The Arctic and the Antarctic are melting quickly. We may have waited too long to get started. But this is a day for optimism because the battle is fully joined, and the idea that big oil is unbeatable is no longer true.

You can have a healthy fossil-fuel balance sheet, or a relatively healthy planet

Where people aren't as deeply reliant on fossil fuel as in the United States, it's far easier for them to imagine change on this scale. When you go to Europe, they're much more ready. They use half the amount of energy per capita that we use. They can imagine using less than that. They see the benefits. They're ready to go.

What makes us different? We're the creature that can decide not to do something that we are capable of doing.

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.

We'd won the argument 15 years before, we were just losing the fight. And so it became clear to some of us that we would need to organise to fight, that we weren't going to win.

If you were running a solar company you may be okay - you may be able to keep growing. The question for physics is: Can you grow fast enough to begin to catch up with the damage?