DAILY EXPRESS
Elements of Surprise
by Gregg Easterbrook
Only at TNR Online
Post date: 01.07.05
Nature does not know best," the ecologist Rene Dubos--best known for coining the expression "think globally, act locally"--once wrote. Dubos's worry was that the environmental movement was beginning to depict the natural condition as Edenic and benign, when in fact nature is a mass murderer. The Indian Ocean tsunami tragedy ought to be seen as a reminder that the Earth can be a very dangerous place to live.
Set aside disease as a concern, though disease has been, since humanity appeared, its greatest adversary. An estimated 60 million men and women were killed by wars in the twentieth century, a horrible accounting; in the same period, at least 1 billion people died owing to disease. (The figure is for early deaths from communicated disease, not deaths in old age from degenerative disease.) But progress against disease has been steady--vaccines, antibiotics, and better public sanitation have caused most rates of disease to go into decline. Even taking into account emergencies such as AIDS in Africa and Asia, it seems reasonable to hope that through the twenty-first century, disease will continue to decrease as a cause of death, even in the developing world. Future generations may view infectious illness as a relatively minor worry. The trends here have turned positive because disease may be opposed by technology and medical knowledge.
Natural disasters, on the other hand, cannot be immunized against and perhaps cannot be stopped. Some 240,000 dead in the 1976 China earthquake; about 300,000 killed by the 1970 Bangladesh cyclone; some 30,000 killed by the 1954 Yangtze River flood; perhaps 110,000 dead in the 1948 Soviet Union earthquake. Productivity and planning might reduce the harm done by natural disasters--anti-earthquake building engineering, for example. But unlike in the realm of disease, where it is realistic to forecast that people can outsmart the underlying problem, there is no foreseeable technology that could prevent earthquakes, hurricanes, or similar deadly expressions of natural energy. We might eventually think our way out of letting microbes make us sick; we're not going to think our way out of weather and tectonic forces.
Now consider that natural disasters of recent centuries have been mild by the standards of history. In fact, it may be that one reason human civilization has prospered during what academics now call the "common era" is that natural disasters have been relatively few, the 1755 Lisbon earthquake and other horrible events notwithstanding. Most likely it is sheer chance that catastrophic natural harm has been rare in the common era, and though humanity's good luck may last, our good luck could easily change to bad. More important, many natural disasters of the past have been far worse than anything that has occurred since writing was invented. That may be another reason civilization is here--mega-disasters have not happened "recently," in geologic terms. That may not last, either.
Most people are aware, at least, that asteroid and comet strikes happened in the far past and might happen again: Let's leave that topic for last. Consider first that the civilization centuries have been almost entirely spared the ravages of volcanism. Pompeii was destroyed by an eruption in the year 79, and much of the world had a frigid winter following the Krakatau volcanic explosion in Indonesia in 1883. But these were children's sparklers compared to eruptions of the past. A mega-volcano called Toba exploded near Sumatra about 73,000 years ago. All life was devastated for dozens of miles in all directions--devastation equivalent to the explosions of multiple nuclear bombs. The Toba eruption pumped an estimated five billion tons of sulfuric acid into the atmosphere, which would have caused global acid rain corrosive enough to singe the flesh. Evidence suggests Toba put so much sun-blocking ash into the atmosphere that global temperatures fell nine degrees Fahrenheit for several years, and nine degrees is the difference between current climate and the climate of the Pleistocene ice age. The Toba mega-eruption probably caused mass deaths across the world, and a similar mega-eruption might kill huge numbers today.
Going further back, there have been entire eras of mega-volcanism. Much of India sits on a basalt formation geologists call the Deccan Traps. Hundreds or thousands of huge volcanoes are once believed to have erupted in this region and to have kept erupting for many millennia--not single eruptions like in the movies, or single explosions such as Mount Saint Helens in 1980, but entire volcanic regions continuously active for hundreds or thousands of years. An even longer era of global volancism created the huge basalt formation called the Siberian Traps, which forms most of the surface of Siberia. Each of these volcanic eras would have caused an ice age, choking global smog, and global acid rain that burns the skin.
The Deccan Traps occurred about 65 million years ago--the same time the dinosuars fell extinct. Some researchers think the comet usually blamed for the dinosaurs' disappearance struck with such violence that it cracked tectonic plates, setting in motion unimaginable seismic upheaval; other researchers think the volcanoes themselves were the cause of the mass extinction, the comet strike of the same period a coincidence. The Siberian Traps occurred about 250 million years ago, and coincided with the "Permian extinction," the disappearance of 98 percent of known life forms--a much worse event than the extinction of the dinosaur period. And don't think volcanos bursting everywhere at once could only have happened in the primordial mists of the young Earth. Our world is 4.5 billion years old; that means the Siberian volcanos occurred when the planet was 94 percent of its present age, and the Deccan volcanoes occurred when the planet was 99 percent of its present age. There's no reason to believe that the geologic stresses that cause volcansim are in decline--Earth's core is thought to have lost only a fraction of its heat since the planet was formed. If regional volcanism began in our era, for parts of the world the effects would be similar to general nuclear war.
