26 April 2019, Roger Jones (Professional Research Fellow), Understanding climate risk: On simplicity. This is a long screed in response to a reading list posted by Massimo Pigliucci (so he bears no responsibility) where he nominated a post on simplicity in science by Elliot Sober on Aeon. Why is simplicity better? As it happens, I am in the midst of an argument with the climate science community over simplicity as applied to statistical inference. A couple of days ago I bought Probability, Confirmation and Simplicity: readings in the the philosophy of inductive logic Foster and Martin 1966, which contains six essays on simplicity. Not as simple as it’s cracked up to be – exactly the ammunition I require. Accordingly, I disagree with Sober. He refers to the Akaike Information Criterion, which measures simplicity but says that it refers to the same underlying reality. But we see it being repeatedly used for different underlying realities by people who don’t read the small print. They are being simplistic (#OccamsRazor). By mixing probabilities with theory Sober is making a fundamental mistake. I can apply probabilities to an experiment or a test, but I cannot to a theory. At best I can severely test (Mayo) a hypothesis and by attaching it to probative criteria in such a way that the alternatives are as unlikely as the hypothesis is likely, then I have a chance of confirming that theory. In climate science, simplicity is represented by trend-like change. Under increasing greenhouse gases, forcing leads to warming as the logarithm of the increasing forcing plus feedbacks. In the Earth system, this leads to monotonic warming, linear to forcing. Trouble is, most of this heat is absorbed by the ocean and it is the atmosphere that needs to respond. The atmosphere-ocean relationship is a dissipative system driven by thermodynamics and decidedly nonlinear. So, if I assume the atmosphere warms according to the linear radiative forcing concept, I have a simple model that is predictive over demi-century-long timescales. If I assume that warming obeys the dissipative pathway, then it proceeds via enhanced climate variability as a series of step-like regime changes. Over both pathways, warming reaches close to the same destination but its mode of getting there is very different. One contains more inherent risk than the other. Read more here