ROME — A draft of a highly anticipated letter on the environment by Pope Francis casts climate change as a threat largely caused by humans and urges action to reduce the emissions that cause global warming.

The Roman Catholic leader’s message, delivered in a letter called an encyclical, a draft of which was leaked Monday by an Italian magazine, is expected to prompt a range of responses in the coming months.

It may help galvanize international opinion in advance of an important United Nations conference on climate change that begins in late November, roil the American presidential race by injecting religion into the already contentious politics of global warming and increase questions about the morality and sustainability of a world economy driven by capitalism and consumption.

The 192-page draft, called “Laudato Si, on the care of the common home,” was posted online Monday in Italian by the magazine L’Espresso and news outlets scrambled to translate it into English. Many cited a passage that says global warming has been “mostly” caused by “the great concentration of greenhouse gases (carbon dioxide, methane, nitrogen oxide and others)” that are “generated by human action” or “due to human activity.”

The draft says there is an “urgent and compelling” need for nations to reduce carbon emissions by replacing fossil fuels with new sources of renewable energy.

Viewed as a bold act by the pope to sway global opinion on a controversial issue, the encyclical, which the pope planned to release Thursday, in many ways reflects a religious movement that has been growing for decades, sometimes on the margins, with some Catholic and Christian academics and individual church leaders and congregations increasingly making “creation care” a theological pursuit and a central ministry.

What matters most about the encyclical, many of these people say, is that those who have long cared about climate change now have a formidable new messenger.

“He is taking all the messages that we have been speaking about for 30 years and taking them to an international stage,” said Jessie Dye, who is Catholic and is the program and outreach director of Earth Ministry, an ecumenical nonprofit in Seattle.