The pope does not have a charism in regard to climate or the weather, and global warming is not being asserted by him to be divinely revealed. That something is in an encyclical generally elevates the nature of what is taught, but that does not mean that everything in an encyclical demands assent by the faithful.
To tell you what exactly are the parts that are formal papal teaching and what opinion would require a parsing of the whole encyclical, and there is no space for that here. However, Catholic teaching on the environment is well summarized in the Catechism of the Catholic Church as follows:
“The seventh commandment enjoins respect for the integrity of creation. Animals, like plants and inanimate beings, are by nature destined for the common good of past, present, and future humanity. Use of the mineral, vegetable, and animal resources of the universe cannot be divorced from respect for moral imperatives. Man’s dominion over inanimate and other living beings granted by the Creator is not absolute; it is limited by concern for the quality of life of his neighbor, including generations to come; it requires a religious respect for the integrity of creation” (No. 2415). “In God’s plan man and woman have the vocation of ‘subduing’ the earth as stewards of God. This sovereignty is not to be an arbitrary and destructive domination. God calls man and woman, made in the image of the Creator ‘who loves everything that exists,’ to share in his providence toward other creatures; hence their responsibility for the world God has entrusted to them” (No. 373).
And thus whether or not there is global warming (climate change), and what is causing it, is a scientific debate. The Pope notes that fact in Laudato Si’, but he has no special expertise or charism to render a binding opinion on it. His role is to remind us that if we do become aware of ways we are unjustly using God’s creation and/or harming the lives of others, present or future, we do have obligations insofar as possible to move to a more just usage of the resources of the environment that God has entrusted to our care.
Rev. Msgr. Charles E. Pope has a Master of Arts in Moral Theology from Mount St. Mary’s University, Emmitsburg, Md. He was ordained to the priesthood on June 24, 1989, and is currently a pastor in Washington, D.C.