Hysteresis and irreversibility in permafrost physical response to increase and decrease of CO<sub>2</sub> emissions

Watanabe, Natsuki; Watanabe, Masahiro; Hajima, Tomohiro; Yokohata, Tokuta; Melnikova, Irina

doi:10.5194/egusphere-2025-4088

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https://doi.org/10.5194/egusphere-2025-4088

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11 Sep 2025

| 11 Sep 2025

Status: this preprint is open for discussion and under review for Earth System Dynamics (ESD).

Hysteresis and irreversibility in permafrost physical response to increase and decrease of CO₂ emissions

Natsuki Watanabe, Masahiro Watanabe, Tomohiro Hajima, Tokuta Yokohata, and Irina Melnikova

Abstract. Boreal permafrost over the Northern Hemisphere high latitudes, defined as areas where the ground temperature is below 0 °C for two or more years, stores more than twice as much carbon as the atmosphere. Therefore, thawing of the permafrost, an important tipping element, due to global warming may lead to additional carbon emissions and accelerate the warming. To investigate the permafrost response to increase and decrease of CO₂ emissions, we conducted a series of numerical experiments using an emission-driven Earth System Model, MIROC-ES2L, and adopting idealized overshooting scenarios in which a prescribed CO₂ emission of 10 PgC is given until the global warming level reaches different values between 2 and 8 °C followed by the negative emission until the cumulative emission becomes zero.

We found that the response of permafrost area to surface warming and cooling is reversible but has hysteresis for all the emission scenarios. Furthermore, the permafrost property was shown to have irreversibility in the deep soil layer; part of the frozen area in the initial condition was replaced by a mixed water-ice area in the final state despite ground temperature turned almost to the initial condition. Sensitivity experiments reveal that the hysteresis and irreversibility are attributed to the delay of the soil freezing and melting associated with the soil heat conductivity and specific heat of water phase change. This result indicates that once permafrost thaws with warming it will continue for decades after warming diminishes and the delay in the permafrost recovery is larger at global warming levels greater than 2 °C. An offline calculation shows that the additional CO₂ emission during the permafrost hysteresis cycle accounts for about 0.6–41 % of the prescribed cumulative carbon emission.

Received: 21 Aug 2025 – Discussion started: 11 Sep 2025

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Natsuki Watanabe, Masahiro Watanabe, Tomohiro Hajima, Tokuta Yokohata, and Irina Melnikova

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RC1:
'Comment on egusphere-2025-4088', Anonymous Referee #1, 05 Nov 2025 reply
Review of “Hysteresis and irreversibility in permafrost physical response to increase and decrease of CO₂ emissions” by Watanabe et al. 2025.

The authors present new emissions driven simulations of the MIROC-ES2L earth system model, incorporating developments to the land surface model since the CMIP6 configuration, and accompanying offline simulations of the PDGEM GHG model, focussing on research questions related to the physical response of permafrost and quantifying the additional CO₂ and CH₄ emissions from thawing permafrost. The authors also perform a perturbed parameter ensemble to diagnose the drivers of hysteresis in the physical soil properties.
The idealised experimental design and land surface model developments are well suited to answering these relevant research questions, although the analysis could be improved with several clarifying points, and further detail on certain features of the results, listed below. In general, the figures should be bigger, including a larger font size.

Major comments:
Definition of permafrost and “sherbet”. The initial value of permafrost area in this model (~2.5 x 10¹³ m²) is very large compared to previous studies which have quantified and permafrost area using previous definitions found in the literature (Burke et al. 2020, Steinert et al. 2023). Updates to the land surface scheme, designed to improve the representation of permafrost relative to the CMIP6 configuration, are detailed in Yokohata et al. 2020a. However, the total permafrost area, which is the principal metric of evaluation in this study, is not quantified in Yokohata et al. 2020a, it is only presented spatially in comparison to observations. Therefore, section 2.3 of the present study would benefit from discussing why the permafrost extent in MIROC used here is much larger than observational estimates and a justification of this choice compared to previous literature definitions. This paper could also be improved by including the boundary of observed permafrost in the maps, as done in Figure 2 of Yokohata et al. 2020a.

