Comment on cp-2021-170
Mukund Palat Rao
The 852/3 CE eruption of Mount Churchill, Alaska, was one the largest first millennium volcanic events, with a magnitude 6.7 (VEI 6) and tephra volume 39.4–61.9 km3 (95 % confidence). spatial extent ash fallout from this event is considerable cryptotephra (White River Ash east; WRAe) extends as far Finland Poland. Proximal ecosystem societal disturbances have been linked eruption; however, wider impacts on climate society are unknown. Greenland ice-core records show that occurred in winter ± 1 associated relatively moderate sulfate aerosol loading, but large abundances chlorine. Here we assess potential broader impact using palaeoenvironmental reconstructions, historical model simulations. We also use fortuitous timing Churchill its extensively widespread deposition White (east) (WRAe) to examine climatic expression warm Medieval Climate Anomaly period (MCA; ca. 950–1250 CE) precisely peatlands North Atlantic region. reconstructed forcing compared magnitude, tree-ring-inferred temperatures report significant atmospheric cooling 0.8 °C summer 853 CE. Modelled scenarios CE, although average smaller (0.3 °C). simulated patterns generally similar those generated temperature reconstructions. Tree-ring inferred begins prior date suggesting natural internal variability may increased system’s susceptibility further cooling. could suggest be underestimated, thereby highlighting need for greater insight into, consideration of, role halogens when estimating potential. Precise comparisons across America Europe, facilitated by presence WRAe isochron, reveal no consistent MCA signal. These findings contribute growing body evidence characterizes hydroclimate time-transgressive heterogeneous, rather than well-defined period. isochron demonstrates long-term (multidecadal) or were identified beyond areas proximal eruption. Historical Europe subsistence crises demonstrate degree temporal correspondence interannual timescales, events reported outside common 9th century. exemplifies difficulties identifying confirming single eruption, even it dated.