From a fascinating piece written by Associated Press science writer Seth Borenstein:
Obama looks at climate-engineering to cool Earth
by Seth Borenstein / Associated Press
Wednesday April 08, 2009, 4:49 PM
WASHINGTON -- The president's new science adviser said Wednesday that global warming is so dire, the Obama administration is discussing radical technologies to cool Earth's air.
John Holdren told The Associated Press in his first interview since being confirmed last month that the idea of geoengineering the climate is being discussed. One such extreme option includes shooting pollution particles into the upper atmosphere to reflect the sun's rays. Holdren said such an experimental measure would only be used as a last resort.
"It's got to be looked at," he said. "We don't have the luxury of taking any approach off the table."
... Another geoengineering option he mentioned was the use of so-called artificial trees to suck carbon dioxide -- the chief human-caused greenhouse gas -- out of the air and store it. At first that seemed prohibitively expensive, but a re-examination of the approach shows it might be less costly, he said.