Amongst heightened awareness of CAT as a phenomenon, there has been a growing conversation around whether CAT events are becoming more common, and if climate change is a driver of these events. The apparent increase in incidents aligns with scientific observations and projections that climate change is intensifying atmospheric conditions conducive to CAT, making it a pressing issue for aviation safety. Let’s take a look. What causes Clear Air Turbulence?The primary cause of CAT is wind shear, which is a difference in wind speed or direction over a short distance in the atmosphere. When fast-moving air currents, such as those found in jet streams, come into contact with slower moving air, the resulting friction can create turbulence. This is particularly common around the tropopause, the boundary layer between the troposphere and the stratosphere, at altitudes between 7,000 and 12,000 meters (23,000 to 39,000 feet).Several factors contribute to the formation of CAT.Jet Streams: Jet streams are narrow bands of strong wind in the upper levels of the atmosphere. These winds can reach speeds of over 160 kilometers per hour (100 miles per hour). The edges of these streams often experience significant wind shear, which can lead to turbulence. Temperature Gradients: Sharp changes in temperature can cause changes in air density, which in turn can lead to turbulence. For instance, the temperature difference between the warm air in the jet stream and the colder surrounding air can contribute to instability. Mountain Waves: When strong winds blow over mountain ranges, they can create waves in the atmosphere that propagate upwards. These waves can become turbulent, especially if the air is stable and the wind is strong and steady. Atmospheric Circulation: Large-scale atmospheric circulations, such as the Rossby waves and the Coriolis effect, also play a role in the formation of CAT by causing the jet stream to meander, creating regions of intense wind shear.