The TIPMIP Earth system model experiment protocol: phase 1

Jones, ﻿Colin; Bossert, Isaline; Dennis, Donovan P.; Jeffery, Hazel; Jones, Chris D.; Koenigk, Torben; Loriani, Sina; Sanderson, Benjamin; Séférian, Roland; Wyser, Klaus; Yang, Shuting; Abe, Manabu; Bathiany, Sebastian; Braconnot, Pascale; Brovkin, Victor; Burger, Friedrich A.; Cadule, Patrica; Castruccio, Frederic S.; Danabasoglu, Gokhan; Dittus, Andrea; Donges, Jonathan F.; Fröb, Friederike; Frölicher, Thomas; Georgievski, Goran; Guo, Chuncheng; Hu, Aixue; Lawrence, Peter; Lerner, Paul; Licón-Saláiz, José; Otto-Bliesner, Bette; Romanou, Anastasia; Shevliakova, Elena; Silvy, Yona; Swingedouw, Didier; Tjiputra, Jerry; Walton, Jeremy; Wiltshire, Andy; Winkelmann, Ricarda; Wood, Richard; Yokohata, Tokuta; Ziehn, Tilo

doi:10.5194/egusphere-2025-3604

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https://doi.org/10.5194/egusphere-2025-3604

Preprints

23 Sep 2025

| 23 Sep 2025

Status: this preprint is open for discussion and under review for Geoscientific Model Development (GMD).

The TIPMIP Earth system model experiment protocol: phase 1

Colin Jones, Isaline Bossert, Donovan P. Dennis, Hazel Jeffery, Chris D. Jones, Torben Koenigk, Sina Loriani, Benjamin Sanderson, Roland Séférian, Klaus Wyser, Shuting Yang, Manabu Abe, Sebastian Bathiany, Pascale Braconnot, Victor Brovkin, Friedrich A. Burger, Patrica Cadule, Frederic S. Castruccio, Gokhan Danabasoglu, Andrea Dittus, Jonathan F. Donges, Friederike Fröb, Thomas Frölicher, Goran Georgievski, Chuncheng Guo, Aixue Hu, Peter Lawrence, Paul Lerner, José Licón-Saláiz, Bette Otto-Bliesner, Anastasia Romanou, Elena Shevliakova, Yona Silvy, Didier Swingedouw, Jerry Tjiputra, Jeremy Walton, Andy Wiltshire, Ricarda Winkelmann, Richard Wood, Tokuta Yokohata, and Tilo Ziehn

Abstract. We describe a new Earth system model (ESM) experiment protocol, as part of the international Tipping Points Modelling Intercomparison Project (TIPMIP) project. We propose this as a protocol for the Coupled Model Intercomparison Project 7 (CMIP7). The protocol requires ESMs to run in CO₂-emission mode, with atmospheric CO₂ a predicted variable. Forcing for the protocol consists solely of a constant emission of CO₂, based on each model’s transient climate response to cumulative emissions of carbon dioxide (TCRE) value, to give a common global mean warming rate of 2 °C per century. This positive emission experiment is started from the pre-industrial state of a given model. When the ramp-up run first exceeds a specified level of global warming (2 °C and 4 °C) relative to the model’s pre-industrial global mean surface air temperature (GMSAT), CO₂ emissions are set to zero and the positive emission run is branched into a zero-emission run. The zero-emission runs continue for 300 years. At 50 years into each zero-emission run, CO₂emissions are set to the negative of the positive emission rate and the model run until GMSAT cools below the original pre-industrial value. Additionally, when the negative emission run started from global warming level (GWL) = 4 °C first drops below GWL = 2 °C, a zero-emission run is branched off this, completing the set of experiments. Using this protocol, we are able to control the rate of global warming and cooling across participating models. TIPMIP experiments will support a range of analyses, including; an assessment of abrupt/rapid Earth system change, the long-term response to zero CO₂ emissions, the response to negative CO₂ emissions, the efficacy of negative emissions in driving cooling, and the reversibility of Earth system change under a pathway of positive (warming), zero (stabilization), and negative (cooling) CO₂ emissions.

How to cite. Jones, ., Bossert, I., Dennis, D. P., Jeffery, H., Jones, C. D., Koenigk, T., Loriani, S., Sanderson, B., Séférian, R., Wyser, K., Yang, S., Abe, M., Bathiany, S., Braconnot, P., Brovkin, V., Burger, F. A., Cadule, P., Castruccio, F. S., Danabasoglu, G., Dittus, A., Donges, J. F., Fröb, F., Frölicher, T., Georgievski, G., Guo, C., Hu, A., Lawrence, P., Lerner, P., Licón-Saláiz, J., Otto-Bliesner, B., Romanou, A., Shevliakova, E., Silvy, Y., Swingedouw, D., Tjiputra, J., Walton, J., Wiltshire, A., Winkelmann, R., Wood, R., Yokohata, T., and Ziehn, T.: The TIPMIP Earth system model experiment protocol: phase 1, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-3604, 2025.

