NOTE FOR 2022 READERS: This is the 19th in a series of award-winningopen letters to the next century, now just one generation away. Babiesborn this year in the U.S., and more than 60 other countries, are expected to live to 2100 and beyond. Dear 22nd Centuryexamines likely scenarios for their future, and how we can make the best one happen.

Dear 22nd century,

Are you receiving me? 

In our one-way dialogue up to this point, I've been doubtful at times (that you'll ever travel to the starsor buy a ton of flying cars) and optimistic at others (that you'll live longer, get smarter, end extreme poverty, and grow your own veg). But one thing I've always believed is that there is a civilization to which I can write. Our most educated guess is that there will be basic continuity, the coming catastrophe of climate changenotwithstanding — at least for the next eight decades, at least in a form which preserves the internet in which these time capsules live. 

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Still, it is always worth re-examining our assumptions, especially where the future is concerned. No one wants to risk sounding like a pollyanna in hindsight. So weird as this may sound, dear correspondents, I must question your existence. I confess, I'm doing so all the time, thanks to one frequent response to these letters I get from my contemporaries: How do you know there's even going to bea 22nd century?

My age is one where apocalyptic fears are never far from the surface; perhaps yours is, too. Perhaps it's just part of the human condition to always imagine our grisly end. Personally, I developed a perverse fascination for potential ends of the world in childhood. I grew up in the 1980s, in the twin shadows of the Cold War and Chernobyl, then converted my nuclear-phobia to climate-phobia in the early 1990s. In 1995, the movies Outbreakand 12 Monkeysput pandemics in my nightmare rotation; in 1998, Deep Impactand Armageddonadded the fear of asteroid impacts. 

Then the tragedy of 9/11 rolled around, and I saw a traumatized nation lose its mind for years. The U.S. shed trillions of dollars and thousands of lives fighting a supposed threat that was, it turned out, vanishingly small. (On average, far more Americans lose their lives every year to unsecured furniturethan to terrorism.) My instinct was to redress the balance in the media — which, according to one analysis, was overrepresenting terrorism as a cause of death by a factor of 4,000— by writing about the true civilization-ending threats I'd long feared. 

But every time I did so, I found my nightmare ends-of-the-world had also been overhyped — and that was before we entered a pandemic that, though truly deadly and fundamentally disruptive, will likely kill far less than 0.1 percent of all 7.8 billion people currently on the planet. Climate change can and will do much, muchworse than that, but good luck finding a climate scientist who believes it will literally destroy civilization, even in our worst-case scenario for your century. (Which is, by the way, getting better, because we keep making small improvements in the right direction.) 

As for asteroids? Well, we've logged everything in the neighborhood that could wipe us out, and the only one with as much as a 0.3 percent chance of hitting won't arrive until 2880. (I'll have to remember that one for my forthcoming series, "Dear 29th Century.") 

Why isn't this more widely known? Why did many news outlets just this month hype the threat of an asteroid that was never going to come near Earth? Why was a 2018 international scientific report that said we need to cut carbon emissions 45% by 2030, and hit net zero by 2050, translated into "climate change will end the world in 12 years" scare headlines by media organizationsthat should know better? (When that raft of stories hit, one Washington lobbyist lamented that the same lawmakers who once denied climate change on Capitol Hill were now justifying inaction because "the world is ending anyway.") 

Why? Because of one thing that is more potentially deadly than the problems themselves: the attitude that author Rebecca Solnit calls "naive cynicism." Even in the face of evidence that activism works (getting a single oil pipeline shut down, say), plenty of people in my era seem to take a preemptive "It's all fucked, so why bother" approach. "The shift back to failure is a defensive measure," Solnit writes. Naive cynicism "is, in the end, a technique for turning away from the always imperfect, often important victories that life on Earth provides — and for lumping things together regardless of scale."

So for the rest of this letter, let's take seriously threats that could, in theory, kill off humanity at scale. But let's keep oursense of scale about each one, as we should have done about terrorism, and remind ourselves that science and ingenuity can and have seen off a lot of genuine threats to our species so far. Here are the threats that count as existential risks, in reverse order of their likelihood of murdering multiple billions before the 21st century is out.  

