For an earnest young Christian named Ben Lowe, revelation came on the shores of Lake Tanganyika, in Africa. A relentless warming of the lake was reducing the catch of fish, the people were going hungry — and he had learned of scientific evidence that climate change was to blame.

For the Rev. Brian Sauder, who grew up attending a small Anabaptist church in rural Illinois, the moment came in a college classroom. Studying the fallout from environmental degradation, he learned of poor people who had to walk hours longer each day to gather firewood from depleted forests.

For both men, Christian duties that their upbringing had led them to regard as separate — taking care of the earth and taking care of the poor — merged into a morally urgent problem. “Why haven’t I ever made this connection before?” Mr. Sauder recalled asking himself.

It is a connection that many people of faith all over the world are starting to make.

The sweeping pastoral letter issued by Pope Francis on Thursday may prove to be a watershed, highlighting the issues of social justice at the heart of the environmental crisis. But the pope’s encyclical is, in a sense, simply an exclamation mark on a broad shift in thinking that has been underway for decades and extends far beyond the Roman Catholic Church.

Many faith traditions are awakening to the burden that climate change is placing on poor people, and finding justification for caring for the environment in their scripture. The pope’s urgent call is likely to intensify this discussion, provoking what could be one of the most important dialogues between science and religion since the days of Charles Darwin.

Environmental scientists who are themselves people of faith are in rising demand, valued as translators between two camps that have often seen the world in radically different ways. These scientists have known for a long time that the facts and data produced by their research colleagues would not be sufficient to rouse the public to act. For that to happen, the science had to be reframed in moral terms, they said.

“The science is critical, but it’s not enough,” said Nathaniel P. Hitt, a fisheries biologist who is active in a Presbyterian church in Shepherdstown, W.Va. “Science is like a compass. It can tell us where north is, but it can’t tell us if we want to go north. That’s where our morality comes in.”

Dr. Hitt and the congregation to which he belongs are, to borrow his phrase, heading north. They recently put solar panels on the roof of their church and linked their home water heaters into a network that can help balance the grid fluctuations from renewable power, and they are avidly studying other ways to tackle the emissions causing global warming.

Hundreds of other churches, mosques and synagogues across the country have put up solar panels in recent years or retrofitted their buildings to cut energy use, or both. With the cost of renewable energy falling, that number could soon be in the thousands.

Politicians who try to reduce incentives for renewable power can find themselves contending with a new force: upset preachers packing the front row of the hearing room. A pastor in Fort Wayne, Ind., Brian Flory, recently helped stall such a bill in his state, citing the right of churches to “generate electricity from God’s free sunshine.”

For a long time, people of faith who felt a sense of urgency about the environment were outnumbered in their congregations by parishioners who disagreed with them on the issue or simply saw more immediate concerns. That is still true in many churches, perhaps in most of them, but the evidence suggests that the priorities are starting to change.

Polls show that a majority of American Christians view climate change as real, but fewer than a third of them understand the point, thoroughly documented in scientific studies, that poor people are already being harmed by it.

Men like Mr. Lowe and Mr. Sauder have dedicated their lives to helping other people of faith grasp the connection.

Mr. Sauder, ordained in the Mennonite denomination, is the executive director of Faith in Place, an interfaith group in Illinois that helps houses of worship with energy retrofits, solar panel installations and other steps that cut planet-warming emissions. Similar groups have sprouted across the country under the banner of a national organization called Interfaith Power and Light.

Mr. Lowe traveled as a college student, nearly a decade ago, to Lake Tanganyika, where he studied with an environmental scientist named Catherine O’Reilly. Dr. O’Reilly had documented that rising temperatures in the lake were depleting the surface waters of nutrients. That, in turn, was damaging fish populations that historically helped feed millions of people.

“I realized that climate change was already having impacts, and not just on God’s creation, but on many of my brothers and sisters around the world,” Mr. Lowe said.

The situation has grown only worse since, with overfishing being a possible factor, said Dr. O’Reilly, now an assistant professor at Illinois State University. She visited the lake again last year, and “the price of a small pile of fish has gone up 10 times, which is huge for people who are living day to day,” she said.

After college, Mr. Lowe helped found, and is now the spokesman for, Young Evangelicals for Climate Action, a national organization that has allied with other faith and environmental groups to push for change.

Despite shifting public opinion, Mr. Lowe and others who employ the slogan “creation care” are still viewed with suspicion by many fellow evangelicals.

Polls suggest that evangelicals are the American religious group least likely to believe that global warming is real or caused by humans. Many of them are politically conservative and are influenced by groups that question established climate science and defend the rising use of fossil fuels.

Among Christians and Jews, theological discussion sometimes centers on exactly what God meant in the first chapter of Genesis when he granted human beings “dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creepeth upon the earth.”

Does this passage — in Christian theology, it is called the dominion mandate — mean that people can do no ecological wrong? Some conservative politicians do seem to interpret the verse, and related ones, as a promise that God would not let humans wreck their only home.

“My point is, God’s still up there,” Senator James M. Inhofe, an Oklahoma Republican who is one of the leading climate-science doubters in Congress, said on a Christian radio program in 2012. “The arrogance of people to think that we, human beings, would be able to change what he is doing in the climate is, to me, outrageous.”

In his encyclical, Francis disputed this view, declaring not only that humans are altering the climate but that the dominion mandate encompasses a duty to care for creation. Katharine Hayhoe, a climate scientist at Texas Tech University who is an evangelical Christian, lines up with the pope on the issue.

If God granted humanity free will, she sometimes asks audiences, why would that not include the capacity to harm the planet?

Religious conservatives who oppose environmentalism profess a deep concern for the plight of the poor. But they point out that economic success has historically been closely linked to the use of fossil fuels.

“The policies meant to mitigate global warming would oppress the poor by depriving them of the energy without which they cannot rise out of poverty,” E. Calvin Beisner, a leader of an American group called the Cornwall Alliance for the Stewardship of Creation, declared this year in Rome at a symposium held to pre-emptively counter Francis’ message.

Liberal groups often dismiss that view as tendentious, yet it is precisely the fear that preoccupies countries like India that have refused to commit to serious emissions limits.

The stated goal of the environmental movement is to break the link between fossil fuels and economic success.

Perhaps the biggest question now is whether rising concern about the environment among religious groups will translate into stronger political demands that governments find ways to reduce the cost of low-carbon energy supplies, improve their reliability and speed their deployment.

This month, more than 350 American rabbis issued a letter of their own, declaring that the time for action was at hand.

“The hope is that over and over in our history, when our country faced the need for profound change, it has been our communities of moral commitment, religious covenant and spiritual search that have arisen to meet the need,” the rabbis declared. “So it was 50 years ago during the civil rights movement, and so it must be today.”