In addition, the bulk of the explanation of the permafrost hysteresis is attributed to the presence of a soil condition referred to as “sherbet”. I cannot find any reference to this in the literature, and it appears to be a new metric introduced in section 3.2.2, therefore it needs defining in much greater detail. If this is referring to a certain proportion (%) of water in a grid cell below 0 C being frozen, then this proportion should be clearly defined, and if available, a reference should be provided.
Explanation of hysteresis. In sections 3.2 and 3.3, the proposed mechanism of permafrost hysteresis could include additional analysis of the hydrological cycle, such as clarifying whether additional moisture is present in the soil later in the simulation. Also, the step between sections 3 and 4 of the diagram in Figure 7a is quite abrupt and should be described in more detail in the text.

Representation of GHG emissions. Use of an offline GHG model is a logical inclusion, but the framing of results in this section needs a greater consideration of uncertainty, given the tendency of the assumptions to overs estimate permafrost carbon release. Previous applications of the model (Yokohata et al. 2020b) highlight this large range of uncertainty for SSPs with positive emissions. Section 3.5 of the present study should quantify or at least discuss the magnitude of uncertainty in the flat10 simulation, and the increased uncertainty introduced by PDGEM assuming no cessation on emissions from refrozen soils. In addition, when relating the carbon emissions during the negative emissions phase, it is not clear which “cumulative emissions” the authors are referring to. I think it is the total negative emissions, and it would be clearer to refer it in a different way. Framing the results as a percentage of the total negative emissions is not particularly helpful for the higher global warming levels, so I suggest including greater discussion of the permafrost carbon release during the flat10 simulation up to these global warming levels.

Minor comments:
The last paragraph of the introduction should include a stronger justification for investigating the response of permafrost to an overshoot scenario and discuss in the context of more recent research in this field (e.g., Park et al. 2025, Schleussner et al. 2024).

In the methods section, such an in-depth description off the ESM is not needed. It can either be referred to in other publications or added to a supplementary information. At this point, the manuscript would also benefit from a description of the carbon cycle processes that are included in the model coupling, hence justifying the emissions driven simulations.

Technical corrections:
Line 35: replace “10 Pc G” with “10 Pc G yr^-1”.
Line 65: “IPCC, 2021” use reference for the specific chapter.
Line 163: First sentence too similar to the subtitle, so this sentence is unnecessary.
Line 155: Unclear use of “overshoot simulations”, clarify if these are the NEC experiments.
Line 176: replace “he” with “the”.
Line 217: replace “cumulative emission” with “cumulative emissions”.
Lines 251, 252 and 256: measures of area are incorrectly referred to in “m³”, and I recommend referring to permafrost area in units of “10⁶ km²”, instead of “10¹³ m²”, throughout the manuscript.
Line 298: replace “keeps 0C” with “remains at 0C”.
Line 456: remove “about”.
Line 520: replace “become” with “reaches”.
Line 566: replace “ground models” with “land surface models”

