David Wallace-Wells, the acclaimed science journalist and author of The Uninhabitable Earth, says the past few years have given him reason to feel both "buoyant optimism" and "abject despair" about the future of climate change.

As the COP27 climate summit kicks into gear, we're speaking to Wallace-Wells about both — and we're going to start by talking about the good news. While we aren't currently on track to keep global warming down to the levels the scientific community has called for, the worst-case scenarios are also looking far less likely than they did even a few years ago.

There's more and more evidence that the actions the world has taken so far really have made a difference — and that we still have significant capacity to determine the kind of world that lies ahead.