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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 StatementThis 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. 

Abstract Much previous modeling work on the climate response to volcanic eruptions has focused on specific past events. Here, we explore the climate response over a whole range of amplitudes covering (and exceeding) all events of the last six millennia, by simulating eruptions with 5, 10, 20, 40, 80, and 160 Tg of stratospheric injected sulfur. Our simulations show a strongly non‐linear relationship between eruption magnitude and climate response, with temperature and precipitation responding differently. Global mean surface cooling saturates at 40 TgS, whereas precipitation decreases all the way to 160 TgS. We also find that the precipitation responds and recovers faster than the temperature, especially for the larger events. Our findings imply that a severe reduction in precipitation, rather than a dramatic surface cooling, might be the most important climatic impact associated with very large eruptions. 

Abstract Volcanic aerosols reduce global mean precipitation in the years after major eruptions, yet the mechanisms that produce this response have not been rigorously identified. Volcanic aerosols alter the atmosphere's energy balance, with precipitation changes being one pathway by which the atmosphere acts to return toward equilibrium. By examining the atmosphere's energy budget in climate model simulations using radiative kernels, we explain the global precipitation reduction as largely a consequence of Earth's surface cooling in response to volcanic aerosols reflecting incoming sunlight. These aerosols also directly add energy to the atmosphere by absorbing outgoing longwave radiation, which is a major cause of precipitation decline in the first post‐eruption year. We additionally identify factors limiting the post‐eruption precipitation decline, and provide evidence that our results are robust across climate models. 

Abstract We critically reexamine the question of whether volcanic eruptions cause surface warming over Eurasia in winter, in the light of recent modeling studies that have suggested internal variability may overwhelm any forced volcanic response, even for the very largest eruptions during the Common Era. Focusing on the last millennium, we combine model output, instrumental observations, tree-ring records, and ice cores to build a new temperature reconstruction that specifically targets the boreal winter season. We focus on 20 eruptions over the last millennium with volcanic stratospheric sulfur injections (VSSIs) larger than the 1991 Pinatubo eruption. We find that only 7 of these 20 large events are followed by warm surface temperature anomalies over Eurasia in the first posteruption winter. Examining the 13 events that show cold posteruption anomalies, we find no correlation between the amplitude of winter cooling and VSSI mass. We also find no evidence that the North Atlantic Oscillation is correlated with VSSI in winter, a key element of the proposed mechanism through which large, low-latitude eruptions might cause winter warming over Eurasia. Furthermore, by inspecting individual eruptions rather than combining events into a superposed epoch analysis, we are able to reconcile our findings with those of previous studies. Analysis of two additional paleoclimatic datasets corroborates the lack of posteruption Eurasian winter warming. Our findings, covering the entire last millennium, confirm the findings of most recent modeling studies and offer important new evidence that large, low-latitude eruptions are not, in general, followed by significant surface wintertime warming over Eurasia. 

Common Era temperature variability has been a prominent component in Intergovernmental Panel on Climate Change reports over the last several decades and was twice featured in their Summary for Policymakers. A single reconstruction of mean Northern Hemisphere temperature variability was first highlighted in the 2001 Summary for Policymakers, despite other estimates that existed at the time. Subsequent reports assessed many large-scale temperature reconstructions, but the entirety of Common Era temperature history in the most recent Sixth Assessment Report of the Intergovernmental Panel on Climate Change was restricted to a single estimate of mean annual global temperatures. We argue that this focus on a single reconstruction is an insufficient summary of our understanding of temperature variability over the Common Era. We provide a complementary perspective by offering an alternative assessment of the state of our understanding in high-resolution paleoclimatology for the Common Era and call for future reports to present a more accurate and comprehensive assessment of our knowledge about this important period of human and climate history.