Posted: 07/12/2004 | Author: H. Sterling Burnett
Breaking the "Hockey Stick"
The amount and rate of the earth’s current temperature rise is unprecedented in the past (pick your time period, i.e., one thousand, two thousand, ten thousand) years. This is one of the central articles of faith on which climate alarmists agree. It is not open to challenge or debate within the environmental community. It should be.
The United Nations’ Intergovernmental Panel on Climate Change (IPCC) claim that human activities are responsible for nearly all earth’s recorded warming during the past two centuries is based largely upon the work of Michael Mann of the University of Virginia and Phil Jones of the University of East Anglia. Mann and Jones produced a widely circulated image that dramatically depicts two millennia worth of temperatures that resembles a hockey stick with three distinct parts: a flat “shaft” extending from A.D. 200 to 1900, a “blade” shooting up from A.D. 1900 to 2002, and a range of uncertainty in temperature estimates that envelops the shaft like a “sheath.
Unfortunately for the IPCC, the credibility of Mann and Jones’ work is suspect. A recent report by Dr. David Legates, director of the University of Delaware’s Center for Climatic Research and an NCPA adjunct scholar, shows that five separate groups of researchers have uncovered a variety of problems with Mann and Jones’ reconstruction, calling into question all three components of their “hockey stick.”
First, Mann and Jones indicate that globally- and hemispherically-averaged air temperatures from A.D. 200 to 1900 were nearly constant. This is central to their assertion that recent warming is unprecedented. Yet missing from their timeline are the widely recognized Medieval Warm Period (about A.D. 800 to 1400) and the Little Ice Age (A.D. 1600 to 1850). Most proxy records from around the globe, including tree rings, ice cores and bore holes variously from Argentina, Chile, Southern Peru, Southern Africa and Northern China show these climatic events.
Scientists trying to verify Mann and Jones’s work found several fatal flaws. For example, to construct their climate trend data, Mann and Jones selected beginning and end points in their data series and ignored temperature fluctuations within the series. If they had chosen different starting or ending points, the graphic reconstruction could have been quite different – likely including the Medieval Warm Period and the Little Ice Age. This, among other errors, led scientists in the journal Geophysical Research Letters to conclude that Mann and Jones’ methods were “just bad science” and that they had undertaken a “selective and inappropriate presentation” of results.
In June, the accumulated weight of criticisms led to a retraction by Mann (and Scott Rutherford) in the Journal of Geophysical Research. However, while Mann admits to substantially underestimating historical temperature variations he amazingly goes on to argue that this error has no effect on their analysis of present temperature trends.
This is surprising since Mann and Jones’ most recent reconstruction shows warming over the last century of 0.95 °C (1.5 °F) — a temperature rise more than 50 percent larger than even the IPCC claims, which is largely the basis for the oft repeated claim that the 1990s were the warmest decade of the last two millennia. However Legates, along with Harvard scientists Willie Soon and Sallie L. Baliunas, found that this steep warming, or the “blade” of their hockey stick, could not be reproduced using either the same techniques employed by Mann and Jones, or by other common statistical measures. Since reproducibility is the hallmark of scientific inquiry, and the blade does not represent the observed climate record, it is unreliable. Strike two.
The third component of the “hockey stick” is Mann and Jones’ uncertainty assessment — the estimate of how much warmer or cooler than their reconstruction the temperature could actually have been. This also suffers from a variety of errors, including biases in hemispheric air temperature estimates resulting from sparse and irregularly distributed instrumental records that under-represent the oceans, high latitude regions, mountainous areas (i.e., high altitudes) and non-populated landscapes, and data sets to small to fairly represent regional air temperatures.
If even one component of Mann and Jones’ — and, consequently, the IPCC’s —temperature reconstruction is in error, let alone all three, then we can’t say with any confidence that the 1990s were the warmest decade of the last two millennia, or that 1998 was the warmest year, much less that the last century’s rise in temperature is unprecedented.
And if we don’t know with any certainty whether the earth’s present temperature trend is truly unique, or whether it simply represents the normal state of flux of the global climate system, it would seem premature at best to embark on the costly energy diet demanded by those who claim that only by reducing energy use can we stop the rise in greenhouse gases responsible for the past century and a half’s dangerous global warming.