The weirdest millennium

Much research effort over the past years has gone into reconstructing the temperature history of the last millennium and beyond. The new IPCC report compiles a dozen reconstructions for the temperature of the Northern Hemisphere (including of course the original “hockey stick” reconstruction, despite opposite claims by the Wall Street Journal). Lack of data does not permit robust reconstructions for the Southern Hemisphere. Without exception, the reconstructions show that Northern Hemisphere temperatures are now higher than at any time during the past 1,000 years (Figure 1), confirming and strengthening the conclusions drawn in the previous IPCC report of 2001.

Fig. 1: Figure 6.10 (panel b) from the paleoclimate chapter of the current IPCC report (see there for details).

“Climate sceptics” do not like this and keep coming up with their own temperature histories. One of the weirdest has been circulated for years by German high-school teacher E.G. Beck (notorious for his equally weird CO2 curve). This history shows a medieval warm phase that is warmer than current climate by more than 1 ºC (see Figure 2). So how did Beck get this curve?

Fig. 2, modified from E.G. Beck (we added the green parts).

The curve is a fake in several respects. It originally is taken from the first IPCC report of 1990: a scan of the original is shown in Figure 3. At that time, no large-scale temperature reconstructions were available yet. To give an indication of past climate variability, the report showed Lamb’s Central England estimate. (Unfortunately this was not stated in the report – an oversight which shows that IPCC review procedures in the early days were not what they are now. We will post in more detail on the history of this curve another time.)

Fig. 3. The past millennium as shown in the first IPCC report of 1990, before quantitative large-scale reconstructions were available. This curve was based on Lamb’s estimated climate history for central England.

But Beck did not stop at simply using this outdated curve, he modified it as highlighted in green in Figure 2. First, he added a wrong temperature scale – the tick marks in the old IPCC report represent 1 ºC, so Beck’s claimed range of 5 ºC exaggerates the past temperature variations by more than a factor of three. Second, the original curve only goes up to the 1970’s. Since then, Northern Hemisphere temperatures have increased by about 0.6 ºC and those in central England even more – so whatever you take this curve for, if it were continued to present, the current temperature would be above the Medieval level, as in the proper reconstructions available today. As this would destroy his message, Beck applied another fakery: he extended the curve flat up to the year 2000, thereby denying the measured warming since the 1970s. With this trick, his curve looks as if it was warmer in Medieval times than now.

Page 1 of 2 | Next page