Most of us pay some attention to the weather forecast. If it says it will rain in your area tomorrow, it probably will. But if it says the same for a month, let alone a year, later, it is much less likely to be right. There are too many imponderables. The theory of global warming is a gigantic weather forecast for a century or more. However interesting the scientific inquiries involved, therefore, it can have almost no value as a prediction. Yet it is as a prediction that global warming (or, as we are now ordered to call it in...