Steven Koonin's Misuse of the Berner 2001 Geocarb III Model

Figure 3.3 from Steven Koonin, Unsettled

A recent book by Steven Koonin called Unsettled: What Climate Science Tells Us, What It Doesn't, and Why It Matters attempts to show us that much of climate science isn't really settled at all, despite political claims to the contrary. On of the chief targets of his criticism is the use of models in climate science, and he argues that the predictions of these models are not being seen in empirical data, so we should not put much stock in what they say.

Now before I continue, I want to acknowledge a couple things. First, the introductory chapters on how climate change happens as a result of changing greenhouse gas concentrations is quite good. I was actually particularly impressed with it, not just because it's accurate but because he offers some very helpful illustrations of how the science works that can be helpful for those just learning the science. Second, Koonin acknowledges that his evaluation of climate science is a bit one-sided. He's not as interested in evaluating all of the areas where climate science is properly "settled," but pointing to areas where he believes it isn't settled but we're being led to believe that it is. So for instance, he was critical of model calculations of equilibrium climate sensitivity (ECS), but he's also acknowledged that other research not using models have arrived at values near 3 C, and he offers no apologetic against this. My evaluation of Koonin's book will take a similar approach. That is, I want to point out areas where Koonin's book gets the science wrong, but I also want to acknowledge at the outset that there are some parts of this book that I consider quite good.

There's a portion of his book where Koonin attempts to put current CO2 levels into geologic perspective using Berner 2001. His explanation of the paper and its relevance is completely wrong and demonstrates that he hasn't read the paper (his citation is to the abstract not the full paper). The graph he's trying to explain is Figure 3.3, which looks to be on p. 67 on my kindle version of the book. He wrongly describes the values in this graph as "determined from the isotopic ratio in carbonate sediments and fossilized soils." But as the title of the paper he cited clearly says, it's a model. Berner used a GCM model to reproduce rCO2 for the Phanerozoic. There were several lines of evidence that were used for the GCM model. He summarized them in the abstract:[1]

"(1) new GCM (general circulation model) results for the dependence of global mean surface temperature and runoff on CO2, for both glaciated and non-glaciated periods, coupled with new results for the temperature response to changes in solar radiation;

(2) demonstration that values for the weathering-uplift factor fR(t) based on Sr isotopes as was done in GEOCARB II are in general agreement with independent values calculated from the abundance of terrigenous sediments as a measure of global physical erosion rate over Phanerozoic time;

(3) more accurate estimates of the timing and the quantitative effects on Ca-Mg silicate weathering of the rise of large vascular plants on the continents during the Devonian;

(4) inclusion of the effects of changes in paleogeography alone (constant CO2 and solar radiation) on global mean land surface temperature as it affects the rate of weathering;

(5) consideration of the effects of volcanic weathering, both in subduction zones and on the seafloor;

(6) use of new data on the d13C values for Phanerozoic limestones and organic matter;

(7) consideration of the relative weathering enhancement by gymnosperms versus angiosperms;

(8 ) revision of paleo land area based on more recent data and use of this data, along with GCM-based paleo-runoff results, to calculate global water discharge from the continents over time."

The problems with this are four-fold. First, it's proof that he didn't do his homework on paleoclimate. This paper is available and easily accessible online. It's quite possible he had somebody working for him that produced this research for him, but it's his name on the book. It's up to him to make sure that what ends up there is correct.

Berner 2001 showing the uncertainty for GEOCARB III

Second, Koonin makes a big deal about the need to show both estimates and the uncertainty. The uncertainty in Berner's model are clearly identified in Berner's paper, but Koonin did not bother to include it in his book, showing he's not terribly consistent with the values he's trying to advocate.  Third, Koonin spends a good deal of time claiming that GCMs are completely unreliable in reproducing the last 100 years and predicting the next 80, yet he here he uncritically accepts a GCM that attempted to reproduce CO2 levels over the last 550 million years.

Proxy Evidence for CO2 Concentrations over the last 420 Million Years[2]

Fourth, this paper is 20 years old, and there are several studies that build on this one, as well as many that deal explicitly with proxy data,[2] that he could have used. They would have been more appropriate, given his doubts about GCMs, but he didn't use them, probably because he doesn't know anything about them.

This last point is symptomatic of a larger concern I have with a great deal of contrarian literature (whether books, papers, blogposts, or videos). There seems to be a strong tendency to reuse the talking points of others. Somebody used Berner's GEOCARB III model to criticize climate science, and this particular model now shows up in almost all contrarian treatments of climate change when dealing with paleoclimate. In another post I've summarized a great deal of the paleoclimate literature evaluating the relationship between CO2 and global temperatures. There are obviously newer and better sources to choose from. But it seems once a talking point gets solidified, it rarely changes or gets updated to reflect newer research. 

One of the chief components of skepticism is to check up on the stuff we say before we say it. We shouldn't just rely on what others have said in the past. We should verify that it is in fact correct, and we should also consider that maybe newer research can provide further insights into an issue. Without this essential component of skepticism, false claims can perpetuate forever. It's sad to see that Koonin is continuing the contrarian tradition of misrepresenting studies he likely has never read.

References

[1] Robert A. Berner, “Geocarb III: A Revised Model of Atmospheric CO2 Over Phanerozoic Time,” American Journal of Science 300 (2001):182-204.
http://earth.geology.yale.edu/~ajs/2001/Feb/qn020100182.pdf

[2] Gavin L. Foster, Dana L. Royer & Daniel J. Lunt, “Future climate forcing potentially without precedent in the last 420 million years,” Nature Communications 8.14845 (2017).
https://www.nature.com/articles/ncomms14845