December 5, 2011

Huh? A Reply to Nathan Urban

Filed under: Climate Forcings

A few weeks ago, we ran a story about a paper which was (then) soon to be published in Science magazine which generally concluded that the earth’s climate sensitivity (how much the earth’s average temperature will rise from a doubling of the atmospheric carbon dioxide concentration) was likely lower than the IPCC’s best guess (which is 3°C) and known with far less uncertainty—especially at the high end. While the IPCC’s vision of the uncertainty as to the true value of the climate sensitivity included a “fat tail” at the high end (that is, a non-negligible possibility that the true climate sensitivity was greater than 6°C), the new Science paper put the kibosh on that notion, concluding “In summary, using a spatially extensive network of paleoclimate observations in combination with a climate model we find that climate sensitivities larger than 6 K are implausible.” And adding “Assuming paleoclimatic constraints apply to the future as predicted by our model, these results imply lower probability of imminent extreme climatic change than previously thought.”

A pretty provocative finding to say the least!

In our article, “A new, lower estimate of climate sensitivity,” we described the paper—by a team led by Andreas Schmittner—in a positive light, presented and commented on the paper’s main findings and conclusions, reprinted the abstract in its entirety, and included a link to where (a free version) of the paper was available at the personal website of one of the paper’s co-authors (Nathan Urban). We also included a link to another place on the web where the paper was being discussed (in a slightly more critical manner).

Shortly after our WCR post went live, it was picked up by Watt’s Up With That?, and shortly after that, the link to the paper on Nathan Urban’s site was taken down.

About a week and a half later, the paper was announced by Science magazine and was made available (behind a pay wall) in Science ExpressScience magazine’s early on-line release of papers that will eventually appear in the paper version of the magazine. The Science Express publication was accompanied by a press release from the Oregon State University (Schmittner’s institution) and a lot of coverage both in the traditional press as well as at virtually every climate-related website (from both sides of the aisle).

At about the same time, a lengthy and quite informative interview with Nathan Urban was posted at the website Planet 3.0. In the informal Q&A format Urban candidly went into more detail about the strengths and weaknesses of their research findings as well as gave some insight as to why they did things the way that they did. While Urban went into a lengthy description of the paper’s caveats, he answered the question “What did you find, and what is the significance of your findings?” with the following:

The scientific community generally believes that the climate sensitivity is likely to lie between 2 and 4.5 degrees Celsius per doubling of atmospheric CO2, with a best estimate of 3°C. I will call this the “IPCC” or “consensus” estimate, since it is based on a review of the scientific literature found in the latest report of the Intergovernmental Panel on Climate Change (IPCC).

In our LGM [Last Glacial Maximum] study we find that ECS [Equilibrium Climate Sensitivity] is “likely” (66% probability) to lie between 1.7 and 2.6 degrees, and “very likely” (90% probability) to lie between 1.4 and 2.8 degrees, with a best estimate of around 2.2 or 2.3 °C. Our estimate of the warming effect of CO2 is therefore on the low end of, and less uncertain than, the currently accepted IPCC range.

Our low sensitivity is interesting, but within the range of previous studies. What is probably more significant is the fact that our analysis seemingly rules out the higher sensitivities (above the IPCC “best” estimate of 3°C) which other studies have been unable to exclude. (Note the word “seemingly”: more on that later.)”
[final parenthetical in original –eds]

This answer pretty much is a perfect summary of our WCR coverage of the paper—with the exception that in our article summarizing the paper and its larger implications, we didn’t delve into why the results only “seemingly” indicated a lower sensitivity. After all, “seemingly” applies to virtually all scientific research results (so it effectively goes without mention), and if the reasons why their results shouldn’t show the results that they did were greater than the reasons why they did show the results that they did, the paper would have been considered only highly speculative, and neither the authors, nor the reviewers, nor the editors would have thought it Science-worthy.

So, we spotlighted the main findings—as summed up by the authors in their abstract—and provided ample places to go to find more details about the work.

However, Nathan Urban didn’t take very kindly to our coverage, which he made clear in this exchange on Planet 3.0:

Q: Any other thoughts on the skeptics’ reception of your paper?

[Urban]: One blog did surprise me. World Climate Report doctored our paper’s main figure when reporting on our study. This manipulated version of our figure was copied widely on other blogs. They deleted the data and legends for the land and ocean estimates of climate sensitivity, and presented only our combined land+ocean curve:

Upper: World Climate Report’s manipulated image removing the Land and Ocean data.

Lower: The actual figure as it appears in Science, with the Land and Ocean curves included.

They did note that their figure was “adapted from” ours, and linked to our paper containing the real figure. On the other hand, Pat Michaels duplicated this doctored version of our figure again in an article at Forbes, and didn’t mention at all that it had been altered. (A side note with respect to the Forbes article: Science didn’t “throw a tantrum” about posting our manuscript on the web. They never contacted us about that. I took it down myself as a precaution, due to the journal’s embargo policy.)

I find this data manipulation problematic. When I created the real version of that figure, it occurred to me that it would be reproduced in articles, presentations, or blog posts. Because I find the difference between our land and ocean estimates to be such an important caveat to our work, I made sure to include all three curves in the figure, so that anyone reproducing it would have to acknowledge these caveats. I didn’t anticipate that anyone would simple edit the figure to remove our caveats. I can’t say why they deleted those curves. If you were to ask them, I’d guess they’d say it was to “clarify” the figure by focusing attention on the main result we reported.

