Want to be green? Consider keeping your "clunker."

The wildly popular "Cash for Clunkers" program is one of a number of policies funded by this year's stimulus package that encourage consumers to make major purchases in the name of the environment. The program offers incentives for car owners to trade in automobiles getting fewer than 18 miles per gallon for more fuel-efficient vehicles. State-run rebate programs for Energy Star appliances operate similarly, encouraging consumers to replace their washers, dryers and refrigerators with new models that meet efficiency standards set by government agencies.

These programs presumably benefit the economy and the environment in two ways: Increased consumer spending helps manufacturers and retailers, while increases in fuel efficiency reduce the amount of fossil fuels consumed and greenhouse gases generated. But these consumption-promoting policies are not necessarily a boon to the environment.

First, even when new cars and appliances are more efficient than the ones they replace, the act of replacing them entails environmental costs not accounted for in the stimulus programs. Building a new car, washing machine or refrigerator takes energy and resources: The manufacture of steel, aluminum and plastics are energy-intensive processes, and some of the materials used in durable goods, especially plastics, use non-renewable fossil fuels as feedstocks as well as energy sources. Disposing of old products, a step required by most incentive and rebate programs, also has environmental costs: It takes additional energy to shred and recycle metals; plastic components often cannot be recycled and end up as landfill cover; and the engine fluids, refrigerants and other chemicals essential to operating products end up as hazardous wastes.

Policies that encourage purchases of energy-efficient products may also increase, rather than decrease, energy use by confusing efficiency with consumption. For example, Energy Star refrigerators, which now qualify for rebates in many states, are certified to be 10 to 20 percent more efficient than "standard" models. Yet the Energy Star rating is awarded overwhelmingly to refrigerators far larger than would have been the norm two decades ago, and smaller models of refrigerator, which use less energy simply because they have a smaller volume of air to cool, were not even included in the Energy Star program until 2002.

Beyond these concrete environmental drawbacks, product-replacement policies also send a message that old things are dirty and inefficient, while new ones are necessarily green and efficient. Under the Cash for Clunkers program, for example, old cars must be traded in for new ones. Yet plenty of used cars exceed the required 22 mpg. By assuming that only new products can be environmentally friendly, these policies lead us to discount the environmental gains that could be made through well-established and low-tech means.

Cash for Clunkers and related incentive programs have stimulated consumer spending and might well be deemed successful economic policies. They have certainly also pushed some consumers toward more energy-efficient products than they might otherwise have bought. But that in itself does not make them successful environmental policies. The environmental issues surrounding durable goods are too complex to be reduced to consumer-level measures of environmental efficiency.

If policymakers sincerely want to use stimulus money to further environmental goals, they need to look past narrow definitions of efficiency, incorporate environmental analyses of product lifecycles from manufacturing through disposal, and refuse to broadly equate "old" with "obsolete." Only then can they craft policies that will serve both the economy and the environment.

Gwen Ottinger is a program researcher in environmental history and policy at the Chemical Heritage Foundation's Center for Contemporary History and Policy in Philadelphia. She wrote this commentary for The Washington Post.