Jan and Ulf’s Nature Trick: The Hottest Summer in 2000 Years
A couple of weeks ago, the New York Times and other institutional media proclaimed that “tree rings” (sometimes “ancient tree rings”) had “shown” that 2023 was the warmest summer in 2000 years (link link) Almost 25 years to the day since they had similarly proclaimed that 1998 was the warmest year in 1000 years. The recent proclamation, as in 1998, was based on an article in Nature (Esper et al, 2024); the proclamation in 1998 was similarly based on an article in Nature (Mann et al, 1998), together with its companion article in Geophysical Research Letter (link).
A “Confidence Interval” Trick
In addition to the similarity of the conclusions to the two article, the structure of the money diagram in both cases is almost identical, as shown in the comparison below.
Figure 1. Left – On the left is the money diagram from Mann et al (1999) showing confidence intervals from the Mann reconstruction in light grey, the reconstruction in black. The reconstruction itself only went to 1980. The instrumental temperature (as an “anomaly”) for 1998 was shown as a point. A horizontal line was then drawn across the diagram to show that the 1998 instrumental temperature exceeded the confidence interval for all prior dates of the reconstruction – hence the “warmest year in 1000 years”. Right – the Esper et al 2024 reconstruction only went to 2010. The point estimate for 2023 exceeds the confidence intervals for all prior years.
Each diagram shows purported confidence intervals around the reconstruction in light/medium gray. Each diagram also denotes a the recent instrumental estimate featured in the headline as a highlighted point. In each case, the highlighted instrumental point is more than 10 years after the end of the reconstruction. In each case, the conclusion is obtained by observing that the instrumental point is higher than any of the upper confidence limits of the corresponding reconstruction. In other words, both Esper et al (2024) and Mann et al (1998-99) used the same technique.
https://climateaudit.org/2024/05/24/jan-and-ulfs-nature-trick-the-hottest-summer-in-2000-years/
