The risk to Muslim pilgrims embarking on the hajj posed by extreme heat worsened by global warming could increase five-fold with just a 2.7°F (1.5°C) increase over preindustrial levels, a new study in Environmental Research Letters shows. With 4.32°F (2.4°C) of warming, the risk of life threatening heat stroke doubles again. Temperatures in Mecca are expected to hit 111°F (44°C) this week as a COVID-limited 60,000 pilgrims complete the trek. Completing the annual hajj pilgrimage to Islam’s holiest sites in Saudi Arabia is once-in-a-lifetime duty for able-bodied Muslims who can afford it. The extreme heat, and the health risks it poses, “will compromise the very essence of this religion,” Fahad Saeed, lead author of the study, told Thomson Reuters. (Thomson Reuters Foundation; Current temps: Bloomberg $; Climate Signals background: Extreme heat and heatwaves)