While not insignificant, I think it's worth asking what effect a 10% reduction in US passenger vehicle emissions would have in the long term. To put it in pers

While not insignificant, I think it's worth asking what effect a 10% reduction in US passenger vehicle emissions would have in the long term. To put it in perspective, there's (what appears to be) an excellent new paper in Science that proposes a roadmap for reducing global emissions to a level that is estimated to have a 2/3 chance of keeping warming below 2C until 2100. The paper is "A roadmap for rapid decarbonization" by Rockström1, Gaffney, Rogelj, Meinshausen, Nakicenovic, and Schellnhuber. While a valuable and probably required step, doubling US passenger vehicle efficiency is just one of many things that would need to be done, and done quickly. I think it's worth reading the paper closely to understand the steps that would be required according to our current understanding of the science: http://science.sciencemag.org/content/355/6331/1269 http://science.sciencemag.org/content/355/6331/1269 The full article is unfortunately behind a paywall, but since I think a reasonable argument can be made that breaking the logjam on the global warming debate is more urgent than following the nuances of US copyright law, I'll mention that plugging DOI:10.1126/science.aah3443 into sci-hub.bz will let you read the full paper.