At a glance, the environmental benefits to electric vehicles seem obvious. No exhaust pipe means no harmful pollutants, right? Well, wrong, of course. It's well known that where the electricity comes from to power the car is a huge factor, and the manufacturing of electric cars is more environmentally taxing than producing conventional cars as well. In fact, a new study from the Norwegian Institute of Science and Technology investigates just this idea, and finds, among other things, that electric vehicle production produces twice as much climate change potential as does the production of conventional cars. As they say:
The global warming potential from electric vehicle production is about twice that of conventional vehicles.
The report also states
...EVs exhibit the potential for significant increases in human toxicity, freshwater eco-toxicity, freshwater eutrophication, and metal depletion impacts, largely emanating from the vehicle supply chain. Results are sensitive to assumptions regarding electricity source, use phase energy consumption, vehicle lifetime, and battery replacement schedules.
Much of the performance of EVs environmentally has to do with how long they're kept on the road. They are efficient, so the longer they stay on the road, the more they can make up for the impacts of their production. And, in places like Europe where electricity is generated from a wide variety of sources, including renewable energy, they do represent a "10% to 24% decrease in global warming potential (GWP) relative to conventional diesel or gasoline vehicles assuming lifetimes of 150,000 km."
If you live somewhere with oil or coal-fired power plants, then having an electric car is actually far worse for the environment than a comparable gas or diesel car. This includes many areas of the US.
The electric cars themselves do have significant efficiency and environmental advantages (as well as maintenance) over internal-combustion vehicles, but they're only part of the overall system. Eventually, manfacturing methods will improve, and more and more electricity will be generated from renewable, green sources.
If you have an electric car, and are genuinely concerned about the environmental impact (which is admirable, of course) then I hope you like your car, because to make it return on its green promises, you need to keep it a good long time. Battery pack replacement is still a bit of an unknown, but, according to one Ford engineer I spoke with, they're holding up much better than previously anticipated. His information came from studies of fleet hybrid vehicles used in heavy-use cab service.
So, feel free to keep a copy of this study handy to present to the next insufferable Leaf owner who corners you at a party.