Dominance of Obliquity over Precession in Polar Temperature Variability: Insights from an Energy Balance Model

Abstract. The sensitivity of a Zonally Averaged Energy and Moisture BAlance Climate Model (ZEMBA) to changes in the Earth’s orbit is investigated. The model is intended to explore the dynamics of Quaternary glacial-interglacial cycles, particularly the dominance of 41-kyr obliquity cycles in ice volume and ocean temperature during the Early Pleistocene, despite summer insolation being primarily influenced by 19- and 23-kyr precession cycles. Through equilibrium simulations for the Pre-Industrial and Last Interglacial Period, we demonstrate that ZEMBA's response to strong orbital forcing qualitatively matches the behavior of climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6). Transient simulations of ZEMBA over the Early Pleistocene reveal a pronounced 41-kyr cyclicity in surface temperatures at the polar latitudes, in correspondence to variations in the Earth’s obliquity. Sensitivity experiments underscore the essential role of sea ice in driving temperature variability in the polar regions. The dominant 41-kyr cyclicity in surface air temperature is attributed to obliquity’s influence on winter sea ice extent, which governs the release of substantial ocean heat to the atmosphere. The more subdued effect of precession on surface air temperature is linked to the counterbalancing relationship between insolation intensity and summertime duration, which constrains variability in both winter sea ice and ocean heat fluxes.