John Kerry: “I sat here and said we are skeptical. I sat here and said they have got to prove it.”

People think this is now, you cannot reverse it, it is irreversible.

It's a matter of mathematics and physics, not politics, not ideology. It is a response to the science.

Depending on what it involves, shadow diplomacy has also saved us from a war.

The message is, let's find a way to be able to make sure when we fly, we're not leaving emissions that we cannot capture.