I think it's harder for people than it should be. But as more and more of us become carbon neutral and change the patterns in our lives to be part of the solution instead of part of the problem, we are now beginning to see the changes in policy that are needed.

American democracy is in grave danger from the changes in the environment in which ideas either live and spread or wither and die.

Researchers at the Naval Postgraduate School have told us that the entire Arctic ice cap may totally disappear in summer in as little as five years if nothing is done to curb emissions of greenhouse gas pollution.

There's a law of physics: For every action there's an equal and opposite reaction. And sometimes that shows up in politics and society. And I think that the reaction to President Trump's decision on the Paris Agreement has been much stronger than I had even hoped for. And the determination being expressed by so many people in state governments, city governments, in the business community, the investor community, is really heartening to me.

There's such a wide variation in tax systems around the world, it's difficult to imagine a harmonized CO2 tax that every country agrees to. That's not in the cards in the near term. But the countries that are doing the best job, like Sweden, are already doing both of these. I think that eventually we'll use both of them but we need to get started right away and the cap-and-trade is a proven and effective tool.

Our world faces a true planetary emergency. I know the phrase sounds shrill, and I know it's a challenge to the moral imagination.

Traditionally the United States has been the natural leader of the world. That's not just pride as an American speaking; it's just the reality. Without the U.S. being involved in Paris Climate Agreement, it's hard for the world community to move forward as effectively.