In April this year, on Earth Day, Pope Francis urged everyone to see the world through the eyes of God, as a garden to cultivate.
"May the way people treat the Earth not be guided by greed, manipulation, and exploitation, but rather may it preserve the divine harmony between creatures and creation, also in the service of future generations," he said.
On Thursday, the Vatican will release the pontiff's hotly anticipated encyclical on the environment and poverty. The rollout of the teaching document has been timed to have maximum impact ahead of the U.N. climate change conference in December aimed at slowing global warming — and has angered climate change skeptics.
Past popes have also spoken about man's duty to protect the environment. Pope Benedict XVI was known as the "Green Pope" for installing solar panels at the Vatican.
Francis has made it clear that he believes climate change is mostly man-made.
"It's man," he said earlier this year, "who has slapped nature in the face."
Safeguard creation, Francis warned — because if we destroy it, it will destroy us.
Statements like these are generating controversy in some quarters. For example, Republican presidential candidate Rick Santorum — who is Catholic — believes the pope should focus on problems that Santorum says are more pressing than climate change.
"The church has gotten it wrong a few times on science, and I think that we probably are better off leaving science to the scientists, and focusing on what we're really good at, which is theology and morality," Santorum said.
As a young man, the future pope studied chemistry and worked as a chemist before entering seminary, so he may have more scientific training than most of his critics.
"It's nice — for once the Catholic Church is on the side of science," says the Rev. Thomas Reese, senior analyst for the National Catholic Reporter.
The encyclical won't be just about economics and politics, he says, but will focus on a moral issue that could affect many millions of lives.
"This is a call to respond, to help people, to protect people from the disasters that can come from climate change," Reese says. "The pope sees it as one of the most important challenges that we face as humanity."
As the first Latin American pope, Francis warns against what he calls the myth of trickle-down economics and the "throw-away culture" whose primary victims are the poor. As a result, some conservatives have labeled the leading voice of the global south a "closet Marxist."
But Mary Evelyn Tucker, professor of religion and ecology at Yale University, says the pope focuses on inequities in incomes and distribution of resources in societies across the world. She believes the papal document will stress not just sustainability, but development centered on human beings and on justice.
"Not development that allows the poor to sink and the rich to rise," she says, "so this is a new integration called eco-justice."
The title of the document is Laudato Sii, or "Praised Be," a refrain from the "Canticle of the Creatures" written in the 13th century by St. Francis of Assisi, patron saint of the environment — and the man from whom the pope took his name.
The pope's encyclical, says Reese of the National Catholic Reporter, will help rid environmentalists of their image as tree-huggers and Gaia worshippers and bring the movement into the mainstream.
He's also convinced it will have a far-reaching impact, encouraging Catholics to make major changes in what they consume and how they live their daily lives, and inspiring leaders of other religions to pick up the challenge.
"Religion is one of the few things that can motivate people to self-sacrifice — to give up their own self-interest for something else," Reese says. "This is going to be extremely important because people are not going to change their lifestyles to save the polar bears."