Doing it Ourselves
Posted by Jeff Id on December 1, 2010
After ten months of reviews and rewrites we have successfully published an improved version of Steig et al. 2009. While we cannot publish the paper here, we can discuss the detail. Personally I’ve never seen so much work put into a single paper as Ryan did and it’s wonderful to see it come to a successful conclusion. This is the initial post on the subject, in the coming weeks there will be more to follow.
Guest post by lead author Ryan O’Donnel.
DOING IT OURSELVES. . . a tongue-in-cheek reference to the RC post here:
Improved methods for PCA-based reconstructions: case study using the Steig et al. (2009) Antarctic temperature reconstruction
(Accepted 11/30/10, Journal of Climate)
A detailed analysis is presented of a recently published Antarctic temperature reconstruction that combines satellite and ground information using a regularized expectation-maximization algorithm. Though the general reconstruction concept has merit, it is susceptible to spurious results for both temperature trends and patterns. The deficiencies include: (a) improper calibration of satellite data; (b) improper determination of spatial structure during infilling; and (c) suboptimal determination of regularization parameters, particularly with respect to satellite principal component retention. We propose two methods to resolve these issues. One utilizes temporal relationships between the satellite and ground data; the other combines ground data with only the spatial component of the satellite data. Both improved methods yield similar results that disagree with the previous method in several aspects. Rather than finding warming concentrated in West Antarctica, we find warming over the period of 1957-2006 to be concentrated in the Peninsula (≈0.35oC decade-1). We also show average trends for the continent, East Antarctica, and West Antarctica that are half or less than that found using the unimproved method. Notably, though we find warming in West Antarctica to be smaller in magnitude, we find that statistically significant warming extends at least as far as Marie Byrd Land. We also find differences in the seasonal patterns of temperature change, with winter and fall showing the largest differences and spring and summer showing negligible differences outside of the Peninsula.
Copyright © 2010 American Meteorological Association
(early online release to be available on or around Dec. 7th)
Some of you remember that we intended to submit the analysis of the Steig Antarctic reconstruction for publication. That was quite some time ago . . . and then you heard nothing. We did, indeed, submit a paper to Journal of Climate in February. The review process unfortunately took longer than expected, primarily due to one reviewer in particular. The total number of pages dedicated by just that reviewer alone and our subsequent responses – was 88 single-spaced pages, or more than 10 times the length of the paper. Another contributor to the length of time from submission to acceptance was a hardware upgrade to the AMS servers that went horribly wrong, heaping a load of extra work on the Journal of Climate editorial staff.
With that being said, I am quite satisfied that the review process was fair and equitable, although I do believe excessive deference was paid to this one particular reviewer at the beginning of the process. While the other two reviews were positive (and contained many good suggestions for improvement of the manuscript), the other review was quite negative. As the situation progressed, however, the editor at Journal of Climate – Dr. Anthony Broccoli – added a fourth reviewer to obtain another opinion, which was also positive. My feeling is that Dr. Broccoli did a commendable job of sorting through a series of lengthy reviews and replies in order to ensure that the decision made was the correct one.
The results in the paper are generally similar to the in-process analysis that was posted at CA and here prior to the submission. Overall, we find that the Steig reconstruction overestimated the continental trends and underestimated the Peninsula – though our analysis found that the trend in West Antarctica was, indeed, statistically significant. I would hope that our paper is not seen as a repudiation of Steig’s results, but rather as an improvement.
In my opinion, the Steig reconstruction was quite clever, and the general concept was sound. A few of the choices made during implementation were incorrect; a few were suboptimal. Importantly, if those are corrected, some of the results change. Also importantly, some do not. Hopefully some of the cautions outlined in our paper are incorporated into other, future work. Time will tell!
Lastly, I’ll give a shout out to other folks whose comments helped shape the paper by their comments and analysis. In particular, Roman, Hu, and Carrick . . . thanks!