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Reductions in labour capacity from heat stress under climate warming


A fundamental aspect of greenhouse-gas-induced warming is a global-scale increase in absolute humidity1,2. Under continued warming, this response has been shown to pose increasingly severe limitations on human activity in tropical and mid-latitudes during peak months of heat stress3. One heat-stress metric with broad occupational health applications4,5,6 is wet-bulb globe temperature. We combine wet-bulb globe temperatures from global climate historical reanalysis7 and Earth System Model (ESM2M) projections8,9,10 with industrial4 and military5 guidelines for an acclimated individual’s occupational capacity to safely perform sustained labour under environmental heat stress (labour capacity)—here defined as a global population-weighted metric temporally fixed at the 2010 distribution. We estimate that environmental heat stress has reduced labour capacity to 90% in peak months over the past few decades. ESM2M projects labour capacity reduction to 80% in peak months by 2050. Under the highest scenario considered (Representative Concentration Pathway 8.5), ESM2M projects labour capacity reduction to less than 40% by 2200 in peak months, with most tropical and mid-latitudes experiencing extreme climatological heat stress. Uncertainties and caveats associated with these projections include climate sensitivity, climate warming patterns, CO2 emissions, future population distributions, and technological and societal change.

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Figure 1: Ten-year maximum monthly mean WBGT from WBT and 2 m reference temperature (Tref) as a proxy for globe temperature (WBGT = 0.7×WBT+0.3×Tref; °C) from ESM2M Tref, 2 m reference relative humidity, and surface pressure after mean and variance bias correction to reanalysis.
Figure 2: Population-weighted individual labour capacity (%) during annual mimimum (upper lines) and maximum (lower lines) heat stress months.

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The scientific results and conclusions, as well as any views or opinions expressed herein, are those of the authors and do not necessarily reflect the views of NOAA or the US Department of Commerce. The authors thank I. Held, T. Delworth, T. Knutson and V. Ramaswamy for constructive criticisms to improve the manuscript.

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J.P.D. designed the study, conducted the analysis and wrote the manuscript. J.G.J. performed experiments and gave technical advice. R.J.S. provided technical and conceptual advice.

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Correspondence to John P. Dunne.

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The authors declare no competing financial interests.

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Dunne, J., Stouffer, R. & John, J. Reductions in labour capacity from heat stress under climate warming. Nature Clim Change 3, 563–566 (2013).

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