The relative role of orbital forcing, CO2 and ice sheet feedbacks on Quaternary climate

Abstract During the Quaternary (the last 2.58 million years), Earth’s climate has fluctuated between a series of glacials and interglacials, paced by external forcings and mediated by internal feedbacks. Global Climate Models (GCMs) resolving the general circulations of the atmosphere and the oceans are useful for addressing the mechanisms associated with these variations; however, such models require substantial computational resources, meaning they are not suitable for exploring transient orbital-scale variability on million-year timescales. Here, to overcome this limitation, we use a climate model to calibrate a faster statistical model, or emulator, and apply this to the Quaternary. Firstly a model-data comparison suggests a good agreement with proxy data over the last 800,000 years, especially concerning the timing of glacial-interglacial cycles, and to achieve these results takes several orders of magnitude less computational cost. The efficiency of this approach allows us to carry out a quasi-transient simulation through the entire Quaternary, and allows projections of possible future drilling results from deep Antarctic ice cores; for example, beyond the existing record of 800,000 years the simulation suggests more frequent glacial-interglacial cycles but less of a temperature range between each cycle. Secondly, an investigation into the primary driving components suggests that a combination of the CO2 forcing and ice sheet feedbacks provide the dominant contribution to the temperature signal, both globally and at individual sites of existing proxy data.