The data presented on the two sites is pretty much the same, both ranking my home state of Texas as having the largest "carbon footprint". Texas' dubious distinction is dependent on several factors, among which are the following:
- The petroleum refining industry isn't going away any time soon, so there will continue to be pollution related to that (along the upper Texas coast).
- The population is spread out over an enormous area, complicating the production and distribution of electricity and natural gas.
- Ample space means that Texas communities are more likely to grow out than up (unlike the more densely populated areas of the country), thus increasing vehicle miles traveled. Wherever you're going, it's probably too far to get there by bicycle. The more dispersed a population is, the less practical mass transit solutions become.