the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Jul 2024
The Effectiveness of Agricultural Carbon Dioxide Removal using the University of Victoria Earth System Climate Model
Abstract. A growing body of evidence suggests that to achieve the temperature goals of the Paris Agreement, carbon dioxide removal (CDR) will likely be required in addition to massive carbon dioxide (CO2) emissions reductions. Nature-based CDR, which includes a range of strategies to sequester carbon in natural reservoirs, could play an important role in efforts to limit climate warming to well below 2 °C above preindustrial levels. Agricultural CDR could enhance soil carbon sequestration, though the climate efficacy of such methods remains uncertain. Here, we use an intermediate complexity climate model to perform simulations of agricultural CDR in the form of soil carbon sequestration at a range of possible rates for different costs under three future emissions scenarios. We found that plausible levels of agricultural CDR were able to reduce CO2 concentration by 5–19 ppm and global surface air temperature by 0.02–0.10 °C by the end of century. This temperature decrease was non-linear with respect to cumulative removals, as any carbon removed remained part of the active carbon cycle, lessening the climate benefit compared to if the removed carbon was permanently stored in geological reservoirs. CDR was found to be more effective at reducing surface air temperature in low emissions scenarios, but less effective at reducing atmospheric CO2, compared to high emissions scenarios. This was because the weaker CO2 sinks in a high CO2 world had a more muted response to removal, so a substantially higher proportion of carbon was removed from the atmosphere for a given amount of CDR in a higher emissions scenario. The enhanced temperature response to CDR in lower emissions scenarios was due to the logarithmic response of radiative effects to changes in CO2, where at low atmospheric CO2 concentrations, small changes in CO2 are more effective at changing the global radiative balance than at higher CO2 concentrations. CDR was substantially more effective when implemented at a higher rate, as CDR makes a proportionally larger difference in a climate with lower cumulative air fraction of CO2. Land and soil carbon responses were driven by the scenario-dependent balances between the impacts of CDR on primary productivity from CO2 fertilization, and the impacts on soil respiration from increased soil carbon availability and global temperatures.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(3757 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-1810', Yi Yang, 31 Aug 2024
Overall comments:
This paper uses the UVic ESCM earth system model to evaluate and assess the effectiveness and impacts of agricultural carbon dioxide removal. Carbon dioxide removal is an important issue in the era of climate change, and nature based climate solutions are potential pathways to partially address the climate crisis. Therefore, the issue that the paper is trying to address is relevant to the broad geoscience community. The results and analysis on the model simulation are comprehensive and thorough, and several insights are highlighted based on the results.
However, there are some major issues of this paper, including language and writing, methodological rigor, and the lack of discussion on the limitations. I encourage the authors to address these issues and improve the paper before publishing.
Major comments:
1. The writing of this paper needs to be improved. Although the topic of this paper is of broad interest to the geoscience community, the way it is presented lacks clarity, especially the introduction section. In the introduction, the authors only mention the research gap in the last paragraph, which is confusing and unconventional for an introduction in a research paper. Instead, I suggest the authors restructure the introduction section to follow a more clear logic, for example, general topic – research gap – how this paper addresses the gap.
2. There should be more explanation and discussions on how agricultural CDR is implemented. The paper only says that the agricultural CDR was achieved by prescribing an atmosphere-to-soil carbon flux in agricultural areas, and any changes in natural carbon storage and fluxes occurring will be considered as feedback effects. While I believe may be reasonable to do so, a more thorough explanation on how each type of CDR is implemented in real life (e.g., nutrient management, reforestations, etc.), and if it can be more accurately incorporated into the model should be provided. If there are more accurate ways of modeling them, the authors should adopt them. Also, even if the simplification is reasonable, the implications of this simplification should also be discussed. For example, will there be any constraint that the CDR and the feedback jointly have to satisfy?
3.While the simulation results are comprehensive and thorough, the paper does not provide any uncertainty quantification, nor does it discuss any implications about uncertainty. I suggest the authors use some commonly used uncertainty quantification metrics for the results. If the uncertainty quantification is too challenging given the context or too cumbersome for this paper, possible sources of uncertainty and its implications should be at least discussed.
4. I suggest the authors add a dedicated session to discuss the implications.
Citation: https://doi.org/10.5194/egusphere-2024-1810-RC1 -
AC1: 'Reply on RC1', Rebecca Evans, 08 Oct 2024
The authors would first like to thank you for your very helpful and constructive feedback. We find all of your major comments agreeable and will address each of them individually below.
