A well-known theorem by Herfindahl states that the low-cost nonrenewable resource must be exploited first. Consider resources that are differentiated only by their pollution content. For instance, both coal and natural gas are used to generate electricity, yet coal is more polluting. We show that the ordering of extraction need not be driven by whether a resource is clean or dirty. Coal may be used first, followed by natural gas, and again by coal. Such “vacillation” does not occur under cost heterogeneity. A perverse policy implication is that regulating pollution may accelerate use of the polluting resource.

A model of global warming with endogenous substitution of energy resources and multiple energy demands is developed. It suggests that, if historical rates of cost reduction in the production of solar energy are maintained, most of the world's coal will never be used. The world will move from oil and natural gas use to solar energy. Temperatures will rise by only about 1.5-2.0 degrees centigrade by the middle of the twenty-first century and then decline to preindustrial levels. These results are significantly lower than those predicted by the Intergovernmental Panel on Climate Change and suggest that the case for global warming may be seriously overstated.