That's the gist of a new study by the Union of Concerned Scientists (UCS). From the executive summary (PDF), we learn that, "On average, BEVs representative of those sold today produce less than half the global warming emissions of comparable gasoline-powered vehicles, even when the higher emissions associated with BEV manufacturing are taken into consideration." UCS says that when it comes to the two most-popular EVs sold today, the Leaf and the Tesla Model S, "excess manufacturing emissions are offset within 6 to 16 months of driving."
In most of the US (by population), an EV contributes less global warming emissions than a 50-mile-per-gallon gasoline. When you look at the electric grid in the places where most EVs are sold, you would need a 68 mpg car to be well-to-wheels better than the average EV. And, since more and more electricity is coming from renewable energy, EVs will continue to get cleaner. This is just what the UCS said in its last report like this, in 2012, and we expect to hear the same thing in the next report.
You can download the full report here (PDF). There is no mention of hydrogen cars – and only one mention of diesels – in the report. If you don't want to read that much, you can get just watch the video above.