| 1. |
- Brehm, Nicolas, et al.
(författare)
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Tree-rings reveal two strong solar proton events in 7176 and 5259 BCE
- 2022
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- The Sun sporadically produces eruptive events leading to intense fluxes of solar energetic particles (SEPs) that dramatically disrupt the near-Earth radiation environment. Such events have been directly studied for the last decades but little is known about the occurrence and magnitude of rare, extreme SEP events. Presently, a few events that produced measurable signals in cosmogenic radionuclides such as 14C, 10Be and 36Cl have been found. Analyzing annual 14C concentrations in tree-rings from Switzerland, Germany, Ireland, Russia, and the USA we discovered two spikes in atmospheric 14C occurring in 7176 and 5259 BCE. The ~2% increases of atmospheric 14C recorded for both events exceed all previously known 14C peaks but after correction for the geomagnetic field, they are comparable to the largest event of this type discovered so far at 775 CE. These strong events serve as accurate time markers for the synchronization with floating tree-ring and ice core records and provide critical information on the previous occurrence of extreme solar events which may threaten modern infrastructure.
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| 2. |
- Büntgen, Ulf, et al.
(författare)
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Global wood anatomical perspective on the onset of the Late Antique Little Ice Age (LALIA) in the mid-6th century CE
- 2022
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Ingår i: Science Bulletin. - : Elsevier BV. - 2095-9273. ; 67:22, s. 2336-2344
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Tidskriftsartikel (refereegranskat)abstract
- Linked to major volcanic eruptions around 536 and 540 CE, the onset of the Late Antique Little Ice Age has been described as the coldest period of the past two millennia. The exact timing and spatial extent of this exceptional cold phase are, however, still under debate because of the limited resolution and geographical distribution of the available proxy archives. Here, we use 106 wood anatomical thin sections from 23 forest sites and 20 tree species in both hemispheres to search for cell-level fingerprints of ephemeral summer cooling between 530 and 550 CE. After cross-dating and double-staining, we identified 89 Blue Rings (lack of cell wall lignification), nine Frost Rings (cell deformation and collapse), and 93 Light Rings (reduced cell wall thickening) in the Northern Hemisphere. Our network reveals evidence for the strongest temperature depression between mid-July and early-August 536 CE across North America and Eurasia, whereas more localised cold spells occurred in the summers of 532, 540–43, and 548 CE. The lack of anatomical signatures in the austral trees suggests limited incursion of stratospheric volcanic aerosol into the Southern Hemisphere extra-tropics, that any forcing was mitigated by atmosphere-ocean dynamical responses and/or concentrated outside the growing season, or a combination of factors. Our findings demonstrate the advantage of wood anatomical investigations over traditional dendrochronological measurements, provide a benchmark for Earth system models, support cross-disciplinary studies into the entanglements of climate and history, and question the relevance of global climate averages.
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| 3. |
- Büntgen, Ulf, et al.
(författare)
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Prominent role of volcanism in Common Era climate variability and human history
- 2020
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Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865 .- 1612-0051. ; 64
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Tidskriftsartikel (refereegranskat)abstract
- © 2020 Elsevier GmbH Climate reconstructions for the Common Era are compromised by the paucity of annually-resolved and absolutely-dated proxy records prior to medieval times. Where reconstructions are based on combinations of different climate archive types (of varying spatiotemporal resolution, dating uncertainty, record length and predictive skill), it is challenging to estimate past amplitude ranges, disentangle the relative roles of natural and anthropogenic forcing, or probe deeper interrelationships between climate variability and human history. Here, we compile and analyse updated versions of all the existing summer temperature sensitive tree-ring width chronologies from the Northern Hemisphere that span the entire Common Era. We apply a novel ensemble approach to reconstruct extra-tropical summer temperatures from 1 to 2010 CE, and calculate uncertainties at continental to hemispheric scales. Peak warming in the 280s, 990s and 1020s, when volcanic forcing was low, was comparable to modern conditions until 2010 CE. The lowest June–August temperature anomaly in 536 not only marks the beginning of the coldest decade, but also defines the onset of the Late Antique Little Ice Age (LALIA). While prolonged warmth during Roman and medieval times roughly coincides with the tendency towards societal prosperity across much of the North Atlantic/European sector and East Asia, major episodes of volcanically-forced summer cooling often presaged widespread famines, plague outbreaks and political upheavals. Our study reveals a larger amplitude of spatially synchronized summer temperature variation during the first millennium of the Common Era than previously recognised.