1 - Introduction. We are happy to improve the writing of all sections but especially the introduction so that the focus of the paper is clearer from the outset and with more clarity on discussion. Thank you for your feedback.
2 - Methodology discussion related to agricultural CDR prescribed flux. With the current model setup, it is not currently possible to model the components of agricultural CDR flux (biochar, nutrient management etc.). This is because several of the important components of agricultural CDR (in particular pyrogenic carbon storage from biochar and human activities in agriculture) are not currently modeled by the UVic ESCM. However, in the near future our research group plans to write new modules to incorporate these components in to the UVic ESCM, thus more accurate portrayal of the components of agricultural CDR should be possible after that is complete. In lieu of being able to model these components, a simple flux was used in this study. We are happy to add an explanation to the paper of why that simplification was used in the study, and implications of doing so.
3 - Uncertainty. We will look in to quantifying uncertainty and believe it should be possible. If not, we are happy to add a discussion on the topic as you suggested.
4 - Dedication implications section. Thank you for the suggestion, we will do so.
Citation: https://doi.org/10.5194/egusphere-2024-1810-AC1
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AC1: 'Reply on RC1', Rebecca Evans, 08 Oct 2024
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RC2: 'Comment on egusphere-2024-1810', Anonymous Referee #2, 19 Sep 2024
The manuscript investigates the potential for agricultural carbon dioxide removal (CDR) to mitigate climate change by simulating soil carbon sequestration using the University of Victoria Earth System Climate Model (UVic ESCM).
However, the paper’s simplified treatment of agricultural CDR presents a key limitation by applying a uniform atmosphere-to-soil carbon flux across agricultural areas. This generalization does not account for the significant variability in the efficacy of different agricultural management practices, which critically affect carbon retention and sequestration longevity. Therefore, it's difficult to judge the robustness and uncertainty level of the assessed numbers. A comparison between the current study and previous assessment would be appreciated.
Missed Mechanistic Detail:
Treating all agricultural CDR methods as a uniform flux from the atmosphere to the soil ignores the inherent complexities of soil carbon turnover. Different agricultural techniques impact microbial activity, soil structure, and decomposition rates differently. For example, practices that increase soil aeration (like tilling) could accelerate carbon release through respiration, undermining long-term sequestration.
- Biochar: This method results in long-term carbon sequestration, as biochar can persist in soils for hundreds to thousands of years. Its resistance to decomposition means that biochar acts as a more permanent carbon sink.
- No-Till Farming: While this method reduces soil disturbance and thereby helps increase soil organic carbon in the short term, its long-term efficacy may be more variable. The retained carbon could be vulnerable to re-release through natural processes like soil respiration.
- Cover Cropping and Crop Rotations: These practices can increase soil organic matter, but the degree of sequestration depends heavily on crop types, climate, and soil properties. They generally offer more temporary sequestration benefits compared to biochar.
Limited Exploration of Economic and Practical Feasibility: While the authors mention the costs associated with low, moderate, and high CDR scenarios, there is no rigorous exploration of how economically feasible these interventions would be, or how they could be integrated into current agricultural systems without significant trade-offs.
Another significant limitation of the paper lies in its failure to rigorously address uncertainties inherent in the Shared Socioeconomic Pathways (SSPs) used in the simulations. These pathways—SSP1-1.9, SSP2-4.5, and SSP5-8.5—represent different global development and emissions scenarios, but the uncertainties associated with these scenarios are not thoroughly explored.
Overall, the manuscript is in good shape but could benefit from further refinement.
Citation: https://doi.org/10.5194/egusphere-2024-1810-RC2 -
AC2: 'Reply on RC2', Rebecca Evans, 08 Oct 2024
The authors would first like to thank you for your helpful comments. We will address each comment in more detail below, but we overall believe they will be very useful in improving the paper.
1 - Limitation of using a uniform atmosphere-to-soil carbon flux. This is very important to note and we plan to incorporate this into the (new) discussion section as well as more discussion of uncertainty. For this study, we opted to prescribe a uniform flux to show, to the first order, what climate responses could theoretically occur given some rates of CDR. One reason for this choice is that the UVic ESCM, with the current available modules, cannot model some important components of agricultural CDR (such as pyrogenic carbon storage from biochar, and managed land practices). Planned work in the near future by our lab includes writing modules for the UVic ESCM that will be able to model these components. Thus in the near future, we should be able to more accurately model (in both a spatial and biogeochemical sense) the components of agricultural CDR and thus have a more robust estimate of its climate mitigation possibilities. This study was intended to be a first order approximation, so we are happy to add more discussion of why that choice was made and the implications on the results. We are happy to add comparisons with other studies as well.
