the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Comment on “An approach to sulfate geoengineering with surface emissions of carbonyl sulfide” by Quaglia et al. (2022)
Christoph Brühl
Sinikka T. Lennartz
Mary E. Whelan
Aleya Kaushik
Abstract. Solar radiation management through artificially increasing the amount of stratospheric sulfate aerosol is being considered as a possible climate engineering method. To overcome the challenge of transporting the necessary amount of sulfur to the stratosphere, Quaglia and co-workers suggest deliberate emissions of carbonyl sulfide (OCS), a long-lived precursor of atmospheric sulfate. In their paper, published in Atmospheric Chemistry and Physics in 2022, they outline two scenarios with OCS emissions either at the Earth’s surface or in the tropical upper troposphere and calculate the expected radiative forcing using a climate model. In our opinion, the study (i) neglects a significantly higher surface uptake that will inevitably be induced by the elevated atmospheric OCS concentrations and (ii) overestimates the net cooling effect of this OCS geoengineering approach due to some questionable parameterizations and assumptions in the radiative forcing calculations. In this commentary, we use state of the art models to show that at the mean atmospheric OCS mixing ratios of the two emissions scenarios, the terrestrial biosphere and the oceans are expected to take up more OCS than is being released to reach these levels. Using chemistry climate models with a long-standing record for estimating the climate forcing of OCS and stratospheric aerosols, we also show that the net radiative forcing of the emission scenarios suggested by Quaglia and co-workers is smaller than suggested and insufficient to offset any significant portion of anthropogenically induced climate change. Our conclusion is that a geoengineering approach using OCS will not work under any circumstances and should not be considered further.
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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
(1308 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.
Journal article(s) based on this preprint
Marc von Hobe et al.
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-268', Daniele Visioni, 01 Mar 2023
As the second author of the Quaglia et al. (2022) , I'm very happy to have been asked to review this, and of this comment in general (also useful to point this out at the very beginning for COI reasons).
The authors make a lot of excellent points (no doubt, given their expertises), and highlight multiple reasons why OCS as a substitute to SO₂ injections would be not feasible as a form of stratospheric aerosol sources for climate intervention. While true that this had been mentioned in the past literature in a few occasions, using climate models to test out the hypotesis is always a useful exercise. If the evidences start to pile up around its unfeasibility, that can only be good news, it's Science after all. I strongly reccomend publication of this piece - hoping the authors can address some of my comments below around Section 4.
Sections 2 and 3 are really informative and well written and I have no comments over them.
Section 4:
- point well taken on the IR differences between our estimates and the authors' (but I wish the authors explained more why they see such a discrepancies with our estimates in the LW. What in the radiative-convective model they use changes the results compared to ours?)
- in ULAQ-CCM, evaporation is indeed calculated at every vertical level as a function of H2SO4 vapor pressure, surface area density and kernel for condensation.
- while the authors correctly point out to Fig. S2, looking at Fig. S3 clearly highlights that the peak in extinction and SAD appears much lower than 35 km, at around 21-22km, so - while there might be discrepancies between the forcing we calculate and the authors to this piece calculate - the reason why ours is higher and theirs is lower is not the fact that the ULAQ-CCM aerosols are so higher up, or at least that's not the main factor.
- differences in forcing could be due to many factors, such as aerosol size (which is report in Table 1 for ULAQ-CCM), H2O changes, ozone etc.. If the overall value the authors obtain is -0.4 W/m2 that is absolutely fair, but in the conclusions to the section I would just say "which is less than a third than was estimated in Quaglia et al. (2022), and would not be able to fully compensate for the forcing by anthropogenic CO₂ at the suggested injection rates" rather than just "which cannot compensate for forcing by anthropogenic CO₂"
- My last comment is that it's my understanding that ACP does not accept "available from the authors upon request" as a data availability statement, and so that part should be amended to include a DOI where data could be publicly accessed.
Citation: https://doi.org/10.5194/egusphere-2023-268-RC1 -
AC1: 'Reply on RC1', Marc von Hobe, 26 Apr 2023
We thank Daniele for his openness towards the scientific discourse expressed in his opening statement. Exchanging scientific evidence and arguments, and taking them into consideration and allow conclusions to evolve, is indeed what good Science should be about. We also appreciate the important questions and comments on Section 4 of our paper, which we respond to below (in italics).
