In Part 1 of this post, we examined Patrick Michaels' self-defense for deleting two of Hansen and colleagues' 1988 global warming projections in his 1998 testimony before Congress. As we saw, Michaels' excuse relied on a comment by Hansen that Scenario A was "business as usual." However, given that we did not follow a business-as-usual path from 1988 to 1998, and Scenario C was the most accurate representation of actual greenhouse gas (GHG) emissions, Michaels' presentation to Congress remains a distortion of Hansen's actual results.
Here in Part 2, we examine what Michaels' presentation to Congress should have looked like, had it been accurate, and what this tells us about the accuracy of Hansen's climate model and real-world climate sensitivity.
As noted in Part 1, if we're going to only show one emissions scenario, it should be the one closest to reality. In Michaels' case in his 1998 Congressional testimony, that should have been Scenario C. Currently, Scenario B is closest to the actual forcing, according to Skeie et al., but running about 16% too high (since 1988). Figure 1 reproduces Hansen's Scenario B with a 16% reduction in the warming trend, to crudely correct for the discrepancy between it and the actual radiative forcing. This might be what Michaels' graphic would look like if he were to give an accurate version of his presentation today:
Figure 1: Observed temperature change (GISTEMP, blue) and with solar, volcanic and El Niño Southern Oscillation effects removed by Foster and Rahmstorf (green) vs. Hansen Scenario B trend adjusted downward 16% to reflect the observed changes in radiative forcings since 1988, using a 1986 to 1990 baseline.
In Figure 1 we've included both GISTEMP data, and GISTEMP with solar, volcanic, and El Niño Southern Oscillation influences removed by Foster and Rahmstorf (2011). The 1988 to 2010 trends are similar, 0.20°C per decade with the natural effects, 0.18°C per decade without. Scenario B has a 0.23°C per decade trend, but when removing a simulated volcanic eruption in 1996, the trend decreases to about 0.22°C per decade.
As the figure above shows, Hansen's 1988 model overpredicted the ensuing global warming. However, it only overpredicted the warming by approximately 15 to 25%, which is a far cry from the 300% overprediction claimed by Michaels in his 1998 congressional testimony.
If we weren't true skeptics, we might stop here and simply conclude that Hansen was wrong and his model was too sensitive, as some fake skeptics have in the past. However, we know that Skeptical Science readers expect more from our site, and one major question remains unanswered.
As we saw in our previous post regarding Patrick Michaels' serial data deletions, he has a tendency to specifically delete data which would suggest that climate sensitivity is not low (and he also ignores all research which does not suggest low sensitivity). This is because Michaels' main argument against taking action to address global warming is that the climate is not very sensitive to greenhouse gas changes, and thus there is no urgency or need to reduce those emissions.
However, Hansen's results add to the long list of evidence that climate sensitivity is not low. While it's true that Hansen's 1988 model was too sensitive, this is not news. The sensitivity of his model was 4.2°C for a doubling of atmospheric CO2 (see Section 6.1 on page 4398 of his paper), which is towards the high end of the IPCC likely climate sensitivity range.
However, as noted above, Hansen's model overpredicted the ensuing global warming thus far by approximately 15 to 25%. Thus if we estimate that the sensitivity of his model was 25% too high (which is an oversimplification, but will give us a conservative estimate), this suggests the actual climate sensitivity is approximately 3.4°C for doubled CO2, which is close to the IPCC best estimate of 3°C.
Michaels made a number of major errors in response to the Skeptical Science post criticizing his repeated deletions of inconvenient data. He claimed that it was appropriate to only present Hansen's Scenario A to Congress because we had followed "business as usual" emissions, when in fact the Montreal Protocol and other major events had resulted in substantially reduced GHG emissions. Moreover, Michaels claimed that Scenario A was Hansen's model prediction, when in fact it was just one of three projections; of those three, as of 1998 Scenario C was the most representative of the actual radiative forcing, and Scenario A the least representative.
Thus Michaels grossly misled Congress by claiming that Hansen's prediction was wrong by 300%. In reality it overpredicted the subsequent global warming by closer to 20%, which also suggests that climate sensitivity is not low. Michaels' assumption that Scenario A was the appropriate comparision based on one comment Hansen had made, rather than actually examining the data to determine which scenario was most representative of actual emissions, reveals a gross lack of scientific rigor. This lack of scientific competency was particularly problematic given that the distorted results were presented to our policymakers as they attempted to decide whether to ratify the Kyoto Protocol and commit to GHG emissions reductions (which they subsequently did not). This is not the type of behavior we should expect from someone presenting himself to U.S. Congress as a climate expert.
Michaels made a number of other errors in his response post, including claiming that we at Skeptical Science "try to obliterate evidence which paints a less than alarming picture of our climate future." This is both false and classic psychological projection - in our presentations of Hansen 1988, Schmittner 2011, and Gillet 2012, we provided a thorough analysis of all aspects of each paper, without "obliterating" any evidence, contrary to Michaels, who deleted inconvenient data from each in order to present a very distorted picture of the results of each research paper, and ignored the key caveats and limitations noted by the papers' authors.
In fact, the fundamental purpose of Skeptical Science is to accurately represent what the peer-reviewed scientific literature says. Michaels began his response by stating:
"When the battle is being lost, there is a tendency to try to raise a level of distraction to shift the attention away from the desperate situation at hand."
This is a rather damning admission, since it is Michaels who tries to shift the attention from the full body of research by deleting the inconvenient data, and who has tried to shift the attention from his scientific distortions by accusing Skeptical Science of committing his own misdeeds.
Rather than wasting his efforts coming up with faulty excuses to defend his indefensible behavior and lashing out at those who have called him on it, and in the process making ever more fallacious and easily-debunked claims, Michaels should simply admit his errors and put an end to his serial deletions of inconvenient data. Until he does, websites which purport to exhibit climate skepticism but which continue to publish Michaels' serial scientific distortions greatly diminish their own credibility.
Note: This post has been used to update the Advanced rebuttal to "Hansen's 1988 prediction was wrong"
Posted by dana1981 on Wednesday, 25 January, 2012
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