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| 4. |
- Büntgen, Ulf, et al.
(författare)
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Reply to 'Limited Late Antique cooling'
- 2017
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 10:4, s. 243-243
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 5. |
- Büntgen, Ulf, et al.
(författare)
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The influence of decision-making in tree ring-based climate reconstructions
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Tree-ring chronologies underpin the majority of annually-resolved reconstructions of Common Era climate. However, they are derived using different datasets and techniques, the ramifications of which have hitherto been little explored. Here, we report the results of a double-blind experiment that yielded 15 Northern Hemisphere summer temperature reconstructions from a common network of regional tree-ring width datasets. Taken together as an ensemble, the Common Era reconstruction mean correlates with instrumental temperatures from 1794–2016 CE at 0.79 (p < 0.001), reveals summer cooling in the years following large volcanic eruptions, and exhibits strong warming since the 1980s. Differing in their mean, variance, amplitude, sensitivity, and persistence, the ensemble members demonstrate the influence of subjectivity in the reconstruction process. We therefore recommend the routine use of ensemble reconstruction approaches to provide a moreconsensual picture of past climate variability.
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| 6. |
- Charpentier Ljungqvist, Fredrik, et al.
(författare)
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Linking European building activity with plague history
- 2018
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Ingår i: Journal of Archaeological Science. - : Elsevier BV. - 0305-4403 .- 1095-9238. ; 98, s. 81-92
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Tidskriftsartikel (refereegranskat)abstract
- Variations in building activity reflect demographic, economic and social change during history. Tens of thousands of wooden constructions in Europe have been dendrochronologically dated in recent decades. We use the annually precise evidence from a unique dataset of 49 640 tree felling dates of historical constructions to reconstruct temporal changes in building activity between 1250 and 1699 CE across a large part of western and central Europe largely corresponding to the former Holy Roman Empire of the German Nation. Comparison with annual records of 9772 plague outbreaks shows that construction activity was significantly negatively correlated to the number of plague outbreaks, with the greatest decrease in construction following the larger outbreaks by three to four years after the start of the epidemics. Preceding the Black Death (1346-1353 CE) by five decades and the Great Famine (1315-1322 CE) by two decades, a significant decline in construction activity at c. 1300 CE is indicative of a societal crisis, associated with population stagnation or decline. Another dramatic decline in building activity coincides with the Thirty Years' War (1618-1648 CE) and confirms the devastating nature of this conflict. While construction activity was significantly lower during periods of high grain prices, no statistically robust relationship between the number of felling dates and past temperature or hydroclimate variations is found. This study demonstrates the value of dendrochronological felling dates as an indicator for times of crisis and prosperity during periods when documentary evidence is limited.
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| 7. |
- Charpentier Ljungqvist, Fredrik, 1982-, et al.
