What changed in the United States with Hurricane Katrina was a feeling that we have entered a period of consequences.

I want to extend condolences to the families of those who died in the service of the United Nations.

The insistence on complete certainty about the full details of global warming-the most serious threat we have ever faced-is actually an effort to avoid facing the awful, uncomfortable truth: that we must act boldly, decisively, comprehensively, and quickly, even before we know every last detail about the crisis. Those who continue to argue that the appropriate response is merely additional research are simply seeking to camouflage timidity or protect their vested interest in the status quo.

My parents were true believers in the efficacy of American constitutional democracy, and I was thoroughly inculcated with reverence for what we the people are capable of doing. The complication in that simple narrative is that as I got older, the Vietnam War shook my confidence in how our democracy was working. I ended up serving in that war, but it started with a lie, and I was very proud of my father for being one of its earliest opponents.

When our founders created America, it was in the age of the printing press, when individuals could freely join the conversation. And that robust, democratic dialogue more often than not lifted up the best available evidence and asserted what was more likely to be true than not.

The struggle to save the global environment is in one way much more difficult than the struggle to vanquish Hitler, for this time the war is with ourselves. We are the enemy, just as we have only ourselves as allies.

Political will is a renewable resource, and everyone can have it in abundance if they so choose.