Geoengineering Could Be a Disaster for Astronomy
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The 2010 Perseid meteor shower over the VLT. Image: ESO/Flickr

Geoengineering is one of those things that sounds like maybe a good idea on paper but could also go horribly, apocalyptically wrong. But if the prospect of plunging Earth's weather systems into chaos isn't enough to convince scientists we need to tread very cautiously with the ultimate global warming tech-fix, perhaps this will: geoengineering could be a disaster for science.

That's according to new models by Charlie Zender , an atmospheric physicist at the University of California, Irvine who presented the provacatively-titled research poster " Death of Darkness: Artificial Sky Brightness in the Anthropocene " at the the American Geophysical Union conference this month. In a nutshell, Zender found that injecting light-scattering particles into the stratosphere-one of the most widely-discussed strategies for rapidly cooling the planet-would have the unintended side-effect of messing with the incoming light from distant stars and planets.

As you might imagine, this would be very bad news for the scientists who study said stars and planets. "If we geoengineered globally, this would effect all telescopes around the world," Zender told Gizmodo.

The idea behind stratospheric aerosol injection (SAI) is pretty simple: if we can get a bunch of sulfate particles high enough into sky, they'll spread around the Earth and act like sunscreen, scattering light back into space and yielding a cooling effect. (SAI was inspired in part by volcanic eruptions, which do essentially the same thing.) Although our planet could really use some help cooling off right now, SAI has come under heavy fire for an obvious reason: conducting a worldwide experiment on our one and only shared global atmosphere is inherently dangerous.

Among the more frightening possibilities critics have raised, SAI could alter weather patterns, suppressing summer monsoons in parts of the world where crops are utterly dependent on monsoon rainfall. Much more speculatively, SAI could work too well and trigger a runaway cooling scenario, a la Snowpiercer.

There's one other rather obvious side-effect of SAI that's received scant attention, and that's the impact on incoming starlight. Zender's models, which are not yet published, suggest this effect could be big. When he added a few megatons of sulfur dioxide to a computer model of the stratosphere-an amount that may be required to cool the Earth back to pre-industrial temperatures-Zender found that the night sky over urban areas would become roughly 25 percent brighter. That's because our stratospheric shield would backscatter light from ground sources, namely, electricity. "It's like when you're driving through fog with your high beams on," he said.

Of course, most astronomy doesn't take place anywhere near cities. The best observatories in the world are located on remote mountaintops, high above air pollution and far away from light pollution. Here, Zender's models show a somewhat different, but equally bad effect: SAI would actually make the sky darker .

"Our telescopes are in positions where most of the [night] light comes from the stars," Zender explained. "There, what the aerosols do is they backscatter light from outer space. That means you're not getting as much starlight, and the starlight you do get is less pristine. The stars would look fuzzier."

According to Zender's calculations, at an approximate "telescope elevation" of 10,000 feet (3,000 meters) the amount of diffuse or scattered starlight would roughly double, if we went whole hog on the SAI-to-reverse-global-warming idea. Given that astronomers rely on pencil-like beams of light to capture accurate spectral information about stars and exoplanets, this would amount to a serious headache.

Of course, the part of SAI where we trigger a global famine would also be bad, so maybe we should try reducing our carbon emissions before rushing to the tech-fix, eh?

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