The science is crystal clear: we humans are the primary cause of global warming, and we face a bleak future if we fail to act quickly.

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.

If Americans in 2100 came to see 12 meters sea-level rise as inevitable by 2200, who can even begin to fathom how the nation would respond?

The best thing about improvements in health care is that all the climate-change deniers are now going to live long enough to see how wrong they were.

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?

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.

Protecting dozens of major coastal cities from future flooding will be challenging enough-rebuilding major coastal cities destroyed by super-hurricanes will be an almost impossible task.