the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Aug 2026
MioMIP2: Experimental design for Phase 1 & 2 of the Miocene component of the CMIP7/PMIP7 Deep-time Model Intercomparison Project (DeepMIP-Miocene)
Abstract. The Miocene Epoch has emerged as an important paleoclimate model intercomparison target due to its dynamic nature, global warmth, and reconstructed atmospheric CO2 concentrations. Miocene CO2 estimates range from as low as 300–600 ppmv to as high as 800–1100 ppmv. The formalized Miocene Model Intercomparison Project (MioMIP2) aims to address questions about the mechanisms driving the climatic changes and tipping points seen in the geological record and improve confidence in the ability of climate models to predict future climates and constrain climate sensitivity. Through alignment with PlioMIP and DeepMIP-Eocene efforts, a coordinated MioMIP (DeepMIP-Miocene) effort will allow for cross-time-period studies that sample the full range of Shared Socioeconomic Pathway paleo analogues. Building on the MioMIP1 “MIP of opportunity”, the Miocene community has been developing the experimental design for MioMIP2. The MioMIP1 effort was an ensemble of opportunity that leveraged existing Miocene simulations run with different models, boundary conditions, and reference datasets. MioMIP2 will be the first formal Miocene MIP with common boundary conditions and will target the Miocene Climatic Optimum (MCO; 16.75–14.5 Ma). We present the experimental design for coordinated “CORE” MCO simulations and sensitivity studies. This community effort synthesizes paleogeography, ice sheet, CO2, and vegetation boundary conditions based on the latest available literature and will use geological data from companion proxy synthesis efforts to evaluate the simulations.
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Status: final response (author comments only)
- RC1: 'Review on egusphere-2026-3595 (by Chris Brierley)', Chris Brierley, 15 Sep 2026
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RC2: 'Comment on egusphere-2026-3595', Anonymous Referee #2, 22 Oct 2026
I have read the manuscript by Burls et al. with great interest, and I believe it represents an excellent contribution to the modelling community by establishing a protocol that will help modellers conduct consistent Middle Miocene climate simulations. This will ultimately lead to a better understanding of the MCO climate and facilitate more reliable model inter-comparisons. While I fully support the publication of this work, there are a few details that require some attention, which I have outlined below.
Specific comments
Line 135 Maybe add a half sentence about early Miocene from the beginning of the epoch to MCO to give a full picture of Miocene temperature change.
Line 144 Figure 1. I do not understand. Do the Miocene temperature ranges and Tipping Point Elements represent anomalies? If they do, the caption is not clear, if they do not and these are absolute temperatures, where is the absolute temperature scale on the figure?
Lines 207-215 This is my greatest concern. Your choice of mandatory experiments has one important implication: you cannot compare two simulations with Miocene and modern continental configurations. From my point of view, a simulation with the Miocene configuration and 280 ppm should be mandatory (as was the case for the Eocene simulation in the Eocene DeepMIP phase 2). Furthermore, a simulation that allows you to compare two different continental configurations under high CO2 should either be mandatory or have the highest priority among the sensitivity experiments.
You have two options here: either the Miocene with 4x pCO2 and/or the PI with 3x pCO2 should become mandatory, or (though this would be my second choice) they should be given top priority among the sensitivity experiments. It is crucial to investigate feedbacks under elevated CO2 that are independent of continental configurations, which is currently not possible with the present design.
Given the large number of choices for sensitivity testing, it might happen that different groups will have different high-CO2 simulations for the Miocene and modern configurations (for example, 2x and 3x pCO2 for the Miocene, and 4x pCO2 for the modern). My guess is that, given the computational expense, most groups will conduct only one or at most two sensitivity experiments. For the Eocene, most of the groups ran only three or four simulations with a maximum of 3x pCO2.
Lines 231 From my experience even 300 years would not be enough to equilibrate the simulations even close to the ocean surface.
Lines 430-442 Maybe a half sentence on elevation or timing of formation of Sierra Madre Oriental?
Lines 565 You write that “higher Himalayan front (>5 km) during the Middle Miocene remains debated…” and later, in lines 569-570 you write that “Water isotope and paleobotanical evidence suggest the Himalayas exceeded 5 km elevation during the Early–Middle Miocene (18–15 Ma)”. Is the height of Himalayan front still uncertain or does the newest evidence suggest higher elevation? If this is debated what are the other existing estimates? Lines 565-569 I would move the sentences “, while its elevation and ability to redirect moisture … wind speed, and precipitation (Johnson et al., 2016)” somewhere later. It disrupts the discussion about the height of Himalayas started in line 565 and later continued in line 570.
