The poverty fighters resent the climate-change folks; climate folks hold summits without reference to biodiversity; the food advocates resist the biodiversity protectors. They all need to go on safari together.

Pessimists are usually right and optimists are usually wrong but all the great changes have been accomplished by optimists.

When people get frustrated, it's when they feel they are living in a context that deprives them of dignity, deprives them of justice and deprives them of the freedom to realize their full potential, and that to me is what the Arab awakening was all about. I think it applied to every country, and so I have been an unmitigated supporter of it.

What we do know is that the planet is going from 7 billion people today to 9 billion. More people want to live like us, drive American- size cars, live in an American-size home, and eat American-size Big Macs. What does that mean? It means that energy demand is going to be going up.

Big breakthroughs happen when what is suddenly possible meets what is desperately needed

Saudi hijackers first came into contact with al-Qaeda and went through Terrorism 101 when they signed up for the jihad in Afghanistan.

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.