the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Magnitude, frequency and climate forcing of global volcanism during the last glacial period as seen in Greenland and Antarctic ice cores (60–9 ka)
- 1Physics of Ice, Climate and Earth, Niels Bohr Institute, University of Copenhagen, 2100, Denmark
- 2Climate and Environmental Physics, Physics Institute & Oeschger Center for Climate Change Research, University of Bern, Sidlerstrasse 5, Bern, Switzerland
- 3Department of Chemistry, University of Florence, Florence, Italy
- 4British Antarctic Survey, Cambridge, UK
- 5Centre for Earth Observation Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2
- 1Physics of Ice, Climate and Earth, Niels Bohr Institute, University of Copenhagen, 2100, Denmark
- 2Climate and Environmental Physics, Physics Institute & Oeschger Center for Climate Change Research, University of Bern, Sidlerstrasse 5, Bern, Switzerland
- 3Department of Chemistry, University of Florence, Florence, Italy
- 4British Antarctic Survey, Cambridge, UK
- 5Centre for Earth Observation Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2
Abstract. Large volcanic eruptions occurring in the last glacial period can be detected in terms of their deposited sulfuric acid in continuous ice cores. Here we employ continuous sulfate and sulfur records from three Greenland and three Antarctic ice cores to estimate the emission strength, the frequency and the climatic forcing of large volcanic eruptions that occurred during the second half of the last glacial period and the early Holocene, 60–9 ka years before AD 2000 (b2k). The ice cores are synchronized over most of the investigated interval making it possible to distinguish large eruptions with a global sulfate distribution from eruptions detectable in one hemisphere only. Due to limited data resolution and to a large variability in the sulfate background signal, particularly in the Greenland glacial climate, we only detect Greenland sulfate depositions larger than 20 kg km−2 and Antarctic sulfate depositions larger than 10 kg km−2. With those restrictions, we identify 1113 volcanic eruptions in Greenland and 740 eruptions in Antarctica within the 51 ka period – where the sulfate deposition of 85 eruptions is defined at both poles (bipolar eruptions). Based on the relative Greenland and Antarctic sulfate deposition, we estimate the latitudinal band of the bipolar eruptions and assess their approximate climatic forcing based on established methods. The climate forcing of the five largest eruptions is estimated to be higher than −70 W m−2. Twenty-seven of the identified bipolar eruptions are larger than any volcanic eruption occurring in the last 2500 years and 69 eruptions are estimated to have larger sulfur emission strengths than the VEI-7 Tambora eruption that occurred in Indonesia in 1815 AD. The frequency of eruptions larger than the typical VEI-7 (VEI-8) eruption by the comparison of sulfur emission strength is found to be 5.3 (7) times higher than estimated from geological evidence. Throughout the investigated period, the frequency of volcanic eruptions is rather constant and comparable to that of recent times. During the deglacial period (16–9 ka b2k), however, there is a notable increase in the frequency of volcanic events recorded in Greenland and an obvious increase in the fraction of very large eruptions. For Antarctica, the deglacial period cannot be distinguished from other periods. These volcanoes documented in ice cores provide atmospheric sulfate burden and climate forcing for further research on climate impact and understanding the mechanism of the Earth system.
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Jiamei Lin et al.
Interactive discussion
Status: closed
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CC1: 'Comment on cp-2021-100', Alan Robock, 14 Aug 2021
This looks like an excellent paper, but I noticed a few things that could be improved.
In the abstract, change “The frequency of eruptions larger than the typical VEI-7 (VEI-8) eruption by the comparison of sulfur emission strength is found to be 5.3 (7) times higher than estimated from geological evidence.” to “The frequency of eruptions with sulfur emissions larger than the typical VEI-7 eruption is found to be 5.3 times higher than estimated from geological evidence, and for VEI-8 eruptions it is 7 times higher.” Using parentheses to save space only serves to confuse and make it difficult to read. Furthermore, the sentence is awkwardly constructed. But VEI is not an index of sulfur emission. Why use VEI at all when discussing the impacts of volcanic eruptions on climate?
It would be much easier for reviewers if you put the table and figure captions on the same page as the tables and figures.
Table 1 uses acronyms that are not defined. What are NHHL, SH, or LL?
Table 2 needs to be corrected. Radiative forcing from volcanic eruptions is negative. For example, for those with forcing larger than Tambora, they are for forcing < –17 W m‑2.
The notation in Fig. 6 needs correction. The correct unit for radiative forcing is W m‑2, with W capitalized, and m not in italics. Italics are for variables, and not for units. Similarly, km should not be in italics.
Review by Alan Robock
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AC1: 'Reply on CC1', Jiamei Lin, 23 Nov 2021
The comment was uploaded in the form of a supplement: https://cp.copernicus.org/preprints/cp-2021-100/cp-2021-100-AC1-supplement.pdf
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AC1: 'Reply on CC1', Jiamei Lin, 23 Nov 2021
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RC1: 'Comment on cp-2021-100', Chaochao Gao, 29 Aug 2021
The paper titled “Magnitude, frequency and climate forcing of global volcanism during the last glacial period as seen in Greenland and Antarctic ice cores (60-9 ka)” is the first effort to reconstruct the volcanic history of the last glacial period, utilizing six bipolar ice core records. Results from this work will provide an essential forcing scenario for model simulations and climate investigation of this period. I recommend publication of this work, after careful consideration of the following questions and suggestions:
- Section 2.2, please explain briefly the choice of different filter length, i.e., 45yr for the Antarctic cores and NGRIP while 181yr for GISP2 & NEEM.
- Also in section 2.2, it is a bit confusing about which parameter was used to measure the volcanic signals, the depth or the yr. Based on the text, the background was filtered by window length indicated by year, while the duration of the volcanic signal was indicated by depth.
- Section 2.4 please provide some description of how the manual correction was performed. For example, what are the resolutions for the ECM and DEP records? How many or what percentage of the signals have been corrected. It would also be great to give an example of how the correction was done.
- “A sulfate deposition of 20 kg km-2 corresponds to half the Greenland deposition from the 1815 AD Tambora eruption, thus refers to quite large events in terms of total sulfur injections into the atmosphere.” Please explain briefly how was the 20 kg km-2 (and also the 10 kg km-2 for Antarctic) cutoff line estimated. And was the 40 kg km-2 1815 AD Tambora deposition corresponding to the average deposition from the three Greenland cores?
- Section 2.6 Please provide more details on the SVM model. For example, what are the requirements, the pro. and cons of the model in this particular application. What validation had been done on the model performance? For example, taken one of the 21 eruption signals used to train the model out from the analysis, could the model accurately simulate its location?
- Ln 305-307, the comparison between IC and CFA records in Fig 2e needs further demonstration. For example, what is the exact meaning of “very large uncertainties”? What is the implication of the uncertainties on the interpretation of the “face value”?
