Global heating has "fundamentally altered" the climate of Mecca, exposing millions of hajj pilgrims to extreme and dangerous heat even in months outside summer, according to a new analysis. The study reveals that carbon dioxide emissions from fossil fuels mean scorching temperatures of 40C (104F) are now regularly experienced in May, whereas in past decades such peaks only occurred in summer.
Impact of Climate Change on Hajj
The researchers warn that without a rapid transition away from fossil fuels, the hajj—the annual Islamic pilgrimage to Mecca—will take place amid dangerous heat almost all year round by the end of the century. Saudi Arabia, the host country, is the world's second biggest oil producer and has been a long-term obstructer of climate action.
Muslims around the world are currently celebrating Eid al-Adha as devotees in Mecca complete their rituals during this year's pilgrimage. The hajj follows the Islamic lunar calendar, which causes it to fall earlier each successive year. All Muslims who are able are expected to make the pilgrimage at least once in their lives, which involves walking long distances outdoors over five days.
Record Heat and Fatalities
In 2024, when hajj occurred in June, more than 1,300 pilgrims died due to extreme heat and humidity. Historically, May has been cooler, with 40C temperatures being rare. However, the analysis found that 40C is now expected in May once every two to three years as a result of the climate crisis.
The average temperature for May is now 3.5C hotter than before human-caused global heating. Scientists from the World Weather Attribution group stated that hajj in May "is now as dangerous as the height of summer used to be."
Current Mitigation Measures
The Saudi authorities have implemented heat action plans, including shaded walkways, cooling stations, misting systems, and expanded medical services. These measures have helped reduce cases of heat-related illnesses among pilgrims. However, Prof Friederike Otto at Imperial College London, an author of the study, emphasized: "This requires more than just reactive mitigation. If we don't rapidly reduce our dependence on fossil fuels—an industry at the very centre of the Saudi economy—we are resigning ourselves to the fact that millions of Muslims will be forced to carry out the hajj rituals in a climate that is simply unsuitable for it."
Dr Clair Barnes, also at Imperial College London, added: "Our analysis shows very clearly that less of the year is now safe for the millions of Muslims who wish to undertake the hajj. As long as we continue to burn fossil fuels, the window for bearable hajj temperatures will continue to shrink."
The Lunar Calendar and Future Risks
The hajj pilgrimage to Mecca is one of the five pillars of Islam. The Islamic lunar calendar is 10–11 days shorter than the solar Gregorian calendar, causing the dates of hajj to shift earlier each year relative to the seasons. Over a cycle of about 33 years, hajj moves through every season.
A 2022 study found that if global temperatures rise by 3C by the end of the century—in line with the current trajectory of the world's climate policies—about 97% of all hajj pilgrimages would endure dangerous levels of heat in Mecca. The Imperial researchers concluded: "Thus, a rapid transition away from fossil fuels is essential to avoid ever more dangerous hajj."
Dr Emmanuel Raju at the Copenhagen Centre for Disaster Research commented: "Extreme heat during the hajj presents a unique humanitarian challenge because it involves millions of people moving through an outdoor environment for days on end. Measures like misting fans and water stations are vital, but we must face the reality that if temperatures continue to climb at this pace, the health and lives of millions during their pilgrimage is at risk."
The Ministry of Hajj and Umrah in Saudi Arabia was contacted for comment.
