Exposure to Excessive Heat and Impacts on Labour Productivity Linked to Cumulative CO2 Emissions

Cumulative CO2 emissions are a robust predictor of mean temperature increase. However, many societal impacts are driven by exposure to extreme weather conditions. Here, we show that cumulative emissions can be robustly linked to regional patterns of a heat exposure indicator, as well as the resulting socio-economic impacts associated with labour productivity loss in vulnerable sectors. We estimate historical and future increases in heat exposure using simulations from eight Earth System Models. Both the global intensity and spatial pattern of heat exposure evolve linearly with cumulative emissions across scenarios (1%CO2, RCP4.5 and RCP8.5). The pattern of heat exposure at a given level of global temperature increase is strongly affected by non-CO2 forcing. Global non-CO2 greenhouse gas emissions amplify heat exposure, while high local emissions of aerosols moderate it. Considering CO2 forcing only, an annual loss of labour productivity of about 3% of GDP per unit of trillion tonne of carbon emitted is projected. This loss doubles when adding non-CO2 forcing of the RCP8.5 scenario. This represents an economic loss of about 4,400G$ every year (i.e. 0.59$/tCO2), varying across countries with generally higher impact in lower-income countries