life after warming

Welcome to the End of the ‘Human Climate Niche’

A man walks past as waves hit a breakwater at Kasimedu fishing harbor in Chennai on May 19, 2020, as Cyclone Amphan barrels toward India’s eastern coast. Photo: Arun Sankar/AFP via Getty Images

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On Wednesday, a “super cyclone,” now the equivalent of a Category 5 hurricane, is expected to make landfall on the border of India and Bangladesh. The storm will weaken as it approaches land, but in India, it is already forcing evacuations in the thousands just as the country has begun easing its coronavirus lockdown, the world’s largest. In Bangladesh, Earther reports, “the super cyclone is expected to cause heavy precipitation and flooding in the Cox’s Bazar refugee camps, which house more than a million refugees from the Rohingya crisis and are already flood-prone.”

It has become commonplace to say that the coronavirus pandemic is the latest preview of the climate-change future. We have been shown repeatedly, and yet do not learn, that we live within nature, subject to its laws and limits and brutality, and that many of the fortresslike features of modern life that we once assumed were unshakable and unmovable turn out to be very fragile and vulnerable indeed. But it is not just metaphorically true that the pandemic is showing us a preview of the climate-change future, it is also literally true, because the global economic slowdown has meant a reduction of air pollution, which, in general, cools the planet by reflecting sunlight back into space — perhaps, in total, by as much as a half-degree or even full degree Celsius. Less air pollution means, as a result, warmer temperatures. And though the decline in pollution produced by the coronavirus is not total (meaning we won’t be leaping forward a full degree of warming this year), the reduction may well be enough to make 2020 the warmest year on record and produce a summer defined by extreme heat. In other words, we will be living through climate conditions we wouldn’t have otherwise encountered for at least a few more years — living through something like the summer of 2025 in 2020.

We will be facing other extreme events too. Here in the United States, hurricane season is about to begin — an unusually intense one is expected, perhaps even record-breaking, with scientists predicting that there is a 70 percent chance that a major hurricane strikes the continental U.S., which will almost certainly be handling evacuations and precautions in the midst of continued social distancing. (The hurricane season has gotten going early this year, with a named tropical storm appearing before the official onset of hurricane season for the sixth year in a row). And then there’s wildfire season.

In my book, The Uninhabitable Earth, I called the threat of simultaneous or successive disasters like these “climate cascades” — each making it harder to respond to the next. In California, Governor Gavin Newsom has worried that the states’ coronavirus prison furloughs, intended to reduce the risk of coronavirus spreading within prisons, may undermine its ability to fight wildfires this season, since a large share of the states’ firefighters are actually prisoners facing down flames for as little as $1 a day. Usually, they are outfitted for protection with N95 respirator masks. This season, those will almost certainly be in short supply as well. We tend to think of climate impacts as discrete threats: a wildfire, a hurricane, a drought. By the year 2100, it’s possible that parts of the planet will be hit by six climate-driven natural disasters at once. Wildfires tearing through communities cowering terrified by a rolling pandemic only counts as two.

This is what it means to be living already outside the “human niche.” The term comes from a landmark paper published late last month in the Proceedings of the National Academy of the Sciences, “Future of the Human Climate Niche.” What do the authors mean by it? In short, that the range of temperatures that make human flourishing possible is quite narrow, and that climate change promises to close that window — not entirely, but enough to meaningfully diminish how much of the planet can support prosperous, comfortable life.

Today, at just 1.1 degrees Celsius of warming, the planet is already hotter than it has ever been in the entire history of human civilization, which means everything we have ever known as a species is the result of climate conditions we have already left behind — as though we have landed on a new planet, with a new climate, and have to sort out what of the civilization we’ve brought with us can survive these new conditions, and what cannot. How different will things get? The last time there was as much carbon in the atmosphere as there is today, there were palm trees in the arctic.

This is what gives rise to the idea of the “Goldilocks zone” — a term used by astrobiologists to describe just what kind of climate conditions would be necessary for the rise of intelligent life, and which suggests both how rare and how precarious such conditions are. But the authors of the “human niche” paper have gone further, examining not just planetwide climate conditions but regional ones, and both investigating the past to see how many kinds of climates could support large human populations and projecting the future to see how many of those kinds there would be under climate conditions like this century. Looking back, the answer is, not many kinds of climates can support the kind of life we’ve gotten used to—indeed evolved and developed human civilization under. “Humans have concentrated in a surprisingly narrow subset of Earth’s available climates, characterized by mean annual temperatures around ∼13 °C,” the authors write. They continue:

For millennia, human populations have resided in the same narrow part of the climatic envelope available on the globe, characterized by a major mode around ∼11 degrees Celsius to 15 degrees Celsius mean annual temperature. Supporting the fundamental nature of this temperature niche, current production of crops and livestock is largely limited to the same conditions, and the same optimum has been found for agricultural and nonagricultural economic output of countries through analyses of year-to-year variation.

Looking forward, they project that, even under a best-case emissions scenario, one that allows us to meet the goals of the Paris accords and pull up at about two degrees Celsius of warming, regions that are today home to 1.5 billion people would become, practically speaking, unlivable by 2070. Under those conditions, with no large-scale migration, roughly 13 percent of the global population in 2070 would be living in areas with a mean average temperature of 29 degrees Celsius — a mean temperature today found on less than one percent of the planet’s surface, mostly in the Sahara.

The headline finding was even more dramatic — that in a worst-case emissions scenario, Sahara-like conditions would grow so dramatically that they would envelop parts of the planet that are today home to 3.5 billion people. This scenario is unlikely, but so is the probability that we stay below two degrees and avoid the need for 1.5 billion to move, in most cases quite far, many from cities that today are home to many millions of people, to find environments that satisfy the climate requirements of habitability that have held for literally all of human history.

Now, of course, the fact that humans could not flourish under these conditions hundreds of thousands of years ago, or even just hundreds of years ago, does not mean that none of us would be able to live under them in the second half of this century. Already, we have adapted to some degree to the unprecedented climate conditions that we face today, and further adaptations are inevitably on the way. But the question is not merely what portions of the world will become so hot and inhospitable that human life becomes entirely impossible. It is also: How degraded will human life be? In how many places? How many resources will need to be directed toward climate adaptation? And how will the resulting suffering be distributed between and within nations, leaving which communities to wither and which to scramble?

And this is perhaps the most distressing way that the pandemic gives us a preview of the climate-change future: What we are seeing now is not a vision of a worst-case scenario, in which destabilizing impacts run uncontrolled, but an adaptation success story. In the face of terrifying tumult, for which we found ourselves woefully underprepared, most of the world has managed to survive, yes, but under previously unthinkable conditions, struggling to catch a sliver of “normalcy” and hopefully counting the months until we think this might all end. Now imagine it never will.