According to the study, the year 2024 was recorded as the hottest year, where global temperature was 1.5˚C or more above the pre-industrial average for the whole year.
Human-caused climate change added an average of 30 days of extreme heat for about half of the world’s population over the past year. A new report by World Weather Attribution, Climate Central, and the Red Cross Climate Centre found that heatwaves are becoming longer with ongoing fossil fuel burning.
The study takes into account the analysis of over a 12-month period, from May 2024 to May 2025. It showed that in 195 countries and territories, climate change has at least doubled the number of extreme heat days, compared to a world without climate change. It noted that all 67 major heat events in the past year were made more likely by climate change.
Dr Mariam Zachariah of World Weather Attribution said that frequent, intense spells of hot temperatures are associated with a range of impacts, including heat illness, crop losses, lowered productivity, and transport disruptions.
Disproportional and underreported impact
The report highlighted that the impact of extreme heat on other sectors such as water and agriculture, particularly in low- and middle-income countries, remained underrepresented. Among vulnerable populations such as older adults, people with pre-existing medical conditions, extreme heat has increased the cardiovascular strain, respiratory distress, and premature death.
Outdoor workers and people working indoors without cooling face heightened occupational risks including dehydration, heat stress, and reduced productivity. Heat stress has impaired agricultural productivity, reduced water availability, strained health systems, and disrupted energy infrastructure. Heat also compounded with other extremes such as droughts, amplifying the other impacts.
Urban areas are especially vulnerable to stressors like power grid failures, water scarcity, loss of productive wage hours, and increased rates of interpersonal conflict.
Way forward
The study suggested a range of interventions at the individual and systemic levels that had been shown to reduce the health and societal impacts of extreme heat. At the individual level, adjusting strenuous activity to cooler times of day, resting frequently, and staying hydrated. At the household level, low-cost adaptations such as improved ventilation, shading, reflective roofing, and behavioural changes can lower exposure.
City Heat Action Plans (HAPs) have become a key mechanism for coordinating municipal departments, health systems, and emergency responders and are increasingly adopted in cities across South Asia, North America, Europe, and Australia, according to the study.
The study recommended scaling heat-health early warning systems, strengthening emergency health services, incorporating cooling support into social protection programs, and reinforcing critical infrastructure such as water, electricity, and transport systems. Legislative actions — such as updating building codes, enforcing occupational heat safety, and implementing heat-resilient urban design —can further institutionalise risk reduction.
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