The last word: What are the odds?

Certain natural and man-made events that loom on the near horizon have the power to completely transform our world. Below, the editors of Scientific American contemplate a handful of possibilities and rate their likelihood of happening by 2050. Some may bring to mind long-standing dystopian visions—species extinction, war-waging machines, Frankenstein’s monster. Yet the best thinking today suggests that many events that have been widely feared will not unfold as popular conceptions have predicted they will.

Synthetic life

Odds: Almost certain

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A scientist adds a few chemical compounds to a bubbling beaker and gives it a swirl. Subtle reactions occur, and, lo and behold, a new life form assembles itself, ready to go forth and prosper.

Such is the popular imagining of synthetic biology, or life created in the lab. But even after last month’s announcement that researchers at the J. Craig Venter Institute had successfully booted up a cell using a synthetically created genome, scientists remain far from understanding the basic processes that could allow inert, undirected compounds to assemble into living, self-replicating cells. Most scientists working in synthetic biology today are exploring the effects of modifying only parts of existing genetic codes. In fact, manipulating genomes has become so widespread that even high schoolers do it.

A major aim of such work is to bring the principles of large-scale engineering to biology. Imagine a world where bamboo is programmed to grow into a chair, or where self-assembling solar panels (otherwise known as leaves) feed electricity to houses. Reprogrammed bacteria might even be able to invade our bodies to heal, acting as an army of living doctors inside us.

“In principle, everything that is manufactured could be manufactured with biology,” argues George M. Church, a geneticist and technology developer at Harvard Medical School. It is already happening on a small scale: Enzymes from high-temperature microbes used in laundry detergent have been re-engineered to perform in cold water, thereby saving energy.

With great promise comes great risk, of course—namely in the form of modified organisms escaping the lab. Most such creations today are too ungainly to survive in the wild. For more sophisticated creations in the future, synthetic biologists expect that various safeguards would have to be instituted, such as including a new kind of self-destruct sequence in the genetic code.

Asteroid collision

Odds: Unlikely

The good news is that no giant asteroids appear poised to rewrite history anytime soon. The bad news is that we can expect that in the next 200 years, a small space rock will burst into the atmosphere with enough force to devastate a small city.

NASA classifies any asteroid or comet that comes within 195 million kilometers of

the planet as a near-Earth object, or NEO. Of the estimated 1,100 that are one kilometer or more in diameter, 85 percent have been spotted, and none of those will collide with Earth.

The bigger threat now, however, involves smaller rocks, according to a National Research Council report released earlier this year. These asteroids and comets are too small to bring about an Armegeddon—as did the 10-kilometer-wide asteroid that wiped out the dinosaurs—but any that are 140 meters or more could still deliver an impact energy of 300 megatons of TNT.

Researchers concerned about the greatest risk are thinking even smaller, because the most likely NEO scenario is a 30- to 50-meter “city killer,” a fireball that would detonate in the atmosphere. The most famous of such devastating “airbursts” occurred in 1908 over Tunguska, Siberia, an event that flattened an area the size of London. The famous Meteor Crater in Barringer, Ariz., resulted from a meteorite in this size category.

The NRC report estimates that 25-meter airbursts occur every 200 years. Most explode over oceans, where the direct risk to life is low but where the initiation of a tsunami is possible.

But what would we do if we spotted an NEO with our name on it? For these smaller, city-detroying rocks the choices are limited, perhaps restricted to evacuation.

Nuclear exchange

Odds: Unlikely

The threat of global nuclear annihilation has been greatly reduced by the end of the Cold War and ongoing arms-control efforts by the U.S., Russia, and other countries. But rogue nations and continued tensions make a local exchange of nuclear firepower all too real a possibility.

A single detonation could cause horrible death in several ways. The Hiroshima blast generated supersonic wind speeds that crushed concrete buildings near ground zero. Heat from the blast scorched to death anyone within one kilometer. People many kilometers away eventually succumbed to radiation poisoning and cancer.

Global effects, however, would not happen unless dozens of bombs exploded, as might occur in an exchange between Pakistan and India. In modeling the effects, scientists have assumed that those nations would unload their entire arsenals, so that about 100 Hiroshima bombs would go off.

Aside from the 20 million killed in the war, many outside the conflict would perish over time. That is because the blasts would throw 5 million metric tons of soot into the upper atmosphere. Within two months they would blanket the planet. Darkened skies would rob plants of sunlight and disrupt the food chain for 10 years. The resulting famine would kill the 1 billion people who now survive on marginal food supplies.

