Between 1998 and 2012 the global economy more than doubled in size—to some $71 trillion in GDP from $30 trillion. That's the good news. Over the same period the world pumped more than 100 billion tons of carbon dioxide into the atmosphere. That is supposedly the bad news. Yet global surface temperatures have remained essentially flat. That's the mystery: If emitting CO2 into the atmosphere causes global warming, why hasn't the globe been warming?

That's the question we would have liked to see answered by the U.N. Intergovernmental...