Around the world, ever more countries and regions are promising to stop emitting carbon dioxide sometime in the future. The European Union is winning plaudits from green activists for aiming to be “carbon neutral” by 2050. Cities from Adelaide to Boston to Rio de Janeiro are announcing similar goals, with Copenhagen saying it will get there already in 2025. Such promises should be greeted with a healthy dose of skepticism. Copenhagen, for example, will likely miss its target, even after spending twice the planned cost of going carbon neutral. In fact, we can learn a lot about the emptiness of...