What is carbon debt of a new car?

February 24, 2006 10:52 AM

How much energy/CO2 debt in used/incurred in the production of a new car? The fpp about the group who pledged to buy nothing new (which I can't find) got me thinking: some consumerism is spurred by the idea that newer products are more energy efficient than the older ones. But new products may use a lot of energy in their production and the break-even point may be beyond their lifespan.

I seem to remember hearing that it takes several tons of coal to refine 1 ton of steel, does anyone know how many with modern processes? And the other materials in a car take even more energy per pound (which is why they cost more: aluminum is $3.50 a pound while steel is $0.50 a pound even though the raw material is cheaper). This makes me think that a new car may have racked up a 10-20,000 lb. CO2 debt before it is ever driven (just in raw materials, not including manufacturing and transportation). Plus the enviromental impact of the plastic, electronics and paint.
Is there a good estimate for this sort of thing?

posted by 445supermag to science & nature (11 comments total)

According to Ford's recently released report The Business Impact of Climate Change (pdf):

We recognize that only about 10 percent of the lifetime GHG emissions from a vehicle occur during its production. The remaining 90 percent attributed to each vehicle is emitted when the customer is using it – when it burns gasoline or diesel fuel from fossil sources.

posted by alms at 10:58 AM on February 24, 2006

what alms said - the life cycle of a car is largely determined by its use phase.
posted by whatzit at 11:12 AM on February 24, 2006

what alms said - the life cycle of a car is largely determined by its use phase.
posted by whatzit at 11:12 AM PST on February 24 [mark as best answer] [!]

Right, so what I want to be able to do is make a spreadsheet to calculate how many miles/years of use you have keep a new car depending on the ratio of gas milage use. What I need is a rough number. For instance if it takes 3 tons of coal per ton of steel, a car might have a 44,000 lb. CO2 debt before its driven. Thats 3 tons coal * 2 tons weight of car * 44/12 carbon to CO2 ratio. What I need is that number.
posted by 445supermag at 11:24 AM on February 24, 2006

We recognize that only about 10 percent of the lifetime GHG emissions from a vehicle occur during its production. The remaining 90 percent attributed to each vehicle is emitted when the customer is using it – when it burns gasoline or diesel fuel from fossil sources.

But at what gas mileage? An suv at 10 mpg will use 5 times as much as a hybrid for the same miles. On the other hand if you only drive a couple 1000 mi. a year, an old suv will be better than a new hybrid.
posted by 445supermag at 11:31 AM on February 24, 2006

445, I don't understand what you mean by debt. There is no debt. CO2 is released when the raw materials are turned into the car, and more CO2 is released when the car is used. There is no payback going on.

Ford doesn't give their methodology in their report, but I'd imagine that it's something like a 12 year life span for the car at about 15K miles per year. In terms of the other details of mileage, weight of car, etc I don't think anyone is going to be able to come up with a canned formula for you. Different cars are made out different materials using different processes, and they have different fuel economy. So the devil will be in the details. (One thing, though, is that heavier cars use more materials and have lower mileage. So the emissions caused by production and the emissions caused by use would both tend to increase with the weight of the car.)
posted by alms at 11:54 AM on February 24, 2006

BTW, I'm pretty sure the Ford number takes into account the entire GHG footprint of production, i.e. everything from getting the ore out of the ground to getting the car off the assembly line. So it would include the steel production, the plastics, the shipping, etc.
posted by alms at 11:56 AM on February 24, 2006

Alms--I think that 445 is using "debt" in the sense of the handicap (I think that's a more suitable word) that you start off with in buying a new, efficient car when compared to continued use of an old, inefficient car.

That is to say, it's too simplistic to trade in your 1971 Chevy Suburban on a shiny new Prius and say "look at me, I'm saving the environment" because you just incurred N tons of CO2 emission, etc by having Toyota build the thing for you. The question then becomes, "assuming I've got this old inefficient vehicle that gets X mpg, and I trade it in for this new efficient vehicle that gets Y mpg, how many miles do I need to drive before the new one has a lower overall environmental burden than the old one?"
posted by adamrice at 12:14 PM on February 24, 2006

What I want is a rough idea of how many lbs. of CO2 are produced in making a new car. One way to guess at a low-ball number would be to know how many tons of coal are used per the refining of a ton of steel. If you know the weight of a new car and its fuel efficiency, the gas milage of your current car and how many miles a year you drive, you can calculate how many years it will be till the breakeven point. If its past the lifespan of the new car, you are better off rebuilding your old one.
Many people calculate this and find that its not worth the money (say, for a new prius vs. a fairly fuel efficient new car), I want to know, irrespective of cost, if it's worth it in CO2 savings.
posted by 445supermag at 12:24 PM on February 24, 2006

On non-preview, what adamrice said.
posted by 445supermag at 12:26 PM on February 24, 2006

Is there a good estimate for this sort of thing?
Yeah, but they're not always simple. The easiest way to look at it is from major contributing segments of the car. The major contributor will be from processing the metal used to manufacture the body in white. You're looking at about 450 kg CO2/BIW in a Steel body and around 1100 kg CO2/BIW in an Aluminum body. Plastics are small potatoes - they are a much smaller weight fraction of the car and have significantly lower emissions in manufacturing than the main metal work.

What happens when the car has larger weight fractions of plastics and composites is that the recyclability decreases by a lot. Right now, energy savings in car manufacturing come from the large recycling rates of all the metals. Plastics are scrapped for the most part. Also, notice that this material choice - steel vs aluminum and, eventually, greater composite use - has major effects on the use phase because, in the metal case, a steel BIW is 250 kg on average compared to 141 kg for aluminum, leading to differnt fuel efficiencies on otherwise identical cars.

You might find this presentation on systems analysis methodologies interesting for making the overall comparison. Specifically slides 20, 22, and 23.

Sources:
The Materials which make up an automobile
ESD.123 Industrial Ecology of the Automobile - one-stop shop for lots of stuff about the environment and automobile manufacturing
Total Energy Cycle Assessment of Electric and Conventional Vehicles: An Energy and Environmental Analysis - focuses more on the use phase than manufacturing, but interesting nonetheless

Like I said it's never going to be a short answer, and your best estimates will come from making a specific case. I can hunt around more of the literature for another ballpark but not at the moment. The keywords you want for your own search should include "life cycle analysis" "LCA".
posted by whatzit at 1:53 PM on February 24, 2006

If you have access to academic journals, you might find this helpful: life cycle optimization of vehicle replacement, a big project that looks at a number of factors, including CO2 emissions, across the full lifecycle of a car's lifetime (use phase, manufacturing, material extraction and production, end of life). Going through quickly, it doesn't look like any of the reports are freely available online, but going through and looking at them all you might find one or two.
posted by claxton6 at 2:45 PM on February 24, 2006