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Short abstract:

Tracing the emergence of wet-bulb temperature as a heat stress index, I show how this physiological knowledge, crucial for assessing the health effects of global warming, grew out of the problems raised by scorching artificial microclimates imposed on industrial workers in the early 20th century.

Long abstract:

Today, wet-bulb temperature has become a key factor in assessing the potential health effects of global warming. When the wet-bulb temperature exceeds a certain maximum, the organism loses its ability to dissipate heat through perspiration and evaporation rapidly. If this persists, the body overheats inexorably to the point of death within a few hours. This thermo-physiological threshold represents an "upper limit of human survivability". How did this heat stress index emerge? In this presentation, 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.