the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Mar 2026
Dominance of Obliquity over Precession in Polar Temperature Variability: Insights from an Energy Balance Model
Abstract. The sensitivity of a Zonally Averaged Energy and Moisture BAlance Climate Model (ZEMBA) to changes in the Earth’s orbit is investigated. The model is intended to explore the dynamics of Quaternary glacial-interglacial cycles, particularly the dominance of 41-kyr obliquity cycles in ice volume and ocean temperature during the Early Pleistocene, despite summer insolation being primarily influenced by 19- and 23-kyr precession cycles. Through equilibrium simulations for the Pre-Industrial and Last Interglacial Period, we demonstrate that ZEMBA's response to strong orbital forcing qualitatively matches the behavior of climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6). Transient simulations of ZEMBA over the Early Pleistocene reveal a pronounced 41-kyr cyclicity in surface temperatures at the polar latitudes, in correspondence to variations in the Earth’s obliquity. Sensitivity experiments underscore the essential role of sea ice in driving temperature variability in the polar regions. The dominant 41-kyr cyclicity in surface air temperature is attributed to obliquity’s influence on winter sea ice extent, which governs the release of substantial ocean heat to the atmosphere. The more subdued effect of precession on surface air temperature is linked to the counterbalancing relationship between insolation intensity and summertime duration, which constrains variability in both winter sea ice and ocean heat fluxes.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-1151', Anonymous Referee #1, 29 Apr 2026
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RC2: 'Comment on egusphere-2026-1151', Anonymous Referee #2, 07 May 2026
Review of Gunning et al.
Gunning et al. utilize the zonally averaged energy balance model (ZEMBA) to evaluate the impact of orbital forcing on surface air temperature (SAT) and snow/ice during the Early Pleistocene. The authors first validate ZEMBA’s performance by comparing modern and Last Interglacial (LIG) simulations with PMIP models, demonstrating that ZEMBA yields comparable SAT and sea-ice changes. They subsequently perform transient and sensitivity experiments for the Early Pleistocene. Their results indicate that changes in obliquity strongly influence annual mean polar temperatures by affecting winter sea ice and ocean-atmosphere heat exchange, leading to a climate response synchronized with the 41-kyr obliquity cycle. Regarding climatic precession, the authors show a strong impact on summer snow/ice, however the net effect on annual mean temperature remains limited due to the seasonal compensation of insolation anomalies between winter and summer.
I find the experiments interesting, the manuscript is clearly written, and the topic is well-suited for the readership of Climate of the Past. Based on the points outlined below, however, I recommend a moderate-major revision.
Major Points
- Several studies have pointed out the seasonal impacts of obliquity and precession on temperature (Erb et al. 2013) and ocean heat flux (Tabor et al. 2014). The authors should discuss their findings in the context of existing literature. That said, the sensitivity experiments conducted by fixing sea ice and snow cover are novel. I suggest including further analysis (somewhat similar to Fig. 6) on these sensitivity runs to discuss how snow and sea ice and their interactions influence the seasonality of temperature anomalies. This would effectively differentiate this work from previous studies.
- A large portion of the Discussion section currently repeats the Results and could be streamlined. Instead, I suggest the authors expand the discussion on factors not currently accounted for in the model, such as vegetation feedbacks (e.g., Tabor et al. 2014; O’ishi et al. 2021), cloud feedbacks (e.g., Erb et al. 2013; Arima et al. 2026) and the potential impact of CO2 level on the results.
Specific Comments
L57: Please add a reference here.
L103: The spatial extent of the mixed layer depth seems unusual. Please provide a justification for why this specific location was set.
L165-167: What is the reasoning here? Is it because the sea-ice albedo is set to 0.7?
L168-169: I’m asking out of curiosity, but if the model was re-tuned to allow less Arctic sea ice during the LIG (127ka) by lowering the sea ice albedo, would this result in a model where precession exerts a stronger influence?
L181: Is this a typo for 71%?
