James Hansen: Why I must speak out about climate change | Video on TED.com.

So the reasons I post external stuff on my blog are varied: some are funny, some are inspiring, some are cool, some I connect with on some level. This one speaks to one of the defining issues of my generation and future generations. The biggest problem in America is that this issue has been politicized. People listen to the loudest, not the smartest. I want it to be known for the sake of posterity that I did not ignore the warnings and I contributed, in what ways I could, to the preservation of our ecosystem.

Humanity is on the verge of one of our greatest challenges. I am quite cynical about human nature and fear it will take many humongous disasters to shake us into action, and by that time the opportunity for effective action will have passed. However I am also optimistic that we _can_ avert catastrophe if only we listen to our planet, our home: the only one we have.