Global warming drives a rise in clear-air turbulence in the upper atmosphere. This increase poses growing safety risks and operational challenges for aviation worldwide. This article summarizes the major findings from a recent study by Joana de Medeiros and Paul D. Williams at the University of Reading, published in the Journal of the Atmospheric Sciences.

Climate Change and Turbulence: What’s Happening?

Recent climate models show that vertical wind shear—the difference in wind speed at flight altitudes—is strengthening. This effect stands out in the jet stream at 250 hPa altitude. Importantly, over the period 2015–2100, models project that wind shear will increase by 16–27% in some areas under high-emission scenarios. Such shifts create conditions that favor clear-air turbulence, the invisible and unexpected bumpy air that aircraft encounter.

What is Clear Air Turbulence (CAT)?

Clear-air turbulence (CAT) is a turbulent movement of air that occurs in cloudless skies, making it invisible to pilots and radar systems. The primary cause is wind shear, which is a significant difference in wind speed or direction over a short distance. This phenomenon is most common at high altitudes, typically above 15,000 feet, especially near the edges of powerful jet streams. The friction between the fast-moving air within the jet stream and the slower surrounding air mass creates eddies and chaotic air movement. Other factors that can generate CAT include atmospheric waves created by strong winds flowing over mountain ranges (mountain waves) and sharp temperature gradients between different air masses.

The Richardson Number Explains Turbulence Risk

A key measure called the Richardson number (Ri) gauges atmospheric stability. When $Ri$ values drop, the atmosphere becomes unstable, raising turbulence risk. The study finds that Ri could decrease by as much as 47% in the Northern Hemisphere mid-latitudes and 69% in the Southern Hemisphere under high emissions. This decline occurs alongside a reduction in atmospheric stability , further increasing turbulence danger at cruising altitudes.

Jet Stream Changes Worldwide

Both the Northern and Southern Hemispheres will experience stronger wind shear and shifting temperature patterns. Arctic warming and tropical upper-atmosphere heating drive these changes. Seasonal variations cause turbulence risks to peak during Northern Hemisphere winters, when patterns briefly resemble those seen in the Southern Hemisphere. These dynamics will affect many mid-latitude flight routes, increasing the likelihood that pilots encounter turbulence.

What This Means for Aviation

Turbulence already causes over 70% of weather-related aviation incidents, leading to injuries and costly disruptions. As turbulence becomes more frequent and severe, pilots will need to keep seatbelt signs illuminated longer. Cabin service might face more interruptions, and flights may require rerouting to avoid unstable areas. Airlines must improve turbulence forecasting and update safety procedures to better protect crews and passengers.

To read the official publication by Joana de Medeiros & Paul D. Williams : click here