AI Insight
Researchers have found that the mixing of dry air into rising plumes of warm, moist air—a process called entrainment—significantly influences extreme moist heat events outside tropical regions. Using climate reanalysis data and global climate models, they discovered that this mixing allows near-surface air to become more humid and hot, intensifying wet-bulb temperatures. As the climate warms and the lower atmosphere becomes drier, this mechanism is expected to drive even more severe moist heat extremes in extratropical continental areas.
Why it matters
High wet-bulb temperature events, which combine heat and humidity, pose serious health risks as they impair the body's ability to cool through sweating. Understanding the physical mechanisms driving these extremes will improve predictions of future dangerous heat conditions and help communities prepare for increasingly severe moist heat events as the climate continues to warm.
Understand the Science
Source: Geophysical Research Letters
As climate change has led to more frequent high-heat events around the world, moist heat metrics such as wet-bulb temperature, which combines temperature and humidity, have become increasingly relevant. Days with both high heat and high humidity are dangerous for human health; understanding how these extreme events will change in the future is important.
Jha and Byrne examined moist heat extremes over extratropical continents using ERA5 reanalysis data (the fifth generation of reanalysis from the European Centre for Medium-Range Weather Forecasts) and the Community Earth System Model Version 2 (CESM2) global climate model. They paid special attention to the ways dry air mixes into plumes of warm, moist air traveling upward in convective environments.
The authors simulated varying rates at which dry air mixes into these plumes rising from near Earth’s surface to the upper troposphere and found that this process, known as entrainment, exerts a significant influence on moist heat extremes outside of the tropics. The authors say this process alters the relationship between the amounts of stored energy in the air near the ground and higher up in the troposphere. This mixing of dry air into rising plumes enables the near-surface air to become more energetic through higher humidity and temperature, leading to more severe moist heat events.
Using simulations, the authors found that as climate warms and the lower troposphere becomes drier, the entrainment mechanism will continue to drive up wet-bulb temperatures at the surface, potentially leading to moist heat extremes that are even more severe.
Future work examining in more detail how global warming is changing rates of dry-air entrainment into rising plumes will be useful to better understand how wet-bulb temperatures will increase in the future, the authors say. (Geophysical Research Letters, https://doi.org/10.1029/2026GL122678, 2026)
—Nathaniel Scharping (@nathanielscharp), Science Writer
