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?

We have been getting rich by depleting all our natural stocks - water, hydrocarbons, forests, rivers, fish and arable land - and not by generating renewable flows.

Replacing half of the U.S. ground-transport fuels with hydrogen from wind power by 2050, for example, might require 1,400 gigawatts of advanced wind turbines or more... replacing those fuels with electricity might require less than 400 GW.

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 our government won't spend the money to protect New Orleans sufficiently today, what are the chances we will spend the money to protect dozens of coastal cities post-2050, once everyone knows that sea levels will keep rising and intense hurricanes will occur relentlessly?

As long as a handful of U.S. scientists, most receiving funds from the fossil fuel industry, get equal time with hundreds of the world's leading climate scientists, the public inevitably ends up with a misimpression about the state of our scientific understanding.

We created a way of raising standards of living that we can't possibly pass on to our children.