Out of all the arguments against AGW, the complaints by McIntyre against the Mann analysis are the only ones I've heard that seem to warrant being taken seriously. If you really can get rid of the entire 20th century warming by removing a small set of proxies, regardless of the statistical analysis, it's a serious problem.
And the response on the "skeptical science" web site, that new data has confirmed the hockey stick shape, doesn't sound convincing either. You can't both say "ok, the Mann analysis was wrong, and the field has moved on" and then say "subsequent data confirm the hockey stick" without needing to explain the remarkable coincidence that the initial incorrect study ended up getting exactly the same shape as the new "correct" data.
What I've not seen anywhere is an analysis of the extent to which projections about future warming is driven by the exact shape of the 20th century temperature record and how changing the temperature record would feed back on the GCM projections. If anyone knows of such a study, please post the reference.
My reading of it is that the original Mann analysis stands up, ie. Mann 1999 is largely correct, and that McIntyre's analysis is flawed. The Wahl 2007 paper contains some "interesting" language:
"Altogether new reconstructions over 1400–1980 are developed in both the indirect and direct analyses, which demonstrate that the Mann et al. reconstruction is robust against the proxy-based criticisms addressed. ... Also, recent “corrections” to the Mann et al. reconstruction that suggest 15th century temperatures could have been as high as those of the late-20th century are shown to be without statistical and climatological merit. Our examination ... leaves entirely unaltered the primary conclusion of Mann et al. (as well as many other reconstructions) that both the 20th century upward trend and high late-20th century hemispheric surface temperatures are anomalous."
The projections are based completely on the temperature record, and changing the temperature record would produce different projections. The projections are essentially fudged to get the result that is desired for political reasons.
I'm guessing you haven't been exposed to many arguments against AGW, or maybe not many good ones. But since you have an open mind, I'd suggest you look into the absorbtion of IR By CO2, the actual proportion of CO2 in the atmosphere, the lack of tropophere warming (where it should show up) and the historical correlation of CO2 and temperasture-- CO2 has been a lagging indicator and has, in the past, been much higher than it is now from natural events without causing a runaway greenhouse effect. These are basic facts that don't take much analysis and greatly undermine the AGW theory. Also, the planet is getting colder in recent years (past decade) while CO2 has been rising.
Radiation transfer is what I do my research on (though not in the atmosphere), and it's something we know how to do. I really doubt the scientific field has screwed that up. Certainly all arguments I've seen regarding that have had crackpot quality. (I have some hope of getting around to actually running that problem myself, but "real" work always seems to get in the way.)
The projections were not based entirely on the Mann temperature record. There are satellite data, other analyses, etc., and I haven't seen to what extent changing one of those data sets impacts the projections.
And the response on the "skeptical science" web site, that new data has confirmed the hockey stick shape, doesn't sound convincing either. You can't both say "ok, the Mann analysis was wrong, and the field has moved on" and then say "subsequent data confirm the hockey stick" without needing to explain the remarkable coincidence that the initial incorrect study ended up getting exactly the same shape as the new "correct" data.
What I've not seen anywhere is an analysis of the extent to which projections about future warming is driven by the exact shape of the 20th century temperature record and how changing the temperature record would feed back on the GCM projections. If anyone knows of such a study, please post the reference.