Suppose we have two hypotheses: 1) The likelihood of extreme rain events hasn't changed over the last hundred years. This recent extreme rain event was just a

Suppose we have two hypotheses: 1) The likelihood of extreme rain events hasn't changed over the last hundred years. This recent extreme rain event was just a four sigma event. Such outliers sometimes happen. 2) The likelihood of extreme rain events has shifted over the past hundred years. Here's a plausible mechanism (omitted). The recent rain event was only a two sigma event. We may not have enough data yet to definitively select one hypothesis and reject the other, but which is more likely?