The Sun-Earth system changes on timescales from decades
to millennia. Solar activity has declined from the twentieth-century
Grand Maximum, geomagnetic activity has followed with its own lag and
response, and the coupled magnetosphere-ionosphere-thermosphere
system responds to these drivers while also undergoing anthropogenic
change from increasing greenhouse gases and ozone recovery.
Disentangling these trends and their interactions is essential for
understanding the long-term behaviour of the heliosphere and for
interpreting historical, proxy, and instrumental records.

This session brings together the communities studying long-term change
across all sub-systems of Sun-to-planet interactions. We invite
contributions on: secular variability of solar activity, irradiance
and magnetic field, including proxy reconstructions and the
solar-stellar connection; the long-term evolution of the solar wind,
heliospheric magnetic field, and cosmic-ray modulation; centennial
trends in geomagnetic activity and solar-terrestrial coupling; trends
in the ionosphere, thermosphere and mesosphere and their separation
into solar, geomagnetic, and anthropogenic components; and the
multi-cycle response of planetary upper atmospheres and ionospheres,
notably at Mars and Venus, as revealed by long-lived orbiter missions.
Observational, proxy-based, and modelling studies are welcome, as are
contributions on data homogeneity and trend-detection methodology.
Contributions from international working groups and programmes addressing long-term trends in solar-terrestrial relations (e.g. SCOSTEP, IAU, ISSI) are particularly welcome.