Projection of Heat Stress and its Impact on Labor Capacity for North America

Global warming increases heat stress. Extreme heat stress affects human health and labor capacity especially for outdoor workers, such as farmers and construction workers. The World Health Organization estimates climate change is expected to cause approximately 250,000 additional deaths per year between 2030 and 2050, including 38,000 deaths due to heat exposures. This study provides future projection of heat stress and its possible effect on labor capacity in North America based on 3-hourly output of the Canadian Regional Climate Model version 4 (CanRCM4) large ensemble simulation under the Representative Concentration Pathway 8.5 (RCP8.5) emission scenario. We first provide projected changes in the wet bulb globe temperature (WBGT), a heat stress indicator that combines the effects of both temperature and humidity, and then estimate the impacts of the projected changes in WBGT on the labor capacity for conducting different levels (light, moderate, and heavy) outdoor work. The original CanRCM4 simulations overestimate overall heat stress. This bias was corrected using Quantile Delta Mapping procedure such that the model simulated climatology of heat stress is consistent with those computed based on North American Regional Reanalysis data. WBGT is projected to increase more in Canada due to larger temperature increase, but the occurrence and duration of severe heat stress that limit outdoor activities increase more in southern United States because already warm climate there. For example, the capacity to perform heavy work outdoor is projected to decrease by 60% or more in parts of southern United States by the end of this century under the RCP8.5 scenario.