Just as an addendum to this post, I wanted to point out that Real Climate has a discussion of the paper in question[PDF].
The authors include not only Mike Mann, but also Bradley and Hughes, so we have the whole infamous MBH cabal in one place again! Let the mud-slinging begin!
But some useful stuff from RC’s post includes noting the substantial increase in the number of proxy data sources:
1209 back to 1800; 460 back to 1600; 59 back to 1000 AD; 36 back to 500 AD and 19 back to 1 BC (all data and code is available here). This is compared with 400 or so in MBH99, of which only 14 went back to 1000 AD.
- Did everybody get that?? Data and code is available here!
So what does it all mean? First off, this paper (like MBH98 before it) is not an attribution study. That means that the reasons for any of the ups-and-downs in the records are not demonstrated by these papers alone. Attribution of the recent trends (as discussed in IPCC AR4) to anthropogenic effects has mostly focussed on the last 150 years and did not use any paleo-data.