Climate change is narrowing the safe temperature-humidity window for the annual Hajj pilgrimage in Mecca, Saudi Arabia, according to a new report.

The findings suggest that the intersection of rising global temperatures and humidity is creating an increasingly hazardous environment for millions of worshippers. As the window of tolerable heat shrinks, the risk of heat-stress and heat-related fatalities increases during the performance of sacred rituals.

The report was published Friday by the World Weather Attribution group and experts from the European Geosciences Union. Researchers, including Atta Ullah, said that global heating is pushing conditions beyond the physiological limits of the human body.

This environmental shift reduces the amount of time pilgrims can safely spend outdoors. When humidity is high, the body cannot cool itself through sweat as effectively, which can lead to rapid overheating even at temperatures that might otherwise be manageable.

Scientists said that these dangers are not theoretical. The study references conditions observed during the 2024 pilgrimage, where extreme heat and humidity already pushed human physiological limits [1].

The report indicates that the combination of heat and moisture creates a dangerous synergy. This makes the pilgrimage more hazardous for a diverse global population, many of whom may not be acclimated to the extreme climate of the region.

Researchers said that without mitigation strategies or changes to how the pilgrimage is managed, the risk to human life will continue to grow as global temperatures rise.

“Climate change is narrowing the safe temperature-humidity window for the annual Hajj pilgrimage.”

The narrowing of the 'safe window' implies that the traditional timing and structure of the Hajj may eventually clash with biological survival limits. Because the pilgrimage is tied to a specific lunar calendar, it cannot be easily moved to cooler months, meaning Saudi authorities may need to implement drastic cooling infrastructure or modified schedules to prevent mass casualty heat events.