the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 May 2026
The Geoengineering Model Intercomparison Project (GeoMIP) contribution to CMIP7 – description of new experimental protocols and preliminary results
Abstract. The Geoengineering Model Intercomparison Project (GeoMIP) is a coordinated international model intercomparison effort with the aim of providing robust experimental protocols for simulations of various Solar Radiation Modification (SRM) methods. Through many iterations and discussions within the GeoMIP community, it has become clear that balancing simplicity with scientific realism and policy relevance and associated complexities is fundamental when designing modeling experiments. Such experiments must both diagnose areas of model agreement and disagreement through the lens of climate science and provide results useful for understanding the potential downstream impacts of SRM across different sectors. Here we present a suite of new climate model experiments designed for the Coupled Model Intercomparison Project Phase 7 (CMIP7), building on lessons learned from previous GeoMIP experiments, recent SRM research, and new simulations developed for CMIP7. We provide detailed experimental designs and their underlying rationale, including preliminary results from sensitivity analyses performed with CMIP6 models. Compared to previous GeoMIP iterations, we organize experiments into three categories: i) Preparatory Experiments, designed to diagnose model responses and inform more complex experimental designs; ii) Tier 1 experiments, the core simulations that all participating models are encouraged to run; and iii) Tier 2 experiments, which provide a flexible framework for exploring structural and scenario uncertainties under SRM, including the potential interaction with temporary overshoot scenarios and tipping elements dynamics. This framework encourages modeling groups to propose their own experiments building upon the Tier 1 backbone, enabling more targeted exploration while ensuring cross-model compatibility.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Geoscientific Model Development.
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.- Preprint
(6824 KB) - Metadata XML
- BibTeX
- EndNote
Status: open (until 15 Jul 2026)
- RC1: 'Comment on egusphere-2026-2417', Anonymous Referee #1, 01 Jun 2026 reply
-
CC1: 'Comment on egusphere-2026-2417', Sarah Doherty, 02 Jun 2026
reply
It's good to see this paper describing the next stage of GeoMIP studies. I particularly like the context given in the Conclusions section.
There is one point of contention I have with the paper, which is the use of the term "preindustrial" in declaring the target of these runs to be "PI+1.5degC". The paper specifies that PI is defined here as the 2020-2039 GMST average. Given that in 2025 temperatures have already warmed by ~1.2degC since the mid 1800's the 2030 average is likely to be even higher than that, so the target is really closer to 2.7+degC above the true pre-industrial. While the definition of "preindustrial" being used here is specified, the reality is that results are likely to be conveyed in a way that this detail is lost. Given that the effects of SRM depend on background climate I think it is important to use terminology that is not misleading. As such, I strongly recommend that these runs are not referred to as targeting "preindustrial + 1.5degC" but rather something like "present-day + 1.5degC".
Smaller points:
In Section 3.4 it is specified that "MCB is applied by increasing injected sea salt aerosol emissions". While the size of sea salt to be injected is mentioned elsewhere, it would be good to again note here that this sea salt would be of a different size than the naturally emitted sea salt. This is not the same as just increasing sea salt emissions, and “increasing injected sea salt aerosol emissions" could be read to mean just increase the model’s natural sea salt emissions. Given the strong size-dependence of cloud responses on aerosol size, increasing natural sea salt emissions will have very different effects than adding sea salt aerosol that is mostly or all in the coarse mode, as is the case for natural sea salt emissions.
lines 341-342: The Rasch et al. (2025) paper should be cited here in and the sentences that follow, as their runs were also focused on low latitude MCB.
lines 457-458: I found this statement odd, as it implies that the equator-to-pole gradient could only be controlled by deploying MCB at polar latitudes, and this may not be the case. Unless there’s a basis for this assumption, I’d suggest rewording to a more general statement that more research would be needed to determine how well the equator-to-pole gradient could be controlled through different MCB deployment patterns.
line 531: In the SH much of the area south of 60S is land, as is some of the area north of 60N. Are clouds over land also perturbed in these runs, or only clouds over sea ice?
line 532: Regarding the specification of winter as "(Nov, Dec, Jan and Feb)": presumably this is May, Jun, Jul, Aug for the SH winter.
Finally I'll note that I disagree with the Anonymous Reviewer #1 that Figures 3, 5 7 and 8 should all be moved to a supplemental section. I agree that Figure 3 is rather confusing as to what it's trying to convey but I would encourage perhaps revising that figure rather than (re-)moving it. Figure 5 seems to be a pretty important visualization of the G6-1.5K-MCB protocol. Figure 7 similarly is a helpful demonstration of the MCT protocol -- though Figure 8, I'll agree, is less essential given that this is not a Tier 1 (or even Tier 2) protocol, so could be omitted or moved to a supplemental section but I don't think it necessarily should be.
Citation: https://doi.org/10.5194/egusphere-2026-2417-CC1
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 396 | 190 | 17 | 603 | 17 | 17 |
- HTML: 396
- PDF: 190
- XML: 17
- Total: 603
- BibTeX: 17
- EndNote: 17
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
Visioni et al. describe the plans for the contribution of a geoengineering MIP to CMIP7. This is a very laudable community effort, and the modelling community evidently organised the process of defining the simulations and simulation protocols in a very open and transparent way. The paper states that much of the definitions is based on the outcomes of a workshop to which the community was invited.
