It seemed like a straightforward question on a second-tier issue: Would Mitt Romney disavow the science behind global warming?

The putative Republican presidential front-runner, eager to prove his conservative bona fides, could easily have said what he knew many in his party’s base wanted to hear.

Instead, the former Massachusetts governor stuck to the position he has held for many years — that he believes the world is getting warmer and that humans are contributing to that pattern.

Romney’s answer to the question about climate change last Friday during his first town hall meeting since announcing his second presidential campaign allowed him to demonstrate what he hopes voters will see as a new and improved candidate — an authentic leader with core convictions.

But the exchange in New Hampshire also served as a fresh indicator of Romney’s great quandary. He must shed the flip-flopper reputation that haunted his last presidential campaign while also appealing to conservative voters wary of his past support for near-universal health care, abortion rights, same-sex marriage and other positions befitting a politician elected in liberal Massachusetts.

So far, Romney’s reviews from the right are not positive. His views about climate change in particular put him at odds with many in his party’s base.

“Bye-bye, nomination,” Rush Limbaugh said Tuesday on his radio talk show after playing a clip of Romney’s climate remark. “Another one down. We’re in the midst here of discovering that this is all a hoax. The last year has established that the whole premise of man-made global warming is a hoax, and we still have presidential candidates that want to buy into it.”

Then came the Club for Growth, which issued a white paper criticizing Romney. “Governor Romney’s regulatory record as governor contains some flaws,” the report said, “including a significant one — his support of ‘global warming’ policies.”

And Conservatives4Palin.com, a blog run by some of former Alaska governor Sarah Palin’s more active supporters, posted an item charging that Romney is “simpatico” with President Obama after he “totally bought into the man-made global warming hoax.”

A Romney spokeswoman declined to comment about the criticism but did provide excerpts from Romney’s 2009 book, “No Apology ,” in which the candidate articulates the same environmental positions.

The episode suggests that Romney and his team, trying to market the candidate as authentic, see more of a benefit in sticking with his position and taking heat than in shifting to win over a crucial segment of the conservative base.

“The fact that he doesn’t change his position . . . that’s the upside for us,” said one Romney adviser, who spoke on the condition of anonymity because he was not authorized to speak on behalf of the campaign. “He’s not going to change his mind on these issues to put his finger in the wind for what scores points with these parts of the party.”

Romney, in his full answer to the question about climate change, maintained his position while offering enough nuance to extend an open hand to those who disagree.

“I don’t speak for the scientific community, of course, but I believe the world’s getting warmer,” he said. “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.”

Romney added that “it’s important for us to reduce our emissions of pollutants and greenhouse gases that may be significant contributors.” He also said he does not support a cap-and-trade policy, saying it would put American companies at a competitive disadvantage in the world. “We don’t call it ‘America warming,’ ” he said. “We call it ‘global warming.’ ”

But it was his line that “humans contribute” that sparked the conservative backlash.

Romney has long known that the health-care legislation he signed in Massachusetts — like Obama’s federal health-care overhaul, it includes an individual mandate — could be his Achilles’ heel in pursuit of the Republican nomination.

Now, some conservatives say, he should add climate change to that list.

“If [voters] get past Romneycare, then this will be a ‘do not pass go’-type issue,” said Christopher Horner, a senior fellow at the conservative Competitive Enterprise Institute and a leading global warming skeptic. “This could just be the last straw.”

Four years ago, Romney drew scorn from some conservatives when he appeared to veer to the right and disavow his formerly liberal positions. And after he lost the 2008 nomination, polling suggested that many Republican voters doubted his authenticity.

This time, Romney is trying to turn around that narrative. That effort began last month in Michigan with a PowerPoint presentation on health care.

Trying to stop a drumbeat of conservative criticism, Romney said that the law he signed as governor was “a state solution to a state problem” and that he stands by it. But if elected president, he said, he would issue an executive order on his first day in office paving the way for states to opt out of the new federal law.

In the 2008 presidential campaign, climate change was not a major issue. Although Sen. John McCain (Ariz.), the Republican nominee, said he believed the science behind global warming, he did little to highlight his earlier bipartisan work in the Senate on climate change.

Public opinion is politicized on the issue. A March Gallup poll found that 32 percent of Republicans think the effects of global warming are already being felt and 36 percent believe the rise in the Earth’s temperatures is caused by humans, while 67 percent say the seriousness of global warming is exaggerated in the news.

The same survey found the opposite trend on the other side of the political fence. Sixty-two percent of Democrats polled said the effects of global warming have begun, and 71 percent said humans are causing the rising temperatures, while 22 percent think the situation is exaggerated. Among independents, there was a fairly even split on those questions.

For Romney, the past few weeks have been encouraging. He raised more than $10 million in a single day last month and has since crisscrossed the country vacuuming up many more checks. He is widely expected to trounce other candidates when he posts his fundraising total for the quarter that ends June 30.

Meanwhile, a Washington Post-ABC News poll this week showed Romney as the strongest current or prospective Republican candidate in the 2012 presidential field. Among all Americans, Obama and Romney are locked in a dead heat, at 47 percent each. But the poll found that among registered voters, Romney is numerically ahead of Obama, 49 percent to 46 percent, while independents split for Romney 50 percent to 43 percent.

“I hate to disagree with Rush Limbaugh, but I don’t think the campaign’s over,” said Katon Dawson, a former chairman of the South Carolina Republican Party, pointing to Romney’s strength in fundraising and organization. As for climate change, he added, “I’m not sure that’s a deal-breaker for Mitt Romney.”

Polling director Jon Cohen contributed to this report.