One feature of climate change is the increasing heat exposure in many workplaces where efficient cooling systems cannot be applied. Excessive heat exposure is a particular problem for working people because of the internal heat production when muscle work is carried out. The physiological basis for severe heat stroke, other clinical effects, and heat exhaustion is well known. One feature of this health effect of excessive workplace heat exposure is reduced work capacity, and new research has started to quantify this effect in the context of climate change. Current climate conditions in tropical and subtropical parts of the world are already so hot during the hot seasons that occupational health effects occur and work capacity for many working people is affected. The Hothaps-Soft database and software and ClimateCHIP.org website make it possible to rapidly produce estimates of local heat conditions and trends. The results can be mapped to depict the spatial distribution of workplace heat stress. In South-East Asia as much as 15% to 20% of annual work hours may already be lost in heat-exposed jobs, and this may double by 2050 as global climate change progresses. By combining heat exposure data and estimates of the economic consequences, the vulnerability of many low- and middle-income countries is evident. The annual cost of reduced labor productivity at country level already in 2030 can be several percent of GDP, which means billions of US dollars even for medium-size countries. The results provide new arguments for effective climate change adaptation and mitigation policies and preventive actions in all countries.