The encyclical letter Laudato Si is available here on the Vatican website. One of the biggest obstacles to action:
173. Enforceable international agreements are urgently needed, since local authorities are not always capable of effective intervention. Relations between states must be respectful of each other’s sovereignty, but must also lay down mutually agreed means of averting regional disasters which would eventually affect everyone. Global regulatory norms are needed to impose obligations and prevent unacceptable actions, for example, when powerful companies dump contaminated waste or offshore polluting industries in other countries.
So nations must come to an internal consensus on action–that will give the right motivation without the sense of imposition by the more powerful.