How green is your electric vehicle?

Glide out of the Tesla showroom with a new electric car,

and you’d probably feel like you’re doing your bit for the planet.

But ... keep going.

You’ll have to drive another thirteen and a half thousand miles before you're doing less harm to the environment than a gas-guzzling saloon.

That's the result of a Reuters analysis calculating vehicles’ lifetime emissions, a hot topic as governments eye greener transport to meet climate targets.

The model was developed by the Argonne National Laboratory in Chicago.

It includes thousands of parameters from the type of metals in an EV battery to the amount of aluminium or plastic in a car.

Analysts say making electric vehicles generates more carbon than combustion engine cars, mainly due to the extraction and processing of minerals in EV batteries and production of the power cells.

But let’s not swear off EVs just yet.

We’ll get a false reading if we only consider them at the start of their life cycle, says Daniel Auger from Cranfield University.

"If you just measure when they come off the production line you may well find that EVs are higher than some others but you are not going to be burning the same amount of fossil fuels during the rest of the EV lifecycle. Really you need to be looking at the product right at the end, after you've disposed of it. So what are the recycling and disposal costs? What can you re-use? So you need the production, you need the disposal and you need the use and without any of those three things it's not a good comparison."

So really we’ve got to consider how the carbon gap will vary over time, where that crucial "break-even" point comes, and how it can vary.

The payback period depends on factors such as the size of the EV's battery, the fuel economy of a gasoline car and the power used to charge an EV.

It can also depend on what country the car is being driven in.

Let’s circle back to that 13 and a half thousand mile figure.

Reuters plugged a series of variables into the Argonne model,

to compare driving a Tesla 3 in the United States with a gasoline-fueled Toyota Corolla.

But if that same Tesla was being driven in Norway, which generates almost all its electricity from renewable hydropower, the break-even point would come after just 8,400 miles.

Equally, if it was somewhere like China or Poland, which largely rely on coal-based energy, you would have to drive 78,700 miles.

That may sound like a lot of mileage. But EVs still generally emit far less carbon over a 12-year lifespan.

[Daniel Auger from Cranfield University] "Yes, EVs are very intensive at the beginning of their lifecycle but, really, you've got to add that to the fact that they are not very energy intensive when they are being used. They are better than an internal combustion engine then. With any product you've also got to think about the disposal costs but the consensus does seem to be very strongly that EVs are a better option over the whole lifecycle than a conventional, internal combustion engine car, a petrol or diesel car."