When Will Humanity Finally Die Out?

Homo sapiens have been around for at least a hundred thousand years, and civilisation for maybe a few thousand. These timescales are far longer than your minuscule lifespan, but given our 13 billion-year-old galaxy, they're shorter than a cosmic heartbeat. And unlike galaxies that require a major wallop to tear apart, humans are fragile things susceptible to disease, famine, war, meteors... really, we're quite pathetic.

Illustration: Angelica Alzona/Gizmodo

Focusing on today, apocalypse feels inevitable. We've reported on Dear Leaders egging each other towards the brink of nuclear war, superbugs becoming impossible to eradicate with antibiotics, and governments preparing for the asteroid that will send us the way of the dinosaurs. As a sort of stress reliever, for this week's Giz Asks, we asked futurists, anthropologists, science fiction authors and others: When will the powers that be finally rip the Band-Aid off? When will humanity finally die out?

Anders Sandberg

Senior Research Fellow at The Future of Humanity Institute at Oxford University

Currently, the most likely cause of human extinction is a human-caused disaster. While natural risks are still around (meteor impacts, gamma ray bursts, a really nasty pandemic...) they are less likely than human-caused disasters like nuclear war, bioweapons, or wrecking the civilisational and ecological infrastructure we need to survive. Some emerging technologies like AI, misuse of synthetic biology, or self-replicating machines may also produce exciting new threats. The actual disaster likely to do us in is likely a combination of several kinds: A disaster wipes out most humans, leaves the survivors vulnerable, and then something else makes the situation worse until all are extinct.

The probability of this happening is uncertain. There has been probability estimates ranging from 40-50 per cent over the next century, over an informal poll among researchers suggesting 19 per cent risk, to calculations suggesting nine per cent. The research community does not know, but the risk does seem to be nonzero and is potentially high enough that we are more likely to be killed by an extinction event than a car crash across our lives. If this is true, then we should expect humanity to die out within a few decades or centuries.

But if we get our act together and reduce the risk, what then? Mammalian species tend to survive one to two million years, so were we just a normal species the best bet would be something like 800,000-1.8 million years (we have been around for about 200,000 years already).

H. sapiens isn't a very normal species, though. We are unusually populous and well dispersed (although also need a lot of food and have a slow generation time). We might be particularly tenacious since we can adapt to nearly any lifestyle. That might mean we are unlikely to go extinct unless there is a mass extinction level not of our own making. Such things happen about once every 100 million years, so that would give us a very long species lifespan.

But we are a technological species too. We are pretty likely to change ourselves before long, and settling space does not appear to be impossible. Even if it doesn't happen in our lifetime, it seems odd to claim we would not do it if it can be done over spans of millennia or millions of years. Once we are multiplanetary the risk goes down tremendously — now there will be independent, self-sufficient groups of humans spread across vast distances. Once you can thrive on sunlight and asteroid regolith in vacuum (or build habitats for it) you have access to a vast ecological niche that stays stable for billions of years.

In a few billion years the sun will start to become a red giant. That would be the end of Earth-bound humans (although one could get some extra time by moving the planet outward). But by this point it is rather likely that we will long have moved to other stars, either using slow generation ships or by sending robots to build new civilisation or by having become non-organic posthumans ourselves that can handle the trip. Even a slow expansion means the Milky Way gets colonised in some tens of millions of years, and intergalactic settlement seems doable too (except for the accelerating expansion of the universe which will limit the total spread to within five gigaparsec — much less if we go slow). That kind of vast spread means that local extinctions are irrelevant: There will always be somebody from elsewhere picking up the torch.

In the truly long run stars burn out and cease to form (in a few trillion years), so that is theend of normal planet-life. We can likely make artificial heating lasting much longer but over time energy will become scarce. Living as software would give us an enormous future in this far, cold era but it is finite: Eventually energy runs out. If not, we still have the problem that matter is likely unstable due to proton decay on timescales larger than 10^36 years — one day there is not going to be anything for humans to be made of. That is likely the upper limit.

Another answer is that long before this happens humanity will have changed so much - through random genetic mutations, selection effects or deliberate engineering - that it will have become new species. So our species might never die but just get a happy ending by becoming something else, hopefully even better.

