Global climate simulations at 3000-year intervals for the last 21 000 years with the GENMOM coupled atmosphere-ocean model

Abstract

We apply GENMOM, a coupled atmosphere-ocean climate model, to simulate eight equilibrium time slices at 3000-year intervals for the past 21 000 years forced by changes in Earth-Sun geometry, atmospheric greenhouse gases (GHGs), continental ice sheets, and sea level. Simulated global cooling during the Last Glacial Maximum (LGM) is 3.8 °C and the rate of post-glacial warming is in overall agreement with recently published temperature reconstructions. The greatest rate of warming occurs between 15 and 12 ka (2.4 °C over land, 0.7 °C over oceans, and 1.4 °C globally) in response to changes in radiative forcing from the diminished extent of the Northern Hemisphere (NH) ice sheets and increases in GHGs and NH summer insolation. The modeled LGM and 6 ka temperature and precipitation climatologies are generally consistent with proxy reconstructions, the PMIP2 and PMIP3 simulations, and other paleoclimate data-model analyses. The model does not capture the mid-Holocene "thermal maximum" and gradual cooling to preindustrial (PI) global temperature found in the data. Simulated monsoonal precipitation in North Africa peaks between 12 and 9 ka at values ∼ 50% greater than those of the PI, and Indian monsoonal precipitation peaks at 12 and 9 ka at values ∼ 45% greater than the PI. GENMOM captures the reconstructed LGM extent of NH and Southern Hemisphere (SH) sea ice. The simulated present-day Antarctica Circumpolar Current (ACC) is ∼ 48% weaker than the observed (62 versus 119 Sv). The simulated present-day Atlantic Meridional Overturning Circulation (AMOC) of 19.3 ± 1.4 Sv on the Bermuda Rise (33° N) is comparable with observed value of 18.7 ± 4.8 Sv. AMOC at 33° N is reduced by ∼ 15% during the LGM, and the largest post-glacial increase (∼ 11%) occurs during the 15 ka time slice.