Virtually indistinguishable – Comparing early 20th Century warming to late 20th Century warming

Guest essay by Andy May

Many writers, including Professor Richard Lindzen and Ed Caryl have noticed the remarkable similarity in global warming observed from around 1910 to 1944 and 1975 to 2009. The similarity in slopes exists in all global surface temperature datasets. Figure 1 shows the HadCRUT version 4 dataset and the NASA GISS land (GHCN v3) and ocean (ERSST v4) temperature dataset. We’ve identified the two periods of interest on the figure. All datasets also show some cooling between 1945 and 1975.

Figure 1

Figure 2 shows the two periods overlain with data from the HadCRUT version 4 dataset. This display is scaled to actual average temperature. Unlike Figure one this figure and the next one use smoothed monthly data. In that way, we can see some of the variation within each year.

Figure 2

The left side of Figure 2 represents 1910 for the blue line…