Dry air mixing may intensify humid heat, study finds

A new study published in Geophysical Research Letters suggests that dry air in the lower atmosphere may be intensifying humid heat conditions near the Earth's surface. Researchers from the University of St Andrews found that a process known as entrainment—where dry air mixes into rising columns of warm, moist air—weakens these plumes, allowing more heat and moisture to accumulate close to the ground.

This accumulation increases wet-bulb temperatures, which measure the combined effect of heat and humidity and indicate how effectively the human body can cool itself through sweat. By comparing atmospheric data from 1991 to 2020 with climate model simulations, researchers R. Jha and M. P. Byrne demonstrated that removing dry-air mixing from models significantly reduced the predicted occurrence of extreme wet-bulb events, suggesting this hidden process is a critical factor in extreme heat intensity.