Icesheet Domain

TIPMIP-ICE SHEETS aims to systematically explore ice-sheet tipping risks in Greenland and Antarctica across multiple ice-sheet models, based on the TIPMIP framework (Winkelmann et al., in review). In the following, we summarize the TIPMIP-ICE SHEETS experimental protocol (Winkelmann/Klose et al., in prep.).

Icesheet Domain Leads

Alex Robinson

Ann Kristin Klose

Heiko Goelzer

Marisa Montoya

Ricarda Winkelmann

Robin Smith

Protocol

Last update: 5 August 2026

Contact

Timeline

List of experiments

Initializaton

Forcing

• Atmospheric forcing

• Ocean forcing

GIA

Calving

README

Data distribution

Acknowledgements

Appendix

References

Overall, we expect participating ice-sheet models to fulfill a number of high-level features which are needed to study ice-sheet tipping dynamics: 

• The present-day ice sheets on Greenland and in Antarctica are not in steady state. The initial ice-sheet state for the TIPMIP-ICE SHEETS simulations should either be interpretable as pre-industrial state or overall capture the observed mass imbalance in the present-day. In addition, if interpreted as a pre-industrial state, a pre-industrial control simulation should not show substantial retreat (or collapse). 

• We expect participating ice-sheet models to represent the surface melt-elevation feedback.
• A representation of the response of the solid Earth to ice-sheet changes is required for participation in TIPMIP-ICE SHEETS. 
• Ice-sheet models participating in TIPMIP-ICE SHEETS should represent calving from a freely retreating ice front.

Please find further details and examples on how to implement these high-level features in the ice-sheet models below. 

Beyond fulfilling these high-level features, the TIPMIP-ICE SHEETS experimental protocol adopts an open approach. This includes ice-sheet model input data / boundary conditions (e.g. geothermal heat flow), and, in particular, applies to the translation of changes in climate provided by TIPMIP-ICE SHEETS to the ice-sheet model forcing. The open approach aligns well with the ISMIP7 protocol, allowing ice-sheet modelling groups to use the same or at least very similar ice-sheet model setup for both model intercomparisons.

TIPMIP-ICE SHEETS experiments are organized in three Tiers. Participation in TIPMIP-ICE SHEETS requires running at least the experiments in Tier 1, which sum up to 1800 – 10400 model years. We encourage participating ice-sheet modelling groups to run as many additional experiments as possible in Tier 2 and 3 with a total of 20800 model years in each Tier.

Contact

TIPMIP-ICE SHEETS Domain Leads: icesheets@tipmip.org

TIPMIP Icesheets Listserv: tipmip-icesheets-wg@listserv.dfn.de

Timeline

08.2026 Ice-sheet model forcing available via DKRZ (see Data access and distribution)

End of 10.2026 Submission of ice-sheet model contributions  (at least Tier 1 to be part of the first multi-model analysis papers)

List of experiments

The TIPMIP-ICE SHEETS protocol (Winkelmann/Klose et al., in prep.) includes three types of experiments based on the overarching TIPMIP experimental design (Winkelmann et al., in review; Fig. 1): 

• Climate ramp-up from pre-industrial climate 
• Climate stabilization at 2°C and 4°C global warming
• Climate reversal to 2°C global warming and to pre-industrial climate 

Using these experiments, the aim of TIPMIP-ICE SHEETS is to quantify the likelihood of crossing critical thresholds, the resulting committed ice-sheet changes and their reversibility. Different sources of uncertainty are systematically explored across three Tiers (see Table 1 and 2). 

Climatic boundary conditions for each type of experiment are based on output from Earth System Models in TIPMIP-ESM (Jones et al., in review). TIPMIP-ICE SHEETS provides a set of variables suitable for translating the changes in climate to the ice-sheet models within the open approach, see Atmospheric forcing and Ocean forcing for details. Since TIPMIP-ESM focuses on timescales up to 200 years, a forcing extension is needed for the climate stabilization experiments in TIPMIP-ICE SHEETS. In particular, for the climate stabilization experiments, the first 50 years of the respective TIPMIP-ESM output are randomly sampled. Due to the large file size up to 1000 years of forcing for the climate stabilization and reversal experiments, the extended forcing is not directly available for download. Instead, Python scripts are provided that allow the ice-sheet modelling groups to generate the extended forcing after the download (see Data access and distribution).

