Simulation of Glacial Cycles with an Earth System Model

It is generally accepted that, as postulated by the Milankovitch theory, variations of the Earth’s orbital parameters play a fundamental role in driving glacial cycles. However, many aspects of glacial climate variability, such as strongly nonlinear response of the ice sheets to orbital forcing and the role of carbon-dioxide climate ice-sheet feedback, still remain poorly understood. In recent years, it became increasingly clear that solving of the glacial cycle problem requires application of comprehensive Earth system models. Here we use the Earth system model of intermediate complexity CLIMBER-2 to simulate the last eight glacial cycles. The model was forced by variations of the Earth’s orbital parameters and atmospheric concentration of the major greenhouse gases. Simulated temporal dynamics of ice volume and other climate characteristics agree favorably with the paleoclimate reconstructions. Additional experiments performed with fixed concentrations of the greenhouse gases demonstrate that the 100-kiloyear cyclicity appears even in model simulations with constant greenhouse forcing as a direct and strongly nonlinear response to orbital variations. However, the simulated 100-kiloyear cyclicity is much weaker with constant CO₂, which suggests that the carbon-dioxide climate ice-sheet feedback strongly amplifies the 100-kiloyear cycles. Our experiments also reveal the important role of eolian dust in shaping of glacial cycles and, especially, glacial terminations. Simulations with fully interactive carbon and dust cycle models are required for a better understanding of Quaternary climate dynamics.