- Section 3.3 Please explain why borrow the bipolar eruptions from the previous studies, rather than estimate a list using the results from this study.
- Ln 532-534 In my understanding, the VEI list is a discrete (i.e., it is not a complete but continuously evolving) reconstruction of historical volcanism based on geological investigation. So I am not sure it is appropriate to directly compare the event frequency from the ice-core-based reconstruction (which is assumed to be continuous) with that from geological investigation.
- Section 4.4 Please explain why do some events have forcing estimation in a range (for example, the #2 largest signal has forcing ranging from 17.8 to 176.5 W/m2), while others have finite forcing estimation (for example, the #3 largest signal has a forcing estimation of 82.8 W/m2)? If it was due to the number of ice cores available for signal extraction, this should be clarified.
- Is there any reason why the authors choose Tambora & Samalas for the magnitude comparison of #3 and #4 events, respectively?
- Please add captions for the supplementary figures.
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AC2: 'Reply on RC1', Jiamei Lin, 23 Nov 2021
The comment was uploaded in the form of a supplement: https://cp.copernicus.org/preprints/cp-2021-100/cp-2021-100-AC2-supplement.pdf
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RC2: 'Comment on cp-2021-100', Eric Wolff, 02 Sep 2021
This paper represents a huge amount of work to identify the deposition of volcanic sulfate in the polar regions and to try and draw conclusions about the occurrence of volcanism over the last 60 kyr. I really applaud the effort, and the attempt to draw large-scale conclusions from it. I have a lot of relatively minor comments on the paper (which put it somewhere between minor and major revision), and I think the authors could have made some better choices in the way they treated the data. However I accept that they made mainly reasonable choices and so I do not propose to insist on any significant reanalysis of the data – just in places an extra sentence is needed to discuss the choices made. I found some of the messages that end up in the abstract too strong given the nature of the data and I will comment on those in the text, expecting the authors also to address them in the abstract.
A final point is that the paper is extremely hard to follow – while I appreciate the need for a lot of supplementary material, the fact that the figures in the main text and the supplement seem to be called in almost random order is very unhelpful, and I suggest the authors renumber the figures to provide a more logical flow.
Before I give a detailed set of comments, I should add that (as I think several of the authors are aware) I have been involved in a similar exercise, using only the EDC ice core, but for a period of 200 kyr. This has been presented a few times and has been (in a paper involving also terrestrial and marine data) under review for a considerable time. My comments should therefore be taken with the knowledge that I have used slightly different methods and criteria but am not seeking to impose the same methodology on the authors here.
Detailed comments:
The paper will need a thorough copy edit as the English at times is awkward and occasionally hard to follow.
Line 165. I think the authors have misunderstood the MSA correction. This had to be done for WAIS Divide because ICPMS measures elemental S, and therefore the values obtained are (sulfate + MSA). This is not the case for any of the FIC/IC methods, where sulfate itself is measured, so no correction would be required and no correction should have been made for any other sites. Please clarify this in your text.
Line 188. I found myself a little confused about the volcanic detection threshold. I understand the idea behind the use of RRM and RMAD. But then in the end you just use a threshold of 10 or 20 kg km-2 so I am not sure what purpose the statistical threshold serves.
Equation 1: please be careful to define the units when describing this equation. I assume concentration is in ppb or ng/g (as in the figures), and D is in m ice equivalent (this is important as if you had included the top 100 m where density is less than that of ice, then the equation is not correct if in real depth), and 0.917 is in g/cm3. By fluke, after cancelling factors of 10 to change the units this does indeed work out as kg km-2, but the reader needs that to be stated.
Line 209. Please also be careful to define what T is, ie layer thickness/original layer thickness. It’s confusing otherwise because you talk next about a 60% reduction of the layer thickness which is equivalent to a T of 0.4. Perhaps that is the best way to deal with it, “60% reduction of the layer thickness (T=0.4)”.
Supp table S1: Please explain what the column “Name” is: I assume it’s the age model used. But I’m surprised because the standard for a 60ka period is GICC05. I appreciate you may have to use a model to derive a smooth acc rate, but then you need to explain the relationship between ss09seabm1 and GICC05 as few of your readers will have heard of the former.
Fig S1 and caption. Please clarify that in part c the y-axis “thinning function” is equivalent to “T” in the text as I don’t think you ever explain that in the text. Also in the caption, what does “thinning file” mean? The second sentence of the caption doesn’t make sense, please re-word.
Line 220. This is wrong. The volcanic sulfate flux calculation does not assume anything about wet or dry deposition: it is simply the product of concentration and snow acc rate. It’s true that the flux is affected by whether there is significant wet deposition in addition to the dry deposition and this is a point worth making, but the flux as calculated is definitely correct.
Table S4, column O, kg not Kg please.
Table S5. Why is N/A written for WD2014 ages below 30 ka. WD2014 extends from the surface to 68ka even if it changes from layer counted to methane-tied at 31 ka.
Tables S4 and S5: Are the values given for individual sites before or after the rescaling of Antarctic concentrations. I think before – if not then it’s hard to understand the averages you give for the Antarctic. Please clarify this in the captions, ie that the individual values are as measured while the average is after rescaling.
Line 241. What matters is of course not the value of the sulfate background but its variability. I think this is what you mean but from this wording it isn’t quite clear. I think you need to explain your 10 and 20 kg m-2 criteria better – how is it derived? In my own work we estimated the “negative” peaks to understand how big a deviation from the median could be generated in a given section from noise alone, and then we used that to establish a threshold (which was 20 kg km-2 for the 200 ka record). So I think your thresholds are probably fine, but could be explained more clearly.
Line 255. The Antarctic plots shown in Fig S2 are really not impressive with very small r^2. They don’t seem at all a good basis for the rescaling you do. While I accept there may be higher fluxes for a given volcano at WD because it receives more wet deposition (this is the only reason the accumulation rate is relevant), the values you derive here have a huge uncertainty which you have not apparently propagated into your 26% error estimate (line 265). We know there is a huge uncertainty anyway because of local variability in deposition (as shown eg by Gautier et al (2016). I suggest you do an alternative error estimate where you use the rescaled data from the 123 Antarctic eruptions where you have 3 sites and find the average 1-sigma and/or 2-sigma between the 3 sites. This would give you an alternative way to estimate the uncertainty in the values you end up with. 26% is certainly way too small an error in the cases where you have only 1 site.
Line 268. I am familiar with the paper by Marshall (not Martshall) but I don’t know what you mean by “The volcanic sulfate deposition in Greenland and Antarctica shows a distribution pattern (Table S5 and Table S6), similar to that derived from the aerosol-climate modeling of volcanoes over past 2500 years”. I can believe that you are assuming they show such a distribution and that this is how you decide on the latitude, but you have no evidence to say that they do show such a pattern.