Tier 1 covers an idealized climate ramp-up, stabilization and reversal as listed above. Participation in TIPMIP-ICE SHEETS requires running the full set of experiments with (at least) one ice-sheet model setup. Here, ice-sheet model setup refers to one set of “parameters” (e.g. friction law, friction law exponent) and fixed boundary conditions (e.g. geothermal heat flux, atmospheric/ocean climatology). Any change in parameters is considered as a distinct ice-sheet model setup. The changes in climate are based on output from a recommended Earth System Model from TIPMIP-ESM (Röntgen et al., in prep.). Tier 1 focuses on quantifying the ice-sheet tipping risks across as many individual ice-sheet models as possible (uncertainties in the ice-sheet model structure). 

The climate stabilization and reversal experiments should ideally be run over 1000 years – if this is computationally not feasible, we have included an option to only run the stabilization experiment over 200 years and reverse thereafter (see Table 1 and 2). We also encourage modelling groups to run the reversal after 200 years as an additional experiment even when the reversal after 1000 years is possible.

Tier 2 experiments quantify uncertainties in key processes and feedbacks associated with ice-sheet tipping dynamics by repeating the set of experiments in Tier 1 with different model parameters. In particular, we ask each modelling group to choose parameter values representing 

• a lower and higher strength of the surface melt – elevation feedback (e.g. atmospheric lapse rate in a lapse rate correction of the near-surface air temperature with changes in ice-sheet geometry, see Atmospheric forcing), compared to the ice-sheet model setup submitted in Tier 1. 
• a lower and higher sub-shelf / frontal melt sensitivity for the Antarctic / Greenland Ice Sheet compared to the ice-sheet model setup submitted in Tier 1. 

Uncertainty ranges for these key processes and feedbacks can be obtained from the references given in Atmospheric forcing and Ocean forcing.

Tier 3 samples uncertainties in the regional climate simulated by the TIPMIP ESMs. Three TIPMIP ESMs have been chosen to cover a wide range of atmospheric-to-oceanic warming trajectories in Greenland and Antarctica under the same change in global mean warming during the climate ramp-up experiment (Röntgen et al., in prep.). 

We encourage the participating ice-sheet modelling groups to run as many Tier 2 and Tier 3 experiments as possible. For modeling groups running the Tier 1 climate stabilization and reversal experiments over 200 years only due to computational constraints, we still welcome submissions of Tier 2 and 3 experiments over this shorter timescale (even if not listed in Table 1 and 2 explicitly). We also welcome submissions exploring additional sources of uncertainty (such as parametric uncertainty associated with ice-sheet dynamics, initial state uncertainty, …). We are happy to coordinate across modelling groups to align ensemble designs. If such an uncertainty analysis is planned, we encourage modelling groups to email us (see Contact).

Table 1: List of TIPMIP-ICE SHEETS experiments (Tiers 1–3) for Antarctic Ice Sheet.

Table 2: List of TIPMIP-ICE SHEETS experiments (Tiers 1–3) for Greenland Ice Sheet. 

Initialization

The TIPMIP-ESM climate ramp-up, which forms the basis for the TIPMIP-ICE SHEETS experiments, starts from a pre-industrial climate. In TIPMIP-ICE SHEETS, we therefore aim to start experiments from an initial ice-sheet state representing pre-industrial conditions. Approaches typically applied for the initialization of ice-sheet models, e.g. inversion or spin-up, are associated with different assumptions on the ice-sheet state, as well as different advantages for applications in TIPMIP-ICE SHEETS. A perfect initial state representing pre-industrial conditions may not be generated with any of these initialization methods. 

