The World Health Organization (WHO) has sounded the alarm over the growing dangers of extreme heat, calling it a “public health crisis” for workers across the globe. A new joint report with the World Meteorological Organization (WMO) highlights that outdoor workers—such as those in construction, farming, and other physically demanding jobs—are increasingly vulnerable to heat stroke, dehydration, cardiovascular strain, and kidney damage. The risks, however, extend indoors as well, particularly in factories and plants where machinery radiates heat in already humid environments.
“The workers keeping our societies running are paying the highest price,” said Rüdiger Krech, WHO’s director of environment, climate change and health. He emphasized that vulnerable communities with limited access to cooling, health care, and labour protections suffer the most severe consequences.
Canadian workers are far from exempt. Glen Kenny, a University of Ottawa research chair in environmental physiology, explained that Canada’s climate extremes create an added challenge. After months of cold weather, workers lose much of their heat adaptation, making them more susceptible when sudden summer heatwaves strike. “We go from cold to hot, and our bodies essentially lose that adaptation during the winter,” Kenny said.
The report stresses that once a worker’s core body temperature surpasses 38°C, the likelihood of heat exhaustion grows rapidly. It calls on governments and employers to adopt heat-health action plans, such as scheduling heavy tasks during cooler hours, ensuring frequent rest breaks, and providing hydration. Employers are also urged to implement buddy systems so workers can monitor one another for signs of heat stress.
Doctors warn that the impact of heat stress is not only physical but cognitive. Vancouver physician Dr. Melissa Lem, president of the Canadian Association of Physicians for the Environment, explained that overheating can impair concentration, reduce performance, and increase workplace injuries. She added that rapid breathing caused by heat also exposes workers to higher levels of air pollution, compounding health risks.
Symptoms of heat exhaustion include fatigue, dizziness, muscle cramps, and thirst, while severe cases can lead to confusion, nausea, blurred vision, and slowed reaction times. The most dangerous condition, heat stroke, is a medical emergency requiring immediate cooling and hospitalization.
Experts note that older workers, those with chronic conditions, or those who are less physically fit are at even greater risk. Kenny warned that the cumulative effect of heat across a workweek diminishes the body’s ability to recover, leaving workers more compromised by Friday than they were at the start of the week.
The WHO/WMO report calls for a fundamental shift in how societies protect workers from climate change-driven heat. Beyond immediate coping strategies, Dr. Lem stressed that cutting greenhouse gas emissions and reducing fossil fuel use remain the most effective long-term solutions to safeguard workers’ health while improving air quality.
“This isn’t just about adapting to extreme heat,” Lem said. “It’s about tackling the root causes of climate change to keep workers safe now and in the future.”