Next is the possibility of a magnetic field collapse, which must not be dismissed just because this is a subject of Internet chat rooms. It is believed that on a cyclical basis the Earth's magnetic field fizzles out, then the poles reverse--compasses would point south--then the field regenerates. What causes these reversals is a mystery. (The magnetic field is projected by spinning molten metal in Earth's core, about which almost nothing is known.) Magnetic effects preserved in a magma flow in Oregon suggest that a field reversal happened 16 million years ago, but some researchers speculate that Earth's polarity may change as often as every 10,000 years. Recent data shows that Earth's magnetic field has weakened about 10 percent since measurements began in 1845: whether this is natural variation or presages a field collapse is unknown.
What would happen during a magnetic field reversal? Charged bodies of underground magma might become repelled by areas that once attracted them, causing earthquakes and other seismic disturbances--it's possible that field reversals are what ignited the Siberian and Deccan volcanic eras. Any field collapse would play havoc with electronics. More important, Earth's magnetic field repels some forms of solar and cosmic rays. If the field faltered, radiation on the surface would increase, killing animals, causing cancer in people, and perhaps causing global crop failures. (Many plants are sensitive to ultraviolet rays.)
Another natural disaster that has not occurred during the era of writing is the "nearby" supernova explosion. When stars explode, they emit strong gamma rays, the most dangerous form of "hard" radiation. Astronomers estimate there is a star explosion about once per century in the Milky Way, most very distant in the galactic center. We're much of the way to the galactic rim, so supernovae at the galactic center don't affect Earth. But a "nearby" supernova explosion might bathe the Earth in lethal radiation, in addition to blowing off much of the stratospheric ozone layer, which provides protection against routine solar ultraviolet rays.
The most recent "nearby" supernova, Cassiopeia A, occurred in the year 1680. (Occurred in this sense means when the light reached Earth; the detonation came long before.) Cassiopeia A was about 11,000 light years away and had little impact on our biosphere. But 340,000 years ago, a supernova called Geminga, just 180 light-years away--much too close--was bright enough to rival the full moon and is believed to have blown off much of the ozone layer, while killing huge numbers of mammals, including many of our ancestors. Another supernova, Vela, detonated 11,300 years ago and was about 1,500 light years away, close enough to harm Earth. Past mass extinctions, today puzzling, may someday turn out to have been caused by "nearby" star detonations. If you follow archeology, you know that about 11,000 years ago, many large mammals of North America and Eurasia fell extinct--the wooly mammoth, the giant sloth, the glyptodon (an armadillo three times the size of a person). There's a lively archeological debate about whether these extinctions were caused by climate change or by people armed with new hunting tools such as bow and arrow. Maybe the extinctions were caused by a "nearby" supernova--and a "nearby" supernova might bathe our world in lethal radiation at, oh, pretty much any moment.
Now, to asteroid and comet strikes. The Chicxulub comet or meteorite, which left a 186-mile-long mark on Mexico's Yucatan Peninsula, is now thought to have triggered the instant ice age that killed the dinosaurs. But that was 65 million years ago. These things could only happen in the primordial mist, right? About 10,000 years ago, something enormous struck the Argentine pampas, obliterating a significant chunk of the South American ecology with a force thought to be 18,000 times that of the Hiroshima bomb. In the year 535, multiple medium-sized meteorite strikes around the world caused several years of cruel winters, and may have pushed Europe, always on the borderline of cold, into its Dark Ages. In 1908, a rock or comet about 250 feet across hit Tunguska, Siberia, detonating with a force estimated at 700 times the power of the Hiroshima blast. If today, a Tunguska-sized object hit a major city, the result would be the same as a strike from the largest nuclear bomb.
Estimates hold that perhaps 500,000 asteroids roughly the size of the Tunguska rock wander in the general area of Earth's orbit, along with perhaps 1,000 asteroids big enough to cause a Chicxulub-class impact. Comets originate at the boundary of the solar system, about which little is known, but there are believed to be billions of comets in the outer solar system, and what "perturbs" them and causes them to fall inward toward the planets is conjectural. No near-Earth asteroid or distant comet is known to be on a collision course with our world. But many have hit in the past, and more are certain to hit in the future. Astronomers of the modern era have seen dangerous-sized rocks strike the Moon. If asteroid strikes are essentially random, it could be millennia before one happens again, or large numbers of strikes could commence tomorrow.
I've left rocks-from-space for last because, unlike super-volcanoes or supernovas or the Earth's magnetic field, rocks are something we can build a defense against. Right now, NASA has nothing that could be used to stop a dangerous asteroid or comet approaching Earth. Such systems are imaginable; building them would require huge amounts of money and years or decades of effort. But what does the public get from the current space shuttle-space station project, on which taxpayers spend about $10 billion per year? Almost nothing; tangible benefits from the space shuttle and space station are hard to name, other than make-work for aerospace contractors and the astronaut corps. If the shuttle and space station were shut down and the capital from these programs diverted to an asteroid defense--enduring the inevitable Leno-Letterman ridicule--within a decade or two, the world might be able to protect itself from one of the worst of all natural disasters.
An asteroid defense would be a step, at least, toward diminishing the risk we wake up to a natural event inexpressibly worse than the Indian Ocean tsunami. Nature has the means to wipe us out. The tsunami is not just a humanitarian horror; it is a reminder that we should protect ourselves when we can.
Gregg Easterbrook is a senior editor at TNR and a visiting fellow at the Brookings Institution.
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