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

Several times in Earth's history, rapid global warming occurred, apparently spurred by amplifying feedbacks. In each case, more than half of plant and animal species became extinct. New species came into being over tens and hundreds of thousands of years. But these are time scales and generations that we cannot imagine.

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

If humanity wishes to preserve a planet similar to that on which civilisation developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO₂ will need to be reduced from its current 385 ppm [parts per million] to at most 350 ppm... If the present overshoot of this target CO₂ is not brief, there is a possibility of seeding irreversible catastrophic effects.

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

The five-year mean global temperature has been flat for the last decade

We have at most ten years—not ten years to decide upon action, but ten years to alter fundamentally the trajectory of global greenhouse emissions.