Earth’s plate tectonic activity regulates the carbon cycle, and hence, climate, via volcanic outgassing and silicate-rock weathering1,2,3. Mountain building, arc-continent collisions, and clustering of continents in the tropics have all been invoked as controlling the weathering flux4,5,6, with arcs also acting as a major contributor of carbon dioxide (CO2) to the atmosphere7. However, these processes have largely been considered in isolation when in reality they are all tightly coupled. To properly account for the interactions between these processes, and the inherent multi-million-year time lags at play in the Earth system, we need to characterise their complex interdependencies. Here we analyse these interdependencies over the past 400 million years, using a Bayesian network to identify primary relationships, time lags and drivers of the global chemical weathering signal. We find that the spatial extent of continental volcanic arcs — the fastest-eroding surface features on Earth — exerts the strongest control on global chemical weathering fluxes. We find that the rapid drawdown of CO2 tied to arc weathering stabilises surface temperatures over geological time, contrary to the widely held view that this stability8 is achieved mainly by a delicate balance between weathering of the seafloor and the continental interiors.