A chapter in The Deniers by Lawrence Solomon treats the work of Hendrik Tennekes on the problems of modelling complex systems. Clouds are a great example of complex systems and Tennekes was pleased to find a paper by Karl Popper on the challenge of exploring the dynamics of cloudlike systems compared with clocks or the movement of the planets in the solar system.
Tennekes was a director of research in the Royal Netherlands Meteorological Institute and chairman of the Scientific Advisory Committee of the European Centre. He wrote a bestselling popular book The Simple Science of Flight and a scholarly work A First Course on Turbulence.
He was a critic of some aspect of climate models from the beginning and in 1986 he delivered an important speech in Reading UK “No Forecast Is Complete Without a Forecast of Forecast Skill”. His point was that predictions of climate and weather beyond about three days are beyond the limits of testable science. “The goal of science is prediction but we stand in front of the limits of prediction.” Given the efforts of model builders since then there has been some success but only on the scale he predicted.
He did not consider that the response using “ensemble forecasting” and “multi-model forecasting” got over the fundamental difficulty that is rooted in the nature of cloudlike systems. “Fundamental questions concerning the prediction horizon are being avoided like the plague”. That sounds too much like unsettled science! Solomon reported that Tennekes found the philosophical key to his concern in Popper’s challenge to determinism in the essay “Of Clouds and Clocks: An Approach to the Problems of Rationality and the Freedom of Man” published in the 1972 Collection Objective Knowledge: An Evolutionary Approach. The essay alone is on line here.
The question is whether we can find out enough about clouds to predict their behaviour in the way that we can predict the future states of relatively stable and isolated systems. The case for determinism and the possibility of accurate prediction depends on the calculation of future states of a system based on full knowledge of the current situation. (Hayek developed philosophical counter-arguments to criticise the idea of central economic planning). Popper saw determinism as false and dangerous, leading to arrogant and unfalsifiable predictions pretending to be scientific. Tekkes saw how this mindset was playing out in climate studies although the driver was political and opportunistic more than philosophical.
The idea that perfect knowledge (or just more data) would lead to better predictions provided an escape route for predictions that failed – just get more data and build bigger models. The approach would survive because the model builders can always claim that more data and the next development in supercomputers or linked models will deliver the goods. Tekkes drew on Popper’s ideas in his critique of the climate models, especially the demand for a specification of the amount of inaccuracy that would be required to disqualify the model as a contender.
The response in the modelling community was to check against other models rather than the reality of the world “outside the window”. So the results from one model that ignores fundamental issues is compared with the results of other models that ignore the same issues and the increasing agreement between the models is celebrated as progress. Moreover a lot of code is common to many models and it would be a gigantic exercise to start building a model from scratch. On top of that the models were built when CO2 and temperature were marching in step and they enabled CO2 based models to give good results until the pace of warming changed and the relationship ceased to hold after the turn of the century (the debacle of diverging models).
Tennekes noted that sophisticated climate models had been running for twenty years and it had become evident that “these models cannot be made to agree on anything except a possible relationship between greenhouse gases and a slight increase in the globally averaged temperatures”. The reward for his critical commentary was to be forced to leave the Royal Netherlands Meteorological Institute. Solomon wrote “Lesser scientists, seeing that even a man of Tenneke’s reputation was not free to voice dissent learned their lesson. Those who harbour doubts about climate science do better to bite their tongues and keep their heads down”.
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