That's when the vast consensus of the world's climatologists, brought together by the UN and The Intergovernmental Panel on Climate Change, really announced that this was going on, and since then the accumulation of data and wickedly hot years has served to only congeal that consensus much more firmly.

I think fracking for gas will reduce the incentive to turn to renewables, and I think it will do a lot of other damage across the countryside.

There's no happy ending where we prevent climate change any more. Now the question is, is it going to be a miserable century or an impossible one, and what comes after that.

It drives me crazy to see so much of this planet's life so casually endangered. The first steps are so easy (drive smaller cars, for instance) that it's very hard to understand why we haven't taken them. But I know that this is the issue our generation will be judged by.

I've got no advice. You guys know where you are and what will work. Just know that there are people all over the place working on this and that there's a great deal of solidarity around the world and we should try to build this big, sprawling movement that looks like the kind of energy system that we want - building lots of solar panels on lots of rooftops that are all interconnected.

All the science in the last few years, or almost all of it, really serves to show that the [climate] effects are larger and more rapid than we had thought even a decade ago.

Probably nothing that we have ever managed to do quite equals the basic undermining of the physical stability of the planet on which most of the world's poor people depend.