How Does Increasing CO ₂ Concentration Affect the Ionospheric Sporadic‐E Formation?

Abstract Increasing CO 2 concentration is known to cause global‐scale changes throughout the atmosphere and ionosphere. However, how the global change affects smaller‐scale ionospheric phenomena remains unclear. This study investigates for the first time the impact of increasing CO 2 on the formation of sporadic‐E layer, a key space weather element links to HF/VHF communications. Using the Ground‐to‐topside model of Atmosphere and Ionosphere for Aeronomy (GAIA), simulations were conducted for normal (315 ppm) and doubled CO 2 (667 ppm) levels to evaluate changes in the vertical ion convergence (VIC). Simulation results reveal that the VIC is enhanced in the 100–120 km altitude range globally. Furthermore, VIC hotspots shift downward by approximately 5 km and exhibit changes in their diurnal pattern. The reduction of the ion‐neutral collision frequency alongside changes in the zonal wind shear contributes significantly to these changes. Our study suggests that, as CO 2 concentrations continue to rise, future Es layers may become more intense, last longer, and form at lower altitudes compared to present‐day conditions. These changes could potentially challenge the reliability of HF communication systems in the future.