Mike Berners-Lee and Duncan Clark at The Guardian have a recent post in the series examining the carbon footprints of daily life activities. Their post asks how much carbon emissions results from the direct and indirect activities of building a car.
The carbon footprint of making a car is immensely complex. Ores have to be dug out of the ground and the metals extracted. These have to be turned into parts. Other components have to be brought together: rubber tyres, plastic dashboards, paint, and so on. All of this involves transporting things around the world. The whole lot then has to be assembled, and every stage in the process requires energy. The companies that make cars have offices and other infrastructure with their own carbon footprints, which we need to somehow allocate proportionately to the cars that are made.
….The best we can do is use so-called input-output analysis to break up the known total emissions of the world or a country into different industries and sectors, in the process taking account of how each industry consumes the goods and services of all the others. If we do this, and then divide by the total emissions of the auto industry by the total amount of money spent on new cars, we reach a footprint of 720kg CO2e per £1000 spent.
This is only a guideline figure, of course, as some cars may be more efficiently produced than others of the same price. But it’s a reasonable ballpark estimate, and it suggests that cars have much bigger footprints than is traditionally believed. Producing a medium-sized new car costing £24,000 may generate more than 17 tonnes of CO2e – almost as much as three years’ worth of gas and electricity in the typical UK home.
17 (metric) tons is 17,000 kg or about 37,400 pounds. The U.S. EPA estimates that the average passenger vehicle in the U.S. emits 5-5.5 metric tons CO2e per year, assuming 12,000 miles driven.
If you do the math, this means the embodied CO2e emissions to make a car is about 3-3.5 years worth of tailpipe emissions from driving. Assuming that most people own their cars for longer than three years, this figure doesn’t jive with what the authors claim:
The upshot is that – despite common claims to contrary – the embodied emissions of a car typically rival the exhaust pipe emissions over its entire lifetime. Indeed, for each mile driven, the emissions from the manufacture of a top-of-the-range Land Rover Discovery that ends up being scrapped after 100,000 miles may be as much as four times higher than the tailpipe emissions of a Citroen C1.
If people held onto their cars for 10 years (assuming 120,000 miles), tailpipe emissions would equal 50 metric tons of CO2e, and embodied emissions would be about 34% of tailpipe emissions. If people drove their cars for 20 years (assuming 240,000 miles), the exhaust emissions would rise to 100 metric tons CO2e, with embodied emissions dropping to 17% of tailpipe emissions.
While most folks generally agree with the notion of driving their vehicle into the ground (as my recently dead 16-yr-old truck illustrates), you’d have to be driving a Toyota Prius to get a lifetime tailpipe emission that equals the embodied emissions of building it (assuming that a Prius achieves three times the mpg of a typical car, which would drop CO2e tailpipe emissions from 5 to 1.7 metric tons CO2e per year, making a 10-year total tailpipe emission of 17 metric tons reasonable).
Thus, if you drive an average car for 10 years, your lifetime tailpipe emissions (50 metric tons) will be a lot larger than the embodied emissions to build the car (17 metric tons) (for a total emission of 67 metric tons). If you drive a hyper-efficient vehicle for 10 years, tailpipe and embodied emissions may be comparable (17 metric tons each, 34 metric tons total). This means you could buy a new Prius every three years, and the embodied emissions from all of these purchases plus tailpipe emissions would roughly equal a normal car driven for 10 years.
This raises an important question: What matters here? If the goal is to reduce total emissions, the best thing is to buy a car with a very high fuel efficiency and drive it for its full life, as the above examples illustrate.
Photo credit: atomicshark
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