Much of the scientific community has been astonished that their increasingly strong and detailed warnings have been either ignored or attacked.

On moral grounds, I think that if you believe a certain outcome is a very possible outcome, you have an obligation to tell people that. With global warming, the probability of a bad outcome if we stay on our current emission trends is incredibly high. If you know a bad outcome is likely to happen, what right do you have not to communicate that? You go into a doctor's office, what are they going to do - not tell you the diagnosis?

By the end of the third decade of this century, all of American life - politics, international relations, our homes, our jobs, our industries, the kind of cars we drive - will be forever transformed by the climate and energy challenge.

The United States could dramatically reduce its carbon emissions per kilowatt-hour without raising its overall energy bill.

Some 3 million years ago, when the earth was a little more than 3°C warmer than preindustrial levels (about 2.2°C warmer than today), Antarctica had far less ice and sea levels were a stunning 25 meters higher than today. If we stay on our current emissions path, the planet will almost certainly be that warm by the century's end.

I've always believed that you should stick as closely to the science as possible. And my biggest advice to reporters has been, if you're doing a climate story, talk to climate scientists. The best climate stories are done by the people who talk to climate scientists.

You must become a climate champion, a single-issue voter. You must take whatever action you can. You must use whatever influence you have wherever it would make a difference, even if it is only to educate the people around you.