Nature Communications October 2017

Additional information

Here you will find additional information related to the Volcanic Impacts on Climate and Society (VICS) paper published in Nature Communications on 17 October 2017. Click on the orange links and headings below.

Title: Volcanic suppression of Nile summer flooding triggers revolt and constrains interstate conflict in ancient Egypt
Authors: Manning JG, Ludlow F, Stine AR, Boos WR, Sigl M & Marlon J

DOI: https://doi.org/10.1038/s41467-017-00957-y
Available on Nature Communications here.
Available on the PAGES Product Database here.
This paper originated from Joe Manning’s presentation at the first VICS workshop in June 2016.

Abstract

Volcanic eruptions provide tests of human and natural system sensitivity to abrupt shocks because their repeated occurrence allows the identification of systematic relationships in the presence of random variability. Here we show a suppression of Nile summer flooding via the radiative and dynamical impacts of explosive volcanism on the African monsoon, using climate model output, ice-core-based volcanic forcing data, Nilometer measurements, and ancient Egyptian writings. We then examine the response of Ptolemaic Egypt (305–30 BCE), one of the best-documented ancient superpowers, to volcanically induced Nile suppression. Eruptions are associated with revolt onset against elite rule, and the cessation of Ptolemaic state warfare with their great rival, the Seleukid Empire. Eruptions are also followed by socioeconomic stress with increased hereditary land sales, and the issuance of priestly decrees to reinforce elite authority. Ptolemaic vulnerability to volcanic eruptions offers a caution for all monsoon-dependent agricultural regions, presently including 70% of world population.

Access the following official Press Releases (PDFs):
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Corresponding author

Francis Ludlow
School of Histories & Humanities, Trinity College
Dublin, Ireland
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Author list

Joseph Manning
Department of Classics, Yale University
New Haven, USA
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Alexander R. Stine
Department of Earth & Climate Sciences, San Francisco State University
San Francisco, USA
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William R. Boos
Department of Geology and Geophysics, Yale University
New Haven, USA
Tel: +1 203 432 2627
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Michael Sigl
Laboratory of Environmental Chemistry, Paul Scherrer Institut
Villigen PSI, Switzerland
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Jennifer Marlon
School of Forestry and Environmental Studies, Yale University
New Haven, USA
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Q1: We've known that explosive volcanic eruptions can impact the African monsoon. What is new about this study?

A: Our previous knowledge of a causal connection between volcanic eruptions, the African monsoon and Nile flow variability was limited to very few large events, including Laki, (1783-84 CE) and Eldgja (939 CE), both located in Iceland. Due to the lack of direct observations, we did not know if the hydroclimatic response to volcanic eruptions in east Africa was stationary through time. By precisely extracting the eruption dates of all major global eruptions that occurred over the past 2500 years and having the world’s longest observational climate record at hand in the form of the Islamic Nilometer with coverage from 622 CE onward, we had the unique opportunity to assess how volcanic eruptions forced Nile variability by influencing global monsoon patterns over multiple centuries to millennia. By stacking and aligning observations of Nile river flood stands relative to the volcanic eruption dates as indicated by ice cores from Greenland we could isolate the volcanically forced contribution from random variability. This approach profits from the large number of eruptions we considered and the exceptional dating precision in all records we studied.

Q2: What is the most important new conclusion from the study?

A: There are two fundamental conclusions from our work. The first is that we can for the first time see dynamic human responses to Nile flood shocks over centuries. It has always been understood that Nile flood variability had some impact on socio-economic performance and political stability, but we can now get some understanding of a premodern coupled natural-human system over a long time period. High resolution climate proxy data will change in a fundamental way how ancient historians work by adding detail to explanations of change over time. In the past, most causal explanations of historical change in ancient history came down to politics. But very clearly the politics, economics, religion and so on of a particular state like Ptolemaic Egypt, which was a major power in the Mediterranean, was intimately coupled to environmental constraints.

The second major conclusion is that when one looks at the reconstruction of volcanic eruptions from the ice core work of Michael Sigl and colleagues, it is clear that there were some periods in human history that were quiescent volcanically; what we are calling the "Roman Quiet Period" in the first two centuries CE is one. The period we are in now is another. Because the impact of explosive eruptions on monsoon-dependent regions such as East Africa is clear, we can expect more active periods of explosive eruptions to affect the region’s hydro-politics. This is an especially urgent matter considering the imminent completion of the Grand Ethiopian Renaissance Dam on the Ethiopian-Sudanese border at the headwaters of the Blue Nile, the largest source of water for Egypt, in a construction project that has already caused tensions between Ethiopia and Egypt.

