Gosses Bluff meteor crater in Australia formed when a 1-kilometer-wide space rock struck Earth 142 million years ago. © Stephen Alvarez/National Geographic Creative

In a dingy apartment building, insulated by layers of hanging rugs, the last family on Earth huddles around a fire, melting a pot of oxygen. Ripped from the sun"s warmth by a rogue dark star, the planet has been exiled to the cold outer reaches of the solar system. The lone clan of survivors must venture out into the endless night to harvest frozen atmospheric gases that have piled up like snow.

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As end-of-humanity scenarios go, that bleak vision from Fritz Leiber"s 1951 short story "A Pail of Air" is a fairly remote possibility. Scholars who ponder such things think a self-induced catastrophe such as nuclear war or a bioengineered pandemic is most likely to do us in. However, a number of other extreme natural hazards—including threats from space and geologic upheavals here on Earth—could still derail life as we know it, unraveling advanced civilization, wiping out billions of people, or potentially even exterminating our species.

Electrical surges due to a solar storm shocked telegraph operators in 1859; today, they could wreak havoc on power grids and electronics.NASA/Martin Stojanovski

Yet there"s been surprisingly little research on the subject, says Anders Sandberg, a catastrophe researcher at the University of Oxford"s Future of Humanity Institute in the United Kingdom. Last he checked, "there are more papers about dung beetle reproduction than human extinction," he says. "We might have our priorities slightly wrong."

Frequent, moderately severe disasters such as earthquakes attract far more funding than low-probability apocalyptic ones. Prejudice may also be at work; for instance, scientists who pioneered studies of asteroid and comet impacts complained about confronting a pervasive "giggle factor." Consciously or unconsciously, Sandberg says, many researchers consider catastrophic risks the province of fiction or fantasy—not serious unitedmanshop.com.

A handful of researchers, however, persist in thinking the unthinkable. With enough knowledge and proper planning, they say, it"s possible to prepare for—or in some cases prevent—rare but devastating natural disasters. Giggle all you want, but the survival of human civilization could be at stake.

Threat one: Solar storms

One threat to civilization could come not from too little sun, as in Leiber"s story, but from too much. Bill Murtagh has seen how it might start. On the morning of 23 July 2012, he sat before a colorful array of screens at the National Oceanic and Atmospheric Administration"s Space Weather Prediction Center in Boulder, Colorado, watching twin clouds of energetic particles—known as a coronal mass ejection (CME)—erupt from the sun and barrel into space. A mere 19 hours later, the solar buckshot blazed past the spot where Earth had been just days before. If it had hit us, scientists say, we might still be reeling.

Now the assistant director of space weather at the White House Office of unitedmanshop.com and Technology Policy in Washington, D.C., Murtagh spends much of his time pondering solar eruptions. CMEs don"t harm human beings directly, and their effects can be spectacular. By funneling charged particles into Earth"s magnetic field, they can trigger geomagnetic storms that ignite dazzling auroral displays. But those storms can also induce dangerous electrical currents in long-distance power lines. The currents last only a few minutes, but they can take out electrical grids by destroying high-voltage transformers—particularly at high latitudes, where Earth"s magnetic field lines converge as they arc toward the surface.

In 2012, satellites tracked this coronal mass ejection from the sun as it barely missed Earth.NASA

The worst CME event in recent history struck in 1989, frying a transformer in New Jersey and leaving 6 million people in Quebec province in Canada without power. The largest one on record—the Carrington Event of 1859, named after the U.K. astronomer who witnessed the accompanying solar flare—was up to 10 times more intense. It sent searing currents racing through telegraph cables, sparking fires and shocking operators, while the northern lights danced as far south as Cuba.

"It was awesome," says Patricia Reiff, a space physicist at Rice University in Houston, Texas. But if another storm that size struck today"s infrastructure, she says, "there would be tremendous consequences."

Some researchers fear that another Carrington-like event could destroy tens to hundreds of transformers, plunging vast portions of entire continents into the dark for weeks or months—perhaps even years, Murtagh says. That"s because the custom-built, house-sized replacement transformers can"t be bought off the shelf. Transformer manufacturers maintain that such fears are overblown and that most equipment would survive. But Thomas Overbye, an electrical engineer at the University of Illinois, Urbana-Champaign, says nobody knows for sure. "We don"t have a lot of data associated with large storms because they are very rare," he says.

