Pope Francis said Wednesday the world was facing a "critical moment" in the fight against climate change, welcoming US President Barack Obama's efforts to curb air pollution.

"Mr. President, I find it encouraging that you are proposing an initiative for reducing air pollution. Accepting the urgency, it seems clear to me also that climate change is a problem which can no longer be left to a future generation," the pontiff, speaking in English, said at the White House.

"When it comes to the care of our 'common home,' we are living at a critical moment of history. We still have time to make the changes needed."