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New Analysis on the Carbon Impact of Electric Cars: Still Better than Gas

| Thursday March 31st, 2011 | 4 Comments

Image from Ehow.com

A new study released this month by Ecometrica, comprehensively extrapolates the carbon dioxide (CO2) emissions of cars powered by either gasoline, diesel, or electricity. As such,  Ecometrica’s findings allow us to answer the question – does driving an electric vehicle reduce CO2 emissions?

Before I reveal the answer to that, here’s a bit of background. The company authoring the report is a Scottish based specialist in greenhouse gas (GHG) accounting, ecosystem services, and climate change policy. They are the carbon-calculator partner of the Carbon Disclosure Project (CDP), which speaks to their credibility. The data they collected was crunched to measure equivalency in terms of grams of CO2 emitted per kilometer traveled (gCO2/km). They looked at range and battery capacity of EVs on the market, and used data on grid carbon intensities, to calculate CO2 emissions per kilowatt hour (kWh),  taking into account power station energy losses, and transmission losses. And to make for a suitably rigorous comparison, they chose highly fuel efficient gasoline and diesel powered vehicles in order to, as they claim, paint the worst case scenario for the electric car.

And so, to the results!

1) An efficient new diesel car emits 99 gCO2/km. An efficient new gasoline powered car emits 159 gCO2/km. The UK government figure for the average car on UK roads is 208 gCO2/km. And to put these numbers into perspective, the perennial benchmark of efficiency – the Toyota Prius – achieves 89 gCO2/km.

2) EV emissions, by comparison, are much more variable, because their carbon emissions are directly related to the mix of power generation by each country. In order of lowest to highest, here are the emissions for EVs driven in the countries included in the study:

CountryEmissions (gCO2/km)


Only residents of China and Greece will increase their carbon footprints by switching to EVs, that is if they’re already driving efficient diesels. This is because of the prevalence of coal fired power generation in these countries, which put EVs at a disadvantage. Hat’s off to France for coming in at a rock-bottom 12 gCO2/km, the EV wins by a huge margin – but um…nuclear power, anyone? The UK and USA use a mix of coal, oil, gas, nuclear and renewable generation for their grids, so on today’s blend, EVs win here too. But Canada has to be the winner: with its high proportion of hydro-electric power generation, EVs take the day with lots of renewable energy, without the risk of reactor melt-downs.

So really, despite the continued existence of range anxiety, the case for the EV is very strong. They are almost always better from a carbon emissions perspective, but while noting that, we cannot – based on this data – categorically assume that no matter however electricity is generated, its all good. It’s vitally important that renewable energy be an increasing part of the mix of power generation in future, if we are to be assured that electric vehicles will bring to bear promised carbon emissions reductions. Either that, or we’ll need to build more nuclear plants, but I hardly need to highlight the downside of that approach. I’m sure many other studies have been done to answer the question as to EV CO2 emissions, so it would be great to hear about those that support, or run contrary to, this most recent study.


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  • http://www.ArchitectureWeek.com/ Kevin Matthews

    Thanks for sharing this report.

    My take-aways are that without aggressively reducing the carbon footprint of our electricity, mass conversion to electric cars won’t get us where we need to go (carbon-wise).

    Also, as we do reduce the carbon footprint of our electricity, it may also improve the embodied energy of cars.

    That becomes really important in the long run, because even as the “fuel” used in motion becomes 80-90% carbon-free, the embodied energy in car manufacturing looms larger, perhaps defining a floor below which carbon emissions from car driving will not be further reduced.

    That, in turn, starts to define how much driving we’re likely to be able to afford in terms of carbon emission 20 and 40 years out. (Which in turn starts to calibrate what we should be doing in land use and transportation infrastructure, now…)

    It all fits together, and this report addresses an important piece, rather nicely.

  • Paul Scott

    I’m curious if you included the upstream pollution for the internal combustion vehicles. EVs have zero tailpipe pollution, so you included the pollution from generating the kWh. Fair enough. However, the gasoline and diesel didn’t magically appear in the gas tank. It was extracted from the ground, shipped or piped to a refinery, refined and then trucked to the gas station where electricity was used to pump it into the car. This represents a significant amount of pollution that is apparently not in your figures.

    • Phil Covington

      Paul. Thanks for your comments. Just to be clear, these are not my figures but those of the company doing the study, Ecometrica. I linked to the full report in my article so you will be able to see exactly how they came up with the figures there. However, to give you an extract that I think speaks to your point, the report states, quote..

      ” What happens if we include the emissions associated with manufacturing the fuels that go into the power station? The effect of adding in these so called ‘upstream’ emissions is that our 75gCO2/km – (UK EV figure) – increases to 85 gCO2/km. If we do the same for diesel and petrol cars, so that we continue comparing on a like for like basis, we see that the figures increase from 99 to 118 and 159 to 187 gCO2/km respectively. Assessing the CO2 impacts in this way is known as a ‘wells-to-wheels analysis’ unquote.

      So, good point, to account fully we have to get the gas to the gas tank, but we also have to get the fuel to the power stations to generate electricity. Ecometrica’s study however, suggests the impact is greater to get the fossil fuel to the gas tank though. For the EV there is a 10 gCO2/km impact for power station upstream emissions, but getting the fossil fuels from the refinery to the vehicle increases the CO2 footprint by between 19 and 28 gCO2/km, which is an even bigger impact.

  • Max

    I’d have some concerns over the French values. Carbon isn’t big in their system but Nuclear power is and with the example of Japan front and centre I’d have to think this may be a bit misleading as to “overall environmental impact”.