What we've often seen is that when we Americans say, look, we've got to reduce pollution, business - some businesses complain about it, but almost every time, it's turned out to be easier and cheaper and accomplished faster, and they've gained confidence, and then we go farther.

I flew on Air Force Two for eight years, and now I have to take off my shoes to get on an aeroplane.

I have felt for a long time that the pathway to solving the climate crisis is through the building of a massive grassroots army of men and women who will go out there and win the conversation on climate, and persuade businesses, and universities, and towns to switch to renewable energy and to reduce emissions. And the big change from ten years ago is that people are way more receptive, not only to the message that we have to act, not only to the message that now we can act, we have the solutions now - that's the biggest change - but also willing to make a commitment that we will act.

I think I may have a future as a disembodied head.

The truth is that we're at a critical juncture in the history of our species and if we don't act soon, we could inhabit a world we don't recognize anymore. But the most important truth is that we are capable of stopping climate change before the worst of its consequences are locked in. The solutions exist - all we need is the will to do something about it.

We now face the prospect of a kind of global civil war between those who refuse to consider the consequences of civilization's relentless advance and those who refuse to be silent partners in the destruction. More and more people of conscience are joining the effort to resist, but the time has come to make this struggle the central organizing principle of world civilizations.

Airplane travel is nature's way of making you look like your passport photo.