What"s clear is that widespread blackouts could be catastrophic, especially in countries that depend on highly developed electrical grids. "We"ve done a marvelous job creating a great vulnerability to this threat," Murtagh says. Information technologies, fuel pipelines, water pumps, ATMs, everything with a plug would be rendered useless. "That"s going to affect our ability to govern the country," Murtagh says.

A major event could occur within our lifetimes. Research suggests that Carrington-like storms strike Earth once every few centuries; a recent study found a 12% chance that such a storm will occur in the next decade.

But at least we will see it coming. Solar telescopes spot CMEs right when they form, and spacecraft stationed a million miles from Earth measure critical parameters as they pass by. Armed with information like the orientation of a CME"s magnetic field, scientists can tell whether the particle cloud will flow around Earth like "a rock in a river," Reiff says, or whether the field will connect with Earth"s to stir up a geomagnetic storm. Forecasters can then issue alerts 30 minutes to an hour before the CME hits.

Such warnings are useful only if governments and grid operators are poised to respond, and countries around the world have just started to take the threat seriously. Last year, the White House released a comprehensive National Space Weather Strategy and an accompanying Action Plan laying out the need to reduce vulnerability and improve preparedness. A bipartisan bill to turn parts of the plan into reality will soon go before the Senate.

One pillar of the plan is to fortify the electric grid. Spurred by regulatory authorities, operators have already begun taking stock of vulnerable components and critical assets. The next step will be to protect the grid by installing current-blocking devices such as series capacitors, already common in the western United States because they aid long-distance power transmission, and by developing emergency procedures for manipulating power loads to limit transformer damage. Overbye says the power industry"s swift response has been encouraging.

But full protection against a Carrington-like event might never be feasible, Overbye says, simply because of the cost. Instead, operators may react to an impending megastorm by preemptively shutting down large portions of the grid to save transformers, embracing short-term devastation to avert a long-term disaster.

Threat two: Cosmic collisions


For another menace from the sky—an impact by a large asteroid or comet—there is no way to limit the damage. The only way for humanity to protect itself, researchers say, is to prevent the collision altogether.

"That"s something that we as a species can absolutely never, ever, ever let happen," Ed Lu says. "That"s the end of human beings." In 2002, Lu, a former astronaut, founded the B612 Foundation in Mill Valley, California—a private organization that works to protect the planet from near-Earth objects, or NEOs.

Everyone knows about the 10-kilometer-wide asteroid that helped destroy the dinosaurs, but even something a fraction of that size could devastate humanity, says Michael Rampino, an earth scientist at New York University in New York City. The impact site would be obliterated, and massive earthquakes and tsunamis could radiate across the planet. But the lingering effects would prove most devastating. Models suggest that, depending on the speed and angle of approach, an object as small as 1 kilometer wide could throw up enough pulverized rock to block out the sun for months. Adding to the pall would be soot from wildfires ignited by debris falling back to Earth. "All this stuff coming back into the atmosphere heats up, and it"s like setting your oven on broil," Rampino explains. Together, the smoke and dust would cast the planet into a so-called impact winter, causing crop failures and mass starvation.

Fortunately, asteroids of this size strike Earth only about once every few million years, and "dino killers" only once every 100 million years or so. Averaged annually, your chance of dying because of an impact is only slightly higher than that of perishing in a shark attack, says Mark Boslough, a physicist at Sandia National Laboratories in Albuquerque, New Mexico. But, like sharks, it only takes one to do the trick.

