(CNN) - Mitt Romney found himself taking hits from both a Republican rival and Democrats Friday over his stance on climate change, which both sides said had changed over the course of a few months.
On Thursday, the former Massachusetts governor told voters at a campaign event in Pittsburgh that he didn't know what was causing climate change.
"My view is that we don't know what's causing climate change on this planet," Romney said. "And the idea of spending trillions and trillions of dollars to try to reduce CO2 emissions is not the right course for us."
Romney's opponents quickly noted that his stance seemed to have changed, using comments Romney had made in the past to support the notion he was flip-flopping on the issue. His campaign immediately pushed back calling the critics full of hot air.
Perry's campaign and the Democratic National Committee highlighted a statement Romney made when speaking to voters in New Hampshire in June, when he said "I believe based on what I read that the world is getting warmer. And number two, I believe that humans contribute to that."
In a statement, Perry's spokesman said the comments reflected a substantial change in position.
"Mitt Romney's positions change, often dramatically, depending on the audience or location," Ray Sullivan said. "Voters need to consider the fact that Romney, in one week, changed positions on manmade global warming, capping carbon emissions, and Ohio's efforts to curb union powers."
The DNC produced a web video using a similar criticism, punctuated with the question, "Which Mitt?"
Romney's campaign said that the governor's full quote provided more context.
"I don't speak for the scientific community, of course, but I believe the world's getting warmer," Romney said in June. "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. And so 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 the global warming that you're seeing."
Andrea Saul, Romney's spokesperson, said the criticism doesn't hold up.
"This is ridiculous," Saul said in a statement. "Governor Romney's view on climate change has not changed. He believes it's occurring, and that human activity contributes to it, but he doesn't know to what extent. He opposes cap and trade, and he refused to sign such a plan when he was governor. Maybe the bigger threat is all the hot air coming from career politicians who are desperate to hold on to power."
Between the comments in June and his comments Thursday, Romney has taken a skeptical approach to climate change. On Aug. 8, Romney told a group in Nashua, New Hampshire, "I'm not a scientist. I think the Earth is probably getting warmer, but I'm not sure how much we contribute to it."
A few weeks later, on Aug. 24, Romney's expressed similar skepticism at an event in Lebanon, New Hampshire.
"Do I think the world's getting hotter? Yeah, I don't know that but I think that it is," he said. "I don't know if it's mostly caused by humans."
He continued, "What I'm not willing to do is spend trillions of dollars on something I don't know the answer to."