Clinton, Obama, and McCain have a lot in common on climate, but also perhaps a lot less than you might think. So, see here for what I think a race between two of them might mean for global warming policy. An excerpt:
Clinton's and Obama's cap and trade plans would auction off 100 percent of the initial pollution permits, using the proceeds for needed causes like investing in clean energy technologies that will reduce carbon emissions. In contrast, the Liberman-Warner bill - closer to McCain's favored approach - would auction off only a small percentage of allowances initially. Major emitters would be granted many allowances to pollute for free at the outset. That's an idea that leaves some environmentalists tearing their hair out. McCain's approach is a good way to get needed support for the bill from industry. But giving away so many allowances not only massively subsidizes special interests, but ignores the principle that the polluter ought to pay for harming the environment. In essence, then, we're looking at a classic conflict between idealism and political pragmatism - with the fate of the planet at stake. Moreover, it's not obvious which approach is more viable: pushing for a moderate Republican bill on global warming that can definitely pass Congress, or pushing for a more ambitious Democratic bill that assures stronger congressional opposition.
You can read the entire column here.