- point well taken on the IR differences between our estimates and the authors' (but I wish the authors explained more why they see such a discrepancies with our estimates in the LW. What in the radiative-convective model they use changes the results compared to ours?)
We believe that the discrepancy arises from the method chosen by Quaglia et al. to calculate the infrared forcing. For a steady state change of the mixing ratio profile of a greenhouse trace gas, the change in infrared forcing should be calculated directly and not via the GWP concept, which is designed for comparing the effect of emissions of two greenhouse gases. We have added a corresponding statement in the manuscript. We also added an additional reference that gives more detailed information on the radiative-convective model used.
- in ULAQ-CCM, evaporation is indeed calculated at every vertical level as a function of H2SO4 vapor pressure, surface area density and kernel for condensation.
We replaced “neglected” by “underestimated”.
- while the authors correctly point out to Fig. S2, looking at Fig. S3 clearly highlights that the peak in extinction and SAD appears much lower than 35 km, at around 21-22km, so - while there might be discrepancies between the forcing we calculate and the authors to this piece calculate - the reason why ours is higher and theirs is lower is not the fact that the ULAQ-CCM aerosols are so higher up, or at least that's not the main factor.
Still, the sulfate maximum at ~35 km is unrealistic and also not supported by observations (as noted in the revised manuscript). Overall, the different results of the two models are consistent with findings in the model intercomparison paper by Quaglia et al. (2023), where ULAQ-CCM is near the high end and EMAC more at the low side concerning stratospheric optical depth. We added a corresponding statement and a reference to the Quaglia et al. (2023) paper in the revised manuscript.
- differences in forcing could be due to many factors, such as aerosol size (which is report in Table 1 for ULAQ-CCM), H2O changes, ozone etc.. If the overall value the authors obtain is -0.4 W/m2 that is absolutely fair, but in the conclusions to the section I would just say "which is less than a third than was estimated in Quaglia et al. (2022), and would not be able to fully compensate for the forcing by anthropogenic CO₂ at the suggested injection rates" rather than just "which cannot compensate for forcing by anthropogenic CO₂"
We changed the sentence at the end of Section 4 to: “In our calculations we get only -0.4 W m-2 for the TTL scenario and present-day conditions (2017 to 2021), which can only partially compensate for forcing by anthropogenic CO2 at the suggested injection rates.”
In the conclusions, we changed “insignificant” to “insufficient” in the concluding statement on the expected net cooling from OCS addition.
- My last comment is that it's my understanding that ACP does not accept "available from the authors upon request" as a data availability statement, and so that part should be amended to include a DOI where data could be publicly accessed.
We have uploaded our data in zenodo (one record for each model) and include the appropriate references and DOIs in the revised manuscript.
Citation: https://doi.org/10.5194/egusphere-2023-268-AC1
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AC1: 'Reply on RC1', Marc von Hobe, 26 Apr 2023
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RC2: 'Comment on egusphere-2023-268', Anonymous Referee #2, 29 Mar 2023
Review of “Comment on “An approach to sulfate geoengineering with surface emissions of carbonyl sulfide” by Quaglia et al. (2022)”
This short article seeks to point out deficiencies or oversights in the Quaglia et al. paper. They look specifically at 4 topics: uptake by plants, uptake by oceans, implications for toxicity due to higher concentrations resulting from geoengineering scenarios envisaged and revisit radiative effects. The paper is clear and succinct in that it soundly points to the non-viability of OCS injection to counter radiative warming due to increasing atmospheric CO2 and points to yet to be studied though likely toxic effects to terrestrial biosphere and the marine ecosystem. It does this with existing, available models that show how sensitive the ecosystem and oceanic are to atmospheric OCS concentrations and that they will uptake excess OCS to their likely detriment.
Major Issues
None.
Minor Issues
None.
Reviewer general comment.
