Many politicians, scientists, economists, and businesspeople have become concerned about the potential implications of global warming. The largest source of the emissions thought to contribute to global warming is from coal-fired power plants. The cost of alternative energy has declined, but it is still higher than coal. In 1980, wind-power electricity cost 80 cents per kilowatt hour. Using today's highly efficient turbines with rotor diameters of up to 125 meters, the cost can be as low as 4 cents (about the same as coal), or as much as 20 cents in places with less wind.

Some people have recently suggested that conventional cost comparisons are not adequate because they do not take environmental costs into account. For example, while coal is a very cheap energy source, it is also a significant contributor of greenhouse gases. Should environmental costs be incorporated into decision formulas when planners evaluate new power plants? The basic argu- ments for and against are as follows.