The Earth’s crust releases or absorbs heat energy in response to changes in the thermal regime. Numerical simulations of basin-scale heat transport which use the sediment–basement interface as a thermal boundary assume that near-surface temperature changes have no effect on basement rocks and vice versa (unbuffered model). We test this assumption by comparing numerical models of transient fluid flow and heat transport in the Arkoma foreland basin with and without thermal buffering by basement rocks. Thermal buffering by basement rocks reduces cooling (by fresh water recharge) of deep basin sediments near the fold–thrust belt and reduces warming (by upward fluid discharge) of basin margin sediments. The unbuffered model predicts a temporary warming of basin margin sediments which is largely an artefact of the model thermal boundary conditions. In all cases, the buffered model produces no significant thermal transient. Exaggerated temperature predictions also can occur in numerical simulations of uplift and erosion or heat refraction.