We therefore adapt an open approach with respect to the specific model initialization, and require the initial ice-sheet states for the TIPMIP-ICE SHEETS simulations to match certain features based on observations and the current understanding of the ice-sheet history as much as possible: 

• The present-day ice sheets cannot be considered to be in steady state, and have overall lost mass over the contemporary period (Otosaka et al., 2023). Examples of initialization approaches that may be used to match this feature include but are not limited to: 
  • (Quasi) equilibrium spin-up under pre-industrial boundary conditions (e.g., Reese et al., 2023) or paleo spin-up (e.g., Albrecht et al., 2020), resulting in an ice-sheet state that can be interpreted as pre-industrial. 
  • Inversion with dynamic constraints, resulting in a state that overall captures the observed mass imbalance in the present-day.  

• The ice sheets are not characterized by widespread retreat (or collapse) in the present day (Rignot et al, 2026), while it cannot be excluded that such a retreat has already been triggered in the past. This will be tested as follows for the initialization approaches described above:
  • For ice-sheet models using the spin-up initialization, a pre-industrial control run is planned. Ice-sheet states must show stable grounding lines to be included. 
  • For ice-sheet models using the inversion method under present-day conditions, a pre-industrial control run will not be possible. In this case, the ice-sheet models need to overall capture the observed mass imbalance at present-day, and we assume that any longer-term ice-sheet changes in response to past climate conditions are “baked in”. 

This open approach allows ice-sheet modelling groups to use the same or at least very similar ice-sheet model setup for TIPMIP-ICE SHEETS and ISMIP7. We encourage modelling groups to contact us (see Contact) in case of questions on the ice-sheet model specific initialization in the context of the TIPMIP-ICE SHEETS experiments. 

Forcing 

Ice-sheet model forcing provided by TIPMIP-ICE SHEETS (Klose et al., in prep.) is based on TIPMIP-ESM output and includes the following spatially-varying and time-dependent variables: 

• Atmosphere: Monthly near-surface air temperature, precipitation 
• Ocean:
  • Antarctic Ice Sheet: Annual temperature (for different depth levels), salinity (for different depth levels)
  • Greenland Ice Sheet: Monthly thermal forcing 

These variables (generally given by $\Phi$ in the following) are provided as anomalies $\Delta \Phi_{ESM}(x,y,t)$, and, for precipitation, as ratios $\epsilon_{\Phi_{ESM}}(x,y,t)$, to avoid absolute negative precipitation, so that the total forcing for the ice-sheet model experiments $\Phi_{ISM}(x,y,t)$ reads as: 

with the ice-sheet model’s reference climatology $\bar{\Phi}_{ISM}(x,y)$ (e.g. involved in the initialisation in the case of a spin-up approach). The reference climatology and the anomalies/ratios should be combined by each ice-sheet modelling group. Note that ocean temperature and salinity in Antarctica are provided on different depth levels (i.e. as $\Delta \Phi_{ESM}(x,y,z,t)$).

The anomalies/ratios are computed from TIPMIP-ESM output $\Phi_{ESM}(x,y,t)$ with respect to the pre-industrial climatology $\bar{\Phi}_{ESM}(x,y)$ as follows: 

Here, the pre-industrial climatology $\bar{\Phi}_{ESM}(x,y)$ is based on the TIPMIP-ESM pre-industrial control experiment.

Models starting the experiments from a present-day as opposed to pre-industrial ice-sheet state (e.g. using an inversion method in the present-day for the model initialization) will not run the full ramp-up period and the forcing will be shifted accordingly. An example is described in Figure 2. Please contact us by e-mail in case of questions.

The ice-sheet modelling groups can choose how to translate these variables to the models, e.g. in terms of the surface mass balance or sub-shelf melt, depending on the approaches available for each model. More details as well as example approaches for the translation and respective references are provided below. We would like to stress that the lists of examples are not exclusive. Other approaches are welcome, and should be detailed in the README accompanying the submitted simulations (see README).

Atmospheric forcing

In TIPMIP-ICE SHEETS, the atmospheric forcing includes monthly near-surface air temperature anomalies and precipitation ratios (based on the CMIP variables tas and pr). 