References:
Burke, E. J., Zhang, Y., and Krinner, G.: Evaluating permafrost physics in the Coupled Model Intercomparison Project 6 (CMIP6) models and their sensitivity to climate change, The Cryosphere, 14, 3155–3174, https://doi.org/10.5194/tc-14-3155-2020, 2020.
So-Won Park et al. Continued permafrost ecosystem carbon loss under net-zero and negative emissions, Sci. Adv. 11, eadn8819(2025). DOI:10.1126/sciadv.adn8819.
Schleussner, CF., Ganti, G., Lejeune, Q. et al. Overconfidence in climate overshoot. Nature 634, 366–373 (2024). https://doi.org/10.1038/s41586-024-08020-9
Norman J Steinert et al 2024, Evaluating permafrost definitions for global permafrost area estimates in CMIP6 climate models, Environ. Res. Lett. 19 014033
Yokohata, T., Saito, K., Takata, K. et al. Model improvement and future projection of permafrost processes in a global land surface model. Prog Earth Planet Sci 7, 69 (2020a). https://doi.org/10.1186/s40645-020-00380-w
Yokohata, T., Saito, K., Ito, A. et al. Future projection of greenhouse gas emissions due to permafrost degradation using a simple numerical scheme with a global land surface model. Prog Earth Planet Sci 7, 56 (2020b). https://doi.org/10.1186/s40645-020-00366-8

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Citation: https://doi.org/10.5194/egusphere-2025-4088-RC1
RC2:
'Comment on egusphere-2025-4088', Anonymous Referee #2, 20 Jan 2026 reply
General assessment
This study uses the emission-driven configuration of the MIROC-ES2L Earth system model – which includes new developments in permafrost physics compared to the CMIP6 version – to assess the physical response of permafrost in idealized scenarios. The focus is on the reversibility and hysteresis behavior of the permafrost area under symmetrical positive and negative emission pathways reaching different warming levels. The authors provide a mechanistic explanation of the simulated hysteresis and perform a sensitivity analysis to assess the impact of soil thermal conductivity and specific heat of water phase change on the reversibility and hysteresis of the permafrost area. Permafrost CO₂ and CH₄ emissions are diagnosed using an offline permafrost carbon emission model (PDGEM), driven by MIROC-ES2L physical permafrost state.
Overall, this is a nice study on an important topic, with potential policy-relevant implications. The simulation setup is relevant (although some choices should be clarified/discussed) and the use of emission-driven ESM simulations is well suited to studying the coupled response of the Earth system to positive and negative emissions. I found the separation between sherbet and ice areas particularly interesting and novel. However, there are some comments that I would like the authors to address, that are listed below.

Major Comments
The definition of permafrost area used in this study (Sect.2.3) is uncommon. Burke et al. (2020) use the temperature at the depth of zero annual amplitude, whereas Koven et al. (2013) use the criterion ALT < 3m. Steinert et al. (2024) showed that the choice of permafrost definition has significant impact on the value of the permafrost area. Could you please justify this choice ? Additionally, what impact does the permafrost definition have on the rate of decrease of permafrost area during warming, and on the delay to recovery ? In other words, do you still observe a two-time response during warming and a similar time lag with another permafrost definition (for example ALT<3 m) ?

The sensitivity of permafrost extent to global warming was very low in MIROC6, which was an outlier among CMIP6 models (Burke et al. (2020)). The effect of the modifications made in MATSIRO on this sensitivity should be discussed, as this was not assessed in Yokohata et al. (2020) (although the sensitivity of permafrost volume to warming was assessed), particularly since this study focuses on permafrost physics. Fig.3 b suggests that this sensitivity has increased, but it is unclear whether or not the model remains an outlier.

Using an offline model to diagnose permafrost carbon emissions is an interesting intermediate step before including permafrost carbon in the coupled ESM. However, some of the choices made in the offline PDGEM model require justification. In particular:

l.186-187 : Please justify the use of a random turnover time for soil organic carbon. To which “region” are you referring ? Is there a different turnover time for each grid cell ?

eq.1 : If the values of π are those in Table 1 of Yokohata et al. (2020) (0.025 for fast and 0.45 for slow pool → shouldn’t it be the opposite ?), does this mean that 45% of SOC from the slow pool is lost to the atmosphere right after permafrost thaw ? This seems overestimated (see for instance Fig.2 from Schuur et al. (2015) summarizing results from soil incubation experiments).

Is C_thaw a prognostic variable of the model (or is it read from an external map) ? If so, how is C_thaw initialised ? Its initial value is an important driver of SOC emissions from already thawed permafrost (second term of the right-hand side of eq.1).

