The question at this point is not whether climate change is underway, but rather what the extent of climatic change will be. We can be certain that the changes will be dramatic and challenging; we must hope that they will not be catastrophic. Above all else, we must take action to address greenhouse gas emissions today.

Meeting the challenge posed by climate change will require action at multiple levels. National governments around the world must work together to craft comprehensive international climate agreements and national policies. State and local governments must examine what can be done in their respective areas of responsibility. Most importantly, each of us must take steps to reduce our greenhouse gas emissions, and thereby our impact on the climate.