the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Apr 2026
Climatic Impacts of the 536 and 540 CE Volcanic Eruptions Simulated with COSMO-CLM over the Middle East and Africa
Abstract. The past 2500 years were marked by major historical developments across the eastern Mediterranean, the Middle East, the Arabian Peninsula, and the Nile Basin from Lake Victoria to the Nile Delta. Modeling efforts by both the global and regional climate modeling communities remain limited in this region. Here, we address this gap by presenting the first transient regional climate simulation for the area spanning 2350 years, from 500 BCE to 1850 CE, using the COSMO-CLM model. The simulation reveals an exceptionally pronounced climatic response to the consecutive volcanic eruptions of 536 and 540 CE, which motivated an additional century-long ensemble experiment to investigate this interval in greater detail. The eruptions produce marked surface cooling through reduced incoming solar radiation and are accompanied by large-scale circulation anomalies. In the simulation, widespread cooling persists until around 550 CE, with boreal summers showing the strongest anomalies during the first two to three years after the eruptions. Precipitation responses display strong regional contrasts: anomalously wet conditions occur over the Mediterranean, the Middle East, and Southeast Africa, particularly during the climatologically dry Northern Hemisphere summer season, whereas the Sahara, the Arabian Peninsula, Central Africa, and Northeast Africa experience concurrent dryness concentrated in their respective rainy seasons. The most severe climatic anomalies occur within the first one to two years after the eruptions and gradually weaken over the following years.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Climate of the Past.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: open (until 28 Jun 2026)
- RC1: 'Comment on egusphere-2026-1636', Anonymous Referee #1, 27 May 2026 reply
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RC2: 'Comment on egusphere-2026-1636', Anonymous Referee #2, 09 Jun 2026
reply
Review of: Climatic Impacts of the 536 and 540 CE Volcanic Eruptions Simulated with COSMO-CLM over the Middle East and Africa
1. Does the paper address relevant scientific questions within the scope of CP?
This manuscript describes regional climate simulations over a region spanning the eastern mediterranean and middle east with a focus on the impacts of two major sixth century volcanic eruptions. These eruptions and their climate impacts have been widely studied, with proxy evidence and prior modeling studies suggesting strong temperature anomalies especially in Northern Europe, and eyewitness accounts of solar dimming in the Mediterranean. This general topic falls well within the remit of Climate of the Past, however, the authors fail to identify specific scientific questions that the study addresses. It reads as if the rationale is that no regional simulation has been performed yet for this period and region, so here it is.
2. Does the paper present novel concepts, ideas, tools, or data?
This study appears to be the first to perform regional simulations for this time period over this particular region. However, it fails to highlight any advantage of the regional simulations compared to existing simulations or any aspect of the results which advances our understanding of the time period or events studied.
3. Are substantial conclusions reached?
From the abstract, the main conclusions are vague and not novel—it has already been shown many times that the sixth century eruptions have a major impact on temperature, and it is not surprising that the precipitation anomalies are small and spatially variable. It is not clear what new knowledge this study provides. The conclusions section seems mostly to summarize the results, and suffers from a lack of comparing those results to prior studies, which would help to highlight the (potential) novelty of the regional simulations.
4. Are the scientific methods and assumptions valid and clearly outlined?
The models and methodology are fairly well described. Given the importance of the volcanic aerosol forcing, it could be useful to describe the spatial and temporal structure of the forcing in some detail. The use of regional subdomains in the analysis I think it detrimental to the description of results and attempt to understand them, more details are given below.
5. Are the results sufficient to support the interpretations and conclusions?
Generally the manuscript provides few conclusions and interpretations based on the results. However, there are some instances of conjecture in the conclusions section, particularly starting at line 406 regarding the links between circulation and precipitation anomalies.
6. Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)?
There is a fairly good description of the simulations.
