Pictures of climate change

Spencer Weart’s article on climate impacts (Physics Today, September 2015, page 46 ) describes the sociology of how opinion has evolved on anthropogenic change, but it says little about the opinion’s scientific content. It is remarkable that the scientific giant in this field, Svante Arrhenius (1859–1927), without knowledge of the Planck function—much less the quantum mechanics of molecular opacity or computer codes—made predictions of climate sensitivity that are within a factor of two or three of modern estimates. Was that a lucky guess, or is the phenomenon so robust that even the crudest estimates are almost as good as the most sophisticated?

Weart describes, but does not explain, how the consensus about the effects of climate change has shifted from equanimity to fear and trembling that a great disaster will ensue. Is climate change a phenomenon to be observed, like the weather? Is it of direct concern mostly to farmers? Or is it a problem to be solved, and if so, how urgently? The shift is a sociological phenomenon that calls for explanation, but not by physicists.

The physical principles have long been known, and François Massonnet’s Commentary in the same issue (page 8 ) explains that even our present understanding and computational capabilities are not sufficient to predict regional effects such as droughts and floods. The fact that multiphysics codes—which combine multiple models to simulate complex phenomena—could not predict the failure of National Ignition Facility targets should make us skeptical of their power to predict any complex phenomenon, and climate is more complicated than a laser target.