Not so long ago, people talked about global warming in apocalyptic terms--imagining the Statue of Liberty up to its chin in water or an onslaught of tropical diseases in Oslo. Recently, however, advances in our understanding of climate have moved global warming from a subject for a summer disaster movie to a serious but manageable scientific and policy issue.
Here's what we know. Since sunlight is always falling on the earth, the laws of physics decree that the planet has to radiate the same amount of energy back into space to keep the books balanced. The earth does this by sending...