L185: Please refer to the specific Figure being discussed to improve readability.
Section 4.4: There appears to be some confusion between Fig. 8 and Fig. 5. Please clarify.
L282-305: While informative, this paragraph does not seem directly relevant to the results and could be removed. If retained, please provide a concise explanation of how ZEMBA differs from other EBMs to justify the differing results.
L306-317: This is a repetition of the Methods and Results sections and should be removed.
L329: Should the large thermal inertia of the ocean also be highlighted as a key factor here?
L355-373: These lines repeat the Results section and should be condensed.
Figures
Fig. 6: Please include an explanation of the horizontal dashed lines (mx and mn) in the caption.
Fig. 7: Please specify in the caption which experiment is being analyzed.
Reference
Arima, N., Yoshimori, M., Abe-Ouchi, A., O'ishi, R., Chan, W.-L., Sherriff-Tadano, S., and Ogura, T.: Impact of the temperature-cloud phase relationship on the simulated Arctic warming during the Last Interglacial, Clim. Past, 22, 891–913, https://doi.org/10.5194/cp-22-891-2026, 2026.
Erb, M. P., Broccoli, A. J., and Clement, A. C.: The Contribution of Radiative Feedbacks to Orbitally Driven Climate Change, J. Climate, 26, 5897–5914, https://doi.org/10.1175/JCLI-D-12-00419.1, 2013.
O'ishi, R., Chan, W.-L., Abe-Ouchi, A., Sherriff-Tadano, S., Ohgaito, R., and Yoshimori, M.: PMIP4/CMIP6 last interglacial simulations using three different versions of MIROC: importance of vegetation, Clim. Past, 17, 21–36, https://doi.org/10.5194/cp-17-21-2021, 2021.
Tabor, C. R., Poulsen, C. J., and Pollard, D.: Mending Milankovitch's theory: obliquity amplification by surface feedbacks, Clim. Past, 10, 41–50, https://doi.org/10.5194/cp-10-41-2014, 2014.
Citation: https://doi.org/10.5194/egusphere-2026-1151-RC2 -
RC3: 'Comment on egusphere-2026-1151', Anonymous Referee #3, 09 May 2026
This paper uses an energy balance model to examine the response to orbital parameters during the early Pleistocene. I tend to believe that the integrated insolation idea provides a satisfactory explanation for the 41 kyr cycles, but it is always a good idea to question accepted dogmas. One specific motivation that is mentioned here and that I found interesting is a possible cancellation of 21-kyr cycles between the NH ice sheets and Antarctica (Raymo et al. 2006). I therefore find the problem and motivation interesting and relevant. The tool of an inexpensive and well-tuned energy balance model seems appropriate for such a task. The analysis is careful and interesting, but I do feel some additional experiments and analyses are necessary to make a solid case, and could turn this into an even more meaningful contribution. I therefore recommend a major revision.
The first major issue is that to be relevant to the 41 kyr ice ages, the authors should, in my opinion, diagnose the surface mass balance (SMB) of the ice sheets rather than the temperature. The SMB depends on the temperature, radiation, accumulation, etc., and only it can provide the needed link to the ice age problem. This needs to be added as another panel to something like the current Figure 5.
The other major issue is that to test alternative ideas for the 41 kyr cycles, it seems to me that the paper needs to explicitly compare the results (specifically the SMB) to those of the integrated insolation idea. This requires adding another curve to Figure 5 (including the SMB panel), showing the results of an integrated insolation calculation. This requires finding the optimal insolation threshold to be used for calculating this diagnostic. The optimal threshold would give an SMB time series that is closely correlated with the time rate of change of the observed ice volume record.
A third and final major issue is that while the introduction discusses the cancellation idea, etc., the results do not address that explicitly. By adding an SMB diagnostic, the authors could actually address the problem they pose as their motivation.
Finally, I find it interesting that sea ice plays an important role here (sections 4.3, 4.4, and conclusions). There is some literature on the role of sea ice in glacial cycles, and it may be helpful to compare the current results to such related papers and discuss similarities and differences.
