Abstract

Climate change will cause increasing environmental heat levels in large parts of the world. The heat levels for millions of people working outdoors or indoors without air conditioning, particularly in tropical areas, are already so high that physiological limits are exceeded and health risks and productivity loss occurs.

Using data on climate and working population size for 67,000 geographic grid cells (size = 0.5 × 0.5 degrees) based on internationally refereed sources we produced global heat stress maps for different calendar months and time periods. We combine these estimates with exposure-response relationships for heat stress indices to calculate heat strain risks and work capacity loss at global, regional and country level. The physiological laboratory evidence concerning heat impacts on workers is extensive, but more quantitative epidemiological studies are needed to improve risk assessments of occupational health risks due to climate change.

For example, we calculated that the global number of people subjected to extremely high monthly average heat levels (WBGT > 30°C, when even moderate work is restrained) during the hottest month may rise to over 400 million at the end of this century from the current value of less than 1 million. At country level we find up to 2–4% of current daylight work hours are too hot for almost any work at moderate intensity. Our impact assessment model incorporates climate conditions, location of work (in sun, in shade or indoors), work intensity, and age distribution of the local population. Further developments of the model will be discussed.