In Copenhagen, the major polluting governments—including the United States and China—signed a nonbinding agreement pledging to keep temperatures from increasing more than 2 degrees Celsius above where they were before we started powering our economies with coal. (That converts to an increase of 3.6 degrees Fahrenheit.) This well-known target, which supposedly represents the “safe” limit of climate change, has always been a highly political choice that has more to do with minimizing economic disruption than with protecting the greatest number of people.
