Americans have the biggest fridges in the world. Not only that, the U.S. outstrips the rest of the world in the use of air-conditioning. Now developing countries like India and China are catching up. But there is an environmental cost. Last week, negotiators for nearly 200 countries agreed to limit the use of HFCs, or hydrofluorocarbons, the greenhouse gases commonly used in refrigeration and air conditioning. Do we need to reign in our addiction to keep things chill? Or is there a clean alternative to HFCs?