And it's ugly.

I’ve just been watching an interesting show on BBC World about plug-in hybrid cars. Instead of using petrol, they rely on a big slab of high-capacity lithium-ion batteries to deliver 40 miles of range with zero emissions. (They’re made from modified Priuses (Prii?), so if you want to go further than 40 miles - say, to flee from the stinky hippies who sold you the plug-in hybrid - it switches over to the gasoline engine for a quick getaway.)

This got me thinking. Power stations generate carbon, so the plug-in marijuana-mobile must have some sort of carbon footprint. And if there’s a carbon footprint, we can price the carbon footprint and see how much it should really cost you to run a gas-guzzler.

**Warning: the next section contains math. **And I apologise in advance for all the imperial unit conversions.

Let’s say you go to the blokes at EDrive Systems and say “Please sir, can I have a plug-in hybrid?” It’ll set you back $12,000 just for the conversion. Keep that in mind.

Now. The average carbon intensity of American electricity is 1363 pounds per megawatt hour, or about 618kg/MWh. (Numbers from here; punch in any valid zip code (try 90210 if you’re from the eighties) to see the national average.)

Per the FAQ page at EDrive, a full battery charge takes 6kWh, and that’ll get you 40 miles - let’s say 65km. So that’s 618 grams/kWh, and about 11km/kWh, so 618 grams of CO2 per 11km, or about 56 grams of carbon per kilometre from your treehugging hippie bus.

Or, you could have a petrol car - let’s pick something sensible and economical, like the six-litre V12-powered Aston Martin DB9 Coupe.

Now, according to the EPA, this zippy little econobox gets 14 miles to the gallon - or, if you’re not living in the 17th century, 17 litres per 100km. (Thanks, Google Calculator!)

A gallon of gasoline - sorry, petrol - produces 20 pounds of carbon dioxide when burned - sorry, a litre of petrol produces 2.4 kilos of carbon dioxide when burned. So if you drive 1km in the Aston Martin, you’ll burn 0.17 litres of petrol, and produce 0.17 * 2.4 = 408 grams of carbon dioxide.

Now, halfway down this page, we find that the average American car drives about 12,000 miles a year - call it 20,000km/year. So you’re pumping out an extra 350 grams of carbon per kilometre, over 20,000km; that’s an extra seven tons of carbon dioxide a year.

Or, at current going rates, €175.

So you’re spending US$12,000 to replace about US$250 of emissions.

That doesn’t sound so great to me.