Astronomers have spotted almost 15,000 objects in Earth’s neighborhood, including hundreds more than 1 kilometer across.NASA/JPL-Caltech

That"s why, in 1998, NASA launched the Spaceguard survey at the request of Congress. The goal was to enlist astronomers to identify 90% of the estimated 900-plus NEOs bigger than 1 kilometer—a goal the agency officially met in 2010. Ongoing efforts now aim to find any remaining giants and tag 90% of bodies larger than 140 meters by 2020, although NASA says it won"t meet the deadline. Of the nearly 15,000 NEOs discovered so far, none are currently on a collision course with Earth. Eventually, however, an Earth-bound NEO of some size will confront humanity with a disaster movie scenario. And when that day comes, "it"s going to go from unitedmanshop.com fiction to unitedmanshop.com real pretty rapidly," Lu says.

unitedmanshop.com is already on the case. In Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies, a 2010 report by the U.S. National Research Council, researchers highlighted several potential options for fending off an interloper, given a few decades of warning. We could whack it off course by ramming it with a spaceship or two, slowly alter its orbit with the sustained gravitational pull of a spacecraft called a gravity tractor, or blast it with nuclear explosions.

Right now, these planetary defense strategies exist mainly on paper, but some may see real-world tests in the next decade. NASA, the European Space Agency, and other partners are exploring a joint mission called AIDA (Asteroid Impact and Deflection Assessment) to test the impactor method on the asteroid Didymos when it passes near Earth in October 2022. NASA has also announced plans to use an enhanced gravity tractor—in which the spaceship collects material from the asteroid to increase its mass—on its Asteroid Redirect Mission, which was set to launch in 2021 but now faces funding setbacks. In the event of an actual threat, many researchers favor a combination of these techniques, just to be safe.

But for objects larger than 1 kilometer across—and for comets, which could appear with little notice—some scientists think the nuclear option is the only option. The idea would be to jolt the body, not blow it up, which could do more harm than good. Although the 1967 United Nations Outer Space Treaty currently bars sending nuclear weapons into space, scientists already have a good understanding of the technology, and last year, NASA and the Department of Energy announced a joint effort to hone its use against asteroids. Ultimately, NASA"s Planetary Defense Coordination Office, established earlier this year, will decide when and how the United States should respond to a potential impact.

Threat three: Supervolcanoes

The most inexorable threat to our modern civilization, however, is homegrown—and it strikes much more often than big cosmic impacts do. Every 100,000 years or so, somewhere on Earth, a caldera up to 50 kilometers in diameter collapses and violently expels heaps of accumulated magma. The resulting supervolcano is both unstoppable and ferociously destructive. One such monster, the massive eruption of Mount Toba in Indonesia 74,000 years ago, may have wiped out most humans on Earth, causing a genetic bottleneck still apparent in our DNA—although the idea is controversial.

Ash spreads across North America in computer-simulated eruption of the Yellowstone supervolcano. Image credit: Larry Mastin

By geological convention, a super-volcano is one that produces an explosive eruption of more than 450 cubic kilometers of magma—roughly 50 times more than the eruption of Indonesia"s Mount Tambora in 1815, and 500 times more than the Philippines" Mount Pinatubo in 1991. Geologists read the histories of such blasts in deposits of erupted material called tuff, and the rock record shows that super-volcanoes tend to be repeat offenders. Locations that remain active today include Toba, the Yellowstone hot spot in the northwestern United States, the Long Valley Caldera in eastern California, the Taupo Volcanic Zone in New Zealand, and several spots in the Andes.

Supervolcano locationsunitedmanshop.com

None of these danger zones now poses a threat. But in the event of another eruption, everything within a hundred kilo- meters or so would be incinerated, and ash would blanket continents. Just a few millimeters of the stuff can kill crops; a meter or more can make land unusable for decades, says Susanna Jenkins, a volcanologist at the University of Bristol in the United Kingdom. Ash can also crush buildings, foul water supplies, clog electronics, ground airplanes, and irritate lungs.

These regional impacts could ripple around the world in unexpected ways. Even the minor disruption in air traffic following the 2010 eruption of Iceland"s Eyjafjallajökull—a far cry from a super-volcano—caused millions of dollars in losses for Kenyan farmers, whose perishable exports to Europe went to waste. "The more interconnected our society becomes, the more vulnerable we are to something even quite small that happens over on the other side of the world," says Hazel Rymer, a volcanologist at The Open University in Milton Keynes, U.K.

