Late in this century, some regions along the coast of the Persian Gulf may experience heat waves that are literally intolerable, climate simulations suggest. If increases in emissions of carbon dioxide continue unabated, concentrations of the planet-warming gas will reach about 940 parts per million (ppm) at the end of the century, researchers estimate. (For comparison, before the Industrial Revolution began in the late 1700s, natural concentrations of CO 2 were about 280 ppm.) Under such conditions, high temperatures in Kuwait City will top 60°C (140°F) during the summer months in some years between 2071 and 2100, the researchers report online today in Nature Climate Change. Moreover, temperatures exceeding 45°C (113°F) will be routine for many of the low-lying cities around the Persian Gulf. These sweltering conditions, when combined with the relatively high humidity typically found in coastal areas surrounding the gulf, can easily be fatal, the researchers say: In many cities of the region, including Dubai, United Arab Emirates (skyline shown); Doha; and Bandar Abbas, Iran, one measure of mugginess (which considers a combination of heat and humidity measured over a 6-hour period) will become so high outdoors that even young, healthy people will have difficulty sweating to shed body heat, never mind the threat to children and elderly people with lower heat tolerance. Another way to look at this region’s future climate, the team notes: Extreme temperatures that are now seen only three times per summer, on average, will become normal and occur, on average, every other day in the summers between 2071 to 2100.