The scientific excitement in comparing theory with data, and developing some understanding of global changes that are occurring, is what makes all the other stuff worth it.

A level of no more than 350 ppm is still feasible, with the help of reforestation and improved agricultural practices, but just barely - time is running out.

The urgency derives from the nearness of climate tipping points.

The forcings that drive long-term climate change are not known with an accuracy sufficient to define future climate change.

It has become very difficult for anyone to argue that observed global warming is natural variability. We have good reason for being able to say that the world will be warmer by about a quarter of a degree in the next decade. It's the same reason we had 10 years ago when we said that the 1990s would be warmer than the 1980s: The planet is out of equilibrium.

What we are doing to the future of our children, and the other species on the planet, is a clear moral issue.

The United States did not sign Kyoto, yet its emissions are not that different from the countries that did sign it.