Continuing Rabett Run's excerpts from the US EPA responses to challenges to its Endangerment Finding for increasing CO2 concentrations, Eli has it in for Essex, Beenstock, Reingewertz (really go to Our Changing Climate for this) and VS, Bart's little Mrs. Calabash.
A commenter (3722) suggests that average global temperature is not an adequate “starting point” as an indicator of climate change “[c]onsidering the multitude of physical processes that control climate.” The comment indicates that “global temperature systems are not homogeneous, and are indeed characterized by large differences and variability.” The comment refers to Essex et al. (2007), who conclude “Physical, mathematical, and observational grounds are employed to show that there is no physically meaningful global temperature for the Earth in the context of the issue of global warming to support this notion.”
We have reviewed the paper by Essex and considered the commenter’s view regarding the usefulness of global temperature as a “starting point” and we disagree that it is not a useful indicator. We note that the TSD does not rank the importance of any individual indicator or suggest that global average temperature is the most important indicator. Rather, it summarizes the scientific literature on a large set of indicators (including changes in sea level and ocean heat content, glaciers, snow cover, precipitation, and a large number of physical and biological systems).
With respect to the Essex et al. study, the authors claim that “physical, mathematical, and observational grounds are employed to show that there is no physically meaningful global temperature for the Earth in the context of the issue of global warming.” We do not dispute that a single global average temperature may not be particularly meaningful to understanding global warming and concur that global temperature systems are not homogeneous. But Essex et al. are neglecting the fact that climate scientists are not particularly interested in a single average value, but rather the change or variation in temperature expressed as anomalies over time at a range of spatial scales, from local to regional to global. Analysis of temperature anomalies is a legitimate, extensively peer-reviewed, expertly assessed methodology for understanding temperature trends at all scales.
Thus, the TSD appropriately summarizes the literature and that its discussion of global temperature is reasonable, informs our understanding of climate change, and is consistent with the scientific literature.