There are waves piling on waves in the weather.A new press release tells us that there have been an “exceptional” number of weather extremes in summer. Weather extremes in the summer — such as the record heat wave in the United States that hit corn farmers and worsened wildfires in 2012 — have reached an exceptional number in the last ten years. Human-made global warming can explain a gradual increase in periods of severe heat, but the observed change in the magnitude and duration of some events is not so easily explained. Heatwaves lend themselves to headlines. Not only are...