The encyclical letter Laudato Si is available here on the Vatican website. Following logically from LS 91:
92. Moreover, when our hearts are authentically open to universal communion, this sense of fraternity excludes nothing and no one. It follows that our indifference or cruelty towards fellow creatures of this world sooner or later affects the treatment we mete out to other human beings. We have only one heart, and the same wretchedness which leads us to mistreat an animal will not be long in showing itself in our relationships with other people. Every act of cruelty towards any creature is “contrary to human dignity”.[CCC 2418]
To think otherwise is to fall for the seduction that we can compartmentalize our lives, that somehow we can create boundaries that permit kindness to one segment, and ruthlessness to others. Another CELAM bishops’ conference is cited:
We can hardly consider ourselves to be fully loving if we disregard any aspect of reality: “Peace, justice and the preservation of creation are three absolutely interconnected themes, which cannot be separated and treated individually without once again falling into reductionism”.[Conference of Dominican Bishops, Pastoral Letter Sobre la relación del hombre con la naturaleza (21 January 1987)] Everything is related, and we human beings are united as brothers and sisters on a wonderful pilgrimage, woven together by the love God has for each of his creatures and which also unites us in fond affection with brother sun, sister moon, brother river and mother earth.
The theme of our collective pilgrimage as a whole planet’s community surfaces again. With our sun, moon, companion planets, and all life on our Earth, we are literally on a pilgrimage through our galaxy and universe.