U.N. Secretary-General Ban Ki-moon will open a key Vatican meeting this month on Pope Francis' highly anticipated teaching document on climate change.

The U.N. chief will join American economist Jeffrey Sachs and the pope's top representative on the environment, Cardinal Peter Turkson, at the April 28 event in Rome. Turkson, head of the Pontifical Council for Justice and Peace, helped write the first draft of the pope's encyclical on global warming and the environment, which is scheduled to be released in June or July.

The conference was announced on the websites for the Pontifical Academy of Sciences, the Pontifical Academy of Social Sciences and the Vatican's "End Slavery" initiative. Called "Protect the Earth, Dignify Humanity," the event will feature scientists and world religious leaders, aiming to build a global movement toward curbing climate change, according to the online program. Speakers will have "a special focus on the most vulnerable, to elevate the moral dimensions of protecting the environment in advance of the papal encyclical," according to the program.

While Popes John Paul II and Benedict XVI took strong stands in favor of environmental protection, Francis will be the first to address climate change in such a significant way. Encyclicals are theological documents traditionally used for the most important papal teachings.

Environmental groups are thrilled that the pope is putting his popularity and moral authority behind fighting global warming, but climate change skeptics have been critical, accusing the pontiff of addressing an issue beyond his understanding. Francis has said global warming is "mostly" man-made. And he said he wanted his encyclical out in time to be absorbed before the next round of U.N. climate change talks in Paris in November.

Turkson has been giving talks widely considered to be previews of the upcoming papal document. The cardinal has written a new book called "Land and Food," which he will introduce Thursday at an event alongside U.N. officials. The book covers some of the key issues the encyclical is expected to cover, including the right to food and the exploitation of natural resources, alongside core points in church teaching on creation and bioethics. The book includes policy recommendations, such as investing in improved education for businesses, political and financial leaders.

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AP Science Writer Seth Borenstein contributed from Washington; Associated Press writer Nicole Winfield contributed from Rome.