The Republicans’ unyielding approach has even sympathizers shaking their heads.

“Paris could provide a chance for the Republican Party to get on the right side of history,” said Andy Karsner, who was an assistant secretary of energy under President George W. Bush.

At the International New York Times Energy for Tomorrow Conference in Paris on Wednesday, Mr. Karsner, now an adviser to Google X, Google’s research and development arm, urged climate-change skeptics to leave the realm of the ideological and view the promotion of renewable energy in economic terms.

That is the view espoused by Mr. Schwarzenegger, who in a Facebook post on Monday said that even if climate science was bunk, Americans should support a shift to clean energy because of the deaths caused by air pollution; because fossil fuels are not inexhaustible; and because renewable power sources are a better bet economically.

“As long as you can give Republicans the choice of saying, ‘Well, I don’t really think that 20 years from now there will be a sea level rising,’ or ‘I don’t think that is human-caused,’ and stuff like that, you give them an opening, and they will use it,” he said in an interview on Tuesday. He added that it was far more effective to frame the argument in terms of the immediate effects on health and the economy.

Secretary of State John Kerry took a similar tack in a speech here on Wednesday.

“For a moment — and a moment only — let’s give the climate deniers the benefit of the doubt,” he said. Even if the overwhelming scientific consensus is wrong, he asked rhetorically, “what is the worst that could happen” by shifting away from fossil fuels toward renewable energy?

“Well, we absolutely would create millions of new jobs,” he said. “We would boost our economies, and for some countries where they’ve slowed down, they need that boost. They need the capital that would flow into energy investment. We would see a healthier population, healthier children.”