The study, Esper, J. et al. Nature, 2023, is using an old statistical trick pioneered by Michael Mann, PhD. in his hockey stick graph controversy, where estimated temperatures from tree rings and other proxies (used because no thermometer readings exist prior to about 1850) far into the past are grafted onto more reliable temperatures measured in the present and presented as one unified dataset, when in fact they are different.
For example, an article about the study in the BBC showed this graph, which is highly reminiscent of Mann’s original “hockey stick” graph.
That graph is highly misleading, if not flat-out fabrication. It suffers from the same sort of issues in Mann’s original “hockey stick” graph such as suppressed climate variability over the past 2000 years. We know from other studies that the Roman Warm Period (from 1–250 AD) and the Medieval Warm Period (950 to c. 1250) existed, but they have been erased from the graph presented to the public.
The fact that these well-known, documented, and scientifically certified climate events have been removed from the graph touted by the media indicate that this is more likely science being used as propaganda rather than science based on the scientific method.
Plus, the 95 percent uncertainty range indicated in the graph cited by the BBC is as large as the temperature gain in 2023. Who’s to say that such single year warm summer events didn’t happen before? The 1757 summer heatwave in Europe, said to be similar to historically known and recent heatwaves around the world, doesn’t show up in the study graph displayed by the BBC.
Another issue with the study is the well-known fact that tree year-on-year growth rings are not necessarily exclusive indicators of temperature, as proven in Liebig's law of the minimum. Often simply called Liebig's law, or the law of the minimum, it is a principle developed in agricultural science by Carl Sprengel (1840) and later popularized by Justus von Liebig. It states that growth is dictated not by total resources available, but by the scarcest resource (limiting factor).
In other words, plant growth factors from year to year such as available sunlight (varied by cloud cover), available water as rainfall, available nutrients in the soil, and local air temperature all combine to determine growth of a tree, not just temperature alone. It is impossible to distinguish and disentangle the factors that contribute to tree growth in any given year, and to claim that tree growth rings are exclusive indicators of temperature is just dishonest.
The lead author, Jan Esper, confirms by quotes given to the BBC, that he is in fact using this study as a vehicle to elicit change.
The authors say the key conclusion from their work is the need for rapid reductions in emissions of planet-warming gases. “The longer we wait, the more expensive it will be and the more difficult it will be to mitigate or even stop that process and reverse it,” said lead author, Prof Jan Esper from Johannes Gutenberg University, in Germany.
“That is just so obvious,” he said. “We should do as much as possible, as soon as possible.”
This admission makes the study more about climate advocacy than science, and the media fell for it. This sort of journalistic malfeasance has become increasingly more common in recent years as grants for journalists to produce climate related stories have increased. The study authors, by their own admission, are clearly doing advocacy instead of science, but the editors and fact checkers that media outlets employ did not catch the advocacy factor nor the flawed claims. If they were actually doing their jobs as journalists to report the truth, this story would never have been published.
Anthony Watts ([email protected]) is a senior fellow for environment and climate at The Heartland Institute.
