Pope Francis is no devotee of Gaia.
I think he's going to critique some of the main errors of radical environmentalism. He's going to defend the exceptionalism of our species; he's going to say environmentalism has to exist at the service of human beings, that while we are respectful of snail darters, we are more important than snail darters, just as Jesus said "The Father cares for sparrows, but you are worth more than many sparrows."
I think he's going to oppose the population-controllers, the people who just see each new baby as a CO2-producing unit. He's going to reiterate that the fertility-haters are in error: abortion is wrong, contraception is wrong (yes, he'll "go there.")
He's going to affirm the God-designed goodness of natural sex, natural gender, natural marriage and the natural family. The people who are into promoting sterile sex in all its forms are going to find no comfort here.
I predict Jeffrey Sachs and Ki Ban-Moon are going to get heartburn over how to suppress the parts they don't like.
Like everybody, I do have fears. I fear he's going to say some stupid stuff about "climate change," and an enlarged role for both national governments and international regulation (the real political danger of this encyclical)--- but the encyclical will not center on that. I hope that Francis will not uncritically trumpet the Al Gorrible stuff, but will maximize the more broadly Biblical themes: our duty to care for the Garden and exercise godly dominion over the planet, invoking God's help to safeguard the goodness of Creation for future generations.
This article by Robert Royal sums up a lot of what I'm thinking in this regard.
I hope you are right.