1. Asteroids

As of late 2021, Deep Impact and Armageddonhave company in the movie-loving public consciousness. Adam McKay's satire Don't Look Upshows a celestial body hurtling towards Earth, and a disintegrating culture that can't get it together to believe or care enough. It was received as the director intended, as a metaphor for our current epidemic of basic science denial. The choice of metaphor was ironic, however: Humanity has actually, quietly, done a fantastic job at tracking large rocks and their orbits over the past few decades. Thanks in large part to NASA's Spaceguard Survey, we can cross the extinction-level asteroid fear off our list for many centuries to come. "We've discovered everything out there that's larger than 1 km across," astrophysicist Michael Busch told me in 2018. "Anything smaller than a kilometer would only cause regional destruction." 

Which is not to say we shouldn't look up. We absolutely should! There are plenty of rocks out there that could potentially annihilate a large populated area. Spotting all the 100 meter-plus wide city-killers are the next frontier for telescope watchers. The largest impact in recorded history, an explosion that leveled 500,000 acres of Siberian forest in 1908, is now thoughtto have been caused by a 200-meter wide asteroid or comet. We're discovering about 3,000 of these puppies per year, and a new NASA monitoring systemexpects an uptick in that number, so we should have them all tagged by the time you come along. You're welcome. 

Bottom line: We're really good at orbital math, and there's just a lotof empty space out there – which is why we can be sure that Elon Musk's tiny spacebound Tesla Roadsterwon't collide with any planet for the next million years. Those fears of a 10-kilometer rock like the one that killed the dinosaurs … well, as far as you and I are concerned, they belong with the dinosaurs. 

2. Pandemics

As I noted in the wake of HBO Max's series, Station Elevenmay be the last great pandemic-ends-the-world story. Even the author of the book on which it was based, Emily St. John Mandel, has admitted her fictional flu could not actually spread in the way she depicted. The virus "would have burned out before it could kill off the entire population," Mandel noted calmly as COVID-19 began its troubling journey around the world. 

While we should expect more pandemics in my century and yours, Mandel was right. Viruses seem to have a tough evolutionary row to hoe. They can be extremely deadly like Ebola, with an average fatality rate of 50 percent, and kill their hosts before they can spread far and wide, or they can be relatively mild and infect millions of hosts — like COVID-19 and its mutations, which is much more effective at causing some form of "long COVID" damage (which one paper estimates in the region of 100 million casesso far, or nearly a quarter of total infections), and in crippling our healthcare systems, than in actually killing us (5.67 million deaths and counting.) 

It's hard for a virus to kill fast if it also wants to spread. Not impossible; ongoing human encroachment into the natural world could easily churn out some nasty new mix of animal diseases (like the 1918-9 pandemic, which likely began on a pig farm in Kansasthat was on the flight path for migratory birds). But even if a virus hits the mutation lottery — combining extreme deadliness with a 30-day incubation period, say — it has to face an increasingly wily human race. 

Just look at what we did to slow COVID-19: an unprecedented amount of masking and social distancing that saved millions of lives in 2020(compare to 1918, when San Francisco was one of the few cities to try a mask mandate, and authorities failed to keep it in place) followed by safe and effective vaccines developed at unprecedented speed. Then the largest health campaign in history fully vaccinated half the planet in one year. There was shameful inequality in the distribution (much of Africa will remain without vaccine doses until 2023) as well as surprising success stories (Brazil is now more vaccinated than the U.S., thanks to our old friend the universal healthcare system).   

Regardless, the world seems on high alert. When the next pandemic arrives, be it in my time or yours, the human race is ready. Our medical community is already debating how to fix the mistakes and systemic weaknesses revealed by COVID. We're looking at what worked and what didn't with COVAX, a well-intentioned, first-of-its-kind international effortto distribute vaccines to developing nations. By your century's first pandemic, we would hope that (and not vaccine hoarding by rich nations) is the norm. Who knows, maybe you'll even convince the scientifically-challenged minority that a little "research" is a dangerous thing, especially the kind gleaned from online grifters. 

3. Population growth

I arrived too late for the great population growth scare of the 1970s. It was driven by the 1972 report The Limits of Growth, which claimed we'd hit the limit of human resources by the 21st century, and was widely criticized for using a wildly pessimistic computer model. The report sold like crazy regardless — you'll never go broke predicting the end of the world as we know it — and it remains a vague background fear for the naive cynics of the 2020s.   

Population prophets have been predicting doom ever since Thomas Malthus, an 18th century thinker who believed in forced sterilization of the poor. Thanos, the villain of several Marvel movies — remember those? — had a similarly sinister outlook. But Malthusian fears of too many mouths to feed never came to pass, because agriculture has always kept pace. As it did in the Green Revolution that tripled crop production around the world, right around the time the Limits of Growthteam was feeding incorrect figures into its computers. Now here we are in 2022 with 7.8 billion humans, and somehow we still don't live in the overpopulated Soylent Greencannibalistic dystopia predicted for this year. 

While world population keeps growing, its pace is slowing — so much so that our prediction for the number of humans on the planet in your century keeps getting revised downwards. (Our current best guess: somewhere in the 10 to 11 billion range, and dropping steadily thereafter.) Urbanization and the education of women are sending birth rates plummeting all over the globe. Already, according to the UN, half the world's population live in countries where fertility rates are below the replacement rate. 

What about the opposite fear — that fertility rates will drop to zero everywhere at once, the Children of Menscenario? I love that film as much as anyone, but it was a fantasy primarily designed to illustrate treatment of immigrants during the war on terror. Set in 2027, it posited that the youngest person on Earth was born in 2009, for reasons left deliberately unclear. The Y chromosome is definitely in trouble, but not thatmuch trouble; we're likely stuck with it for the next four million years or so. If a sudden fertility crisis hits our century or yours, we should have enough egg and sperm banks and IVF treatments to ride it out.  

4. Nuclear war

Sometimes, I still go there in nightmares: The supposed four-minute gapbetween the sirens' wail and missiles hitting Newcastle, the nearest large city to where I grew up in the UK. Would my house, 12 miles away, survive the initial blast? And if it did, would we wish it hadn't? The answer was reinforced throughout the 1980s by terrifying TV movies like Threadsand The Day After: Yes, the after-effects of nuclear war are legion. The living would soon envy the dead. And that was before we understood much about the "nuclear winter" that would blanket the planet in ash, likely causing long-term famine almost everywhere for years. 

During the Cold War, the U.S. and Soviet Union stockpiled up to 70,000 nukes between them. Since then, various agreements — including the new START treaty of 2021 — have helped slash the world's total to 13,000, all but a thousand of them held by the U.S. and Russia. This would have sounded like an unimaginable utopia when I was a kid, back when every prediction for the 21st century suggested that at least a few nukes would have been fired in anger by now. 

Let's be clear: That is still waytoo many nuclear weapons, enough to wipe out humanity many times over if they were all launched. We still have way too much launch authority vested in too few people, a fact that troubled my sleep from January 2017 to January 2021. But the world managed to survive a U.S. president who had to keep asking his generals why he shouldn't consider using nukes for all kinds of purposes (including attacking an incoming hurricane). When it came to war, the doctrine of Mutual Assured Destruction kept even Donald Trump in check. 

Will that doctrine hold throughout the 21st century? Will North Korea fire off its arsenal on a whim? Will India and Pakistan blunder into war? Will the U.S., Russia, or China send birds flying, perhaps with Ukraine or Taiwan providing the flashpoints? Your existence depends entirely on the leaders of nuclear-armed countries, and everyone in their chains of command, knowing in their bones that even a small exchange could ultimately destroy us all. We survived this century's Trump. We may not be so lucky next time. 

In other words, every generation may need to film its own Threadsin order to ensure it never happens. Ongoing nuclear nightmares for all of us would be an unfortunate, but possibly necessary, side effect. 

5. Climate change

I outlined the dangers of what you may well call The Catastrophein a previous letter. So let me not dwell too long on the floods, the famines, the droughts, the wildfires, the polar vortexes, the billion-plus climate refugees by midcentury, the "wet bulb" heatwaves so deadly they cook the internal organs of anyone unlucky enough to be without AC. These and other results of our failure to cut carbon emissions fast enough could be recent history to you.

Or maybe not. Because here's the thing about our ongoing bout of global weirding — it will remain within our power to reduce its effects. "We will always have the ability to make our next decade better or worse than the last one," says climate writer David Wallace-Wells in his otherwise extremely pessimistic summary of the science, The Uninhabitable Earth: A Story of the Future.  

We're already making progress in ramping up renewables and drawing down fossil fuel use. The number of climate pledges from countries and companies mentioning 2035 as a date for full decarbonization would have been unimaginable just a few years ago. Shareholder revolts at oil giants, funding for mines and wells withdrawn around the world, coal plants shuttering ahead of schedule everywhere: Emissions may not have peaked yet, but our creaking supertanker of a civilization has started to turn in the right direction. 

It's already too late for us to save the 2030s from worsening climate change. Maybe it's even too late for the 2040s. But our actions now could help ease life in the 2050s and beyond, reducing the need for future leaders to authorize some risky mitigation strategy, like seeding the upper atmosphere with pollutants in order to reflect more of the sun's rays. 

