This year’s Hajj in Mecca, Saudi Arabia, could be one of the biggest and hottest in history. More than 2.5 million people have made the pilgrimage — the first without pandemic restrictions — in a region heating twice as fast as the planetary average. Wet bulb temperatures, a metric that reflects heat stress on the human body, in Mecca are nearly 3.6°F (2°C) hotter in Mecca than they were just 30 years ago — an increase largely attributable to climate change. The human impact of the climate-fueled heat is exacerbated by the Islamic calendar and the demographics of Hajj participants.

The dates of the Hajj follow the lunar calendar and as such, the pilgrimage has taken place in Saudi Arabia’s hottest months since 2017 and will continue to do so for the next three years. Hajj participants are also disproportionately elderly, having saved for decades to be able to afford to make the pilgrimage expected of every Muslim who is physically capable and has the financial means at least once in their lifetime. (Heatmap $, AP, Deutsche Welle, AFP via Barron’s; Climate Signals background: Extreme heat and heatwaves)