Citation: https://doi.org/10.5194/egusphere-2026-1151-RC3
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- 1
Review of Gunning et al. submitted to Climate of the Past: “Dominance of Obliquity over Precession in Polar Temperature Variability: Insights from an Energy Balance Model”
In this manuscript, the authors investigate the climate and atmospheric response to the 41-kyr glacial cycles in the Early Pleistocene using their ZEMBA model (Gunning et al., 2025). ZEMBA is a one-dimensional energy-balance climate model that considers atmosphere, land, and ocean at each latitudinal grid point, as well as hydrological cycles. The performance of the model was evaluated in their previous study (Gunning et al., 2025) for the preindustrial and the Last Glacial Maximum (LGM) periods. In this study, they first present the model's performance in reproducing the Last Interglacial (LIG) period, evaluating its performance under different astronomical forcing. I like the concept of ZEMBA, which is a useful tool for understanding long-term climate change. However, the present manuscript lacks context on the 41-kyr problem, and the absence of ice-sheet modeling limits the model's applicability. My comments are summarized below, with capital Ls representing the line number.
Gunning, D. F., Nisancioglu, K. H., Capron, E., & van de Wal, R. S. (2025). ZEMBA v1. 0: an energy and moisture balance climate model to investigate Quaternary climate. Geoscientific Model Development, 18(9), 2479-2508.
Major Comments
1.
The authors elegantly summarize the so-called 41-kyr problem in the Introduction. They clearly explained two standing hypotheses (Huybers, 2006; Raymo et al., 2006) and their issues in accounting for the lack of precession periodicity in δ18O; however, they did not explain how the ZEMBA investigation can help resolve the 41-kyr problem, which makes the contribution of the present study very unclear. Explaining the 41-kyr problem ultimately requires ice-sheet modeling, which is not included in the current ZEMBA model, thereby limiting its contribution to the 41-kyr problem. When I first read through the manuscript, I thought it extended the hypothesis presented by Raymo and Nisancioglu (2003), who suggested that the latitudinal insolation gradient, dominated by 41-kyr cyclicity, affects heat and moisture fluxes to high-latitude regions and hence the 41-kyr periodicity in ice-sheet mass. In this sense, I think this study contributes to the 41-kyr problem even without ice-sheet modeling, but the linkage between what this study did and the 41-kyr problem is very unclear in the present manuscript. I recommend clearly situating this study within the context of the 41-kyr problem in the Introduction and enriching the Discussion.
Huybers, P. (2006). Early Pleistocene glacial cycles and the integrated summer insolation forcing. Science, 313(5786), 508-511.
Raymo, M. E., & Nisancioglu, K. H. (2003). The 41 kyr world: Milankovitch's other unsolved mystery. Paleoceanography, 18(1).
Raymo, M. E., Lisiecki, L. E., & Nisancioglu, K. H. (2006). Plio-Pleistocene ice volume, Antarctic climate, and the global δ18O record. Science, 313(5786), 492-495.
2.
As I mentioned in the comment above, the current ZEMBA model does not couple to the ice-sheet model. The authors discuss temperature responses in high-latitude regions, particularly the dominance of the 41-kyr periodicity, accounting for the effects of variations in ice-sheet mass. However, the formation of ice sheets affects the climate via many feedbacks, including changes in surface albedo, altitude, and atmospheric circulation. Without ice-sheet variations, it is difficult to assess the robustness of their results, especially their discussion of snow cover and sea-ice distributions. I think ice-sheet modeling is highly recommended to discuss the 41-kyr problem in this study, as was done using both a simplified model (Huybers and Tziperman, 2008) and more sophisticated models (Tabor et al., 2015; Tabor and Poulsen, 2016; Willeit et al., 2019; Watanabe et al., 2023). Even if it is difficult, careful justification, mention of the robustness of their results, and the uncertainty associated with the lack of feedback, especially the ice-sheet variability, and the potential impact of the snow cover change and heat-moisture budgets discussed in this study on ice-sheet mass balance are required.
