The North American Transportation Statistics Database released its new transportation data for 2007 covering the three countries in North America. After a quick glance, it was interesting to see how much of a percentage total CO2 emissions from all particular transportation modes would be in the U.S. Below is a chart showing the total amount of CO2 emissions for each transportation mode over the total amount of CO2 emissions for all transportation.* (Click the chart to maximize it) 82% of all CO2 emissions from transportation is from road travel, making it the mode of transportation that contributes the greatest amount of CO2, with all other sectors combined contributing only 18%. Air is the second greatest contributor with 10% of CO2 emissions for all transportation modes.
What seems to be an obvious point…everyone knows that the greatest contributor to CO2 for transportation has to be from road travel, correct? So, for the sheer volume of travel being done on the road, the amount of CO2 will always be a significant amount.
If you were to divide the total amount of CO2 by the total amount of energy consumed by mode of transportation for 2007, you would end up with an interesting result. Air travel would come out to be roughly 94 thousands of metric tons per petajoule (10 to the 15th joules) of energy. Likewise, road travel comes out to be around 66, rail comes out to be 69 and water transport comes in at around 35. When comparing air travel to road travel, you find that given the energy put in, less CO2 is exerted for road travel than rail or air travel. Water transport seems to exert the least amount of CO2 for every petajoule used.
In a way, this is a crude measure of pollution efficiency. Unfortunately, we can’t compare apples to apples by using CO2 per mile since the metrics given won’t translate into clean numbers. So, for now, we can only make assumptions about these numbers. If they could evenly be subdivided by the number of miles traveled, then we would be able to have an accurate picture of efficiency. What assumptions can be made from these differences? I feel that this is beyond my understanding.
*The chart says “% Total Greenhouse Gas Emissions by Transportation Sector for 2007.” However, in my post, I kept on indicating C02 only. In the tables from the primary source, that would also include NO2 and CH4, however, I only used CO2 as the NO2 and CH4 numbers were negligible and I wished to only focus on CO2.