Think Progress, a liberal blog, posted video of Romney's remarks Thursday night, The Hill reported. The presidential candidate was speaking at a fundraising event.
"My view is that we don't know what's causing climate change on this planet, and the idea of spending trillions and trillions of dollars to try to reduce CO2 emissions is not the right course for us," Romney said.
Conservatives blasted Romney in June when he said in New Hampshire that emissions of greenhouse gases must be cut because human activity is responsible for global warming. Radio talk-show host Rush Limbaugh suggested Romney had killed his campaign, saying "Bye-bye nomination," The Washington Post reported at the time.
Back in New Hampshire in August, Romney's position had shifted to one of doubt.
"Do I think the world's getting hotter? Yeah, I don't know that, but I think that it is," Romney said in New Hampshire in August. "I don't know if it's mostly caused by humans."