Q3: Why did the study focus on ancient Egypt?

A: The Nile river was central to Egyptian civilization and, as a result, was carefully observed. Ancient records of Nile behavior, primarily qualitative observations recorded in land leases and letters, survive in large numbers beginning with the Ptolemaic period (305-30 BCE) at a time when Greeks governed the country. In fact, the Ptolemaic period in Egypt provides one of only a small handful of cases from the Ancient World in which the density of documentary information available is sufficient to conduct fine-scale comparisons to data from ice core records and other climate proxy data. This density of human archival information and the fact that the Nile appears to have been especially sensitive to volcanic forcing makes Egypt an excellent place to study societal responses to short term climatic change.

Q4: Can you describe the kinds of historical records you are using?

A: The main historical sources for the Ptolemaic period in Egypt are documents written on papyrus in either Greek or the Egyptian language. We have also used information from the well known series of trilingual (Hieroglyphic, demotic Egyptian, and Greek) priestly decrees most famously instantiated by the Rosetta Stone now in the British Museum in London. The papyrus records provide us with qualitative evidence for Nile flood behavior, noticed in letters and in land leases. The priestly decrees record a kind of contract between the kings and the influential priestly class of Egypt and sometimes give us important details of political and social events at the time when the decrees were promulgated. Occasionally the papyrus records give us valuable insight into technical innovations (e.g. into irrigation technologies) that were developed in response to severe Nile flood suppression.

Q5: What is the Cairo Nilometer record and why did you use it for your study of the Ptolemaic period?

A: The Cairo Nilometer is an annual record of Nile flood heights measured at the Nilometer on Roda island just south of modern Cairo. It is among the longest and most important historical climate records in the world, presently extending from 622 CE up to the twentieth century. We analyze this long flood record with reference to the ice-core-based record of explosive volcanism and show (in a ranked comparison between volcanic and non-volcanic years) a systematic Nile flood suppression in this record. In doing so we have constructed a significantly greater time depth to the history of the teleconnection between explosive eruptions and Nile river behavior and we can understand better the historical drivers of Nile river variability.

Q6: Can you explain briefly how you connected societal responses in Ptolemaic Egypt to the ice core record?

A: The Nilometer record - while exceptionally long - does not extend back into the Ptolemaic Era. But we can assume by analogy (and there is strong support also from qualitative descriptions of flood quality from ancient papyri and inscriptions) that the strong forcing/response relation we have established between volcanic eruptions and Nile flood heights from 622 AD onward also holds true also during the Ptolemaic Era. We could thus analyze in a quite similar way to our statistical analyses of the Nilometer record how volcanic eruptions may have triggered socio-cultural responses. We did this by aligning those societal parameters (e.g. internal revolts, terminations of wars, issuance of priestly decrees, frequencies of land scales) against the dates of the volcanic eruptions and by quantifying the degree to which the observed co-associations between eruptions and the various societal responses can be explained by chance alone.

Q7: Which eruptions are most likely to affect monsoon rainfall and to cause "Nile failures"

A: Several eruption parameters are important for the response of global and regional hydroclimate. We find in our analyses a dominant role for the strength of the volcanic eruptions with Nile flood height anomalies being roughly proportional to the stratospheric sulfur burden in the Northern Hemisphere estimated from the ice cores. In particular such eruptions that result in a strong hemispheric asymmetry (i.e. towards the Northern Hemisphere) in the spread of sulfur aerosols resulted frequently in severe "Nile failures". Eldgja in 939 CE and Laki 1783 CE are the most well known historical eruptions that have been credited with this effect, prior to our study. The asymmetry in the aerosol forcing is understood to be responsible for limiting the northward migration of summer monsoon precipitation centers causing reduced rainfall in the Ethiopian Highlands, which are the main water source for the annual summer flood of the Nile.

Q8: Are there any implications from your results for the modern world?

