Tinkering with Earth's climate to chill runaway global warming - a radical idea once dismissed out of hand - is being discussed by the White House as a potential emergency option, the president's new science adviser [John Holdren] said. The concept of using technology to purposely cool the climate is called geoengineering. One option raised by Holdren and proposed by a Nobel Prize-winning scientist includes shooting pollution particles into the upper atmosphere to reflect the sun's rays. Using such an experimental measure is only being thought of as a last resort, Holdren said. It's got to be looked at," he said. "We don't have the luxury ... of ruling any approach off the table." At first, Holdren characterized the potential need to technologically tinker with the climate as just his personal view. However, he went on to say he has raised it in administration discussions. The 65-year-old physicist is far from alone in taking geoengineering seriously. The National Academy of Sciences is making it the subject of the first workshop in its new climate challenges program for policymakers, scientists and the public. The British Parliament has also discussed the idea. At an international meeting of climate scientists last month in Copenhagen, 15 talks dealt with different aspects of geoengineering. The American Meteorological Society is crafting a policy statement that says "it is prudent to consider geoengineering's potential, to understand its limits and to avoid rash deployment."