When I first started studying climate change back in the 1980s, I was struck by how difficult it was be for people to understand this issue.

If I drive my car to the store, those carbon molecules that are emitted actually get into the atmosphere circulation systems and affect climate in a global basis. This is shocking, this is amazing! No one in the 18th Century would have believed that anything like this were at all possible and I don't think we have, as part of our common sense, morality, norms and values that are really responsive to those kinds of issues, to the kind of power that we now are able to exert over the future and over people who live very far from us.

Most of what we think of as distinctively human has occurred in the last 10,000 years in the Holocene - a period in which the Earth was abnormally quiet.

We're not good at noticing slow, steady changes in our environments, our senses are not very acute compared to those of many animals, and we're pretty awful at abstract thought, much less acting on it.

The density of human population combined with the development of powerful and largely unconstrained technology has given us the problems of the anthropocene and the serious possibility of self-caused extinction.

I think the challenge of climate change in particular is the challenge for us to create and produce new norms for a new kind of world. And that's why I think as important as the issue of climate change is, it's even more important than it seems because if we can't evolve very quickly, new norms to deal with issues like climate change, we're not going to be able to survive in the kind of world we've created. So I think, really, the whole nature of democracy, of governance, of global community and of solving the kinds of problems of the 21st Century are really at stake.

Bentham spent much of his life writing constitutions and proposing legal reform in the light of his utilitarianism. The evaluation of particular acts was hardly his concern. The psychology of his day was hedonistic and he worked in that framework and passed it on to Mill, but it is clear as day that Mill was not a hedonist in the sense in which we use that term today, though he used the language of pleasure and pain to express his views.