I have a few somewhat overarching suggestions for improvements, and then a number of smaller suggestions.
– Some of the propositions/requests in my view are too vague to be a meaningful MIP contribution. Of course each modelling group can (and should) do their own simulations, and smaller groups can always come up with own ideas. The very meaning of a MIP is that it is a strict protocol and that a meaningfully large number of groups submit simulations that exactly follow this protocol. So my suggestion is to omit everything that is only vaguely defined. There could be for example an appendix to the paper in which such suggestions – potentially these are minority opinions from the workshop that didn’t make it to the Tier-1 MIP proposal? – can be listed as examples.
– A bit related comment: The real MIP proposal is the Tier-1 simulations. However, they are impossible to do without some of the Preparatory experiments. These Preparatory experiments, in turn, are not understandable really before one understood the Tier-1 experiments. To the reader of the paper, a much more logical structure would be to describe the Tier-1 experiments, and include in these the Preparatory experiments (except for the third block, Inj-Sulf-15N etc., which seem to be of rather little use except for the zoo of Tier-2 experiments). Of course I acknowledge it might be difficult to change such things after the workshop, though. In the Tier-2 experiments, to me only the experiments listed in Table 3 are well-enough defined to be part of CMIP7. The other experiments are very vague and would better be done and consolidated within the community. They could be described here in an Appendix making clear such ideas were discussed but then not included as being well-defined enough for a large MIP effort as part of CMIP7. Again I acknowledge that the community may have discussed such arguments in detail and the harm done in listing such ideas here is probably minor since groups will carefully select what they contribute anyway.
– The integration of GeoMIP into CMIP7 should be discussed. In particular, what are the synergies with AerChemMIP and DAMIP?
– There are very important aspects of the Earth system models that may have a large influence on the outcomes (e.g. the cloud microphysical schemes for MCB and CCT). The protocol should define a way to document these particularly relevant ESM aspects in an easily accessible and transparent manner.
– Several figures show results but these rather distract from the MIP description. Fig. 3, 5, 7, 8 in my view contribute little to the paper but are rather confusing. They could go to an appendix or to a separate paper.
L12 – “that all participating models are encouraged to run”: the corollary is that models are discouraged to run tier-II simulations
L15 – “propose their own experiments” links to my main comment above: this is not a contribution to a MIP but the bread-and-butter of every modelling team. It should be omitted from this paper or at best be moved to an appendix
L26 – “increase of Earth’s albedo through _increased_ cloud brightness”
L26 – what could be “other cloud changes”? cloud coverage?
L47 – the “potential asymmetries” should be explained
L111 – “this could include metrics”: I would expect from a MIP definition a definition of specific metrics. Maybe the text could point here to Section 5 (Data request) and take up this point in that section 5.
L125 – “Models can also perform…” this seems to be a redundant statement, of course they could. If there is a reason to state this here, this reason should be made transparent (e.g. “The GeoMIP community has also discussed simulations at other latitudes… but decided not to include those in the Tier-1 request.” or so).
L141 – Only later the emission height and size distribution are defined, it would be useful to point to this here.
l147 – The community uses the term “aerosol-cloud interactions” since AR5, “aerosol indirect effects” is outdated.
l155 – It should be clearly defined how this careful documentation should look like.
L160 – The Table said it is run for 20 years (not 40 years)
L202 – Only one ensemble member run to 2150, was stated in the table.
L225 – “as little as possible” is a difficult statement, maybe simply “little”?
L232 – I don’t understand the “Legendre polynomials” explanations. A clear definition of who T1 and T2 are computed should be provided.
L248 – For the MCB experiment, a definition for “maintain the PI+1.5°C temperature target” is provided, in line 332, at ±0.2°C. This seems meaningful.
L254 – “it is possible” rather than saying what is possible the protocol should describe how it should be done exactly.
L258 – “can be computed” similar point, it should be said what should be computed and how.
L267 – “can request a dataset” – how exactly, to whom to address?
L327 – “lowest model layer” seems to be too vague. Models have vastly different vertical resolutions. The request should clarify a height range instead.
L329 – I would find a map useful.
L334 – Only one ensemble member to 2150, right?
L363 – Also the number is evenly distributed since the size distribution is given.
L411/Figure 6 – The “intervention magnitude” curve for G7-0.5K-SAI seems to be wrong to me. The magnitude should be much larger very early after 2035.
L421 – If “ramped up linearly”, the temperature evolution would look very different from the one depicted in Fig. 6.
L424 – But here no overshoot is considered?
L435 – Same question, there is no overshoot in this scenario.
L517/Section 4.3 – This entire section deviates a lot from the other Tier-2 descriptions. As stated above, in my view best would be to move these very vaguely defined simulations out of the actual MIP description (e.g. to an appendix). If the authors choose they want to include these, the description of the mixed-phase cloud thinning experiments should be harmonised with the description of the other Tier-2 simulations.
L567 – specifically this section should be incorporated into Section 5.
L660 – “technique is” or “techniques are”