Global warming may get to the point where drastic "geo-engineering" measures to cool the earth will be necessary, President Obama’s top science adviser tells the AP. John Holdren said shooting reflective particles into the upper atmosphere to reflect some sunlight is a last resort, but one he's raised with other administration officials. "We don't have the luxury of taking any approach off the table," said Holdren.
There are several possible signs that would show global warming to be reaching a “tipping point” which would necessitate drastic measures, Holdren said. One indicator would be the disappearance of all summertime Arctic sea ice. But it’s difficult to tell how close the earth is to such watersheds, said Holdren, who likened global warming to being “"in a car with bad brakes driving toward a cliff in the fog."