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.
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CMIP5 model data provided by the World Climate Research Programme’s Working Group on Coupled Modelling, and climate modelling groups can be accessed at https://esgf-node.llnl.gov/projects/cmip5. ERA-Interim data provided by European Centre for Medium-Range Weather Forecast (ECMWF) can be accessed at http://go.nature.com/3piVLPO. HadISD global sub-daily station dataset (v184.108.40.206909p) provided by Met Office Hadley Centre can be accessed at https://www.metoffice.gov.uk/hadobs/hadisd. HadISST data provided by the Met Office Hadley Centre can be accessed at https://www.metoffice.gov.uk/hadobs/hadisst.
The computer code used in this paper is available from the corresponding author.
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Y.Z. thanks J. Lin and G. Vecchi for suggestions on the manuscript. Y.Z. acknowledges support under award NA18OAR4320123 from the National Oceanic and Atmospheric Administration, US Department of Commerce (the statements, findings, conclusions, and recommendations are those of the author and do not necessarily reflect the views of the National Oceanic and Atmospheric Administration or the US Department of Commerce). S.F. acknowledges support from National Science Foundation under award AGS-1733818.
The authors declare no competing interests.
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Zhang, Y., Held, I. & Fueglistaler, S. Projections of tropical heat stress constrained by atmospheric dynamics. Nat. Geosci. 14, 133–137 (2021). https://doi.org/10.1038/s41561-021-00695-3
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