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.

When widely followed public figures feel free to say anything, without any fact-checking, it becomes impossible for a democracy to think intelligently about big issues.

I am being very humble about the Arab Spring. There's kind of a competition out there, you might have noticed, of who can be the first to say the Arab Spring is going to fail. Everyone says, "I told you so, I told you so about the Muslim Brotherhood." I have no desire to tell anyone anything. I don't know. I'm just listening, watching. It may turn out all these people are right, they may be wrong. They may be right this year and wrong next year, by the way. I'm just trying to listen day to day, figure it out.

Every sport needs its temple, its cathedral.

Basically all the world's computer parts come from the same supply chain that runs from Korea, down through coastal China, over to Taiwan, and down to Malaysia.

Until we fully understand what turned two brothers who allegedly perpetrated the Boston Marathon bombings into murderers, it is hard to make any policy recommendation other than this: We need to redouble our efforts to make America stronger and healthier so it remains a vibrant counterexample to whatever bigoted ideology may have gripped these young men....And the best place to start is with a carbon tax.

I am always a little skeptical on the water thing because I have been hearing that for 30 years, but one year it's going to be true. With the rising populations, Yemen could be the first country in the world, or Sana'a the first major city in the world, to run out of water, that's from Yemeni hydrological engineers and the United Nations. Sooner or later, all of these people, from 7 to 9 billion, all of them want to live like America, will be consuming so much more water that some of the societies will hit a wall without more sustainable environmental practices.