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?

The world beyond 450 ppm atmospheric concentrations of carbon dioxide, the world that crosses carbon cycle tipping points that quickly take us to 1000 ppm, is a world not merely of endless regional resource wars around the globe. It is a world with dozens of Darfurs. It is a world of a hundred Katrinas, of countless environmental refugees

Do believe that if we fail to act in time, it will be the single biggest regret any of us has at the end of our lives.

On our current path, all our great Gulf and Atlantic coast cities are at risk of meeting the same fate as New Orleans.

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

The first few feet of sea-level rise alone will displace more than 100 million people worldwide and turn all our major Gulf and Atlantic coast cities into pre- Katrina New Orleans - below sea level and facing super-hurricanes.

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.