Our friends at Streetsblog found a new report by the EPA that contained the chart below. It shows the dirtiness of the vehicles produced each year in grams of carbon dioxide emitted per mile. As you can see, there was a huge drop in how much our cars polluted around 1980, but the situation has been pretty level by comparison over the last two decades.Elana Schor says this casts doubt on the theory that high gas prices make for cleaner cars. She writes:It's a storyline that the media and the auto industry have embraced: Higher gas prices are the magic ingredient that U.S. carmakers need in order to sell more fuel-efficient vehicles to consumers.The narrative is tempting, especially for those who believe federal gas taxes need to rise in order to fairly price the environmental impact of driving. But if it were true, the record rise in U.S. fuel prices that began in 2007 and lasted through 2008 might be expected to spur a notable increase in production of cleaner cars.I'd respectfully disagree. A lot depends on why the price of gas is high. If you were thinking about getting a new car in 2008 and decided that high gas prices weren't a big deal because you figured they might go down, you would have been right! Gas prices did go down. If we had a $4 per gallon floor on the price of gas, however, consumers would plan for a long future of expensive gas and, it's reasonable to think, buy more efficient cars. This chart doesn't invalidate the idea that "federal gas taxes need to rise in order to fairly price the environmental impact of driving." It just shows that people don't decide what cars to buy based on temporary fluctuations in gas price.We should also take a step back from the trees and check out the forest: For advocates of a high gas tax, the end goal isn't cleaner cars per se, but a cleaner atmosphere. And the high gas prices of 2008 had a dramatic effect on the total miles we drove.High gas prices mean less driving and less driving means a cleaner atmosphere. High gas might not be "the magic ingredient," but magic doesn't exist. They still have a positive effect. Especially if we can keep them consistently high.