Sunday, December 3, 2006

A Paucity of Evidence, pt. 2 - Let's make a quick reply to a comment on a previous post. "Anonymous" (BTW, I think I know who you are) made note of "[t]he problem of so many contrarians..." My only question for "Anonymous" is why does the word "contrarian" have the same ring in it's modern context as "heretic" must have to Copernicus? Why do Al Gore and his ilk claim papal authority over an issue that is in yet and still an open question, imposing their "morality" on a scientific hypothetical?

If you come up with a good answer for me "Anonymous," you know where to stick it! For the rest of you we'll pick up where we left off.

The divergence of simulations from observations is a metaphor for the divergence of opinion within the scientific community. These differences of opinion become apparent when one reads the many scholarly journals that deal with environmental research, with scientists rallying on both sides of the global warming issue to fire rhetorical volleys at each other. In 1998, Michael Mann, Ph.D., currently the Director of the Earth System Science Center at Penn State University, was the lead author of "Global-scale temperature patterns and climate forcing over the past six centuries" and was published in Nature, Volume 392, 23 April 1998, pp. 779-787.

Dr. Mann’s paper summarized various proxy data (such as tree ring widths and densities, coral calcification rates and ice cores) and compared that data with actual measured temperatures from 1900 onward, in order to conclude that "Northern Hemisphere mean annual temperatures for three of the last eight years are warmer than any other year since 1400 A.D." and that greenhouse gases were the dominant factor in temperature increases during the 20th Century. (When depicted graphically, these temperature changes resemble a hockey stick.) The publication of Dr. Mann’s paper, and its "hockey stick" graphic provided the foundation for much of the current thinking surrounding global warming, as evidenced by the use of the data in a 2001 report by the United Nations’ Intergovernmental Panel on Climate Change (IPCC), currently chaired by Dr. Rajendra Pachauri.

Predictably, given the healthy skepticism within the scientific community, there was a fairly immediate questioning of Dr. Mann’s research. In 2003, minerals consultant Stephen McIntyre and Ross McKitric, Associate Professor of Economics at the University of Guelph in Ontario, Canada wrote a paper entitled, "Corrections to the Mann et al. (1998) Proxy Data Base and Northern Hemisphere Average Temperature Series" that was published in Energy and Environment, Volume 14, Number 6, 1 November 2003, pp. 751- 772.

In their report, McIntyre and McKitric contend that, "the data set of proxies of past climate used in Mann … for the estimation of temperatures from 1400 to 1980 contains collation errors, unjustifiable truncation or extrapolation of source data, obsolete data, geographical location errors, incorrect calculation of principal components and other quality control defects." McIntyre and McKitric go on to say, "the particular 'hockey stick' shape derived in the proxy construction – a temperature index that decreases slightly between the early 15th century and early 20th century and then increases dramatically up to 1980 — is primarily an artifact of poor data handling, obsolete data and incorrect calculation of principal components."†

Since the publication of the McIntyre and McKitric article, there has been considerable back and forth between the supporters of Dr. Mann and those who side with Mr. McIntyre and Dr. McKitric. As reported by Antonio Regaldo in the October 26, 2005 issue of the Wall Street Journal, a study by Peter Huybers, entitled "Comment on 'Hockey sticks, principal components, and spurious significance' by S. McIntyre and R. McKitrick," published in October of 2005 in Geophysical Research Letters argued that the statistical errors were not as significant as the Canadians suggested. Dr. Huybers was quoted as saying, "The truth is somewhere in between, but closer to Dr. Mann," although he conceded that he had not met all of the objections raised by McIntyre and McKitric.

More recently, the Mann study was the subject of an independent review that was initiated by the House Energy Committee. The House Energy and Commerce Subcommittee on Oversight and Investigations commissioned an ad hoc committee of noted statisticians to investigate the Mann study from a statistical viewpoint in order to determine its soundness, and the committee’s report was published in July of 2006. In the report, authored by Dr. Edward J. Wegman, Ph.D., Dr. David Scott Rice, Ph.D., and Dr. Yasmin Said, Ph.D., the committee determined "the criticisms of [McIntyre and McKitrick] to be valid and compelling," in that the statistical techniques used in the Mann study would produce "hockey stick" shapes irrespective of whatever temperature data was used. The report also concluded that "Mann’s assessments that the decade of the 1990s was the hottest decade of the millennium and that 1998 was the hottest year of the millennium cannot be supported by his analysis."

†According to McIntyre and McKitric, the database used by Mann, et al. was riddled with "errors and defects." Of 112 proxy series of temperature records used in the Mann paper, 19 had "unjustified extrapolations or interpolations to cover missing entries," at least 24 had "obsolete data," 18 were displaced "to one year earlier than apparently intended," and all series 28 that used tree-ring data miscalculated the information obtained by reading the rings. The authors concluded that "the extent of errors and defects in the data means that the indexes computed from it are unreliable and cannot be used for comparisons between the current climate and that of past centuries." Many of the critiques of the Mann study presented by McIntyre and McKitric were validated by a June 2006 report from the National Academies entitled "Surface Temperature Reconstructions for the Last 2,000 Years." The report pointed out that based upon uncertainties in assessing large-scale temperature changes prior to 1600 A.D., "[e]ven less confidence can be placed in the original conclusions by Mann et al. that 'the 1990s are likely the warmest decade, and 1998 the warmest year, in at least a millennium.' "

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