Important Timeline
Initial protocol testing and feedback phase: June 2026
Protocol release and data release: July, 2026
Model submission deadline: October 31st, 2026
Analysis and initial manuscript : Winter 2026-Spring 2027
Manuscript submission: Spring-Summer, 2027
Introduction
Redistribution of mass on the Earth's surface induces perturbations in the planet's gravitational and rotational potentials, as well as deformation of the solid surface, collectively referred to as gravitational, rotational, and deformational (GRD) effects. GRD effects occur over a wide range of timescales, from the immediate elastic response to viscoelastic adjustment over tens of thousands of years following surface mass redistribution. The long-timescale viscoelastic adjustment of the solid Earth and the associated sea-level response to glacial loading and unloading are commonly referred to as Glacial Isostatic Adjustment (GIA), which produces distinct sea-level fingerprints that reflect the geometry and timing of ice-mass evolution.
Modeling GIA is essential for inferring the past ice-sheet loading history and the solid Earth structure. It is also crucial for quantifying regional sea-level changes, which often significantly deviate from global mean sea-level trends. Moreover, modern geodetic observations of present-day ice mass changes from satellite gravimetry (e.g. GRACE and GRACE-FO), ice-elevation changes from satellite altimetry, and solid Earth deformation from GNSS require knowledge of ongoing GIA signals resulting from surface mass redistribution over paleo glacial cycles.
However, modeling GIA involves uncertainties related to ice mass history, solid Earth structure and rheology, and model assumptions. As GIA models of varying complexity continue to emerge, it is increasingly important to characterize the spread in model predictions, which reflects the underlying uncertainties in these contributing components.
To systematically assess these uncertainties, we introduce the GIA Model Intercomparison Project (GIAMIP), a coordinated community effort focused on the Last Glacial Cycle (~122,000 years ago to present). GIAMIP aims to bring together a diverse set of numerical models incorporating a range of solid Earth rheologies and ice-sheet histories to evaluate the spread in GIA and sea-level predictions. This ensemble-based approach provides a physically grounded range of model predictions to support the interpretation of a wide range of datasets, including geodetic observations, relative sea-level records, and paleo-sea-level constraints. The products of this activity will be available to the public, enabling assessment of the effects of GIA-related uncertainties in a range of applications in the sea-level and geodetic communities.
Objectives and Deliverables
Assess uncertainties in modeled GIA arising from input ice history, solid Earth structure and rheology, and differences in numerical formulation and model implementation
Quantify measurements of GIA-derived uncertainties for the geodetic observation community for better inference of physical quantities from geodetic and space observations (e.g., ice mass and elevation changes, vertical land motions of the solid Earth)
Provide background GIA signal for ice sheet models: quantify the uncertainty-bounded contribution of ongoing GIA associated with past deglaciation to future solid Earth deformation and sea-level change. Because the prescribed paleo ice histories contain no recent or future ice-loading changes, the GIA response may be approximated as linear over centennial projection timescales for many Earth models. Where appropriate, these fields may be superposed on GRD responses associated with contemporaneous ice-loading changes to provide background solid Earth deformation signals for ice-sheet simulations submitted to the Ice Sheet Model Intercomparison Project (ISMIP).
List of experiments (more details in the protocol document)
List of Experiments.xlsxUpdates
2025 December: GIAMIP initial benchmark activity was presented at the 2025 AGU Fall meeting (agu.confex.com/agu/agu25/meetingapp.cgi/Paper/1901607).
Poster_GIAMIP_AGU2025_Final.pdf