As Pope Francis steps up his moral campaign for global action on climate change, Republican Roman Catholics in Congress are more likely to listen to fossil fuel interests and party leaders than their pontiff, religious and political researchers say, based on lawmakers' track records.

The pope hosted a global warming summit at the Vatican this week with economists, scientists and religious and government leaders. The global leader of the Catholic Church plans this summer to issue the first-ever encyclical, a high-level Catholic teaching document, devoted to global warming and its effects on the world's poor.

But as much sway as the pope has with a sixth of the world's population, party doctrine will probably trump church doctrine in Congress, experts told InsideClimate News. The position of Pope Francis on climate change—and nearly every mainstream climate scientist—bucks that of American conservatives and fossil fuel interests such as the billionaire Koch brothers, who have spent millions of dollars casting doubt on the reality of human-driven climate change and supporting candidates who oppose action to address it.

"If the science hasn't persuaded Republican politicians, the Pope won't," said R.L. Miller, founder of Climate Hawks Vote, a super PAC that works to elect climate-conscious candidates. "American Catholics have been in the habit of mixing and matching parts of Catholic doctrine when it suits them for decades. I don't see this as an exception."

The pope's doctrinal statement will come as world leaders prepare to meet in December in Paris on global warming. They plan to hash out an international accord to fight climate change and address the needs of billions of poor people who suffer from the worst effects of warming.

It also comes at a time when fossil fuel divestment campaigns are sweeping college campuses across the nation and the world. Like the pope, divestment activists have the goal of turning global warming action into the moral issue of this generation. Campaigns are underway at 500 colleges. Thirty schools worldwide—along with 41 cities, 72 religious institutions, 30 foundations and hundreds of individuals—have divested or pledged to divest from fossil fuels.

"Morality moves politicians. Politicians can dodge policy questions, it's harder to dodge a question like, 'why are you choosing Exxon over our kids?' said Jamie Henn, director of strategy and co-founder of 350.org, the environmental group behind the divestment movement. "When climate is about widgets and circuits, you lose people. When it's about our health, our families, and our future, you start seeing people in the streets."

Catholics make up nearly 32 percent of the House of Representatives and 26 percent of the Senate, compared with 22 percent of the U.S. population.

The list of Catholics in Congress includes several of the GOP's most prominent climate denialists, such as presidential contender Marco Rubio, a Florida senator; House Speaker John Boehner of Ohio; and former vice presidential candidate and Wisconsin Rep. Paul Ryan. Likely presidential contenders Jeb Bush, a former governor of Florida; Gov. Chris Christie of New Jersey; and Gov. Bobby Jindal of Louisiana are also Catholic. Those three question the science of human-caused global warming and oppose climate policy.

No Republican politician has yet commented on the pope's climate agenda, but conservatives such as the Heartland Institute, a right-wing tank that has received funding from the Kochs, have lambasted the Catholic leader's efforts.

The Heartland Institute sent a group of climate denialists to Rome earlier this week to, "inform Pope Francis of the truth about climate science: There is no global warming crisis!" according to a press release. Just nine journalists showed up to its press event.

At the invitation of Boehner, Pope Francis will address Congress in September, shortly after the publication of his climate encyclical.

Rubio, Boehner and Ryan, among others, will probably ignore the pope's calls for action in favor of following the Republican party line on climate change, political researchers said. None responded to InsideClimate News' requests for comment. On the other side of the aisle, Catholics including House minority leader Nancy Pelosi of California, Sen. Dick Durbin of Illinois and Sen. Patty Murray of Washington, may use the encyclical to bolster their party's climate agenda, the researchers said.

"If you ask any politician, most say their faith is central to what they do," said Dan Cox, director of research at the Public Religion Research Institute, a nonprofit organization that examines the intersection of religion, values and public life. "But when you look at specific issues, like the death penalty and abortion, you're better off knowing their party then their religion."

Invoking Their Faith

Still, Catholic politicians, particularly Republicans, have a history of invoking their faith to justify policy decisions.

When Ryan, the Republican representative from Wisconsin, proposed in 2012 to slash social welfare programs including Medicaid and food stamps in his overhaul of the federal budget, he cited his Catholic faith.

"The preferential option for the poor, which is one of the primary tenants of Catholic social teaching, means don't keep people poor, don't make people dependent on government so that they stay stuck at their station in life," Ryan told the Christian Broadcasting Network at the time.

Rubio, the Republican senator from Florida who is running for president, often makes the religious case for immigration reform. In 2012, he told Christianity Today, "If your faith is real, burning inside of you, it's going to influence the way you view everything. That belief influences your job and the responsibilities you have."

Rubio has also criticized Pope Francis for helping to negotiate the opening of relations between the U.S. and Cuba.

Virginia Democratic Senator Tim Kaine has spoken openly about how his Catholic faith drives his "moral position" against capital punishment. As an attorney, Kaine defended several death row inmates pro-bono.

Most Catholic politicians invoke their faith more selectively than they did two decades ago, choosing which teachings to follow instead of following the full church doctrine, experts said. It's the same with the majority of the American Catholic public.

"In today's Congress, party matters much more than the faith tradition you come from," said Geoff Layman, a political scientist at the University of Notre Dame, a Roman Catholic institution in South Bend, Indiana. "Catholic Democrats tend to vote like any other Democrat, and Catholic Republicans like any other Republican."

Future Impacts

Following publication of the Pope's climate encyclical this summer, Catholic bishops will spend 12 weeks discussing global warming in sermons, media interviews and letters to editors, the New York Times reported.

This could have an impact on the public and policymakers. Americans who attend a church where the pastor even occasionally preaches about climate change are more likely to accept the scientific evidence for global warming than those who don't, according to a 2014 poll by the Public Religion Research Institute.

The institute's Cox said the pope currently enjoys widespread popularity among American Catholics, but that his climate campaign and Congressional visit could polarize opinions of him among politicians. But either way, he said, Francis' push for action could "raise the profile of climate change in the U.S."

Correction: An earlier version of this story misidentified Senator Tim Kaine's political affiliation. He is a Democrat.