Extreme heat under global warming is a concerning issue for the growing tropical population. However, model projections of extreme temperatures, a widely used metric for extreme heat, are uncertain on regional scales. In addition, humidity needs to be taken into account to estimate the health impact of extreme heat. Here we show that an integrated temperature–humidity metric for the health impact of heat, namely, the extreme wet-bulb temperature (TW), is controlled by established atmospheric dynamics and thus can be robustly projected on regional scales. For each 1 °C of tropical mean warming, global climate models project extreme TW (the annual maximum of daily mean or 3-hourly values) to increase roughly uniformly between 20° S and 20° N latitude by about 1 °C. This projection is consistent with theoretical expectation based on tropical atmospheric dynamics, and observations over the past 40 years, which gives confidence to the model projection. For a 1.5 °C warmer world, the probable (66% confidence interval) increase of regional extreme TW is projected to be 1.33–1.49 °C, whereas the uncertainty of projected extreme temperatures is 3.7 times as large. These results suggest that limiting global warming to 1.5 °C will prevent most of the tropics from reaching a TW of 35 °C, the limit of human adaptation.

全球变暖下的极端高温是热带人口不断增长的一个令人担忧的问题。然而，极端温度的模型预测（一种广泛使用的极端高温指标）在区域尺度上是不确定的。此外，需要考虑湿度来估计极端高温对健康的影响。在这里，我们展示了用于热对健康影响的综合温湿度指标，即极端湿球温度 (TW)，由已建立的大气动力学控制，因此可以在区域尺度上稳健地预测。对于热带平均升温 1 °C，全球气候模型预测极端 TW（日平均值或 3 小时值的年最大值）在 20° S 和 20° N 纬度之间大致均匀地增加约 1°C。该预测与基于热带大气动力学的理论预测和过去 40 年的观测结果一致，这为模型预测提供了信心。对于一个升温 1.5°C 的世界，区域极端 TW 的可能增加（66% 置信区间）预计为 1.33–1.49°C，而预计极端温度的不确定性是 3.7 倍。这些结果表明，将全球变暖限制在 1.5°C 将阻止大多数热带地区达到 35°C 的 TW，即人类适应的极限。7倍大。这些结果表明，将全球变暖限制在 1.5°C 将阻止大多数热带地区达到 35°C 的 TW，即人类适应的极限。7倍大。这些结果表明，将全球变暖限制在 1.5°C 将阻止大多数热带地区达到 35°C 的 TW，即人类适应的极限。