The PMIP4 contribution to CMIP6 – Part 2: Two interglacials, scientific objective and experimental design for Holocene and Last Interglacial simulations

Abstract

Abstract. Two interglacial epochs are included in the suite of Paleoclimate Modeling Intercomparison Project (PMIP4) simulations in the Coupled Model Intercomparison Project (CMIP6). The experimental protocols for simulations of the mid-Holocene (midHolocene, 6000 years before present) and the Last Interglacial (lig127k, 127 000 years before present) are described here. These equilibrium simulations are designed to examine the impact of changes in orbital forcing at times when atmospheric greenhouse gas levels were similar to those of the preindustrial period and the continental configurations were almost identical to modern ones. These simulations test our understanding of the interplay between radiative forcing and atmospheric circulation, and the connections among large-scale and regional climate changes giving rise to phenomena such as land-sea contrast and highlatitude amplification in temperature changes, and responses of the monsoons, as compared to today. They also provide an opportunity, through carefully designed additional sensitivity experiments, to quantify the strength of atmosphere, ocean, cryosphere, and land-surface feedbacks. Sensitivity experiments are proposed to investigate the role of freshwater forcing in triggering abrupt climate changes within interglacial epochs. These feedback experiments naturally lead to a focus on climate evolution during interglacial periods, which will be examined through transient experiments. Analyses of the sensitivity simulations will also focus on interactions between extratropical and tropical circulation, and the relationship between changes in mean climate state and climate variability on annual to multi-decadal timescales. The comparative abundance of paleoenvironmental data and of quantitative climate reconstructions for the Holocene and Last Interglacial make these two epochs ideal candidates for systematic evaluation of model performance, and such comparisons will shed new light on the importance of external feedbacks (e.g., vegetation, dust) and the ability of state-of-the-art models to simulate climate changes realistically.

Ice Sheet Model Intercomparison Project (ISMIP6) contribution to CMIP6

“…The forcing is derived from observations of solar variability and changes in atmospheric composition, including both anthropogenic and volcanic sources (see Appendix A2 of . The more distant past is the focus of PMIP4, which designs paleoclimate experiments (Kageyama et al, 2016;Otto-Bliesner et al, 2016). ISMIP6 collaborates with PMIP4 for experiment lig127k, a simulated time slice of the Last Interglacial (LIG): the warm period from 129 000 to 116 000 years ago when global mean sea level was 5-10 m higher than present (Masson-Delmott et al, 2013).…”

Impact of Multiscale Variability on Last 6,000 Years Indian and West African Monsoon Rain

“…The initial state of each experiment comes from a 1,000-year-long simulation performed with the corresponding model version and the Paleoclimate Modeling Intercomparison Project 6,000 years BP boundary conditions (Kageyama et al, 2018). Then, Earth's orbital parameters and atmospheric composition derived from ice-core reconstructions (Otto-Bliesner et al, 2017) were updated each year from 6,000 ka BP to 0 ka BP (1950 which is the reference for Earth's orbital parameters; Berger, 1978).…”

A Review of Paleo El Niño-Southern Oscillation

“…Recently, water isotope-enabled CGCMs allowing direct model-data comparison of oxygen isotopes have been applied to paleo-ENSO [54][55][56]. Paleo ENSO modeling has benefitted significantly from the Paleoclimate Modelling Intercomparison Project (PMIP) [19] (https:// pmip4.lsce.ipsl.fr/doku.php/exp_design:index) for two periods: the mid-Holocene (MH,~6000 years ago) [57] and the Last Glacial Maximum (LGM,~21,000 years ago) [58]. The MH simulations provide an opportunity to explore ENSO response to orbital forcing, while the LGM simulations focus on ENSO sensitivity to the presence of vast continental ice sheets, reduced greenhouse gas (GHG) concentrations and a generally cold mean climate.…”