A Nature Climate Change study used ERA5 reanalysis from 1940 to 2025 and found robust increases in atmospheric-duct occurrence probability, strength and top height over mid- and low-latitude oceans. Atmospheric ducts form from unusual refractivity gradients and trap electromagnetic energy within certain layers. They can extend beyond-line-of-sight propagation but also create blind zones, clutter and ranges that standard models do not predict. The sustained warming and increased static stability of the marine boundary layer explain the long-term shift; interannual modes such as El Niño modulate anomalies but do not dominate the trend. The result matters directly for ship communication, radar, navigation and maritime safety, while system-level impact still depends on regional weather and equipment frequency.