Pope Francis will call for swift action to protect the Earth and fight global warming, according to a leaked draft of the pontiff's encyclical.
The document - published by Italy's L'Espresso magazine - says global warming is directly linked to human activities and the intensive use of fossil fuels.
The Vatican called the leaking of the draft a "heinous" act.
It said the final version would be released on Thursday as planned.
The 192-page draft of the encyclical - which is the highest level of teaching document a pope can issue - is entitled "Laudato Si: On the care of the common home".
In the paper, Pope Francis presents both scientific and moral reasons for protecting God's creation.
He puts much of the blame for global warming on human activities, mentioning the continual loss of biodiversity in the Amazonian rainforest and the melting of Arctic glaciers among other examples.
The draft also says that developing countries are bearing the brunt of the "enormous consumption" of some of the richest.
The pontiff calls on all humans - not just Roman Catholics - to prevent the destruction of the ecosystem before the end of the century and to establish a new political authority to tackle pollution.
The encyclical has been months in the writing, and the Pope is said to be keen for it to set the tone for the debate at a UN summit on climate change in November in Paris, the BBC's Caroline Wyatt says.