The birth of thermopolitics: Wet-bulb temperatures, industrial microclimates, and class struggle in the early 20th century.

Today, wet-bulb temperature is of vital importance in assessing the health effects of global warming. How did this heat stress index emerge? In this article, I turn to the research of industrial hygienist J.S. Haldane, who studied working conditions in mines in the early 20th century. The first warming of the thermo-industrial era was local, not global. It affected work environments, providing a fertile field of observation for occupational medicine and experimental physiology. These investigations revealed a wet-bulb temperature threshold beyond which efficiency deteriorates, which I interpret as the manifestation of an internal, climato-physiological contradiction between microclimates of production and labor power. However, as the long struggle of the Lancashire weavers against 'steaming' illustrates, an emerging labor environmentalism targeted these hostile atmospheric conditions. There, wet-bulb temperature and class struggle are combined in what I propose to call thermopolitics, which is understood as both government and conflict over temperatures. It was not just about controversies over regulatory standards; it was also about a clash between two opposing normativities, one quantitative, reduced to the physio-economy of productive efficiency, the other qualitative, vital, inviting us to rethink the notion of a democratic atmospheric politics. This article also shows that the theoretical wet-bulb temperature threshold used in some recent scientific literature is overestimated compared to empirical results exhumed from the history of science. This implies that, without decisive action, the tipping point for human heat tolerance could be reached sooner and more widely than anticipated.