GOP New Hampshire Senate candidate Scott Brown said Saturday that climate change is not man-made, a reversal of the position he held when he unsuccessfully defended his Massachusetts Senate seat in 2012.

When asked whether "the theory of man-made climate change has been scientifically proven," Brown responded, "Uh, no," during a three-person GOP debate in a video NextGen Climate Action, the super PAC started by billionaire ex-hedge fund manager Tom Steyer, sent to reporters.

In 2012, Brown was asked a similar question — in a debate with eventual winner Democratic Sen. Elizabeth Warren, Brown said, "Yes, yes I do. I absolutely believe that climate change is real and I believe there's a combination between man-made and natural."

Elizabeth Guyton, a spokeswoman for the Brown campaign, told the Washington Examiner that the GOP candidate "believes that the climate is changing by a combination of natural and manmade causes," a statement that aligns with Brown's 2012 remarks.

An overwhelming scientific consensus is that humans are contributing to climate change, largely by burning greenhouse gas-emitting fossil fuels.

Brown is closely trailing Democratic Sen. Jeanne Shaheen, 44 percent to 46 percent, in a poll of likely voters released Thursday. Nine percent of respondents were uncertain who they would vote for, according to the WMUR-sponsored poll that was conducted by the University of New Hampshire Survey Center.

Shaheen slammed Brown for the climate change comments, saying in a statement that, "Scott Brown is wrong. Climate change is very real and here in New Hampshire we are already seeing consequences."

Outside groups hit Brown in 2012 and then again this year in New Hampshire for his past support of maintaining tax incentives for oil and gas companies. NextGen Climate announced a nearly $1 million TV and radio ad buy in the Granite State last week that sought to tie Brown to "Big Oil" and the conservative industrial billionaire Koch brothers.

"New Hampshire voters see Scott Brown for what he is: someone more interested in his own political career than in the issues that matter to Granite State voters," Pete Kavanaugh, state director for NextGen Climate, said in a statement on Brown's climate change comments. "From health care reform to immigration to a woman's right to choose and now to climate change, Scott Brown can't make up his mind about what he believes."