Received: 25 Jul 2025 – Discussion started: 23 Sep 2025

Competing interests: One author is a member of the editorial board of GMD.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.

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'Comment on egusphere-2025-3604', Anonymous Referee #1, 12 Nov 2025 reply
Thank you for inviting me to review the paper: “The TIPMIP Earth system model experiment protocol: phase 1” by Jones et al.

With climate science under intense scrutiny, papers like these are extremely important. Such a manuscript demonstrates that the research community is open and transparent.

The role of description or methodological papers is just that, to set out proposed frameworks for simulations. And in that sense, the manuscript does well and fulfils the intended purpose. However, to provide some context and reasoning, it might be worthwhile to add a couple of sentences (at the beginning and in the discussion) explaining why there is such a rapidly growing interest in “overshoot” forcings. I would argue that there are four main reasons for modelling such scenarios.

Society is likely to find many aspects of substantial climate change difficult to manage, leading to an eventual strong push to lower global temperatures.

Society has set thresholds for global warming that it aims to stabilise at, notably around 1.5 or 2.0 degrees above pre-industrial levels. Since we are close to these benchmarks, achieving them will most likely involve a period of “overshoot”.

Studying the cooling period really helps understand the amount of negative emissions needed, raising challenges for others to question their feasibility (e.g., levels of geoengineering).

If climate change triggers regional tipping points, then the second less-discussed issue is that of hysteresis. By definition, this might become an issue with “overshoot” scenarios, and so things are not reset for falling temperatures. The TIPMIP projections described might be useful to drive offline impact models believed to potentially exhibit hysteresis.

Although the paper is generally clear throughout, my main concern is that the key assumptions underlying how the scenarios are constructed are spread over a very large number of paragraphs. Is there a way to present everything together in an easier form. Possibilities could include an extra “text box”, a schematic, or some other display item. It took me quite some time to fully grasp the assumptions, as I had to jump back and forth within the manuscript. Here are the points that should really stand out:

At the very top level, we set temperature profiles we wish our ESMs to follow. That includes ramp up, no warming, ramp down.

We cannot invert ESMs, to get out precisely the emissions to track these profiles. Hence, we need to estimate the emissions that get as close as possible to temperature profiles.

For the upward trajectory, we use the TCRE of each model.

For the stable part, we assume no net emissions into the atmosphere (ZEC). And maybe mention this clearly, because for most models, CO2 drawdown balances additional warming towards equilibrium. Hence, why temperatures are stable.

The ramp down assumes a negative value of emissions (i.e. “-X”) that were used in the ramp up.

I realise that the manuscript is mainly a presentation of protocol, but it might be worth adding a little more in the Discussion that [A] the analysis reconfirms with these ESMs that the ZEC is appropriate for Net Zero aims – getting net emissions down to zero does stabilise the climate. And [B], in the Allen et al. (2009) paper on TCRE, I think there was always an assumption that this was well-defined for positive emissions, specifically increasing temperatures. It is of much interest that the reversal also seems to give a good near-linear correspondence between -X and d_Temp / d_time, and of a similar ratio.

Small things

The paper can appear overly heavy on abbreviations (for instance, the left-hand column of Table 1). It may be worth reiterating at a few key points in the manuscript that these names are actually those associated with the metadata of the simulations themselves. Hence, their importance. One possibility is to put them in quotes, maybe?.

Please reiterate towards the end that the analysis is highly idealised. That is fine, and avoids more convoluted emissions scenarios (e.g. to match some sort of upturned parabola in global temperature). However, in reality, unless there is a massive global economic collapse, an instantaneous switch from business-as-usual to ZEC is unlikely.

Given the interest in Net Zero, then perhaps mention more strongly that this is often regarded as corresponding to the ZEC runs. Having these key buzzwords of phrases will enable more people to find this manuscript, and so appreciate that ESMs are now being configured for Overshoot and/or periods of Net Zero.

I am happy to see any further manuscript version.

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Citation: https://doi.org/10.5194/egusphere-2025-3604-RC1

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Short summary

We introduce a new Earth system model experiment protocol to help researchers understand how Earth might respond to positive, zero, and negative carbon emissions. This protocol enables different models to be compared following similar warming and cooling rates. Researchers use the models to explore how the Earth reacts to different climate futures, including the risk of tipping points being exceeded and whether changes can be reversed. The results will support improved long-term climate policy.


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