the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 01 Sep 2026
More than Laki. Compound Climate Shocks and Icelandic Volcanism in the Nordic World of the 1780s
Abstract. The article investigates the 1783–1784 Laki flood lava eruption as a case of regionally differentiated volcanic climate impacts and compound climate–society shocks in the Nordic countries. Drawing on recent advances in paleoclimate reanalysis (ModE-RA), early instrumental weather observations, dendroclimatology, and local environmental histories, it reconstructs seasonal and spatial patterns of climate anomalies and their societal repercussions from Iceland to Finland. A model–data comparison reveals marked regionality: while ModE-RA indicates pronounced post-eruption cooling from 1784 to 1786, instrumental and proxy evidence show strong sub-regional contrasts, including a preceding unrelated severe spring–summer drought in southern Scandinavia and notable discrepancies between ensemble simulations and observed autumn 1783 and winter 1783/84 temperature patterns. The study conceptualizes the Laki crisis as a compound event in the Nordic countries, in which volcanic cooling interacted with antecedent warmth and drought, atmospheric pollution, societal tensions, and institutional vulnerabilities. Pre-eruption drought and grain harvest failures in Denmark and southern and central Sweden, eruption-related toxic haze and vegetation damage in Iceland, and subsequent cold seasons combined to produce cascading impacts on harvests, food prices, mortality, and social protest, with peak demographic and political effects lagging 2–3 years after the eruption and food crises. By systematically integrating “archives of nature” and “archives of society” across multiple Nordic polities, this study illustrates how an interdisciplinary climate history framework can capture the regional complexity of volcanic forcing and climatic anomalies, clarify tensions between models and observations, and explain divergent societal trajectories under compound climatic stress.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Climate of the Past.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: open (until 27 Oct 2026)
- RC1: 'Comment on egusphere-2026-5137', Anonymous Referee #1, 03 Sep 2026 reply
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- 1
This study combines the ModE-RA palaeoclimate reanalysis, early instrumental observations, tree-ring data, historical documents, grain-trade records and demographic data to reconstruct the climatic and societal impacts of the 1783-1784 Laki eruption across the Nordic region. Its most valuable move is to argue against Laki as a spatially uniform "European disaster" with immediate effects, and to show how pre-eruption warmth and drought, post-eruption cooling, market structures and institutional vulnerabilities interacted. The source base is unusually broad, and the regional framing deserves to be developed. The core inferential chain, however, is not yet adequately supported. Observations already assimilated into ModE-RA are reused as if they provided independent validation; an ensemble mean is compared directly with a single historical realization; the compound/cascading framework does not consistently distinguish hazards, preconditioned vulnerabilities and downstream impacts; and temporal sequence is used to infer a climate–society causal cascade. Consequently, harvest failures, warmth, drought and political-economic tensions already present in 1781–1783 are too readily folded into a “Laki-triggered” narrative. As it stands, the evidence supports an interpretive, hypothesis-generating interdisciplinary synthesis, but not the stronger volcanic-attribution and societal-causation claims made in the current version. I therefore recommend major revision.
Main comments
1. Compound hazards, vulnerabilities and cascading impacts are not kept apart
Lines 712-734 and Figure 10 place climatic anomalies, pollution, institutional dependence, slow information flow, market shocks, disease and political outcomes in one compound/cascading frame, without saying which are hazards, which vulnerabilities and which downstream impacts. Compound-event typologies also separate preconditioned, multivariate, temporally compounding and spatially compounding cases; the manuscript gives one broad definition instead of assigning a type to each region. A workable split would be: hazards (antecedent warmth and drought, volcanic pollution, the following cold seasons, early frosts), preconditions (earlier harvest failures, import dependence, the grain monopolies, poverty), cascading impacts (crop loss, prices, nutrition, disease, mortality, protest) and response feedback (imports, relief, migration, reform).
2. The societal analysis rests on temporal proximity and has no common comparative design
Section 3 says only that demographic, administrative and narrative records were combined and cross-checked. It gives no search scope, inclusion criteria, assessment of source independence, translation practice, unit of comparison or alternative explanations. The results and discussion nevertheless use causal verbs: "driven by", "helped seed", "averted", "resulted in". Please apply one comparative design at different levels (e.g., polity, region, locality) with the same indicators at each: climatic exposure, harvest, grain prices, imports, relief, disease, mortality, protest. If quantitative identification is not possible, state that the method is comparative-historical process tracing and label each conclusion as demonstrated, a plausible contributing factor, associated but not identified, or speculative.