Self-aware robots

Odds: Likely

Today’s computers and robots are for the most part designed to perform specific tasks under known conditions. Tomorrow’s machines, though, could have more autonomy. They should be able to self-replicate, teach themselves, and adapt to different conditions. “As the kinds of tasks that we want machines to perform become more complex, the more we need them to take care of themselves,” says Hod Lipson, a mechanical and computer engineer at Cornell University. As machines get better at learning how to learn, he says, “I think that leads down the path to consciousness and self-awareness.”

Once a machine can understand its own existence and construction, it should be able to design an improvement for itself. That will be a “critical measurement of when things get interesting,” says Will Wright, creator of the SimCity videogames and co-founder of the Berkeley, Calif.–based robotics workshop the Stupid Fan Club. Improvements would be manifested in subsequent generations, which, for machines, can arise in only a few hours. “Personally, I’ve always been more scared of this [doomsday] scenario than a lot of others,” he says. “This could happen in our lifetime. And once we’re sharing the planet with some form of superintelligence, all bets are off.”

Not everyone is so pessimistic. Selmer Bringsjord, a logician and philosopher at Rensselaer Polytechnic Institute, says that because machines follow the logic of their programming, “the machine isn’t going to get some supernatural power” if the programming is done properly. The emergence of more intelligent AI won’t come on “like an alien invasion of machines,” agrees futurist and prominent author Ray Kurzweil. Machines, he says, will follow a path that mirrors the evolution of humans. Ultimately, however, self-aware, self-improving machines will evolve beyond humans’ ability to control or even understand them, he says.

Wright, for one, wonders if people should even try to govern this new breed of AI. “Who says that evolution isn’t supposed to go this way?” he asks. “Should the dinosaurs have legislated that the mammals not grow bigger and take over more of the planet?”

Cloning of a human

Odds: Likely

Ever since the birth of Dolly the sheep in 1996, human cloning has seemed inevitable. Yet despite the success scientists have had with other animals, the process had proved much more difficult in humans.

Scientists generate clones by replacing the nucleus of an egg cell with that from another individual. They have cloned human embryos, but none has yet successfully grown past the early stage where it is a solid ball of cells known as a morula. It may be that the act of transferring the nucleus disrupts the ability of chromosomes to align properly during cell division. “Whenever you clone a new species, there’s a learning curve,” says Robert Lanza of Advanced Cell Technologies in Worcester, Mass., who made headlines in 2001 for first cloning human embryos. Especially tricky steps include discovering the correct timing and mix of chemicals to properly reprogram the cell.

Even with practiced efforts, some 25 percent of cloned animals have overt problems, Lanza notes. This is because minor slips during the reprogramming, culturing, or handling of the embryos can lead to developmental errors. Attempts to clone a human would be so risky, Lanza says, it “would be like sending a baby up into space in a rocket that has a 50-50 chance of blowing up.”

If human cloning happens, it probably will be performed “in a less restrictive area of the world, probably by some wealthy eccentric individual,” Lanza conjectures.

Will the rest of us recoil in horror? It’s possible that we’ll grow to accept cloning, for reproductive purposes, as readily as we accepted in vitro fertilization.

Polar meltdown

Odds: Likely

The U.S. is shrinking—physically. It lost nearly 20 meters of beach from its East Coast during the 20th century. The oceans have risen by roughly 6.7 inches since 1900 through expansion (warmer water taking up more space) and the ongoing meltdown of polar ice.

That increase, however, is a small fraction compared with what’s to come. “Plan on 1 meter [of ocean rise] by the end of this century,” says glaciologist Robert Bindschadler, an emeritus scientist at NASA. “The heat in the ocean is killing the ice sheet.”

Some of the famous predictions—Florida under 5 meters of sea-level rise and a gaping bay where Bangladesh used to be—may be centuries away. But because ice sheets are shrinking faster than scientists expected even a few years ago, expect an ice-free Arctic and different coastal contours by 2100. By the reckoning of economist Nicholas Stern of the London School of Economics, 200 million people live at altitudes within 1 meter of the present sea level, including eight of the world’s largest cities. “They’re going to have to move,” Bindschadler suggests.

Even if greenhouse gas emissions decline, the polar meltdowns will be difficult to avoid because ice sheets lag the overall climate and, once melted, have a hard time re-forming. Just how humans will adapt to a more watery world is not known. Of today’s trend, Bindschadler notes, “We’re not going to avoid this one.”

From the June issue of Scientific American. Reprinted with permission. ©2010 by Scientific American, a division of Nature America, Inc. All rights reserved.