Over the 21st century, human-caused climate change is projected to vastly increase the occurrence of severe heat, which has deleterious health, economic, and societal impacts. Over the same period, global human population is expected to increase from 7.8 to 10.9 billion, placing more people in harm's way. Here, we combine projections of sustained heat from climate models with spatially explicit population projection scenarios. We find that: (1) by 2090, high climate change and population growth scenarios show a ~5-, ~10-, and ~100–1000-fold increase in the population exposed to a mean hottest monthly temperature of 30 ºC, 35 ºC, and 40 ºC, respectively; (2) globally, population growth, warming, and their interaction, are the major drivers for the increase in exposure at milder, harsher, and extreme, temperatures, respectively; and (3) differences between population growth scenarios show that policy can potentially reduce the level of increase in exposure by up to 70%. Based on our analyses, the major driver for the increased heat exposure is the dangerous combination between global warming and population growth in already-warm cities in regions like Africa, India, and the Middle East.

在 21 世纪，预计人为造成的气候变化将大大增加酷暑的发生率，这对健康、经济和社会造成有害影响。在同一时期，全球人口预计将从 7.8 增加到 109 亿，使更多人处于危险之中。在这里，我们将气候模型的持续热量预测与空间明确的人口预测情景相结合。我们发现：(1) 到 2090 年，高气候变化和人口增长情景显示，暴露于平均最热月度 30 ºC、35 ºC 和 40 ºC，分别；(2) 在全球范围内，人口增长、变暖及其相互作用分别是在更温和、更严酷和极端温度下暴露增加的主要驱动因素；(3) 人口增长情景之间的差异表明，政策有可能将风险增加水平降低多达 70%。根据我们的分析，高温暴露增加的主要驱动因素是全球变暖与非洲、印度和中东等地区已经温暖的城市人口增长之间的危险组合。