Huybers, P., & Tziperman, E. (2008). Integrated summer insolation forcing and 40,000‐year glacial cycles: The perspective from an ice‐sheet/energy‐balance model. Paleoceanography, 23(1).
Tabor, C. R., Poulsen, C. J., & Pollard, D. (2015). How obliquity cycles powered early Pleistocene global ice‐volume variability. Geophysical Research Letters, 42(6), 1871-1879.
Tabor, C. R., & Poulsen, C. J. (2016). Simulating the mid-Pleistocene transition through regolith removal. Earth and Planetary Science Letters, 434, 231-240.
Watanabe, Y., Abe-Ouchi, A., Saito, F., Kino, K., O’ishi, R., Ito, T., ... & Chan, W. L. (2023). Astronomical forcing shaped the timing of early Pleistocene glacial cycles. Communications Earth & Environment, 4(1), 113.
Willeit, M., Ganopolski, A., Calov, R., & Brovkin, V. (2019). Mid-Pleistocene transition in glacial cycles explained by declining CO2 and regolith removal. Science Advances, 5(4), eaav7337.
Specific Comments
L129–135: According to Table 1, it seems that the authors conducted transient simulations from 2.45 to 1.2 Ma using a constant atmospheric CO2 level at the preindustrial value (284 ppm). This value is too high for the mean value representing the early Pleistocene. This should be explained and justified in the main text of the Methods section. The potential impact of the atmospheric CO2 level may be discussed in the latter part.
L144–146: The peak month of the isolation anomaly will differ if the authors apply the calendar-effect adjustment (Bartlein and Shafer, 2019). I recommend that the authors apply the calendar-effect adjustment, which will allow readers to better understand and compare the results with those of previous studies, such as Otto-Bliesner et al. (2021).
Bartlein, P. J., & Shafer, S. L. (2019). Paleo calendar-effect adjustments in time-slice and transient climate-model simulations (PaleoCalAdjust v1. 0): Impact and strategies for data analysis. Geoscientific Model Development, 12(9), 3889-3913.
Otto-Bliesner, B. L., Brady, E. C., Zhao, A., Brierley, C. M., Axford, Y., Capron, E., ... & Zheng, W. (2021). Large-scale features of Last Interglacial climate: results from evaluating the lig127k simulations for the Coupled Model Intercomparison Project (CMIP6)–Paleoclimate Modeling Intercomparison Project (PMIP4). Climate of the Past, 17(1), 63-94.
L187–193:
Are the changes of atmospheric and oceanic heat transport rates associated with different astronomical forcing compatible with previous results obtained using a general circulation model (e.g., Mantsis et al., 2011; 2014; Erb et al., 2013; Tabor et al., 2014)?
Erb, M. P., Broccoli, A. J., & Clement, A. C. (2013). The contribution of radiative feedbacks to orbitally driven climate change. Journal of climate, 26(16), 5897-5914.
Mantsis, D. F., Clement, A. C., Broccoli, A. J., & Erb, M. P. (2011). Climate feedbacks in response to changes in obliquity. Journal of Climate, 24(11), 2830-2845.
Mantsis, D. F., Lintner, B. R., Broccoli, A. J., Erb, M. P., Clement, A. C., & Park, H. S. (2014). The response of large-scale circulation to obliquity-induced changes in meridional heating gradients. Journal of Climate, 27(14), 5504-5516.
Tabor, C. R., Poulsen, C. J., & Pollard, D. (2014). Mending Milankovitch's theory: obliquity amplification by surface feedbacks. Climate of the Past, 10(1), 41-50.
L199: There should be a period at the end of the sentence.
Figure 5: Consider using a color set that is accessible for people with color vision deficiencies. Same for Figure S4.
L317–326: Same as my comment for L187–193.