Pope Francis has had a wealth of documentation from his predecessors and church fathers to draw from in writing his encyclical on the environment. Here are key quotes that have informed the church's social teaching on caring for God's creation, and are thus likely to be cited by Francis in the encyclical.

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ST. FRANCIS OF ASSISI

"Be praised, my Lord, for all your creation and especially for our Brother Sun, who brings us the day and the light ... Be praised, my Lord, for our Brothers Wind and Air and every kind of weather by which you, Lord, uphold life in all your creatures. Be praised, my Lord, for Sister Water, who is very useful to us, and humble and precious and pure. ... Be praised, my Lord, for Sister Earth, our Mother, who nourishes us and sustains us, bringing forth fruits and vegetables of many kinds and flowers of many colors." The Canticle of Creation, 13th century. Francis' encyclical, "Laudato Si (Be Praised), On the Care of Our Common Home," takes its name from this famous prayer of the pope's namesake.

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POPE PAUL VI

"This consciousness of the environment around us is more pressing today than ever. For men who have the means and the ability to construct and ennoble the world about them can also destruct it and squander its goods. Human science and technology have made marvelous gains. But care must be taken that they are used to enhance human life and not to diminish it." Message for the World Day of Environment, 1977.

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ST. JOHN PAUL II

"The dominion granted to man by the creator is not an absolute power, nor can one speak of a freedom to 'use and misuse,' or to dispose of things as one pleases. The limitation imposed from the beginning by the Creator himself and expressed symbolically by the prohibition not to 'eat of the fruit of the tree' shows clearly enough that, when it comes to the natural world, we are subject not only to biological laws but also to moral ones, which cannot be violated with impunity." Encyclical Sollicitudo Rei Socialis (The Social Concern of the Church), 1987.

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ST. JOHN PAUL II and ECUMENICAL PATRIARCH BARTHOLOMEW I

"Respect for creation stems from respect for human life and dignity. It is on the basis of our recognition that the world is created by God that we can discern an objective moral order within which to articulate a code of environmental ethics." Common Declaration on Environmental Ethics, 2002. Bartholomew is the spiritual leader of the world's Orthodox Christians.

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EMERITUS POPE BENEDICT XVI

"Respect for creation stems from respect for human life and dignity. It is on the basis of our recognition that the world is created by God that we can discern an objective moral order within which to articulate a code of environmental ethics." Encyclical Caritas in Veritate (Charity in Truth), 2009.