The PDGEM model assumes a uniform SOC density throughout the profile in eq.4. This means that permafrost thawing at the surface or at depth would lead to the same carbon losses. However, global SOC (and soil properties) maps, such as SoilGrids (Poggio et al. (2021)) or HWSD2 (FAO and IIASA (2023)), have depth-resolved SOC profiles and could be used to estimate depth-dependent SOC emissions from permafrost thaw. Could you please justify and discuss the implications of this choice (in addition to l.470-472) ? Also, why does a uniform distribution lead to the overestimation of SOC emissions (as stated at l.470) ?

The choice to set d_SOC to 14m should be justified as this directly affects SOC losses from permafrost thawing (eq.4). The circum-Arctic SOC content from Saito et al. (2020) is 1032 PgC – which is comparable to the value from the Northern Circumpolar Soil Carbon Database v2 for the 0-3 m upper soil layers (1119 PgC) – and is unlikely to describe soil carbon down to 14 m. Therefore, using a depth of 14m (instead of, for example, 3m) to calculate SOC density could lead to underestimation. Please justify this choice.

It is not very clear what the percentages of permafrost CO₂ emissions refer to (0.6% for NEC8 and 41% for NEC2). I believe they correspond to the amount of thawed permafrost emissions during the negative-emission phase (NEC) divided by the total permafrost emissions during both the flat10 and NEC phases. If this is correct, this should be clarified, as the use of “prescribed cumulative carbon emissions” (l.46), “total cumulative emissions” (l.452) and “global carbon budgets” (l.560) is confusing and may suggest that this percentage refers to the fraction of permafrost emissions to total cumulative anthropogenic emissions (which does not seem to be the case). I also do not think that this metric is particularly meaningful. More policy-relevant metrics could be used instead, such as the percentage of additional negative emissions required to counter thawed permafrost emissions (i.e. permafrost emissions (during flat10+NEC) divided by cumulative (negative) anthropogenic emissions during the NEC phase), or the additional warming induced by permafrost emissions (calculated offline using the TCRE from MIROC-ES2L). These issues should be addressed at l.46, l.450-454 and l.559-561.

Minor comments
The use of 10¹³ m² for permafrost area is unusual. I suggest using either Mkm² or 10⁶ km².

The use of “permafrost property” without further precision is unclear (l.38, l.81, l.304, l.545). Please specify which property you are referring to.

l.31 : The general consensus on permafrost thaw is that it is not a global tipping element, but rather responds quasi linearly to climate warming (e.g. Nitzbon et al. (2024)). I suggest removing “an important tipping element”.

l.56 : The term “NH permafrost area” generally refers to the area underlain by permafrost, and its extent is ~15 Mkm² (Obu et al. 2021). Here, you probably refer to the permafrost region (the area covering continuous, discontinuous, sporadic and isolated permafrost, as defined in Obu et al., 2021), which covers ~21 Mkm².

l.76-79 : I think the authors should qualify this point. The inclusion of permafrost as a tipping element is still being debated. There is no evidence that permafrost is a global tipping element and only local to regional processes, such as talik development, are considered as tipping processes (Nitzbon et al. (2024)). Brovkin et al. (2025) suggest that permafrost could be a tipping element, but on centennial timescale, without sudden tipping. McKay et al. (2022) separate permafrost dynamics into its gradual thaw, abrupt thaw and collapse components. Only permafrost collapse could be a global tipping element but the level of confidence is low.

l.87-89 : A brief explanation of the proposed mechanism by Eliseev et al. (2014) could be included here or later in the Discussion.