Section 2.6 and Fig S3. I apologise for my lack of technical knowledge but this section is not comprehensible to someone coming at it new. I think you need to explain what you are trying to achieve here (which I think is to use the Greenland/Antarctic ratio of known eruptions to classify the latitude of unknown bipolar eruptions). Then please try to explain SVM better. To anyone not in the know Fig S3 b and c cannot be understood.
Line 282, I think you mean Fig S10, not S9.
General comment: this reminded me that the calling of figures, especially supplementary ones, in apparently random order is really confusing. Please sort this out.
Line 360. I don’t really understand your statement that “the layer thinning becomes stronger which makes it increasingly difficult to detect smaller eruptions signals”. If that is really so then your threshold of 10 or 20 kg km-2 is too low. The whole point of it should be to ensure that detection is the same throughout.
Section 3.4. The previous comment raises a more general comment on this section. It’s really obvious that you shouldn’t use cores where the resolution is worse than the expected peak width. However it’s difficult to know what that means: in the case of EDC, if thinning were the only thing happening then it would be hopeless to detect eruptions reliably in the early parts of the record with resolution 5 years. However it turns out that the diffusion at Dome C keeps the peak width quite constant with age, and therefore allows resolution of peaks where the age resolution is 5 years (because the peaks at this depth have diffused to 10 or 20 years wide). However I’d be very surprised if you can expect to resolve most volcanoes, even large ones, in GISP2 with the stated resolution in Table S1. For NEEM, given the variable depth resolution, I suspect the age resolution is normally much better than 10 years (I suggest checking this again), but if it were 10 years again I think detection would be hopeless. I think you need a somewhat deeper discussion here, and also to consider whether it is worthwhile to contaminate a great dataset by including data from sites where detection must be severely degraded.
Fig S5 and line 375. Please be careful here. I believe the Rasmussen analysis makes some sense for the kind of CFA set up used by Bigler where there is a large reaction cell that is being continually mixed leading to quite a large mixing volume. In such a setup there can be a nominal data resolution of mm which is not real. The FIC setups are a bit different as they inject a slug of liquid every 2 cm (or whatever each system uses) so the resolution could never be better than that in any sense. I’m not sure your analysis really makes that distinction.
Line 389. You call Fig 4 before Figs 2 and 3.
Line 419. I found this very confusing. I am looking at Fig 2 where you show the Holocene, deglacial, stadial and interstadial. You then state that the number of eruptions is higher in cold periods when the figure shows the most in the deglacial and really no difference between the glacial and Holocene. Eventually I realised that you are only talking about stadials versus interstadials within the glacial. So firstly please make this clear throughout this section. But really is that statement true at a significant level: perhaps so in the 1 year data in Fig S6, but the reader isn’t looking at that, they are seeing Fig 2. You need to be much clearer that you are using Fig S6 to discuss whether the difference is an artefact and that the conclusion, as illustrated in Fig 2 is that it probably is. I realise you do say this in the end, but by pointing at Fig 2 initially you leave the reader who doesn’t take the trouble to look at the supplement lost.
Line 488 (2-0) Do you mean 2-0 ka? When I look at Fig 2, I don’t really see a 34% increase. At least for the small (blue) category, there is no change. Perhaps describe this more precisely as to what you mean.
Line 535-544. I don’t find this comparison of the ice core eruption rates against Lameve data helpful. Firstly you should also look at the analysis by Rougier et al (Rougier, J., R. S. J. Sparks, K. V. Cashman, and S. K. Brown (2018), The global magnitude–frequency relationship for large explosive volcanic eruptions, Earth planet. Sci. Lett., 482, 621-629, doi:https://doi.org/10.1016/j.epsl.2017.11.015.). It is very clear in that paper that the community is well aware that Lameve under-reports so I don’t really see the value of the comparison you are making.
I am unconvinced by section 4.4 Given the huge uncertainties, especially for eruptions where there is only 1 core represented in one of the ice sheets, the values are so uncertain that trying to call out individual positions in the medal table seems a bit pointless. At the least please add a column where you state how many cores are represented in each ice sheet. But I feel this section of the paper is given too much weight and should be shortened. Remember also that you certainly show no eruptions that are bipolar between 16.4 and 24.5 ka, but this is not because they were absent but only because the tie points are not good enough to know whether they are bipolar. Given this kind of issue I think the league table, while it can be included should be downplayed and put into context.
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AC3: 'Reply on RC2', Jiamei Lin, 23 Nov 2021
The comment was uploaded in the form of a supplement: https://cp.copernicus.org/preprints/cp-2021-100/cp-2021-100-AC3-supplement.pdf
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AC3: 'Reply on RC2', Jiamei Lin, 23 Nov 2021
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CC2: 'Comment on cp-2021-100', Jihong Cole-Dai, 05 Sep 2021
This paper by Lin and colleagues extends the records of explosive volcanism constructed systematically from polar ice cores from the Holocene into the last glacial period. This is much valuable and needed research on volcanic records and the volcanic impact on climate.
To reconstruct volcanic records from ice cores for the glacial periods, the authors faced several daunting challenges not encountered when compiling such records for the Holocene or shorter periods. First, detection of volcanic signals in ice cores depends critically on quantifying the non-volcanic background, and the background is much more variable during the last glacial period than during the Holocene; the larger variability is the result of both climatic variations (stadials vs. interstadials) and the presence of significant non-marine biogenic sulfate. Second, the Greenland and Antarctica cores in this study were analyzed with various sampling and analytical methods, resulting in datasets of various quality. Third, due to significant layer thinning with very old ice, temporal resolution of chemical analysis is reduced in glacial ice and, as a result, further complicates the detection and quantification of volcanic signals. Fourth, significant layer thinning at much older ages makes quantitative estimation of volcanic deposition difficult. In my opinion, the authors succeeded quite well in tackling these thorny issues and came up with a remarkable record of large volcanic eruptions for the last 60,000 years. It is worth noting that, due to the highly variable background sulfate levels during the glacial part of the period covered in this study, only extremely large eruptions are detected and quantified. Nonetheless, a record of extremely large eruptions is very valuable when it comes to assessing the climate impact of explosive volcanism, for we know from other studies that very large eruptions exert the most significant impact on climate.
The conclusions of this study are significant, not only because it is the first time that a systematic study of volcanism during the last 60 ka yields a robust record, but also it demonstrates that ice cores are capable of providing valuable information regarding volcanism and its climatic impact on time scales of millennia and longer, supplementing and/or enhancing knowledge from geological records.
