Comparison of Global Climatic Responses to Large Tropical Volcanic Eruptions over the Last Millennium in Paleoclimatic Reconstructions and Model Simulations

Abstract Large volcanic eruptions are known to significantly impact global climate for several years, yet a comprehensive comparison across the growing number of paleoclimate datasets has not been performed. Here, we assess the impacts of major eruptions over the Last Millennium on surface air temperature (SAT), Palmer drought severity index (PDSI), and 500-hPa geopotential height using tree-ring reconstructions, nine data assimilation (DA) products, and two climate model ensembles. We confirm robust global SAT cooling but find large differences in magnitude and persistence: Reconstructions based on tree-ring density show shorter, physically consistent cooling, whereas products dominated by tree-ring widths show longer persistence, likely reflecting biological memory. PDSI responses reveal coherent wetting over the western United States, the Mediterranean Basin, and southern South America, and coherent drying over northern and European Russia, central Asia, and southern Siberia, with divergence elsewhere. El Niño–Southern Oscillation responses differ across products, suggesting that any volcanically forced signal is weak relative to internal variability and highly sensitive to the background climate state. Geopotential height anomalies reveal widespread posteruption tropospheric contraction and robust extratropical circulation shifts, including negative height anomalies over mid- to high latitudes and wave-like patterns in the Southern Hemisphere. These anomalies are dynamically consistent with the spatial patterns of wetting and drying in PDSI, suggesting that volcanic forcing reorganizes large-scale atmospheric circulation in ways that influence hydroclimate. Together, these findings provide a comprehensive framework for interpreting volcanic impacts, strengthen confidence in regions with robust signals, and identify priority areas—particularly in the tropics and the Southern Hemisphere—where additional proxy coverage could reduce current uncertainties. Significance Statement This study presents the first comprehensive intercomparison of volcanic impacts on temperature, hydroclimate, and atmospheric circulation from tree-ring reconstructions, data assimilation products, and climate model ensembles. Reconstructions based on tree-ring density are the physically most consistent benchmark, showing shorter and more realistic duration of cooling, whereas products dominated by tree-ring widths overestimate persistence resulting from biological memory. Hydroclimate responses reflect coherent wetting in the western United States, the Mediterranean, and southern South America, and coherent drying in northern and European Russia, central Asia, and southern Siberia, with minimal agreement elsewhere. Responses of the El Niño–Southern Oscillation phenomenon remain inconsistent between products. We also connect hydroclimate signals with posteruption atmospheric height anomalies and associated extratropical circulation changes to provide a clearer framework for interpreting how volcanoes impact interactions between the ocean and atmosphere. This linkage also helps pinpoint priority regions—especially across the tropics and the Southern Hemisphere—where expanded, high-resolution proxy records could most effectively narrow current uncertainties.