Before Catholics start freaking out (in fear or joy) over Pope Francis' recent comments on global warming, Robert P. George offers up some important things to keep in mind:
1. The Pope has the right and responsibility to teach and even bind the consciences of the faithful on the truth of proposed moral norms, including those norms pertaining to our obligations concerning the natural environment.
2. Pursuant to the norms set forth in Lumen Gentium and other relevant documents pertaining to the teaching authority of the magisterium (including the papal magisterium), Catholics are bound to give religious assent to the norms formally proposed for such assent by the Holy Father. There is no area of morality in which the papal writ does not run. The Pope can speak authoritatively on questions of our moral responsibility to care for the natural environment, just as he can speak authoritatively on the obligation of truth-telling, the sanctity of human life, questions of marriage and sexual morality, matters of war, religious liberty, criminal punishment, and so forth.
3. The Pope has no special knowledge, insight, or teaching authority pertaining to matters of empirical fact of the sort investigated by, for example, physicists and biologists, nor do popes claim such knowledge, insight, or wisdom. Pope Francis does not know whether, or to what extent, the climate changes (in various directions) of the past several decades are anthropogenic—and God is not going to tell him. Nor does he know what their long term effects will be. If anything he teaches depends on views about these things, all he will have to go on is what everybody else has to go on, namely, the analyses offered by scientific specialists who have studied the matter. He has (just as we have) no guarantee of the soundness of the views of any scientist or group of scientists. A view that he adopts based on what a climate-change scientist or group of scientists—be he or they believers (known to their critics as “alarmists”) or skeptics (known to their critics as “deniers”)—say, could be wrong.
4. Although faithful Catholics are not bound by positions adopted by the Pope on such matters, they are bound by the moral norms he proposes for them to hold definitively. So, for example, let’s imagine that a Pope writing in an encyclical says that pregnant women should not take ibuprofen (as they might do for a headache or toothache) because it will cause the death of the children they are carrying, and there is a basic moral responsibility not to cause the death of a child at any stage of development. The fact that one need not believe that ibuprofen is an abortifacient (since there are very good reasons for believing it is not—and, in fact, it is not) does not affect the validity of the norm against causing the death of unborn children, nor does it alter the authority of the Pope to teach the norm as a norm to be held definitively by the faithful. So to disagree with a pope on the question of empirical fact about whether ibuprofen is an abortifacient is not necessarily to dissent from his teaching that a child has a right not to be killed by abortion—a right corresponding to a duty to refrain from causing embryonic or fetal death. (I’m prescinding here, of course, from the analytically separate question of when performing an act that forseeably results in death as an unintended side-effect of an otherwise morally permissible action is not unjust and may therefore itself be morally permissible.)
It's a bit complicated to digest, but the important distinction is between the positions themselves and the moral norms associated with them.