I would like to offer a comment on a technical aspect. I find that in several places in this paper, the authors use terms such as “measurement techniques” and “measurement methods” for how ice core analysis yields sulfate data and how different “techniques” or “methods” yield data of various quality. Regarding the chemical measurement of sulfate, there are only two techniques: ion chromatography (IC) and mass spectrometry (ICP-MS for sulfur). The quality of data from these techniques is the same or similar, for any ice core samples. Where data quality may vary is when different sampling methods are used: discrete, continuous melting with online IC or ICP-MS measurement, or continuous melting followed by off-line IC measurement. Often, these sampling methods determine measurement resolution or temporal resolution. For example, when sulfate was measured using IC on discrete samples, the resolution is lower than that when the measurement was using FIC on samples from a melter, due to the higher sampling resolution of the melter. The quality of sulfate data is the same, as sulfate in both cases were measured with ion chromatography.
In addition, I ask the authors to consider the following comments on specific passages in the paper.
Line 68. Small deposition at low accumulation sites could be also, or even mostly, due to reduced wet deposition.
Line 88-91. Are you saying that uncertainty in thinning-rate estimates also contributes to uncertainty/variability of volcanic deposition?
Line 113. In my opinion, the main problem with tephra ID is not that tephra does not deposit with sulfate simultaneously. The difference in timing of tephra and sulfate deposition is usually small, less than one year. The main problem is that it is impossible to perform continuous search and analysis of tephra in any deep/long ice core with the current analytical (or technological) tools. Additionally, there are no objective standards on matching the tephra in ice core to ash from a particular eruption.
Line 150. The word “analytical” should be inserted in “different methods”.
Line 166-169. MSA correction is needed only when sulfur, not sulfate, was measured. In fact, the correction should not or cannot be applied to sulfate data.
Line 220. Is there such an assumption?
Line 294. “sulfate deposition strongly influenced by sulfate record type (IC, FIC, CFA)”? See my comment on a technical aspect.
Lines 301-304. Deposition variation is due to different sampling methods, not measurement methods or techniques. See my comment on a technical aspect.
Line 350. “Two bipolar volcanic eruptions are known from tephra to be Icelandic origin: Could signals in Antarctica ice cores be from contemporaneous eruptions in SH? I notice that the authors use the term “bipolar volcanic eruptions” for contemporaneous signals in both Greenland and Antarctica ice cores. I think it is acceptable to use this term, with the caveat that such contemporaneous signals may be left by simultaneous eruptions in both hemispheres, rather than a single eruption.
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AC4: 'Reply on CC2', Jiamei Lin, 23 Nov 2021
The comment was uploaded in the form of a supplement: https://cp.copernicus.org/preprints/cp-2021-100/cp-2021-100-AC4-supplement.pdf
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AC4: 'Reply on CC2', Jiamei Lin, 23 Nov 2021
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CC3: 'Comment on cp-2021-100 (Thomas Aubry, Lauren Marshall and Anja Schmidt)', Thomas Aubry, 28 Sep 2021
This manuscript by Jiamei Lin and co-authors represents the first effort to constrain stratospheric volcanic SO2 emissions for the 60-9 ka period using a bipolar array of ice cores, and these emissions are then used to estimate the corresponding volcanic forcing. This will without doubt be a very useful contribution for the community working on volcano-climate interactions.
We would like to draw the attention of the authors to potential improvements for estimating volcanic forcing from emissions.
First, to estimate a global-mean Stratospheric Aerosol Optical Depth (SAOD), the authors use a linear scaling between SAOD and the aerosol loading. However, it is well known that for large eruptions this relationship is not linear (e.g. Crowley and Unterman, 2013). As highlighted by the authors, the scaling used in their work is calibrated against the 1991 Mt. Pinatubo eruption and the reference used does not employ the latest estimates of SO2 mass and SAOD for this eruption. For example, the post-Pinatubo peak global mean SAOD in Crowley and Unterman (2013) (ca. 0.14-0.15) is 16% larger than in the GloSSAC dataset (0.12-0.13, Kovilakam et al. 2020). We suggest that the authors consider either using the EVA model (Toohey et al., 2016) or the EVA_H model (Aubry et al., 2020) to obtain SAOD. EVA is calibrated using more up-to-date data for Pinatubo and is also a reference model for the community as it has been used to derive the volcanic forcing for CMIP6’s Paleoclimate Model Intercomparison Project (PMIP4). EVA_H is an extension to EVA that was calibrated using the full 1979-2015 period with state-of-the-art observational datasets. Additionally, in EVA_H the predicted global mean SAOD depends on the eruption latitude, which is not the case in EVA.
Second, to convert global-mean SAOD to global-mean radiative forcing, the authors use the scaling factor of Hansen et al. (2005). This scaling factor was constrained using climate model simulations for the 1991 Mt. Pinatubo eruption without full consideration of rapid adjustments. Several recent studies have suggested that consideration of rapid adjustments leads to a reduction in the scaling factor (e.g., Gregory et al., 2016; Larson & Portmann, 2016; Schmidt et al., 2018; Marshall et al., 2020). Revised scaling factors for a wide range of eruptions are available in Marshall et al. (2020). Collectively, these studies suggest a reduced conversion factor compared to Hansen et al. (2005) and IPCC AR5.
We acknowledge that using more recent methods will result in differences in reconstructed forcings that are likely small relative to uncertainties in ice-core derived estimates of the SO2 mass. We nonetheless think that it remains important to acknowledge and use the latest tools developed by the community to provide volcanic forcing estimates. At the minimum, the authors should discuss differences that may emerge from using different scaling factors.
Thanks again for a very interesting manuscript.
Thomas Aubry, Lauren Marshall and Anja Schmidt.
References:
Aubry, T. J., Toohey, M., Marshall, L., Schmidt, A., & Jellinek, A. M. (2020). A new volcanic stratospheric sulfate aerosol forcing emulator (EVA_H): Comparison with interactive stratospheric aerosol models. Journal of Geophysical Research: Atmospheres, 125, e2019JD031303. https://doi.org/10.1029/2019JD031303
Crowley, T., & Unterman,M. (2013). Technical details concerning development of a 1200 yr proxy index for global volcanism. Earth System Science Data, 5(1), 187–197. https://doi.org/10.5194/essd-5-187-2013
Gregory, J.M., Andrews, T., Good, P. et al. Small global-mean cooling due to volcanic radiative forcing. Clim Dyn 47, 3979–3991 (2016). https://doi.org/10.1007/s00382-016-3055-1
Hansen, J., Sato, M., Ruedy, R., Nazarenko, L., Lacis, A., Schmidt, G. A., et al. (2005). Efficacy of climate forcings. Journal of Geophysical Research:Atmospheres, 110. Review, D18104, https://doi.org/10.1029/2005JD005776
Marshall, L. R., Smith, C. J., Forster,P. M., Aubry, T. J., Andrews, T., & Schmidt, A. (2020). Large variations in volcanic aerosol forcing efficiency due to eruption source parameters and rapid adjustments. GeophysicalResearch Letters, 47, 2020GL090241. https://doi.org/10.1029/2020GL090241
Kovilakam, M., Thomason, L. W., Ernest, N., Rieger, L., Bourassa, A., and Millán, L.: The Global Space-based Stratospheric Aerosol Climatology (version 2.0): 1979–2018, Earth Syst. Sci. Data, 12, 2607–2634, https://doi.org/10.5194/essd-12-2607-2020, 2020.
