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  1. Abstract A first synthesis of available data for the period of Rome’s expansion in Italy (about 400–29 b.c.e.) shows the role of climate and environment in early Roman imperialism. Although global indices suggest a warmer phase with relatively few short-term climate events occuring around the same time as the expansion, local data emphasize the highly variable timing and expression of these trends. This variability casts doubt on ideas of a unitary, historically consequential “Roman Warm Period.” The historical importance of climate and environment to socioeconomic development merits emphasis, but should be understood in terms of evolving, contingent forms of resilience and risk-mitigating behavior by Italian communities during Roman expansion. 
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  2. Abstract. The injection of sulfur into the stratosphere by volcanic eruptions is thedominant driver of natural climate variability oninterannual to multidecadal timescales. Based on a set of continuous sulfateand sulfur records from a suite of ice cores from Greenland and Antarctica,the HolVol v.1.0 database includes estimates of the magnitudes andapproximate source latitudes of major volcanic stratospheric sulfurinjection (VSSI) events for the Holocene (from 9500 BCE or 11 500 years BP to1900 CE), constituting an extension of the previous record by 7000 years.The database incorporates new-generation ice-core aerosol records with asub-annual temporal resolution and a demonstrated sub-decadal dating accuracyand precision. By tightly aligning and stacking the ice-core records on theWD2014 chronology from Antarctica, we resolve long-standing inconsistenciesin the dating of ancient volcanic eruptions that arise from biased (i.e.,dated too old) ice-core chronologies over the Holocene for Greenland. Wereconstruct a total of 850 volcanic eruptions with injections in excess of 1 teragram of sulfur (Tg S); of these eruptions, 329 (39 %) are located in the low latitudes with bipolarsulfate deposition, 426 (50 %) are located in the Northern Hemisphere extratropics (NHET) and 88 (10 %) are located in the Southern Hemisphere extratropics (SHET). The spatial distribution of the reconstructed eruption locationsis in agreement with prior reconstructions for the past 2500 years. Intotal, these eruptions injected 7410 Tg S into thestratosphere: 70 % from tropical eruptions and 25 % from NHextratropical eruptions. A long-term latitudinally and monthly resolvedstratospheric aerosol optical depth (SAOD) time series is reconstructed fromthe HolVol VSSI estimates, representing the first Holocene-scalereconstruction constrained by Greenland and Antarctica ice cores. These newlong-term reconstructions of past VSSI and SAOD variability confirm evidencefrom regional volcanic eruption chronologies (e.g., from Iceland) in showingthat the Early Holocene (9500–7000 BCE) experienced a higher number ofvolcanic eruptions (+16 %) and cumulative VSSI (+86 %) compared withthe past 2500 years. This increase coincides with the rapid retreat of icesheets during deglaciation, providing context for potential future increasesin volcanic activity in regions under projected glacier melting in the 21stcentury. The reconstructed VSSI and SAOD data are available at (Sigl et al., 2021). 
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  3. Abstract. The mid-17th century is characterized by a clusterof explosive volcanic eruptions in the 1630s and 1640s, climatic conditionsculminating in the Maunder Minimum, and political instability andfamine in regions of western and northern Europe as well as China and Japan. This contribution investigates the sources of the eruptions of the 1630s and 1640s and their possible impact on contemporary climate using ice core, tree-ring, and historical evidence but will also look into thesocio-political context in which they occurred and the human responses theymay have triggered. Three distinct sulfur peaks are found in the Greenlandice core record in 1637, 1641–1642, and 1646. In Antarctica, only oneunambiguous sulfate spike is recorded, peaking in 1642. The resultingbipolar sulfur peak in 1641–1642 can likely be ascribed to the eruption ofMount Parker (6∘ N, Philippines) on 26 December 1640, but sulfateemitted from Komaga-take (42∘ N, Japan) volcano on 31 July 1641has potentially also contributed to the sulfate concentrations observed inGreenland at this time. The smaller peaks in 1637 and 1646 can bepotentially attributed to the eruptions of Hekla (63∘ N, Iceland)and Shiveluch (56∘ N, Russia), respectively. To date, however,none of the candidate volcanoes for the mid-17th century sulfate peakshave been confirmed with tephra preserved in ice cores. Tree-ring andwritten sources point to cold conditions in the late 1630s and early 1640sin various parts of Europe and to poor harvests. Yet the early 17thcentury was also characterized by widespread warfare across Europe – and in particular the Thirty Years' War (1618–1648) – rendering any attribution of socio-economic crisis to volcanism challenging. In China and Japan, historical sources point to extreme droughts and famines starting in 1638 (China) and 1640 (Japan), thereby preceding the eruptions of Komaga-take (31 July 1640) and Mount Parker (4 January 1641). The case of the eruptioncluster between 1637 and 1646 and the climatic and societal conditionsrecorded in its aftermath thus offer a textbook example of difficulties in(i) unambiguously distinguishing volcanically induced cooling, wetting, ordrying from natural climate variability and (ii) attributing politicalinstability, harvest failure, and famines solely to volcanic climaticimpacts. This example shows that while the impacts of past volcanism mustalways be studied within the contemporary socio-economic contexts, it isalso time to move past reductive framings and sometimes reactionaryoppositional stances in which climate (and environment more broadly) eitheris or is not deemed an important contributor to major historical events. 
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  4. Abstract. Volcanic fallout in polar ice sheets provides important opportunities to date and correlate ice-core records as well as to investigate theenvironmental impacts of eruptions. Only the geochemical characterization of volcanic ash (tephra) embedded in the ice strata can confirm the sourceof the eruption, however, and is a requisite if historical eruption ages are to be used as valid chronological checks on annual ice layercounting. Here we report the investigation of ash particles in a Greenland ice core that are associated with a volcanic sulfuric acid layer previouslyattributed to the 79 CE eruption of Vesuvius. Major and trace element composition of the particles indicates that the tephra does not derive fromVesuvius but most likely originates from an unidentified eruption in the Aleutian arc. Using ash dispersal modeling, we find that only an eruptionlarge enough to include stratospheric injection is likely to account for the sizable (24–85 µm) ash particles observed in the Greenlandice at this time. Despite its likely explosivity, this event does not appear to have triggered significant climate perturbations, unlike some otherlarge extratropical eruptions. In light of a recent re-evaluation of the Greenland ice-core chronologies, our findings further challenge the previousassignation of this volcanic event to 79 CE. We highlight the need for the revised Common Era ice-core chronology to be formally accepted by the widerice-core and climate modeling communities in order to ensure robust age linkages to precisely dated historical and paleoclimate proxy records. 
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