Fig. 1: Impact of tropical volcanic eruptions on the circumglobal teleconnection (CGT).

a Tree-ring-based reconstruction of the CGT index (black), overlaid with the ERA5-based CGT index (1948–2020; red) for comparison. Shading indicates the ±1 root-mean-square error (RMSE) uncertainty range of the reconstruction. Blue dots mark the first boreal summer following large tropical eruptions. b CGT index from the Community Earth System Model Last Millennium Ensemble (CESM-LME; black), with ensemble spread (±1 standard error, SE) in gray shading. c Superposed epoch analysis (SEA) of CGT anomalies relative to a 5-year pre-eruption baseline, composited across n = 9 volcanic eruptions. The red dashed line denotes the eruption year (Year 0); the blue line shows the multi-event mean; gray dashed lines indicate the 95% confidence interval. d Same as (c), but using the CESM-LME ensemble mean, composited across n = 91 eruption events drawn from 13 ensemble members. e Spatial pattern of volcanically induced CGT anomalies relative to the 5-year pre-eruption baseline, based on CESM simulations. Shading shows composite June–July–August 200-hPa meridional wind anomalies in the first post-eruption summer, and contours denote the climatological summer CGT pattern, defined as the leading empirical orthogonal function (EOF) mode of the ERA5 200-hPa meridional wind (solid and dashed lines indicate positive and negative values, respectively). Green triangles mark tree-ring sites used in the reconstruction. Stippling indicates regions where ≥10 out of 13 ensemble members agree on the sign of the anomaly.