Nothing Obama’s done yet as president compares in scale to the climate talks. The Iran nuclear agreement is a landmark achievement, but it’s focused on one unhinged regime threatening one region of the world. The White House spent the last day being pummeled for admitting the obvious, that it wasn’t actively pursuing an Israeli-Palestinian peace process during the rest of Obama’s term, but those are just two countries. Obamacare’s changed the health of millions of people, but that’s millions, not billions, and just in the United States.

Climate change affects everyone, everywhere, and that’s how they think about it in the White House. Securing real movement to stop it would make Obama not just a world leader, but a leader of the world. This is securing the planet, and redirecting the course of billions of lives, and Obama’s been talking more and more in those kind of bigger terms and the position that puts him in.

Not insignificantly, if Obama gets his way, he’ll also reverse one of the most embarrassing moments of his own presidency, when he rushed to Copenhagen in December 2009 for an eleventh-hour speech urging the world to sign an agreement at the last big climate conference, only to have the speech knocked for its halfheartedness and the talks collapse right after he gave it.