If you do a search at this blog site for ‘hockey stick’, Google will provide you with about 70 links and the first will link to a question I posted a year ago:
“What is the evidence for the medieval warm period? My understanding is that the Vikings were able to settle Greenland and grow grapes in Canada over several hundreds of years because the climate was significantly warmer. Yet this period is not evident in the famous ‘hockey stick’ graph.”
[from BBC News]
The graph was the creation of Dr Michael Mann, et al, and was used by the United Nation’s Intergovernmental Panel on Climate Change (IPCC) to conclude in their influential 2001 assessment report that the 1990s was the warmest decade and 1998 the warmest year of the last millenium.
Indeed the ‘hockey stick’ has emerged as something of an icon for believers in anthropogenic global warming (AGW), while global warming skeptics have dismissed it as shoddy science and another example of ‘believers’ using models to support a position at odd with the evidence in particular the existence of the medieval warm period.
Now a prominent statistician who is also a Univeristy Professor, Chair of the National Academy of Sciences Committee on Applied and Theoretical Statistics, and a member of the board of the American Statistical Association, has published a rather damning report on the hockey stick. As Paul Williams commented in the thread following my blog post last Friday, “… the hockey stick has just been hit for six”!
Following are some of the conclusions from Dr Edward Wegman as summarized by the US House Committee on Energy and Commerce:
1. Mann et al., misused certain statistical methods in their studies, which inappropriately produce hockey stick
shapes in the temperature history. Wegman’s analysis concludes that Mann’s work cannot support claim that
the1990s were the warmest decade of the millennium.
Report: “Our committee believes that the assessments that the decade of the 1990s was the hottest
decade in a millennium and that 1998 was the hottest year in a millennium cannot be supported by
the MBH98/99 analysis. As mentioned earlier in our background section, tree ring proxies are
typically calibrated to remove low frequency variations. The cycle of Medieval Warm Period and
Little Ice Age that was widely recognized in 1990 has disappeared from the MBH98/99 analyses,
thus making possible the hottest decade/hottest year claim. However, the methodology of
MBH98/99 suppresses this low frequency information. The paucity of data in the more remote past
makes the hottest-in-a-millennium claims essentially unverifiable.”
2. A social network analysis revealed that the small community of paleoclimate researchers appear to review
each other’s work, and reuse many of the same data sets, which calls into question the independence of peerreview and temperature reconstructions.
Report: “It is clear that many of the proxies are re-used in most of the papers. It is not surprising that
the papers would obtain similar results and so cannot really claim to be independent verifications.”
3. Although the researchers rely heavily on statistical methods, they do not seem to be interacting with the
Report: “As statisticians, we were struck by the isolation of communities such as the paleoclimate
community that rely heavily on statistical methods, yet do not seem to be interacting with the
mainstream statistical community. The public policy implications of this debate are financially
staggering and yet apparently no independent statistical expertise was sought or used.”
4. Authors of policy-related science assessments should not assess their own work.
Report: “Especially when massive amounts of public monies and human lives are at stake,
academic work should have a more intense level of scrutiny and review. It is especially the case
that authors of policy-related documents like the IPCC report, Climate Change 2001: The Scientific
Basis, should not be the same people as those that constructed the academic papers.”
5. Policy-related climate science should have a more intense level of scrutiny and review involving statisticians.
Federal research should involve interdisciplinary teams to avoid narrowly focused discipline research.
Report: “With clinical trials for drugs and devices to be approved for human use by the FDA, review
and consultation with statisticians is expected. Indeed, it is standard practice to include statisticians
in the application-for-approval process. We judge this to be a good policy when public health and
also when substantial amounts of monies are involved, for example, when there are major policy
decisions to be made based on statistical assessments. In such cases, evaluation by statisticians
should be standard practice. This evaluation phase should be a mandatory part of all grant
applications and funded accordingly.”
6. Federal research should emphasize fundamental understanding of the mechanisms of climate change, and
should focus on interdisciplinary teams to avoid narrowly focused discipline research.
Report: “While the paleoclimate reconstruction has gathered much publicity because it reinforces a
policy agenda, it does not provide insight and understanding of the physical mechanisms of climate
change… What is needed is deeper understanding of the physical mechanisms of climate change.”
Read the full report here: http://energycommerce.house.gov/108/home/07142006_Wegman_Report.pdf .