News•February 15, 2013

Climate Change a Bigger Extinction Threat than Asteroids

As teaching moments go, it doesn’t get much better than this. NASA scientists have known for nearly a year that a small asteroid called 2012 DA14, about 150 ft. across, would whiz past Earth at the nail-biting distance of 17,000 miles or so — significantly closer than the 22,500-mile altitude occupied by geosynchronous satellites. It happened right on schedule on Friday morning, with no consequences at all for Earth.

But nobody had a clue that a space rock about a third as large would scream into the atmosphere in the early hours of Friday morning, blaze across the Siberian sky at a blistering 40,000 m.p.h., and explode, triggering a shock wave that broke windows and toppled walls in and around the city of Chelyabinsk, inuring more than 1,000 people, mostly with flying glass. It was, said Paul Chodas, of NASA’s Near Earth Object Program, at a press conference, “an incredible coincidence.”

A dashboard camera caught the meteorite soaring over Chelyabinsk, Russia on Friday.

Taken together, the two events were a grim reminder that the Earth faces dangers from outer space that has nothing to do with alien invaders. Back in 1908, a meteor exploded over the Tunguska region of Siberia with estimated force of 80 megatons, flattening some 80 million trees in a largely uninhabited area. 50 million years ago an asteroid fragment slammed into the Arizona desert, excavating a crater a mile across and 550 feet deep.

Either of those historic strikes could have killed hundreds of thousands of people if they’d happened in or over a major metropolitan area — or if they’d plunged into the ocean, triggering a massive tsunami.

But devastating as that would be, it pales next to the strike that happened 65 million years ago, when a much bigger chunk of space rock, a few miles across, slammed into the sea right off the Yucatan Peninsula in what is now Mexico. The debris thrown into the atmosphere in the aftermath of that gigantic impact is thought by many to have caused one of the greatest mass extinctions of species in the planet’s history, by blocking off enough sunlight to chill the planet dramatically.

About 70 percent of all living species disappeared during that episode of abrupt climate change. Now many scientists believe another mass extinction is under way — this one entirely of our own making. A combination of pollution, habitat destruction and the global warming from greenhouse-gas emissions has already driven the species-extinction rate well above normal, and there’s every reason to believe it will continue to skyrocket as the warming starts to overwhelm these other effects during the coming century and beyond.

Unlike the extinction that wiped out the dinosaurs, this one will result from rising temperatures, not abrupt cooling, making it tempting to wonder if a well-placed asteroid strike could actually be a good thing. If it hit out in the middle of nowhere, it could generate a pall of atmospheric dust that would cool things for a while, counteracting the heat-trapping effects of greenhouse gases. Scientists are already speculating about doing this sort of thing on purpose (albeit less dramatically) in the process known as “solar radiation management,” a type of geoengineering.

It probably wouldn’t work out so well, of course — but then, we won’t have a lot to say about it one way or another. If astronomers discover a miles-wide chunk of asteroid headed in our direction, they currently have few options for action. In principle, you could set off a nuclear explosion on the asteroid’s surface, nudging into a safer orbit, or you could try to blast it into smaller pieces (but then they all might hit Earth individually), or you could even spray-paint one side of the asteroid white, relying on the faint but steady radiation pressure of sunlight bouncing off the bright surface to push the thing just slightly off course.

None of this is anywhere close to being ready for prime time, however, so the best anyone can do for now is simply hope that the next space rock to come in our direction is either a lot further away than 2012 DA14, or a lot smaller than the chunk that triggered a blast as big as 10 Hiroshima bombs in the skies above Chelyabinsk on Friday.