Leading figures on the American right are launching a series of pre-emptive attacks on the pope before this week’s encyclical, hoping to prevent a mass conversion of the climate change deniers who have powered the corps of the conservative movement for more than a decade.

The prospect that the pope, from his perch at the pinnacle of the Catholic church, will exhort humanity to act on climate change as a moral imperative is a direct threat to a core belief of US conservatives. And conservatives – anxious to hang on to their flock – are lashing out.

“The pope ought to stay with his job, and we’ll stay with ours,” James Inhofe, the granddaddy of climate change deniers in the US Congress and chairman of the Senate environment and public works committee, said last week, after picking up an award at a climate sceptics’ conference.

Rick Santorum, a devout Catholic and a long-shot contender for the Republican nomination, told a Philadelphia radio station: “The church has gotten it wrong a few times on science, and I think we probably are better off leaving science to the scientists and focusing on what we’re good at, which is theology and morality.”

A majority of Republicans in Congress deny the existence of climate change and oppose regulations to cut greenhouse gas emissions. Among the ultra-conservative Tea Party set, climate change scepticism reaches epidemic proportions, about 80% of those on the far right, according to the Pew research centre. Only one of the nearly 20 Republicans running for president will acknowledge the danger of climate change, another long-shot contender, Lindsey Graham.

The fossil fuel industry, including the American Petroleum Institute lobby group and Peabody Coal, has cast fossil fuels as a route out of poverty in the developing world. Ultra-conservative and climate change denial thinktanks, such as the Heartland Institute, which has been funded by the oil industry, have argued that climate change was the cure for drought and famine in Ethiopia in the 1980s.

“In the US for the past 10 years we have allowed climate change to become an ideological political issue instead of being the moral issue that it is,” said the Rev Mitchell Hescox, leader of the Evangelical Environmental Network. “The idea that climate change is a liberal issue has just permeated the thought of those in the conservative movement, and those in the denier campaign have taken advantage of that to continue to drive home the message that climate change is not a moral issue,” added Hescox, who identifies himself as a conservative.

But it gets much harder to dismiss climate change as a fringe concern of liberals such as Al Gore, and environmental regulations as a sneaky first step to sweeping regulations and a government takeover of private lives, once the pope becomes involved.

“If I were a Catholic climate denier, I would be worried about the pope,” said Patrick Regan, who teaches the politics of climate change at the University of Notre Dame. “And if I had a vested interest in not changing climate policy, the pope would be a threat to my political stance.”

In the case of climate change, conservatives face multiple threats to the world view.

This week, the pope will cast climate change as the moral cause of our times. Over the summer, Barack Obama will finalise new rules cutting carbon pollution from power plants. In September, the pope will be back to stir up talk of climate change again, in the first ever speech by a pope to Congress – just at a time when hard-core conservatives had hoped to be voting on long-shot legislation to block the power plant rules or cut climate aid to developing countries.

Meanwhile, Jay Faison, a conservative Christian businessman from North Carolina, last week pledged $175m of his own money to try to get Republicans to face up to the reality of climate change and the American Enterprise Institute, the establishment conservative thinktank in Washington, gave a platform – and respectful hearing – to two Democratic senators launching a bill for a carbon fee.

The church has made an effort to prepare the ground for the pope, with the US Conference of Catholic Bishops meeting leading Republican and Democratic Catholics in Congress on climate change.

“I think sceptics have their work cut out for them to overpower the pope’s influence,” said Marc Morano, a climate change denier notorious for a blog that attacks scientists. “The pope being involved in this is a huge coup for promoters of manmade global warming,” he said.

It also puts conservatives in an uncomfortable spot – not unlike the Reagan era of the 1980s when bishops came out against nuclear weapons. “Conservative politicians will be in a position now of being where many liberals are when it comes to Catholic teaching,” Morano said. “It makes conservative politicians look like they are against Catholic teaching.” Other pontiffs have called for “creation care”, and Francis’s immediate predecessor at the Vatican, Benedict, was seen as the “green pope”. An encyclical raises the prospect of speeches on climate change from the pulpit of more than 17,000 Catholic parishes.

The discomfort will only increase in September when the pope is due to address the US Congress, said Sheldon Whitehouse, a Democratic senator from Rhode Island, who has made more than 100 speeches about climate change in Congress.

“Speaker John Boehner is a very proud and sincere Catholic, and I think it can’t not have an effect,” Whitehouse said. “I also think it will change the debate in public because it isn’t just an encyclical that goes up on the Vatican website. Every Catholic school will teach to it. Every Catholic parish will teach to it. Catholic universities will teach to it. It will be a significant force in the community and create very significant ripples.”Those ripples will likely travel well beyond Catholics, who make up about a quarter of the US population. Other conservatives will be influenced by the pope’s message too, said Hescox and they are unlikely to be receptive to the conservatives’ attacks.

“I think it is very hard to discredit the pope,” he said. “This completely destroys most of their arguments that climate change is not real, that it is funded by a “mass UN conspiracy”, that it is all to do with Al Gore and not to do with people of world.”