I’m glad you’ve bought an electric vehicle. But your conscience isn’t clean | John Naughton

So you've finally taken the plunge and bought an electric vehicle (EV)? Me too. You're basking in the warm glow that comes from doing one's bit to save the planet, right? And now you know that smug feeling when you are stuck in a motorway tailback behind a hideous diesel SUV that's pumping out particulates and noxious gases, but you're sitting there in peace and quiet and emitting none of the above. And when the traffic finally starts to move again you notice that the fast lane is clear and you want to get ahead of that dratted SUV. So you put your foot down and - whoosh! - you get that pressure in the small of your back that only owners of Porsche 911s used to get. Life's good, n'est-ce pas?

Er, up to a point. True, there's nothing noxious coming out of your exhaust pipe, because you don't have one; and the electric motors that power your wheels certainly don't burn any fossil fuel. But that doesn't mean that your carbon footprint is zero. First of all, where did the electricity that charged that big battery of yours come from? If it came from renewable sources, then that's definitely good for the planet. But in most countries, at least some of that electricity came from non-renewable sources, maybe even - shock, horror! - coal-burning generating stations.

Even if all the charging energy came from renewable sources, you're still not in the clear. Your lovely new vehicle comes with a kind of embedded carbon debt. The factory that made it - the industrial plant that shaped and stamped and assembled all that steel and glass and plastic and rubber into a vehicle - emitted a lot of CO2 in the process. So you will have to drive a long way before the savings of CO2 that you would have emitted in driving the same distance in a fuel-burning car exceed the carbon emitted in its manufacture.

That doesn't mean that your EV wasn't a smart purchase, by the way - only that it's not as good as it looked at first sight. After the Tesla Model 3 hit American roads, Reuters commissioned a study to see how its overall carbon footprint compared with that of an equivalent conventional car - in this case a Toyota Corolla. The researchers were looking for the "break-even point" - where the EV began to be less environmentally damaging than the Toyota.

The results were instructive. The break-even point depended on the source of the electricity used to charge the Tesla. For one charged entirely by renewable energy, it was 8,400 miles; for cars charged using the average US electricity generation mix (23% coal-fired, plus other fossil fuels and renewables), break-even came at 13,500 miles; and for electricity coming entirely from coal-fired stations, it was a whopping 78,700 miles.

Sobering, isn't it. So the first lesson is that if you really want to minimise your EV's environmental damage, then charge it using electricity from renewable sources.

But carbon emissions are not the only way these vehicles impose a burden on the planet and its inhabitants. If you look at an EV, what you're really looking at is a giant skateboard with wheels at the four corners. The "board" is the battery, and it's huge. The composition of a typical battery (by weight) looks like this: lithium 3.2%, cobalt 4.3%, manganese 5.5%; nickel 15.7%; aluminium 18.9%; other materials 52.5%. Many of these materials have been mined, shipped around the world and put through complex chemical processing before being assembled into a battery. These processes all have carbon footprints, and quantifying them isn't easy, but they're certainly substantial.