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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. 

Related Content
Geoengineering: Risky To Do, Riskier to Ignore
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Approaching a Mass Extinction?


By climatehawk1 (Norwich, VT 05055)
on February 16th, 2013

Which in turn gives rise to an interesting question: how large an asteroid would it take to generate the amount of heat that 400 ppm of CO2 in the atmosphere will add over the next 20 or 50 years? 500 ppm?

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By Dave (Basking Ridge, NJ 07920)
on February 16th, 2013

This is a nice commentary. I appreciate the sentiments. I would tend to agree.

Apophis is expected to ‘fly by’ in 2029 missing Earth by only about 30,000 km.  That’s a pretty big rock and an expected near miss. Apparently right now the planet has no funded project to develop a response system to an extinction level asteroid collision, albeit a very, very low probability event in a human lifespan.  Practical ways to do it have been worked out for large as well as a-bit-less-dangerous-but-still-nasty, low probability collisions. But as I understand it those ideas are all basically on paper. So, if one considers federal plans in place to combat climate change, one might conclude that the US government does appear to be consistent in the manner in which it deals with global threats with the potential for mass extinction – of which I would also consider climate change as the most dangerous.

I considered climatehawks question and did an order of magnitude estimate out of curiosity.  Using some fairly crude but reasonable numbers and assuming that all the energy of the collision would be realized as heat, I determined a mean diameter of about 50 kilometers - while waiting for the clothes drier to finish. According to Alvarez, the Yucatan asteroid (65 Myr ago) was between 10 and 14 kilometers diameter. So the hypothetical GW equivalent one is clearly quite a bit bigger than even that. Also I think I was conservative.

However, not wishing to spoil the ‘fun’ here, it is technically a very poor analogy to equate an asteroid collision or numbers of nuclear bomb explosions for that matter with global warming to try to get some sense of it. This is because the energy in those analogies is released almost instantaneously and in highly concentrated areas compared with global warming. It is just not apples to apples when considering destructiveness or net impacts on civilization.  For instance the total energy expended (over days) by one medium sized Atlantic hurricane far exceeds that of the potential of very many modern nuclear warheads exploded all at once and detonating in a split second.  However the latter could indeed end human civilization while the former would not.

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By Mike Smith (Oakville, Ontario L6L 5J2)
on February 17th, 2013

The only way an asteroid hit would save the planet is if it could wipe out about 4 billion people in the highest oil consuming countries.

The planet would continue cooling even after the debris settled because the fossil fuel carbon emissions would be down permanently.  The other 3 billion would exist in a hot climate for about 200 years and after that their descendents would see the climate return to temperatures of the 1880’s.

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