Owen Gaffney

Anthropocene analyst and science writer at the Stockholm Resilience Centre and Future Earth

So, North Korea has just fired a rocket in Japan's direction and the one person the world would typically turn to for leadership in crisis — the US president — is unhinged, yet, still, I am an optimist. Reports of humanity's imminent extinction have been greatly exaggerated, to paraphrase Mark Twain.

Spread over all continents we are a pretty resilient lot so it would take a substantial effort to shove us all from this mortal coil in one fell swoop. But there are reasons to proceed through this century with a certain degree of existential caution if we value a global civilisation at the very least. If we make it to 2100, then observing aliens might conclude planetary intelligence has emerged on Earth, and give a quiet round of applause.

The main obstacles in this end-of-the-century dash are formidable: A technologically advanced civilisation with the capacity and capriciousness to wipe itself out at the drop of an atomic hat; and the slings and arrows of outrageous fortune in the form of uncomfortably large asteroids, gamma ray bursts, virulent disease and supervolcanic eruptions. The latter would plummet our planet in to a dark volcanic winter bringing havoc to life and a global food system.

On the former — our own agency — I am convinced civilisation will do the right thing, after it has exhausted all other alternatives. We live in the Anthropocene. The future is in our hands. The first colony on Mars has moved from an "if" question to a "when" question. Such a move will turn us into a multi-planetary species overnight. This alone will greatly reduce risk of extinction in the medium term, though in the short run a colony will not be self-sustaining and dependent on supplies from Earth.

But here's the rub. The Anthropocene is characterised by speed, scale, connectivity and surprise. All new technologies, whether it is artificial intelligence or nanotech, have unintended consequences. In the Anthropocene, if unintended consequences scale at a rate greater than one then pretty soon we have a planet-sized problem. Worryingly, innovation is accelerating. Who knows, the last words ever spoken on Earth may well be "I knew this would work!"

In Homo sapiens 200,000-year history, we know about several close shaves with extinction. One came 70,000 years back when the numbers of fertile Homo sapiens dropped to just 10,000. The cause may have been linked to the Toba supervolcanic eruption around this time (74,000 years) — the biggest eruption in 2.5 million years — which would have led to a volcanic winter enveloping the planet, possibly for centuries. Indeed, eruptions continued 15-20,000 years after the first blast according to recent research. However, the supereruption theory for H. sapiens population crash is disputed.

The second close shave is a little more recent and linked to our love of cold beer. In 1928, scientists created "safe" new chemicals for refrigerators and air conditioners — CFCs. But the first C in CFCs is an angry little element, chlorine. Apparently unbeknownst to the scientists and their corporate overlords, these chemicals had a vociferous appetite for ozone in the upper atmosphere. The ozone layer has protected life on Earth for billions of years. Without it, the sun's radiation would sterilise the surface. Even weakening this shield would lead to crop damage making our survival questionable even if we shovelled on the sun cream. When the ozone hole was discovered in the 1980s nations agreed to outlaw CFCs and disaster was averted.

If we had not noticed the growing hole, or decided to sit on the problem, humans would have run into a catastrophe more serious than warm beer by the end of this century. Worse, if chlorine had been swapped out for its angrier, less stable sister, bromine — an entirely logical choice that would have kept beer just as cool — then H sapiens demise may have been sooner than expected. Bromine's ozone killing properties make it almost one hundred times more dangerous than chlorine. By the 1970s there could have been a catastrophic ozone hole everywhere all year round according to Paul Crutzen who was awarded the Nobel Prize for his work on ozone.

New environmental risks have become as urgent. We have run out of all alternatives on greenhouse gas emissions. We must now halve emissions every decade or risk crossing the 2C threshold. Some argue industrialised societies could hit the levers of Earth so hard we get a runaway climate spinning out of control in to an uninhabitable Venus state. Even with concerted effort, a runaway Venus world is probably beyond even our reach, though without drastic efforts to curb emissions, global temperatures will reach dangerous levels for civilisation.

Earth has been much warmer in the deep past and a runaway Venus state did not result, as you may have noticed. Without importing carbon-based fuels from elsewhere in the solar system, fossil fuels will likely run dry before we reach a Venus tipping point. Space mining has become a thing recently, so we cannot entirely rule out this eventuality. Moreover, in the Anthropocene all bets are off: Earth's current state is unprecedented - this is terra incognita.

