For almost a generation now, engineers and futurists have contemplated the practical implications of this phenomenon, and the prospect of suppressing global temperature with a program of suspended particles—that is, polluting the air on purpose to keep the planet cooler. Often grouped together under the umbrella term “geoengineering,” this prospect has been received by the public as a worst-case scenario, nearly science fiction—and has, in fact, informed much of the recent sci-fi that has addressed itself to the climate crisis. And yet it has gained a terrific amount of currency among the most concerned climate scientists, many of whom will also note that none of the quite modest goals of the Paris climate accords can be achieved without negative-emissions technologies—at present prohibitively expensive.
Carbon capture may indeed prove to be “magical thinking,” but the cruder technologies—we know these will work. Rather than sucking carbon out of the atmosphere, we could shoot pollution into the sky on purpose; perhaps the most plausible version involves sulfur dioxide. That would turn our sunsets very red, would bleach the sky, would make more acid rain.
It would also cause tens of thousands of additional premature deaths each year, through its effect on air quality. A 2018 paper suggested it would rapidly dry the Amazon, producing many more wildfires. The negative effect on plant growth would entirely cancel out the positive effect on global temperature, according to another 2018 paper; in other words, at least in terms of agricultural yield, solar geoengineering would offer no net benefit at all.
Once we began such a program, we could never stop. Even a brief interruption, a temporary dispersal of our red sulfur umbrella, could send the planet plunging several degrees of warming forward into a climate abyss. Which would make whatever installations were sustaining that umbrella quite vulnerable to political gamesmanship and terrorism, as its advocates themselves would acknowledge. And yet many scientists still describe geoengineering as an inevitability—it’s just so cheap, they say. Even an environmentalist billionaire, going rogue, could make it happen on their own.
Plagues of Warming
Rock is a record of planetary history, eras as long as millions of years flattened by the forces of geological time into strata with amplitudes of just inches, or just an inch, or even less. Ice works that way, too, as a climate ledger, but it is also frozen history, some of which can be reanimated when unfrozen. There are now, trapped in Arctic ice, diseases that have not circulated in the air for millions of years—in some cases, since before humans were around to encounter them. Which means our immune systems would have no idea how to fight back when those prehistoric plagues emerge from the ice. Already, in laboratories, several microbes have been reanimated: a 32,000-year-old “extremophile” bacteria revived in 2005, an 8-million-year-old bug brought back to life in 2007, a 3.5-million-year-old one a Russian scientist self-injected, out of curiosity, just to see what would happen. (He survived.) In 2018, scientists revived something a bit bigger—a worm that had been frozen in permafrost for the last 42,000 years.
The Arctic also stores terrifying diseases from more recent times. In Alaska, researchers have discovered remnants of the 1918 flu that infected as many as 500 million, and killed as many as 50 million—about 3 percent of the world’s population, and almost six times as many as had died in the world war for which the pandemic served as a kind of gruesome capstone. Scientists suspect smallpox and the bubonic plague are trapped in Siberian ice, among many other diseases that have otherwise passed into human legend—an abridged history of devastating sickness, left out like egg salad in the Arctic sun.
Many of these frozen organisms won’t actually survive the thaw; those that have been brought back to life have been reanimated typically under fastidious lab conditions. But in 2016, a boy was killed and twenty others infected by anthrax released when retreating permafrost exposed the frozen carcass of a reindeer killed by the bacteria at least seventy-five years earlier; more than two thousand present-day reindeer died.
—
What concerns epidemiologists more than ancient diseases are existing scourges relocated, rewired, or even re-evolved by warming. The first effect is geographical. Before the early modern period, human provinciality was a guard against pandemic—a bug could wipe out a town, or a kingdom, or even in an extreme case devastate a continent—but in most instances it couldn’t travel much farther than its victims, which is to say, not very far at all. The Black Death killed as much as 60 percent of Europe, but consider, for a gruesome counterfactual, how big its impact might have been in a truly globalized world.
Today, even with globalization and the rapid intermingling of human populations, our ecosystems are mostly stable, and this functions as another limit—we know where certain bugs can spread, and know the environments in which they cannot. (This is why certain vectors of adventure tourism require dozens of new vaccines and prophylactic medications, and why New Yorkers traveling to London don’t need to worry.)
But global warming will scramble those ecosystems, meaning it will help disease trespass those limits as surely as Cortés did. The footprint of every mosquito-borne illness is presently circumscribed, but those borders are disappearing rapidly, as the tropics expand—the current rate is thirty miles per decade. In Brazil, for generations, yellow fever sat in the Amazon basin, where the Haemagogus and Sabethes mosquitoes thrived, making the disease a concern for those who lived, worked, or traveled deep into the jungle, but only for them; in 2016, it left the Amazon, as more and more mosquitoes fanned out of the rain forest; and by 2017 it had reached areas around the country’s megalopolises, São Paulo and Rio de Janeiro—more than thirty million people, many of them living in shantytowns, facing the arrival of a disease that kills between 3 and 8 percent of those infected.
Yellow fever is just one of the plagues that will be carried by mosquitoes as they migrate, conquering more and more of a warming world—the globalization of pandemic disease. Malaria alone kills a million people each year already, infecting many more, but you don’t worry much about it if you are living in Maine or France. As the tropics creep northward and mosquitoes migrate with them, you may; over the course of the next century, more and more of the world’s population will be living under the shadow of diseases like these. You didn’t much worry about Zika before a couple of years ago, either.
As it happens, Zika may also be a good model of a second worrying effect—disease mutation. One reason you hadn’t heard about Zika until recently is that it had been trapped in Uganda and Southeast Asia; another is that it did not, until recently, appear to cause birth defects. Scientists still don’t entirely understand what happened or what they missed, even now, several years after the planet seemed gripped by panic about microcephaly: it could be that the disease changed as it came to the Americas, the result of a genetic mutation or in adaptive response to a new environment; or that Zika produces those devastating prenatal effects only when another disease is present, possibly one less common in Africa; or that something about the environment or immunological history in Uganda protects mothers and their unborn children.
But there are things we do know for sure about how climate affects some diseases. Malaria, for instance, thrives in hotter regions, which is one reason the World Bank estimates that by 2030, 3.6 billion people will be reckoning with it—100 million as a direct result of climate change.