Aims. Miyake et al. (2012, Nature, 486, 240, henceforth M12) recently reported, based on 14C data, an extreme cosmic event in about AD775. Using a simple model, M12 claimed that the event was too strong to be caused by a solar flare within the standard theory. This implied a new paradigm of either an impossibly strong solar flare or a very strong cosmic ray event of unknown origin that occurred around AD775. However, as we show, the strength of the event was significantly overestimated by M12. Several subsequent works have attempted to find a possible exotic source for such an event, including a giant cometary impact upon the Sun or a gamma-ray burst, but they are all based on incorrect estimates by M12. We revisit this event with analysis of new datasets and consistent theoretical modelling.Methods. We verified the experimental result for the AD775 cosmic ray event using independent datasets including 10Be series and newly measured 14C annual data. We surveyed available historical chronicles for astronomical observations for the period around the AD770s to identify potential sightings of aurorae borealis and supernovae. We interpreted the 14C measurements using an appropriate carbon cycle model.Results. We show that: (1) The reality of the AD775 event is confirmed by new measurements of 14C in German oak; (2) by using an inappropriate carbon cycle model, M12 strongly overestimated the event’s strength; (3) the revised magnitude of the event (the global 14C production Q = (1.1 − 1.5) × 108 atoms/cm2) is consistent with different independent datasets (14C, 10Be, 36Cl) and can be associated with a strong, but not inexplicably strong, solar energetic particle event (or a sequence of events), and provides the first definite evidence for an event of this magnitude (the fluence >30 MeV was about 4.5 × 1010 cm-2) in multiple datasets; (4) this interpretation is in agreement with increased auroral activity identified in historical chronicles.Conclusions. The results point to the likely solar origin of the event, which is now identified as the greatest solar event on a multi-millennial time scale, placing a strong observational constraint on the theory of explosive energy releases on the Sun and cool stars.

: 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.

Significance: The first century BCE fall of the Roman Republic and Ptolemaic Kingdom and subsequent rise of the Roman Empire were among the most important political transitions in the history of Western civilization. Volcanic fallout in well-dated Arctic ice core records, climate proxies, and Earth system modeling show that this transition occurred during an extreme cold period resulting from a massive eruption of Alaska’s Okmok volcano early in 43 BCE. Written sources describe unusual climate, crop failures, famine, disease, and unrest in the Mediterranean immediately following the eruption—suggesting significant vulnerability to hydroclimatic shocks in otherwise sophisticated and powerful ancient states. Such shocks must be seen as having played a role in the historical developments for which the period is famed.

The mid-17th century is characterized by a cluster of explosive volcanic eruptions in the 1630s and 1640s, climatic conditions culminating in the Maunder Minimum, and political instability and famine 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 the socio-political context in which they occurred and the human responses they may have triggered. Three distinct sulfur peaks are found in the Greenland ice core record in 1637, 1641–1642, and 1646. In Antarctica, only one unambiguous sulfate spike is recorded, peaking in 1642. The resulting bipolar sulfur peak in 1641–1642 can likely be ascribed to the eruption of Mount Parker (6^∘ N, Philippines) on 26 December 1640, but sulfate emitted from Komaga-take (42^∘ N, Japan) volcano on 31 July 1641 has potentially also contributed to the sulfate concentrations observed in Greenland at this time. The smaller peaks in 1637 and 1646 can be potentially 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 peaks have been confirmed with tephra preserved in ice cores. Tree-ring and written sources point to cold conditions in the late 1630s and early 1640s in various parts of Europe and to poor harvests. Yet the early 17th century 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 eruption cluster between 1637 and 1646 and the climatic and societal conditions recorded in its aftermath thus offer a textbook example of difficulties in (i) unambiguously distinguishing volcanically induced cooling, wetting, or drying from natural climate variability and (ii) attributing political instability, harvest failure, and famines solely to volcanic climatic impacts. This example shows that while the impacts of past volcanism must always be studied within the contemporary socio-economic contexts, it is also time to move past reductive framings and sometimes reactionary oppositional stances in which climate (and environment more broadly) either is or is not deemed an important contributor to major historical events.