More than two decades ago, the hypothesis of Anthropogenic Global Warming (AGW) seemed logical to me. I bit into it hook, line, and sinker. (See following note) Until recent times, most articles and papers presented both sides of the AGW debate. The one sentence used by skeptical authors or resources back then that always seemed like a way to avoid a concrete data-based statement was something to the effect of “The change in global temperature is well within the realm of Natural Variability.” I have mixed feelings about the term “Natural Variability” even to this day, yet I will conclude this post with it.
Note: My understanding of and position on AGW changed more than 10 years ago. I would now be classified as a full-fledged, bona fide, card-carrying AGW skeptic. Well, I’d have a card if one was available.
THE DIP AND REBOUND IN LATE 19th TO EARLY 20th CENTURY SST ANOMALY
Figure 1 illustrates Global SST anomalies from Jan 1854 to October 2008. The data is raw and smoothed with an 11-year (133-month) filter. (The reason for the 11-year filter: I was plotting Monthly Sunspot Numbers for an upcoming post and I liked the way it smoothed global SST anomaly data. No other reason.) I’ve also circled the period from 1870 to 1940, during which SST anomalies dipped and rebounded.
As shown in Figure 2, which isolates the data over the period of January 1870 to December 1939, the variation is more than 0.3 deg C. I have yet to find an explanation for the dip and rebound in any IPCC or CCSP report. Are the IPCC and CCSP taking advantage of a natural decline in Global SST anomaly to reinforce or amplify their claims of an unprecedented rise in 20th Century Global Temperatures caused by anthropogenic forcings? Of course, they are.
Figure 3 contains the same data as Figure 2, except the data has been inverted. It’s supplied simply as a reference for the next illustration.
In Figure 4, I took the inverted 1870-to-1939 data and shifted it 90 years. I also shifted the temperature range a few tenths of a degree (I did not scale it) so that there was agreement in the starting points of the rises in the two curves after 1960. Note how the two curves have very similar trends from 1960 to 2000.
Note: I do not intend the broken extension of the red curve from present to the year 2030 as a prediction of future events. It simply seemed appropriate to include it. We’ll just have to wait and see what the future holds.
Using the unexplained 1870 to 1939 dip and rebound as reference, as of now, the rise in Global SST over the term of the instrument temperature record is well within the range of Natural Variability.
Sea Surface Temperature Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).