KENNEBUNKPORT — In his critique (Maine Voices, March 3) of a Feb. 19 column by M.D. Harmon on climate change, Marc Anderson accuses Harmon of fallacious reasoning for thinking that the non-controversial refutation of the “hockey stick” graph refutes the notorious global warming argument.

Anderson apparently believes that because we cannot explain the unprecedented recent warming depicted in the hockey stick graph by appeal to natural forces, we can only account for it in terms of human behavior associated with ever-increasing CO2 emissions.

However, the argument Anderson refuted is not the argument offered by Harmon, who was asserting that real global warming in the Medieval Warm Period was distorted and suppressed by the introduction of questionable proxy evidence.

This made it look as if the warmth we have recently experienced is unprecedented, when demonstrably it is not. There is nothing fallacious about Harmon’s argument.

But there is more to say here. It is well known that the hockey stick graph offered by Michael Mann, Philip Jones and others found acceptance in the scientific community associated with the U.S. Intergovernmental Panel on Climate Change.

They cited it as a correct depiction of a sharp and unprecedented increase in global temperature in the last century. Thus it served as solid evidence for future predictions of extreme global warmth.

It was also featured in Al Gore’s sci-fi documentary “An Inconvenient Truth.” and was listed as one of 10 serious errors noted by the High Court in London when the court ruled the film was propaganda.

The First IPCC Assessment, issued in 1990, presented the traditional history of climate in the past 1,100 years.

There was a Medieval Warming Period (roughly 800-1400) that was somewhat warmer than the present (2010); and there was a Little Ice Age (1500-1850) that was cooler than the present.

The presence of a period warmer than the present – but without the presence of man-made greenhouse gases – embarrassed those enthusiastic alarmists who hold that global warming can only be attributed to the activities of man coordinated with corresponding increases in CO2 emissions.

So, efforts were made to conceal the Medieval Warm Period, and the most successful was offered by Mann and Jones, of “Climategate” fame.

This used a small number of tree ring records to reconstruct Northern Hemisphere temperatures going back a thousand years that no longer showed the Medieval Warm Period. The new graph ended in a sharp warming period beginning in the 19th century.

This uptilt came to be known as “the hockey stick” and was quite clearly featured in the next IPCC report, where it was then rhapsodically affirmed as indicating that the present warming was unprecedented in the last thousand years, was clearly caused by increasing CO2 emissions, and is likely to get worse without drastic reduction in CO2 emissions caused by human activity.

As has been frequently noted elsewhere, apart from the manipulation of the database to fit a preconceived hypothesis of unprecedented recent warmth attributed to human activity, the most acute criticism was written by two Canadian statisticians and two other independent assessments of the hockey stick graph.

All found the statistics not adequate to justify the claims. Because the existence of the Medieval Warm Period is amply documented in historical accounts for the North Atlantic Region, Mann and his allies countered that the warming had to be regional, but was not characteristic of the whole Northern Hemisphere and especially not the planet.

On this, climatologist Richard Lindzen said: “Given that an underlying assumption of their analysis was that the geographic pattern of warming had to have remained constant, this (regional variation) would have invalidated the analysis . Indeed the 4th IPCC Assessment (2007) no longer featured the hockey stick, but the claim that current warming is unprecedented remains, and Mann’s reconstruction is still shown in chapter 6 of the 4th Assessment buried among other reconstructions.”

Finally, several scientifically respectable studies have recently established that normal global warming and normal global sea-level rise pretty much stopped in late 1993-94 with the exception of 1998, and that every year after 1998 until now has been cooler than 1998.

None of this, however, was predicted by the models used by IPCC, and thus IPCC has failed to satisfy the conditions of a good scientific hypothesis.