The authors note in the introduction, that in the original review process of the Quaglia et al. paper an objection was made for not investigating the effect of higher atmospheric concentrations on the terrestrial biosphere. The editors allowed a brief statement to sidestep the opportunity to address this critical point and apparently others. Although an author can make any statement they deem valid and escape thoroughness via caveats, this is quite an obvious oversight. Through this comment these points have been made and the record set on an improved path. Though we are left to wonder why a critical stance was not taken at the time of the original review to strengthen the Quaglia paper. That decision was the consequence of the editorial staff’s commitment to standards for scientific rigor or not.
Citation: https://doi.org/10.5194/egusphere-2023-268-RC2 -
AC2: 'Reply on RC2', Marc von Hobe, 26 Apr 2023
We thank the reviewer for the appreciation of our initiative to write this short comment.
We are also grateful for the closing remark at the end of the review comment. We fully agree and have nothing to add, really.
Citation: https://doi.org/10.5194/egusphere-2023-268-AC2
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AC2: 'Reply on RC2', Marc von Hobe, 26 Apr 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-268', Daniele Visioni, 01 Mar 2023
As the second author of the Quaglia et al. (2022) , I'm very happy to have been asked to review this, and of this comment in general (also useful to point this out at the very beginning for COI reasons).
The authors make a lot of excellent points (no doubt, given their expertises), and highlight multiple reasons why OCS as a substitute to SO₂ injections would be not feasible as a form of stratospheric aerosol sources for climate intervention. While true that this had been mentioned in the past literature in a few occasions, using climate models to test out the hypotesis is always a useful exercise. If the evidences start to pile up around its unfeasibility, that can only be good news, it's Science after all. I strongly reccomend publication of this piece - hoping the authors can address some of my comments below around Section 4.
Sections 2 and 3 are really informative and well written and I have no comments over them.
Section 4:
- point well taken on the IR differences between our estimates and the authors' (but I wish the authors explained more why they see such a discrepancies with our estimates in the LW. What in the radiative-convective model they use changes the results compared to ours?)
- in ULAQ-CCM, evaporation is indeed calculated at every vertical level as a function of H2SO4 vapor pressure, surface area density and kernel for condensation.
- while the authors correctly point out to Fig. S2, looking at Fig. S3 clearly highlights that the peak in extinction and SAD appears much lower than 35 km, at around 21-22km, so - while there might be discrepancies between the forcing we calculate and the authors to this piece calculate - the reason why ours is higher and theirs is lower is not the fact that the ULAQ-CCM aerosols are so higher up, or at least that's not the main factor.
- differences in forcing could be due to many factors, such as aerosol size (which is report in Table 1 for ULAQ-CCM), H2O changes, ozone etc.. If the overall value the authors obtain is -0.4 W/m2 that is absolutely fair, but in the conclusions to the section I would just say "which is less than a third than was estimated in Quaglia et al. (2022), and would not be able to fully compensate for the forcing by anthropogenic CO₂ at the suggested injection rates" rather than just "which cannot compensate for forcing by anthropogenic CO₂"
- My last comment is that it's my understanding that ACP does not accept "available from the authors upon request" as a data availability statement, and so that part should be amended to include a DOI where data could be publicly accessed.
Citation: https://doi.org/10.5194/egusphere-2023-268-RC1 -
AC1: 'Reply on RC1', Marc von Hobe, 26 Apr 2023
We thank Daniele for his openness towards the scientific discourse expressed in his opening statement. Exchanging scientific evidence and arguments, and taking them into consideration and allow conclusions to evolve, is indeed what good Science should be about. We also appreciate the important questions and comments on Section 4 of our paper, which we respond to below (in italics).
- point well taken on the IR differences between our estimates and the authors' (but I wish the authors explained more why they see such a discrepancies with our estimates in the LW. What in the radiative-convective model they use changes the results compared to ours?)
We believe that the discrepancy arises from the method chosen by Quaglia et al. to calculate the infrared forcing. For a steady state change of the mixing ratio profile of a greenhouse trace gas, the change in infrared forcing should be calculated directly and not via the GWP concept, which is designed for comparing the effect of emissions of two greenhouse gases. We have added a corresponding statement in the manuscript. We also added an additional reference that gives more detailed information on the radiative-convective model used.
- in ULAQ-CCM, evaporation is indeed calculated at every vertical level as a function of H2SO4 vapor pressure, surface area density and kernel for condensation.
We replaced “neglected” by “underestimated”.