Sect. 2.1 : Please consider adding a brief description of the equations governing soil heat dynamics and the calculation of soil physical properties, as these drive soil physics, which is the central topic of this study.

l.125 -127 : Is the organic soil (vertical) distribution similar to Yokohata et al (2020b) ? Considering fully organic soil physical properties (e.g. organic thermal conductivity) in 0.05-1 m in tundra and 0.25-2 m in taïga is probably overestimated and is likely to yield a very strong insulation effect. Except in peatlands, permafrost soils are generally not fully organic and organic matter generally amounts to a few percents in mass (e.g. Schiedung et al. (2022), Poggio et al. (2021)). Please discuss this assumption here or in the discussion section.

l.141 : Is this correction only applied to piControl, or also to flat10 and NEC experiments ?

l.143 : Does “in a year 100” means that the flat10 experiment starts after 100 years of piControl ? In that case, is the model already close to equilibrium after 100 years (i.e. is the drift already equal to 0.068 PgC/yr or is it larger) ?

l.143 : A 1000-year flat10 experiment results in extreme cumulative emissions (10 000 PgC) and global warming. Please justify the choice of this experiment.

l.151-160 : Although these are idealized scenarios that are not intended to be fully realistic, negative emission rates of 10 PgC/yr are likely to be unattainable (e.g. Zhang et al. (2024)). Could you please add a sentence discussing the realism and feasibility of these scenarios here or in the discussion ?

l.204 : Please give the unit of σ_SOC and ρ_SOC.

eq.1 : If I understand correctly, the first term on the right-hand side describes immediate carbon emissions that occur when permafrost thaws, and the second term describes the soil respiration that occurs in soil layers that have already thawed ? Could you please add a sentence to explain this, or if I am wrong, provide a detailed explanation of these two terms ?

eq.3 : Is ALT set to one of the soil layers of the model, or is it calculated by interpolating temperatures along the vertical profile (which allows for greater precision and avoids temporal “jumps”) ?

l.216 : I know it is difficult to disentangle feedbacks in coupled ESMs but could you explain why you think this slight non-reversibility is due to an albedo feedback ?

l.240-241 : Which observations are you referring to ? The initial state is pre-industrial and to my knowledge, there is no observational map of the permafrost region for that period.

l.245 : The very thick organic layer considered in this study is also likely to strongly insulate permafrost in summer and lower its sensitivity to warming.

l.254 : Why not in NEC8 ? It seems that the permafrost region continues to decrease for about 200 years in Fig.3 (a).

Fig.4 : Including the time evolution of the change in surface atmospheric temperature (SAT) over the permafrost region would help support the following explanation of the sherbet/ice role in the permafrost area dynamics. Otherwise, we cannot exclude that the two-time decrease during warming is due to a change in the Arctic amplification (and therefore in regional SAT given that GSAT increases linearly with time).

l.283 : Sentence starting with “On the other hand…”. The 1-2m (resp. 2-4 m) soil layer starts recovering around year 500 (resp. year 550), but the permafrost area only starts recovering around year 600. Therefore, permafrost recovery seems to start later than upper layers expansion.

l.299 : Is “sherbet” a common feature of permafrost soils ? I could not find any reference in existing literature.

l.303-327 : I found this separation between ice and sherbet very interesting and helpful to explain the hysteresis behavior.

l.347-354 : I found this paragraph hard to understand. Clearer connections between Fig.4 and Fig.6 may help to follow the explanation.

l.359 : Should a reference to Fig.5 be added as well ?

eq.5 : How does soil heat conductivity depend on soil organic content ? Does k_g0 varies depending on soil type ?

l.385 : Please add the unit of k_g, k_g0 and w_kg.

l.391 : Please add the unit of θ_i, C_g, ρ_w and l_mlt.

l. 403-406 : I do not fully agree with these statements. Increased soil conductivity seems to change the dynamics of the sherbet area (not its final state though), and to greatly reduce the hysteresis for the permafrost area.

l.420-421 : I agree that permafrost hysteresis is affected by heat conductivity and specific latent heat but it is not clear that they impact permafrost reversibility (permafrost area is quasi-reversible in all sensitivity experiments).

l.429-430 : The time of water phase change indeed depends on the soil moisture content. An additional analysis showing the evolution of soil moisture would help supporting statements of l.426-430. In particular, is there a change in the total soil moisture content between the warming and cooling phases ?

