Without a movement pressing for change, there's little hope. We've got to work the political system to make this happen fast. The physics and chemistry are daunting. The resources on the other side are very large.

These things are happening in large measure because of us. We in this country burn 25 percent of the world's fossil fuel, create 25 percent of the world's carbon dioxide. It is us - it is the affluent lifestyles that we lead that overwhelmingly contribute to this problem. And to call it a problem is to understate what it really is. Which is a crime. Crime against the poorest and most marginalized people on this planet. We've never figured out, though God knows we've tried, a more effective way to destroy their lives.

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.

In reality, climate change is actually the biggest thing thats going on every single day.

We also have to engage - and I think this is important - in national politics because there is no way to address questions of this scale in the short time that we have to address them without engaging in real political change.

Scientists are telling us that 350 parts per million [of carbon] in the atmosphere is the upper limit. We're at 387 parts per million now, and we're up in that zone where the risk of going past irrevocable tipping points is elevated. It's no different than going to a doctor and learning your cholesterol is too high, and you're at risk for a heart attack. You have to work to lower your cholesterol and hope to get there before the heart attack comes.

Sometimes, I, anyway, get tired of playing defence, and like to play offence.