Revisiting the response of the Asian monsoon system to volcanic eruptions over the last millennium

Volcanic eruptions are the most important natural climate forcing over the last millennium.  Reductions in top of the atmosphere incoming shortwave radiation and the concomitant declines in global temperatures are expected to cause a weaker hydrological cycle, a reduction in precipitable water, and a drier monsoon.  The putative response of the ENSO system to volcanic eruptions should likewise result in drought of south and southeast Asia, enhancing this effect.  And while models produce both these effects in response to volcanic forcing, proxy records over the last millennium are more equivocal.  Here, I revisit the question of the Asian monsoon system's response to volcanic forcing using both traditional and stable isotope tree-ring data.  Stable isotope series in particular show no clear response to volcanism, in contrast to isotope-enable climate models.  Large-scale drought reconstructions using ring width reveal wetter conditions in tropical southeast Asia associated with some of the largest last millennium eruptions, but there are substantial differences across the region and between individual eruptions.  The potential role of pre-conditioning and stochastic variability are explored in the context of the ENSO system and it's linked to the Asian monsoon.