•From Chris Vautier.

GERALD White’s recent letter (JEP 3 September) regarding Michael Mann’s infamous “hockey stick” graph deserves a considered and detailed response.

More than two decades ago, Mann et al (1999) published a reconstruction in which the temperatures of the pre-industrial period 1000-1850 AD appeared flat and uneventful, followed by fast and allegedly unprecedented warming since 1850… thus resembling a hockey stick.

While this graph was prominent at that time, many scientists were (and are) sceptical about its accuracy.

One significant concern revolved around the statistical methods Mr Mann used to create the graph. He employed a technique known as “principal component analysis” to analyse various temperature data sources, including tree rings of two (yes, two!) bristlecone pines, ice cores, and, of course, computer modelling.

His critics rightly argued that this method could produce misleading results if certain data sets were favoured while others were ignored, with the belief that this selectivity might have overly amplified the recent warming trend, making it appear more severe than what a broader analysis would suggest. In fact, when the data set is extended to the last 12,000 years rather than just the last 1,000, it becomes clear that we are not experiencing anything unusual.

Another issue was the transparency of the data used in the research.

Many scientists felt that the original data and methods should have been available for others to review and verify. In the past, some of Mr Mann’s data was withheld, making it difficult for independent researchers to replicate his findings.

Indeed, researchers had to submit FoI requests in an attempt to simply gain access to the data. Even this was resisted.

Given that reproducibility is a key principle in science, if researchers cannot validate a study’s results, it raises serious doubts about its conclusions.

Scientists also believed that the graph oversimplified the complexities of earth’s climate, potentially overlooking natural climate variations throughout history, such as volcanic eruptions or variations in solar energy.

Mr Mann’s hockey stick graph was (and is) highly questionable due to justifiable concerns about statistical methods, data transparency, the complexities of climate variability and the politicisation of climate science. It should be noted that none of the above suggests that human activities and associated CO2 emissions have no impact on warming.

However, it should be remembered that the climate emergency (and the self-harm inflicted by the ideological pursuit of net zero) are political constructs, not scientific ones.

Le Catel, Rue du Câtel, Trinity.