20 Ways The World Could End

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Human-Triggered Disasters

9 Global warming The Earth is getting warmer, and scientists mostly agree that humans bear some blame. It's easy to see how global warming could flood cities and ruin harvests. More recently, researchers like Paul Epstein of Harvard Medical School have raised the alarm that a balmier planet could also assist the spread of infectious disease by providing a more suitable climate for parasites and spreading the range of tropical pathogens (see #8). That could include crop diseases which, combined with substantial climate shifts, might cause famine. Effects could be even more dramatic. At present, atmospheric gases trap enough heat close to the surface to keep things comfortable. Increase the global temperature a bit, however, and there could be a bad feedback effect, with water evaporating faster, freeing water vapor (a potent greenhouse gas), which traps more heat, which drives carbon dioxide from the rocks, which drives temperatures still higher. Earth could end up much like Venus, where the high on a typical day is 900 degrees Fahrenheit. It would probably take a lot of warming to initiate such a runaway greenhouse effect, but scientists have no clue where exactly the tipping point lies.

10 Ecosystem collapse Images of slaughtered elephants and burning rain forests capture people's attention, but the big problem— the overall loss of biodiversity— is a lot less visible and a lot more serious. Billions of years of evolution have produced a world in which every organism's welfare is intertwined with that of countless other species. A recent study of Isle Royale National Park in Lake Superior offers an example. Snowy winters encourage wolves to hunt in larger packs, so they kill more moose. The decline in moose population allows more balsam fir saplings to live. The fir trees pull carbon dioxide out of the atmosphere, which in turn influences the climate. It's all connected. To meet the demands of the growing population, we are clearing land for housing and agriculture, replacing diverse wild plants with just a few varieties of crops, transporting plants and animals, and introducing new chemicals into the environment. At least 30,000 species vanish every year from human activity, which means we are living in the midst of one of the greatest mass extinctions in Earth's history. Stephen Kellert, a social ecologist at Yale University, sees a number of ways people might upset the delicate checks and balances in the global ecology. New patterns of disease might emerge (see #8), he says, or pollinating insects might become extinct, leading to widespread crop failure. Or as with the wolves of Isle Royale, the consequences might be something we'd never think of, until it's too late.

11 Biotech disaster While we are extinguishing natural species, we're also creating new ones through genetic engineering. Genetically modified crops can be hardier, tastier, and more nutritious. Engineered microbes might ease our health problems. And gene therapy offers an elusive promise of fixing fundamental defects in our DNA. Then there are the possible downsides. Although there is no evidence indicating genetically modified foods are unsafe, there are signs that the genes from modified plants can leak out and find their way into other species. Engineered crops might also foster insecticide resistance. Longtime skeptics like Jeremy Rifkin worry that the resulting superweeds and superpests could further destabilize the stressed global ecosystem (see #9). Altered microbes might prove to be unexpectedly difficult to control. Scariest of all is the possibility of the deliberate misuse of biotechnology. A terrorist group or rogue nation might decide that anthrax isn't nasty enough and then try to put together, say, an airborne version of the Ebola virus. Now there's a showstopper.

12 Particle accelerator mishap Theodore Kaczynski, better known as the Unabomber, raved that a particle accelerator experiment could set off a chain reaction that would destroy the world. Surprisingly, many sober-minded physicists have had the same thought. Normally their anxieties come up during private meetings, amidst much scribbling on the backs of used envelopes. Recently the question went public when London's Sunday Times reported that the Relativistic Heavy Ion Collider (RHIC) on Long Island, New York, might create a subatomic black hole that would slowly nibble away our planet. Alternately, it might create exotic bits of altered matter, called strangelets, that would obliterate whatever ordinary matter they met. To assuage RHIC's jittery neighbors, the lab's director convened a panel that rejected both scenarios as pretty much impossible. Just for good measure, the panel also dismissed the possibility that RHIC would trigger a phase transition in the cosmic vacuum energy (see #3). These kinds of reassurances follow the tradition of the 1942 "LA-602" report, a once-classified document that explained why the detonation of the first atomic bomb almost surely would not set the atmosphere on fire. The RHIC physicists did not, however, reject the fundamental possibility of the disasters. They argued that their machine isn't nearly powerful enough to make a black hole or destabilize the vacuum. Oh, well. We can always build a bigger accelerator.

