Volcanic stratospheric sulfur injections and aerosol optical depth from 500ĝ€BCE to 1900ĝ€CE

Abstract

The injection of sulfur into the stratosphere by explosive volcanic eruptions is the cause of significant climate variability. Based on sulfate records from a suite of ice cores from Greenland and Antarctica, the eVolv2k database includes estimates of the magnitudes and approximate source latitudes of major volcanic stratospheric sulfur injection (VSSI) events from 500ĝ€BCE to 1900ĝ€CE, constituting an update of prior reconstructions and an extension of the record by 1000 years. The database incorporates improvements to the ice core records (in terms of synchronisation and dating) and refinements to the methods used to estimate VSSI from ice core records, and it includes first estimates of the random uncertainties in VSSI values. VSSI estimates for many of the largest eruptions, including Samalas (1257), Tambora (1815), and Laki (1783), are within 10ĝ€% of prior estimates. A number of strong events are included in eVolv2k which are largely underestimated or not included in earlier VSSI reconstructions, including events in 540, 574, 682, and 1108ĝ€CE. The long-term annual mean VSSI from major volcanic eruptions is estimated to be ĝ1/4 0.5ĝ€Tgĝ€†[S]ĝ€†yrĝ'1, ĝ1/4 50ĝ€% greater than a prior reconstruction due to the identification of more events and an increase in the magnitude of many intermediate events. A long-term latitudinally and monthly resolved stratospheric aerosol optical depth (SAOD) time series is reconstructed from the eVolv2k VSSI estimates, and the resulting global mean SAOD is found to be similar (within 33ĝ€%) to a prior reconstruction for most of the largest eruptions. The long-term (500ĝ€BCE-1900ĝ€CE) average global mean SAOD estimated from the eVolv2k VSSI estimates including a constant background injection of stratospheric sulfur is ĝ1/4 0.014, 30ĝ€% greater than a prior reconstruction. These new long-term reconstructions of past VSSI and SAOD variability give context to recent volcanic forcing, suggesting that the 20th century was a period of somewhat weaker than average volcanic forcing, with current best estimates of 20th century mean VSSI and SAOD values being 25 and 14ĝ€% less, respectively, than the mean of the 500ĝ€BCE to 1900ĝ€CE period. The reconstructed VSSI and SAOD data are available at https://doi.org/10.1594/WDCC/eVolv2k-v2..