If every car purchased in the U.S. over the next year got 50 MPG, total U.S. carbon emissions would be reduced by 0.3 percent.

Each year, 7.5 million cars are purchased in the U.S. If all of those new cars got at least 50 miles per gallon (which is the estimated mpg of the 2011 Prius*), drivers would save a whole lot of gas.  The average MPG of cars currently on the road is about 23.

The change might not scale up the way you would expect it to because the 7.5 million new cars are a small percentage of the total number of cars on the road (137 million passenger cars, 256 million registered vehicles). But, overtime, the percentage would go up...and up

*Do any of you Prius drivers actually get 50 MPG?

Prius hybrid vehicles leave the factory. Toshifumi Kitamura/AFP/Getty Images

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