Larson, E. J. L., & Portmann, R. W. (2016). A temporal kernel method to compute effective radiative forcing in CMIP5 transient simulations. Journal of Climate, 29(4), 1497– 1509. https://doi.org/10.1175/JCLI-D-15-0577.1
Schmidt, A., Mills, M. J., Ghan, S., Gregory, J. M., Allan, R. P., Andrews, T., et al. (2018). Volcanic radiative forcing from 1979 to 2015. Journal of Geophysical Research: Atmospheres, 123, 12,491– 12,508. https://doi.org/10.1029/2018JD028776
Toohey, M., Stevens, B., Schmidt, H., & Timmreck, C. (2016). Easy Volcanic Aerosol (EVA v1.0): An idealized forcing generator for climate simulations. Geoscientific Model Development, 2016, 1–40. https://doi.org/10.5194/gmd-2016-83
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AC5: 'Reply on CC3', Jiamei Lin, 23 Nov 2021
The comment was uploaded in the form of a supplement: https://cp.copernicus.org/preprints/cp-2021-100/cp-2021-100-AC5-supplement.pdf
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AC5: 'Reply on CC3', Jiamei Lin, 23 Nov 2021
Peer review completion
Post-review adjustments
Interactive discussion
Status: closed
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CC1: 'Comment on cp-2021-100', Alan Robock, 14 Aug 2021
This looks like an excellent paper, but I noticed a few things that could be improved.
In the abstract, change “The frequency of eruptions larger than the typical VEI-7 (VEI-8) eruption by the comparison of sulfur emission strength is found to be 5.3 (7) times higher than estimated from geological evidence.” to “The frequency of eruptions with sulfur emissions larger than the typical VEI-7 eruption is found to be 5.3 times higher than estimated from geological evidence, and for VEI-8 eruptions it is 7 times higher.” Using parentheses to save space only serves to confuse and make it difficult to read. Furthermore, the sentence is awkwardly constructed. But VEI is not an index of sulfur emission. Why use VEI at all when discussing the impacts of volcanic eruptions on climate?
It would be much easier for reviewers if you put the table and figure captions on the same page as the tables and figures.
Table 1 uses acronyms that are not defined. What are NHHL, SH, or LL?
Table 2 needs to be corrected. Radiative forcing from volcanic eruptions is negative. For example, for those with forcing larger than Tambora, they are for forcing < –17 W m‑2.
The notation in Fig. 6 needs correction. The correct unit for radiative forcing is W m‑2, with W capitalized, and m not in italics. Italics are for variables, and not for units. Similarly, km should not be in italics.
Review by Alan Robock
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AC1: 'Reply on CC1', Jiamei Lin, 23 Nov 2021
The comment was uploaded in the form of a supplement: https://cp.copernicus.org/preprints/cp-2021-100/cp-2021-100-AC1-supplement.pdf
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AC1: 'Reply on CC1', Jiamei Lin, 23 Nov 2021
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RC1: 'Comment on cp-2021-100', Chaochao Gao, 29 Aug 2021
The paper titled “Magnitude, frequency and climate forcing of global volcanism during the last glacial period as seen in Greenland and Antarctic ice cores (60-9 ka)” is the first effort to reconstruct the volcanic history of the last glacial period, utilizing six bipolar ice core records. Results from this work will provide an essential forcing scenario for model simulations and climate investigation of this period. I recommend publication of this work, after careful consideration of the following questions and suggestions:
- Section 2.2, please explain briefly the choice of different filter length, i.e., 45yr for the Antarctic cores and NGRIP while 181yr for GISP2 & NEEM.
- Also in section 2.2, it is a bit confusing about which parameter was used to measure the volcanic signals, the depth or the yr. Based on the text, the background was filtered by window length indicated by year, while the duration of the volcanic signal was indicated by depth.
- Section 2.4 please provide some description of how the manual correction was performed. For example, what are the resolutions for the ECM and DEP records? How many or what percentage of the signals have been corrected. It would also be great to give an example of how the correction was done.
- “A sulfate deposition of 20 kg km-2 corresponds to half the Greenland deposition from the 1815 AD Tambora eruption, thus refers to quite large events in terms of total sulfur injections into the atmosphere.” Please explain briefly how was the 20 kg km-2 (and also the 10 kg km-2 for Antarctic) cutoff line estimated. And was the 40 kg km-2 1815 AD Tambora deposition corresponding to the average deposition from the three Greenland cores?
- Section 2.6 Please provide more details on the SVM model. For example, what are the requirements, the pro. and cons of the model in this particular application. What validation had been done on the model performance? For example, taken one of the 21 eruption signals used to train the model out from the analysis, could the model accurately simulate its location?
- Ln 305-307, the comparison between IC and CFA records in Fig 2e needs further demonstration. For example, what is the exact meaning of “very large uncertainties”? What is the implication of the uncertainties on the interpretation of the “face value”?
- Section 3.3 Please explain why borrow the bipolar eruptions from the previous studies, rather than estimate a list using the results from this study.
- Ln 532-534 In my understanding, the VEI list is a discrete (i.e., it is not a complete but continuously evolving) reconstruction of historical volcanism based on geological investigation. So I am not sure it is appropriate to directly compare the event frequency from the ice-core-based reconstruction (which is assumed to be continuous) with that from geological investigation.
- Section 4.4 Please explain why do some events have forcing estimation in a range (for example, the #2 largest signal has forcing ranging from 17.8 to 176.5 W/m2), while others have finite forcing estimation (for example, the #3 largest signal has a forcing estimation of 82.8 W/m2)? If it was due to the number of ice cores available for signal extraction, this should be clarified.
- Is there any reason why the authors choose Tambora & Samalas for the magnitude comparison of #3 and #4 events, respectively?
- Please add captions for the supplementary figures.
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AC2: 'Reply on RC1', Jiamei Lin, 23 Nov 2021
The comment was uploaded in the form of a supplement: https://cp.copernicus.org/preprints/cp-2021-100/cp-2021-100-AC2-supplement.pdf
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RC2: 'Comment on cp-2021-100', Eric Wolff, 02 Sep 2021
This paper represents a huge amount of work to identify the deposition of volcanic sulfate in the polar regions and to try and draw conclusions about the occurrence of volcanism over the last 60 kyr. I really applaud the effort, and the attempt to draw large-scale conclusions from it. I have a lot of relatively minor comments on the paper (which put it somewhere between minor and major revision), and I think the authors could have made some better choices in the way they treated the data. However I accept that they made mainly reasonable choices and so I do not propose to insist on any significant reanalysis of the data – just in places an extra sentence is needed to discuss the choices made. I found some of the messages that end up in the abstract too strong given the nature of the data and I will comment on those in the text, expecting the authors also to address them in the abstract.
