Projections of Heat Stress and its Impact on Labour Capacity in North America

Global warming intensifies heat stress, which can exceed the human body's coping capacity, negatively impacting health and reducing outdoor labour productivity. This study assesses projected heat stress and its effects on labour capacity in North America at two future global warming levels: 2°C and 4°C above the pre-industrial level. We utilise 3-hourly outputs from the Canadian Regional Climate Model version 4 (CanRCM4) large ensemble under a high emissions scenario to compute the wet-bulb globe temperature (WBGT), a heat stress indicator incorporating both temperature and humidity. We then bias correct model simulations to align with the historical heat stress climatology from the North American Regional Reanalysis (NARR). The corrected WBGT projections are used to evaluate labour capacity loss for light, moderate, and heavy outdoor work. Results indicate that the WBGT will increase more in Canada due to a greater increase in temperature. However, heat stress intensity will increase more in the southern United States, where the climate is already warm and humid. Labour capacity loss for heavy workloads in Louisiana, southern Texas, and northeastern Mexico will rise from the current 40% during summer to over 80% under a 4°C global warming scenario. Labour capacity loss uncertainty increases over time at the grid point scale, but spatial labour capacity loss uncertainty decreases over time for all workloads. Additionally, regions experiencing labour capacity loss will expand northward as global temperature rises. The projected increase in labour capacity loss with global warming should be an important aspect to consider for climate change adaptation.