Andrew Dessler

There's nothing intrinsically wrong with this definition, but it sure seems arbitrary. Why 4 days? Why 1-in-10 events? When doing science, you should always be worried that arbitrary decisions (e.g., thresholds in an index) will give you arbitrary results.

So the question is: if you change your definition of "heat wave", would you get a different answer? Let's find out. The most obvious thing to do is to just count the number of hot days.

Let's take Berkeley Earth's gridded daily maximum land temperature over the (approx.) continental US. For each grid cell, find the 95th-percentile temperature from the entire time series (1880-2020) and then count the number of days each year that exceed that.

So what's going on? This is what we call cherry picking. Cherry picking is when you analyze a small amount of data to reach a conclusion that the full data set does not support.

There are really two cherry picks here. First is the choice of an obscure (and frankly weird) metric. This metric almost certainly gives an answer that is opposite to what a more exhaustive set of metrics would show.