Introduction.- Atmospheric Changes and Observations.- Atmospheric Changes and Observations.- GNSS Ionospheric Sounding.- Detection methods for ionospheric disturbances.- Seismic lower-atmospheric anomalies.- Pre-seismic Ionospheric Anomalies.- Co-/Post-seismic Ionospheric Disturbances.- Two-mode seismo-ionospheric disturbances.- Seismo-ionospheric Rayleigh waves.- Epicenter from Ionospheric Disturbances.- Tsunami Ionospheric Disturbances.- Volcano Atmospheric Disturbances.- Volcanic Plumes Detection from GNSS SNR.- Summary and Prospective.- Index.