Estimating population heat exposure and impacts on working people in conjunction with climate change.

Increased environmental heat levels as a result of climate change present a major challenge to the health, wellbeing and sustainability of human communities in already hot parts of this planet. This challenge has many facets from direct clinical health effects of daily heat exposure to indirect effects related to poor air quality, poor access to safe drinking water, poor access to nutritious and safe food and inadequate protection from disease vectors and environmental toxic chemicals. The increasing environmental heat is a threat to environmental sustainability. In addition, social conditions can be undermined by the negative effects of increased heat on daily work and life activities and on local cultural practices. The methodology we describe can be used to produce quantitative estimates of the impacts of climate change on work activities in countries and local communities. We show in maps the increasing heat exposures in the shade expressed as the occupational heat stress index Wet Bulb Globe Temperature. Some tropical and sub-tropical areas already experience serious heat stress, and the continuing heating will substantially reduce work capacity and labour productivity in widening parts of the world. Southern parts of Europe and the USA will also be affected. Even the lowest target for climate change (average global temperature change = 1.5 °C at representative concentration pathway (RCP2.6) will increase the loss of daylight work hour output due to heat in many tropical areas from less than 2% now up to more than 6% at the end of the century. A global temperature change of 2.7 °C (at RCP6.0) will double this annual heat impact on work in such areas. Calculations of this type of heat impact at country level show that in the USA, the loss of work capacity in moderate level work in the shade will increase from 0.17% now to more than 1.3% at the end of the century based on the 2.7 °C temperature change. The impact is naturally mainly occurring in the southern hotter areas. In China, the heat impact will increase from 0.3 to 2%, and in India, from 2 to 8%. Especially affected countries, such as Cambodia, may have losses going beyond 10%, while countries with most of the population at high cooler altitude, such as Ethiopia, may experience much lower losses.