We need scientists to design new fuels. We need farmers to help grow them. We need engineers to invent new technologies. We need entrepreneurs to sell those technologies. We need workers to operate assembly lines that hum with high-tech, zero-carbon components. We need builders to hammer into place the foundations for a clean energy age. We need diplomats and businessmen and women, and Peace Corps volunteers to help developing nations skip past the dirty phase of development and transition to sustainable sources of energy. In other words, we need you.

There's one issue that will define the contours of this century more dramatically than any other, and that is the urgent and growing threat of a changing climate.

It is true, I worry about the hype. The only person more over-hyped than me is you.

To look at the issue of life and abortion, actually we're moving in that direction where most Americans oppose most abortions.

What I think is fair to say is that, coming out of the Republican camp, there have been efforts to suggest that perhaps I'm not who I say I am when it comes to my faith - something which I find deeply offensive, and that has been going on for a pretty long time.

By 2025 we expect new spacecraft designed for long journeys to allow us to begin the first ever crewed missions beyond the Moon into deep space. So we'll start by sending astronauts to an asteroid for the first time in history. By the mid-2030s I believe we can send humans to orbit Mars and return them safely to Earth. And a landing on Mars will follow and I expect to be around in see it.

It's important to make sure that governments have some checks on what they do, that people can oversee what's being done so the government doesn't abuse it.