Projections of Tropical Heat Stress Constrained by Atmospheric Dynamics

Thursday, Mar 11, 2021
Congratulations to AOS Graduate Student Yi Zhang, whose paper published online March 8 in Nature Geoscience has been featured in the New York Times, The Guardian and other media. Together with AOS Senior Meteorologist Isaac Held and AOS Director Stephan Fueglistaler, Yi Zhang addresses the problem of heat stress in the tropics in a warming world.

Humans’ ability to regulate body heat is dependent on the temperature and humidity of the surrounding air, and heat stress will occur when it is too hot and humid. There exists an upper survival limit, beyond which humans are no longer able to effectively cool themselves. This threshold is reached when the wet-bulb temperature — a measure of air temperature and humidity — passes 35 °C. There is concern that ongoing climate warming could result in extreme heat events that exceed this limit.
Yi Zhang and co-authors find that relatively simple atmospheric dynamics control the maximum wet-bulb temperatures in the tropical regions between 20°S and 20°N. A combination of theory, observations, and global climate models points to the conclusion that the annual-maximum wet-bulb temperature will increase uniformly by 1°C for each 1°C of tropical mean warming. These findings suggest that limiting global warming to 1.5 °C could prevent tropical regions between 20°S and 20°N of the equator from reaching the limit of human adaptability. However, the authors indicate further research will be needed as serious health impacts can still occur well below this limit.