Sect.3.5 : Although this is clearly described in the Methods, it could be useful to recall that only permafrost emissions are assessed in this study, and that negative feedbacks such as increased vegetation productivity under increasing CO₂concentrations, or increased nitrogen availability from permafrost thaw and warming are not accounted for.

Fig.9 : Does this figure also include soil respiration from thawed soil (second term of the right hand side in eq.1) or only immediate SOC losses from permafrost thaw (first term in eq.1) ?

l.451-454 : In NEC8, shouldn’t thawed permafrost continue to emit carbon as a legacy effect, even when permafrost has completely thawed ?

l.482 : Please precise which metrics is irreversible (as permafrost area is quasi-reversible, but not ice/sherbet areas).

Fig. 10 a : Is this temperature over land only or land+ocean ?

Fig.11 a : The caption should mention that this corresponds to the NEC6 experiment.

Fig.11 c : Although the overall NH high latitudes show a cooling, the soil temperature change (4-14 m) at the end of NEC6 has marked cold and warm biases, especially in Siberia. Do you know the reason for these patches of colder/warmer temperatures ? Is it related with permafrost state and local surface-atmosphere energy exchanges (these patches do not correspond to area with remaining sherbet in Fig.5 (b)) ?

l. 532 : “This is because the surface cooling pattern is not uniform (Fig.11c).” → Doesn’t Fig.11 c show the change in deep soil temperature (not surface) ?

l.532-534 : Permafrost has also recovered in the northeastern Siberian area despite a strong positive deep soil temperature bias. More generally, I do not see a clear correlation between the pattern in deep soil temperature bias at the end of NEC6 and the sherbet distribution. Is there a significant correlation between permafrost recovery and deep soil temperature bias, or between sherbet presence and deep soil temperature bias ?

The discussion section is mainly composed of additional analyses and results but does not discuss the “Results” section. In particular, the results should be compared to existing modeling studies (partially) dealing with physical permafrost (ir)reversibility (Park et al. (2025), Boucher et al. (2012)).

l.542-543 : What does “reversible to both warming and cooling” mean ?

l.573-574 : This has not been clearly demonstrated in this study (although Fig.1 provides some insights) and should be supported by a figure and/or numbers. This paragraph would be more appropriate in the Discussion section.

l.576 : Which uncertainty are you referring to ? Hysteresis/irreversibility in the TCRE ? If so, Koven et al. (2022) should be included in the discussion, as they have assessed TCRE reversibility for six ESMs under the SSP5-3.4-OS scenario.

Technical corrections
l.35 : replace "PgC" by "PgC yr⁻¹".

l.163 : replace “grid” by “grid cell”.

l. 175 : remove “dates” ?

Fig.1 : the zero line (and other horizontal gray dashed lines) is slightly shifted from the y axis.

l.245 : replace “of” by “to” ?

l.251-257 : replace “m²” by “m³”. The use of Mkm² or 10⁶ km² is more common.

l.282 : replace “Fig.4 a, c” by “Fig.4 b, c”.

l.423 : typo in “Eliseev".

Fig.11 c and d : The label of the colorbar is incorrect and there is an error in the caption (it should be “(c) the end of NEC6”).

