The real deniers keep trying to repair the infamous climate hockey stick. They focus on the blade, but it was not the major issue originally. The bulwark claim of the anthropogenic global warming (AGW) hypothesis and the objective of the stick are that current global annual average temperatures are the warmest ever. This meant the upturn of the blade in the 20th century was only relevant if it was higher and steeper than any previous record.
Earlier warm periods were not a threat in the first reports of the Intergovernmental Panel on Climate Change (IPCC). Their mandate required they only look at human causes, which they interpreted to mean the industrial period. However, as experts who were denied participation in the IPCC process began to examine what was said they identified earlier warmer periods, especially the Medieval Warm Period (MWP), and more rapid temperature increases.
The MWP was problematic as the most recent and clearly pre-industrial. Figure 1 shows temperatures for Europe for the last 1000 years shown in the 1995 Intergovernmental Panel on Climate Change (IPCC) Second Assessment Report.
It shows general warming from 1680 following the cold of the Little Ice Age (LIA) that was coincident with the Maunder Minimum of sunspots. This warming shows why charges that others and I were global warming deniers were false. What we questioned was the claim that humans were the cause. “Dickens Winters” relate to Charles Dickens and the cold weather, poor harvests, and hard economic times typified by A Christmas Carol. The period correlates with the Dalton Minimum of reduced sunspots. Conditions of that time are similar to those anticipated for the next 30–40 years.
Dominance of the graph by the MWP was the challenge. As IPCC participant Jay Overpeck said in his email to Professor Deming, “We have to get rid of the Medieval Warm Period.” This was achieved by the Mann, Bradley, and Hughes 1998 paper in Nature titled, Global–scale temperature patterns and climate forcing over the past six centuries, the original peer-reviewed hockey stick article. Reviewers failed to catch several errors, including the assumption that tree rings only represent temperature, a plethora of evidence for existence of the Medieval Warm Period, and inappropriate statistical method and application. Problems with the hockey stick were identified, but not before it grabbed world attention. A modified (but no more valid) version appeared in the 2007 IPCC Report. It had the same problems as the original with a few more added, including the error of assuming growth rate of stalactites and sediment layers were due to temperature, not precipitation.
They Don’t Know When to Quit
The latest attempt to resurrect the hockey stick by Tingley and Huybers was quickly dismissed as more of the same using some statistical manipulation. Continued denial of the failure of the statistical methods by a select few is a story in itself. But there’s a major diversion in the latest resurrection with the focus only on the blade. Here is the graph, reshaped by Steve McIntyre for comparison with other hockey stick examples.
Coverage is from 1450 (by which time cooling associated with the Sporer Minimum had begun – see Figure 1) to the present. The MWP is not included, suggesting that the present warm period is not unique. The 2007 IPCC diagram also hints at an MWP. So apparently, because they failed to eliminate the MWP, it’s back to the blade of the hockey stick. A brief overview of historical climate shows the MWP is not unique nor the rate either.
The world is currently in an Interglacial, and though warm compared to the nadir of the Ice Age approximately 20,000-years ago, it’s not as warm as previous Interglacials. Figure 3 shows the temperature reconstructions from Antarctic ice cores for the last 420,000 years covering four previous Interglacials. Three at 130,000, 230,000, and 340,000 years ago were warmer than the current temperatures on the right. Also consider the variability that signifies rate of change. This curve is smoothed by a 70-year moving average, which eliminates variability. It means two readings for the 20th century.
More recently, there is the warm period known as the Holocene Optimum (from 3,000 to 8,000 years ago) and shown in ice core temperatures from Greenland (Figure 4). On the right is the rapid emergence from the Ice Age 10,500 years ago with current temperatures on the left. This record shows you can argue it was warmer than today for most of the last 10,000 years. It shows temperatures up to 3°C warmer than at present, and a measure of the range of variability in relatively short time periods. You can also argue that the world has cooled from the peak of warming approximately 3,000 years ago.
Close examination of the last 3,500 years in Figure 5 shows more detail about the variability of temperature change.
The appearance changes significantly from Figure 4 because of the technique used to display the data. There are three distinct warmer periods relative to the current warmer period. Notice that cooler periods dominate as they do in the 400,000 Antarctic records.
Current Climate Change is Normal
Current global temperatures are not the highest ever, and the rate of change is historically equaled. More importantly, the previous warm periods cannot be due to human CO2 as the IPCC claims for current temperatures. Global warming is not a concern, but that is already partially conceded by the shift to climate change. We’re told that climate changes as if it is a revelation. A review of history shows how much climate changes and that current conditions are not unique. The real revelation is the degree to which people have been misled on the issue. As Heraclites said,
There is nothing permanent except change.