Fifty percent of the world's population lives in cities. In a couple of decades, 70 percent of the world's population will be living in cities. Cities are where the problem is. Cities are where the solution is, where creativity exists to address the challenges and where they have most impact. This is why, in 2005, the C40 was founded, an organization of cities that address climate change. It started with 18 cities; now it's 91. Cities simply are the key to saving the planet.

I'm not going to talk about supporting somebody for a long time. I don't know who the two party candidates are going to be.

Fighting climate change isn't just an obligation we owe to future generations. It's also an opportunity to improve public health - and drive economic growth - in the here and now.

In New York City, a lot of people think "the great outdoors" is the area between your front door and a taxi cab.

Unemployment in America today is too high. And part of the reason, unfortunately, is that many companies cannot fill the high-skilled jobs increasingly at risk of going overseas.

It's no fun to protest on an empty stomach.

Leading from the front: It's what built America. But these days, the federal government isn't at the front - it's cowering in the back corner of the room, ducking responsibility and hoping no one notices.