The 852/3 CE Mount Churchill eruption: examining the potential climatic and societal impacts and the timing of the Medieval Climate Anomaly in the North Atlantic Region

Abstract

Abstract. The 852/3 CE eruption of Mount Churchill, Alaska, was one of the largest first millennium volcanic events, with a magnitude of 6.7 (VEI 6) and a tephra volume of 39.4–61.9 km3 (95 % confidence). The spatial extent of the ash fallout from this event is considerable and the cryptotephra (White River Ash east; WRAe) extends as far as Finland and Poland. Proximal ecosystem and societal disturbances have been linked with this eruption; however, wider eruption impacts on climate and society are unknown. Greenland ice-core records show that the eruption occurred in winter 852/3 ± 1 CE and that the eruption is associated with a relatively moderate sulfate aerosol loading, but large abundances of volcanic ash and chlorine. Here we assess the potential broader impact of this eruption using palaeoenvironmental reconstructions, historical records and climate model simulations. We also use the fortuitous timing of the 852/3 CE Churchill eruption and its extensively widespread tephra deposition of the White River Ash (east) (WRAe) to examine the climatic expression of the warm Medieval Climate Anomaly period (MCA; ca. 950–1250 CE) from precisely linked peatlands in the North Atlantic region. The reconstructed climate forcing potential of 852/3 CE Churchill eruption is moderate compared with the eruption magnitude, but tree-ring-inferred temperatures report a significant atmospheric cooling of 0.8 °C in summer 853 CE. Modelled climate scenarios also show a cooling in 853 CE, although the average magnitude of cooling is smaller (0.3 °C). The simulated spatial patterns of cooling are generally similar to those generated using the tree-ring-inferred temperature reconstructions. Tree-ring inferred cooling begins prior to the date of the eruption suggesting that natural internal climate variability may have increased the climate system’s susceptibility to further cooling. The magnitude of the reconstructed cooling could also suggest that the climate forcing potential of this eruption may be underestimated, thereby highlighting the need for greater insight into, and consideration of, the role of halogens and volcanic ash when estimating eruption climate forcing potential. Precise comparisons of palaeoenvironmental records from peatlands across North America and Europe, facilitated by the presence of the WRAe isochron, reveal no consistent MCA signal. These findings contribute to the growing body of evidence that characterizes the MCA hydroclimate as time-transgressive and heterogeneous, rather than a well-defined climatic period. The presence of the WRAe isochron also demonstrates that no long-term (multidecadal) climatic or societal impacts from the 852/3 CE Churchill eruption were identified beyond areas proximal to the eruption. Historical evidence in Europe for subsistence crises demonstrate a degree of temporal correspondence on interannual timescales, but similar events were reported outside of the eruption period and were common in the 9th century. The 852/3 CE Churchill eruption exemplifies the difficulties of identifying and confirming volcanic impacts for a single eruption, even when it is precisely dated.

Bucking the trend: Population resilience in a marginal environment

“…From the opening of the record around 950 up until ~1200, the paleoclimate proxies from Slieveanorra Bog show limited fluctuations. This part of the record falls within the age-range of the Medieval Climate Anomaly, a period of general warmer conditions in Europe [ 89 ] although paleoclimate records from the North Atlantic region, including Ireland, show that this was a time of variable climate conditions [ 90 ]. Subsequently, testate amoeba-based water-table reconstructions and peat humification values signal three phases of wetter conditions, namely at ~1220–1300, ~1390–1490 and ~1700–1850 ( Fig 2 ).…”

Investigating hydroclimatic impacts of the 168–158 BCE volcanic quartet and their relevance to the Nile River basin and Egyptian history

“…For historical eruptions to act as tests in this manner or to be studied as potential "revelatory" crises, knowledge of their dating alone is insufficient, particularly given the regional and seasonal variability of volcanic hydroclimatic impacts and the sensitivity of these impacts to multiple variables such as the location, season, chemical composition, and height attained by volcanic ejecta (Robock, 2000;Cole-Dai, 2010;Ludlow et al, 2013). Even where instrumental or natural archives are available, but especially where these are thin or absent, climate modeling can provide insights into the expected impacts for particular regions, seasons, and related physical (e.g., riverine) systems (e.g., Toohey et al, 2016;McConnell et al, 2020;Mackay et al, 2022). This is true for modeling of idealized eruptions, but potentially even more so for models that produce "historical realizations" based upon actual forcing reconstructions (e.g., Tardif et al, 2019).…”

“…When this causes a "failure" of the Nile summer flood, many adverse societal impacts may follow. These include harvest failure (seen also in other periods of Egyptian history; e.g., Hassan, 1997a, b;Mikhail, 2015), potentially prompting subsistence-driven migration to urban areas, with inability to meet state taxation demands (payable in grain) also potentially necessitating the sale of hereditary familial lands (Manning, 2003;Manning et al, 2017). These stressors might work in tandem with the psychological and religious significance of a "failed" Nile flood, something widely feared, and which could be interpreted (even propagandized to foment revolt) as signaling divine displeasure at the Pharaoh (Ludlow and Manning, 2021;Ludlow et al, 2023).…”