Gene:
I've been following this issue closely and this is what I take away from it:
1) Tree ring-based temperature reconstructions are fraught with so much uncertainty, they have no value whatever. It is impossible to tease out the relative contributions of rainfall, nutrients, temperature and access to sunlight. Indeed a single tree can, and apparently has, skewed the entire 20th century temperature reconstruction.
2) The IPCC peer review process is fundamentally flawed if a lead author is able to both disregard and ignore criticisms of his own work, where that work is the critical core of the chapter. It not only destroys the credibility of the core assumptions and data, it destroys the credibility of the larger work - in this case, the IPCC summary report and the underlying technical reports. It also destroys the utility and credibility of the modeling efforts that use assumptions on the relationship of CO2 to temperature that are based on Britta's work, which is, of course, the majority of such analyses.
As Corcoran points out, "the IPCC has depended on 1) computer models, 2) data collection, 3) long-range temperature forecasting and 4) communication. None of these efforts are sitting on firm ground."
Nonetheless, and even if the UNEP thinks it appropriate to rely on Wikipedia as their scientific source of choice, greenhouse gases may (at an ever diminishing probability) cause a significant increase in global temperature. Thus, research, including field trials, on the leading geoengineering techniques are appropriate as a backstop in case our children find out that the current alarmism is justified.
David Schnare