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Home arrow Blog arrow Cars and Global Warming

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Cars and Global Warming Print
Written by Mike Noel   
Thursday, 31 May 2007
For some reason Global Warming and fuel consumption are becoming big items in the news and blogs. Maybe it's because of rising gas prices? Maybe it's because of elections coming up soon? I don't know the reason but these things always make me think. As always, with politically charged issues, there are numerous opinions floating around and lots of unsubstantiated ideas. For example, I recently read an opinion piece by some guy who was saying he was glad gas prices were going up since that would "punish" those "arrogant and foolish" people who choose to drive an SUV. In his opinion those SUV drivers are reckless and irresponsible when it comes to greenhouse gases. The article was completely bereft of any actual data or references to back up the guy's opinion. That's ok, it just needs to be noted that the guy might be completely wrong. But that's another article.
I did become curious, though, about the impact of passenger cars on greenhouse gases (in particular, CO2). After doing so online research I ended up at a US government site that had tons of data concerning the amount of CO2 generated by the world and the USA. The data also showed the different sources of CO2 within the USA. The data was based on 2006 values.
It turns out that the USA produces about 0.25 of the CO2 in the world. Of that number 26% is coming from the transportation sector. The transportation sector is further broken down into categories. Passenger cars make up %35 of that group. That means that 9% of the CO2 generated by the USA comes from passenger cars. Globally this adds up to a bit over 2%.
If everyone driving a passenger car in the USA was to increase their gas efficiency by 50% (going from 30 MPG to 45 MPG) and drive the same number of miles each year that would result in reducing the CO2 generated by USA passenger cars to about 1.5%.
It is also interesting to look at the infamous SUV. An SUV gets about 1/3 the gas mileage that a passenger car gets (that's a gross estimate) but there are no where near as many SUV drivers as passenger car drivers. My informal observations say that about 5% of cars on the road are SUV style. So we could modify the percentage of passenger car emissions by adding an adjustment for low efficiency vehicles. If we say that roughly 5% of the vehicles have 1/3 of the efficiency of the rest then we would increase the emissions by 0.05 * 300% = 15%. The new emissions level is .35 * 1.15 = 40%. This means that the total global emissions due to passenger cars and SUVs from the USA is approximately 2.5%
If everyone who drives an SUV was to convert to a passenger car then the number of passenger cars would increase and those emissions too. The net effect would be dropping the global CO2 contribution by less than 0.005. That might be worth it but I'm pretty sure there are better ways to improve our CO2 emissions.
I know that my math here is a bit fuzzy. My intention wasn't get provide rock solid numerical analysis. I was looking for ball-park kinda numbers. Just trying to look at the whole issue and see where there are interesting areas to make a more thorough investigation.

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