Scientists have long known that it's possible to artificially cool the planet by injecting tiny sulfur particles into the air to reflect sunlight. When Mount Pinatubo erupted in 1991, the large volcano injected so much sulfur-dioxide into the air that it cooled the Northern Hemisphere by as much as 2°C the following summer. The catch, unfortunately, is that this sort of geoengineering could have all sorts of unexpected side effects, like mucking up the world's rainfall patterns.

Nice and cool. (AP)

But what if people tried to do this locally? Imagine if — to throw out a wild hypothetical — certain regions of the United States were suffering from a severe heat wave. Would it be possible for a state or local community to inject sulfate aerosols into the air just to cool these areas down?

In theory, yes. But it's a very risky move. Four UCLA scientists recently wrote a paper on this exact topic and have just submitted it to the journal Atmospheric Chemistry and Physics. The researchers looked at the July 2006 heat wave in California, which lasted for 17 days and killed at least 140 people.

In theory, the scientists found, it would have been possible to artificially cool California by injecting sulfate aerosols into the atmosphere, some seven miles up. Computer modeling suggests that temperatures in the Central Valley would have dropped by as much as 7°C in the hottest part of the afternoons, with smaller heat relief in Los Angeles and other coastal areas.

But there would be serious downsides, too: For one, this would require a substantial amount of aerosol to be "lofted" into the atmosphere — and it would have to be launched into the air repeatedly, and for each region. That's not an easy task. More significantly, lacing the atmosphere with aerosols could mess with local rainfall patterns — a risky move for a region that's often afflicted by drought. It could also further deplete the ozone layer.

Those side effects, the authors argue, make this sort of geoengineering a much riskier and less-preferable climate solution than cutting carbon emissions and slowing the pace of global warming the old-fashioned way.

Yet this paper also highlights one of the legal quandaries around geoengineering. Right now, there are few rules governing these techniques. And at some point in the future, squirting sulfates into the air could become cheap enough that any local community could do it. So what if a region wilting under a heat wave decides to engage in a bit of artificial cooling, even if it ends up screwing up precipitation for a neighboring area or country? Who would stop them? How would that decision get made?

(Link via David Biello.)