Precession-forced asymmetric continental heating shapes ENSO variability

Abstract. Geologic and modelling evidence reveals that the ENSO is strongly affected by the precession of the Earth’s rotation axis, yet the mechanisms remain unclear due to interactions among multiple forcings. Using high-resolution model simulations reconstructing the ENSO activity across a full precessional cycle, we find that ENSO is strongest during austral summer perihelion, as today. This behavior arises from asymmetric continental heating: austral summer perihelion introduces strong warming on Australia, east of the Indo-Pacific ITCZ. Because deep convection favors the warmest areas, this causes the ITCZ and the Warm Pool to shift eastwards. As a result, the Pacific’s east-west thermal contrast is reduced, lowering the threshold for oscillations of convection and amplifying ENSO activity. In contrast, boreal summer perihelion warms Afro-Eurasia, shifts the ITCZ westward and weakens ENSO. Proxy records across the Indo-Pacific support this changes in climate state. Understanding asymmetric continental heating helps us link astronomical modulation to ENSO behavior and improve long-term predictions of tropical climate change.