Collateral Damage from the Death of StationarityJune 10th, 2009
Posted by: Roger Pielke, Jr.
In recent years climate scientists have come to understand that the climate system may not be stationary – meaning that the fundamental statistics of climate vary and change over timescales of relevance to people. For those who consider that the phrase “climate change” is redundant, this will be no surprise. However, decision makers in a wide range of settings, including flood mitigation, reinsurance and insurance, and even aspects of carbon policy, operate from a framework where climate is perceived to be a stationary process.
In a new essay in the GEWEX Newsletter I argue that if indeed stationarity is dead then collateral damage of the new philosophy of climate necessarily must be the notion that we can ever evaluate the skill of climate predictions using empirical methods. That leaves us relying on a few remaining methods of forecast evaluation, among them political expediency and simple faith.
Here is an excerpt from my essay:
Here I suggest a far more consequential implication of the death of stationarity for the role of science in water management decision making than a need for better models and observations. Rather than basing decision-making on a predict (probabilistically of course) then act model, we may have to face up to the fact that skillful prediction of variables of interest to decision makers may simply not be possible. And even if it were possible, we would not be able to identify skill on the same time scales as decisions need to be made. The consequence of this line of argument is that if stationarity is indeed dead, then it has likely taken along with it fanciful notions of foreseeing the future as the basis for optimal actions. Instead, it may be time to rethink how we make decisions in the face of not simply uncertainty, but fundamental and irreducible ignorance. Rather than focus on optimal decisions guided by prediction, we may need instead to focus on robust decisions guided by recognition of the limits of what can be known.
You can read the entire essay, which includes an excursion into how the “guaranteed win scam” conspires with the “hot hand fallacy” to defeat efforts to judge predictive skill in the context of nonstationarity, at the link below.
Pielke, Jr., R.A., 2009. Collateral Damage from the Death of Stationarity, GEWEX Newsletter, May, pp. 5-7. (PDF)