The Book of Why: The New Science of Cause and Effect (Penguin Science)

by Judea Pearl

Next, I will discuss the application of counterfactuals to climate change. Until recently, climate scientists have found it very difficult and awkward to answer questions like “Did global warming cause this storm [or this heat wave, or this drought]?” The conventional answer has been that individual weather events cannot be attributed to global climate change. Yet this answer seems rather evasive and may even contribute to public indifference about climate change. Counterfactual analysis allows climate scientists to make much more precise and definite statements than before. It requires, however, a slight addition to our everyday vocabulary. It will be helpful to distinguish three different kinds of causation: necessary causation, sufficient causation, and necessary-and-sufficient causation. (Necessary causation is the same as but-for causation.) Using these words, a climate scientist can say, “There is a 90 percent probability that man-made climate change was a necessary cause of this heat wave,” or “There is an 80 percent probability that climate change will be sufficient to produce a heat wave this strong at least once every 50 years.”