3. ModE-RA is not independent of the instrumental, tree-ring and documentary records
The manuscript states that many of the series used here were assimilated into ModE-RA. It then reports that ModE-RA "very closely reproduces the observations of instrumental and proxy data across all four seasons", and the conclusion presents reanalysis, proxies and instruments as three mutually supporting lines of evidence. Agreement with assimilated data is an assimilation fit, not a test. ModE-RAclim does not escape this: it replaces the transient prior with randomly drawn years of ModE-Sim, removing the forced signal from the prior but keeping ModE-Sim covariances and the same observations, so it is not an observation-only product. Please add a record-level table of which stations, chronologies and documentary series were assimilated and which were not, describe comparisons against assimilated data as assimilation-fit or consistency checks rather than independent validation, and test the reconstructed spatial anomalies against fully withheld observations.
4. An ensemble mean is not a historical realization, and there is no no-Laki counterfactual
Section 4.1.3 and Figure 6 set the ModE-Sim ensemble mean against ModE-RA and the instrumental records season by season and read the differences as model-data disagreement. An ensemble mean suppresses internal variability and keeps mainly the common forced response, whereas the observed year is one forced response plus one realization of internal variability. The question is not whether the observations equal the mean but whether they fall outside the ensemble distribution. ModE-Sim is also an atmosphere-only ECHAM6 ensemble with prescribed SST and sea-ice boundaries, so its mean smooths the Laki response as well. It is not a no-Laki experiment, and it cannot generate the sea-ice and ocean heat transport feedback. Please show the full ensemble, or at least the 5th-95th range, the rank of the observations within it with exceedance probabilities, and the posterior spread, SD ratio and assimilation increments. Paired Laki / no-Laki simulations or a formal attribution analysis would be needed to provide a more appropriate basis for attribution. Without them, "the radiative response ... led to" and "link the external forcing" should be reduced to consistency with the expected response to volcanic forcing.
Specific comments
1. Lines 266-288 call instrumental observations "the most reliable source of information for assessing past climates" and then work with mixed baselines, 1961-1990 at l. 281 and 1761-1790. Please give, for the series used, instrument exposure and siting, unit conversions, gaps, breakpoints and homogenization uncertainty.
2. Please define the starting point of each lag separately eruption, harvest failure, price peak, epidemic onset and report them one by one.
3. Section 5.2 and the conclusion trace the food crisis through the abolition of the grain monopoly to the declaration of independence in 1814. As currently written, the chain is teleological: the 1814 outcome organizes the interpretation of the earlier events.
4. The 1783 density signal is doing two jobs at once. Lines 244-246 and 677-678 attribute low northern MXD in 1783 to aerosol acting on plant physiology; the same low density also carries the reconstructed northern cooling, in a region the manuscript says has no local instrumental coverage. If those chronologies entered the assimilation under the usual MXD-temperature relationship, direct aerosol damage would be read as cold and spread spatially through the model covariances.
5. Was Laki the trigger of the whole crisis, or a further shock entering a sequence already under way?
6. The three regional groups come from post hoc visual sorting and do not establish latitudinal control. Please use predefined geographical groups, or a reproducible clustering or hierarchical model, controlling for proxy type, target season, elevation and autocorrelation, and report sample depth, EPS/Rbar, calibration-verification statistics and reconstruction uncertainty.
7. Table A1 gives the longitude of Arjeplog as 182 deg E; Table A2 gives 18.20 deg E, which is correct. Cross-referencing is inconsistent throughout: the appendix labels two consecutive tables "Table S2" and "Table A2"; the main text cites Tables S1-S3 and Figures S1, S2 and S4 for material that appears as Tables A1-A2 and Figures A1-A3; and Figure A3 labels its third panel "Group C" where the text says group 3.
8. Figures 3 and 4 use a six-year baseline, 1777-1782; Figure 6 uses 1751-1780; the tree-ring work uses 1733-1782, 1734-1782 or 1773-1782. Line 390 notes that for temperature the two reanalysis baselines agree to within 0.2 deg C in every season, which is useful, but that check is stated only for the area-mean temperature. It does not cover the precipitation field in Figure 4, the spatial patterns, or the three tree-ring baselines. The short baseline also contains the three cold winters of 1780-1782. Please adopt one primary baseline and show how the maps and the tree-ring thresholds respond to the alternatives.
9. Figures 3, 4 and 6 show central estimates only, with no ensemble spread, no posterior uncertainty and no indication of how strongly each region is constrained. Please mask sparsely constrained areas or show the SD ratio alongside.
10. Figure 4 is labelled "large-scale precipitation" while the text compares it with rain-gauge totals. Please state whether the model variable excludes convective precipitation; if the definitions differ, the two are not directly comparable.