A final point is that the paper is extremely hard to follow – while I appreciate the need for a lot of supplementary material, the fact that the figures in the main text and the supplement seem to be called in almost random order is very unhelpful, and I suggest the authors renumber the figures to provide a more logical flow.
Before I give a detailed set of comments, I should add that (as I think several of the authors are aware) I have been involved in a similar exercise, using only the EDC ice core, but for a period of 200 kyr. This has been presented a few times and has been (in a paper involving also terrestrial and marine data) under review for a considerable time. My comments should therefore be taken with the knowledge that I have used slightly different methods and criteria but am not seeking to impose the same methodology on the authors here.
Detailed comments:
The paper will need a thorough copy edit as the English at times is awkward and occasionally hard to follow.
Line 165. I think the authors have misunderstood the MSA correction. This had to be done for WAIS Divide because ICPMS measures elemental S, and therefore the values obtained are (sulfate + MSA). This is not the case for any of the FIC/IC methods, where sulfate itself is measured, so no correction would be required and no correction should have been made for any other sites. Please clarify this in your text.
Line 188. I found myself a little confused about the volcanic detection threshold. I understand the idea behind the use of RRM and RMAD. But then in the end you just use a threshold of 10 or 20 kg km-2 so I am not sure what purpose the statistical threshold serves.
Equation 1: please be careful to define the units when describing this equation. I assume concentration is in ppb or ng/g (as in the figures), and D is in m ice equivalent (this is important as if you had included the top 100 m where density is less than that of ice, then the equation is not correct if in real depth), and 0.917 is in g/cm3. By fluke, after cancelling factors of 10 to change the units this does indeed work out as kg km-2, but the reader needs that to be stated.
Line 209. Please also be careful to define what T is, ie layer thickness/original layer thickness. It’s confusing otherwise because you talk next about a 60% reduction of the layer thickness which is equivalent to a T of 0.4. Perhaps that is the best way to deal with it, “60% reduction of the layer thickness (T=0.4)”.
Supp table S1: Please explain what the column “Name” is: I assume it’s the age model used. But I’m surprised because the standard for a 60ka period is GICC05. I appreciate you may have to use a model to derive a smooth acc rate, but then you need to explain the relationship between ss09seabm1 and GICC05 as few of your readers will have heard of the former.
Fig S1 and caption. Please clarify that in part c the y-axis “thinning function” is equivalent to “T” in the text as I don’t think you ever explain that in the text. Also in the caption, what does “thinning file” mean? The second sentence of the caption doesn’t make sense, please re-word.
Line 220. This is wrong. The volcanic sulfate flux calculation does not assume anything about wet or dry deposition: it is simply the product of concentration and snow acc rate. It’s true that the flux is affected by whether there is significant wet deposition in addition to the dry deposition and this is a point worth making, but the flux as calculated is definitely correct.
Table S4, column O, kg not Kg please.
Table S5. Why is N/A written for WD2014 ages below 30 ka. WD2014 extends from the surface to 68ka even if it changes from layer counted to methane-tied at 31 ka.
Tables S4 and S5: Are the values given for individual sites before or after the rescaling of Antarctic concentrations. I think before – if not then it’s hard to understand the averages you give for the Antarctic. Please clarify this in the captions, ie that the individual values are as measured while the average is after rescaling.
Line 241. What matters is of course not the value of the sulfate background but its variability. I think this is what you mean but from this wording it isn’t quite clear. I think you need to explain your 10 and 20 kg m-2 criteria better – how is it derived? In my own work we estimated the “negative” peaks to understand how big a deviation from the median could be generated in a given section from noise alone, and then we used that to establish a threshold (which was 20 kg km-2 for the 200 ka record). So I think your thresholds are probably fine, but could be explained more clearly.
Line 255. The Antarctic plots shown in Fig S2 are really not impressive with very small r^2. They don’t seem at all a good basis for the rescaling you do. While I accept there may be higher fluxes for a given volcano at WD because it receives more wet deposition (this is the only reason the accumulation rate is relevant), the values you derive here have a huge uncertainty which you have not apparently propagated into your 26% error estimate (line 265). We know there is a huge uncertainty anyway because of local variability in deposition (as shown eg by Gautier et al (2016). I suggest you do an alternative error estimate where you use the rescaled data from the 123 Antarctic eruptions where you have 3 sites and find the average 1-sigma and/or 2-sigma between the 3 sites. This would give you an alternative way to estimate the uncertainty in the values you end up with. 26% is certainly way too small an error in the cases where you have only 1 site.
Line 268. I am familiar with the paper by Marshall (not Martshall) but I don’t know what you mean by “The volcanic sulfate deposition in Greenland and Antarctica shows a distribution pattern (Table S5 and Table S6), similar to that derived from the aerosol-climate modeling of volcanoes over past 2500 years”. I can believe that you are assuming they show such a distribution and that this is how you decide on the latitude, but you have no evidence to say that they do show such a pattern.
Section 2.6 and Fig S3. I apologise for my lack of technical knowledge but this section is not comprehensible to someone coming at it new. I think you need to explain what you are trying to achieve here (which I think is to use the Greenland/Antarctic ratio of known eruptions to classify the latitude of unknown bipolar eruptions). Then please try to explain SVM better. To anyone not in the know Fig S3 b and c cannot be understood.
Line 282, I think you mean Fig S10, not S9.
General comment: this reminded me that the calling of figures, especially supplementary ones, in apparently random order is really confusing. Please sort this out.
Line 360. I don’t really understand your statement that “the layer thinning becomes stronger which makes it increasingly difficult to detect smaller eruptions signals”. If that is really so then your threshold of 10 or 20 kg km-2 is too low. The whole point of it should be to ensure that detection is the same throughout.
Section 3.4. The previous comment raises a more general comment on this section. It’s really obvious that you shouldn’t use cores where the resolution is worse than the expected peak width. However it’s difficult to know what that means: in the case of EDC, if thinning were the only thing happening then it would be hopeless to detect eruptions reliably in the early parts of the record with resolution 5 years. However it turns out that the diffusion at Dome C keeps the peak width quite constant with age, and therefore allows resolution of peaks where the age resolution is 5 years (because the peaks at this depth have diffused to 10 or 20 years wide). However I’d be very surprised if you can expect to resolve most volcanoes, even large ones, in GISP2 with the stated resolution in Table S1. For NEEM, given the variable depth resolution, I suspect the age resolution is normally much better than 10 years (I suggest checking this again), but if it were 10 years again I think detection would be hopeless. I think you need a somewhat deeper discussion here, and also to consider whether it is worthwhile to contaminate a great dataset by including data from sites where detection must be severely degraded.