From near-surface air temperature and precipitation, the surface mass balance (defined as snowfall – rainfall – snow-melt – ice-melt + refreezing) should be calculated “online” by the participating ice-sheet models and as a function of the evolving ice-sheet geometry to capture the surface-melt elevation feedback, one of the key feedbacks associated with ice-sheet tipping dynamics in Greenland (Robinson et al., 2012; Petrini et al., 2025; Gutiérrez-González et al., 2026) and Antarctica (Garbe et al., 2020; Coulon et al., 2024). At the very least, the ESM-based near-surface air temperature $T(x,y,t)$ (from Eq. 1) should be corrected for changes in the ice-sheet surface elevation $\Delta h(x,y,t)$ during the simulation based on a spatially-uniform and time-independent atmospheric lapse rate (as in e.g. Coulon et al., 2024; Coulon/Klose et al., 2025), so that the “effective” near-surface air temperature $T_{atm}(x,y,t)$ reads as:

with the atmospheric lapse rate $\Gamma$. We encourage the ice-sheet modelling groups to use alternative approaches, if available. A description of this approach has to be added in the provided README (see README). 

Snow and ice melt should then be calculated using the adjusted air temperature, for example, using one of the following approaches: 

• Positive-degree day approach (PDD) (e.g., Reeh, 1991; Calov and Greve, 2005; Coulon et al., 2024; Aschwanden et al., 2019)
• Simple diurnal Energy Balance Model (dEBM-simple) (e.g., Zeitz et al., 2021; Garbe et al., 2023)
• Insolation-Temperature-Melt (ITM) (e.g., Pellicciotti et al., 2005; van den Berg et al., 2008; Robinson et al., 2010)

Examples for determining the refreezing and thus runoff of surface meltwater include but are not limited to: 

• Simple thermodynamic parameterisation of refreezing (e.g., Janssens and Huybrechts, 2000; Huybrechts and de Wolde, 1999; Tarasov and Peltier, 2002)
• Refreezing of constant fraction of surface melt (e.g., PISM Manual/Khrulev et al., 2026)

Ocean forcing

In TIPMIP-ICE SHEETS, the Antarctic ocean forcing includes annual mean ocean temperature and salinity anomalies (based on the CMIP variables thetao and so), which were extrapolated to the ice-shelf cavities and in currently ice-covered regions, based on the horizontal Gaussian extrapolation of Jourdain (2024). The Greenland ocean forcing is provided as monthly thermal forcing anomalies (based on the CMIP variables thetao and so). The calculation of the thermal forcing and the extrapolation of ocean properties into the fjords follows the approach of the ISMIP7 GIS Ocean Focus Group (Slater et al., in prep). 

Sub-shelf melting and/or frontal melting should be calculated by the participating ice-sheet models based on ocean temperature and salinity. 

For the Antarctic Ice Sheet, possible approaches for determining sub-shelf melting include, but are not limited to: 

• Local quadratic parameterization (Favier et al., 2019; Burgard et al., 2022)
• ISMIP6 non-local quadratic parameterization (Jourdain et al., 2020)
• Potsdam Ice-shelf Cavity mOdel (PICO; Reese et al., 2018; Reese et al., 2023) 
• Plume parameterization (Lazeroms et al., 2019)
• PICOP (Pelle et al., 2019), combining PICO and the plume parameterization
• LADDIE (Lambert et al., 2023)

Please also see Burgard et al. (2022), Coulon et al. (2024) and Lambert and Burgard (2025) for a comparison of common sub-shelf melt parameterizations and associated parameter ranges.  While not required, frontal melt may be included in Antarctica. 

For the Greenland Ice Sheet, possible approaches for determining frontal melting include, but are not limited to: 

• ISMIP6 submarine melt implementation (Slater et al., 2020), determining frontal melt based on the parameterisation of Rignot et al. (2016)  from subglacial discharge and thermal forcing. Note that the subglacial discharge may be based on the surface runoff determined by the participating ice-sheet models throughout the simulation (see Atmospheric forcing). Only the thermal forcing is provided in TIPMIP-ICE SHEETS (see Ocean forcing).