Our climate modeling seems to be coalescing around a rise in the three degree Celsius range by your century. That's not nothing, and I'm not going to sugar-coat the possibility that a billion or more people may die from its direct and indirect effects in the interim. (Already, as many as 8.7 million people die every year just from the particulate matterproduced by fossil fuels.) 

Even stretched out over a century, a billion deaths would be horrific, by far the greatest tragedy in history. One to be avoided and mitigated at all costs, one that will sooner or later require our world to mobilize on a scale not seen since World War II. (Call it a war on warming, which makes a lot more sense than a war on terror.) 

But is it an existential risk to human civilization itself? When asked this question outright, scientists say no. Even Kim Stanley Robinson, science fiction's most ardent climate change fighter, foresees a world where we change our motivations to make carbon sequestration economically viable for poor and rich alike – by use of a carbon cryptocurrency. 

6. Cascading crises 

There are other once-in-a-blue-moon threats to civilization waiting in the wings. The supervolcano under Yellowstone could erupt without warningand take much of North America with it — then blanket the Earth in ash, cutting temperatures and rainfall and possibly eradicating the rainforests. One giant magnetic solar flare from the sun at just the wrong timecould knock out electric grids around the planet, causing untold calamity. Or Earth could suddenly be blasted with a gamma-ray burst from a nearby star— intense radiation that damages DNA and may have caused previous mass extinctions. 

These are all likely rare events, though in each case we're still not sure exactly how rare. (The solar flare thing, which last happened in 1859, may be the most worrisome.) Whether they happen in my century or yours is just down to a roll of the cosmic dice. 

But there's one more kind of end of the world worth considering. What if a few of the events we've discussed in this letter happen at the same time? 

It has often been remarked that a city-leveling asteroid strike, had it happened during the Cold War, might have been misinterpreted as a nuclear attack and kickstarted a general conflagration between the superpowers. It is not beyond the bounds of reason to imagine a bioengineered bug, a war, and a planetary drought all happening at the same time. Or for one of those to lead to a whole cascade of unfortunate consequences that tear the threads of civilization apart. Living in the midst of a supply-chain crisis caused by COVID makes such things seem troublingly likely. 

"I always deemed 'single failure' apocalypse tales to be simplistic, underrating our civilization's inherent resilience," the science fiction writer David Brin wrotein response to my Station Eleventake. I'd simplified the plot of his similar novel, The Postman, calling it a post-nuclear apocalypse scenario. In fact, as Brin pointed out, nuclear war merely took out 70 percent of ThePostmanworld's population. 

"But it does wreck our deeply competent institutions," he added, "so we become vulnerable to a triple whammy of following blows – disease and climate chaos – and finally onslaught by waves of ultra right-wing militias, bent on recreating feudalism... what the worst males always have done, in rocky times. That it would take all four to blast everything down was a key point."   

Picture one possible cascading crisis, however, and it may lead you to seeing them wherever you turn. And then you have to wonder to what extent you’re loading the dice, in the service of a perverse desire to imagine the worst. Would one trauma, or even a series of traumas, really bring out the worst in people — to the point where this interconnected web we call civilization, this decentralized knowledge network allegedly designed to survive nuclear war, would just fall away in a grand barbaric sweep?

Rebecca Solnit offers a more compelling argument in A Paradise Built in Hell, her history of what actually happens in the wake of disasters such as the 1906 San Francisco earthquake, 9/11, and Hurricane Katrina. In each instance, people band together morefor survival and comfort, not less. Invariably a kind of utopian culture develops for the duration of the crisis. As it did in 1906 in San Francisco, where rich and poor happily rubbed shoulders at soup kitchens in Golden Gate Park, no money changed hands, and the only shootings came when soldiers misidentified people trying to clear the rubble as looters. 

This, then, is my defiant prediction in the face of all oncoming storms. The worse our cascade of crises get, the more human compassion and ingenuity will be unleashed. We will follow the prehistoric programming outlined in 2021’s most important book, The Dawn of Everything, and band together in tribes for mutual aid. The internet will go on, even in diminished form, powered by our ever rising amount of solar and wind power. Civilization, stripped of the nonsense we’ve layered atop it, may feel more real than ever. 

Still, here’s hoping we never have to find out what the truth of the matter is. Cascading crises are things I would not wish on my worst future enemy. 

Yours in anticipation of receipt, 

2022