Pope Francis, in his eagerly awaited encyclical on the environment, says "the bulk of global warming" is caused by human activity and burning of fossil fuels and calls for urgent action to protect the Earth, according to a version obtained by an Italian newsmagazine.

The Rev. Federico Lombardi, the Vatican's spokesman, said the document leaked to the newsweekly l'Espresso and published on its website Monday was an "intermediate version."

He warned that some provisions in it may be different from the official version, to be released Thursday. The draft was translated into English by media organizations.

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Strong initial remarksFrancis, in the draft, firmly backs the science of climate change, saying "plenty of scientific studies point out that the last decades of global warming have been mostly caused by the great concentration of greenhouse gases (carbon dioxide, methane, nitrogen oxide and others) especially generated by human action," according to a translation by The Washington Post.

"The poor and the Earth are shouting," reads the draft of the encyclical, the first of its kind dedicated to the environment and the first wholly written by Francis.

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The pope, who worked as a chemist in Argentina before entering seminary, backs up his comments with science showing the impact of the loss of biodiversity in Amazon rain forests, the melting of arctic glaciers, the overfishing of the seas and the pollution of the world's water supply. Some church experts said the forthcoming document marks a historic moment for the church and the worldwide debate on climate change, and that Francis may be the only man on the planet capable of breaking the logjam to forge a solution.

Papal observers also said some of Francis' words are likely to anger conservative critics.

"This is a prophetic voice speaking out on the most important moral issue of our century -- climate change -- and how it will impact people all over the world," said the Rev. Thomas Reese, an analyst for the National Catholic Reporter. "I think it is going to have a profound impact."

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This encyclical is the most important since Pope Paul VI's 1968 document "Humanae Vitae" rejecting most forms of birth control -- though Francis' will get a much more positive reception, said John Gehring of the Washington, D.C.-based advocacy group Faith in Public Life.

Most striking in the draft, he said, is that "the pope accepts the overwhelming scientific consensus that human activity is exacerbating climate change."

"He's very clear that there's an urgent need to act," Gehring said. "He sees our addiction to oil, consumerism and a culture of waste as obstacles to repairing our broken relationship with creation."

Split reactions Locally, Sister Jeanne Clarke of the Dominican Sisters of Amityville said she is elated the pope decided to take on the issue. She and others have devoted the past 18 years to raising organic produce at "Homecoming Farm," behind the nuns' motherhouse.

"I think it is a marvelous thing," Clark said. "I'm so happy with this pope; I think he really is conveying the message of Jesus. We are out of relationship with the earth. We're not in right relationship."

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Not everyone was cheering the pope's message. Samuel Gregg of the Acton Institute, a Grand Rapids, Michigan, faith-based group that works to promote free markets, said the draft unfairly tarnishes capitalism and blames it as part of the climate change problem.

"The vision that you get of the market economy in this document is generally negative," he said. "It's seen as somehow unregulated, which isn't true. It's seen as a process of exploitation by the strong of the weak."

Some saw the document as the pope's opening salvo on the debate before his planned trip to the United States in late September, when he will address the United Nations and Congress. It also comes before critical UN global meetings on the climate later this year.

Some climate skeptics criticized the pope regarding the science that was included in the draft encyclical, the most authoritative teaching document a pope can issue.

"I disagree with some of the specific scientific and policy claims he makes," said Jay W. Richards, assistant research professor at Catholic University of America in Washington. "For instance, the claim that we have more extreme weather events isn't at all evident in the data."

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Richards, however, said, "I agree with all of his theology and with his emphases on the importance of the issue, especially for the poor."

Scientific, moral appealsIn the draft, Francis lays out both the scientific and the moral reasons for protecting God's creation, noting that the poor suffer the most from air pollution and toxic dumping and will continue to bear the brunt of rising sea levels and extreme weather conditions.

He calls for more investment in renewable energy and for equalizing the "ecological debt" between the Northern and Southern hemispheres, and wealthy and poor countries.

"Enlighten the masters of power and money so that they should not fall prey to the sin of indifference, so that they should love the common good, support the weak, and care about this world that we inhabit," the draft reads.

Population growth isn't to blame for ecological problems, according to the draft, but the consumerist, wasteful behavior of the rich.

This isn't the first time a pope has delved into environmental issues, said Erin Lothes, a theology professor at the College of St. Elizabeth in Morristown, New Jersey.

Both Pope Benedict XVI -- dubbed the "green pope" -- and Pope John Paul II wrote about climate change. St. Francis of Assisi himself, who died in 1226 and is the current pontiff's namesake, is the patron saint of animals and the environment.

What makes Pope Francis' foray different from his predecessors is that he "is a phenomenon," said Charles Camosy, a theology professor at Fordham University. "People are paying attention to Pope Francis in ways that people have not paid attention to any other pope in modern history."