So, regarding the time frame, I'm only too willing to admit that my crystal ball, like everybody else's, is cracked. If I could predict precisely, I would have started predicting the stock market and would now be living with a bunch of young women on Bora Bora, having bought it.

With taxes, if they aren't working right, we can change them with a stroke of the pen. It's basically a market-type mechanism. People make their own choices. You run the taxes, and you get the results.

Recycling helps make people feel involved, and in some cases can be useful. Although you've got to do careful life history studies of what you're recycling. If all you're doing is recycling - if you've got three automobiles, and 10 children, and a 7,000-square-foot dot-com palace and second home up in the mountains that has to be heated - the recycling isn't making much difference.

We know that if you have $20 million, it's better to buy a van Gough print than it is buy an executive jet, from the point of view of the environment. But when you start getting down, it's like the recycling question: What are things we can really afford to do, and how much pleasure do we get out of them? We haven't even started to have that discussion, and it's getting awfully late.

In pushing other species to extinction, humanity is busy sawing off the limb on which it perches.

People have to decide, first of all, how they'd like to live, and how secure they want to be from disaster. After that, scientists can help determine what would be necessary to achieve that.

I don't think scientists can dictate from above what we should do, because it's not a matter of scientific decision. If you want to have everybody living like a Beverly Hills millionaire, then 2 billion people might be too many. If we want to have a battery-chicken kind of world, with everybody having an absolute minimum diet, you might be able to support 10 billion.