Last week, Mitt Romney offered another confusing take on global warming, reviving questions about his convictions. This week, Obama aides joined in, blasting Romney on Sunday and again on Monday for his liquid approach to issues. More evidence that the White House will use the Romney-has-no-core line liberally should President Obama face the former Massachusetts governor in a general election.

But concentrating on the relatively minor evolution in Romney’s climate-change rhetoric misses the big deficiency in his position: It’s long been somewhere between incoherent and irrational.

There is some truth to the latest round of flip-flop criticism; unlike in previous pronouncements about global warming, Romney’s most recent did not mention his professed belief that climate change is occurring and that humans are contributing to it in some way.

But the easiest criticism is not always the best one. In fact, all of Romney’s recent statements on global warming still seem to rest on a few basic points: that he doesn’t know for sure if the earth is warming, that he isn’t certain how much people are responsible, and that he opposes ambitious efforts to cut carbon emissions, such as a cap-and-trade program. On Monday, I asked a Romney campaign official to clarify whether the candidate still favors reducing carbon emissions. He does — in ways that carry no economic cost.

Romney’s frequent admission that he “believes” that Earth is warming — he insists that he doesn’t “know” — has been a transparent way to make the measured heating of the planet seem almost a matter of faith, despite continually mounting evidence that, as the National Oceanic and Atmospheric Administration put it, rising world temperature is “unequivocal.”

Romney also often implies that a lack of absolute certainty about how much human activity contributes to climate change justifies opposition to carbon-cutting policy. He consistently follows up his professions of uncertainty with attacks on cap-and-trade or an exaggerated calculation of the possible cost of reducing greenhouse emissions, which seems to rule out most other policies. Romney’s campaign talks about cost-free, “no-regrets” carbon cutting without explaining how that approach would reduce pollution enough for America to participate credibly in any global anti-carbon effort. It’s a generally negative message meant to placate those who oppose doing anything about climate change.

Then there is what Romney should be saying. There are, of course, inherent uncertainties in predicting the future. Climate scientists’ models can only hope to approximate Earth’s intricate climate system. And yet, scientists can describe the probability that releasing greenhouse gases into the atmosphere will severely enhance the greenhouse effect. Even if they were far less certain than they claim to be, that risk is still harrowing. Even if the probabilities were a lot lower, there would still be a strong argument to hedge against a very bad outcome.

As a former businessman, Romney should know about the literal, dollar value of hedging against bad outcomes in the face of inevitable uncertainty, especially when the experts have such high confidence in their analysis of what’s happening. Romney should understand the danger of limiting one’s future options; it’s a lot easier to take climate change seriously now and back off later than it is to do nothing until really bad things start happening. Romney’s concern about economic efficiency would also be helpful in crafting smart solutions, if he more responsibly grappled with the scale of the threat and the policy needed to address it.

Consistently leaving all of that out is the real trouble with Romney’s position on climate change. But you won’t hear that sort of substantive criticism from his fellow candidates, who are generally even less responsible on climate change than Romney is. And you probably won’t hear it from the White House. The president won’t want even to imply support for higher energy costs this close to an election. Besides, Obama’s own record on climate is far from pristine. It’s easier for all just to decry flip-flopping.