(Charlie Riedel/Associated Press)

The GOP has been “the stupid party” on climate change, its message dominated for years by obstreperous opponents of climate scientists and climate policy. This week brought more evidence that many Republicans haven’t been happy with that: Among other things, several Republican senators admitted on the Senate floor that they believe global warming is a human-caused problem. The question is whether they will grow enough spine to lead their party toward addressing it, which the GOP must do to deserve Americans’ trust.

On Wednesday and Thursday, senators took several votes on how they view climate science. Republicans couldn’t dodge the issue with vapid rhetorical evasions, such as “I’m not a scientist.” Nor could they simply grant that climate change is occurring without taking a position on why. Ninety-eight senators voted for that least-common-denominator proposition, but then they had to clarify what they meant in subsequent votes. The chamber voted on whether humans contribute to global warming. Fifty-nine senators voted that we do. Then senators voted on whether humans contribute “significantly” to climate change. Fifty voted yes.

True, only half the Senate voted for a position that nearly all climate scientists hold. But Democrats no longer run the place. Five Republicans had to vote for the measure to get it to 50: Tennessee’s Lamar Alexander, New Hampshire’s Kelly Ayotte, Maine’s Susan Collins, South Carolina’s Lindsey Graham and Illinois’s Mark Kirk. Ten more Republicans stopped just short, voting for the first two measures but not the last. That list includes Energy Committee Chair Lisa Murkowski (Alaska), former GOP presidential candidate John McCain (Ariz.) and probable presidential contender Rand Paul (Ky.).

In fact, three potential 2016 GOP presidential candidates sided with scientists — to at least some degree — this week. In addition to the votes of Graham and Paul, Mitt Romney said this on Wednesday: “I’m one of those Republicans who thinks we are getting warmer and that we contribute to that.” (h/t National Journal). These ambitious politicians are saying so before submitting themselves to GOP primary voters.

Maybe they are just being honest. Maybe they are calculating that seeming anti-science on global warming is increasingly a potential political liability, particularly in general elections. Either way, GOP base politics might yet snap them into silence.

But there is no question about the logical implications of their positions. If more than half the Senate believes that climate change is real and human-influenced, then more than half the Senate should be working on a policy response. If there is a risk, even one senators see as uncertain, a rational government would hedge against it. And any free-marketer worth her passing Economics 101 grade knows that the efficient way to deal with externalities such as carbon dioxide emissions is to set a price on them, through a carbon tax or similar policy. Now is an ideal time to push this sort of policy, because energy prices are very low.

Even if they are not proactive on carbon policy, those 10 15 Senate Republicans who agreed that humans contribute to climate change will have moments of responsibility in which they will have to choose whether to convert principles into actions. Senate Majority Leader Mitch McConnell (R) has promised a battle on the Environmental Protection Agency’s climate program. At the very least, they should refuse to eviscerate President Obama’s greenhouse gas initiative absent a viable GOP plan to achieve significant emissions reductions.

“Should” often does not translate into “will” in Washington. Holding out hope for Republicans on climate change still seems naive. But at least a little less so than it did last week.