Line 663 I think you should mention here the work of Knorr et al. (2011). Also, you missed this work in Section 3.4. Please discuss it, as it provides an example on how to construct sensitivity experiments for the Miocene vegetation (potentially to include in Table 2) and continental configurations (Miocene vs. Modern).
Line 772 Were these estimates for the whole Miocene (as invariant suggest) or for a specific part of the Miocene?
Lines 913-917 Might be beneficial to refer here to de Boer et al. (2025) manuscript.
Line 914 “deep ocean temperature below ~3000 m” you mean average mean from the bottom to 3000m or only at the one depth level around 3000 m?
Line 983 There are models where equilibration should be based on the TOA imbalance differences between the piControl and Miocene simulations (see Lunt et al. (2021) paragraph 3.1 and Haywood et al. (2013) paragraph 5.3 and Table 2). Ok…. I see it now in Category 2. However, why this criteria is not suitable for Category 1?
Line 1033 For some models conservative remapping does not work and nearest neighbour must be used for all simulations to remain consistent.
Lines 1088-1092 In fact, recent geological evidence indicates that CAS could have been very shallow already in the Late Cretaceous. Please see and discuss Buchs et al. (2019) https://doi.org/10.1016/j.epsl.2018.07.020 and Buchs et al. (2010) in G^3 in the context of your suggested experiment with a 4500 m deep gateway.
Technical corrections
Line 130 Should be 2021.
Lines 146-147 Osman and Nicholls shouldn’t be in the brackets.
Lines 147, 379, 390, 396, 398, 427, 473, 565, 627, 692, 710, 796, 797, 799, 848, 866, 890, 945, 950, 952, 1007,1023, 1095, 1142 These are lines with typos in the citations. The most often is unnecessary coma but also missing dots, wrong order and others. Probably there are more. Please check carefully.
Line 150, 155 CO2 lower index ‘2’
Line 196 Suggest
Lines 308/309 Bracket is not closed.
Line 327 Coma missing after Tethys Seaway
Line 347 Shouldn’t be ‘> ~2000’?
Lines 483 “ to have fluvial systems that connected the Indian Ocean”. Connected what?
Lines 578 Mya or Ma? Be consistent across manuscript. Line 582 the same.
Lines 583 Indicates?
Lines 597 Act as a
Lines 602 Could you revise sentence? Using ‘However’ twice here looks awkward.
Line 645 Caption to Figure 3. b and c are swapped. b) is small and c) large
Lines 774, 784, 790, 798, 816, 842-843, 1048 You have defined earlier CENCO2PIP so why not to use only abbreviation here?
Line 812 Remove “(Bolton et al.,” it is in the next line.
Line 815 Informs
Line 821 (Steinthorsdottir et al., 2021c) reference is identical to (Steinthorsdottir et al., 2021b) in the list of references (lines 2210-2220).
Line 847 largely?
Line 964 simulations
Line 992 suggest
Lines 1020-1024 Maybe provide explicit example?
Line 1057 models
Line 1069 Greenland-Scotland
Line 1157 MCO?
Line 1167 Remove the second “differs”
Lines 1192-1193 In the bracket the two names are identical.
Line 1193 time slices
Line 1200 propose
Line 1221 The link does not work. “Page not found”
Citation: https://doi.org/10.5194/egusphere-2026-3595-RC2
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- 1
This manuscript provides a very solid discussion of the MioMIP2 protocol. It gives a nice explanation of the boundary conditions and a justification for them. The updates are described cleanly and the experiments are laid out in a sensible fashion. I would recommend the three points below are addressed prior to publication, and I've also attached an scan with some solely technical corrections (typos etc).
A) The main point that I would like to raise is that, as written, there is a disconnect between the title and the recommendation in my opinion. I feel that you ought to recommend that those modelling groups with a CMIP7-grade model should post their output onto the Earth System Grid Federation. Perhaps you could also give an experiment name for the CMIP controlled vocabulary: at least for the core experiment. Might I suggest miocene-3x? You might also consider rephrasing L220 to make it explicit that groups can directly use their CMIP6/7 piControl, as it currently reads that they might need to rerun it for Deep-MIP. A brief sentence describing how this fits into wider PMIP and CMIP efforts if undertaken with a CMIP7 model would be appreciated.
B) Section 2 seems too short (esp. compared to Sect 3), and more importantly just states the decision to focus on the MCO, rather than justifies it. Perhaps you could fold this into the literature review (stating that you build upon other work that is all focussed on the MCO).
C) I find the evidence you provide in Fig 1 around the CO2 level to be unhelpful. I've no problem with the CO2 levels chosen for the protocol. But I can't see how they relate to the Miocene CO2 estimates shown in Fig 1. Perhaps adding some horizontal lines would help. But I also do not understand the difference between the solid line in Fig 1 and the (much higher) dots.