7. Do the authors give proper credit to related work and clearly indicate their own new/original contribution?
The introduction includes references to many relevant papers, although some important studies are missing. Foundational works from Stothers (1984) and Larsen et al. (2008) could well have been included. I was surprised that there was no reference to Arjava (2005), who discusses the documentary evidence collected in the Mediterranean region and argues that the climatic impacts in this region were minimal. Recent work on records the Nile flow and the impact of volcanic eruptions (e.g., Manning et al., 2017; Singh et al., 2023) are quite relevant. And more generally, the work of Iles et al. (2013, 2014, 2015) on volcanic eruptions and precipitation would help provide context to the description of precipitation anomalies in this work. On the other hand, aside from the final sentence, the conclusions included no references, which made it near impossible to understand how the study’s results are or are not consistent with past studies and therefore what the present study contributes to the understanding of the climate impacts of the 6th Century eruptions.
8. Does the title clearly reflect the contents of the paper?
Yes.
9. Does the abstract provide a concise and complete summary?
Yes, with a lack of concrete scientific questions and conclusions.
10. Is the overall presentation well structured and clear?
Some figures are borderline unreadable, e.g., Fig. 4-7 due to having too small text and lines. These figures are also overwhelming in terms of the information content and would benefit greatly by further reduction of the data into manageable pieces.
11. Is the language fluent and precise?
Mostly the text is well-written but there are instances where a vagueness in the language is districting and potentially misleading. Examples given below in specific comments.
12. Are mathematical formulae, symbols, abbreviations, and units correctly defined and used?
Fine
13. Should any parts of the paper (text, formulae, figures, tables) be clarified, reduced, combined, or eliminated?
Figures should be revised to increase readability.
14. Are the number and quality of references appropriate?
More references needed in Conclusions.
15. Is the amount and quality of supplementary material appropriate?
Figures in the appendix will generally be ignored, it could be considered whether the information there is important enough to include, and if so if it could be incorporated into the figures of the main text in a more efficient way.
Specific comments:
The results are presented by averaging over 7 sub-domains of the regional model domain, which are defined based on the IPCC reference regions for subcontinental analysis. There are a couple major problems with this. Firstly, it appears that few (perhaps only 1?) of the subdomains are included completely within the domain of the regional model—in fact, in Fig. 1 only 4 of the subdomains are labeled because it seems that 3 subdomains only have extremely small areas within the model domain. It is never explained, but I assume that when these subdomains are referred to in the text, and results given, these results apply to the very small region of the defined subdomain which is included in the regional model domain. This is extremely problematic since the values given in the study will be unrepresentative of the subdomain as a whole, and anybody taking results of the study at face value could be easily misinterpreting the results. I would suggest that at minimum, the 3 subdomains for which only a small part of the subdomain is included in the study region should be excluded completely from the study. Further, the authors should be very clear about what proportion of the other 4 subdomains are included in the simulation domain and so how representative the results given are to those subdomains in general.
On the other hand, I don’t find that analyzing the results in the subdomains is generally helping the interpretation of the results, and that showing maps of the anomalies would instead be much easier for a reader to process, and that if a separation into subdomains was to be used, then one based on actual physical processes (e.g., dry vs. wet areas) would be much more intuitive.
Line 1: There is nothing grammatically wrong with this sentence, but the way it is formed seems to imply that the historical developments in these regions are somehow more “marked” than in other regions, which would not be accurate. I would suggest a rephrasing which is more specific about why there is interest in these regions.
Line 3: Are efforts really “limited” in this region? I would guess most simulations that cover this period are global (i.e. there are few regional simulations for this period) and so the effort is fairly well distributed spatially over the globe. Isn’t it more that the relative abundance of documentary and archaeological evidence in this region makes it so interesting?
Line 7: The sentence structure is implying that the eruptions “are accompanied by large scale circulation anomalies”, but importantly those anomalies are also *produced* by the volcanic aerosol radiative forcing.
Line 8: “simulation” or “simulations”?
Line 27: there are many older studies that quantify the cooling of the 536 and 540 eruptions, we shouldn’t forget about them.
Line 31: the two eruptions were not “concurrent”.
Line 66: simulations cannot “confirm” that something happened or didn’t happen in the real world. They can help explain how things happened, or help us test hypotheses, but they should not be taken as evidence about the real world.
Line 67: “However, discrepancies remain among data sources regarding the timing and regional extent of this cooling.” This statement requires proof—is this the conclusion of prior studies? Or is this your interpretation of a collection of past studies? Those studies need to be discussed and cited!
