Car companies aren't to blame, or maybe are only partially. For automobiles are dependent on the propulsion system which they use. If you want to sue someone for something like this, sue the oil companies for giving the public the stuff that actually harms the atmosphere. Car companies can only do so much, as regardless of whatever system they use to reduce emmission, the fact remains that fossil fuels are still being used which will always have harmful byproducts. Also, it is the oil companies who are stifling progression to newer, cleaner forms of energy, thus they are the ones who must share the blame in this matter of global warming .
However, that being said, the general public must take the rest of the blame for they are allowing this to happen. It is funny, as someone pointed out, that people are much more commonly aware of the harmful effects of the byproducts of fossil fuels, yet they still must use them in order to get where they're going, especially to any courthouse for any number of rediculous lawsuits (not naming any names here). If the general publich truly cared about the harm being done to this planet, we would change our ways or demand a feasible alternative post-haste...which we are not. Thus, we are all to blame; automakers, oil companies, and the public, alike.