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Hansen’s Lousy Accuracy

August 29, 2012

NASA “scientist” Jim Hansen likes to brag that his 1988 prediction of recent climate was accurate. John Christy, PhD describes this episode below. But first note that Hansen predicted temperature for three different situations:

1) modest increase in CO2 emissions

2) CO2 emissions fixed at 1988 levels.

3) Drastic reduction in CO2 emissions.

All three of these are labeled on Hansen’s graph that Christy reproduced below. The lowest line is what actually happened – the temperature rise was much less than predicted with CO2 emissions higher than Hansen’s highest emission line. In other words Hansen’s prediction was a total failure, not the spectacular success he claims. Sadly, most of the press just parrots Hansen’s false claim.


from John Christy, UAHuntsville, Alabama State Climatologist :

In press reports for this paper (e.g., here), Hansen indicated that “he had underestimated how bad things could get” regarding his 1988 predictions of future climate. According to the global temperature chart below (Fig. 2.2), one could make the case that his comment apparently means he hadn’t anticipated how bad his 1988 predictions would be when compared with satellite observations from UAH and RSS:

By the way, a climate model simulation is a hypothesis and Fig. 2.2 is called ”testing a hypothesis.” The simulations fail the test. (Note that though allowing for growing emissions in scenario A, the real world emitted even more greenhouse gases, so the results here are an underestimate of the actual model errors.)

The bottom line of this little exercise is that I believe the analysis of Hansen et al. is based on assumptions designed to confirm a specific bias about climate change and then, like a legal brief, advocates for public acceptance of that bias to motivate the adoption of certain policies (see Hansen’s Washington Post Op-Ed 3 Aug 2012).

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