Perhaps it may be of benefit to point out that Pope Francis, in writing this encyclical, might even be taking SOME queues in this regard from his predecessor, who didn't earn the nickname "The Green Pope" for nothing. As National Geographic reminds us, among the actions of his pontificate:
... He approved a plan to cover the Vatican's Paul VI hall with solar panels, enough to power the lighting, heating, and cooling of a portion of the entire country (which covers, of course, a mere one-fifth of a square mile). He authorized the Vatican's bank to purchase carbon credits by funding a Hungarian forest that would make the Catholic city-state the only country fully carbon neutral. And several years later, he unveiled a new hybrid Popemobile that would be partially electric. (How Green Was the 'Green Pope'? National Geographic (02/28/13).
Pope Benedict XVI appealed for the success of a UN climate change conference [...] in Durban, South Africa. Speaking to the faithful gathered in St Peter’s Square for the Sunday Angelus prayer, Pope Benedict expressed the hope that “all members of the international community might reach agreement on a responsible, credible response,” to the phenomenon of climate change, which he described as “complex” and “disturbing”. [Vatican Radio 11/27/11].In fact, if he had not resigned in 2013, we could reasonably suggest that Pope Benedict might have at some point devoted greater length to this particular topic in some formal manner.
Perhaps the best position present critics of Pope Francis can adopt (and this author is by no means wholly enthusiastic about the present pontiff) is to cultivate the virtue of patience and mindful silence -- and refrain from what is largely speculative criticism until the content of the encyclical is actually released, and we've all had opportunity to read it.
Further reading on the Pope Emeritus' thinking on the environment.
Environmental Justice and Climate Change: Assessing Pope Benedict XVI's Ecological Vision for the Catholic Church in the United States
Lexington Books (November 21, 2013). 322 pgs.
Environmental Justice and Climate Change: Assessing Pope Benedict XVI's Ecological Vision for the Catholic Church in the United States explores four key areas in connection with Benedict XVI’s teachings: human and natural ecology/human life and dignity; solidarity, justice, poverty and the common good; sacramentality of creation; and our Catholic faith in action. The product of mutual collaboration by bishops, scholars and staff, this anthology provides the most thorough treatment of Benedict XVI’s contributions to ecological teaching and offers fruitful directions for advancing concern among Catholics in the United States about ongoing threats to the integrity of Earth.
Ten Commandments for the Environment: Pope Benedict XVI Speaks Out for Creation and Justice
Ave Maria Press (June 1, 2009) 162 pgs.
Woodeene Koenig-Bricker skillfully weaves together Pope Benedicts key statements on environmental justice into one volume. Additionally, she offers commentary that helps to unpack the "Ten Commandments for the Environment," which were recently released by the Pontifical Council for Justice and Peace. Koenig-Bricker helps us understand an environmentally responsible lifestyle as a moral responsibility to protect the poor, who suffer most when climate change creates a shortage of resources. With practical, everyday ideas for reducing ones ecological footprint, this book is a must-read for those seeking the inspiration that the Holy Father radiates to a new generation of Catholics.
The Garden of God: Toward a Human Ecology
The Catholic University of America Press (March 18, 2014) 232pgs.
This book gathers together the audiences, addresses, letters, and homilies of Benedict on a wide-ranging set of topics that deal with the world about us. The major themes and connections he explores are creation and the natural world; the environment, science, and technology; and hunger, poverty, and the earth's resources.