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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.
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A data assimilation approach to last millennium temperature field reconstruction using a limited high-sensitivity proxy network
Abstract We use theNorthern Hemisphere Tree-RingNetwork Development (NTREND) tree-ring database to examine the effects of using a small, highly-sensitive proxy network for paleotemperature data assimilation over the last millennium. We first evaluate our methods using pseudo-proxy experiments. These indicate that spatial assimilations using this network are skillful in the extratropical Northern Hemisphere and improve on previous NTREND reconstructions based on Point-by-Point regression. We also find our method is sensitive to climate model biases when the number of sites becomes small. Based on these experiments, we then assimilate the real NTREND network. To quantify model prior uncertainty, we produce 10 separate reconstructions, each assimilating a different climate model. These reconstructions are most dissimilar prior to 1100 CE, when the network becomes sparse, but show greater consistency as the network grows. Temporal variability is also underestimated before 1100 CE. Our assimilation method produces spatial uncertainty estimates and these identify treeline North America and eastern Siberia as regions that would most benefit from development of new millennial-length temperature-sensitive tree-ring records. We compare our multi-model mean reconstruction to five existing paleo-temperature products to examine the range of reconstructed responses to radiative forcing. We find substantial differences in the spatial patterns and magnitudes of reconstructed responses to volcanic eruptions and in the transition between the Medieval epoch and Little Ice Age. These extant uncertainties call for the development of a paleoclimate reconstruction intercomparison framework for systematically examining the consequences of proxy network composition and reconstruction methodology and for continued expansion of tree-ring proxy networks.
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- PAR ID:
- 10297179
- Date Published:
- Journal Name:
- Journal of Climate
- ISSN:
- 0894-8755
- Page Range / eLocation ID:
- 1 to 64
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1175/JCLI-D-20-0661.1
