Those of us who are Republicans and who also believe that climate change presents serious risks that need to be addressed--see my posts here, here, here and here--have had little cause for enthusiasm about the Republican Party on this issue in recent years. Romney, among the primary candidates, was the second-least-bad (Huntsman, also less than perfect, was the least bad). With the selection of Paul Ryan, Romney has added to the ticket someone whose climate record is worse than his own.
Against this, it is important to remember the fecklessness of the Obama administration on climate change. Failing to pass a cap-and-trade bill, and then mentioning the subject as little as possible, is not a good record either. Yes, the Democrats at least don't declare global warming a hoax and prattle on about "Climategate." But when you get to the question of how much carbon emissions would actually be different depending on who wins the election, there's no clear answer, as far as I can see.
Maybe a Romney administration would follow the advice of longtime Romney advisor Greg Mankiw and impose a carbon tax. Or maybe the Obama administration would get some carbon trading set up that replicates the flaws already evident in carbon trading overseas. Results are what matter.
Furthermore, in weighing the respective merits (or lack thereof) of the candidates, I give some weight to the spectrum of opinion among their supporters. On the Republican side, that includes every shade of denialism and evasion. On the Democratic side, there are those who think the answer is, say, a worldwide "war footing,"with a command economy deliberately set up to depress living standards. The policy emphasis I would want to see--a carbon tax coupled with broader tax reform; and a federal focus on relevant R&D spending rather than Solyndra-like attempts to subsidize corporate operations--is not
on either side's policy agenda currently.
So, bottom line, if I were voting on the basis of climate policy alone, I'd vote for the Democrats. But that's not the case. On the other hand, although I've said I'll vote for Romney, I've also said it's possible I'll change my mind. Watching what the candidates say on climate will be a factor on that score.