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In early 2002, former U.S. Defense Secretary Donald Rumsfeld explained why the lack of evidence linking Saddam Hussein with terrorist groups did not mean there was no connection during a televised press conference.

“[T]here are known ‘knowns’ – there are things we know we know,” said Rumsfeld. “We also know there are known ‘unknowns’ – that is to say we know there are some things we do not know. But there are also unknown ‘unknowns’ – the ones we don’t know we don’t know . . . it is the latter category that tend to be the difficult ones.”

Rumsfeld turned out to be wrong about Hussein, but what if he had been talking about global warming?  Well, he probably would have been on to something there.  Unknowns of any ilk are a real pickle in climate science.

Indeed, uncertainty in climate science has induced a state of severe political paralysis. The trouble is that nobody really knows why. A rash of recent surveys and studies have exonerated most of the usual suspects – scientific illiteracy, industry distortions, skewed media coverage.

Now, the climate-science community is scrambling to crack the code on the “uncertainty” conundrum. Exhibit A: the October 2011 issue of the journal Climatic Change, the closest thing in climate science to gospel truth, which is devoted entirely to the subject of uncertainty.

While I have yet to digest all of the dozen or so essays, I suspect they are only the opening salvo in what is will soon become a robust debate about the significance of uncertainty in climate-change science. The first item up on the chopping block is called post-normal science (PNS).

PNS is a model of the scientific process pioneered by Jerome Ravetz and Silvio Funtowicz, which describes the peculiar challenges science encounters where “facts are uncertain, values in dispute, stakes high and decisions urgent.” Unlike “normal” science in the sense described by the philosopher of science Thomas Kuhn, post-normal science commonly crosses disciplinary lines and involves new methods, instruments and experimental systems.

Judith Curry, a professor at Georgia Tech, weighs the wisdom of taking the plunge on PNS in an excellent piece called “Reasoning about climate uncertainty.” Drawing on the work of Dutch wunderkind, Jeroen van der Sluijs, Curry calls on the Intergovernmental Panel on Climate Change to stop marginalizing uncertainty and get real about bias in the consensus building process. Curry writes:

The consensus approach being used by the IPCC has failed to produce a thorough portrayal of the complexities of the problem and the associated uncertainties in our understanding . . . Better characterization of uncertainty and ignorance and a more realistic portrayal of confidence levels could go a long way towards reducing the “noise” and animosity portrayed in the media that fuels the public distrust of climate science and acts to stymie the policy process.

PNS is especially seductive in the context of uncertainty. Not surprisingly, Curry suggests that instituting PNS-like strategies at the IPCC “could go a long way towards reducing the ‘noise’ and animosity” surrounding climate-change science.

While I personally believe PNS is persuasive, the PNS model provokes something closer to revulsion in many people. Last year, members of the U.S. House of Representatives filed a petition challenging the U.S. Environmental Protection Agency‘s Greenhouse Gas Endangerment seemed less sanguine about post-normal science:

. . . the conclusions of organizing bodies, especially the IPCC, cannot be said to reflect scientific “consensus” in any meaningful sense of that word. Instead, they reflect a political movement that has commandeered science to the service of its agenda. This is “post-normal science”: the long-dreaded arrival of deconstructionism to the natural sciences, according to which scientific quality is determined not by its fidelity to truth, but by its fidelity to the political agenda.

It seems unlikely that taking the PNS plunge would appreciably improve the U.S. public’s perception of the credibility, legitimacy and salience of climate-change assessments. This probably says more about Americans than it does about the analytic force of the PNS model.

Let’s face it. Americans do not agree on a whole hell of a lot. And they never have. Many U.S. institutions were deliberately designed to tolerate the coexistence of free states and slave-owning states. Ironically, Americans appear to agree more on climate-change science than other high-profile scientific controversies like the safety of genetically-modified organisms.

National Science Foundation

While it pains me to admit this, I am increasingly convinced that the IPCC’s role in assessing the science of climate change needs to be scaled back. The IPCC was an overly optimistic experiment in international governance designed for a world that never materialized.  The U.N. General Assembly established the IPCC in the months immediately preceding the fall of the Berlin Wall. Only two few years later, the IPCC’s first assessment report and the creation of the U.N. Framework Convention on Climate Change coincided with the collapse of the Soviet Union and the end of the Cold War.

A new world order seemed to be dawning in those days, which is probably why it seemed like a good idea to ask scientists to tell us what constitutes “dangerous climate change.”   Two decades and two world trade towers later, the world is a decidedly less hospitable place for institutions like the IPCC.

The proof is in the pudding – or, in this case, the atmosphere.

Forbes, 14 October 2011