Future Trends in Upper-Atmospheric Shear Instability from Climate Change

Understanding how jet streams respond to a warming climate is crucial for anticipating changes in atmospheric circulation and their broader impacts. Previous studies have highlighted the influence of anthropogenic warming on the meridional temperature gradient, which directly affects jet stream dynamics and variability. This study investigates projected trends in upper-level jet stream shear instability under future climate change scenarios using CMIP6 multi-model simulations. Building on previous findings linking anthropogenic warming to strengthened meridional temperature gradients, we analyse annual means of zonal wind speed, vertical wind shear, and stratification profiles from 2015 to 2100 globally. Results show strengthened multi model annual-mean vertical shear at 250 hPa, particularly in high-emission scenarios, with trends ranging from 0.04 to 0.11 m s⁻¹ (100 hPa)⁻¹ decade⁻¹ depending on the scenario, and region (a total relative increase of 16 - 27% over 86 years). Decreasing trends are observed in the annual-mean Brunt-Väisälä frequency (N²) at 250 hPa, with multi-model ensemble mean values across regions ranging from -0.018 to -0.040 × 10⁻⁴ s⁻² decade⁻¹ for lower and higher emissions scenarios, respectively (a total relative decrease of -10 to -20%). Similarly, the Richardson number (Ri) shows decreasing trends of -0.014 to -0.050 decade⁻¹ across emissions scenarios and regions (a total relative decrease of -38 to -47%). These findings suggest an increased likelihood of more favourable conditions for stronger and more frequent Clear-Air Turbulence (CAT), posing critical challenges for aviation safety and operations in a warming climate.