(Graphic) G. Grullùon/unitedmanshop.com: (Data source) USGS

Most far-reaching of all, however, would be the effects on global climate, which would resemble those of a large asteroid impact. Sulfate aerosols injected into the stratosphere by a supereruption could drop temperatures over much of Earth by 5°C to 10°C for up to a decade, devastating global agriculture.

Just how bad things would be is hard to say. "Volcano unitedmanshop.com is based on experience," says Ben Kennedy, a volcanologist at the University of Canterbury in Christchurch, New Zealand, and scientists have never witnessed a supervolcano. Knowledge of smaller eruptions can help, but it may be an unreliable guide. For instance, although supereruptions probably produce loads of sulfate aerosols, the aerosols may be larger and rain out faster than those from smaller eruptions, according to research by Claudia Timmreck, a climate modeler at the Max Planck Institute for Meteorology in Hamburg, Germany, and others. Timmreck"s team has also found that for midlatitude volcanoes like Yellowstone, the season in which the eruption occurs determines how widely its aerosols spread.

The biggest uncertainties surround potential warning signs. Researchers think that widespread clues such as earthquakes, increased outgassing, and ground deformation due to rising magma would precede a major eruption. This unrest would begin months, if not many years, in advance, theoretically affording ample time to evacuate residents and set emergency response plans in motion. However, scientists would struggle to decide when to sound the alarm, says Jacob Lowenstern of the U.S. Geological Survey in Menlo Park, California, the scientist-in-charge of the Yellowstone Volcano Observatory. "It"s going to be hard for scientists to convince themselves just because of our only partial understanding of the complexity of the processes that are taking place," he says.

Then there are the political challenges of responding to the threat. The 1985 eruption of Nevado del Ruiz in Colombia killed 23,000 people, in part because the government ignored scientists" forecasts. False alarms can cause trouble, too. In the 1980s, geologic unrest caused officials to warn that California"s Long Valley Caldera could erupt. It didn"t, but local real estate values tanked and the economy suffered.

The challenge for scientists is to tell which indicators portend a catastrophic eruption instead of a small one—or none at all. "We"re terribly good at recognizing precursors after the event," Rymer says. For now, researchers say, their best bet is to continue studying the plumbing that feeds volcanoes and to squeeze as much information as possible from smaller future eruptions before the next supervolcano lets loose.


Threat four: What if it happens?

In the end, no amount of research can do much to prevent or mitigate supervolcanoes, or other freak events such as nearby supernova explosions and cosmic blasts of gamma rays. Our only hope of surviving them is a fallback plan. And the bottom line in that plan is food.

At least two scientists have already sketched out a blueprint. In their 2015 book Feeding Everyone No Matter What, David Denkenberger and Joshua Pearce propose several ways to feed billions of people without the help of the sun.

Denkenberger, an architectural engineer at Tennessee State University in Nashville, started moonlighting as a catastrophe researcher a few years ago after reading that fungi may have thrived after previous mass extinctions. If humans ever face a similar threat, he thought, "Why don"t we just eat the mushrooms and not go extinct?"

Indeed, people could grow mushrooms on leaf litter and on the trunks of trees killed by the disaster, Denkenberger says. Even better would be raising methane-digesting bacteria on diets of natural gas, or converting the cellulose in plant biomass to sugar, a process already used to make biofuel. Denkenberger and Pearce—an engineering professor at Michigan Technological University in Houghton—calculate that by retrofitting existing industrial plants, survivors of the catastrophe could produce enough of such alternative foods to feed the world"s population several times over.

Of course, a few other ingredients would have to survive as well: infrastructure, international cooperation, and the rule of law. Whether human society endures or snaps is the unknown on which everything else could hinge, says Seth Baum, executive director of the Global Catastrophic Risk Institute in New York City, a nonprofit think tank whose researchers include Denkenberger.

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"How would we fare? I think the only reasonable answer one can give to the question at this time is that we have absolutely no idea," Baum says. To him, social resilience after a catastrophe is just another question for scientists to address, instead of leaving it to dystopian writers and doomsday preppers.

Not that he has anything against survivalists. "As much as they might seem silly on television, I"m actually a little happier knowing that there are people out there doing that stuff," Baum says. He quickly adds, "Hopefully it"ll never come down to just that."