Yesterday Mitt Romney clarified that, although he does believe that human activity is contributing to rising global temperatures, he does not support cap and trade or a carbon tax. 

“Do I think the world’s getting hotter? Yeah, I don’t know that but I think that it is,” [Romney] said. “I don’t know if it’s mostly caused by humans.”

“What I’m not willing to do is spend trillions of dollars on something I don’t know the answer to.”

Previously, Romney had asserted that man-made global warming is real and expressed support for emissions reductions. Those remarks left Romney’s stance on measures such as cap and trade a little unclear, until now. 

A majority of Republicans don’t believe that global warming is caused by humans and, accordingly, oppose schemes like cap and trade. Expressing skepticism of the science behind climate change, as for instance Gov. Rick Perry has, allows candidates to assure voters that they won’t support cap and trade or carbon taxes once they’re in office. This assurance is necessary because often Republicans who do believe in global warming end up working with Democrats on climate change bills — John McCain is a good example. 

Romney’s statements, though, bring him into line with fellow Republican candidate Jon Huntsman and New Jersey governor Chris Christie, among others, in opposing major emissions-reductions plans on economic grounds, while not criticizing climate scientists. 

This is a hard stance to explain, which is, in part, why most Republicans avoid it. But it’s not at all inconsistent: all of the major cap and trade or carbon tax proposals that have been introduced in Congress would cost far more than they would be worth in terms of greenhouse gas emissions reductions. There’s no reason a presidential candidate shouldn’t point that out.