New York Times (pg. A19)  [Printer-friendly version]
October 24, 2007


By Ken Caldeira.

Ken Caldeira is a scientist at the Carnegie Institution's department
of global ecology.

Despite growing interest in clean energy technology, it looks as if we
are not going to reduce emissions of carbon dioxide anytime soon. The
amount in the atmosphere today exceeds the most pessimistic forecasts
made just a few years ago, and it is increasing faster than anybody
had foreseen.

Even if we could stop adding to greenhouse gases tomorrow, the earth
would continue warming for decades -- and remain hot for centuries. We
would still face the threat of water from melting glaciers lapping at
our doorsteps.

What can be done? One idea is to counteract warming by tossing small
particles into the stratosphere (above where jets fly). This strategy
may sound far-fetched, but it has the potential to cool the earth
within months.

Mount Pinatubo, a volcano in the Philippines that erupted in 1991,
showed how it works. The eruption resulted in sulfate particles in the
stratosphere that reflected the sun's rays back to space, and as a
consequence the earth briefly cooled.

If we could pour a five-gallon bucket's worth of sulfate particles per
second into the stratosphere, it might be enough to keep the earth
from warming for 50 years. Tossing twice as much up there could
protect us into the next century.

A 1992 report from the National Academy of Sciences suggests that
naval artillery, rockets and aircraft exhaust could all be used to
send the particles up. The least expensive option might be to use a
fire hose suspended from a series of balloons. Scientists have yet to
analyze the engineering involved, but the hurdles appear surmountable.

Seeding the stratosphere might not work perfectly. But it would be
cheap and easy enough and is worth investigating.

This is not to say that we should give up trying to reduce greenhouse
gas emissions. Ninety-nine percent of the $3 billion federal Climate
Change Technology Program should still go toward developing climate-
friendly energy systems. But 1 percent of that money could be put
toward working out geoengineered climate fixes like sulfate particles
in the atmosphere, and developing the understanding we need to ensure
that they wouldn't just make matters worse.

Think of it as an insurance policy, a backup plan for climate change.

Which is the more environmentally sensitive thing to do: let the
Greenland ice sheet collapse and polar bears become extinct, or throw
a little sulfate in the stratosphere? The second option is at least
worth looking into.

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