Woman should have the choice whether to have an abortion or not, but I like what Bill Clinton said: It ought to be safe and rare. You don't want to offend people with it. You try and do as much as you can to let people be different, but also to try and protect them from things that they think are bad. And it's worth all of us giving a little.

It turns out the population issue is an easier thing to deal with than the consumption issue. Some obvious extremes in consumption we can deal with. The standard cure for a stuttering economy is to go out and buy an SUV and three more refrigerators. That's obviously not the way to go.

I kind of like carbon taxes because we already know how to apply them. We already have apparatus in place. When we talk about these other solutions - like a billion tons of iron filings in the ocean or putting sunshades between us and the sun - they're huge. We have no idea if they will work. We have no idea what their nasty consequences might be. And it's unlikely we can do them anyway.

There's all of this stuff where we have so much debate over nonsense; it could be cured if we had a better educational system, if we trained people to really try and look into things on their own. That's a tough thing to do, particularly with the educational system staggering.

Stanford may be the best university in the world, but you can get all the way through here without knowing where your food came from, without being able to say where we came from, without being able to give a coherent description of why the climate is changing and why we should be concerned about it. So I started teaching a course in human evolution and the environment that's open to all Stanford students, no prerequisites.

All scientists who've looked at it know we have to phase away from burning fossil fuels. That means we've got to put a lot of effort into alternate energy technologies, but we're still subsidizing fossil fuels and not subsidizing most of the alternatives. It's not going to be an easy transition.

Most of the scientists I know think civilization is teetering on the brink of a global disaster. They just don't know when it's going to hit. I don't have the answer to that either. I'm scared as hell.