Regardless of their intent, I find the result of their figure manipulation to be very misleading, especially since their blog post strongly implies that our study eliminates the “fat right tail” of the climate sensitivity distribution, and has proven the IPCC’s climate sensitivity range to be incorrect. Our land temperature curve, which they deleted, undermines their implication. They intentionally took our figure out of the context in which it was originally presented, a form of “selective quotation” which hides data that does not support their interpretation.

In summary, I find World Climate Report’s behavior very disappointing and hardly compatible with true skeptical inquiry. I can only imagine how they would respond if they found a climate scientist intentionally deleting data from a figure, especially if they deleted data that undermined the point of view they were presenting.

First off, we are happy to hear that Science didn’t disallow the paper after Urban posted it on his site. Speculation in the Forbes piece that Urban took down his link “probably because Science threw a tantrum about leaking something before they published it” stems from unfortunate incident about a dozen years or so ago when a Technical Comment that we had submitted to Science was (briefly) posted to the web and when Science found out, they disqualified us on this technicality, despite our submission still being reviewed for scientific merit (our paper was eventually published in Geophysical Research Letters and spurred a fair number of subsequent papers using similar techniques and line of investigation).

And as to Urban’s contention that our decision to simplify his graphic for our audience was being “misleading.” We can only reply, “Huh?”

The result that we showed was the foundation for the main conclusions of the paper as reflected in the paper’s abstract (which we reproduced in its entirety in our original post); as reflected in the paper’s concluding paragraph

In summary, using a spatially extensive network of paleoclimate observations in combination with a climate model we find that climate sensitivities larger than 6 K are implausible, and that both the most likely value and the uncertainty range are smaller than previously thought. This demonstrates that paleoclimate data provide efficient constraints to reduce the uncertainty of future climate projections.

and as reflected in Urban’s own answer to the question “What did you find, and what is the significance of your findings?” that we posted above. Not to mention the previously mentioned press release from Schmnitter.

So of course our “blog post strongly implies that our study eliminates the ‘fat right tail’ of the climate sensitivity distribution, and has proven the IPCC’s climate sensitivity range to be incorrect”—that’s precisely what the paper contends! How else do you interpret (from the paper) “we find that climate sensitivities larger than 6 K are implausible” and (from the press release) “[a] new study suggests that the rate of global warming from doubling of atmospheric carbon dioxide may be less than the most dire estimates of some previous studies – and, in fact, may be less severe than projected by the Intergovernmental Panel on Climate Change report in 2007.”

And as to why we didn’t show the results from Schmittner et al.’s “land” only analysis and “ocean” only analysis, is that those results were not the ones being advertised. In fact, one of the main advances of the Schmitter et al. work was combining the land and ocean paleoclimate data from the Last Glacial Maximum to make a better determination of the climate sensitivity—a point stressed both in the paper’s abstract

“Here, combining extensive sea and land surface temperature reconstructions from the Last Glacial Maximum with climate model simulations we estimate a lower median (2.3 K) and reduced uncertainty (1.7–2.6 K 66% probability)”

and again in the methods

“We combine recent syntheses of global sea surface temperatures (SSTs) from the Multiproxy Approach for the Reconstruction of the Glacial Ocean (MARGO) project (12) and surface air temperatures over land based on pollen evidence (13), with additional data from ice sheets, land and ocean temperatures.”

So, it hardly seems “misleading” that we should show only the results from their combination of land and ocean data.

In fact, in the lower panel of the original Figure 3 as it appeared in their paper (we only showed data from the top panel in their original Figure 3, but Nathan Urban didn’t complain about that), the authors only show the results of a sensitivity analysis they performed using the land and ocean combination. No doubt for the same reasons that we only showed their results from the land and ocean combination—that is, it was the major emphasis of their work.

True, as Urban and others have pointed out, the somewhat inconsistency that emerges when using the land only data compared with the ocean only data to compute the climate sensitivity—a result that we elected not to delve into in our coverage of the Schmittner et al. work—point to interesting avenues of research for additional investigation. And we are sure that future research will be aimed toward understanding and resolving those differences. But, by and large, this issue and other caveats in the paper are secondary to the major results—the results by which the paper was accepted and published by Science magazine in the first place. And the results highlighted in the press release put out by Andreas Schmittner the paper’s lead author.

It would seem to us that Nathan Urban’s swipe at us was just done in an attempt to keep in good standing with the RealClimate-type climate scientists after co-authoring a paper that quickly caught their negative attention—although perhaps it wasn’t enough to deflect all scorn.

Can’t say we blame him all that much, after all, as a postdoc in Michael Oppenheimer’s research group at Princeton, presumably with an interest in pursing a future in climate science, the emails contained in the Climategate 1 and 2 made it pretty clear who is pulling all the strings. Crossing such folks is not good for your career. Anyone who does not believe this merely needs to open this link.


Schmittner, A., et al., 2011. Climate sensitivity estimated from temperature reconstructions of the Last Glacial Maximum, Science Express, November 24,2011, DOI: 10.1126/science.1203513.

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