Watts Up With That?

Smearing around data or paint - the results are similar

Jeff Id of The Air Vent emailed me today inviting me to repost Ryan O’s latest work on statistical evaluation of the Steig et al “Antarctica is warming” paper ( Nature, Jan 22, 2009) I thought long and hard about the title, especially after reviewing the previous work from Ryan O we posted on WUWT where the paper was dealt a serious blow to “robustness”. After reading this latest statistical analysis, I think it is fair to conclude that the paper’s premise has been falsified.

Ryan O, in his conclusion, is a bit more gracious:

I am perfectly comfortable saying that Steig’s reconstruction is not a faithful representation of Antarctic temperatures over the past 50 years and that ours is closer to the mark.

Not only that, Ryan O did a more complete job of the reconstruction than Steig et al did, he mentions this in comments at The Air Vent:

Steig only used 42 stations to perform his reconstruction. I used 98, since I included AWS stations.

The AWS stations have their problems, such as periods of warmer temperatures due to being buried in snow, but even when using this data, Ryan O’s analysis still comes out with less warming than the original Steig et al paper

Antarctica as a whole is not warming, the Antarctic peninsula is, which is signficantly removed climatically from the main continent.

Click for a larger image

It is my view that all Steig and Michael Mann have done with their application of RegEm to the station data is to smear the temperature around much like an artist would smear red and white paint on a pallete board to get a new color “pink” and then paint the entire continent with it.

It is a lot like “spin art” you see at the county fair. For example, look (at left) at the different tiles of colored temperature results for Antarctica you can get using Steig’s and Mann’s methodology. The only thing that changes are the starting parameters, the data remains the same, while the RegEm program smears it around based on those starting parameters. In the Steig et al case, PC and regpar were chosen by the authors to be a value of 3. Chosing any different numbers yields an entirely different result.

So the premise of the Steig et al paper paper boils down to an arbitrary choice of values that “looked good”.

I hope that Ryan O will write a rebuttal letter to Nature, and/or publish a paper. It is the only way the Team will back down on this. – Anthony

UPDATE: To further clarify, Ryan O writes in comments:

“Overall, Antarctica has warmed from 1957-2006. There is no debating that point. (However, other than the Peninsula, the warming is not statistically significant. )

The important difference is the location of the warming and the magnitude of the warming. Steig’s paper has the warming concentrated on the Ross Ice Shelf – which would lead you to entirely different conclusions than having a minimum on the ice shelf. As far as magnitude goes, the warming for the continent is half of what was reported by Steig (0.12 vs. 0.06 Deg C/Decade).

Additionally, Steig shows whole-continent warming from 1967-2006; this analysis shows that most of the continent has cooled from 1967-2006. Given that the 1940’s were significantly warmer in the Antarctic than 1957 (the 1957-1960 period was unusually cold in the Antarctic), focusing on 1957 can give a somewhat slanted picture of the temperature trends in the continent.”

Ryan O  adds later:  “I should have said that all reconstructions yield a positive trend, though in most cases the trend for the continent is not statistically significant.”

Posted by Jeff Id on May 28, 2009

There is always something going on around here.

Up until now all the work which has been done on the antarctic reconstruction has been done without statistical verification. We believed that they are better from correlation vs distance plots, the visual comparison to station trends and of course the better approximation of simple area weighted reconstructions using surface station data.

The authors of Steig et al. have not been queried by myself or anyone else that I’m aware of regarding the quality of the higher PC reconstructions. And the team has largely ignored what has been going on over on the Air Vent. This post however demonstrates strongly improved verification statistics which should send chills down their collective backs.

Ryan was generous in giving credit to others with his wording, he has put together this amazing piece of work himself using bits of code and knowledge gained from the numerous other posts by himself and others on the subject. He’s done a top notch job again, through a Herculean effort in code and debugging.

If you didn’t read Ryan’s other post which led to this work the link is:

Antarctic Coup de Grace

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Fig. 1: 1957-2006 trends; our reconstruction (left); Steig reconstruction (right)

HOW DO WE CHOOSE?

In order to choose which version of Antarctica is more likely to represent the real 50-year history, we need to calculate statistics with which to compare the reconstructions. For this post, we will examine r, r^2, R^2, RE, and CE for various conditions, including an analysis of the accuracy of the RegEM imputation. While Steig’s paper did provide verification statistics against the satellite data, the only verification statistics that related to ground data were provided by the restricted 15-predictor reconstruction, where the withheld ground stations were the verification target. We will perform a more comprehensive analysis of performance with respect to both RegEM and the ground data. Additionally, we will compare how our reconstruction performs against Steig’s reconstruction using the same methods used by Steig in his paper, along with a few more comprehensive tests. Read the rest of this entry »