Timing and climate forcing of volcanic eruptions for the past 2,500 years

Abstract

Volcanic eruptions contribute to climate variability, but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings. Here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual-to-decadal temperature variability in the Northern Hemisphere during the past 2,500 years. Our results are based on new records of atmospheric aerosol loading developed from high-resolution, multi-parameter measurements from an array of Greenland and Antarctic ice cores as well as distinctive age markers to constrain chronologies. Overall, cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes. Our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth-century pandemics, famines, and socioeconomic disruptions in Eurasia and Mesoamerica while allowing multi-millennium quantification of climate response to volcanic forcing.

Climatic and societal impacts of a volcanic double event at the dawn of the Middle Ages

“…Based on the ice core data, our simulations suggest very strong radiative forcing in the NH high latitudes resulting from both eruptions, such that the decadal average radiative forcing in the NH extratropics is 50 % larger than the largest such forcing of the past 1200 years. These conclusions are to some degree dependent on the assumption of two single eruptions: if the 536 sulfate peak was due to multiple NH eruptions (a possibility suggested by tephra analysis of a Greenland ice core (Sigl et al 2015)), the resulting radiative forcing could potentially be weaker than that estimated here. Constraining the eruption sequence at this time, and generally the uncertainties related to estimating sulfur injection and radiative forcing from ice core sulfate signals, are topics in need of further study.…”

“…The 536 event has a strong signal in Greenland ice cores, and while a corresponding signal is undetectable in most Antarctic ice cores, a small signal was reported in the high resolution West Antarctic Ice Sheet (WAIS) Divide ice core record (Sigl et al 2013), suggesting some degree of cross-equator stratospheric transport. The resulting Greenland-to-Antarctic sulfate flux ratio of more than 10:1 can be safely assumed to be representative of a mid or high latitude NH eruption, which is consistent with detection of tephra in a Greenland ice core consistent in chemical composition to NH volcanoes (Sigl et al 2015).…”

“…Multiple NH tree ring reconstructions suggest that the year 536 was the coldest single year of at least the past 2000 years, and that 536-545 was the coldest decade of the same period (e.g., Larsen et al 2008;Sigl et al 2015). However, current estimates from ice cores of the global volcanic radiative forcing over the same interval ranks the 536 and 540 eruptions as only the 18th and 5th strongest events respectively (Sigl et al 2015).…”

“…Multiple NH tree ring reconstructions suggest that the year 536 was the coldest single year of at least the past 2000 years, and that 536-545 was the coldest decade of the same period (e.g., Larsen et al 2008;Sigl et al 2015). However, current estimates from ice cores of the global volcanic radiative forcing over the same interval ranks the 536 and 540 eruptions as only the 18th and 5th strongest events respectively (Sigl et al 2015). At face value, the magnitudes of the 536 and 540 eruptions derived directly from ice core data appear inconsistent with the exceptional cooling implied by tree ring reconstructions, and therefore do not necessarily support the theory of widespread societal crisis popularly connected to volcanic activity at the time.…”

“…Larsen et al (2008) reported the presence of two sulfate signals in Greenland ice cores separated by approximately four years around the year 536 CE, and linked the second sulfate peak-the signature of a likely tropical eruption-to the 536 mystery cloud. Updated ice core timescales, proposed initially based on matching of ice core and tree ring volcanic signals (Baillie 1994;Baillie 2008;Baillie and McAneney 2015) and recently confirmed through matching of signatures of cosmogenic isotopes in ice cores and tree rings in the 8th century (Sigl et al 2015), place the two signals at 536 and 540 CE. This double peak structure of the ice core records is in qualitative agreement with the temporal character of many tree ring-based temperature reconstructions for this time period (Baillie 1994), with cooling maxima in 536 and again 4 or 5 years later.…”