Some wags will always try to claim that EVs are just as dirty as regular cars, because electricity is generated in coal-fired power stations. Except, that's not really true anymore, which is why the Union of Concerned Scientists has updated its data on how environmentally friendly electric cars are. The results won't shock you, but an EV is now about as efficient as a gas-powered car that can make 73 miles per gallon.
Back in 2009, the argument was a little muddier, thanks to the makeup of America's energy sources, which has changed significantly. As states have moved from coal towards gas, solar, wind and hyrdo, emissions are falling. As the price of solar and wind energy, especially, continues to fall, emissions are going to get ever smaller over time.
The Union also poured cold water onto the argument that because EVs are more emissions-intensive to build, they're a danger. They found that while the cars create 15 percent more emissions during construction, that is quickly balanced out by the climate savings made by not burning fuel. In fact, the report says that a car like the Nissan Leaf could pay off its carbon "debt" within six months of its purchase. So, in summary, the best thing you can do to help the planet right now is buy an electric car.