ENSO and volcanic forcing of winter and summer interannual temperature variability in East Asia over the past six centuries

Interannual variability is a major source of East Asian temperature extremes impacting the livelihoods of approximately one-third of the global population. However, the drivers of this variability, especially the roles of volcanism and the El Niño‒Southern Oscillation (ENSO), are poorly understood. Here, we address this issue by analyzing up-to-date climate reconstructions of winter (December–February) and summer (June–August) temperatures of East Asia, volcanic forcing, and the ENSO over the period 1376–1995 CE. We reveal substantial seasonality in interannual temperature variability and demonstrate that > 90% of temperature extremes in winter and summer during the past 620 years were asynchronous. This suggests that different climate drivers are responsible for interannual temperature variability in different seasons. Our results show that volcanic forcing is the primary driver of summer temperature variability in East Asia, but the ENSO is the primary driver in winter. We demonstrate that warm (cold) winter temperature extremes in East Asia were associated with positive (negative) ENSO phases over the past 620 years, suggesting a robust relationship between these parameters. Volcanic eruptions can lead to a substantial cooling anomaly of approximately 0.15 ℃ in the post-eruption summer in East Asia, but such an anomaly is absent in the post-eruption winter. We show that volcanic effects on the winter and summer temperatures of East Asia may be insensitive to the initial or background state of the ENSO, suggesting independent roles for volcanism and the ENSO in influencing seasonal temperatures in East Asia. Our findings highlight the importance of improving the future risk assessment of seasonal temperatures by considering the combined potential effects of anthropogenic sources, natural drivers, and internal climate variability.