Let's start by defining terms. An encyclical is, in the strictest sense, simply a circular letter. Originally a letter sent out to bishops in a given area by the pope concerning a matter on which they should focus. Now it tends to be a "letter" (the one due out this week is just shy of 200 pages) intended for the entire world. It is a kind of papal policy paper. It does not have the formal doctrinal weight of a papal bull, but is taken far more seriously than any other speech or statement made by the pope.
Pope Francis has decided to take on climate change, as well he should. Why should he? Because humanity's relationship to the environment is a moral issue,one that can produce either pain and suffering or benefit and joy to not only the animals but also to human beings. It is a serious moral issue for great swathes of the world, where crops are dying from not enough water and villages are drowning from to much. The environment also has direct links to economics and health. They question is not why should the Pope talk about climate change, the question is why it has taken so long.
But who would question the Pope's authority to talk about whatever he wants? I'm not Catholic, but I am pretty sure the Pope can say whatever he wants. It is one thing for a Protestant to say that the preacher on Sunday was full of crap, it is quite another to challenge not just content but the Pope's moral authority to issue a papal encyclical. So who would do such a thing and why?
Republican presidential candidate Rick Santorum thinks the Pope should stick to moral issues and not scientific ones. First, if you do not think that our relationship to the environment has a moral quality you have failed to read Genesis or Romans very carefully. Second, the man has a degree in chemistry, making him more of a scientist than any one currently running for president.
Our society is far to polarized when we challenge someone not on the content of their speech but on their very authority to say anything. What bits I have read, not the whole thing I admit, of the leaked material I support. We all, every human being, need to think how our individual actions affect the world.
Oh and just for the fun of it: