Pope Francis makes an urgent call for protection of the planet and repeats his view that global warming is mostly man-made in his keenly awaited encyclical, according to a draft published by an Italian magazine on Monday.
The Vatican said the document, leaked in its Italian edition by the magazine l'Espresso, was not the final version, which would remain under embargo until its release on Thursday.
It was not clear how advanced in the writing process the leaked document was or how similar it would be to the final version.
Pope Francis has said he wants the document, called "Laudato Si (Be Praised), On the Care of Our Common Home", to be part of the debate at a major U.N. summit on climate change this year in Paris. He said on Sunday it was addressed to all the world's people. In the draft he speaks of "the urgent challenge to protect our common home" and calls for sustainable development.
The leaked draft confirmed what people familiar with the final version told Reuters last week about how the document addresses climate change and the man-made causes of global warming.
As sources said before Monday's leak, the encyclical addresses the impact of climate change on the poorest nations and notes a broad scientific consensus that global warming is mostly caused by fossil fuels.
It also asks rich nations to re-examine their "throw-away" lifestyles, an appeal the first Latin American pope has made often since his election in 2013.
Repeating what he or his top aides have said in recent months, the pope calls for a reduction in carbon emissions, an increase in policies that favor renewable energy and warns of the long-term effects of continuing to use fossil fuels as the main source of the world's energy.
Climate change skeptics, particularly in the United States, have excoriated Francis, who is due to address the United Nations and the U.S. Congress on sustainable development in September.
U.S. Republican presidential candidate Rick Santorum, a Catholic and climate change skeptic, said the Church would be "better off leaving science to the scientists".
Maureen Mullarkey, a commentator for the conservative U.S. website First Things, published by The Institute on Religion and Public Life, called Pope Francis "an ideologue and a meddlesome egoist" who was "sacralizing politics and bending theology to premature, intemperate policy endorsements (on climate change)."
The pope himself hinted at what he would say while talking to reporters about climate change in January.
"I don't know if it is all (man's fault) but the majority is, for the most part, it is man who continuously slaps down nature," he said. "I think man has gone too far ... thank God that today there are voices that are speaking out about this."
At a conference at the Vatican in April, the Holy See teamed up with the United Nations and came down firmly against skeptics who deny human activity helps change global weather patterns.
By making environmental protection a moral imperative, his intervention could spur the world's 1.2 billion Catholics to lobby policymakers on ecology issues.