The World Health Organization (WHO) and World Meteorological Organization (WMO) put out a report on Climate Change and Workplace Heat Stress (September 2025), providing an overview and update of relevant evidence generated since 1969, when the WHO published initial guidance on working under conditions of heat stress.
Human Level’s Take:
- Climate change is intensifying heat stress and is already affecting nearly half the global population, with outdoor, indoor and physically demanding jobs most at risk.
- By 2100, it’s estimated that 318 million people could face high heat stress if warming is limited to 2°C, 540 million under current policies, and over 1 billion with no emissions cuts. This could pose serious impacts not just to individuals, but to broader economies and society.
- For workers, heat stress can cause illness, long-term health problems and even death, while also reducing productivity and increasing healthcare costs. Meanwhile, lost work hours threaten incomes and livelihoods. These issues can have ripple effects across regions, threatening poverty reduction efforts and disrupting global food systems and value chains.
- Companies can collaborate with workers, unions and regulators to develop occupational heat action programmes that include prevention policies, acclimatisation protocols, monitoring, training and emergency response planning.
- They can also assess workplace heat risks by factoring in job-specific and personal characteristics—such as work intensity, protective clothing, age, fitness and exposure to machinery or heat-intensive environments.
- And, they can establish policies to support workers returning after heat-related illness and engage worker representatives to identify risks and opportunities for preventing or mitigating heat stress.
Some key takeaways:
- Why heat stress is an increasing issue for workers (and their employers): Climate change is intensifying heat stress, with nearly half the global population already affected. Outdoor workers and first responders are especially vulnerable to heat but indoor workers can also be at risk if they work in heat-intensive environments (e.g., with heat-emitting machinery or limited air flow) or perform intense physical work. The number of workers likely to face heat stress will only increase as climate change intensifies heatwaves in more and more regions. The report estimates that by the end of the 21st century, 318 million people will face high heat stress if warming is kept below 2°C, 540 million under current policies, and over 1 billion if no emission cuts are made.
- How heat stress can create ripple effects: Heat stress can cause lower productivity, impacting business processes and potentially decreasing worker incomes, especially for piece-rate workers. Heat stress can lead to serious temporary and long-term ill health effects, and even death. The health and productivity impacts of heat stress can cause workers to lose income and employment and incur healthcare costs, threatening livelihoods and family incomes. Where economies are particularly dependent on labour-intensive work like agriculture, construction and fishing, loss of work from heat stress can put broader poverty reduction efforts at risk. These issues in turn create wider economic and social consequences, including disruptions to value chains and food systems as a result of lower production.
- What companies can do: The rise of heat indexes means that employers and regulators will quickly need to act in order to manage the risks of heat stress in the workplace. The report recommends that stakeholders—from employers, to governments, to unions, to workers—collaborate to create occupational heat action programmes that can help reduce the likelihood of heat-related health impacts. These programmes can include workplace heat stress prevention policies, protocols for heat acclimatisation, environmental and medical monitoring of workers, training and education for workers and first responders, and emergency response planning, as well as job-specific controls. Employers will also need to assess heat stress risks, considering personal and job risk factors, like gender, age, physical fitness, heat acclimatisation, type of work, proximity to machinery, the need for heavy protective clothing and location. Importantly, the report recommends that employers and regulators consider what types of issues might arise for workers who return to work after severe health outcomes associated with heat stress, and put in place policies and procedures to ensure decent work. A key component is listening to workers and their representatives to understand the full range of risks and the potential opportunities to prevent or mitigate heat stress.