Line 73: “related contexts” here is precisely the same time period and set of eruptions as studied here! I think given the similarity, the works of van Dijk deserve more than a passing mention in this introduction section.
Line 81: here and elsewhere, some problems with using in text vs. parenthetical citation style.
Line 81: unclear what “reducing uncertainties” means here. What uncertainties? How can one or two simulations reduce those uncertainties?
Line 100: “historically important region” could be taken as somewhat culturally biased or insensitive, I would suggest to keep a neutral stance on the relative importance of different parts of the globe unless there are particular scientific reasons/questions to motivate focus on particular regions.
Line 101: again, isn’t this region actually one where we have more data than is typical for this time period?
Line 144: both the global and regional simulations are transient, so this label does not help to distinguish which simulations are being referred to here (and elsewhere).
Figure 1 caption: I believe “elevation” would be a more appropriate term than “altitude” for the topography. CAP, SEAF, and NEAF are mentioned in the caption but not labeled on the plot.
line 197: This statement seems rather clear but remains unquantified and so rather qualitative. It also is notably consistent with the analysis of tree ring records by Sigl et al. (2015).
Figure 2: unfortunately, the vertical bars highlighting the peak positive and negative T anomalies block out the T values in those years. A better choice of highlighting would allow the reader to see the full timeseries.
Line 199: it’s important to point out these eruptions are strong in terms of their SO2 injection to the stratosphere and associated radiative forcing, not necessarily the magnitude of their magma release (which is how volcanologists rank the severity of eruptions).
Line 208: which two eruptions?
Line 211: Is there a scientific reason to examine longer time periods?
Line 258: This section heading seems misplaced since the last section also dealt extensively with regional anomalies.
Figure 3: see comment to Figure 2.
Figures 4 and 5: The text on these figures is way too small.
Figure 6: again, the text is way too small here, and the reader is wondering what the purpose of this level of detail on the anomalies is. What question is this all relevant to?
Figure 7: At a zoom level of 300% one can start to make out the text labels and arrows on the panels. The authors are asking for a great deal of effort from the reader to process the information in these figures…
Line 388: This statement seems to be a rare case of an interpretation of the results, but I cannot understand it or how the results support the statement. By definition, “climate” includes more than just temperature, so how are the results of this study demonstrating that the climatic response to the 536 and 540 eruptions “cannot be understood in terms of cooling alone”?
Line 401: yes, the anomalies are regionally diverse, but can they be understood in terms of changes in large-scale circulations, e.g. shifting of the ITCZ?
Line 417: It is always hard to quantitatively define the “end” of a decaying signal, I wonder how you are doing it here?
Line 418: The “sustained cold period” you refer to, is this a hypothesis based on evidence that you are addressing with your study? If so, cite the source of this hypothesis and discuss more fully the implications.
Line 422: What modeling work? Give citations.
References:
Arjava, A.: The Mystery Cloud of 536 CE in the Mediterranean Sources, Dumbart. Oaks Pap., 59, 73–94, 2005.
Iles, C. E. and Hegerl, G. C.: Systematic change in global patterns of streamflow following volcanic eruptions, Nat. Geosci., 8, 838–842, https://doi.org/10.1038/ngeo2545, 2015.
Iles, C. E. and Hegerl, G. C.: The global precipitation response to volcanic eruptions in the CMIP5 models, Environ. Res. Lett., 9, 104012, https://doi.org/10.1088/1748-9326/9/10/104012, 2014.
Iles, C. E., Hegerl, G. C., Schurer, A. P., and Zhang, X.: The effect of volcanic eruptions on global precipitation, J. Geophys. Res. Atmos., n/a-n/a, https://doi.org/10.1002/jgrd.50678, 2013.
Larsen, L. B., Vinther, B. M., Briffa, K. R., Melvin, T. M., Clausen, H. B., Jones, P. D., Siggaard-Andersen, M.-L., Hammer, C. U., Eronen, M., Grudd, H., Gunnarson, B. E., Hantemirov, R. M., Naurzbaev, M. M., and Nicolussi, K.: New ice core evidence for a volcanic cause of the A.D. 536 dust veil, Geophys. Res. Lett., 35, https://doi.org/10.1029/2007GL032450, 2008.
