Timeline for Did the IPCC obfuscate the evidence in a way that obscures the discrepancy between previous climate models and recent observations?
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| Oct 27, 2013 at 17:41 | comment | added | matt_black | @gerrit Fair point: i'm reading between the lines of my own question. I thought their worst error was to change a moderate dataviz to a much worse dataviz. Mcintyre also accuses them of fiddling the numbers. I intended the question to focus on the dataviz. | |
| Oct 27, 2013 at 17:09 | comment | added | gerrit | @matt_black is Mcintyre correct to argue that the IPCC have modified their presentation of the data in a way that obscures the discrepancy: No. | |
| Oct 27, 2013 at 15:33 | comment | added | matt_black | I'm still amazed that an answer that fails to even address the key point of the question (which is about the way results were presented not whether the numbers were correct) has so many upvotes. It worries me that there is a herd mentality around climate science where anything supporting the consensus is supported regardless of its logical or scientific quality. | |
| Oct 10, 2013 at 18:37 | comment | added | user18604 | @matt_black It makes very little difference, the outliers don't actually dominate, if you look at the 95% range of the model runs (e.g. here realclimate.org/images/model122.jpg ) the observations clearly lie within the interval. I have verified the RealClimate diagram for myself by downloading the data from climateExplorer, and baselining them properly, and I can confirm that it accurately represents what the models say. Note the observations came closer to leaving the interval in 1998, so why didn't anyone make a fuss about it then? | |
| Oct 10, 2013 at 18:11 | comment | added | matt_black | @DikranMarsupial Showing all the runs in monte-carlo models or other models with statistical uncertainty always exaggerates the true range of variation. This happens because visually the rare extreme outliers dominate the actual statistical bounds (eg the 95%ile of all runs). This visual switch in the IPCC figures almost completely obscures the more reliable statistical bounds of the model projections. | |
| Oct 10, 2013 at 11:29 | comment | added | user18604 | Re: Figure10-26 is a bit too small to really see exactly what is plotted, the uncertainty interval looks a little narrow to me around 2000, but it could well be baselined to a 20 year period as the axis label implies. I'd have to try plotting it myself to be sure though. Incidentally, the observations were about as far above the ensemble mean in 1998 than they are below it now. It is worth noting that nobody was using that fact to imply that the models were wrong back then! ;o) realclimate.org/images/model122.jpg | |
| Oct 10, 2013 at 11:22 | comment | added | user18604 | It is worth noting that the purpose of the IPCC report is to give an objective statement of the mainstream scientific position on climate change. Sadly in the public debate, if some piece of information can be misinterpreted, you can almost guarantee it will be. The IPCC cannot be expected to write a document that cannot possibly be misinterpreted in such an environment. If the IPCC were trying to obfuscate the model-observation difference in 2011/2 you have to ask why they made no attempt to hide the bigger (and equally spurious) disparity in the early 90s. | |
| Oct 10, 2013 at 11:19 | comment | added | gerrit | @DikranMarsupial Figure 10-26 y-axis reads "°C above 1980-2000". Doesn't that mean they're baselining to a 20 or 12-year period? I'm probably misunderstanding still myself. | |
| Oct 10, 2013 at 11:13 | comment | added | user18604 | @Henry no the IPCC's diagram is (I suspect) intended to allow easy visual comparison of modelled and observed rates of warming. But in order to make the rate of warming more clear, they baselined to a single year, which hides uncertainty in the predictions due to offsets between model runs. The diagram was fine for the purpose the IPCC had in mind, it is just that it has been frequently misinterpreted (as McIntyre appears to have done). In my opinion, this misinterpretation completely justifies changing the way the projections are presented to show the full uncertainty. | |
| Oct 10, 2013 at 11:08 | comment | added | Henry | @Dikran: Are you saying that the IPCC did not know how to present its scenario projections in 2007? How much else of what the IPCC published was wrong? | |
| Oct 10, 2013 at 10:46 | comment | added | user18604 | @Henry, the second figure again suffers the problem of baselining to a single year. It makes the trends easier to compare visually, but it doesn't give a fair representation of the true uncertainty, which exagerates the difference between models and observations. In that diagram the observations start out outside the model projections, which suggest that this particular form of diagram can easily be misunderstood (as in the original question here). If there was a huge model-data disparity in the 90's the IPCC report would have mentioned it after the figure! | |
| Oct 10, 2013 at 10:24 | comment | added | Henry | In 2007 in its fourth assessment report the IPCC looked back at previous projections and compared them with observations in Figure 1-1 and a scale running from 1990 to 2007. I am not clear why it would have been confusing to do that again with a scale from 1990 to 2015. They produced new scenario projections in 2007 with ranges which were not individual computer runs in Figure 10-26; again I am unclear why it would have been confusing to show these. | |
