The PMIP4 contribution to CMIP6 – Part 4: Scientific objectives and experimental design of the PMIP4-CMIP6 Last Glacial Maximum experiments and PMIP4 sensitivity experiments

Abstract

Abstract. The Last Glacial Maximum (LGM, 21 000 years ago) is one of the suite of paleoclimate simulations included in the current phase of the Coupled Model Intercomparison Project (CMIP6). It is an interval when insolation was similar to the present, but global ice volume was at a maximum, eustatic sea level was at or close to a minimum, greenhouse gas concentrations were lower, atmospheric aerosol loadings were higher than today, and vegetation and landsurface characteristics were different from today. The LGM has been a focus for the Paleoclimate Modelling Intercomparison Project (PMIP) since its inception, and thus many of the problems that might be associated with simulating such a radically different climate are well documented. TheLGM state provides an ideal case study for evaluating climate model performance because the changes in forcing and temperature between the LGM and pre-industrial are of the same order of magnitude as those projected for the end of the 21st century. Thus, the CMIP6 LGM experiment could provide additional information that can be used to constrain estimates of climate sensitivity. The design of the Tier 1 LGM experiment (lgm) includes an assessment of uncertainties in boundary conditions, in particular through the use of different reconstructions of the ice sheets and of the change in dust forcing. Additional (Tier 2) sensitivity experiments have been designed to quantify feedbacks associated with landsurface changes and aerosol loadings, and to isolate the role of individual forcings. Model analysis and evaluation will capitalize on the relative abundance of paleoenvironmental observations and quantitative climate reconstructions already available for the LGM.

The influence of atmospheric grid resolution in a climate model-forced ice sheet simulation

“…Motivated by the official PMIP boundary conditions (e.g., Kageyama et al, 2017), the vegetation cover in non-glaciated areas is prescribed as the modern distribution.…”

“…The planetary boundary conditions are set to reflect LGM conditions, including the orbital parameters and greenhouse gas concentrations outlined by the Paleoclimate Modeling Intercomparison Project (PMIP) (e.g., Kageyama et al, 2017), the ice sheet reconstruction presented by Kleman et al (2013) (raised to the height of the ICE-5G reconstruction, Peltier, 2004, to encourage ice formation in the "correct" areas in SICOPOLIS), and prescribed monthly varying seasurface conditions (LGM sea-surface temperature and seaice extent) from Otto-Bliesner et al (2006). Motivated by the official PMIP boundary conditions (e.g., Kageyama et al, 2017), the vegetation cover in non-glaciated areas is prescribed as the modern distribution.…”

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

“…provide an overview of the five selected time periods and the experiments. More specific information is given in the contributions for the last millennium (past1000) by Jungclaus et al (2017), for the last glacial maximum (lgm) by Kageyama et al (2017), for the mid-Pliocene warm period (midPliocene-eoi400) by Haywood et al (2016), and the present paper the mid-Holocene (midHolocene) and the previous interglacial (lig127k). PMIP4 has adopted the CMIP6 categorization where the highest-priority experiments are classified as Tier 1, whereas additional sensitivity experiments or dedicated studies are Tier 2 or Tier 3.…”

The PMIP4 contribution to CMIP6 – Part 3: The last millennium, scientific objective, and experimental design for the PMIP4 <i>past1000</i> simulations

“…Kageyama et al (2016) provide an overview of the five selected time periods and the experiments. More specific information is given in the contributions for the mid-Holocene (midHolocene) and the previous interglacial (lig127k) by Otto-Bliesner et al (2017), for the last glacial maximum (lgm) by Kageyama et al (2017), and for the mid-Pliocene warm period (midPliocene) by Haywood et al (2016), and the present paper on the last millennium (past1000). PMIP has adopted the CMIP6 categorisation where the highest-priority experiments are classified as Tier 1, whereas additional sensitivity experiments or dedicated studies are Tier 2 or Tier 3.…”