The President and Congress may not be in agreement about how best to deal with climate change, but it appears that they do agree on at least one thing: they'd like to give you money to trade in your old (polluting) car.

Under the terms of a provisional agreement between the president and Democrats in the House of Representatives, a "Cash for Clunkers" program would look something like this: Anyone who owns a car that gets less than 18 miles-per-gallon could trade it in for a voucher to offset the purchase of a more fuel-efficient car. Depending on exactly how fuel-efficient that new car or truck is, that voucher could be worth as much as $4,500—at least for the lucky first one million trade-ins.

But how enticing will any "cash for clunkers" program be? The appeal of fuel-efficient vehicles tracks with the economy and the cost of gas, said Brett Smith, director of the automotive analysis group at the Center for Automotive Research in Ann Arbor, Michigan. "It's driven for most people by fuel prices and economics," Smith told ScientificAmerican.com earlier this year. "As incentive decreases, you find out what that true percent of the market is that’s buying for environmental passion than the economic incentive." The voucher will, at least, create an economic incentive that backs up the environmental one.

Regardless, all of this will be on hold until the details of the overall climate bill—of which this "Cash for Clunkers" program would be part—are finalized.

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