| Oct 10, 2013 at 6:50 | comment | added | user18604 | @matt_black, what makes you think that plotting the model runs exaggerates the statistical range, rather than representing it more accurately? Even if the models were perfect in every way, there would be no reason to expect the observations to lie any closer to the ensemble mean than within the spread of the individual model runs. Your problem is with the baselining as that is the fundamental difference between the diagrams. | |
| Oct 9, 2013 at 21:39 | comment | added | matt_black | @DikranMarsupial My key problem with the second IPCC figure is not with the baseline (or not yet, I don't pretend to fully understand that issue) but with the visualization. Instead of plotting the model prediction range (as the FT and their own first attempt did) they plot a bunch of specific model runs. That exaggerates the statistical range and hides the statistical bounds which were previously clear. | |
| Oct 9, 2013 at 19:15 | comment | added | user18604 | @matt_black If you want to show model predictions vs outcomes, then the obvious way to do so is to plot the model predictions directly (rather than forcing them to agree with the observations in an arbitrary year) and the observations on one diagram. That is just what the second version of the IPCC diagram does. The first version is (I suspect) intended for visualisation of the trends, not visualisation of the difference between the models and the observations. See my answer for details. | |
| Oct 9, 2013 at 18:50 | comment | added | matt_black | @gerrit Two issues: I still don't understand the explanation and am looking for a clearly argued way to show model predictions vs outcomes; second, the choice of how do display data is far more confusing on the later IPCC chart (aside from any changes to the data) and that was my question's focus. If the IPCC wanted to adjust baselines etc, the format of the early chart would still have worked (or, even better, the format of the FT version). | |
| Oct 9, 2013 at 16:19 | comment | added | user18604 | @matt_black, but the way, I occasionally contribute to skepticalscience.com, if you think a post there is unclear, then please do go over there and post a comment explaining the problem; I'm sure there would be several regular posters there that would be happy to engage in a scientific discussion on this topic. | |
| Oct 9, 2013 at 15:14 | comment | added | user18604 | Essentially the only thing that the new diagram hides is the error in the version found in the draft report. That is the very purpose of having a draft report, which is that it gives an opportunity to fix any errors before the document is made public (unless of course some unscrupulous person leaks the draft so they could get their knickers in a twist about any changes they find in the final version). | |
| Oct 9, 2013 at 15:11 | comment | added | user18604 | @matt_black GCMs are able to reproduce change in temperature in response to changes in forcings better than they are able to reproduce well calibrated absolute temperatures. Thus you need to baseline them before performing comparisons to eliminate the meaningless variation in absolute temperature between model runs. This is well known (except perhaps to McIntyre) and entirely uncontroversial. The original IPCC used a single year baseline, which is sensitive to the internal variability in the model runs. The new version uses a longer period, and is more in keeping with best practice. | |
| Oct 9, 2013 at 14:06 | comment | added | gerrit | @matt_black I don't know if skepticalscience.com and Grant Foster are biased. I couldn't find a discussion on these graphs in the peer-reviewed literature. The explanation makes perfect sense and explains that the way results were represented in the draft were wrong, thus answering the question by that there is no obfuscating going on. If you already state that something has clearly obfuscated the key messages, you seem to already have an answer? Then why do you ask? Or are you going to answer your own question? | |
| Oct 9, 2013 at 12:22 | comment | added | matt_black | skepticalscience.com is no more unbiased in this discussion than climateaudit.org. Moreover the quoted explanation about the charts makes no sense and even if it did it would be irrelevant to the key question which is about the way the results are presented, which has clearly obfuscated the key messages. | |
| Oct 9, 2013 at 12:05 | comment | added | gerrit | @jwenting There are plenty of questions on this site addressing claims made by those "dozens of people", and all are refuted. Indeed, on this site we consider sources on their scientific value, rather than on political agreement. People are free to believe what they want in face of scientific evidence, whether it is about climate change, tobacco, vaccines, GMO, or other aspects where science and politics get muddled. On Skeptics, we address the science. When this conflicts with your views, perhaps you need to reconsider your views. I've been doing that with GMO, perhaps you should for AGW | |
| Oct 9, 2013 at 0:16 | history | edited | gerrit | CC BY-SA 3.0 |
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| Oct 9, 2013 at 0:04 | history | edited | gerrit | CC BY-SA 3.0 |
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| Oct 8, 2013 at 23:58 | history | answered | gerrit | CC BY-SA 3.0 |
