Here's some good news for all you eco-friendly Californians who take pride in driving the greenest car on the block, but have no way to back up your claim. Well now you can prove it. Beginning with all 2009 model cars, a new state law will require all dealers and sellers to post a "Global Warming Score" on each vehicle.

Like the "Smog Score" that already is mandated for new vehicles, the global warming score will be on a scale of one to 10, and based on how other cars in the same model year compare to one another. An average vehicle will have a score of five.

The new score, which will incorporate all classes of vehicles, from electric cars to gas-guzzling SUVs, will take into account direct vehicle emissions, as well as the emissions related to the production of fuel for each car. The higher the score, the cleaner the car.

California, as you might expect, is the first state to mandate such labels. A similar law will take effect in New York beginning with the 2010 model year.