The rate of change of the Earth system is now a function of humanity and it is accelerating. The oceans are acidifying at rates not seen for perhaps 300 million years. Currently, carbon dioxide is entering the atmosphere at rates greater than the largest mass extinction in the history of the planet 252 million years ago. As a reminder, the world lost over 80 per cent of marine species and it took 10 million years to recover. But, boy, when it did, it went large — the dinosaurs emerged.

In Earth's history there have been five mass extinctions. The last, 66 million years ago, ended the reign of the dinosaurs. Earth is currently losing species at mass extinction rates: We are entering a sixth mass extinction and one species is responsible: Us. This is important because biodiversity is integral for the stability of Earth's life support system — the atmosphere, oceans, ice sheets, water cycle and life itself — and the rate of change of this whole system is accelerating (this is the basis of the Anthropocene equation paper we discussed). This has got to concern our global civilisation because civilisation — farming, cities, democracy, law, technology — emerged due to a relatively stable Earth system. There are two ways the acceleration could halt: 1) We change our ways, or 2) civilisation collapses. But if civilisation collapsed, that would not necessarily mean that Homo sapiens would go the way of the dinosaurs.

So, while reports of humanity's imminent extinction have been greatly exaggerated, the Anthropocene is unprecedented in human history so all bets are off. Not least because there may be several unknown unknowns. Be prepared.

N.K. Jemisin

Speculative fiction author and blogger

“Finally?” What a weird way to phrase the question. H. sap hasn’t been around very long, in the grand scale of things. Like, H. erectus lasted a million and a half years; we haven’t even matched a third of that. The question feels to me like how children talk about being “old” at, like, 20. It’s cute.

That said, I’m not really one who subscribes to the notion that we’ll kill ourselves off. What we’re likely to do is kill ourselves back — i.e., we’ll change the environment so much, through climate change or something else, that a lot of us will die, and that will be horrifying. But there are billions of us on the planet, and at least a few are bound to be adaptable enough to survive our own stupidity and selfishness, and continue the species for some time. (Whether we’ll want to continue, given whatever we’re going to do to the world, is an entirely different question, tho’.) So what it’ll boil down to is whether we’re smart enough to get off the planet before something happens to it — a meteor, the sun dying, whatever. Personally, I’m #TeamMeteor, but I guess we’ll see.

Fabien Cousteau

Founder of the Fabien Cousteau Ocean Learning Center and Grandson of Jacques Cousteau

We are the only species in the history of our planet that has the opportunity and foresight to determine our own destiny. That said, some could argue that we are preprogrammed to self destruct. Current trends taken into account, the more pessimistic outlook predicts we will make this planet unlivable within 50-75 years. Personally, I have a tendency to believe in the human drive for self preservation. Immediate implementation of solutions is the only way to mitigate the impact we are having on our life support system, our "planet ocean", which mandates striking a precarious balance to fathom our existence in the future.

Annalee Newitz

Tech Culture Editor at Ars Technica, science and science fiction writer

I don't think humanity will die out, but instead we'll speciate. There were at least half-a-dozen hominin groups wandering around Africa and Eurasia over the past couple hundred thousand years, and it's only really in the past 30-40 thousand that modern humans like us took over. My guess is that over the next 100,000 years, humanity will evolve into several more groups — in part the result of genetic engineering, and in part from the usual forces of natural selection. Especially if we actually start living off-world, it's not going to make sense for us to have bodies that are vulnerable to radiation, or that require a specific balance of oxygen and nitrogen. We're not the pinnacle of evolution! Humans as we know them are just one morphological waypoint on the long road of evolution.

Ian Tattersall

Paleoanthropologist and an emeritus curator with the American Museum of Natural History

It's inevitable. Everything [goes extinct]. Nothing is forever.

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Comments

    Later on this month when Kim & Don throw thier toys at each other.

    Do you know what the world is really lacking.. The supervillain who isn't worried about a belief system or greed, that truly wants to end the world and has the power and desire to make it happen.

    Bow before the POOKIE mortals!

    You will be ended last if you do!

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