Thursday, January 13, 2011

New Peer Reviewed Study Rebuts Steig et al Study on Antarctic

In an earlier post on The Polar Ice Caps -Part 3 I referenced a study conducted by Professor Eric Stieg and others that reportedly showed massive warming over the majority of Antarctica despite much evidence to the contrary. Needless to say it captured the media's attention and was for the most part unquestioned by them with the exception of columnists like Christopher Booker of the U.K. Telegraph.

Now it seems there is another peer reviewed study into this same area and not surprisingly when not relying on an outcome to prove a theory, it had very different results:

Entitled Improved methods for PCA-based reconstructions: case study using the Steig et al. 2009 Antarctic temperature reconstruction its abstract can be viewed here. The following is some analysis of the new paper by Climate Research News:

Remember the Steig et al 2009 Nature paper? As Steve McIntyre points out at Climate Audit: “Like so many Team efforts, it applied a little-known statistical method, the properties of which were poorly known, to supposedly derive an important empirical result. In the case of Steig et al 2009, the key empirical claim was that strong Antarctic warming was not localized to the Antarctic Peninsula (a prominent antecedent position), but was also very pronounced in West Antarctic.”

Well, there is a new paper in press in the Journal of Climate:

Improved methods for PCA-based reconstructions: case study using the Steig et al. 2009 Antarctic temperature reconstruction by Ryan O’Donnell, Nicholas Lewis, Steve McIntyre, Jeff Condon

The abstract states:

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 (≈0.35°C 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.

Another analysis was provided by Anthony Watts at Watts Up With That:


In a blow to the Real Climate “hockey team” one team member’s paper, Steig et al Nature, Jan 22, 2009 (seen above) has been shown lacking. Once appropriate statistical procedures were applied, the real data spoke clearly, and it was done in a peer reviewed paper by skeptics. Jeff Condon of the Air Vent writes via email that he and co-authors, Ryan O’Donnell, Nicholas Lewis, and Steve McIntyre have succeeded in getting a paper accepted into the prestigious Journal of Climate and asked me to re-post the notice here.

The review process was difficult, with one reviewer getting difficult on submitted comments

[and subsequent rebuttal comments from authors ] that became longer than the submitted paper, 88 pages, 10 times the length of the paper they submitted! I commend them for their patience in wading through such formidable bloviation. Anyone want to bet that reviewer was a “team” member?

As WUWT covered in the past, these authors have demonstrated clearly that the warming is mostly in the Antarctic Peninsula. Steig et al’s Mannian PCA math methods had smeared that warming over most of the entire continent, creating a false impression.

WUWT visitors may want to read this primer which explains how this happens. But most

importantly, have a look at the side by side comparison maps below. Congratulations to Jeff, Ryan, Nick, and Steve! – Anthony

Jeff writes:

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)

Ryan O’Donnell Nicholas Lewis Steve McIntyre Jeff Condon

Abstract

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.

Region

RLS C/Dec

E-W C/Dec

S09 C/Dec

Continent

0.06 ± 0.08

0.04 ± 0.06

0.12 ± 0.09

East Antarctica

0.03 ± 0.09

0.02 ± 0.07

0.10 ± 0.10

West Antarctica

0.10 ± 0.09

0.06 ± 0.07

0.20 ± 0.09

Peninsula

0.35 ± 0.11

0.32 ± 0.09

0.13 ± 0.05

Copyright © 2010 American Meteorological Association

(early online release to be available on or around Dec. 7th)

Temperature trend Deg C/Decade .

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 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!

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