Local insolation dominates the global land monsoon precipitation on orbital timescales

Orbital-scale monsoon variability exhibits a strong response to orbital insolation forcing. However, previous studies attributing monsoon behavior to either local insolation from the same hemisphere or remote insolation from the opposite hemisphere have largely relied on qualitative in-phase relationships between monsoon intensity and insolation. In this study, we perform transient simulations that isolate Northern Hemisphere (NH) and Southern Hemisphere (SH) insolation over the past 150,000 years to assess their respective contributions to global land monsoon precipitation variations. These include the North American monsoon, the northern African monsoon, the Asian monsoon (including the South Asia and East Asia), the Australian monsoon, the South American monsoon, and the southern African monsoon. Overall, our model simulations produce regional climate changes that are generally consistent with observations. We demonstrate that the phase and magnitude of precipitation over northern Africa and East Asia respond directly to local summer insolation. In other monsoon regions, both NH and SH insolation contribute to land precipitation changes, but with opposite effects. Nevertheless, local insolation dominates over the remote insolation effect, resulting in net precipitation variations that remain in phase with local summer insolation. This work helps reconcile the ongoing debate over whether the monsoon is driven by NH or SH insolation, as previously suggested by proxy records.