The Working Group (WG) Interglacials of the Paleoclimate Model Intercomparison Project (PMIP) contributes to planning and organizing the model intercomparison within PMIP. Our focus is on orbital time scales, and in particular on warm interglacials. Other PMIP WGs focus on the more recent history of climate (past2k), on the Last Glacial Maximum (lgm 21k), or on periods farther back in time (Pliocene, PlioMIP; Miocene, MioMIP; pre-Miocene climates, DeepMIP). Within PMIP we coordinate work between the different WGs towards creating a framework where model intercomparison can be performed as seamlessly as possible across different time scales.

Modelling setups to be used for the simulations of the WG Interglacials are often rather similar to modern from the viewpoint of paleogeography, and the focus is often on climate forcings like orbital parameters and greenhouse gases. Yet, where necessary and feasible, we consider also geographic changes relevant for shaping the climate on glacial-interglacial time scales, for example by means of modifications to ice sheets.

The aims of the WG Interglacials are twofold: first, we strive to enable exploration of model skill and model uncertainty in the context of warm climates; to this end we provide carefully controlled simulation protocols for a small set of baseline simulations of key climate states like the mid-Holocene and the Last Interglacial.

Second, we see our work as a task towards providing a hub and a laboratory for conducting groundbreaking science - from studying model dependency of simulated climate patterns and modes of variability to exploring reasons for the observed model behavior. To this end, we sample model sensitivity to various forcings and boundary conditions by means of sensitivity studies that are based on, or that extend, the baseline climate simulations.

These two aims call for different, and partly competing, approaches in the simulation design. Tracking the impact of model development on model skill across different generations of climate models necessitates honoring the philosophy that is behind CMIP6 DECK simulations (i.e., protocol and design of key simulations remain unchanged between different iterations of PMIP). On the other hand, enabling interesting science implies that the simulation portfolio is adjusted and extended based on the current state of knowledge. Updates can for example refer to model boundary conditions per most recent inference from proxy data. The simulation design may be adapted towards exploiting recently added model capabilities, like dynamic vegetation or interactive ice sheets.

In PMIP Interglacials we aim to follow both approaches simultaneously. Continuity of simulation design across different iterations of PMIP, and novelty of simulations, are enabled via a protocol that provides a balanced combination of key baseline and extended updated simulations.

Our work in defining the simulation protocol for the next iteration of PMIP is not yet finished, We will inform about the proposed model protocol as soon as possible here on this website. Please refer to our call for involvement in the process of simulation design for the coming iteration of PMIP Interglacials.

Analysis and study of ongoing and already finalized PMIP4 simulations is still ongoing. Yet, as the next phase of CMIP is already being planned, we have also started preparations for the next iteration of PMIP.

Transition from PMIP4 to the next iteration of the Paleoclimate Model intercomparison Project has brought changes to the organization team of the WG Interglacials. The previous lead organizers, Bette Otto-Bliesner (National Center of Climate Research, Boulder, Colorado) and Dan Lunt (University of Bristol, United Kingdom) have passed on the baton to Louise Sime (British Antarctic Survey, Cambridge, United Kingdom) and Christian Stepanek (Alfred Wegener Institute - Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany). Louise and Christian are currently setting up a team of climate scientists who will prepare and organize the next round of PMIP Interglacials. On this occasion we would like to express our heartfelt gratitude to the previous leaders of PMIP Interglacials, who have guided a fruitful intercomparison, and who will still be around in the PMIP Steering Committee and Advisory Board where they support us with their advice and experience.