Climate change is a huge problem, an almost insoluble problem.

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.

By themselves, they are not enough; we also need to engage in political action.

Renewable energy is far more labor-intensive than fossil fuel production.

I think it's going to be a tough century; I also think people are starting to rise up, and that a growth in human solidarity will help compensate for the loss of margin in the natural world that will make life harder.

[Political actions] has to happen on the local and state level; we have to convince our cities to join the growing number of more than 200 American cities who have signed on to the mayor's climate campaign.

In the last two years 24 countries have set new all-time temperature records. We've seen flooding on an epic scale in every continent .