Hate to get on the stump again, but last Friday the current administration rejected the findings of its own appointed experts regarding global warming, thereby initiating a "comment period" that will effectively place the issue on the doorstep of the next president. (Read LA Times article)
The 588-page EPA report identified effects of greenhouse gas emissions on changes in weather and on water/food supplies, and made proposals to limit such emissions - all of which were rejected for imposing "crippling costs on the economy."
Again, it's back to supporting "forward-thinking" leaders who are prepared to tackle the business and economic issues required rather than run from them. After all, Nature isn't slowing its course just because we have some economic problems in dealing with it. Even California's Governor Arnold Schwarzenegger chimed in, commenting on U.S.'s reluctance being comparable to China and India, "We don't wait for other countries to do the same thing. That's what makes America No. 1."
Whoever you support, make sure they are prepared to deal decisively with environmental issues. If their position is not clear, ask. Or better yet, tell them yourself as to what you expect from them.