Do you vote?
Of course I vote!
How optimistic are you feeling about solving the challenge of climate change?
Earlier generations managed to solve the big issues of their time, like slavery or apartheid. And there is nothing stopping us - no technology or knowledge - other than ourselves. The past 30 years we've known about this problem, and now we're right at the end of the time when we can still do something. I'm very optimistic because of the number of people across all sections of society who are realising this and are focusing all of their energies on it.
Do you think it all hangs on Copenhagen?
The only chance is an international deal. Nothing else can do it and Copenhagen is when they are supposed to make the deal. If they fail to make an international deal that's as strong as the science demands, then we're up shit creek.
On 1 January, the 10:10 campaign kicks in. Whatever happens at Copenhagen, whether the politicians succeed or fail, the people and businesses of Britain are going to start cutting their emissions. Understanding climate change and how close to the cliff-edge we are, I couldn't work on anything else. It would be like rearranging the deckchairs on the Titanic.
If you weren't doing this, what would you do?
I could never be a politician because I can't stand the process, but politicians are the ones who get to decide. I would also like to do little things, like getting water fountains installed in Tube stations to encourage people not to buy plastic bottles. I would have liked to be a music producer, in a studio recording music and tweaking drums. Basically, I want to have ten lives so I can do ten different things at the same time.
How do you find time to do everything?
I get bored very easily. I don't want to sit in the pub or watch TV. I was always making up schemes when I was younger - let's put on a pop concert, or get all the teachers to stop driving. Also, I feel very lucky that I have been born in this era, in a great family, with good health. I remember telling a school careers adviser: I want to direct a play, I want to make a feature film, I want to write a book. They said "Jesus, you can't do all that". But we don't have any limits. We are the most privileged who will ever live because everybody who comes after will have to deal with climate change. And for everyone before us, it was a lot harder.
Why don't we all do more about climate change?
I think that nobody wants to cause climate change. It's a mixture of our whole society being set up wrong and laziness. Put those two factors together and it all goes pear shaped. But if I had to pick one fundamental problem with climate change, I would say it's the time-lag. It's the 30 years between what we do and what happens as a result of what we do. And that's an intellectual challenge.
What made you an environmentalist?
My grandmother never used to throw things away. She would say there are only a certain amount of things in the world and so we have to share them. That's the core of environmentalism. We have to use only what we need and consider other people. I argued against her, because she used to shout at me for ripping all the wrapping paper off the presents. But she was clearly right, and I guessed I should change.
Do you argue a lot?
Yes. With my best friends I argue all the time.
Is there a plan?
There isn't a plan. You don't get long in terms of your working life. You only have a short period when you don't have that many responsibilities and you have all your faculties, meaning you have to be fairly young and energetic to push all these kind of projects. So you have about 20 years and I've always felt like I don't want to waste those 20 years doing something pointless. I want to do really good, high-quality stuff, whether that's a film or a campaign or whatever.
Does activism work?
You only have to look at history to see that it does. Nobody can argue that the US civil rights movement didn't work, or that Gandhi didn't work. A lot of people are looking for excuses not to change their lives, and that's one of them. We'll just ignore them.
Do you feel the responsibility of being seen as a leader?
The McLibel defendant, Helen Steel, told me, it's not that she feels brilliant that she did McLibel, but she knows how bad she would have felt if she hadn't, and if she had apologised to McDonald's. And that's kind of the same for me. I have to do this. I have to fight as hard as I can to prevent our species getting wiped out. And if other people think that's good, then I'm glad.
Do you think about climate change all the time?
Yes, but I don't get frustrated, because I am a glass-half-full person. I'm inspired by the people who are working on it. I almost forget that 99 per cent of the population don't give a shit, or that 99 per cent of the population is ignoring the problem.
Will you ever feel like you have done enough?
I feel like I have done enough now, I feel like I have made a good contribution. And if I got hit by a bus tomorrow, I would feel like I did well, which is a profoundly good feeling that I've never had before. My whole life I've been feeling like I want to help, and now I feel I've done something. One of my motivations for working so hard is that I'll hate myself if, when I'm old, I think I stood by. If you stand by and let something happen, you are responsible, too.
Do you have time in your life for anything else?
We are thinking of restarting our singing bar. Karaoke, but around the piano. We used to have that but we had to put it on hold to make The Age of Stupid. But we're going to get it back, at Copenhagen actually! To keep the delegates amused. And we have a football team.
Is there anything you regret?
Only tiny things. We've made mistakes along the way, but I couldn't have done it with a more inspiring group of people.
Are we all doomed?
No. The scientists tell us - the peer-reviewed climate scientists, not the oil industry scientists - that there is still time from a science point of view. But nine out of ten of them don't think that the politics is going to pull it together. And that's where everybody needs to pitch in. At the moment, we, as in humanity, are not going to save ourselves.