We finally know where the red line for climate really is. After the rapid melt of arctic ice in the summer of 2007, our best scientists, led by NASA's Jim Hansen, went back to work and produced a series of papers showing that with more than 350 ppm (parts per million) of carbon dioxide in the atmosphere, we couldn't have a planet "similar to the one on which civilization developed and to which life on earth is adapted."

We have assumed control where once we worked with what we were given.

There's no huge mystery. If you dig up huge amounts of carbon, huge amounts of ancient biology, hundreds of millions of year's worth of ancient biology, and flush it into the atmosphere in a matter of decades, then it stands to reason that we're going to have enormous effects, and now we can see those effects all around us.

In the States, the movement's actually gotten much much much stronger. There really was no climate movement so to speak before that - I think because everybody assumed that reasonable heads would prevail and do the right thing - and why would you need to have a huge movement in order to cause our leaders to deal with the most serious problem that they face. In a rational world you wouldn't. They would deal with it.

I'm far less a leader than a writer.

... the constant flow of images undercuts the sense that there's actually something wrong with the world. How can there really be a shortage of whooping cranes when you've seen a thousand images of them - seen ten times more images than there are actually whooping cranes left in the wild?

Here, there's more of a movement, it doesn't mean we're winning any more, but we're at least fighting.