Optimists are usually wrong. But all the great change in history, positive change, was done by optimists.

The Arab world had a big problem of frankly venal elites. That is why these revolutions happen, because people didn't think the opportunities were being shared fairly.

Every sport needs its temple, its cathedral.

Scientists tend to focus on what they don't know more than what they do know. And there are a lot of things we still don't know about the climate. But we know the difference between climate variability and climate change, and right now the amount of carbon in the atmosphere is well outside the variability pattern - and that's quite quantifiable.

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I think we have lost our groove as a country. One of the reasons was the attack on 9/11. We got knocked off our game. From a country that always exported hope we went into the business of exporting fear.

I don't think that stability and the status quo go together at all, not in a flat world where people are integrated, where women are assuming new roles, where young people want to be consulted and participate. I think the trick is to open up, move down the path of reform, do it in a way that is consistent with your own society's stability and culture, and just don't think you can do nothing.