If all of our marginal efforts to cut carbon don't do the job, and the climate starts changing quickly, we may have to resort to measures more extreme than taking the bus to work (as great as that is). The AP reports that White House science adviser John Holdren is looking into geoengineering-forcing atmospheric changes with direct action."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. ... 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."Other geoengineering schemes include using "fake trees" to suck up carbon, adding clouds to the lower atmosphere that would deflect the sun's rays, and shielding the earth with a giant parasol. Ideally, you don't want one of these Armageddon-style solutions, implemented by practitioners of a very young science, to be your only way of avoiding catastrophe.From an excellent Council on Foreign Relations primer on unilateral geoengineering [pdf]:"All of these 'geoengineering' strategies involve great uncertainty and carry significant risks. They may not work as expected, imposing large unintended consequences on the climate system. While offsetting warming, most strategies are likely to leave other impacts unchecked, such as acidification of the ocean, the destruction of coral reefs, and changes in composition of terrestrial ecosystems."But it's still right for Holdren to be bringing this up in the White House. We have no idea how many feedback loops and other booby-traps global warming might trigger (see the melting-snow-releasing-trapped-carbon phenomenon). And we'd have to cut carbon dioxide emissions by 60 to 80 percent worldwide to just hold global warming steady.Holdren compared global warming to being "in a car with bad brakes driving toward a cliff in the fog." I'd say it's about time to look into seatbelts and airbags.