VATICAN CITY — The Vatican is keeping up the pressure on world governments to listen to PopeFrancis’ dual mantras of fighting climate change and human trafficking by inviting mayors to a Vatican meeting next week on his two pet projects: the exploitation of the Earth and its people.

For the mayors, it’s a photo op of a lifetime: Francis is technically on vacation but he’s expected to address the July 21 conference, which has already attracted 60 or so mayors from Accra (Ghana) to Zagreb (Croatia).

For the Vatican, it’s another move in its unprecedented campaign to keep the momentum alive from Francis’ environment encyclical ahead of U.N. negotiations this year on climate change.

Francis released his encyclical to great fanfare last month, denouncing the “structurally perverse” global economic system in which the wealthy exploit the poor and destroy the Earth in the process.

Francis has tasked his fellow Argentine, Monsignor Marcelo Sanchez Sorondo, to use his Pontifical Academy of the Sciences to engage a broad cross-section of society — Nobel laureates, faith leaders, the United Nations and law enforcement — to rally a global movement in support of his dual environmental-human trafficking campaign.