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WASHINGTON — When John Barrasso, a Republican from oil and uranium-rich Wyoming who has spent years blocking climate change legislation, introduced a bill this year to promote nuclear energy , he added a twist: a desire to tackle global warming.

Mr. Barrasso’s remarks — “If we are serious about climate change, we must be serious about expanding our use of nuclear energy” — were hardly a clarion call to action. Still they were highly unusual for the lawmaker who, despite decades of support for nuclear power and other policies that would reduce planet-warming emissions, has until recently avoided talking about them in the context of climate change.

The comments represent an important shift among Republicans in Congress. Driven by polls showing that voters in both parties — particularly younger Americans — are increasingly concerned about a warming planet, and prodded by the new Democratic majority in the House shining a spotlight on the issue, a growing number of Republicans are now openly discussing climate change and proposing what they call conservative solutions.

“Denying the basic existence of climate change is no longer a credible position,” said Whit Ayers, a Republican political consultant , pointing out the growing climate concern among millennials as well as centrist voters — two groups the G.O.P. will need in the future.