Cardinals, patriarchs and bishops, including representatives of regional bishops' conferences from Asia, Africa, Latin America and Oceania, are expected to sign the appeal today.
Francis outlined his eco-message in a major teaching document in June, denouncing what he called the "structurally perverse" fossil fuel-based world economy that he says exploits the poor and destroys the Earth.
The encyclical was cheered by environmentalists and ignored or criticized by big business interests. In the US, it was met with particular unease and so far no US bishop is scheduled to participate in the conference to launch the appeal.