It all flows from the findings of the Pontifical Academy of Sciences aka the Vatican Academy of Sciences, which is probably not much different from the US Academy of Sciences.
And most don't recall that a few months ago, deniers such as the Heartland Institute and others unsuccessfully tried to assert their way into the climate summit sponsored by the Vatican Academy
The person now in charge of the Pontifical Academy brought in outside scientists (and polemicists)to “confirm” the position that the Pope clearly wanted to accept. They were quite fierce about driving out anybody who didn’t agree and accepting to the summit only those who did agree with them.
Bergoglio himself is ideologically driven and very dictatorial, and in only a couple of short years he has stacked the Vatican commissions and agencies (and, increasingly, bishoprics) with his ideological soul-mates.