millions of Muslims will be forced to perform their religious obligations in a climate simply unsuitable for human activity
For centuries, the hajj pilgrimage has stood as one of humanity's great acts of collective devotion — a journey undertaken by millions in fulfillment of a sacred obligation. Now, the planet's warming atmosphere is quietly closing the window in which that journey can be safely made. Researchers at Imperial College London have found that temperatures once confined to Mecca's peak summer now arrive in May with alarming regularity, driven entirely by fossil fuel emissions, and that more than 1,300 pilgrims died from heat in 2024 alone. The question being raised is not merely one of public health, but of whether the conditions for religious life itself can survive the consequences of how the modern world produces its energy.
- Temperatures of 40°C now strike Mecca in May every two to three years — heat that was historically rare in that month and that turns a five-day outdoor pilgrimage into a life-threatening ordeal.
- More than 1,300 pilgrims died during the 2024 hajj season, a death toll that arrived even as Saudi Arabia deployed cooling stations, misting systems, and expanded medical infrastructure across pilgrimage routes.
- The lunar calendar means hajj rotates through every season over a 33-year cycle, so the pilgrimage cannot simply be rescheduled — millions will inevitably face the months now becoming the most dangerous.
- Saudi Arabia, the world's second-largest oil producer and the nation that hosts and profits from hajj, sits at the center of a sharp irony: its economic foundations are accelerating the very crisis threatening the pilgrimage it stewards.
- Without a rapid transition away from fossil fuels, researchers project that 97% of all future hajj pilgrimages could occur under dangerous heat conditions by century's end, threatening a religious obligation for over a billion people.
The hajj pilgrimage — one of Islam's five central obligations — is being reshaped by a force its practitioners did not create. A new analysis from Imperial College London has found that temperatures of 40 degrees Celsius now occur in Mecca during May roughly once every two to three years, compared to historically rare appearances. May temperatures have climbed 3.5 degrees above their pre-industrial baseline, a shift driven entirely by carbon dioxide emissions from fossil fuels. The pilgrimage's timing, governed by the Islamic lunar calendar, has pushed hajj into months that are becoming increasingly hostile to human life outdoors.
The human cost is already being counted. In 2024, more than 1,300 pilgrims died from extreme heat and humidity during the June pilgrimage, even as Saudi Arabia deployed shaded walkways, cooling stations, and misting systems along pilgrimage routes. Researchers from the World Weather Attribution group concluded that May in Mecca now carries the same danger as peak summer once did. Professor Friederike Otto framed the stakes plainly: without a rapid departure from fossil fuels, millions of Muslims will be compelled to fulfill their religious obligations in a climate no longer suited to human activity.
The irony embedded in the crisis is difficult to ignore. Saudi Arabia, which hosts hajj and draws enormous significance from its role as guardian of the pilgrimage, is also the world's second-largest oil producer and has historically resisted global climate action. The lunar calendar offers no escape route — over its 33-year cycle, hajj will rotate through every season, meaning no permanent scheduling solution exists.
The projections leave little room for comfort. On a trajectory of 3 degrees Celsius of global warming by century's end — consistent with current climate policies — roughly 97 percent of all hajj pilgrimages would unfold under dangerous heat conditions. Dr. Clair Barnes noted the safe window is shrinking each year. Dr. Emmanuel Raju of the Copenhagen Centre for Disaster Research underscored the scale of the humanitarian challenge: millions of people moving through open environments for days at a time cannot be protected by misting fans alone. The researchers were unambiguous — only a genuine transition away from fossil fuels can halt the contraction of the conditions under which this ancient obligation can be safely kept.
The climate of Mecca has shifted so fundamentally that the hajj pilgrimage—one of Islam's five central obligations—is becoming a test of human endurance in ways it never was before. Temperatures that once arrived only in the height of summer now appear regularly in May, when the Islamic lunar calendar has pushed the pilgrimage earlier in the year. A new analysis from researchers at Imperial College London found that 40 degrees Celsius, or 104 Fahrenheit, now occurs in May roughly once every two to three years. Historically, such heat was rare in that month. The shift is not gradual or subtle: May temperatures have risen 3.5 degrees Celsius above their pre-industrial baseline, a change driven entirely by carbon dioxide emissions from fossil fuels.
