If you think about the impact of climate change, [it should be how] a doctor would deal with the problem. A scientific hypothesis is tested to absolute destruction, but medicine can't wait. If a doctor sees a child with a fever, he can't wait for [endless] tests. He has to act on what is there. The risk of delay is so enormous that we can't wait until we are absolutely sure the patient is dying.

If your children want to alter society, listen to their reasons and the idealism behind them. Don't crush them with some clever remark straight away.

To get the best results you must talk to your vegetables.

Scientists themselves readily admit that they do not fully understand the consequences of our many-faceted assault upon the interwoven fabric of atmosphere, water, land and life in all its biological diversity. But things could also turn out to be worse than the current scientific best guess. In military affairs, policy has long been based on the dictum that we should be prepared for the worst case. Why should it be so different when the security is that of the planet and our long-term future?

I think it's something that dawns on you with the most ghastly, inexorable sense. I didn't suddenly wake up in my pram one day and say 'Yippee, I - ', you know. But I think it just dawns on you, you know, slowly, that people are interested in one, and slowly you get the idea that you have a certain duty and responsibility.

There's nothing like a jolly good disaster to get people to start doing something.

I learned the way a monkey learns - by watching its parents.