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The temperature forecast modelled by the Hansen Group 25 years ago is off by about 150%. It is truly regrettable that precisely this modelling is still being viewed as a reliable forecast by our politicians.

At their Die kalte Sonne website, Professor Fritz Vahrenholt and Dr. Sebastian Lüning present a guest post by Prof. Jan-Erik Solheim, who comments on the huge divergence between Hansen’s 1988 forecast and actual observations. I’ve translated his guest post in English:

What ever became of James Hansen’s 1988 temperature forecast? Time for an evaluation

by Prof. Jan-Erik Solheim

One of the most important publications on “dangerous man-made climate change” is one by James Hansen and his colleagues in the year 1988 which appeared in the Journal of Geophysical Research. The title of the publication: Global Climate Changes as Forecast by Goddard Institute for Space Studies Three-Dimensional Model.

Figure 1: Temperature prognosis by the Hansen Group from 1988. The different scenarios assume 1.5% CO2 increase (blue), fixed CO2 emissions (green) and stopped CO2 emissions (red). In reality CO2 emissions have increased about 2.5% per year, which would be more than depicted the the blue curve scenario. The black curve is the actual temperature (smoothed 5-year mean). The Hansen-Model overestimated the temperature by 1,9°C and is thus a full 150% off. Graph supplemented as to Hansen et al. (1988).

In this publication Hansen and his colleagues present the GISS Model II, which simulates climate changes resulting from concentration changes in atmospheric trace gases and airborne aerosols. Here the scientists illustrate three scenarios:

CO2 emissions have increased at rate of about 2.5% since the year 2000 and so according to Hansen’s paper, we would expect a temperature increase greater than the Model A scenario. Figure 1 shows all three of Hansen’s scenarios as well as the real measured global temperature.

  • A: Increase of CO2 emissions of 1.5% per year
  • B: fixed increase CO2 emissions after the year 2000
  • C: No increase in CO2 emissions after the year 2000

The arrow extending beyond Scenario A shows the temperature value that should have been predicted by the Hansen Team based a CO2 increase of 2.5%. According to Hansen’s projection, the temperature should have increased 1.5°C when compared to the 1970s level. In truth the temperature rose only 0.6°C.

It is clearly visible that the temperature forecast modelled by the Hansen Group is off by about 150%. It is truly regrettable that precisely this modelling is still being viewed as a reliable forecast by our politicians.