But this time, they got caught … and not just by me.
The forecast about global warming from James Hansen thirty years so starkly demonstrates that he’s been right all along about the effect of greenhouse gases on our climate, that there’s yet another attempt to make it look bad. The authors, Ross McKitrick and John Christy (“MC”), are so desperate that they resort to making a persuasive argument the only way possible: with bullshit. Shameless bullshit.
Observed temperature since the 1980s has landed between Hansen’s “Scenario B” (what was considered a middle-of-the-road greenhouse-gas future) and “Scenario C” (far less greenhouse gas emissions), but MC (McKitrick & Christy) try to make out that it should have been between “Scenario A” (rapid increase of greenhouse gases) and “Scenario B” because the amount of CO2 in the atmosphere turned out to be between those two scenarios. So, they claim, Hansen’s forecast was way off.
The “original” post by MC (McKitrick & Christy) contained this little gem:
“The whole debate has focused on comparisons of the 1988 and 2017 endpoints. Skeptical Science waived away the differences by arguing that if one adjusts for an overestimation in the rise of greenhouse gas (GHG) forcing, Hansen’s 2017 Scenario B prediction was not far off reality.”
As was pointed out at Skeptical Science, greenhouse gases and their total impact ended up nowhere near as high as scenario “A”, and even less than scenario “B”. Result: temperature increase should (according to Hansen) have been nowhere near as high as scenario “A” and even less than scenario “B”. Just like happened.
MC countered by looking at the rise of one and only one greenhouse gas: CO2. How do they justify ignoring methane (CH4) and N2O and chloroflourocarbons when Hansen had included them in his forecasts? By the following bullshit (emphasis mine):
“Note that Scenarios A and B also represent upper and lower bounds for non-CO2 forcing as well, since Scenario A contains all trace gas effects and Scenario B contains none.”
That’s shameless bullshit.
All three of Hansen’s scenarios include “trace gas effects” from multiple trace gases, not just CO2. Scenario “A” had them rising rapidly, scenario “B” had them rising more moderately, scenario “C” rising less rapidly still (in fact, after the year 2000 not rising at all). And scenario “A” includes even more trace gas effects than “B” and “C” — but the claim that scenario “B” (and “C”) contains none is bullshit.
Here’s what Hansen and his colleagues said in their published research at the time:
“… Scenario A assumes that growth rates of trace gas emissions typical of the 1970s and 1980s will continue indefinitely; the assumed annual growth averages about 1.5% of current emissions, so the net greenhouse forcing increases exponentially. Scenario B has decreasing trace gas growth rates, such the that annual increase of the greenhouse climate forcing remains approximately constant at the present level. Scenario C drastically reduces trace gas growth between 1990 and 2000 such that the greenhouse climate forcing ceases to increase after 2000. The range of climate forcings covered by the three scenarios is further increased by the fact that scenario A includes the effect of several hypothetical or crudely estimated trace gas trends (ozone, stratospheric water vapor, and minor chlorine and flourine compounds) which are not included in scenarios B and C.”
That’s clear. Scenarios “B” and “C” omit “several hypothetical or crudely estimated trace gas trends,” but don’t omit all non-CO2 trace gases. Claiming they do is bullshit.
It was up to Nick Stokes to point out how wrong they were, in a comment to the original blog post, that
If I understand that correctly, it is just wrong. Completely. Scenario B contained lots of trace gas effects, as did C. And the conclusion is completely wrong.
“I have written a detailed analysis of the scenarios here, …”
He even included a graph of how greenhouse gases progressed under the various scenarios, compared to what actually happened:
The upshot is that the total effect of greenhouse gases has fallen between scenarios “B” and “C”, so we would expect temperature change to be between scenarios “B” and “C”. Which is what happened.
The blowback forced MC to revise their original post, the new version starting with
Note: this is a revised version to correct the statement about CFCs and methane in Scenario B.
They then got around the correct appraisal from Skeptical Science by avoiding it, eliminating any mention (and link), instead making the ridiculous claim that
“… Second, applying a post-hoc bias correction to the forcing ignores the fact that converting GHG increases into forcing is an essential part of the modeling. If a correction were needed for the CO2 concentration forecast that would be fair, but this aspect of the forecast turned out to be quite close to observations.”
This isn’t reason, it’s just post-hoc rationalization, and rather desperate rationalization at that. It’s not a “post-hoc bias correction to the forcing” that was needed. It was a correction to how much greenhouse gases were in the atmosphere in the different scenarios. More GHG means more warming, less GHG means less warming. Since actual GHG concentrations for everything except CO2 were less than Hansen’s scenario “B” (and in some cases even less than scenario “C”), it’s no surprise that actual temperature came in between “B” and “C”.
MC seem to have tried to suggest that the greenhouse gases they tried to “wish away” don’t really matter — that it’s only CO2 that’s important. That’s just more bullshit. As Eli Rabett points out:
“Allow Eli to post this again and encourage others to go read the long discussion of trace gas contributions in Appendix B of Hansen, Fung, Lacis, Rind, Lebedeff, Ruedy and Russell
The contributions of the trace gases after 1988 are substantial and shocking, by contrast CO2 is rather boring. Clearly if your point is to evaluate the model, you would run it again using observed forcings. If your point is to evaluate the scenario you would compare the assumed forcings in the paper to the observed ones to date as in the figure from Real Climate seen above. If your mission were to spit on Hansen you would mix and match as needed.”
And, once again Nick Stokes has to correct further misinformation from Ross McKitrick (the “M” of “MC”):
B and C also have N2O. The point is that it is these gases that make the difference. CO2 was scarcely different in forecast in A and B, and the reality followed. What brought the forcing down was the unexpected pause in methane, and the reduction in CFCs that followed Montreal, which A and B were sceptical about (Montreal was 1989) but C allowed for.
There are other aspects of both the original post from MC and its revision which are bullshit. But in my opinion, refuting all the details of their mendacity is less important than shaming them for their shamelessness.
Most important is to note that this, the latest in a series of attempts to discredit Hansen’s work from a host of climate deniers, all use the same strategy: bullshit.
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