13 Nanotechnology disaster Before you've even gotten the keyboard dirty, your home computer is obsolete, largely because of incredibly rapid progress in miniaturizing circuits on silicon chips. Engineers are using the same technology to build crude, atomic-scale machines, inventing a new field as they go called nanotechnology. Within a few decades, maybe sooner, it should be possible to build microscopic robots that can assemble and replicate themselves. They might perform surgery from inside a patient, build any desired product from simple raw materials, or explore other worlds. All well and good if the technology works as intended. Then again, consider what K. Eric Drexler of the Foresight Institute calls the "grey goo problem" in his book Engines of Creation, a cult favorite among the nanotech set. After an industrial accident, he writes, bacteria-sized machines, "could spread like blowing pollen, replicate swiftly, and reduce the biosphere to dust in a matter of days." And Drexler is actually a strong proponent of the technology. More pessimistic souls, such as Bill Joy, a cofounder of Sun Microsystems, envision nano-machines as the perfect precision military or terrorist tools.

14 Environmental toxins From Donora, Pennsylvania, to Bhopal, India, modern history abounds with frightening examples of the dangers of industrial pollutants. But the poisoning continues. In major cities around the world, the air is thick with diesel particulates, which the National Institutes of Health now considers a carcinogen. Heavy metals from industrial smokestacks circle the globe, even settling in the pristine snows of Antarctica. Intensive use of pesticides in farming guarantees runoff into rivers and lakes. In high doses, dioxins can disrupt fetal development and impair reproductive function— and dioxins are everywhere. Your house may contain polyvinyl chloride pipes, wallpaper, and siding, which belch dioxins if they catch fire or are incinerated. There are also the unknown risks to think about. Every year NIH adds to its list of cancer-causing substances— the number is up to 218. Theo Colburn of the World Wildlife Fund argues that dioxins and other, similar chlorine-bearing compounds mimic the effects of human hormones well enough that they could seriously reduce fertility. Many other scientists dispute her evidence, but if she's right, our chemical garbage could ultimately threaten our survival.

Willful Self-Destruction
15 Global war Together, the United States and Russia still have almost 19,000 active nuclear warheads. Nuclear war seems unlikely today, but a dozen years ago the demise of the Soviet Union also seemed rather unlikely. Political situations evolve; the bombs remain deadly. There is also the possibility of an accidental nuclear exchange. And a ballistic missile defense system, given current technology, will catch only a handful of stray missiles— assuming it works at all. Other types of weaponry could have global effects as well. Japan began experimenting with biological weapons after World War I, and both the United States and the Soviet Union experimented with killer germs during the cold war. Compared with atomic bombs, bioweapons are cheap, simple to produce, and easy to conceal. They are also hard to control, although that unpredictability could appeal to a terrorist organization. John Leslie, a philosopher at the University of Guelph in Ontario, points out that genetic engineering might permit the creation of "ethnic" biological weapons that are tailored to attack primarily one ethnic group (see #11).

16 Robots take over People create smart robots, which turn against us and take over the world. Yawn. We've seen this in movies, TV, and comic books for decades. After all these years, look around and still— no smart robots. Yet Hans Moravec, one of the founders of the robotics department of Carnegie Mellon University, remains a believer. By 2040, he predicts, machines will match human intelligence, and perhaps human consciousness. Then they'll get even better. He envisions an eventual symbiotic relationship between human and machine, with the two merging into "postbiologicals" capable of vastly expanding their intellectual power. Marvin Minsky, an artificial-intelligence expert at MIT, foresees a similar future: People will download their brains into computer-enhanced mechanical surrogates and log into nearly boundless files of information and experience. Whether this counts as the end of humanity or the next stage in evolution depends on your point of view. Minsky's vision might sound vaguely familiar. After the first virtual-reality machines hit the marketplace around 1989, feverish journalists hailed them as electronic LSD, trippy illusion machines that might entice the user in and then never let him out. Sociologists fretted that our culture, maybe even our species, would whither away. When the actual experience of virtual reality turned out to be more like trying to play Pac-Man with a bowling ball taped to your head, the talk died down. To his credit, Minsky recognizes that the merger of human and machine lies quite a few years away.

