Pope Francis' eagerly awaited environment encyclical will be published June 18.

The Vatican took the unusual step Thursday of announcing the release date in advance "to avoid confusion over the diffusion of unconfirmed information."

No papal document in recent times has elicited as much anticipation and anxiety as Francis' encyclical. The Vatican has helped fuel interest by mounting an unprecedented roll-out, featuring conferences, speeches and book launches tied to it.

Environmentalists are thrilled the pope is lending his moral authority to the climate change debate ahead of U.N. climate talks this year in Paris. Climate skeptics have voiced alarm that the pope is getting involved.

This week, U.S. Republican presidential hopeful Rick Santorum said he wanted the pope to stop talking climate change and "leave science to the scientists."