The relative role of direct orbital forcing versus CO₂ and ice feedbacks on Quaternary climate

During the Quaternary (the last 2.58 million years), Earth’s climate has fluctuated between glacials and interglacials, paced by external forcings and mediated by internal feedbacks. However, General Circulation Models (GCMs), essential for addressing the mechanisms associated with these fluctuations, require substantial computational resources, meaning they are unsuitable for exploring orbital-scale variability on million-year timescales. Here, we use a GCM to calibrate a faster statistical model, or emulator, and apply this to the Quaternary. We show a good agreement between the emulated climate and proxy data over the last 800,000 years, especially the timing of glacial-interglacial cycles. A series of sensitivity experiments allows us to identify the dominant components driving long-term climate change. The results show that a combination of the CO2 and ice sheet feedbacks provide the dominant contribution to the annual mean temperature signal, with the direct orbital radiative forcing playing only a minor role.