17 Mass insanity While physical health has improved in most parts of the world over the past century, mental health is getting worse. The World Health Organization estimates that 500 million people around the world suffer from a psychological disorder. By 2020, depression will likely be the second leading cause of death and lost productivity, right behind cardiovascular disease. Increasing human life spans may actually intensify the problem, because people have more years to experience the loneliness and infirmity of old age. Americans over 65 already are disproportionately likely to commit suicide. Gregory Stock, a biophysicist at the University of California at Los Angeles, believes medical science will soon allow people to live to be 200 or older. If such an extended life span becomes common, it will pose unfathomable social and psychological challenges. Perhaps 200 years of accumulated sensations will overload the human brain, leading to a new kind of insanity or fostering the spread of doomsday cults, determined to reclaim life's endpoint. Perhaps the current trends of depression and suicide among the elderly will continue. One possible solution— promoting a certain kind of mental well-being with psychoactive drugs such as Prozac— heads into uncharted waters. Researchers have no good data on the long-term effects of taking these medicines.

A Greater Force Is Directed Against Us
18 Alien invasion At the SETI Institute in Mountain View, California, a cadre of dedicated scientists sifts through radio static in search of a telltale signal from an alien civilization. So far, nothing. Now suppose the long-sought message arrives. Not only do the aliens exist, they are about to stop by for a visit. And then . . . any science-fiction devotee can tell you what could go wrong. But the history of human exploration and exploitation suggests the most likely danger is not direct conflict. Aliens might want resources from our solar system (Earth's oceans, perhaps, full of hydrogen for refilling a fusion-powered spacecraft) and swat us aside if we get in the way, as we might dismiss mosquitoes or beetles stirred up by the logging of a rain forest. Aliens might unwittingly import pests with a taste for human flesh, much as Dutch colonists reaching Mauritius brought cats, rats, and pigs that quickly did away with the dodo. Or aliens might accidentally upset our planet or solar system while carrying out some grandiose interstellar construction project. The late physicist Gerard O'Neill speculated that contact with extraterrestrial visitors could also be socially disastrous. "Advanced western civilization has had a destructive effect on all primitive civilizations it has come in contact with, even in those cases where every attempt was made to protect and guard the primitive civilization," he said in a 1979 interview. "I don't see any reason why the same thing would not happen to us."

19 Divine intervention Judaism has the Book of Daniel; Christianity has the Book of Revelation; Islam has the coming of the Mahdi; Zoroastrianism has the countdown to the arrival of the third son of Zoroaster. The stories and their interpretations vary widely, but the underlying concept is similar: God intervenes in the world, bringing history to an end and ushering in a new moral order. Apocalyptic thinking runs at least back to Egyptian mythology and right up to Heaven's Gate and Y2K mania. More worrisome, to the nonbelievers at least, are the doomsday cults that prefer to take holy retribution into their own hands. In 1995, members of the Aum Shinri Kyo sect unleashed sarin nerve gas in a Tokyo subway station, killing 12 people and injuring more than 5,000. Had things gone as intended, the death toll would have been hundreds of times greater. A more determined group armed with a more lethal weapon— nuclear, biological, nanotechnological even— could have done far more damage.

20 Someone wakes up and realizes it was all a dream Are we living a shadow existence that only fools us into thinking it is real? This age-old philosophical question still reverberates through cultural thought, from the writings of William S. Burrows to the cinematic mind games of The Matrix. Hut of the Institute of Advanced Studies sees an analogy to the danger of the collapse of the vacuum. Just as our empty space might not be the true, most stable form of the vacuum, what we call reality might not be the true, most stable form of existence. In the fourth century B.C., Taoist philosopher Chuang Tzu framed the question in more poetic terms. He described a vivid dream. In it, he was a butterfly who had no awareness of his existence as a person. When he awoke, he asked: "Was I before Chuang Tzu who dreamt about being a butterfly, or am I now a butterfly who dreams about being Chuang Tzu?"
with additional research by Diane Martindale


The folks at the Bulletin of Atomic Scientists maintain the famed "Doomsday Clock at www.bullatomsci.org/clock.html


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