If NASA is to reach beyond the Moon and someday reach Mars, it must be relieved of the burden of launching people and cargo to low earth orbit. To do that, we must invest more in commercial spaceflight.

We should educate more women and girls. Because that is the surest route to controllably, manageably reducing the human population. Educated women have fewer kids. And the kids they do have are better cared for and are more successful. As I like to say, it's not one thing that we need to focus on. It's everything all at once.

The natural world is a package deal; you don't get to select which facts you like and which you don't.

It is my mission to change the world. I'm not kidding: Make no small plans, dream mighty things. I feel if we get enough people engaged in climate change, we will get enough people to change the world. We will revolutionize the way we produce electricity and provide clean water to people.

I tell personal stories associated with aspects of the theory, and I hope they are interesting and compelling. I don't feel you're going to change a grownup's mind in one reading. People have to be exposed to scientific ideas over and over again for years. It's also not a textbook.

To leave the world better than you found it, sometimes you have to pick up other people's trash.

If you want grown-ups to recycle, just tell their kids the importance of recycling, and they'll be all over it.