Climate Science

Comment from Scott Saleska (elevated from previous post). The discussion refers to the brief submitted in support of the EPA position organised by CEI in opposition to the ‘Scientists’ brief‘ that Scott was a party to.

Was there was a reply to CEI brief?

There was no formal venue for a reply, at least not before the court. The general consensus of those of us who discussed it was that the CEI brief was pretty poor anyway. For what it is worth, below are some comments I emailed to my colleagues after I reviewed the CEI brief, followed by comments by Dr. Curt Covey, whose work was cited in the CEI brief:

— begin quoted excerpts of my email —

Our climate scientist brief focused narrowly and conservatively on two questions: (1) whether the state of the science was accurately represented by the EPA and by the lower court, and (2) whether the science is sufficiently compelling to support a judgement that the legal standard for regulation is met (i.e., may greenhouse gas emissions “reasonably be anticipated to endanger public health or welfare”?)

A relevant claim that our scientists brief is wrong or misleading would therefore have to consist of an argument that either (1) the state of the science was in fact accurately characterized by the EPA or the Appeals Court, or (2) that in fact, greenhouse gas emissions may NOT be reasonably anticipated to endanger public health or welfare. The CEI brief does neither, so I suspect it will not have much relevance to the case at hand.

The CEI brief discusses a range of broad questions on which the Climate Scientist’s brief takes no position (e.g. whether the “net” effects of CO2 emissions “will” endanger public health or welfare, or what history would have been like if industrial development had taken a less CO2-intensive trajectory), and quibbles with technical details which have little or no effect on the answer to the overall question no matter how they are resolved (e.g. whether the NRC/NAS statement in 2001 that post-1950 ocean warming was 0.050C is meaningfully different from the Levins et al. 2005, more recent figure of 0.037C).

As far as the technical details, a quick survey convinces me there is not much there. Just to cite a few, taken more or less at random (I have not had time to look at all):

CO2 growth rates (CEI, p. 11): arguments about what growth rates for CO2 emissions that some models use are besides the point of what the science says about the climate sensitivity of the earth system (emissions growth rates are if anything an economic question). It is well-recognized that many of the original emissions scenarios in IPCC overstated the trajectories that were actually realized (indeed, this was a minor point made in the NRC/NAS 2001 report that was picked up on, and misunderstood or misrepresented, by the Appeals Court), but so what? Unless they are arguing that actual BAU emissions will be so low as to prevent CO2 from any further significant build up (or at least stay under a doubling), this is a detail entirely irrelevant to climate science, and almost entirely irrelevant to the question about “reasonable anticipation of endangerment”.

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
in their response to greenhouse gases. This point was clearly made by the IPCC report published in 2001. Pages 12-13 ignore all this and instead use “a constant-rate warming” of 1.8 degrees C per century “based on actual observations.” A constant-rate (i.e. straight-line) extrapolation of global warming from the 20th to the 21st century, as in the brief’s Figure 2, is a favorite technique of one of the authors, Pat Michaels. This technique gives 21st century warming at the low end of the spectrum of possibilities resulting from the different model-input scenarios. It is one possible future, but it’s never been clear to me (or to anyone else I know besides Pat) why the other possibilities — all of which involve more global warming — should be ignored.

Sincerely,
Curt Covey

—- end of Covey email —

Hope that is helpful to you and other interested parties.

Best,
Scott