Pope Francis, who pledged on the day of his installation as pontiff to make the environment a priority, is drafting a highly anticipated encyclical on ecology and climate change.

Environmentalists are thrilled by the prospect of a rock-star pope putting his moral weight behind efforts to curb global warming. Francis said last week he wanted the document to be released in time to be read before the next round of U.N. climate treaty talks in Paris at the end of the year.

But skeptics of global warming are irate that Francis is taking up the cause. Several of the critics have accused him of using Catholicism to cloak a radical environmental agenda.

Encyclicals are among the most important means for papal teaching and are written with the help of a small group of advisers under strict secrecy. Still, over the last year, Francis and his top aides have provided some clues about what the document could say.

Here are five things to know ahead of the document's release:

PAPAL PRECEDENT

Francis is extending the work of his predecessors. Popes John Paul II and Benedict XVI both spoke of environmental protection as an urgent moral concern and placed the issue the context of church social teaching on helping the poor and promoting the common good.

In 1990, John Paul II said Catholics had a special religious obligation to protect God's creation from damage caused by "industrial waste, the burning of fossil fuels, unrestricted deforestation" and other practices. Benedict was dubbed "the Green Pope," for his frequent calls to stop ecological devastation and his efforts to bring solar power to the Vatican city-state. "Can we remain indifferent before the problems associated with such realities as climate change?" Benedict said in 2010.

Both pontiffs advocated for conservation as part of a "culture of life" that includes ending abortion. Francis has done the same in his remarks, decrying a "culture of waste" that devalues human life.

HOW FAR WILL HE GO?

Francis has already asserted that climate change is happening and people are partly to blame. "I don't know if it (human activity) is the only cause, but mostly, in great part, it is man who has slapped nature in the face," he said last week. He has also indicated the body of the encyclical will not be consumed with scientific analysis.

"It's not an easy issue because on the protection of creation and the study of human ecology, you can speak with sure certainty up to a certain point then come the scientific hypotheses some of which are rather sure, others aren't," Francis said at a news conference last August. "In an encyclical like this that must be magisterial, it must only go forward on certainties, things that are sure."

At a U.N. Climate Change Summit in New York last September, the pope's top diplomat, Secretary of State Cardinal Pietro Parolin, urged international intervention to curb global warming, "not only strengthening, deepening and consolidating the political process on a global level, but also intensifying our commitment to a profound cultural renewal," according to a Vatican radio transcript.

In a November speech in London, Argentine Bishop Marcelo Sánchez Sorondo, chancellor of the Pontifical Academy of Sciences and a close friend of Francis, called for consideration of such policies as taxing and regulating environmental violations, among other moral and social remedies.

"Market forces alone, with no ethics and collective action, cannot solve the interrelated crises of poverty, exclusion and the environment," Sanchez Sorondo said.

Still, Francis alone will decide what the encyclical will say.

TIMING

On his trip to Sri Lanka and the Philippines last week, Francis said he had sent a third draft of the document for review by the Vatican orthodoxy guardian, the Congregation for the Doctrine of the Faith, along with the Vatican Secretary of State's office and his own theologian and had just received their replies.

The pope said he plans to "take a week" in March to review their suggestions and finish the encyclical, which will then be translated into several languages. The pope said he expects the document to be released in June or July.

GEOGRAPHY MATTERS

So far, the loudest outcry against papal intervention on climate change is coming from political conservatives within the United States. Anthony Leiserowitz, director of the Yale Project on Climate Change Communication, said the greatest resistance to taking action against climate change is centered in the U.S., Canada, Britain and Australia.

The strongest concern about global warming can be found in Latin America. The trend holds within the U.S., where Latinos are far more worried than whites about climate change, according to the Public Religion Research Institute.

Francis, a native of Argentina, is the first non-European pope in more than 1,000 years.

BEYOND CATHOLIC

Over the last two decades, every major religious group has made environmental protection a priority in one way or another. From using solar power for houses of worship to advocating for limits on greenhouse gases, religious leaders have framed the issue as a moral imperative driven by their faith's teachings. Among the most prominent has been Ecumenical Patriarch Bartholomew I of Constantinople, spiritual leader of the world's Orthodox Christians.

Francis said he read Bartholomew's writings as part his research on the encyclical. Sometime this year, Francis is expected to host a summit of world religious leaders to urge decisive action on protecting the environment.