University of California-Davis economist Chris Knittel says that fewer miles being driven might make an important dent in the U.S. contribution to global warming by reducing annual carbon dioxide emissions by tens of millions of tons per year.

Knittel and colleagues told New Scientist magazine they found sales of the least fuel-efficient cars fell by 13 percent for every $1 per gallon increase in the price of gasoline. And for every $1 hike in gas prices there was a corresponding 17 percent sales boost for the most efficient vehicles.

Knittel's findings are similar to those of economist Kenneth Small of the University of California-Irvine. Small projects rising fuel prices could lead to a 20 percent drop in total mileage driven, producing a substantial reduction in carbon emissions.

But politics might intervene. Economist Roberton Williams of the University of Texas at Austin noted Presidential hopefuls John McCain and Hillary Clinton say they would suspend federal gasoline taxes for this summer.

"It's a fantastically stupid idea," said Williams, "but people don't like high gas taxes, so it's popular."