Air conditioning could heat the world.

Global warming predicted for the coming decades may decrease heating bills in some parts of the United States. Ironically, the extra electricity needed for air conditioning could result in increased emissions of planet-warming carbon dioxide.

The atmospheric concentration of carbon dioxide, which traps heat at Earth's surface, has been on the rise for more than 150 years, largely because of the burning of fossil fuels. Some computer simulations suggest that by the end of this century, the global average temperature could be as much as 3.4[degrees]C higher than it is now, says David J. Erickson III, a climate modeler at the Oak Ridge (Tenn.) National Laboratory.

To look at the near-term effects of such global changes in the United States, Erickson and his colleagues ran computer predictions of regional climate changes, population changes, and the patterns of energy consumption and carbon dioxide emissions. Their model suggests that between 2003 and 2025, energy use in northeastern states will drop because of warmer winters but increase in the South and West with increased air conditioning. Overall energy use for the country during this period would be about 1 percent less than consumption in a no-warming scenario, but carbon dioxide emissions would increase about a half a percent.

The boost in the greenhouse gas would result from air conditioners running on electricity primarily from coal-fired power plants, a power source that's less efficient than sources used to heat most buildings. The team reports its results in an upcoming Geophysical Research Letters.--S.P.