by Richard Harris Nevada's Lake Mead had a white 'bathtub ring' upstream from the Hoover Dam in July 2007. A seven-year drought and increased water demand spurred by climate change and explosive population growth in the Southwest has caused the water level at Lake Mead, which supplies water to Las Vegas, Arizona and Southern California, to drop more than 100 feet to its lowest level since the 1960s. Ethan Miller/Getty Images All Things Considered, January 26, 2009 ·  Climate change is essentially irreversible, according to a sobering new scientific study. As carbon dioxide emissions continue to rise, the world will experience more and more long-term environmental disruption. The damage will persist even when, and if, emissions are brought under control, says study author Susan Solomon, who is among the world’s top climate scientists. "We’re used to thinking about pollution problems as things that we can fix," Solomon says. "Smog, we just cut back and everything will be better later. Or haze, you know, it’ll go away pretty quickly." That’s the case for some of the gases that contribute to climate change, such as methane and nitrous oxide. But as Solomon and colleagues suggest in a new study published in the Proceedings of the National Academy of Sciences, it is not true for the most abundant greenhouse gas: carbon dioxide. Turning off the carbon dioxide emissions won’t stop global warming. "People have imagined that if we stopped emitting carbon dioxide that the climate would go back to normal in 100 years or 200 years. What we’re showing here is that’s not right. It’s essentially an irreversible change that will last for more than a thousand years," Solomon says.

Global Warming Is Irreversible, Study Says