2 - Missed Mechanistic Details. We absolutely agree that the complexities of each component of agricultural CDR would impact the results. While future work by our lab plans to address each of these components, for the purposes of this study, many of the components cannot be modeled with the current model setup. As such we will add more detailed discussion of the implications of our simplification of atmosphere-to-soil carbon flux.
3 - Economic and Practical Feasibility. We are happy to add mention of the economic feasibility to this paper. However, this would be an enormous topic on its own and worthy of its own (several) papers. For this reason we believe it to be outside the scope of this study, but are happy to discuss it briefly in the paper for the sake of completeness.
4 - Uncertainty in the SSPs. This is a helpful point, and we will add more explanation of the uncertainties in the baseline scenarios we used and how it may impact our results.
Citation: https://doi.org/10.5194/egusphere-2024-1810-AC2
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-1810', Yi Yang, 31 Aug 2024
Overall comments:
This paper uses the UVic ESCM earth system model to evaluate and assess the effectiveness and impacts of agricultural carbon dioxide removal. Carbon dioxide removal is an important issue in the era of climate change, and nature based climate solutions are potential pathways to partially address the climate crisis. Therefore, the issue that the paper is trying to address is relevant to the broad geoscience community. The results and analysis on the model simulation are comprehensive and thorough, and several insights are highlighted based on the results.
However, there are some major issues of this paper, including language and writing, methodological rigor, and the lack of discussion on the limitations. I encourage the authors to address these issues and improve the paper before publishing.
Major comments:
1. The writing of this paper needs to be improved. Although the topic of this paper is of broad interest to the geoscience community, the way it is presented lacks clarity, especially the introduction section. In the introduction, the authors only mention the research gap in the last paragraph, which is confusing and unconventional for an introduction in a research paper. Instead, I suggest the authors restructure the introduction section to follow a more clear logic, for example, general topic – research gap – how this paper addresses the gap.
2. There should be more explanation and discussions on how agricultural CDR is implemented. The paper only says that the agricultural CDR was achieved by prescribing an atmosphere-to-soil carbon flux in agricultural areas, and any changes in natural carbon storage and fluxes occurring will be considered as feedback effects. While I believe may be reasonable to do so, a more thorough explanation on how each type of CDR is implemented in real life (e.g., nutrient management, reforestations, etc.), and if it can be more accurately incorporated into the model should be provided. If there are more accurate ways of modeling them, the authors should adopt them. Also, even if the simplification is reasonable, the implications of this simplification should also be discussed. For example, will there be any constraint that the CDR and the feedback jointly have to satisfy?
3.While the simulation results are comprehensive and thorough, the paper does not provide any uncertainty quantification, nor does it discuss any implications about uncertainty. I suggest the authors use some commonly used uncertainty quantification metrics for the results. If the uncertainty quantification is too challenging given the context or too cumbersome for this paper, possible sources of uncertainty and its implications should be at least discussed.
4. I suggest the authors add a dedicated session to discuss the implications.
Citation: https://doi.org/10.5194/egusphere-2024-1810-RC1 -
AC1: 'Reply on RC1', Rebecca Evans, 08 Oct 2024
The authors would first like to thank you for your very helpful and constructive feedback. We find all of your major comments agreeable and will address each of them individually below.
1 - Introduction. We are happy to improve the writing of all sections but especially the introduction so that the focus of the paper is clearer from the outset and with more clarity on discussion. Thank you for your feedback.
2 - Methodology discussion related to agricultural CDR prescribed flux. With the current model setup, it is not currently possible to model the components of agricultural CDR flux (biochar, nutrient management etc.). This is because several of the important components of agricultural CDR (in particular pyrogenic carbon storage from biochar and human activities in agriculture) are not currently modeled by the UVic ESCM. However, in the near future our research group plans to write new modules to incorporate these components in to the UVic ESCM, thus more accurate portrayal of the components of agricultural CDR should be possible after that is complete. In lieu of being able to model these components, a simple flux was used in this study. We are happy to add an explanation to the paper of why that simplification was used in the study, and implications of doing so.
3 - Uncertainty. We will look in to quantifying uncertainty and believe it should be possible. If not, we are happy to add a discussion on the topic as you suggested.
4 - Dedication implications section. Thank you for the suggestion, we will do so.
