The Report “Surface Temperature Reconstructions for the Last 2000 Years” has appeared. This Report discusses the IPCC “hockey stick” plot of the multi-century global average surface temperature trends.
When I first saw this plot several years ago, I assumed it would be quickly shown that pasting togther of proxy data with the instrument data for the last few decades is scientifically flawed. These two approaches represent two distinctly different procedures to assess surface temperature trends. However, this hockey stick figure has become an icon for communicating global warming (and climate change, in general) to the public and policymakers.
In the Report, I fail to see an assessment of the following questions:
1. What is the uncertainty associated with the diagnosis of a global average surface temperature trend by pasting the instrument record onto the end of the proxy record? How does proxy data in the last few decades correspond to the measured surface air temperature trends AT THE SAME LOCATIONS?
2. Why is it assumed that “The Earth warmed by roughly 0.6 degrees….during the 20th century..” when we have documented biases in the peer reviewed literature in the assessment of trends in the land surface temperature data (e.g. see “Should light wind and windy nights have the same temperature trends at individual levels even if the boundary layer averaged heat content change is the same?”; “Assessing ‘Global Warming’ with Surface Heat Content”)? In a national assessment, why was such peer reviewed literature ignored?
Ignoring these science questions provides the perspective that the Report is intended to promote a particular perspective on climate science, rather than providing a balanced presentation on the issues. Indeed, the statement in Boston Globe that,
“Our conclusion is that this recent period of warming is likely the warmest in a (millennium),’’ said John Wallace, one of the 12 members on the panel and professor of atmospheric science at the University of Washington”,
clearly shows such a biased view. The Report is a disappointment in not adequately addressing the accuracy of the global surface temperature trend data. Since its accuracy is at the foundation of the entire Report, the absence of such an evaluation very substantially weakens the value of the Report in climate science.