Replies

I am not aware of your source for the "it implies temperatures are higher in 20th century than at any time in 1000 years" so I may be off here. However I have always understood it to show that the warming in the latter part of the 20th century is where the warming is showing. Some "skeptics" used to early part to show it wasn't warmer.

In regards, to Mann's response, if Mann did nothing then people would say that M&M are right because Mann can't refute them (that happened with the initial article). So by your analysis, he is wrong if he doesn't reply or is defensiveness if he is.

"Abstract A compilation of paleoclimate records from lake sediments, trees, glaciers, and marine sediments provides a view of circum-Arctic environmental variability over the last 400 years. From 1840 to the mid-20th century, the Arctic warmed to the highest levels in four centuries. This warming ended the Little Ice Age in the Arctic and has caused dramatic retreats of glaciers, melting of permafrost and sea-ice, and alteration of terrestrial and lake ecosystems. Although significant warming, particularly after 1920, was likely due to increases in atmospheric trace-gases, the initiation of the warming in the mid-19th century suggests that increased solar irradiance, decreased volcanic activity, and feedbacks internal to the climate system played roles."

http://www.ngdc.noaa.gov/paleo/sciencepub/front.htm

I don't need to say "implies" se previous reply ... U.S. Assessment took Mann's work and on that basis (incorrectly) stated directly:

"New studies indicate that temperatures in recent decades are higher than at any time in at least the past 1,000 years. (Overview p.11)" See
http://www.greeningearthsociety.org/Articles/2000/hockey.htm

I leave it to you to decide if this was unwarranted inference or not based on Mann's work. The graph seems stark, but then the U.S. assessment took out the wide 'error bars' in Mann's original report...

Mann's "Myth #3":
MYTH #3: The "Hockey Stick" studies claim that the 20th century on the whole is the warmest period of the past 1000 years.
http://www.realclimate.org/index.php?p=11

"Abstract: The data set of proxies of past climate used in Mann, Bradley and Hughes (1998, “MBH98” hereafter) for the estimation of temperaturefrom 1400 to 1980 contains collation errors, unjustifiable truncation or extrapolation of source data, obsolete data, geographical location errors, incorrect calculation of principal components and other quality control defects. We detail these errors and defects. We then apply MBH98 methodology to the construction of a Northern Hemisphere average temperature index for the 1400-1980 period, using corrected and updated source data. The major finding is that the values in the early 15th century exceed any values in the 20th century. The particular hockey stick chape derived in the MBH98 proxy construction -- a temperature index that decreases slightly between the early 15th century and early 20th century and then increases dramatically up to 1980 -- is primarily an artefact of poor data handling, obsolete data and incorrect calculation of principal components. "
http://www.uoguelph.ca/~rmckitri/research/trc.html

Thus the M+M critique is not simply the PCA, but the underlying data... which is what others (eg Daly) were questioning too ... There are better proxies than tree rings, apparently.

And Mann and M+M are IN AGREEMENT THAT LATE 20TH CENTURY IS NOT WARMEST PERIOD IN LAST 1000 YEARS, both contradicting the 'assessment' reports.

We may have the horrible conclusion that global warming, even if real, is simply bumping the world up slightly to a temperature that the world enjoyed in 1100AD, when the Vikings colonized Greenland.