Manning, J. G., Ludlow, F., Stine, A. R., Boos, W. R., Sigl, M., and Marlon, J. R.: Volcanic suppression of Nile summer flooding triggers revolt and constrains interstate conflict in ancient Egypt, Nat. Commun., 8, 900, https://doi.org/10.1038/s41467-017-00957-y, 2017.
Sigl, M., Winstrup, M., McConnell, J. R., Welten, K. C., Plunkett, G., Ludlow, F., Büntgen, U., Caffee, M., Chellman, N., Dahl-Jensen, D., Fischer, H., Kipfstuhl, S., Kostick, C., Maselli, O. J., Mekhaldi, F., Mulvaney, R., Muscheler, R., Pasteris, D. R., Pilcher, J. R., Salzer, M., Schüpbach, S., Steffensen, J. P., Vinther, B. M., and Woodruff, T. E.: Timing and climate forcing of volcanic eruptions for the past 2,500 years, Nature, 523, 543–549, https://doi.org/10.1038/nature14565, 2015.
Singh, R., Tsigaridis, K., LeGrande, A. N., Ludlow, F., and Manning, J. G.: Investigating hydroclimatic impacts of the 168–158 BCE volcanic quartet and their relevance to the Nile River basin and Egyptian history, Clim. Past, 19, 249–275, https://doi.org/10.5194/cp-19-249-2023, 2023.
Stothers, R. B.: Mystery cloud of AD 536, Nature, 307, 344–345, https://doi.org/10.1038/307344a0, 1984.
Citation: https://doi.org/10.5194/egusphere-2026-1636-RC2
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- 1
Review ‘Climatic Impacts of the 536 and 540 CE Volcanic Eruptions Simulated with COSMO-CLM over the Middle East and Africa’
The authors have carried out climate simulations for the Eastern Mediterranean region to study the regional impact of the mid-6th-century eruptions of 536 and 540 CE. They use both a global climate model (MPI-ESM) and a regional high-resolution model (COSMO-CLM). The authors find that the different regions in the Eastern Mediterranean show diverging hydroclimate responses and cooling duration after the eruptions.
Although the study could contribute to the understanding of the volcanic impact in the studied region, I have several major issues with this manuscript. These should be addressed before I would consider this manuscript to be ready for publication. Below are my main concerns in order of appearance.
Methods:
From the methods and throughout the manuscript it does not become clear which simulations are done for this study and which existing ones are used. In the table it says the simulations for this study cover 500-1850 CE, but the reference period used to calculate the anomalies is somehow covering 1-1850 CE. Past2k simulations for the MPI-ESM model exist (which are mentioned in the methods), as well as a 10-member ensemble for the LALIA. As the authors describe in the introduction, more ensemble members reduce the internal variability, so why don’t the authors include these simulations in their study? And why are the individual simulations presented the figures? Showing them individually does not reduce the internal variability, which was the argument for using more than one ensemble member in the first place.
Results:
It is also unclear which model simulations are presented in the different sections here. Which plots show the MPI-ESM simulations, and which the COSMO-CLM simulations?
The results sections are describing a lot of wetter/dryer/warmer/colder for different regions, which reads a bit chaotically. Having this type of results summarized in a table or map together with the climatology would help streamline the results a lot.
Figures:
The figures in this manuscript are unreadable. The subfigures should be larger, especially in figures 4, 5, and 6, and the font size of figure titles and labels is way too small for all figures. For figure 3, the variation in precipitation is not visible for some regions because the range on the y-axis is too broad. I suggest showing different ranges for the different regions. I am also missing significance testing in figures 2, 3, and 7, as well as a discussion on the significance of the findings.
Discussion:
Perhaps the largest concern I have with the manuscript is the lack of discussion of the results. After the introduction, previous studies are completely ignored. The authors should do a better job at including the relevant papers in a discussion. The results should be compared with previous studies (include citations!), and the findings should be put in a larger context.
I am also missing a discussion on the uncertainties of the study. The authors argue that climate models give insight in the processes behind the anomalies after eruptions, but do not actually discuss in depth why they find the results that they do. I like the atmospheric circulation section, but it seems a bit of an afterthought. Throughout the paper, different regions are indicated with abbreviations, but for this section they use different names/regions. The atmospheric circulation connection back to the precipitation and temperature changes could be a bit more elaborate.
