(UPDATE: well, so much for Mitt. We can only hope he joins the handful of retired Republican leaders that no longer have to win Republican majorities and are telling the truth about climate change.)
Mitt Romney now rebelieves in human-caused climate change:
Romney, though, kept his focus on the issues. He said that while he hopes the skeptics about global climate change are right, he believes it's real and a major problem.
He said it's not enough for Americans to keep their own carbon emissions in check when much of the rise in greenhouse gases globally is coming from countries such as China and India.
Climate change drew little attention from either candidate in 2012, when Romney sought to deny President Barack Obama, a second term. At that time, Romney said he believed global warming was occurring but he was skeptical of its man-made origins and questioned spending to curb carbon emissions.
Mother Jones has more of Romney's history.
My guess from this and some other Romney statements is that he figures there's no point winning the nomination and then losing the general election. American voters want to do something about climate (without paying too much) and that somewhat favors a more activist position. Or he just wants to try something different from the severely conservative tactic he took in 2012.
If he or Christie get the nomination and stick with a semi-realistic position on climate, that would make three out of the last five Republican nominees claiming they want to take action on climate (not Bush in '04 or Romney in 2012). Obviously there's a real issue with whether they could be trusted given subsequent actions by the national Republican Party.