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Rick Santorum loves Pope Francis — as long as the pontiff doesn't talk about climate change.

The former Pennsylvania senator and outspokenly conservative Catholic is making his second bid for the White House. Speaking on a Philadelphia talk-radio show this week, he said he's a "huge fan" of Francis "and his focus on making sure we have a healthier society."

But Santorum said Catholics are "better off sticking to the things that are really the core teachings of the church, as opposed to getting involved in every other kind of issue that happens to be popular at the time."

"The church has gotten it wrong a few times on science," said Santorum, the 2012 Republican presidential primary runner-up. "We probably are better off leaving science to the scientists and focusing on what we're really good at, which is theology and morality. And I think whenwe get involved with controversial scientific theories, I think the Church is not as forceful and not as credible."

But the scientific theory behind climate change is controversial only in political circles. The vast majority of scientists who study the issue say the Earth is being warmed by heat-trapping carbon emissions from the burning of coal, oil, and natural gas. And while it may still be trying to live down its infamous persecution of Galileo centuries ago, the Vatican has firmly embraced the scientific consensus on climate.

Meanwhile, Francis — who studied chemistry before becoming a priest — is about to weigh in on climate change in a big way, with a papal encyclical that's now scheduled to drop on June 18. Dan Misleh, the head of the US-based Catholic Climate Covenant, told VICE News that the document "will generate good deal of talk and energy" in support of protecting the environment, but he expects more criticism like Santorum's as well.

"There are certainly those with vested interests who would rather not see this come out, but it's happening," Misleh said. "So I imagine that there will continue to be voices out there that will be against the moral message that the pope is trying to convey about our lack of care for creation."

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The spiritual leader of the world's 1.2 billion Catholics took his papal name from the patron saint of ecology. He has called for nations to head off the worst effects of climate change, which are expected to fall disproportionately on the world's poor. And he's expected to bring that message to Washington in September, when he's slated to become the first pope to address Congress.

On the other hand, Santorum has called climate change a hoax concocted by liberals "to try to scare you into supporting radical ideas on the environment." He mocked President Barack Obama's insistence that climate change fueled national security risks, telling conservative activists in a January speech: "We don't need a weatherman-in-chief, we need a commander-in-chief." He opened his second presidential bid last month by holding up a chunk of coal — an illustration of his family connection to coal mining.

That stance makes him an outlier among US Catholics, who make up about a quarter of American adults. According to polling from the Yale Project on Climate Change Communication, seventy percent of Catholics believe global warming is happening and are more likely than members of other Christian denominations to believe it's caused by human activity.

They're also more likely than Americans as a whole to support taking action to rein in warming. About 27 percent of Catholics strongly believe God expects them to be good stewards of nature, a higher share than average among other denominations.

Efforts to contact Santorum's campaign for comment were unsuccessful Thursday.

Other leading Catholic Republicans also oppose steps to reduce emissions: House Speaker John Boehner has ducked the issue, while presidential hopeful Marco Rubio said it pointless for the US to curb emissions while developing nations are increase their amounts. Bobby Jindal, a likely contender for the White House, echoed Santorum, calling climate change a "Trojan horse" for more government regulation.

Of course, the American church includes plenty of officeholders who don't toe the Vatican line on other issues, particularly abortion rights. But a papal encyclical — a letter that lays out the position of the church — is one of the most authoritative documents the Vatican can issue. Rob Sisson, executive director of the GOP environmental group ConservAmerica, said that could make it tough on politicians like Santorum, whose Catholicism is a major element of his public career.

"I think the encyclical is going to make a very strong case that environmental protection in general is part of being pro-life," Sisson told VICE News. "It's inextricable with protecting unborn babies and protecting people at the end of life."

That will pose an "intellectual challenge" for candidates who may be trying to appeal to Republican primary voters who oppose taking climate action. "It's going to be very difficult to reconcile being anti-environmental protection and anti-climate action with being pro-life in other areas," he said.

ConservAmerica said in February that Republicans should "stop casting doubt on the reality of climate change and start casting doubt on the wisdom of a 12-year old strategy of denial." A poll by the group found that the most loyal Republican voters aren't likely to switch candidates based on their position on climate change, but general election voters are more likely to be turned off by climate denial.

"In the general election, it will be a liability not to stake out a position in line with the prevailing scientific evidence," Sisson said. As a result, "I think this cycle, we are going to see some leadership from Republican presidential candidates."

"It may not be solution oriented. It may be more like a, 'Hey, this is a problem. We need to deal with it' type of conversation during the primary," he told VICE News. "But that's leaps and bounds beyond where we've been in the past few years."