The World Health Organization and the World Meteorological Organization published their first joint assessment of workplace heat stress in more than half a century, warning that rising temperatures are eroding global productivity and endangering employee health. The UN-backed report, released on 22 August, concludes that about 2.4 billion workers—roughly 70 % of the world’s labour force—now face potentially unsafe heat levels during their shifts. Analysts found that economic output drops by 2 % to 3 % for every degree Celsius above 20 °C, translating into sizable losses for sectors such as construction, agriculture and fisheries. The study also attributes some 23 million occupational injuries each year to excessive heat and lists medical risks ranging from dehydration and heat stroke to kidney failure. “It is a real health risk when body temperature rises above 38 °C for prolonged periods,” said Rüdiger Krech, WHO’s director of environment, climate and health. The agencies urge governments, employers and trade unions to redesign work schedules, invest in cooling technologies and prioritise vulnerable groups, noting that the cost of adaptation would be lower than the productivity losses already being recorded. The guidance arrives amid record-breaking temperatures: 2024 was the planet’s hottest year on record, while heatwaves of 40 °C to 50 °C are no longer confined to the tropics. Fresh academic evidence underscores the warning. A 15-year longitudinal study, published this week in Nature Climate Change and tracking nearly 25,000 adults in Taiwan, shows that cumulative heat exposure accelerates biological aging by eight to 11 days per additional 1.3 °C, with outdoor manual workers aging roughly three times faster than the general population. Lawmakers and labour advocates are seizing on the UN findings to press for stricter occupational-safety rules. In the United States, for example, proposals before Congress would mandate national heat-illness standards, while several states consider similar measures. The WHO and WMO stressed that timely investments in adaptation can avert mounting health costs and safeguard economic resilience as extreme heat events intensify.