A: Our study can also be considered a long-term natural experiment that can provide context into potential hazard risks of solar radiation management. Solar radiation management through artificially injecting stratospheric aerosol is considered as a potential “geo-engineering” approach to reducing some of the impacts of global warming by reflecting a small amount of inbound sunlight back out into space the way natural volcanic aerosols do. Our research based on thousands of years of real-world observations and numerous volcanic injections scenarios shows the consequences of natural sulfur injections for global and regional climate, water availability and food security. This knowledge provides strong constraints when assessing the hazard risk of potential anthropogenic attempts at solar radiation management.

Our study also highlights the dominant role of volcanic eruptions on hydroclimate especially in the monsoon regions where food security and water availability are already a matter of great concern. While living in relative "quiescent" times in terms of climatically effective explosive volcanism, the world community should be prepared that large volcanic eruptions will occur again in the foreseeable future and progress efforts to identify vulnerabilities and mitigation strategies using all data available, including that coming from paleoclimate and historical archives.

Q9: Why has this association between volcanism and ancient Egyptian history via modulations of Nile flood variability only been discovered now?

A: Our previous understanding of the role of volcanism on climate and ancient societies was limited by the lack of a complete record of global volcanism with well-constrained evidence of timing and magnitudes of stratospheric sulphate aerosol injections. Ice-cores obtained from polar ice sheets are arguably the best archive for reconstructing the history of global volcanism over past millennia, but undiagnosed chronological errors have for a long time hampered systematic determinations of a volcanic impact on climate and society before the second millennium CE. Recent revisions made to polar ice-core chronologies (Sigl et al. 2015) have significantly reduced dating uncertainties and allow us now for the first time to systematically track the impact of volcanic eruptions on the climate system and human societies further back in time, including ancient Egypt.

Additional references

Iles CE & Hegerl GC (2014). The global precipitation response to volcanic eruptions in the CMIP5 models. Environ. Res. Lett. 9, 104012.
Kondrashov D, Feliks Y & Ghil M (2005). Oscillatory modes of extended Nile river records (A.D. 622–1922). Geophys. Res. Lett. 32, L10702.
Mikhail A (2015). Ottoman Iceland: a climate history. Environ. History 20, 262–284.
Robock A (2000). Volcanic eruptions and climate. Rev. Geophys. 38, 191–219.
Sigl M et al. (2015). Timing and climate forcing of volcanic eruptions for the past 2,500 years. Nature 523, 543–549.

 

vics paper volc 2500yrs

Figure 1, above: This figure places volcanism into context with the two main time periods of analyses for this study. Greenland ice-core sulphur concentrations used to derive the timing and atmospheric aerosol content of historic volcanic eruptions since 500 BC. “Nile failures” followed the eruptions of Katmai (Alaska), Laki and Eldgjá (Iceland) and repeatedly during the Ptolemaic Era (305-30 BC). Source: M. Sigl.

vics paper volc ptolemaic

Figure 2, above: This figure provides a more detailed look into Ptolemaic Era with two events mentioned in the ancient papyri (e.g. Edfu letter) linked to possible eruptions. Source: M. Sigl. Inset: The Edfu papyrus. Copyright Department of Papyrology, Institute of Archaeology, University of Warsaw (also below).

vics paper ice core sigl 2

Image 1, above (click this link for high-res image): Greenland ice cores used to infer the volcanic eruption dates and atmospheric aerosol burden. Credit: M. Sigl.

vics paper ice core sigl

Image 2, above (click this link for high-res image): Greenland ice cores used to infer the volcanic eruption dates and atmospheric aerosol burden. Credit: M. Sigl.

vics paper papyrus

Image 3, above: The Edfu papyrus. Copyright Department of Papyrology, Institute of Archaeology, University of Warsaw.

vics paper cairo nilometer 2 wiki

Image 4, above: Nilometer at Rawda, Cairo, Egypt. Author: Baldiri. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
By Baldiri (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons.


Volcanic Impacts on Climate and Society (VICS) aims to foster interdisciplinary activities towards better understanding of the impacts of volcanic forcing on climate and societies.

Learn more about the working group's activities, members and mailing list details here: http://pastglobalchanges.org/ini/wg/vics/intro

Past Global Changes (PAGES) was established in 1991 to facilitate international research into understanding past changes in the Earth system to improve projections of future climate and environment, and inform strategies for sustainability. It receives funding mainly from the US National Science Foundation and Swiss Academy of Sciences. PAGES is a core project of Future Earth and a scientific partner of WCRP.

More at: http://pastglobalchanges.org

 

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