Duel of the Titans

Every Fourth of July, pyrotechnics on the Mall in Washington, DC, draw throngs for a “really big shew.” This year, we hope July 29th was on everyone’s calendars. That’s the day U.S. Senator James Inhofe (R-OK), who chairs the Environment and Public Works Committee, convened a landmark hearing concerning recent developments in the science of climate change.
     Ostensibly, Inhofe and the committee want to learn more about the history of the world’s surface temperatures. Most atmospheric scientists are taught that earth’s climate is anything but stable. It is common knowledge that during much of the last 50,000 years, a mile-thick mantle of ice topped what now are sites of some of North America’s most populace cities. It also is known that surface temperatures bounced upward and down many times since the ice receded some 11,000 years ago. We know, too, that the largest temperature excursion took place between 4,000 and 7,000 years ago. It was about one to three degrees (F) warmer then than it has been during recent decades. Textbooks label those millennia the “Climatic Optimum” because they gave rise to agriculture and human civilization.
      But current climate hysteria concerns the last thousand years. Are temperature’s today the warmest in that time?
      Literally thousands of refereed scientific papers have been written about the climate of the last thousand years. Almost all find evidence for two or three cold centuries that ended just before the 20th Century began. They are called the “Little Ice Age.” Nine hundred years before that an equivalent warm era known as the “Medieval Warm Period” reached its peak. Every few weeks, studies are published citing local evidence (in pollen deposits, corals, or tree rings) for either the Little Ice Age, Medieval Warm Period, or both.
      In 1999, Michael Mann, an assistant professor at the University of Virginia, composited a number of studies. He chose only nine that drew on climate information from before 1400. As a result, when he compared those early proxy temperatures with observed temperatures of the last hundred years and traced out an average temperature history back to 1000 A.D., his work “proved” there was no global evidence for the existence of either the Little Ice Age or the Medieval Warm Period. Mann’s “hockey stick” charting of temperature calls into question the synthesis of hundreds of other scientific papers–a synthesis that has been going for some time, as evinced by Sir Hubert Lamb’s profound compendium, Climate Past, Present and Future, published in 1990.
      To Mann’s fans, late-20th century temperatures appear to be anomalous. For them, his work is the basis for the oft-repeated claim that recent decades are the “hottest in the last thousand years.”
      Two Harvard scientists (Willie Soon and Sallie Baliunas) and three coauthors recently inspected a much larger set of the paleoclimatic indicators than did Mann and concluded that both the cold and warm periods were real and that the climate of the 20th century, while warm, isn’t at all unprecedented. This hardly should have come as a surprise based on the voluminous literature available on the subject, but in Washington, DC, climate science is political dynamite. Inhofe and his committee had the makings of hearing filled with scientific pyrotechnics.
      Are Mann’s research and that of Soon and Baliunas irreconciliable? No. A partial reconciliation actually is possible because Mann’s hockey stick incorporates so few climate histories from the early years that its “error bars” (shown in Figure 1a) are able to accommodate the possibility of a very large Medieval Warm Period. But that’s partial reconciliation. Is concordance possible? No. Given the mass of scientific papers on the Little Ice Age, Mann’s study can’t be stretched to allow for the possibility of its existence.

Figure 1a. Temperature reconstruction of Mann et al. (1999) showing the error range (gray region) of the reconstructed annual temperature variations (blue line).      Mann’s work has been published and cited in a number of influential compendia. Seldom are there any accompanying caveats about the nature of its “out-liers.” That was the case when it was featured in the 2001 report of the Intergovernmental Panel on Climate Change. But the most egregious abuse of Mann’s work was when it was assimilated into the Clinton/Gore U.S. National Assessment without its error bars (see Figure 1b). Was Mann asked to review the National Assessment, given the fact his work is so prominently featured? If he did review it, how could he let such a sharp abuse of science stand? Expect a senator or two to light that fuse!

Figure 1b. Mann et al.’s temperature reconstruction as it appears in the U.S. National Assessment (without error bars).       The National Assessment spawned the U.S. Environmental Protection Agency’s 2001 Climate Action Report, the document President Bush dismissed as a “product of the bureaucracy.” Indeed it was. Most of its content was lifted from his predecessors’ bureaucracy in the form of the National Assessment. The political consequences of Mann’s work have been profound: denunciation of President Bush’s stance on climate change and legislative proposals that would cap emissions of carbon dioxide.      Senator Inhofe and the committee’s Republican majority have invited Willie Soon and the University of Delaware’s David Legates (one of Soon/Baliunas coauthors) to testify. As of this writing it is unclear who was to serve as the Democratic minority’s chief spokesperson, but the finger points toward Mann. He won’t be a pushover. Mann is exceedingly talented and has vigorously defended his work in the past. But that past criticism was nothing like what has been served up by Soon and Baliunas.      To get a flavor for the climate going into the hearing, the July 8th edition of EOS, Transactions of the American Geophysical Union carries an article by Mann and ten coauthors defending the “hockey stick” (a rebuttal by Soon and Baliunas is in-press). What seems curious is how everyone knows the hockey stick to be the work of Mann and fellow researcher R.S. Bradley, who is listed among the coauthors. But who are all these other folks and what did they contribute to the original research? For example, Princeton University’s Michael Oppenheimer (former Barbra Streisand Chair at Environmental Defense) lends his prestige to the paper. This latter day piling on seems to be an effort to lend political heft to Mann’s work. If that is so, what does it say about the Hockey Stick Spat: is it politics, science, or that hybrid we like to call “political science?” Reference Cook, E.R., Krusic, P.J., Jones, P.D., 2003. Dendroclimatic signals in long tree-ring chronologies from the Himalayas of Nepal. International Journal of Climatology, 23, 707-732. Ladurie E., 1971. Times of Feast, Times of Famine: Climate Since the Year 1000. Doubleday, Garden City, NJ, pp. 426. Lamb, H. H., 1990. Climate: past, present, future. Routledge, pp. 624, Mann, M.E., Bradley, R.S., Hughes, M.K., 1999. Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations. Geophysical Research Letters, 26, 759-762. Mann, M.E., et al., 2003. On past temperatures and anomalous late-20th century warmth. Transactions of the American Geophysical Union, 84. National Assessment Synthesis Team, 2000. Climate change impacts on the United States: The potential consequences of climate variability and change. U. S. Global Change Research Program, Washington, DC. Soon, W., et al., 2003. Reconstructing climate and environmental changes of the past 1000 years: a reappraisal. Energy and Environment, 14, 233-296. Tan, M., et al., 2003. Cyclic rapid warming on centennial-scale revealed by a 2650-year stalagmite record of warm season temperature. Geophysical Research Letters, 30, 1617-1620 (DOI:10.1029/2003GL017352). Zhang, Q-B., et al., 2003. A 2,326-year tree-ring record of climatic variability on the northeastern Qinghai-Tibetan plateau. Geophysical Research Letters, 30, 1739-1742 (DOI:10.1029/2003GL017425).

Back to Top