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, 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 Republican analysts, consultants and activists, all said they were acutely aware of the rising influence of young voters like Mr Galloway, who identify climate change as a top priority. Those strategists said lawmakers were aware, too, but few were taking action.

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“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.”

Mr Trump has set the tone for Republicans by deriding climate change, using White House resources to undermine science and avoiding even uttering the phrase.

Outside of a handful of states such as Florida, where addressing climate change has become more bipartisan, analysts said Republican politicians were unlikely to buck Mr Trump or even to talk about climate change on the campaign trail at all, except perhaps to criticise Democrats for supporting the Green New Deal.

That, several strategists warned, means the party stands to lose voters to Democrats in 2020 and beyond – a prospect they said was particularly worrisome in swing districts that Republicans must win to recapture a majority in the House of Representatives.

The polling bears out Mr Heye’s prediction of a backlash. Nearly 60 per cent of Republicans between ages 23 and 38 say that climate change is having an effect on the United States and 36 per cent believe humans are the cause. That is about double the numbers of Republicans older than 52.

But younger generations are also now outvoting their elders. According to a Pew Research Centre analysis, voters younger than 53 cast 62.5 million votes in the 2018 midterm elections. Those 53 and older, by contrast, were responsible for 60.1 million votes.

“Americans believe climate change is real, and that number goes up every single month,” Frank Luntz, a veteran Republican strategist, told a congressional panel recently.

He also circulated a memo to congressional Republicans in June warning that climate change was “a GOP vulnerability and a GOP opportunity.”

A Harvard University survey of voters younger than 30 found that 73 per cent of respondents disapproved of Mr Trump’s approach to climate change (about the same proportion as those who object to his handling of race relations). Half the respondents identified as Republican or independent.

“Here’s another gap between our party and younger voters,” said a recent report by a Republican polling firm, Public Opinion Strategies. Speaking of younger Republicans, the firm concluded that “climate change is their most important issue” and called the numbers “concerning” for the party’s future.

The full effect will quite likely not be felt until after the 2020 election cycle. Mr Trump’s campaign appears to have identified a strategy for winning re-election that relies on polarising the electorate on issues like race, immigration and, it seems, climate change. But conservatives said the long-term implications of that gambit were worrisome for the future of the party and the planet.

“He gets to set the national platform,” Joseph Majkut, director of climate policy at the Niskanen Centre, a centre-right research organisation, said of Mr Trump.

But, he noted, “Every year that goes by, where people are going about their lives as if greenhouse gas emissions are a matter of very small concern, we make the problem worse for ourselves.”

Mr Galloway and 45 other young Republicans with the American Conservation Coalition, a group that advocates for conservative environmental policies, brought that message to Washington last month when they lobbied Congress to address greenhouse-gas emissions with free-market solutions.

“You can be sceptical of climate change all you want, but young people aren’t, and there’s no way conservatives are going to win elections if we don’t deal with climate change,” said Benjamin Backer, the coalition’s founder and president.