Conclusions:
The summary given in the conclusions reads a lot better than the results section but is rather lengthy. The flow of the paper would be much approved if this is moved to the results section and call it ‘Results and Discussion’, or if it is given its own ‘Discussion’ section. A comparison with other studies can then be added, as well as putting the results in context. This way a lot of repetition can be avoided, and the results can be discussed right away, which will make the paper more pleasant to read.
The importance of the findings should be strengthened in the conclusion. Mainly mentioning that they can be used for comparison with ‘existing proxy reconstructions, historical documents and observations’ is not sufficient. Why not include the comparison to available proxy reconstructions and historical documents in this study? It would strengthen the paper if a comparison is carried out.
Please find the minor comments below.
Introduction:
Line 25: ‘Existing evidence…’ add from tree ring reconstructions
Line 38-39: ‘Together, these considerations highlight the need to better constrain the spatiotemporal climate response across the Mediterranean, the Middle East, and Africa,…’
This cannot be concluded from the text above. I suggest moving this farther down.
Line 58-61: Here you give previous literature on the topic. Use these studies in the discussion to compare your results to.
Line 66: ‘Simulations…’ Buntgen did not carry out simulations. Be careful not to mix simulations and reconstructions.
Line 73: van Dijk et al. (2022) used global ESM simulations that were analyzed for more local domains. This is not dynamically downscaling.
Line 77: ‘…here we make use of…’ This implies you did not carry out the simulations for this study. But in the methods section, it sounds like you did. This should be clarified.
Line 89: ‘…lower, and the need for multiple realizations and explicit regional analysis is therefore even stronger.’
Do you think two simulations is a large enough ensemble (this should be added to the discussion)? There is a 10 member MPI-ESM ensemble available for the 6th century, including this would strengthen your argument for using multiple ensemble members.
Methods:
Line 116-117: ‘T63). ‘Two realizations are available with identical external
forcings but different initial conditions, enabling an assessment of robustness against internal variability at the regional scale.’
Are these the past2k simulations? What period do they span? More information is needed here.
Line 138-139: ‘simulation. The reconstructions selected for PMIP4 past1000 were officially extended to this period for past2k experiments (Jungclaus et al., 2017).’
This feels a bit out of place. In this section you are describing the COSMO experiments. I suggest moving this up to the MPI-ESM section above. Also clarify if these are the simulations used in this study or not. If not, why are they not included?
Line 142-144: So you ran both the global model and the regional model for this study?
Line 146-147: Two ensemble members is not a lot. I am missing a discussion about this in the manuscript.
Figure 1: Not all the domains described in the caption are visible in the figure. The figure could also be larger.
Line 167: How well is the geographical variability captured in the different model grids?
Line 171-173: ‘Nicholson (2018) shows the general circulation for Africa in the boreal
summer (July/August) and in the boreal winter (January).’
This provides no information. Please explain what they found.
This entire section (2.4) reads a bit difficult. The explanation of the different circulation patterns should be combined with the temperature and precipitation patterns, so the reader gets an overview over the climatic situation for each subregion. This would also make it easier to put the anomalies from the eruptions in context in the results and discussion section.
Results:
Line 195: The 30-year running mean is not described in the results. Why did you choose to show this time interval? I suggest choosing a different time interval that is more relevant, like the 15-year mean.
Line 196: wet and dry is not shown in Figure 2.
Line 196: replace ‘overlaps’ with ‘similarities’
Line 198: Showing the major eruptions described in the text in the figure as well would help the reader.
Figure 2: The figures are hard to read. The blue and red lines indicating the warm and cold year hide the actual temperature. I suggest making these lines transparent so the temperature can still be read from the figures.
Line 199: Also cite Sigl et al. (2015)
Line 207: ‘On a seasonal scale, the results are comparable and are therefore presented in the Appendix.’
In the introduction, you argue for seasonal rather than annual results, yet here you mainly show annual means and have the seasonal means in the appendix. How is this making the study different from previous studies?