While not required, sub-shelf melt may be included in Greenland, e.g. based on one of the following approaches: 

• Potsdam Ice-shelf Cavity mOdel (PICO; REF) 
• Tunable present-day sub-shelf melt combined with linear, scaled anomalies (Tabone et al., 2024; Gutiérrez-González et al., 2026)

GIA 

Given the crucial role of ice-sheet – solid Earth interactions for ice-sheet tipping dynamics (e.g. Gomez et al., 2010; Coulon et al., 2021; Zeitz et al., 2022), a representation of the response of the solid Earth to ice-sheet changes is required for participation in TIPMIP-ICE SHEETS. Examples include: 

• Elastic lithosphere–relaxed asthenosphere (ELRA) model (Le Meur and Huybrechts, 1996)
• Laterally variable ELRA (LV-ELRA) model (Coulon et al., 2021)
• Elastic lithosphere–viscous mantel (ELVA) model (e.g., Lingle-Clark; Lingle and Clark, 1985; Bueler et al., 2007)
• LV-ELVA (e.g. FastIsostasy; Swierczek-Jereczek et al., 2024)

If available, more complex representations of ice-sheet – solid Earth interactions, e.g. including the laterally variable as well as radial structure of the solid Earth on a global domain (e.g., Albrecht et al., 2024), are welcome.

Calving 

Changes in the ice-shelf front through calving have been an important driver in observed glacier speed-up in the Amundsen Sea over the past decades (De Rydt et al., 2021; dos Santos et al., 2021) and may determine the long-term stability of marine ice sheets (Haseloff and Sergienko, 2022). Similarly, calving rules have been shown to impact the steady states and the dynamic behavior of marine terminating glaciers (Sergienko, 2022; Schoof et al., 2017). 

In ice-sheet models participating in TIPMIP-ICE SHEETS, the ice front should be free to retreat. Defining a maximum ice extent such that the ice sheet does not advance beyond e.g. its present-day configuration is allowed. 

In Antarctica, calving at the ice-shelf front should be represented, for example, as

• Eigencalving (Levermann et al., 2012) 
• Von Mises stress calving (Morlighem et al., 2016)
• Thickness calving / Minimum thickness threshold (as applied in, e.g., Garbe et al., 2020)
• Calving depending on surface/basal crevasse penetration depth (Pollard et al., 2015; DeConto and Pollard, 2016) 

These calving laws have recently been assessed for Antarctic ice shelves (Wilner et al., 2023). 

In Greenland, calving at the terminus of outlet glaciers should be included. Possible approaches include, but are not limited to 

• Von Mises stress calving (Morlighem et al., 2016; Choi et al., 2017)
• Height-above buoyancy criterion (Vieli et al., 2001) 
• Crevasse depth calving (Benn et al., 2017; Otero et al., 2010),

which have been compared by Amaral et al. (2020) and Choi et al. (2018) for various glaciers in Greenland.

README 

Each participating ice-sheet modelling group has to submit a README file together with the submission of the simulations, following this template: [Note: README template will be added in the coming weeks.] 

Output variables and file naming 

TIPMIP-ICE SHEETS overall follows the conventions on the naming of ice-sheet model output variables and files from ISMIP7.

Requested ice-sheet model output variables 

Table 3: Requested ice-sheet model output variables in TIPMIP-ICE SHEETS. ST and FL refer to “state variable” and “flux variable”, respectively. While ST variables should be submitted at the end of the modelled year, FL variables should be averaged over the respective year. In addition, time is recorded in different ways, depending on the variable type. Please see Format of ice-sheet model output files below for additional information on the time variable in the submitted file.

Format of ice-sheet model output files 

Since simulations are based on a set of idealized experiments, the basetime in the submitted files should be 0000-1-1. Time should then be given as days since 0000-1-1 across the set of experiments (i.e. climate ramp-up, climate stabilization, climate reversal) with a 365_day calendar. Note that the ice-sheet model output should not be interpolated to this calendar. Instead, we will use a common time axis for the ice-sheet model output to facilitate the analysis. State variables should be given at the end of the modelled year, while flux variables are averaged over the respective year and recorded as the middle of the year. Please see the example in Table 4 below.  

