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.

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.

Sometimes I think the Congress feels that if you only decided tomorrow to switch to wind power that in two years we'd be getting 80 percent of our electricity from wind power. It's nonsense. Normally it takes 20 to 30 years after a new technology is demonstrated and deployed before it powers even 15 or 20 percent of the grid. There's this long lag time, and we haven't even decided which directions to go.

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 see harm reduction as a way of engaging people as part of that path to recovery.

To err is human, but to really foul things up you need a computer.

Too many cars, too many factories, too much detergent, too much pesticides, multiplying contrails, inadequate sewage treatment plants, too little water, too much carbon dioxide - all can be traced easily to too many people.