It's all about controlling people
Religious leaders have always needed something big and scary so that the church could save you from it, especially so the Church of Rome that has so many people to control. These days, governments are using the tactic rather more effectively than churches, though - and with better memes, what with fire and brimstone being a bit old hat.
Unfortunately for the Pope, however, paedophiles are out (for obvious reasons) and terrorists are a bit risky considering how the Romans would have viewed Jesus of Nazereth. So climate change seems to fit the bill nicely.
It's a bit surprising it's taken Rome so long to catch on to the trend everyone's been following for years. But, then, they've only quite recently caught on to the Earth going around the Sun, so I guess you can't expect miracles.