With respect to phenomena like mass extinction, somebody might say why worry about it because in a geological perspective mass extinctions aren't so bad, they wipe out some things and then 10 million years down the road we get new and interesting objects.But I tell you mass extinctions are really awful for folks caught in the midst of them.

I assume the same problem exists in Australia as in America of back-biting and jealousy and parochialism among disciplines - there are the scientists, and there are the humanities people, and there are chemists and the physicists and everybody snipes at everybody else and inter-disciplinary communication is rare. But it's very precious and necessary.

The social scientist is in a difficult, if not impossible position. On the one hand there is the temptation to see all of society as one's autobiography writ large, surely not the path to general truth. On the other hand, there is the attempt to be general and objective by pretending that one knows nothing about the experience of being human, forcing the investigator to pretend that people usually know and tell the truth about important issues, when we all know from our own lives how impossible that is.

I think people who worry about planetary health on geological scales are totally misguided, that's not the point at all.

If I put myself on the side of those who see the world as warming up in a bad way, who see the general march of industrial culture as something undesirable, the one thing I must be beware of doing and which my colleagues on that side don't beware of doing, we must beware of saying we've got to stop changing the environment. There is no 'the' environment which we can change, the world is changing all the time.

In my mind the job of a natural scientist is to bend over backwards to say something which can be demonstrated to be true or at least which is not of such a nature that there's no way to demonstrate that it's false.

If we're going to make a politically responsible and a scientifically sensible claim it should not be stop the world exactly where it is because that's not possible. It has to be to decide what kind of world do we as human beings want to live in.