Further comment on the Supreme Court briefs

Hurricanes (CEI, p. 16). We barely mention this, as a parenthetical (not as a “prediction” but as a citation of IPCC TAR’s reference to “likely increases” in tropical storm intensities). I am surprised they went after this, with all the recent work showing that the evidence for this has only gotten stronger since 2001. Yes, there is still debate about whether it has reached canonical levels of statistical significance (95% confidence), and there are problems with data quality yet to be fully resolved, but the standard in the law is lower (“may reasonably anticipate” endangerment). Are they arguing, in the light of Emanual 2005, and Webster et al., 2005, that it would be entirely unreasonable to anticipate stronger hurricanes in the future? If not, what is the point?

Satellite and surface temp records (CEI p. 23). The main substantive thing we said with respect to this is that “all available data sets show that both the surface and the troposphere have warmed,” which the CEI brief criticizes. But the quote they criticize is not ours, it is from the U.S. CSSP (2006) re-assessment (the subtitle of which is “understanding and reconciling differences”). An author of the CSSP (and of the Executive Summary, from which our quote is taken) is John Christy, who is an amicus on the CEI brief. Is he arguing against himself? Perhaps he didn’t realize this CEI comment was in there when he signed on.

—- end Saleska quotes —-

With regard to the CO2 scenarios, the CEI brief cited a paper by Curt Covey. My colleague and co-amici David Battisti inquired of Dr. Covey if he had any comments about the way CEI cited his work, and he responded, saying we were free to circulate his comments. Here they are:

— begin quote of Covey email —-

Dear Prof. Battisti,

Part of my job here at LLNL is to accurately communicate the results of my work to scientific colleagues and the public. Accordingly, you should feel free to share the comments below.

Page 11 of the brief begins, “As shown below, computer models predicting future warming must overestimate warming, because they generally use an incorrect increase in carbon dioxide concentration of 1% per year.” It is not true that models “generally use” this rate of increase. Model

simulations of 20th century global warming typically use actual observed amounts of atmospheric carbon dioxide, together with other human (for example chloroflorocarbons or CFCs) and natural (solar brightness variations, volcanic eruptions, …) climate-forcing factors. Model simulations of future global warming use analogous input; of course it is not possible to observe the future, so a variety of scenarios involving possible atmospheric concentrations of carbon dioxide, etc., are employed. These range from stabilization of atmospheric carbon dioxide at twice its pre-industrial value by the end of this century (IPCC SRES B1) to continuously increasing atmospheric carbon dioxide at the rate of a bit less than 1% per year (IPCC SRES A2). Each climate model simulating the future is run several times, with several different scenarios. All of this has been standard practice in climate modeling for the past ten years.

Pages 11-12 quote my 2003 review paper correctly regarding idealized simulations in which atmospheric carbon dioxide is assumed to increase at the precise rate of 1% per year. Note that in the end of the quoted passage, I say that this rate of increase could “perhaps” be considered realistic “as an extreme case in which the world accelerates its consumption of fossil fuels while reducing its production of anthropogenic aerosols.” I’m no expert on scenarios, but from what I hear about China and India I wonder if the world is already on that track. In any case, the purpose of the 1%-per-year scenarios is to compare different models’ responses to identical input — not to produce realistic possibilities of future climate. For the latter purpose, climate model output from the IPCC SRES B1, A2 and other scenarios has been widely used for several years and has been publicly available for

over two years on my group’s Web site at http://www-pcmdi.llnl.gov/ipcc/about_ipcc.php.

Finally it is not true, as implied on Page 12, that “sole reliance on models to the exclusion of observed behavior” is the basis of future climate prediction. As noted above, modern climate models are used to

retrospectively simulate the 20th century as well. Simulation of 20th century global warming is an important confidence-builder for climate models. Indeed, the observed warming during the 20th century cannot be explained other than by assuming that the models are reasonably accurate

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