In yesterday’s The Australian science writer Leigh Dayton claims that the northern hemisphere is hotter now than at any time in the past 1500 years. The article qualified her comment with this is “according” to the most comprehensive reconstruction of the earth’s temperature over the last two millenniums.
Dayton is referring to new research soon to be published by Michael Mann – the climate scientist credited with the now infamous 1998 “hockey stick” graph that shows a sharp uptick beginning around 1900 and that featured prominently in the 2001 IPCCs Third Assessment Report.
The graph was contested from the beginning because it did not show the medieval warm period and then
Canadians Stephen McIntyre and Ross McKitrick were unable to replicate Manns’ results and Mann initially refused to provide them with all the input data. The saga is detailed in various publications** and a chapter in Aynsley Kellow’s book ‘Science and public policy: The virtuous corruption of virtual environmental science’
I wonder how his new research by Mann has dealt with the medieval warm period ? Indeed I wonder how, after all the controversy surrounding Mann’s earlier work, Dayton can so uncritically report something so at odd with what is know about the history of Europe over the last 2,000 years.
Update: The paper is available on line
Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia. PNAS, September 9, 2008, vol. 105, no 36.
hat tip to Nexus 6 for the update/link.
** The following text including citations is from Ross McKitrick’s website:
Hockey Sticks, Principal Components and Spurious Significance Geophysical Research Letters, Vol 32(3), Feb 12 2005, copyright 2005 American Geophysical Union (doi: 2004GL012750). Further reproduction or electronic distribution is not permitted. This is a preprint of the GRL paper that shows Mann’s program mines for hockey sticks and overstates the statistical significance of the final result. There have been 4 technical comments submitted to GRL in response. We submitted replies to all 4, and they were sent out for refereeing. Two of the comments have been rejected by GRL. The two that were published were accompanied by our replies. These exchanges are discussed below.
The M&M Critique of the MBH98 Northern Hemisphere Climate index: Update and Implications Energy and Environment 16(1)69-100. AVAILABLE ON-LINE AT ENERGY AND ENVIRONMENT by kind permission of the publisher. This paper shows how Mann’s results can be reconciled to our results based on handling of the PC algorithm and a Gaspe cedar ring series. We also discuss the bristlecone pines in detail and show why they should not have been included in the original data set.
“Corrigendum” by Mann, Bradley and Hughes. Nature 430, July 1, 2004 p. 105. This arose from our Materials Complaint to Nature in the winter of 2004. The story is detailed on the page about our dealings with Nature (see below–link to Archive).
“Verification of multi-proxy paleoclimate studies: A case study”. Accepted abstract for presentation at American Geophysical Union Meetings in San Francisco, December 2004. Steve travelled to the AGU in December 2004 and presented our research–this was the abstract.
“Corrections to the Mann et al (1998) Proxy Data Base and Northern Hemisphere Average Temperature Series” Energy and Environment 14(6) 751-772.
This is the paper that started the whole ball rolling!