- while the authors correctly point out to Fig. S2, looking at Fig. S3 clearly highlights that the peak in extinction and SAD appears much lower than 35 km, at around 21-22km, so - while there might be discrepancies between the forcing we calculate and the authors to this piece calculate - the reason why ours is higher and theirs is lower is not the fact that the ULAQ-CCM aerosols are so higher up, or at least that's not the main factor.
Still, the sulfate maximum at ~35 km is unrealistic and also not supported by observations (as noted in the revised manuscript). Overall, the different results of the two models are consistent with findings in the model intercomparison paper by Quaglia et al. (2023), where ULAQ-CCM is near the high end and EMAC more at the low side concerning stratospheric optical depth. We added a corresponding statement and a reference to the Quaglia et al. (2023) paper in the revised manuscript.
- differences in forcing could be due to many factors, such as aerosol size (which is report in Table 1 for ULAQ-CCM), H2O changes, ozone etc.. If the overall value the authors obtain is -0.4 W/m2 that is absolutely fair, but in the conclusions to the section I would just say "which is less than a third than was estimated in Quaglia et al. (2022), and would not be able to fully compensate for the forcing by anthropogenic CO₂ at the suggested injection rates" rather than just "which cannot compensate for forcing by anthropogenic CO₂"
We changed the sentence at the end of Section 4 to: “In our calculations we get only -0.4 W m-2 for the TTL scenario and present-day conditions (2017 to 2021), which can only partially compensate for forcing by anthropogenic CO2 at the suggested injection rates.”
In the conclusions, we changed “insignificant” to “insufficient” in the concluding statement on the expected net cooling from OCS addition.
- My last comment is that it's my understanding that ACP does not accept "available from the authors upon request" as a data availability statement, and so that part should be amended to include a DOI where data could be publicly accessed.
We have uploaded our data in zenodo (one record for each model) and include the appropriate references and DOIs in the revised manuscript.
Citation: https://doi.org/10.5194/egusphere-2023-268-AC1
-
AC1: 'Reply on RC1', Marc von Hobe, 26 Apr 2023
-
RC2: 'Comment on egusphere-2023-268', Anonymous Referee #2, 29 Mar 2023
Review of “Comment on “An approach to sulfate geoengineering with surface emissions of carbonyl sulfide” by Quaglia et al. (2022)”
This short article seeks to point out deficiencies or oversights in the Quaglia et al. paper. They look specifically at 4 topics: uptake by plants, uptake by oceans, implications for toxicity due to higher concentrations resulting from geoengineering scenarios envisaged and revisit radiative effects. The paper is clear and succinct in that it soundly points to the non-viability of OCS injection to counter radiative warming due to increasing atmospheric CO2 and points to yet to be studied though likely toxic effects to terrestrial biosphere and the marine ecosystem. It does this with existing, available models that show how sensitive the ecosystem and oceanic are to atmospheric OCS concentrations and that they will uptake excess OCS to their likely detriment.
Major Issues
None.
Minor Issues
None.
Reviewer general comment.
The authors note in the introduction, that in the original review process of the Quaglia et al. paper an objection was made for not investigating the effect of higher atmospheric concentrations on the terrestrial biosphere. The editors allowed a brief statement to sidestep the opportunity to address this critical point and apparently others. Although an author can make any statement they deem valid and escape thoroughness via caveats, this is quite an obvious oversight. Through this comment these points have been made and the record set on an improved path. Though we are left to wonder why a critical stance was not taken at the time of the original review to strengthen the Quaglia paper. That decision was the consequence of the editorial staff’s commitment to standards for scientific rigor or not.
Citation: https://doi.org/10.5194/egusphere-2023-268-RC2 -
AC2: 'Reply on RC2', Marc von Hobe, 26 Apr 2023
We thank the reviewer for the appreciation of our initiative to write this short comment.
We are also grateful for the closing remark at the end of the review comment. We fully agree and have nothing to add, really.
Citation: https://doi.org/10.5194/egusphere-2023-268-AC2
-
AC2: 'Reply on RC2', Marc von Hobe, 26 Apr 2023
Peer review completion
Journal article(s) based on this preprint
Marc von Hobe et al.
Marc von Hobe et al.
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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.
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