There are a lot of things that we could do to minimize what we're doing, but we're not getting back those frogs that I saw that no longer exist.

Of the many species that have existed on earth - estimates run as high as fifty billion - more than ninety-nine per cent have disappeared. In the light of this, it is sometimes joked that all of life today amounts to little more than a rounding error.

Some of these species that are now no longer with us were killed off by a fungal disease that was moved around the planet by people.

I don't think there are too many places left that humans haven't pretty thoroughly explored.

As best as can be determined, the world is now warmer than it has been at any point in the last two millennia, and, if current trends continue, by the end of the century it will likely be hotter than at any point in the last two million years.

Humans will eventually become extinct. People treat that as a radical thing to say. But the fossil record shows us that everything eventually becomes extinct. It depends what "eventually" means. But the idea that were going to be around for the rest of global history...I don't think there's any scientist who would suggest that is true. It could be millions of years from now. We may leave descendants that are humanlike.

The Earth is big. There are huge natural forces that have worked over geological time. But it turns out, when you look carefully at the geological time, you can't find anything like us.