2. New Analysis of Global Temperature Claims Human Fingerprint
Ref: T.M.L. Wigley, R.L. Smith, B.D. Santer. "Anthropogenic Influence on the Autocorrelation Structure of Hemispheric-Mean Temperatures" Science 282, 1676-1679 (Nov. 27, 1998)
Yet another attempt to demonstrate a "discernible human influence" by massaging the same old tired data set. This time round, Wigley et al (two of them lead authors of IPCC Chapter 8 that provided meager and disputed evidence for such an "influence") have tried lagged auto-correlations (and cross-correlations between hemispheres) of the temperature data from 1880 to 1995. These correlations are shown to differ from control-runs of two coupled ocean/atmosphere general circultaion models (GCMs) that are run "unforced" (i.e. with no increase in greenhouse gas forcing) and that are thought to encompass all of the natural variations of climate.
This difference between observed and modeled correlations is supposed to be a "fingerprint" of human influence. That's about it.
The problems with this labored approach (trying to prove a preconceived hypothesis) are manifold. Ignore for a moment the poor quality of the data before 1945, esp. in the Southern Hemisphere, and the idea that existing GCMs can simulate all important natural climate fluctuations. The real problem is that there was an unusually large and sustained warming between 1880 and 1940, undoubtedly a natural recovery from the preceding Little Ice Age, as seen in all climate records.* This 60-year warming period is not likely to be representative of the so-called natural variations shown in the GCM runs.
Thus, the Wigley et al. conclusion may simply be an artifact of their analysis. An obvious check would be to divide the data set and analysis into two periods: 1880 - 1940, when the human contribution to atmospheric greenhouse gas level was minor; and 1940 - 1995, when most of carbon dioxide, chlorofluorocarbons, etc were released.
Perhaps the referee who reviewed the paper did make this obvious suggestion -- although the paper seems to have gone through rapidly: submitted September 16 and accepted November 2.
* There is no agreement about the post-1940 temperature data: a decided cooling between 1940 and 1975 (according to publications by Jim Hansen, Tom Karl, and others) -- while the IPCC showed little change. And finally, there is also a conflict (between 1979 and 1995) between the independent balloon data and satellite data (showing no warming) and the surface data (showing a substantial warming, likely due to contamination from urban heat island effect). But that's another story. For more information, read Hot Talk, Cold Science.
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