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Response to a Critique of Our 14 Apr 2004 Editorial
Volume 7, Number 18: 5 May 2004

In an email communication dated 18 Apr 2004 and subsequently posted on the Internet, Dr. Theodore L. Anderson of the University of Washington in Seattle claims that our Editorial of 14 Apr 2004 "distorts and misrepresents" the paper of Anderson et al. (2004), of which he is the senior author.  We disagree.  There are many statements in the paper of Anderson et al. with which we wholeheartedly agree and that we highlighted in our Editorial, as well as a few about which we think differently and, hence, said little; but in no case do we distort or misrepresent what they say.

Anderson begins his critique of our Editorial by claiming he and his coauthors "did not assert that the 'forward calculation' is a 'first-principles' approach based entirely on chemical and physical laws," implying that we either said or suggested they asserted such.  Quite to the contrary, it was we who said that the forward calculation is a first principles approach.  Also, we did not say this approach is based entirely on physical and chemical laws, as Anderson further erroneously implies; we merely stated that the forward calculation utilizes known physical and chemical laws.  By implying we thought that is all the forward calculation utilizes, Anderson constructed a false basis for wrongly insinuating we were not cognizant of the fact that "forward calculations involve models, use extrapolations from limited measurements, and are strongly dependent upon empirical parameterizations."  These latter aspects of the forward calculation approach are accommodations that simply must be employed when attempting to describe the complex operations of real-world systems, which understanding should be almost prenatal knowledge to most thinking people and, therefore, needful of no further comment, which we consequently did not provide.

Anderson next claims that Anderson et al. "did not assert that the 'forward calculations' are superior to the 'inverse calculations'."  Again, we did not say that they did; it was we who said the forward calculations are superior.  What is more, Anderson et al. make a number of statements that seem to agree with our assertion: (1) "to the extent that climate models rely on the results of inverse calculations, the possibility of circular reasoning arises," (2) "unfortunately, virtually all climate model studies that have included anthropogenic aerosol forcing as a driver of climate change have used only aerosol forcing values that are consistent with the inverse approach," and (3) "inferences about the causes of surface warming over the industrial period and about climate sensitivity may therefore be in error."

If what Anderson et al. say in their paper about virtually all climate models is correct, how can Anderson now claim that the aerosol forcing values the climate modelers are using "can logically be argued to be the most likely values"?  One can't have it both ways.  The current status of anthropogenic aerosol modeling is either about as good as it can logically be, as Anderson claims, or it's unfortunate, as Anderson et al. say, proving how difficult it is to be true to the facts of the matter and politically correct at one and the same time.

Finally, Anderson says "Idso et al. fail to mention our concluding point ... that the accumulation of anthropogenic greenhouse gases in the atmosphere 'will inevitably result in a strong, positive forcing of the Earth's climate system' within the next few decades, regardless of the magnitude of negative aerosol forcing."  Of course we did not mention this statement, because it is merely an opinion that is as yet unsubstantiated and far beyond the scope of Anderson et al.'s study, which deals with but a small part of the overall problem.  The ultimate change in the "forcing of the Earth's climate system," as Anderson et al. describe it, includes much more than the sum of the forcings produced by greenhouse gases and anthropogenic aerosols.  It includes a host of forcings provided by both temperature-induced and CO2-induced changes in aerosols that owe their origin to gaseous emissions of earth's plant life, both terrestrial and aquatic [see Aerosols (Biological - Aquatic and Terrestrial in our Subject Index], as well as unrelated changes in many non-aerosol and non-greenhouse gas forcings [see Forcing Factors in our Subject Index], several of which, either individually or in combination, could well result in a far different end result than that so confidently proclaimed by Anderson.  What he describes as Anderson et al.'s concluding point, therefore, is clearly outside the realm of their paper and, as a result, unworthy of reporting, which is why we did not mention it.

In conclusion, we feel we have neither distorted nor misrepresented the salient points of the Anderson et al. (2004) study.  If anyone has, it is Anderson himself.

Sherwood, Keith and Craig Idso

Reference
Anderson, T.L., Charlson, R.J., Schwartz, S.E., Knutti, R., Boucher, O., Rodhe, H. and Heintzenberg, J.  2003.  Climate forcing by aerosols - a hazy picture.  Science 300: 1103-1104.