Wednesday, March 24, 2010

Denial isn't just a river in Egypt, it runs deep in the icecap too

This whine is funny enough to be worth reading. It's McLean et al's attempt at a response to our Comment.

Behind all the hot air (which I'll return to) the basic scientific premise behind their reply (pdf here) is a straightforward bait-and-switch. Remember that the main bones of contention in their original paper were their claims that
"Change in SOI accounts for 72% of the variance in GTTA for the 29-year-long MSU record and 68% of the variance in GTTA for the longer 50-year RATPAC record."
(where SOI = Southern Oscillation Index: GTTA = Global Tropospheric Temperature Anomaly, and the other acronyms are the names of two data sets), and subsequently that their analysis
"shows the potential of natural forcing mechanisms to account for most of the temperature variation" [over the last 50 years].
Of course, our main complaint was that the statistics were based on differenced data, from which any long-term variability had been filtered, and thus their analysis provides no support for the latter claim. In their paper, they specifically claimed that their differencing operation was performed to remove noise:
"To remove the noise, the absolute values were replaced with derivative values based on variations. Here the derivative is the 12-month running average subtracted from the same average for data 12 months later"
which we have shown is not true - instead, it removes long-term variation including any trends.

Their reply first claims that the differencing was only used to establish the lag:
"we used derivatives only to ascertain the existence of the relatively consistent time-lag that exists between changes in the El NiƱo-Southern Oscillation (ENSO) and later changes in the global average lower tropospheric temperature anomaly (GTTA)"
But then they immediately contradict themselves and admit the obvious, that the statistics they presented were in fact based on the differenced data:
"Our comments about the change in Southern Oscillation Index (SOI) accounting for 72% of the variance in satellite (MSU) GTAA, 68% of variance in the radiosonde (RATPAC-A) GTAA and 81% of variance in the tropospheric temperature in the tropics were made in the context of the discussion of our derivatives based on differentials between 12 month averages, and we stand by them. Contrary to Fea10 claims, those figures do not refer to long-term variations but only to the derivatives that were used."
Obviously I'm pleased to see them acknowledge the obvious, that their statistics have no relevance to the analysis of any long-term trends in the data. But that leaves their original claim concerning "potential of natural forcing mechanisms to account for most of the temperature variation" to be devoid of any support whatsoever.

In summary, it seems we all agree that ENSO/SOI accounts for a lot of the short-term variability in global temperature (which has been well established for decades) and McLean et al now appear to explicitly agree that their analysis has no bearing on long-term trends. If only they'd said that at the outset then there would have been no need for all of this.

Oh, and their fluff and bluster...will have to wait for another post. I'm off to bed.


Anonymous said...

James - you optimistically state that "Obviously I'm pleased to see them acknowledge the obvious, that their statistics have no relevance to the analysis of any long-term trends in the data"

However, McLean et al. still seem to be saying "Our analysis supported earlier research that demonstrates a close link between these factors, and indicated that a large portion of the variability in global temperature is explained by ENSO variation, thus leaving little room for a substantial human influence on temperature."

So, um, they seem to be sticking (despite all contrary evidence) to their belief that their analysis leaves "little room" for anthropogenic warming...


Hank Roberts said...

Oh, you're so 20th Century! These guys have moved beyond that, they're doing Blog Science -- explicitly!

Colbert's feeble plan to make reality democratic has been left in the dust by SPPI's approach -- having the Lord Himself do peer review. They've got the only "real peer" in the Blog Science business.

Hank Roberts said...

Well, they've made sure they can't get it published by AGU now. They quote the AGU policy themselves:

"AGU does not knowingly publish reports, letters, and articles that have been previously published ...."

Hank Roberts said...

(Oh, and -- illustrating a fundamental principle of Blog Science -- they equate posting a draft on a blog with actual publication in a science journal, no difference as far as they're concerned)

William M. Connolley said...

They seem to be rather free with selective quotations from reviewers. It would be interesting to see them quote the rejections in full.

SCM said...

They claim to supply a copy of their rejected reply as an appendix to their post but I couldn't find it. I'd never heard of ICECAP before but it seems to feature all the usual suspects. It claims to be

not funded by large corporations that might benefit from the status quo but by private investors who believe in the need for free exchange of ideas...

I wonder where the cash does come from? - but websites are cheap and since I've never heard of them they can't be spending much on PR.

Dave said...


Took me a while to find it too - the pdf linked at the bottom of th page has the appendices mentioned included.

Hank Roberts said...

> icecap

Anonymous said...

... and they're still pushing their dodgy (tricky?) Figure 7 with the shifted baseline and changed dataset.

-William T

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