Francis weighed in on a key and contentious point of negotiations — whether countries should agree to a phase out of coal, oil and natural gas, the fossil fuels that are causing climate change. He is for it. As fast as possible even, he wrote.

He lamented that “the necessary transition towards clean energy sources, such as wind and solar energy, and the abandonment of fossil fuels is not progressing at the necessary speed.”

Using precise scientific data, sharp diplomatic arguments and a sprinkling of theological reasoning, Francis delivered a moral imperative for the world to transition away from fossil fuels to clean energy with measures that are “efficient, obligatory and readily monitored.”

“What is being asked of us is nothing other than a certain responsibility for the legacy we will leave behind, once we pass from this world,” he said.

As it is, Francis’ 2015 encyclical “Praise Be” was a watershed moment for the Catholic Church, the first time a pope had used one of his most authoritative teaching documents to recast the climate debate in moral terms.

In that text, which has been cited by presidents, patriarchs and premiers and spurred an activist movement in the the church, Francis called for a bold cultural revolution to correct a “structurally perverse” economic system where the rich exploit the poor, turning Earth into an “immense pile of filth.”

Even though encyclicals are meant to stand the test of time, Francis said he felt an update to his original was necessary because “our responses have not been adequate, while the world in which we live is collapsing and may be nearing the breaking point.”

He excoriated people, including those in the church, who doubt mainstream climate science about heat-trapping greenhouse gas emissions, sarcastically deflating their arguments and showing his impatience with their profit-at-all-cost mentality.