Yeah, I know, I'm late to the party, but John McCain gave a big speech on climate policy today. When I was writing this piece for the print mag about McCain's topsy-turvy environmental record, a couple of folks told me that he was planning to talk about global warming a lot in the general election, using Schwarzenegger's green-themed lurch to the center in California as a model. So, here we are, talkin' bout the climate...

On the merits, McCain's proposals are far more serious than anything the current administration has ever proposed. (Then again, Bush promised to regulate carbon in his first White House run, too, and we all know how that fared...) But, as Dave Roberts notes in his excellent synopsis, McCain's actual goals for reducing greenhouse-gas emissions—60 percent below 1990 levels by 2050—fall well short of the cuts that many climate scientists deem necessary to avoid a 2 degree C rise in temperatures above pre-industrial levels. And once that happens, we risk runaway warming as feedback effects start kicking in, and, from there, droughts, heat waves, rising sea levels, the works…

That said, I'm (honestly) unsure how important it is to get the long-term targets perfect right away. Some cap-and-trade bills contain "look-back" provisions that allow the targets to be tweaked down the road if new climate science comes in saying the situation's even more FUBAR'ed than previously thought. The major hurdle for climate policy is to get a cap-and-trade regime up and running in the first place. McCain, to his credit, wants to do that, and his short-term goals for reducing carbon emissions aren't much different from Obama's (though Obama's long-term goals—80 percent below 1990 levels by 2050—are much, much more ambitious).

The major differences between McCain and, say, Obama come into focus when we look at how they would design their cap-and-trade regimes. Europe's initial foray into cap-and-trade went badly because governments didn't get the details right—for one, they gave away too many pollution permits for free. McCain favors this handout approach, which would allow polluters to reap windfall profits as energy prices rise. Obama, meanwhile, would rather auction off the credits, making his proposal more closely akin to a carbon tax. (The new carbon cap-and-trade system for electric utilities in the Northeast, RGGI, will auction off most of its permits, too, so that's worth keeping an eye on when it gets underway this fall.)

The biggest potential snakepit in McCain's plan, though, is his proposal to allow emitters to buy an unlimited number of carbon "offsets" to pay for their pollution. Now, in theory, offsets can lower the costs for industry in the short term and can help spur emissions reductions in areas that aren't covered by the cap, such as agriculture. But that's just the theory. In the real world, it's nearly impossible to monitor these offsets to make sure they're actually working properly. A recent Stanford study found that up to two-thirds of the carbon offsets under the Kyoto Protocol's Clean Development Mechanism may well be worthless. Joe Romm rants at length about this aspect of McCain's proposal in his write-up and concludes that the plan is "built on quicksand." That's a real danger.

So there's plenty of daylight between McCain's and Obama's positions on global warming, and it's not enough to say they both favor cap-and-trade and let's just call it a wash. Sadly, many of the disagreements aren't easy to hash out in a stump speech or a two-minute news segment. Overall, Obama is still much stronger on this issue, although, admittedly, the bar for conservatives is so low these days that it's sort of nice to see a Republican make any good-faith effort on climate policy…

More: Kevin Drum has a lucid post summing up the main differences between auctioning off the pollution permits in a cap-and-trade system and handing them out for free. Definitely worth reading.

--Bradford Plumer