I just read the questions posed to Mann & Co. at M&M's site:
http://www.uoguelph.ca/~rmckitri/research/trc.html and it doesn't look like he even tries to answer. However, he does try to obfuscate by raising arcane statistical issues. Here a letter from Prof. Fred Singer that is a lot more to the point: Dear All
There is an additional point I would like to add to Aynsley Kellow's
excellent letter:
1. As Knutti/Joos/Stocker correctly point out, the IPCC conclusion, i.e.,
that the 20th century was the warmest in 1000 years, is based on the
instrumental record of surface temperature and NOT on the Mann et al
reconstruction. They should have said "SOLELY based" since Mann et al
stopped in 1980, at which point their temperature did not exceed the
Medieval values.
2. Mann et al do not show proxy temperatures beyond 1980. When I
questioned him regarding this matter 3 years ago, he replied by e-mail that
there were no suitable data available. I had found several proxy records
[1-6] that extended well beyond 1980; none showed higher temperatures.
3. I have now examined several dozen more [7]; again none show higher
temperatures.
4. I conclude therefore that -- contrary to Mann -- many data sets ARE
available; as far as can tell, none agree with the instrumental
SURFACE record; all agree with the satellite and balloon data that show NO
appreciable atmospheric warming trend after 1979.[8]
5. Hence, the IPCC conclusion is not tenable
Best Fred Singer
************************
References:
1. Briffa K.R. 2000.Annual climate variability in the Holocene:
Interpreting the message of ancient trees. Quat. Sci. Rev. 19: 65-73 ;
2. Broecker W. S. 2001. Was the medieval warm period global? Science 291:
1497-1499;
3. Dahl-Jensen, D., Mosegaard, K., Gundestrup, N., Clow, G.D., Johnsen,
S.J., Hansen, A.W. and Balling, N. 1998. Past temperatures directly from
the Greenland Ice Sheet. Science 282: 268-271;
4. Jacoby et al 1996 Mongolian tree rings and 20th century warming, Science
273: 771-773; Jacoby and DArrigo 1997 Proc Natl Acad Sci USA 94: 8351;
5. Naurzbaev, M.M. and Vaganov, E.A. 2000. Variation of early summer and
annual last two millennia inferred from tree rings. J Geophys Res 105:
7317-7326;
6. Thompson L. G. et al. 2000. Ice core evidence for climate change in the
tropics. Science 289: 1916, Fig 6B
7. Singer, S.F. 2003. Science 301, 595 .
8. A full account is submitted for publication elsewhere.