WASHINGTON — Since his first homily in 2013, Pope Francis has preached about the need to protect the earth and all of creation as part of a broad message on the environment. It has caused little controversy so far.
But now, as Francis prepares to deliver what is likely to be a highly influential encyclical this summer on environmental degradation and the effects of human-caused climate change on the poor, he is alarming some conservatives in the United States who are loath to see the Catholic Church reposition itself as a mighty voice in a cause they do not believe in.
As part of the effort for the encyclical, top Vatican officials will hold a summit meeting Tuesday to build momentum for a campaign by Francis to urge world leaders to enact a sweeping United Nations climate changeaccord in Paris in December. The accord would for the first time commit every nation to enact tough new laws to cut the emissions that cause global warming.
The Vatican summit meeting will focus on the links between poverty, economic development and climate change, with speeches and panel discussions by climate scientists and religious leaders, and economists like Jeffrey Sachs of Columbia. The United Nations secretary general, Ban Ki-moon, who is leading efforts to forge the Paris accord, will deliver the opening address.
Vatican officials, who have spent more than a year helping Francis prepare his message, have convened several meetings already on the topic. Last month, they met with the administrator of the Environmental Protection Agency, Gina McCarthy.
In the United States, the encyclical will be accompanied by a 12-week campaign, now being prepared with the participation of some Catholic bishops, to raise the issue of climate change and environmental stewardship in sermons, homilies, news media interviews and letters to newspaper editors, said Dan Misleh, executive director of the Catholic Climate Covenant in Washington.
But the effort is already angering a number of American conservatives, among them members of the Heartland Institute, a libertarian group partly funded by the Charles G. Koch Foundation, run by the billionaire industrialist Koch brothers, who oppose climate policy.
“The Holy Father is being misled by ‘experts’ at the United Nations who have proven unworthy of his trust,” Joseph Bast, the president of theHeartland Institute, said in a statement. “Though Pope Francis’ heart is surely in the right place, he would do his flock and the world a disservice by putting his moral authority behind the United Nations’ unscientific agenda on the climate.”
The institute plans to hold a news conference and panel event in Rome on Tuesday in protest of the Vatican summit meeting.
But climate policy advocates see a scheduled address by the pope to Congress in September as a potent moment — about 30 percent of members of Congress are Catholics, more than belong to any other religion, according to a study published this year by the Pew Research Center.
Speaker John A. Boehner, Republican of Ohio, invited the pope to speak to Congress, but some Catholics say that Mr. Boehner should prepare for some uncomfortable moments. Mr. Boehner, who is Catholic, has often criticized the Obama administration for what he calls its “job killing” environmental agenda.
“I think Boehner was out of his mind to invite the pope to speak to Congress,” said the Rev. Thomas Reese, an analyst at the National Catholic Reporter. “Can you imagine what the Republicans will do when he says, ‘You’ve got to do something about global warming’? ”
In addition, a number of Catholics — including Jeb Bush, Marco Rubio, Bobby Jindal, Chris Christie and Rick Santorum — are gearing up to compete for the Republican presidential nomination, and most of them question the science of human-caused climate change.
Several conservative Catholic intellectuals who expect the pope’s message to bolster the vast majority of scientists who hold that climate change is induced by human activity, including Robert P. George, a Princeton law professor, have published articles reminding Catholics that papal pronouncements on science are not necessarily sound or binding.
Maureen Mullarkey, a painter and writer, said in the conservative journalFirst Things that “Francis sullies his office by using demagogic formulations to bully the populace into reflexive climate action with no more substantive guide than theologized propaganda.”
Timothy E. Wirth, vice chairman of the United Nations Foundation, said: “We’ve never seen a pope do anything like this. No single individual has as much global sway as he does. What he is doing will resonate in the government of any country that has a leading Catholic constituency.”
Francis, however, is not the first pope to push an environmental message. His predecessor, Pope Benedict XVI, called the “green pope” by some, wrote about the environment and the impact of climate change in documents that have been collected in a book, “The Environment.” But Catholic and climate policy experts acknowledge that those works had little substantive impact on global warming policy.
Francis’ policy moves on climate change, particularly his use of the encyclical, go far beyond what has come before. Catholics point to other papal encyclicals that have had public policy impacts: Pope Leo XIII’s 1891 encyclical on labor and workers’ rights is believed to have spurred the workers’ rights movement and led to the creation of labor unions.
“I think this moves the needle,” said Charles J. Reid Jr., a professor at the University of St. Thomas School of Law. “Benedict was an ivory-tower academic. He wrote books and hoped they would persuade by reason. But Pope Francis knows how to sell his ideas. He is engaged in the marketplace.”
Francis, who chose the name of St. Francis of Assisi, the patron saint of animals and the environment, has had far more influence on the church and public. Born in Argentina, Francis draws cheering crowds from around the world and millions of followers to his social media accounts. He has been embraced for his humility, antipoverty agenda, progressive statements on social issues and efforts to reform the Vatican bureaucracy.
This month he said in a Twitter post: “We need to care for the earth so that it may continue, as God willed, to be a source of life for the entire human family.”
The pope’s influence on the Paris climate accord may be strongest in Latin America. In past years, Latin American countries have resisted efforts to enact climate policy, arguing that developing economies should not have to cut emissions while developed economies continue to pollute.
But over the past year, some Latin American governments have signaled a willingness to step forward on climate policy, and this year Mexico became one of the first nations to submit a plan ahead of the Paris talks.
“This pope is more than just a church leader — he is a political leader, particularly in Latin America,” said Romina Picolotti, president of theCenter for Human Rights and Environment in Argentina. “Youth in Latin America are really following him closely.”