War of words over new climate change report, 'hockey stick' model
Leading scientist says House climate report is "politicized"
July 16, 2006
Paleoclimatologist Michael Mann criticized a report challenging the familiar "hockey stick" temperature record of the past thousand years. The report, commissioned by Texas Representative Joe Barton, chairman of the House Energy Committee, and championed in an op-ed piece appearing in last Friday's issue of The Wall Street Journal said that there is no evidence that the 1990s were the warmest decade in a millennium or that 1998 was the warmest year in the last 1,000.
"The un-peer reviewed report commissioned by Rep. Barton released today adds nothing new to the scientific discourse on climate change and is a poor attempt to further personalize and politicize what should be a matter of scientific debate not politics," wrote Dr. Mann in a response released Friday.
Mann's 1999 paper, which served as the basis for the so-called "hockey stick" graph that shows a sharp increase in global temperatures over the past century or so, has faced criticism since its publication, namely that it "flattened" the spike in temperatures seen in Europe during the Medieval Warm Period from 10th century to the 14th century. Some critics have said that Mann's tree ring proxies were too limited in scope to represent global temperature and inaccuracies exist in his statistical methodology.
In his response to the House study, written by three statisticians -- Edward J. Wegman of George Mason University, David W. Scott of Rice University and Yasmin H. Said of Johns Hopkins University, Mann cited conclusions from the National Academy of Sciences, presented last month in a pre-publication version of its Report-Surface Temperature Reconstructions for the Last 2,000 Years report.
Mann, et al's "hockey stick" graph.
Click for comparison of climate record charts.
Earth at Warmest in 400 Years
There is sufficient evidence from tree rings, boreholes, retreating glaciers, and other "proxies" of past surface temperatures to say with a high level of confidence that the last few decades of the 20th century were warmer than any comparable period in the last 400 years, according to a new report from the National Research Council. Less confidence can be placed in proxy-based reconstructions of surface temperatures for A.D. 900 to 1600, said the committee that wrote the report, although the available proxy evidence does indicate that many locations were warmer during the past 25 years than during any other 25-year period since 900. Very little confidence can be placed in statements about average global surface temperatures prior to A.D. 900 because the proxy data for that time frame are sparse, the committee added.
2005 was the warmest year on record
A new study by NASA indicates that 2005 was the warmest year in at least a century, surpassing 1998. According to their data, the five warmest years over the last century have occurred since 1997: 2005, then 1998, 2002, 2003 and 2004. NASA also announced that over the past 30 years, the Earth has warmed by 0.6 degrees C or 1.08 degrees F, and 0.8 degrees C or 1.44 degrees F over the past 100 years. The NASA study follows two studies from the World Meteorological Organization (WMO) and the National Oceanic and Atmospheric Administration (NOAA) released last year that suggested 1998 was the warmest year. According to the NASA researchers, the primary difference among the conclusions is the inclusion of data from the Arctic in the NASA analysis. 2005 appears to have been unusually warm in the Arctic, resulting in significant loss in sea ice.
World temperatures highest in 1200 years
World temperatures are higher than in any period over the last 1,200 years, according to a study published in the current issue of Science. In reaching their conclusion, a research team from the University of East Anglia in Britain analyzed 14 sets of temperature records including data from rings, fossil shells, ice cores, temperature records, and historical documents from North America, Europe and East Asia.
Carbon dioxide level highest in 650,000 years
Carbon dioxide levels are now 27 percent higher than at any point in the last 650,000 years, according to research into Antarctic ice cores published on Thursday in Science. Analysis of carbon dioxide in the ancient Antarctic ice showed that at no point in the past 650,000 years did levels approach today's carbon dioxide concentrations of around 380 parts per million (ppm). The Intergovernmental Panel on Climate Change (IPCC) projects that atmospheric carbon dioxide levels could reach 450-550 ppm by 2050, possibly resulting in higher temperatures and rising sea levels. There is fear that climate change could create a class of environmental refugees displaced from their homes by rising oceans, increasingly catastrophic weather, and expanding deserts.
"Barton's report, written by statisticians with no apparent background at all in the relevant areas, simply uncritically parrots claims by two Canadians (an economist and an oil industry consultant) that have already been refuted by several papers in the peer-reviewed literature inexplicably neglected by Barton's 'panel'. These claims were specifically dismissed by the National Academy in their report just weeks ago."
The National Academy of Sciences' report actually lends mixed support to Mann's findings.
"There is sufficient evidence from tree rings, boreholes, retreating glaciers, and other "proxies" of past surface temperatures to say with a high level of confidence that the last few decades of the 20th century were warmer than any comparable period in the last 400 years," said the National Research Council. "Less confidence can be placed in proxy-based reconstructions of surface temperatures for A.D. 900 to 1600... although the available proxy evidence does indicate that many locations were warmer during the past 25 years than during any other 25-year period since 900. Very little confidence can be placed in statements about average global surface temperatures prior to A.D. 900 because the proxy data for that time frame are sparse," continued the Council.
Mann also took exception to the Wegman-Scoot-Said study's criticism that the international community of climate researchers do not properly peer-review each other's research. Specifically, the Wegman-Scoot-Said study said, "[W]e judge that the sharing of research materials, data and results was haphazardly and grudgingly done. In this case we judge that there was too much reliance on peer review, which was not necessarily independent. Moreover, the work has been sufficiently politicized that this community can hardly reassess their public positions without losing credibility."
To this, Mann responded, "The panel makes the odd claim that there is "too much reliance on peer-review" which goes against every principle of current scientific practice. Barton in his 'factsheet' goes further and suggests that the anonymous peer reviewers themselves are in some way biased, a claim that he cannot possibly support since peer reviewers are in fact anonymous and this was not studied in the report."
"Climate science, like many multidisciplinary fields, requires broad collaboration with researchers across many areas," he continued. "Any well published scientist would show a wide-ranging pattern of connection with other researchers in the field. While I am flattered that the committee seems to think that I am at the center of the field, the same analysis would have shown a very similar pattern for any researcher engaged in widespread interdisciplinary research."
"My colleagues and I continue to work on reducing the uncertainties in past climate reconstructions and understanding the mechanisms of past and current climate change. Policy-makers should more constructively focus their attention on the consensus findings on climate change as presented by the Intergovernmental Panel on Climate Change (IPCC) and the National Academies of all G8 countries, rather than on pursuing politically-motivated attacks against individual scientists," concluded Mann.
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