The Vatican has announced that the publication date of Pope Francis' second encyclical will be Thursday, June 18th. 

In a statement today, the Vatican said that the rare, advance notice was "to avoid confusion over the date of publication of the long-awaited encyclical." It added that next week "further details" about the document, which will address environmental concerns, will be made public by the Holy See in its daily bulletin. 

There has been much speculation about the date of the publication. In comments to the Register last month, Vatican spokesman Father Federico Lombardi denied the encyclical had been delayed because of alleged opposition from the Congregation for the Doctrine of the Faith to an early draft. 

The document is eagerly anticipated because many expect it to controversially endorse the science of climate change. The Vatican has appeared to fuel the speculation by giving major conferences and speeches on the subject, and publicly hinting that the Pope will give it his support.

Last month, Cardinal Pietro Parolin, the Vatican Secretary of State, said no one is immune from the implications of climate change. “When the future of the planet is at stake, there are no political frontiers, barriers or walls behind which we can hide to protect ourselves from the effects of environmental and social degradation," the cardinal wrote in a message to participants of a Rome conference. 

However, some inside sources claim the Holy Father will not give the science his full backing.

Critics have warned that by falling in with proponents of climate change science, the Pope risks getting too close to other key supporters of the theory who support population control and abortion. They also argue that the science, which could cost world governments hundreds of billions to tackle that would affect poor countries most, has still not been convincingly proven.   

Earlier this week, Catholic presidential hopeful Rick Santorum asked that the Pope no longer discuss climate change and “leave science to the scientists.”

Last week, it was revealed that title of the encyclical is expected to be "Laudato Sii", meaning "Praised Be You", with the subtitle: "Sulla cura della casa comune" (“On the care of the common home”). 

The main title is taken from St. Francis of Assisi’s Canticle of the Sun which praises God for his creation. The prayer reads: “Be praised, my Lord, through all Your creatures, especially through my lord Brother Sun,” and continues to praise God for “Sister Moon,” “Brothers Wind and Air,” “Sister Water,” “Brother Fire, and “Mother Earth.”

A papal encyclical is the name typically given to a letter written by a pope.  It can be addressed to the bishops and priests of a particular region or of the entire world, to specific groups in the Church or to the entire Catholic faithful. It can also be addressed to all people of good will.

The word encyclical comes from the Greek ‘egkyklios’, ‘kyklos’ meaning a circle. It may be considered to be a ‘circular letter’. Encyclicals are used primarily for teaching.  The first encyclical was released by Pope Benedict XIV on December 3, 1740. Since then, popes have written over 300 encyclicals.

Pope Francis' first encyclical, "Lumen Fidei" ("The Light of Faith"), published in 2013, was largely written by his predecessor, Benedict XVI.