2016 Global Temperature Update to Hansen’s 1981 Projection

It is always useful to check past predictions against eventual observations. Below is the NASA GISTEMP observed global temperature (updated through 2016) overlain on top of various projections of CO2-induced warming from calculations published in 1981 (Hansen et al. 1981). 2015 and 2016 are literally off of the chart. This does not imply higher equilibrium climate sensitivity than that represented by the dashed line (5.6C) because these calculations did not include the effects of anthropogenic increases in non-CO2 greenhouse gasses. There are a number of other important caveats to this juxtaposition like Hansen’s model not allowing for unforced/internal variability as well as differences between the assumed and actual growth rate of atmospheric CO2 ect. Nevertheless, it is an interesting comparison.


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2 Responses to 2016 Global Temperature Update to Hansen’s 1981 Projection

  1. For reference, the full paper of Hansen et al 1981 can be found here: http://www.atmos.washington.edu/~davidc/ATMS211/articles_optional/Hansen81_CO2_Impact.pdf
    (The background image showing the prediction is figure 7.)

  2. By the way, you attribute the fact that the measured warming is higher than the prediction to the fact that Hansen et al didn’t include gasses other than CO2. But the mismatch isn’t in the slope, it’s primarily an offset. There’s actually a simple explanation: Hansen et al’s predictions seem to be baselined to 1976 (presumably the last year for which they had data when they wrote the paper), and 1976 happened to be a cooler than average year, so the Hansen predictions started low by exactly that much. Draw a smooth curve through the measured temperatures, and start the Hansen et al prediction in 1976 on that curve, and the match is remarkably good.

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