Fig S5 and line 375. Please be careful here. I believe the Rasmussen analysis makes some sense for the kind of CFA set up used by Bigler where there is a large reaction cell that is being continually mixed leading to quite a large mixing volume. In such a setup there can be a nominal data resolution of mm which is not real. The FIC setups are a bit different as they inject a slug of liquid every 2 cm (or whatever each system uses) so the resolution could never be better than that in any sense. I’m not sure your analysis really makes that distinction.
Line 389. You call Fig 4 before Figs 2 and 3.
Line 419. I found this very confusing. I am looking at Fig 2 where you show the Holocene, deglacial, stadial and interstadial. You then state that the number of eruptions is higher in cold periods when the figure shows the most in the deglacial and really no difference between the glacial and Holocene. Eventually I realised that you are only talking about stadials versus interstadials within the glacial. So firstly please make this clear throughout this section. But really is that statement true at a significant level: perhaps so in the 1 year data in Fig S6, but the reader isn’t looking at that, they are seeing Fig 2. You need to be much clearer that you are using Fig S6 to discuss whether the difference is an artefact and that the conclusion, as illustrated in Fig 2 is that it probably is. I realise you do say this in the end, but by pointing at Fig 2 initially you leave the reader who doesn’t take the trouble to look at the supplement lost.
Line 488 (2-0) Do you mean 2-0 ka? When I look at Fig 2, I don’t really see a 34% increase. At least for the small (blue) category, there is no change. Perhaps describe this more precisely as to what you mean.
Line 535-544. I don’t find this comparison of the ice core eruption rates against Lameve data helpful. Firstly you should also look at the analysis by Rougier et al (Rougier, J., R. S. J. Sparks, K. V. Cashman, and S. K. Brown (2018), The global magnitude–frequency relationship for large explosive volcanic eruptions, Earth planet. Sci. Lett., 482, 621-629, doi:https://doi.org/10.1016/j.epsl.2017.11.015.). It is very clear in that paper that the community is well aware that Lameve under-reports so I don’t really see the value of the comparison you are making.
I am unconvinced by section 4.4 Given the huge uncertainties, especially for eruptions where there is only 1 core represented in one of the ice sheets, the values are so uncertain that trying to call out individual positions in the medal table seems a bit pointless. At the least please add a column where you state how many cores are represented in each ice sheet. But I feel this section of the paper is given too much weight and should be shortened. Remember also that you certainly show no eruptions that are bipolar between 16.4 and 24.5 ka, but this is not because they were absent but only because the tie points are not good enough to know whether they are bipolar. Given this kind of issue I think the league table, while it can be included should be downplayed and put into context.
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AC3: 'Reply on RC2', Jiamei Lin, 23 Nov 2021
The comment was uploaded in the form of a supplement: https://cp.copernicus.org/preprints/cp-2021-100/cp-2021-100-AC3-supplement.pdf
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AC3: 'Reply on RC2', Jiamei Lin, 23 Nov 2021
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CC2: 'Comment on cp-2021-100', Jihong Cole-Dai, 05 Sep 2021
This paper by Lin and colleagues extends the records of explosive volcanism constructed systematically from polar ice cores from the Holocene into the last glacial period. This is much valuable and needed research on volcanic records and the volcanic impact on climate.
To reconstruct volcanic records from ice cores for the glacial periods, the authors faced several daunting challenges not encountered when compiling such records for the Holocene or shorter periods. First, detection of volcanic signals in ice cores depends critically on quantifying the non-volcanic background, and the background is much more variable during the last glacial period than during the Holocene; the larger variability is the result of both climatic variations (stadials vs. interstadials) and the presence of significant non-marine biogenic sulfate. Second, the Greenland and Antarctica cores in this study were analyzed with various sampling and analytical methods, resulting in datasets of various quality. Third, due to significant layer thinning with very old ice, temporal resolution of chemical analysis is reduced in glacial ice and, as a result, further complicates the detection and quantification of volcanic signals. Fourth, significant layer thinning at much older ages makes quantitative estimation of volcanic deposition difficult. In my opinion, the authors succeeded quite well in tackling these thorny issues and came up with a remarkable record of large volcanic eruptions for the last 60,000 years. It is worth noting that, due to the highly variable background sulfate levels during the glacial part of the period covered in this study, only extremely large eruptions are detected and quantified. Nonetheless, a record of extremely large eruptions is very valuable when it comes to assessing the climate impact of explosive volcanism, for we know from other studies that very large eruptions exert the most significant impact on climate.
The conclusions of this study are significant, not only because it is the first time that a systematic study of volcanism during the last 60 ka yields a robust record, but also it demonstrates that ice cores are capable of providing valuable information regarding volcanism and its climatic impact on time scales of millennia and longer, supplementing and/or enhancing knowledge from geological records.
I would like to offer a comment on a technical aspect. I find that in several places in this paper, the authors use terms such as “measurement techniques” and “measurement methods” for how ice core analysis yields sulfate data and how different “techniques” or “methods” yield data of various quality. Regarding the chemical measurement of sulfate, there are only two techniques: ion chromatography (IC) and mass spectrometry (ICP-MS for sulfur). The quality of data from these techniques is the same or similar, for any ice core samples. Where data quality may vary is when different sampling methods are used: discrete, continuous melting with online IC or ICP-MS measurement, or continuous melting followed by off-line IC measurement. Often, these sampling methods determine measurement resolution or temporal resolution. For example, when sulfate was measured using IC on discrete samples, the resolution is lower than that when the measurement was using FIC on samples from a melter, due to the higher sampling resolution of the melter. The quality of sulfate data is the same, as sulfate in both cases were measured with ion chromatography.
In addition, I ask the authors to consider the following comments on specific passages in the paper.
Line 68. Small deposition at low accumulation sites could be also, or even mostly, due to reduced wet deposition.
Line 88-91. Are you saying that uncertainty in thinning-rate estimates also contributes to uncertainty/variability of volcanic deposition?
Line 113. In my opinion, the main problem with tephra ID is not that tephra does not deposit with sulfate simultaneously. The difference in timing of tephra and sulfate deposition is usually small, less than one year. The main problem is that it is impossible to perform continuous search and analysis of tephra in any deep/long ice core with the current analytical (or technological) tools. Additionally, there are no objective standards on matching the tephra in ice core to ash from a particular eruption.
Line 150. The word “analytical” should be inserted in “different methods”.
Line 166-169. MSA correction is needed only when sulfur, not sulfate, was measured. In fact, the correction should not or cannot be applied to sulfate data.
Line 220. Is there such an assumption?
