On The APS Statement on Climate

The American Physical Society has been proceeding with a review of its statement on climate change. Judith Curry and Eli Rabett, among others, have posted the latest draft from the APS Panel on Public Affairs, which has been made available to the APS membership for commentary (each member is allowed one comment of limited length) before being given final edits and provided for a vote of approval to the council. I include below the draft statement and my comment.

The statement seems accurate (aside from some ambiguous wording which I point out in my comment) but rather bland and uninspiring. Perhaps unsurprising for the output of a committee process. There was evidently some high drama and passion involved; this ClimateWire story delves into some of the details. The most dramatic piece involved the resignation of Steve Koonin (a prototypical arrogant physicist, apparently) from the APS panel on public affairs after the larger committee took over the drafting of the statement his subcommittee had started. Koonin punctuated his step down with a wildly inaccurate op-ed in the Wall Street Journal last fall, one statement of which (that the human influence is "small", 1 or 2 %) he was still trying to defend in this article at Judith Curry's site last week.

The incoherence of that 1-2% claim was dissected at ATTP's blog among other places. Koonin’s use of an apples / oranges ratio to come up with a small percentage just highlights his lack of familiarity with the basic science of climate. He is taking the ratio of forcing, defined at the TOP of the atmosphere, to downward thermal radiative flux at the surface (“the greenhouse effect”). But it is fundamental to understanding this that a small imbalance at the tropopause necessarily leads to a much larger surface flux change, as both upward and downward flows are greater there due to the higher temperature of the surface relative to the tropopause, not even worrying about feedback effects. Yes they are measured in the same units, but the flux at TOA and at the surface are very different things and simply cannot be compared in this way. If you did the same sort of comparison for Venus, for instance, any forcing change at the top would be a really tiny fraction of the surface downward IR flux, but it would lead to a far greater flux change at the surface. The ratio of the two is simply not meaningful. His second example of the absorption fraction is similarly inept. Radiative transfer is not terribly complicated, but anybody thinking just looking at absorption gives you any substantive intuition about it has simply not understood the fundamentals of radiative transfer. Pierrehumbert’s book, or even his Physics Today article, gives a great intro – Koonin clearly hasn’t read them or at least not absorbed the basics there. And then he compares the expected 3 K temperature increase from doubling CO2 with the 288 K absolute temperature of Earth's surface as yet another way to get about 1%? The whole episode leaves one almost speechless.

Anyway, here's the statement as it stands, and my commentary below. Rabett's post above is a good place to leave your own further comments if you're not an APS member yourself, or even if you are.

Draft APS Statement on Climate Change

On Climate Change: Earth’s changing climate is a critical issue that poses the risk of significant disruption around the globe. While natural sources of climate variability are significant, multiple lines of evidence indicate that human influences have had an increasingly dominant effect on the climate warming observed since the mid-twentieth century. Although the magnitudes of future effects are uncertain, human influences on the climate are growing. The potential consequences of climate change are great and the policies of the next few decades will determine human influences on the climate for centuries.

On Climate Science: As summarized in the 2013 report of the Intergovernmental Panel on Climate Change (IPCC), there continues to be significant progress in climate science. In particular, the connection between rising concentrations of atmospheric greenhouse gases and the increased warming of the global climate system is more certain than ever. Nevertheless, as recognized by Working Group 1 of the IPCC, scientific challenges remain to our abilities to observe, interpret, and project climate changes. To better inform societal choices, the APS urges sustained research in climate science.

On Climate Action: The APS reiterates its 2007 call to support actions that will reduce the emissions, and ultimately the concentration, of greenhouse gases, as well as increase the resilience of society to a changing climate. Because physics and its techniques are fundamental elements of climate science, the APS further urges physicists to collaborate with colleagues across disciplines in climate research and to contribute to the public dialogue.

Arthur's comment on this draft:

Every claim in this statement appears to be correct according to my understanding of the problem. Succinct is also good. However, several phrases seem ambiguous:
1. "increasingly dominant" - is that saying (accurately - over 100% of warming since 1950 is human-caused by the vast majority of estimates) the human influence is now "dominant" or just that it is increasing? The following sentence also uses the word "growing", redundant with "increasingly". I would recommend to remove "increasingly" from the earlier sentence, it adds nothing but ambiguity to the paragraph.
2. "more certain than ever" - "certain" is accurate, but with the qualifiers it becomes unquantified and ambiguous. Are we at 1% certainty (but more than before) or 99%? How about the word "established" with some explanation of why - for example "the connection ... has been established observationally in accordance with decades-old theoretical predictions".

There is a lot missing from the statement - fundamental physical and chemical principles lead to some of the worst of the expected consequences. Ocean acidification. Rising sea levels (from both ocean warming and melting icesheets) will continue long after we stabilize atmospheric CO2 levels. More extreme weather (heatwaves, drought, rainfall, storms) follows directly from statistics of extremes and the dependence of water vapor partial pressure on temperature, though details on regional impacts are very complicated. Physical intuition regarding chaotic systems suggests poking them by tweaking parameters can lead to completely unexpected responses - accentuating the uncertainty and risk associated with continued human modification of the planet.

The statement as it stands is almost bland, understating the potential (based on physical principles) for grave concern. But - at least the statement appears to be factually correct. It would be interesting to have a bit more openness about the process in which this was developed (what did earlier versions of the statement look like?) but in general some kudos are in order for delivering a concise and accurate statement that at least expresses the most important issues clearly.