Sort of a global warming question. I’ve seen arguments that by running A/C’s in the summer, we’re actually making the Earth hotter, since the heated air that gets exhausted from the A/C unit warms the local climate up slightly (thus creating a vicious cycle). Now we know that lots and lots of asphalt will cause a “heat island” effect, but is the effect from A/C units on the same level, or is it relatively minor in comparison?
This argument is a red herring. True: When you air condition your house, you cool one area and heat another area much more. That’s thermodynamics. But that does not really affect the heating of the Earth so much as this fact: When you use any electricity, you use hydrocarbons to produce carbon dioxide. This is a greenhouse gas. Although it seems that it should contribute only a small amount to the climate (compared to water vapor, for example), all of the climate models and all of the paleontological evidence indicates that the small forcing term in the nonlinear feedback climate system does have a significant effect. See the March 2004 issue of Scientific American.
What about electricity generated from alternative sources? If we switched to those overnight (you know, the electricity faeries come down and swap everything over while we’re sleeping), then we wouldn’t be burning any extra hydrocarbons when we cranked the A/C down to a nippy 60F.
It adds no more heat than any other electrical appliance. Let’s say an air conditioner consumes 300W of power, and moves 200W of heat from a building to the outside air. The net effect to the environment is 300W, not 500W. The 200W is simply moved from one part of the system to the other.
In fact, if you run the a/c continuously, the 200W it removes from the building is balanced by 200W of heat that enters the building through the walls, windows and doors. Otherwise the building will continue to get colder and colder.