I was directed to this article by a blog on the BBC website.
It considers a full analysis of the through-life environmental cost of electric vehicles, compared to petrol and diesel vehicles. By full, it includes things like greenhouse gas emissions from the manufacture process, depletion of the world's mineral resources, and eco-toxicity, as well as of course the greenhouse gas emissions when the vehicle is in use. The key thing about this study is that it looks at the whole life of the car, from manufacture to disposal, and considers 'the environment' to be beyond greenhouse gas emissions.
Include all this into the mix, and the supposedly 'clean' electric vehicles don't look so rosy. For example, to produce such a vehicle requires twice the greenhouse gas emissions as to produce a conventional vehicle. And they include some real chemical nasties in their electrical components - a battery isn't a pleasant thing to deal with. Whether electric is better than conventional then depends on 1. Your definition of 'better', 2. How long you run your car for before it ends up as spare parts/scrap, 3. How your electricity is generated.
The authors have estimated that if an electrical vehicle is used in Europe in much the same way that a conventional vehicle is, that there is significant benefit in terms of reduced global warming potential, by 20 - 30% or so. However, if cars are ditched too early, this dwindles to less than 10%. A major issue here is how long the batteries last for. Anyone with a hybrid car will know that it ain't cheap to get a new battery - and batteries that aren't up to scratch could mean that the car is scrapped long before it should be.
Moreover, there is the issue of where the electricity comes from. The authors assume the mix of generation methods that is currently in use in Europe. However, if the electricity is predominantly generated by fossil fuel burning we aren't going to get much benefit. One has to ask, if electric vehicles take off in a big way, where the extra power generation is going to come from. I have a nagging fear it is more likely to be coal than renewable. Coal power stations are easy to build, and there's a lot of coal in the world still. For example, putting this in a New Zealand context, could NZ up its power generation capability massively (and it would need to be a massive increase if everyone switched to an electric vehicle) while still maintaining the same mix of fossil and renewable sources? I have a suspicion not, at least, not quickly.
Therefore, one might wish to consider things carefully before rushing out to buy that electric car you've always dreamed of. Implemented in the right way, they could be significantly better, but, get it wrong, and you may as well not bother.
Hawkins, T.R., Singh, B., Majeau-Bettez, G. and Stroeman, A. H. (2012), Comparative Environmental Life Cycle Assessment of Conventional and Electric Vehicles. Journal of Industrial Ecolocy. doi: 10.1111/j.1530-9290.2012.00532.x