While apocalyptic beliefs about the end of the world have, historically, been the subject of religious speculation, they are increasingly common among some of the leading scientists today. This is a worrisome fact, given that science is based not on faith and private revelation, but on observation and empirical evidence.

Perhaps the most prominent figure with an anxious outlook on humanity’s future is Stephen Hawking. Last year, he wrote the following in a Guardian article:

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Now, more than at any time in our history, our species needs to work together. We face awesome environmental challenges: climate change, food production, overpopulation, the decimation of other species, epidemic disease, acidification of the oceans. Together, they are a reminder that we are at the most dangerous moment in the development of humanity. We now have the technology to destroy the planet on which we live, but have not yet developed the ability to escape it.

There is not a single point here that is inaccurate or hyperbolic. For example, consider that the hottest 17 years on record have all occurred since 2000, with a single exception (namely, 1998), and with 2016 being the hottest ever. Although 2017 probably won’t break last year’s record, the UK’s Met Office projects that it “will still rank among the hottest years on record.” Studies also emphasize that there is a rapidly closing window for meaningful action on climate change. As the authors of one peer-reviewed paper put it:

The next few decades offer a brief window of opportunity to minimize large-scale and potentially catastrophic climate change that will extend longer than the entire history of human civilization thus far. Policy decisions made during this window are likely to result in changes to Earth’s climate system measured in millennia rather than human lifespans, with associated socioeconomic and ecological impacts that will exacerbate the risks and damages to society and ecosystems that are projected for the twenty-first century and propagate into the future for many thousands of years.

Furthermore, studies suggest that civilization will have to produce more food in the next 50 years than in all of human history, which stretches back some 200,000 years into the Pleistocene epoch. This is partly due to the ongoing problem of overpopulation, where Pew projects approximately 9.3 billion people living on spaceship Earth by 2050. According to the 2016 Living Planet Report, humanity needs 1.6 Earths to sustain our current rate of (over)consumption — in other words, unless something significant changes with respect to anthropogenic resource depletion, nature will force life as we know it to end.

Along these lines, scientists largely agree that human activity has pushed the biosphere into the sixth mass extinction event in the entire 4.5 billion year history of Earth. This appears to be the case even on the most optimistic assumptions about current rates of species extinctions, which may be occurring 10,000 times faster than the normal “background rate” of extinction. Other studies have found that, for example, the global population of wild vertebrates — that is, mammals, birds, reptiles, fish and amphibians — has declined by a staggering 58 percent between 1970 and 2012. The biosphere is wilting in real time, and our own foolish actions are to blame.

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As for disease, superbugs are a growing concern among researchers due to overuse of antibiotics among livestock and humans. These multi-drug-resistant bacteria are highly resistant to normal treatment routes, and already some 2 million people become sick from superbugs each year.

Perhaps the greatest risk here is that, as Brian Coombes puts it, “antibiotics are the foundation on which all modern medicine rests. Cancer chemotherapy, organ transplants, surgeries, and childbirth all rely on antibiotics to prevent infections. If you can’t treat those, then we lose the medical advances we have made in the last 50 years.” Indeed, this is why Margaret Chan, the director general of the World Health Organization, claims that “Antimicrobial resistance poses a fundamental threat to human health, development and security.”

Making matters even worse, experts argue that the risk of a global pandemic is increasing. The reason is, in part, because of the growth of megacities. According to a United Nations estimate, “66 percent of the global population will live in urban centers by 2050.” The closer proximity of people will make the propagation of pathogens much easier, not to mention the fact that deadly germs can travel from one location to another at literally the speed of a jetliner. Furthermore, climate change will produce heat waves and flooding events that will create “more opportunity for waterborne diseases such as cholera and for disease vectors such as mosquitoes in new regions.” This is why some public health researchers conclude that “we are at greater risk than ever of experiencing large-scale outbreaks and global pandemics,” and that “the next outbreak contender will most likely be a surprise.”

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Finally, the acidification of the world’s oceans is a catastrophe that hardly gets the attention it deserves. What’s happening is that the oceans are absorbing carbon dioxide from the atmosphere, and this is causing their pH level to fall. One consequence is the destruction of coral reefs through a process called “bleaching.” Today, about 60 percent of coral reefs are in danger of bleaching, and about 10 percent are already underwater ghost towns.

Even more alarming, though, is the fact that the rate of ocean acidification is happening faster today than it occurred during the Permian-Triassic mass extinction. That event is called the “Great Dying” because it was the most devastating mass extinction ever, resulting in some 95 percent of all species kicking the bucket. As the science journalist Eric Hand points out, whereas 2.4 gigatons of carbon were injected into the atmosphere per year during the Great Dying, about 10 gigatons are being injected per year by contemporary industrial society. Thus, the sixth mass extinction mentioned above, also called the Anthropocene extinction, could turn out to be perhaps even worse than the Permian-Triassic die-off.

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So Hawking’s dire warning that we live in the most perilous period of our species’ existence is quite robust. In fact, considerations like these have led a number of other notable scientists to suggest that the collapse of global society could occur in the foreseeable future. The late microbiologist Frank Fenner, for example, whose virological work helped eliminate smallpox, predicted in 2010 that “humans will probably be extinct within 100 years, because of overpopulation, environmental destruction, and climate change.” Similarly, the Canadian biologist Neil Dawe reportedly “wouldn’t be surprised if the generation after him witness the extinction of humanity.” And the renowned ecologist Guy McPherson argues that humanity will follow the dodo into the evolutionary grave by 2026. (On the upside, maybe you don’t need to worry so much about that retirement plan.)