Citation: https://doi.org/10.5194/egusphere-2024-1810-AC1
-
AC1: 'Reply on RC1', Rebecca Evans, 08 Oct 2024
-
RC2: 'Comment on egusphere-2024-1810', Anonymous Referee #2, 19 Sep 2024
The manuscript investigates the potential for agricultural carbon dioxide removal (CDR) to mitigate climate change by simulating soil carbon sequestration using the University of Victoria Earth System Climate Model (UVic ESCM).
However, the paper’s simplified treatment of agricultural CDR presents a key limitation by applying a uniform atmosphere-to-soil carbon flux across agricultural areas. This generalization does not account for the significant variability in the efficacy of different agricultural management practices, which critically affect carbon retention and sequestration longevity. Therefore, it's difficult to judge the robustness and uncertainty level of the assessed numbers. A comparison between the current study and previous assessment would be appreciated.
Missed Mechanistic Detail:
Treating all agricultural CDR methods as a uniform flux from the atmosphere to the soil ignores the inherent complexities of soil carbon turnover. Different agricultural techniques impact microbial activity, soil structure, and decomposition rates differently. For example, practices that increase soil aeration (like tilling) could accelerate carbon release through respiration, undermining long-term sequestration.
- Biochar: This method results in long-term carbon sequestration, as biochar can persist in soils for hundreds to thousands of years. Its resistance to decomposition means that biochar acts as a more permanent carbon sink.
- No-Till Farming: While this method reduces soil disturbance and thereby helps increase soil organic carbon in the short term, its long-term efficacy may be more variable. The retained carbon could be vulnerable to re-release through natural processes like soil respiration.
- Cover Cropping and Crop Rotations: These practices can increase soil organic matter, but the degree of sequestration depends heavily on crop types, climate, and soil properties. They generally offer more temporary sequestration benefits compared to biochar.
Limited Exploration of Economic and Practical Feasibility: While the authors mention the costs associated with low, moderate, and high CDR scenarios, there is no rigorous exploration of how economically feasible these interventions would be, or how they could be integrated into current agricultural systems without significant trade-offs.
Another significant limitation of the paper lies in its failure to rigorously address uncertainties inherent in the Shared Socioeconomic Pathways (SSPs) used in the simulations. These pathways—SSP1-1.9, SSP2-4.5, and SSP5-8.5—represent different global development and emissions scenarios, but the uncertainties associated with these scenarios are not thoroughly explored.
Overall, the manuscript is in good shape but could benefit from further refinement.
Citation: https://doi.org/10.5194/egusphere-2024-1810-RC2 -
AC2: 'Reply on RC2', Rebecca Evans, 08 Oct 2024
The authors would first like to thank you for your helpful comments. We will address each comment in more detail below, but we overall believe they will be very useful in improving the paper.
1 - Limitation of using a uniform atmosphere-to-soil carbon flux. This is very important to note and we plan to incorporate this into the (new) discussion section as well as more discussion of uncertainty. For this study, we opted to prescribe a uniform flux to show, to the first order, what climate responses could theoretically occur given some rates of CDR. One reason for this choice is that the UVic ESCM, with the current available modules, cannot model some important components of agricultural CDR (such as pyrogenic carbon storage from biochar, and managed land practices). Planned work in the near future by our lab includes writing modules for the UVic ESCM that will be able to model these components. Thus in the near future, we should be able to more accurately model (in both a spatial and biogeochemical sense) the components of agricultural CDR and thus have a more robust estimate of its climate mitigation possibilities. This study was intended to be a first order approximation, so we are happy to add more discussion of why that choice was made and the implications on the results. We are happy to add comparisons with other studies as well.
2 - Missed Mechanistic Details. We absolutely agree that the complexities of each component of agricultural CDR would impact the results. While future work by our lab plans to address each of these components, for the purposes of this study, many of the components cannot be modeled with the current model setup. As such we will add more detailed discussion of the implications of our simplification of atmosphere-to-soil carbon flux.
3 - Economic and Practical Feasibility. We are happy to add mention of the economic feasibility to this paper. However, this would be an enormous topic on its own and worthy of its own (several) papers. For this reason we believe it to be outside the scope of this study, but are happy to discuss it briefly in the paper for the sake of completeness.
4 - Uncertainty in the SSPs. This is a helpful point, and we will add more explanation of the uncertainties in the baseline scenarios we used and how it may impact our results.
Citation: https://doi.org/10.5194/egusphere-2024-1810-AC2
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Rebecca Chloe Evans
H. Damon Matthews
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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