Extreme heat slashes work productivity

August 24, 2025

A joint report by the World Health Organisation and the World Meteorological Organization finds that rising workplace heat is already cutting global productivity and harming health. The study shows that each 1°C increase in wet-bulb globe temperature (WBGT) above 20°C reduces worker productivity by about 2–3 percent while adding physiological strain and raising risks of heat-related illness. WBGT incorporates air temperature, humidity, wind and thermal radiation.

The report notes that exposure to direct sunlight typically raises WBGT by 2–3°C compared with shaded conditions, making outdoor work substantially more hazardous. It defines workplace heat stress as conditions in which a worker’s body gains heat from metabolic activity, the environment and clothing, producing physiological heat strain that can lead to exhaustion, organ damage and death. Outdoor occupations with the highest risk include construction, agriculture and fisheries.

Thermal radiation from sun-heated ground or machinery further increases the heat load for manual workers. The report also highlights serious problems in indoor workplaces such as factories, power looms and metal workshops, where poor ventilation and lack of cooling create extreme conditions. Global trends amplify the danger. The year 2024 was the warmest on record, averaging about 1.45°C above pre-industrial levels, and the decade 2015–2024 was the hottest on record.

The International Labour Organisation estimates that more than 2.4 billion workers are exposed to workplace heat stress. Each year, some 22.85 million occupational injuries, 18,970 fatalities and 2.09 million disability-adjusted life years are directly linked to excessive heat at work.

The report finds that workplace heat stress is an everyday or seasonal problem for roughly 30 per cent of the global population living in climates where high temperatures affect daily activity. More than one-third of people who frequently work in hot conditions show physiological heat strain, with clinical symptoms including hyperthermia, fainting, impaired kidney function, dehydration and neurological dysfunction.