When election time comes next year, Will Galloway, a student and Republican youth leader at Clemson University, will look for candidates who are strong on the mainstream conservative causes he cares about most, including gun rights and opposing abortion.

But there is another issue high on his list of urgent concerns that is not on his party’s agenda: climate change.

“Climate change isn’t going to discriminate between red states and blue states, so red-state actors have to start engaging on these issues,” said Mr. Galloway, 19, who is heading into his sophomore year and is chairman of the South Carolina Federation of College Republicans. “But we haven’t been. We’ve completely ceded them to the left.”

While Donald Trump has led the Republican Party far down the road of denying the scientific consensus of human-caused climate change, Mr. Galloway represents a concern among younger Republicans that has caught the attention of Republican strategists.

In conversations with 10 G.O.P. analysts, consultants and activists, all said they were acutely aware of the rising influence of young voters like Mr. Galloway, who have never lived through a colder-than-average month and identify climate change as a top priority. Those strategists said lawmakers were aware, too, but few were taking action.

“We’re definitely sending a message to younger voters that we don’t care about things that are very important to them,” said Douglas Heye, a former communications director at the Republican National Committee. “This spells certain doom in the long term if there isn’t a plan to admit reality and have legislative prescriptions for it.”  […]