As global warming turns up the heat, researchers are stunned to discover that our planet is actually growing dimmer. Increasing air pollution allows less and less sunlight to reach earth's surface, a "global dimming" that's linked to severe droughts. In an even more alarming twist, there is concern that solving the dimming problem could greatly accelerate global warming, melting ice caps and flooding coastal cities. NOVA examines this baffling climate conundrum and follows the implications of the discovery for our planet's future. Learn more...