Ice-sheet model output should be submitted on the ISMIP grids, which are defined as follows:  

• Greenland Ice Sheet: Polar stereographic projection with standard parallel at 70° N and central meridian of 45° W (315° E), referenced to WGS84 datum (EPSG:3413), Domain from (−720,000 m, −3,450,000 m)/lower-left corner to (960,000 m,−570,000 m)/upper-right corner
• Antarctic Ice Sheet: Polar stereographic projection with standard parallel at 71° S and central meridian of 0° W, referenced to WGS84 datum (EPSG:3031), Domain from (−3,040,000 m, −3,040,000 m)/lower-left corner to (3,040,000 m, 3,040,000 m)/upper-right corner

Table 4: Example for time variable in ice-sheet model output files. Time is given as days since 0000-1-1 with a 365_day calendar. Note that the length of the climate ramp-up experiments may slightly differ depending on the ESM. In addition, the example assumes that the climate stabilization and reversal experiments are run for 1000 years. Participating ice-sheet model groups are encouraged to further extend these experiments, if possible.

Naming of ice-sheet model output files 

Each output variable listed in Table 3 should be submitted in a separate netcdf file, named as follows: 

[variable]_[ice-sheet]_[modelling-group]_[ice-sheet-model]_[experiment-name].nc

For the naming of the experiment ([experiment-name]), please follow Table 1 and 2.

Data access and distribution

TIPMIP-ICE SHEETS data are stored at the German Climate Computing Centre (Deutsches Klimarechenzentrum, DKRZ). A DKRZ account is required for (1) downloading the forcing (input) data (Klose et al., in prep.), and (2) uploading the ice-sheet model (output) data. Please contact data@tipmip.org and icesheets@tipmip.org in both cases for detailed instructions. 

Acknowledgements

• We gratefully acknowledge the work of the Ice Sheet Model Intercomparison Project (ISMIP) and their Focus Groups for establishing a number of methods and common practices for community ice-sheet modelling that we have adapted and made use of for TIPMIP-ICE SHEETS.
• We thank the Earth System modelling groups participating in TIPMIP-ESM for producing and making their model output available to TIPMIP-ICE SHEETS, which have formed the basis for constructing the forcing for the standalone ice-sheet model experiments.
• We thank the participating ice-sheet modelling groups for their commitment to TIPMIP-ICE SHEETS including their contributions to the experimental protocol as well as the submissions of simulations.  
• We thank all colleagues of the wider TIPMIP community, attending the various domain workshops, the WE-Heraeus Seminar on ‘Addressing Key Uncertainties in Modelling Physical and Ecological Tipping Dynamics in the Earth System’ in Templin (Germany, 2023), the TIPMIP General Assemblies in Baltimore (US, 2024) and in Tokyo (Japan, 2026) for fruitful discussions on the experimental design.

Appendix: Shifting forcing 

Table 5: Observed and simulated global surface temperature change above pre-industrial. Observed global surface temperature change is based on the Copernicus Climate Change Service Global Indicators Temperature Dataset (Copernicus Climate Change Service, 2026). The simulated global surface temperature change is based on the TIPMIP-ESM ramp-up simulation by NorESM2-LM and UKESM1-2-LL, chosen as Tier 1 ESMs for the Antarctic and Greenland ice sheets, respectively. Assuming the initial Antarctic ice-sheet state is associated with e.g. the year 2015 with an observed global warming of 0.98 °C above pre-industrial levels (left columns, marked in bold), this ice-sheet model would only consider the TIPMIP-ESM-based ramp-up from the ESM simulation year 56 / 45 onwards (beyond which global warming does not fall below 0.98 °C in the TIPMIP-ESM-based forcing, right columns, marked in bold) in simulations for the Antarctic / Greenland ice sheets. The TIPMIP-ESM-based  forcing would be shifted with respect to the simulation year 56 / 45 (passing through zero at the start of the ice-sheet’s model ramp up) in simulations for the Antarctic / Greenland ice sheets.  

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