Line 229-231: ‘JJA is the wet season in SAH, ARP, CAF, and NEAF under the influence of the ITCZ and the dry season in the northern (MED, WCA) and the southern (SEAF) part of the domain.
Is this in the climatology, or a result? This needs clarification. As mentioned before, a map or table with the climatology and the anomalies for different regions would help organize the results.
Line 235: ‘No clear pattern of distribution of extremes can be identified in either season.’
So, unlike what was stated in the introduction, seasonal patterns do not matter after all? This should be discussed.
Line 242: Figure 2 is referenced here, but it should be Figure 3.
Line 250-251: ‘…also the wettest or driest period, especially at the seasonal scale.’
Are these anomalies outside of the range of variability?
Line 258: I suggest using a different title for the section. You also described regional anomalies in the sections above.
Line 262: ‘…that two realizations are…’ Is this referring to the MPI simulations, or the COSMO simulations? This needs clarification.
Figure 3: The y-axis on the first few subplots is too broad, which makes it hard to read the variations in precipitation for these regions. I suggest using a different y-axis range for the first four regions. In addition, the suggestions for figure 2 apply here as well.
Figure 4: The subfigures are unreadable. Make sure the subfigures are large enough to easily read the titles, labels, tick marks, and legend. It would be more intuitive to plot the average of the simulations. Showing them individually does not reduce the internal variability, which was the argument for using an ensemble in the first place.
Line 314: ‘It should be noted that this is the average value for both the northern and southern hemispheres.’
I don’t see the added value of this sentence.
Line 321-324: ‘. In summary, CAF, NEAF, and SEAF have the smallest annual temperature amplitude but the highest variation in precipitation, which is also associated with high variability within the subdomains. SAH and ARP have a higher temperature amplitude but very low annual precipitation. MED and especially WCA show the largest temperature variation with medium amounts of precipitation, although fluctuations within the subdomains can also be large here.’
It would be nice to explain a bit more where the differences between the different regions come from. I suggest starting with this section before discussing the anomalies and connect the two sections a bit better. This gives an overview (and visualisation) of the climatology of the regions, which should be used to put the anomalies in context.
Line 331: ‘…November, which can be up to twice the reference precipitation amount.’
I do not see this from the figure.
Figure 6: As with the other figures, this figure is hard to read.
Line 342: ‘Overall, these results are consistent with findings from previous studies.’
This is highly insufficient. Explain which studies (use references!) and what exactly the similarities are between the results from those studies and your own.
Figure 7: Again, unreadable figures. Why are the individual simulations plotted?
Line 350-351: ‘…fields at the upper and lower levels of the troposphere.’
Why were these levels chosen?
Line 367-368: ‘Despite the surface warming in some regions, temperatures at approximately 12 km height are cooler than the Common Era mean across the entire domain.’
It is very unsatisfying to end the section with this. Why is this?
Conclusions:
Line 380-382: ‘…spatially extensive cooling in the years following the eruptions. The strongest temperature anomalies occur within the first one to five post-eruption years, while weaker but still discernible cooling persists for up to about 15 years.’
This is not a new finding and should be discussed in relation to previous studies.
Line 405: ‘…confidently confirm the extremely harsh climatic conditions in the 540s within our study area.’
Is a one-degree cooling in the study regions really ‘extremely harsh’? The authors should put the findings in a wider context.
Line 408-411: ‘…and likely, a weakening of the Indian monsoon influence. Reduced incoming solar radiation after the eruptions cools the surface and thus weakens land-sea thermal contrasts. In summer, this likely reduces the influence of the Etesians over the Mediterranean and favors a greater influence of maritime air masses, thereby increasing humidity and precipitation in MED.’
The authors do not show this in this study. Is this theory based on previous studies? These should be cited!
Line 425-426: ‘…therefore offer an important basis for comparison with natural archives, documentary evidence, and historical observations.’
There are a lot of proxy reconstructions available. The authors could compare their study to these available archives to strengthen there findings.
Line 429: ‘…move beyond generalized narratives of volcanic cooling toward a more regionally differentiated understanding…’
Several previous studies have investigated the more regional impact of volcanic eruptions, including for the Near East and Mediterranean areas. These studies should not be ignored.