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."

Delhi is locked in a complete choking smog at the moment - they've had to close schools in one of the world's biggest cities. They have their own reasons for needing to get off fossil fuels fast.

We'll look for almost any reason not to change our attitudes; the inertia of the established order is powerful. If we can think of a plausible, or even implausible, reason to discount environmental warnings, we will.

If it's wrong to wreck the planet, it's wrong to profit from the wreckage.

I think the world on the other side of fossil fuel is more local - the logic of sun and wind is diffuse and spread out, not concentrated like the logic of coal and oil.

Colonialism of one kind or another, imperialism of one kind or another, and slavery, and on and on and on.

In the scientific community, the debate is over, for all intents and purposes, about whether or not the planet is heating and who is causing it. In fact, it's more or less been over since 1995.