Line 294. “sulfate deposition strongly influenced by sulfate record type (IC, FIC, CFA)”? See my comment on a technical aspect.
Lines 301-304. Deposition variation is due to different sampling methods, not measurement methods or techniques. See my comment on a technical aspect.
Line 350. “Two bipolar volcanic eruptions are known from tephra to be Icelandic origin: Could signals in Antarctica ice cores be from contemporaneous eruptions in SH? I notice that the authors use the term “bipolar volcanic eruptions” for contemporaneous signals in both Greenland and Antarctica ice cores. I think it is acceptable to use this term, with the caveat that such contemporaneous signals may be left by simultaneous eruptions in both hemispheres, rather than a single eruption.
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AC4: 'Reply on CC2', Jiamei Lin, 23 Nov 2021
The comment was uploaded in the form of a supplement: https://cp.copernicus.org/preprints/cp-2021-100/cp-2021-100-AC4-supplement.pdf
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AC4: 'Reply on CC2', Jiamei Lin, 23 Nov 2021
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CC3: 'Comment on cp-2021-100 (Thomas Aubry, Lauren Marshall and Anja Schmidt)', Thomas Aubry, 28 Sep 2021
This manuscript by Jiamei Lin and co-authors represents the first effort to constrain stratospheric volcanic SO2 emissions for the 60-9 ka period using a bipolar array of ice cores, and these emissions are then used to estimate the corresponding volcanic forcing. This will without doubt be a very useful contribution for the community working on volcano-climate interactions.
We would like to draw the attention of the authors to potential improvements for estimating volcanic forcing from emissions.
First, to estimate a global-mean Stratospheric Aerosol Optical Depth (SAOD), the authors use a linear scaling between SAOD and the aerosol loading. However, it is well known that for large eruptions this relationship is not linear (e.g. Crowley and Unterman, 2013). As highlighted by the authors, the scaling used in their work is calibrated against the 1991 Mt. Pinatubo eruption and the reference used does not employ the latest estimates of SO2 mass and SAOD for this eruption. For example, the post-Pinatubo peak global mean SAOD in Crowley and Unterman (2013) (ca. 0.14-0.15) is 16% larger than in the GloSSAC dataset (0.12-0.13, Kovilakam et al. 2020). We suggest that the authors consider either using the EVA model (Toohey et al., 2016) or the EVA_H model (Aubry et al., 2020) to obtain SAOD. EVA is calibrated using more up-to-date data for Pinatubo and is also a reference model for the community as it has been used to derive the volcanic forcing for CMIP6’s Paleoclimate Model Intercomparison Project (PMIP4). EVA_H is an extension to EVA that was calibrated using the full 1979-2015 period with state-of-the-art observational datasets. Additionally, in EVA_H the predicted global mean SAOD depends on the eruption latitude, which is not the case in EVA.
Second, to convert global-mean SAOD to global-mean radiative forcing, the authors use the scaling factor of Hansen et al. (2005). This scaling factor was constrained using climate model simulations for the 1991 Mt. Pinatubo eruption without full consideration of rapid adjustments. Several recent studies have suggested that consideration of rapid adjustments leads to a reduction in the scaling factor (e.g., Gregory et al., 2016; Larson & Portmann, 2016; Schmidt et al., 2018; Marshall et al., 2020). Revised scaling factors for a wide range of eruptions are available in Marshall et al. (2020). Collectively, these studies suggest a reduced conversion factor compared to Hansen et al. (2005) and IPCC AR5.
We acknowledge that using more recent methods will result in differences in reconstructed forcings that are likely small relative to uncertainties in ice-core derived estimates of the SO2 mass. We nonetheless think that it remains important to acknowledge and use the latest tools developed by the community to provide volcanic forcing estimates. At the minimum, the authors should discuss differences that may emerge from using different scaling factors.
Thanks again for a very interesting manuscript.
Thomas Aubry, Lauren Marshall and Anja Schmidt.
References:
Aubry, T. J., Toohey, M., Marshall, L., Schmidt, A., & Jellinek, A. M. (2020). A new volcanic stratospheric sulfate aerosol forcing emulator (EVA_H): Comparison with interactive stratospheric aerosol models. Journal of Geophysical Research: Atmospheres, 125, e2019JD031303. https://doi.org/10.1029/2019JD031303
Crowley, T., & Unterman,M. (2013). Technical details concerning development of a 1200 yr proxy index for global volcanism. Earth System Science Data, 5(1), 187–197. https://doi.org/10.5194/essd-5-187-2013
Gregory, J.M., Andrews, T., Good, P. et al. Small global-mean cooling due to volcanic radiative forcing. Clim Dyn 47, 3979–3991 (2016). https://doi.org/10.1007/s00382-016-3055-1
Hansen, J., Sato, M., Ruedy, R., Nazarenko, L., Lacis, A., Schmidt, G. A., et al. (2005). Efficacy of climate forcings. Journal of Geophysical Research:Atmospheres, 110. Review, D18104, https://doi.org/10.1029/2005JD005776
Marshall, L. R., Smith, C. J., Forster,P. M., Aubry, T. J., Andrews, T., & Schmidt, A. (2020). Large variations in volcanic aerosol forcing efficiency due to eruption source parameters and rapid adjustments. GeophysicalResearch Letters, 47, 2020GL090241. https://doi.org/10.1029/2020GL090241
Kovilakam, M., Thomason, L. W., Ernest, N., Rieger, L., Bourassa, A., and Millán, L.: The Global Space-based Stratospheric Aerosol Climatology (version 2.0): 1979–2018, Earth Syst. Sci. Data, 12, 2607–2634, https://doi.org/10.5194/essd-12-2607-2020, 2020.
Larson, E. J. L., & Portmann, R. W. (2016). A temporal kernel method to compute effective radiative forcing in CMIP5 transient simulations. Journal of Climate, 29(4), 1497– 1509. https://doi.org/10.1175/JCLI-D-15-0577.1
Schmidt, A., Mills, M. J., Ghan, S., Gregory, J. M., Allan, R. P., Andrews, T., et al. (2018). Volcanic radiative forcing from 1979 to 2015. Journal of Geophysical Research: Atmospheres, 123, 12,491– 12,508. https://doi.org/10.1029/2018JD028776
Toohey, M., Stevens, B., Schmidt, H., & Timmreck, C. (2016). Easy Volcanic Aerosol (EVA v1.0): An idealized forcing generator for climate simulations. Geoscientific Model Development, 2016, 1–40. https://doi.org/10.5194/gmd-2016-83
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AC5: 'Reply on CC3', Jiamei Lin, 23 Nov 2021
The comment was uploaded in the form of a supplement: https://cp.copernicus.org/preprints/cp-2021-100/cp-2021-100-AC5-supplement.pdf
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AC5: 'Reply on CC3', Jiamei Lin, 23 Nov 2021
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