One dumb thing that scientists sometimes say about global warming is that we are conducting an experiment in the atmosphere. In fact, what we are conducting, or trying to conduct, is a civilization. Characterizing the economic activities that emit greenhouse gases as some kind of insane scientific experiment is to miss the most important part of the story. Global warming and other environmental problems are fundamentally economic problems. Physical scientists know next to nothing about economics. Actually, they know just about as much about economics as economists know about physical science. The difference is that, these days at least, physical scientists are not shy about holding forth on economic issues while economists are generally silent on physical science.