Imagine spending your whole career working on a question to which you don’t want to know the answer. We know that greenhouse gas emissions can and do warm the planet, but we don’t know one very basic thing: how hot, exactly, is it going to get? The main reason for this, of course, is that human behavior is so hard to predict. How will the people of the late twenty-first century get their energy? Will they need as much as we do, or will they have reconciled themselves to fundamentally different lives?
