Those who I refer to as ‘the new deniers’ keep trying to repair the infamous climate “hockey stick”. This is a term coined for a chart of temperature variation over the last 1,000 years, which suggests a recent sharp rise in temperature caused by human activities. The chart is relatively flat from the period AD 1000 to 1900, indicating that temperatures were relatively stable for this period of time. The flat part forms the stick’s ‘shaft’. However, after 1900, temperatures appear to shoot up, forming the hockey stick’s ‘blade’.
Those who support the hockey stick focus on the blade, but it was not the major issue originally. The bulwark claim of the anthropogenic global warm (AGW) hypothesis and the objective of the stick are that current global annual average temperatures are the warmest ever. This meant that the upturn of the blade in the twentieth 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 that 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) dating from 900AD to 1300AD, and more rapid temperature increases.
The MWP was problematic because it is the most recent and clearly pre-industrial period of warmth. Fig. 1 shows temperatures for Europe for the last 1,000 years shown in the 1995 IPCC Second Assessment Report.
It shows general warming from 1680 following the cold of the Little Ice Age that was coincident with the Maunder Minimum of sunspots. This warming shows why the charge that others and I were global warming deniers was 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 his masterpiece, A Christmas Carol. The period correlates with the Dalton Minimum of reduced sunspots. Conditions of that time were similar to those anticipated for the next 30 to 40 years.
Dominance of the graph by the MWP was the challenge for supporters of the hockey stick. As Jay Overpeck, an IPCC participant 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 entitled, 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 tree rings only represent temperature, a plethora of evidence for existence of the MWP, 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 by people like me as more of the same using some statistical manipulation. (See, for example, the article by Steve McIntyre entitled Tingley and Huybers (2010?) at: http://www.climateaudit.org/?p=7524.)
Continued denial of the failure of the statistical methods by a select few is a story in itself. However, 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 (see Fig. 1) had begun, to the present. The MWP is not included, suggesting that the present warm period is unique. The 2007 IPCC diagram also hints at a 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 is not as warm as previous interglacials. Fig. 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. Such a long moving average means that you could have only a single reading any century and at most two readings.
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 (Fig. 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.
Current climate change is normal
Current global temperatures are not the highest ever and the rate of change is historically equalled. 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.”
Timothy Francis Ball is a British-born, Canadian environmental consultant and former professor of geography at the University of Winnipeg, where he specialised in the relation of climate to human settlement.