An increase of one degree beyond 20 degrees Celsius (°C) in wet-bulb global temperature (WBGT) slashes global worker productivity by 2-3 per cent, while also causing additional physiological strain and an increased risk of ill health, a new joint report by the World Health Organization (WHO) and the World Meteorological Organization (WMO) has found.
Workplace heat stress was significantly higher when working in the sun, where WBGT, which takes into account exposure to thermal radiation, typically increases by 2°C to 3°C compared to working with shade protection, the report noted.
It describes ‘workplace heat stress’ as circumstances under which a worker’s body accumulates heat due to the combined effects of metabolic heat, environmental factors and clothing worn. This heat stress causes physiological heat strain in the body, which can lead to exhaustion, pathological conditions and even death.
Occupations such as construction, agricultural work and fisheries, which involve working outdoors in the sun during the hot hours of the day, are often regarded as the highest-risk occupations for experiencing morbidity and mortality associated with workplace heat stress.
In addition to direct solar radiation, thermal radiation from the ground or surrounding machinery further exacerbates the associated heat stress for manual workers, the report, titled Climate change and workplace heat stress, said.
The year 2024 was the warmest on record, with the global temperature averaging 1.45°C above pre-industrial levels. The past decade (2015-2024) has also been the warmest on record, with the frequency and intensity of extreme heat events rising sharply, increasing risks for both outdoor and indoor workers.
Estimates from the International Labour Organization (ILO) show that worldwide more than 2.4 billion workers were exposed to workplace heat stress, while every year 22.85 million occupational injuries, 18,970 fatalities and 2.09 million disability-adjusted life years are directly linked to exposure to excessive heat at work.
The WHO-WMO report highlighted that workplace heat stress was an everyday or seasonal problem for 30 per cent of the global population living in climates where high environmental temperatures affect daily activities.
In addition, more than one third of all persons who frequently worked in hot conditions experienced physiological heat strain, which was associated with clinical symptoms such as hyperthermia, syncope, impaired kidney function, dehydration and neurological dysfunction — and was often linked with worsening poverty and socioeconomic inequality.
To sustain an eight-hour work shift, core body temperature should not exceed 38°C, which is the long-established safety threshold set by the 1969 WHO guidance on working in conditions of heat stress.
Last year, Down To Earth reported in depth on how this crisis is playing out on the ground in India and how, across indoor and outdoor workplaces, informal workers bear the brunt of a warming world.
In brick kilns and on construction sites, workers may shift their work before sunrise to avoid the worst of the heat, yet they face dehydration, dizziness and lost wages as soaring temperatures shorten workable hours.
Meanwhile, in indoor settings such as factories, power looms and metal workshops, poor ventilation and lack of cooling turn shop floors into virtual furnaces, with workers reporting chronic fatigue, heat rashes and long-term health risks such as kidney strain and even death due to heat stroke.
According to the ILO, in 2020 there were an estimated 26.2 million persons living with chronic kidney disease attributable to workplace heat stress.
Climate change projections suggest that the prevalence of workplace heat stress and the associated adverse health and productivity consequences will increase during the 21st century, affecting more and more people, particularly in the less developed parts of the world, according to the WHO-WMO report.
It noted that daytime temperatures of more than 40°C and even above 50°C were becoming increasingly common.
As extreme heat worsens worldwide, occupational heat stress is no longer confined to countries located close to the Equator, said WMO Deputy Secretary-General Ko Barrett. “Protection of workers from extreme heat is not just a health imperative but an economic necessity.”
The report called for the implementation of occupational heat action plans tailored to specific industries and regions and advisories that consider local weather patterns and worker vulnerabilities, developed in collaboration with employers, workers, unions and public health experts.