Modeling Earth's future mantle convection with evolving surface temperature

Earth is the only known rocky planet to have sustained long-lived plate tectonics, a type of mobile lid regime that has profoundly influenced our planet's mantle cooling, volatile cycling, crustal recycling, and long-term surface habitability. Because present-day surface heat loss exceeds the combined contributions from radiogenic heating and basal heat supplied from the core, Earth’s mantle is not in thermal steady state and continues to cool. Progressive decline of internal heat sources is therefore expected to reduce convective vigor, thicken the lithosphere, and eventually weaken the stresses required to sustain subduction and mobile-lid tectonics. Yet Earth’s future tectonic evolution will not be governed by interior cooling alone. As the Sun continues to brighten during its main-sequence evolution, increasing stellar flux at Earth may drive substantial long-term surface warming through atmospheric and climate feedbacks. Rising surface temperature modifies the upper thermal boundary condition of mantle convection, alters lithospheric temperature gradients, and may partly counteract cooling-induced lithospheric strengthening.

Here we investigate the coupled long-term future of Earth’s mantle dynamics and surface boundary conditions by linking stellar evolution calculations to geodynamic mantle convection models. We first compute the future luminosity evolution of a solar-mass star using established stellar evolutionary tracks calibrated to reproduce the present Sun, and derive the corresponding changes in incident flux at Earth’s orbit and equilibrium surface temperature through time. These calculations are used to construct time-dependent surface temperature scenarios that span moderate warming associated with continued solar brightening and stronger warming cases that approximate amplified greenhouse evolution. We then apply these boundary conditions to two-dimensional spherical annulus thermochemical mantle convection simulations using the geodynamic code StagYY. All models begin from a reference case that reproduces first-order present-day Earth conditions after 4.5 Gyr of evolution, including realistic mantle thermal structure, plate-like surface mobility, and geologically plausible plate velocities. From this present-day state, simulations are extended for a further 8 Gyr under contrasting surface temperature pathways, allowing direct comparison of tectonic longevity, mantle cooling rates, volcanic productivity, and lithospheric behavior.

In the constant-temperature reference future, Earth remains tectonically active for several billion years, but convection steadily weakens as radiogenic heating and core heat flux decline. Mantle plumes and subduction downwellings become less frequent, thermal boundary layers thicken, and surface mobility gradually slows. These results support the view that mobile-lid tectonics on Earth is unlikely to persist indefinitely in the absence of renewed internal energy sources.

When solar-driven warming is imposed, the long-term tectonic trajectory changes. Increasing surface temperature reduces the viscosity contrast across the lithosphere and weakens the near-surface thermal lid. In moderately warmed scenarios, sluggish-lid tectonics develops sooner and is accompanied by enhanced intrusive magmatism. In stronger warming scenarios, plate tectonics is sustained only for a limited time after which transitions to sluggish-lid and ultimately stagnant-lid regimes occur earlier than in the reference case. The different evolutionary pathways are quantitatively compared in terms of tectonic mobility, mantle cooling, magmatic productivity, and lithospheric behavior.

Our results imply that Earth’s tectonic future depends on a balance between diminishing internal heat production, core cooling, and increasing stellar forcing. More broadly, these findings demonstrate that tectonic regime evolution on rocky planets cannot be inferred from interior properties alone. Stellar age, luminosity evolution, and planetary climate history exert control on whether planets maintain mobile lids, transition to stagnant lids, or occupy intermediate states. This has direct relevance for interpreting Earth-like exoplanets observed at different evolutionary stages, as well as Venus and Venus-like worlds, where strong stellar forcing, elevated surface temperatures, and uncertain tectonic histories may fundamentally shape mantle dynamics, volcanic resurfacing, and long-term (in)habitability.