We are on the precipice of climate system tipping points beyond which there is no redemption.

The climate is nearing tipping points. Changes are beginning to appear and there is a potential for explosive changes, effects that would be irreversible, if we do not rapidly slow fossil-fuel emissions over the next few decades.

The greatest danger hanging over our children and grandchildren is initiation of changes that will be irreversible on any time scale that humans can imagine.

The last time the world was three degrees warmer than today-which is what we expect later this century-sea levels were 25m higher. So that is what we can look forward to if we don't act soon.

Some Democrats deserve to be criticized.

The question is not whether to close the parks, but how to accomplish this goal.

We have to, in the next ten years, begin to decrease the rate of carbon dioxide emissions and then flatten it out. If that doesn't happen in ten years, we're going to be passing certain tipping points. If the ice sheets begin to disintegrate, what can you do about it? You can't tie a rope around an ice sheet.