References
Boucher O. et al 2012 Environ. Res. Lett. 7 024013
Brovkin, V., Bartsch, A., Hugelius, G. et al. Permafrost and Freshwater Systems in the Arctic as Tipping Elements of the Climate System. Surv Geophys 46, 303–326 (2025). https://doi.org/10.1007/s10712-025-09885-9
Burke, E. J., Zhang, Y., and Krinner, G.: Evaluating permafrost physics in the Coupled Model Intercomparison Project 6 (CMIP6) models and their sensitivity to climate change, The Cryosphere, 14, 3155–3174, https://doi.org/10.5194/tc-14-3155-2020, 2020.
David I. Armstrong McKay et al., Exceeding 1.5°C global warming could trigger multiple climate tipping points.Science377,eabn7950(2022).DOI:10.1126/science.abn7950
FAO & IIASA. 2023. Harmonized World Soil Database Version 2.0. Rome and Laxenburg.
Koven, C. D., W. J. Riley, and A. Stern, 2013: Analysis of Permafrost Thermal Dynamics and Response to Climate Change in the CMIP5 Earth System Models. J. Climate, 26, 1877–1900, https://doi.org/10.1175/JCLI-D-12-00228.1.
Koven, C. D., Arora, V. K., Cadule, P., Fisher, R. A., Jones, C. D., Lawrence, D. M., Lewis, J., Lindsay, K., Mathesius, S., Meinshausen, M., Mills, M., Nicholls, Z., Sanderson, B. M., Séférian, R., Swart, N. C., Wieder, W. R., and Zickfeld, K.: Multi-century dynamics of the climate and carbon cycle under both high and net negative emissions scenarios, Earth Syst. Dynam., 13, 885–909, https://doi.org/10.5194/esd-13-885-2022, 2022.
Nitzbon, J., Schneider von Deimling, T., Aliyeva, M. et al. No respite from permafrost-thaw impacts in the absence of a global tipping point. Nat. Clim. Chang. 14, 573–585 (2024). https://doi.org/10.1038/s41558-024-02011-4
Obu, J. (2021). How much of the Earth's surface is underlain by permafrost? Journal of Geophysical Research: Earth Surface, 126, e2021JF006123. https://doi.org/10.1029/2021JF006123
Park SW et al., Continued permafrost ecosystem carbon loss under net-zero and negative emissions.Sci. Adv.11,eadn8819(2025).DOI:10.1126/sciadv.adn8819
Poggio, L., de Sousa, L. M., Batjes, N. H., Heuvelink, G. B. M., Kempen, B., Ribeiro, E., and Rossiter, D.: SoilGrids 2.0: producing soil information for the globe with quantified spatial uncertainty, SOIL, 7, 217–240, https://doi.org/10.5194/soil-7-217-2021, 2021.
Schiedung, M., Bellè, S.-L., Malhotra, A., Abiven, S., 2022. Organic carbon stocks, quality and prediction in permafrost-affected forest soils in North Canada. Catena 213, 106194. https://doi.org/10.1016/j.catena.2022.106194.
Schuur, E., McGuire, A., Schädel, C. et al. Climate change and the permafrost carbon feedback. Nature 520, 171–179 (2015). https://doi.org/10.1038/nature14338
Steinert N.J. et al 2024 Environ. Res. Lett. 19 014033
Zhang, Y., Jackson, C. & Krevor, S. The feasibility of reaching gigatonne scale CO₂ storage by mid-century. Nat Commun 15, 6913 (2024). https://doi.org/10.1038/s41467-024-51226-8

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Citation: https://doi.org/10.5194/egusphere-2025-4088-RC2

Natsuki Watanabe, Masahiro Watanabe, Tomohiro Hajima, Tokuta Yokohata, and Irina Melnikova

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Permafrost stores a large amount of carbon which will be released as green house gases (GHGs) if thawing occurs during global warming. Using a CMIP6-class Earth System Model, we studied permafrost response to CO₂ emission changes. We found permafrost area is reversible but with hysteresis, while permafrost property shows irreversibility. These arise from delay in soil moisture phase change. Because of hysteresis, permafrost thaws even during climate recovery, releasing additional GHGs.


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Hysteresis and irreversibility in permafrost physical response to increase and decrease of CO2 emissions

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Hysteresis and irreversibility in permafrost physical response to increase and decrease of CO₂ emissions