’t think of the price of a stock or government bond as an insurmountable barrier to the returns you’ll receive, you probably shouldn’t think of climate adaptation as expensive, either. In 2018, one paper calculated the global cost of a rapid energy transition, by 2030, to be negative $26 trillion—in other words, rebuilding the energy infrastructure of the world would make us all that much money, compared to a static system, in only a dozen years.
Every day we do not act, those costs accumulate, and the numbers quickly compound. Hsiang, Burke, and Miguel draw their 50 percent figure from the very high end of what’s possible—truly a worst-case scenario for economic growth under the sign of climate change. But in 2018, Burke and several other colleagues published a major paper exploring the growth consequences of some scenarios closer to our present predicament. In it, they considered one plausible but still quite optimistic scenario, in which the world meets its Paris Agreement commitments, limiting warming to between 2.5 and 3 degrees. This is probably about the best-case warming scenario we might reasonably expect; globally, relative to a world with no additional warming, it would cut per-capita economic output by the end of the century, Burke and his colleagues estimate, by between 15 and 25 percent. Hitting four degrees of warming, which lies on the low end of the range of warming implied by our current emissions trajectory, would cut into it by 30 percent or more. This is a trough twice as deep as the deprivations that scarred our grandparents in the 1930s, and which helped produce a wave of fascism, authoritarianism, and genocide. But you can only really call it a trough when you climb out of it and look back from a new peak, relieved. There may not be any such relief or reprieve from climate deprivation, and though, as in any collapse, there will be those few who find ways to benefit, the experience of most may be more like that of miners buried permanently at the bottom of a shaft.
Climate Conflict
Climatologists are very careful when talking about Syria. They want you to know that while climate change did produce a drought that contributed to the country’s civil war, it is not exactly fair to say that the conflict is the result of warming; next door, for instance, Lebanon suffered the same crop failures and remained stable.
But wars are not caused by climate change only in the same way that hurricanes are not caused by climate change, which is to say they are made more likely, which is to say the distinction is semantic. If climate change makes conflict only 3 percent more likely in a given country, that does not mean it is a trivial effect: there are almost two hundred countries in the world, which multiplies the likelihood, meaning that rise in temperature could yield three or four or six more wars. Over the last decade, researchers have even managed to quantify some of the nonobvious relationships between temperature and violence: for every half degree of warming, they say, societies will see between a 10 and 20 percent increase in the likelihood of armed conflict. In climate science, nothing is simple, but the arithmetic is harrowing: a planet four degrees warmer would have perhaps twice as many wars as we do today. And likely more.