Update, 6:30 p.m.: The Romney campaign argues that the candidate has been consistent in his stance on climate change. The campaign has a point. Romney stressed his uncertainty about global warming earlier this year, too; Phil Rucker quoted him in June:

“I don’t speak for the scientific community, of course, but I believe the world’s getting warmer,” he said. “I can’t prove that, but I believe based on what I read that the world is getting warmer. And number two, I believe that humans contribute to that. I don’t know how much our contribution is to that, because I know that there have been periods of greater heat and warmth in the past, but I believe we contribute to that.”

Meanwhile, though Romney on Wednesday said, “I don’t know if [climate change is] mostly caused by humans,” he also said, “Do I think humans contribute to it? Yes.” So Romney has been more consistent than I gave him credit for.

Yet, that still makes him consistently timid on the science, particularly when it comes to the recent temperature record — the warming that NOAA calls “unequivocal” and that Romney shouldn’t need to cast in such uncertain terms in the first place.

And what about the actual policy, which was the real point? A Romney campaign spokesperson wouldn’t elaborate when asked about the key line I discuss below: “What I'm not willing to do is spend trillions of dollars on something I don't know the answer to.” The big idea is this: Just because there is uncertainty about whether something bad might happen doesn’t mean you should decline to hedge carefully against that outcome. There should be more room in the GOP primary race for that logic.

Original post:

It’s another “What does Mitt Romney really believe?” moment.

Here’s what Romney said about climate change before Wednesday:

“I believe that climate change is occurring — the reduction in the size of global ice caps is hard to ignore. I also believe that human activity is a contributing factor.”

And: “I think it’s important for us to reduce our emissions of pollutants and greenhouse gases that may well be significant contributors to the climate change and global warming that you’re seeing.”

That’s not a resounding endorsement of the science, but it’s certainly better than Rick Perry’s speculations about scientists deliberately falsifying data. With Perry surging in the polls, however, Romney is softening his stance. On Wednesday, Romney said:

“Do I think the world’s getting hotter? Yeah, I don’t know that, but I think that it is.”

He thinks?

As Romney once pointed out, this is among the easiest conclusions in climate science. The 2000s were hotter than the 1990s, which were hotter than the 1980s, and so forth. There are many uncertainties about how the earth’s climate works, and yet more about what a warming planet will look like. But the notion that we have seen warming is, as the National Oceanic and Atmospheric Administration insisted last summer, “unequivocal.”

“I don’t know if it’s mostly caused by humans,” Romney continued. “What I’m not willing to do is spend trillions of dollars on something I don’t know the answer to.”

First, Romney’s accounting is off. Good anti-carbon policy (which Romney explicitly opposes ) pays for itself in the federal budget. Over many years, maybe the whole world economy will devote “trillions” to greening the energy sector, but Romney’s is a pretty misleading way to present the tradeoffs.

(Jim Cole/AP)

Romney’s statement is like saying that you don’t need flood insurance unless you know — for sure — that you are going to have a flood. Actually, it’s even worse. It’s like saying that when thousands of specialists have told you that you are very likely to have a flood.

So there is some uncertainty in scientists’ predictions about how the climate will respond to more carbon dioxide in the atmosphere? The conservative — in the sense of cautious — policy is to account for the extremely high probability that pumping greenhouse gases into the air might enhance the greenhouse effect, then backing off if the risk subsides — instead of betting our climate on the notion that it’s not happening.

In fairness to Romney, he is not all that unique in his new rhetoric. For years, politicians have confessed uncertainty on the science and, from that, concluded that the government should do too little or nothing to address it. This line might continue to have political appeal in GOP primaries. But it’s still non-sensical on the merits.