The human toll is already visible. In 2024, when hajj fell in June, more than 1,300 pilgrims died from extreme heat and humidity. That number arrived despite Saudi Arabia's efforts to manage the crisis—shaded walkways, cooling stations, misting systems, and expanded medical services now dot the pilgrimage routes. Yet these measures, while necessary, address only the symptom. The underlying problem is that the window of survivable temperatures for hajj is closing year by year.
For Muslims worldwide, hajj is not optional for those able to undertake it. The pilgrimage involves walking long distances outdoors over five days, a physical ordeal that becomes genuinely dangerous when ambient heat reaches the levels now common in Mecca. The timing of hajj shifts because it follows the Islamic lunar calendar, which is 10 to 11 days shorter than the Gregorian calendar. Over a cycle of roughly 33 years, hajj rotates through every season. This means that in coming decades, the pilgrimage will increasingly fall during months that are now becoming unsurvivable.
Researchers from the World Weather Attribution group concluded that hajj in May is now as dangerous as the height of summer used to be. Professor Friederike Otto of Imperial College London, one of the study's authors, framed the problem starkly: without a rapid shift away from fossil fuels, millions of Muslims will be forced to perform their religious obligations in a climate simply unsuitable for human activity. The irony is sharp. Saudi Arabia, which hosts hajj and profits enormously from the pilgrimage's spiritual significance, is the world's second-largest oil producer and has historically obstructed global climate action.
The projections are grim. If global temperatures rise by 3 degrees Celsius by the end of the century—a trajectory consistent with current climate policies—roughly 97 percent of all hajj pilgrimages would occur under dangerous heat conditions. Dr. Clair Barnes, also at Imperial College London, noted that the safe window for hajj temperatures is shrinking with each passing year. As long as fossil fuel burning continues, that window will keep contracting.
Dr. Emmanuel Raju of the Copenhagen Centre for Disaster Research emphasized the unique humanitarian dimension of the crisis. Hajj involves millions of people moving through outdoor environments for days on end—a scale and duration that makes heat mitigation extraordinarily difficult. Misting fans and water stations help, but they cannot solve a problem rooted in the planet's warming atmosphere. The researchers were clear: a rapid transition away from fossil fuels is essential. Without it, the health and lives of millions during their pilgrimage will remain at escalating risk, year after year, as the climate continues its shift.
Citações Notáveis
If we don't rapidly reduce our dependence on fossil fuels, 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.— Professor Friederike Otto, Imperial College London
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.— Dr. Clair Barnes, Imperial College London
A Conversa do Hearth Outra perspectiva sobre a história
Why does the timing of hajj matter so much to this story?
Because hajj follows the lunar calendar, not the solar one. It shifts earlier by about ten days each year. So over 33 years, it rotates through every season. Right now it's moving into months that used to be cooler. May used to be safe. Now 40 degrees Celsius happens there regularly.
And that's the trap—the pilgrimage can't be moved to a cooler time, because the date is fixed by Islamic tradition.
Exactly. Muslims are obligated to go when hajj falls. They can't wait for a better season. So as the climate warms, more and more pilgrims will be forced to endure dangerous heat during months they historically would have avoided.
Saudi Arabia profits from hosting hajj, but also profits from oil. That seems like a conflict.
It's more than a conflict. Saudi Arabia is the world's second-largest oil producer. The economy depends on fossil fuels. So the country that hosts the pilgrimage is also one of the biggest obstacles to the climate action that would make the pilgrimage safer.
The cooling stations and misting systems—are those not enough?
They help reduce heat-related illness. But they're treating the symptom, not the cause. If the ambient temperature keeps rising, no amount of water stations will make it safe for millions of people walking outdoors for five days straight.
What does 97 percent of pilgrimages facing dangerous heat actually mean?
It means that by the end of the century, if we stay on our current path, almost every hajj will be a health crisis. The pilgrimage becomes not just difficult but genuinely unsafe for the elderly, the young, the already ill. It becomes a test of survival, not faith.
Is there any scenario where this gets better?
Only if there's a rapid, large-scale shift away from fossil fuels. The researchers are clear about that. Without it, the window of safe temperatures for hajj keeps shrinking until there almost isn't one.