The Bulletin of the Atomic Scientists also recently moved the minute hand of the Doomsday Clock 30 seconds closer to midnight, or doom, primarily because of President Donald J. Trump and the tsunami of anti-intellectualism that got him into the Oval Office. As Lawrence Krauss and David Titley wrote in a New York Times op-ed:

The United States now has a president who has promised to impede progress on both [curbing nuclear proliferation and solving climate change]. Never before has the Bulletin decided to advance the clock largely because of the statements of a single person. But when that person is the new president of the United States, his words matter.

At two-and-a-half minutes before midnight, the Doomsday Clock is currently the closest to midnight that it’s been since 1953, after the U.S. and the Soviet Union had both detonated hydrogen bombs.

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But so far we have mostly ignored threats to our existence that many leading risk scholars believe are the most serious, namely those associated with emerging technologies such as biotechnology, synthetic biology, nanotechnology and artificial intelligence. In general, these technologies are not only becoming more powerful at an exponential rate, according to Ray Kurzweil’s Law of Accelerating Returns, but increasingly accessible to small groups and even lone wolves. The result is that a growing number of individuals are being empowered to wreak unprecedented havoc on civilization. Consider the following nightmare disaster outlined by computer scientist Stuart Russell:

A very, very small quadcopter, one inch in diameter can carry a one- or two-gram shaped charge. You can order them from a drone manufacturer in China. You can program the code to say: “Here are thousands of photographs of the kinds of things I want to target.” A one-gram shaped charge can punch a hole in nine millimeters of steel, so presumably you can also punch a hole in someone’s head. You can fit about three million of those in a semi-tractor-trailer. You can drive up I-95 with three trucks and have 10 million weapons attacking New York City. They don’t have to be very effective, only 5 or 10 percent of them have to find the target.

Russell adds that "there will be manufacturers producing millions of these weapons that people will be able to buy just like you can buy guns now, except millions of guns don’t matter unless you have a million soldiers. You need only three guys," he concludes, to write the relevant computer code and launch these drones.

This scenario can be scaled up arbitrarily to involve, say, 500 million weaponized drones packed into several hundred semi-trucks strategically positioned around the world. The result could be a global catastrophe that brings civilization to its knees — no less than a nuclear terrorism attack or an engineered pandemic caused by a designer pathogen would severely disrupt modern life. As Benjamin Wittes and Gabriella Blum put it in their captivating book "The Future of Violence," we are heading toward an era of distributed offensive capabilities that is unlike anything our species has ever before encountered.

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What sort of person might actually want to do this, though? Unfortunately, there are many types of people who would willingly destroy humanity. The list includes apocalyptic terrorists, psychopaths, psychotics, misanthropes, ecoterrorists, anarcho-primitivists, eco-anarchists, violent technophobes, militant neo-Luddites and even “morally good people” who maintain, for ethical reasons, that human suffering is so great that we would be better off not existing at all. Given the dual technology trends mentioned above, all it could take later this century is a single person or group to unilaterally end the great experiment called civilization forever.

It is considerations like these that have led risk scholars — some at top universities around the world — to specify disturbingly high probabilities of global disaster in the future. For example, the philosopher John Leslie claims that humanity has a 30 percent chance of extinction in the next five centuries. Less optimistically, an “informal” survey of experts at a conference hosted by Oxford University’s Future of Humanity Institute puts the probability of human extinction before 2100 at 19 percent. And Lord Martin Rees, co-founder of the Centre for the Study of Existential Risk at Cambridge University, argues that civilization has no better than a 50-50 likelihood of enduring into the next century.

To put this number in perspective, it means that the average American is about 4,000 times more likely to witness civilization implode than to die in an “air and space transport accident.” A child born today has a good chance of living to see the collapse of civilization, according to our best estimates.

Returning to religion, recent polls show that a huge portion of religious people believe that the end of the world is imminent. For example, a 2010 survey found that 41 percent of Christians in the U.S. believe that Jesus will either “definitely” or “probably” return by 2050. Similarly, 83 percent of Muslims in Afghanistan and 72 percent in Iraq claim that the Mahdi, Islam’s end-of-days messianic figure, will return within their lifetimes. The tragedy here, from a scientific perspective, is that such individuals are worried about the wrong apocalypse! Much more likely are catastrophes, calamities and cataclysms that cause unprecedented (and pointless) human suffering in a universe without any external source of purpose or meaning. At the extreme, an existential risk could tip our species into the eternal grave of extinction.

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In a sense, though, religious people and scientists agree: We are in a unique moment of human history, one marked by an exceptionally high probability of disaster. The difference is that, for religious people, utopia stands on the other side of the apocalypse, whereas for scientists, there is nothing but darkness. To be clear, the situation is not by any means hopeless. In fact, there is hardly a threat before us — from climate change to the sixth mass extinction, from apocalyptic terrorism to a superintelligence takeover — that is inevitable. But without a concerted collective effort to avert catastrophe, the future could be as bad as any dystopian sci-fi writer has imagined.

Parts of this article draw from my forthcoming book "Morality, Foresight, and Human Flourishing: An Introduction to Existential Risks."