(författare)
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Regional Patterns of Late Medieval and Early Modern European Building Activity Revealed by Felling Dates
- 2022
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Ingår i: Frontiers in Ecology and Evolution. - : Frontiers Media SA. - 2296-701X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Although variations in building activity are a useful indicator of societal well-being and demographic development, historical datasets for larger regions and longer periods are still rare. Here, we present 54,045 annually precise dendrochronological felling dates from historical construction timber from across most of Europe between 1250 and 1699 CE to infer variations in building activity. We use geostatistical techniques to compare spatiotemporal dynamics in past European building activity against independent demographic, economic, social and climatic data. We show that the felling dates capture major geographical patterns of demographic trends, especially in regions with dense data coverage. A particularly strong negative association is found between grain prices and the number of felling dates. In addition, a significant positive association is found between the number of felling dates and mining activity. These strong associations, with well-known macro-economic indicators from pre-industrial Europe, corroborate the use of felling dates as an independent source for exploring large-scale fluctuations of societal well-being and demographic development. Three prominent examples are the building boom in the Hanseatic League region of northeastern Germany during the 13th century, the onset of the Late Medieval Crisis in much of Europec. 1300, and the cessation of building activity in large parts of central Europe during armed conflicts such as the Thirty Years’ War (1618–1648 CE). Despite new insights gained from our European-wide felling date inventory, further studies are needed to investigate changes in construction activity of high versus low status buildings, and of urban versus rural buildings, and to compare those results with a variety of historical documentary sources and natural proxy archives.
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| 8. |
- Frank, Thomas, et al.
(författare)
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Testing different Earlywood/Latewood delimitations for the establishment of Blue Intensity data : A case study based on Alpine Picea abies samples
- 2020
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Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865 .- 1612-0051. ; 64
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Tidskriftsartikel (refereegranskat)abstract
- For dendroclimatological Blue Intensity (BI) studies based on earlywood (EW) or latewood (LW) information, a demarcation between the two is necessary, which can be difficult to establish for species where the transition is subtle. Often, a percental value k is used that calculates an EW/LW boundary value for each tree ring individually based on the difference between maximum and minimum absorption. Several laboratories and authors have used different values for k (e.g. k = 30 % or k = 50 %), while wood anatomical and visual studies suggest that k is on the order of 80 %. Here, we test how different settings of k, and thus different definitions of the EW and LW proportions of a tree ring, influence the dendroclimatic potential of derived time series. To this end, we correlate instrumental temperature measurements with tree ring chronologies that are based on EW and LW information (e.g. EW absorption (EWBI), LW absorption (LWBI)), where the EW/LW proportion is varied by setting different values for k. The tree ring samples utilized are 30 cores of spruce (Picea abies) trees from a high-elevated site (ca. 1700 m a.s.l.) in the northern Alps, Austria. Overall, we achieve high correlations between temperature data and our tree ring chronologies. Regarding the stability of the climate signal under different k values, the results show that absorption intensity based parameters (Delta BI, EWBI, LWBI) are only mildly influenced by different settings of k, while width based parameters (EW width, LW width) show a larger dependence on k. LW width, for instance, was stronger correlated with temperature, the smaller the LW was chosen (and thus the higher k was set). Based on our results and the wood anatomical definition of the EW/LW boundary, we suggest that k = 80 % may be a good choice for future studies. However, since this is only a case study from one site, careful screening of the respective data set regarding an appropriate k value must accompany each dendroclimatological study.
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| 9. |
- Heiri, Oliver, et al.
(författare)
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Palaeoclimate records 60-8 ka in the Austrian and Swiss Alps and their forelands
- 2014
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 106, s. 186-205
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Tidskriftsartikel (refereegranskat)abstract
- The European Alps and their forelands provide a range of different archives and climate proxies for developing climate records in the time interval 60-8 thousand years (ka) ago. We review quantitative and semi-quantitative approaches for reconstructing climatic variables in the Austrian and Swiss sector of the Alpine region within this time interval. Available quantitative to semi-quantitative climate records in this region are mainly based on fossil assemblages of biota such as chironomids, cladocerans, co-leopterans, diatoms and pollen preserved in lake sediments and peat, the analysis of oxygen isotopes in speleothems and lake sediment records, the reconstruction of past variations in treeline altitude, the reconstruction of past equilibrium line altitude and extent of glaciers based on geomorphological evidence, and the interpretation of past soil formation processes, dust deposition and permafrost as apparent in loess-palaeosol sequences. Palaeoclimate reconstructions in the Alpine region are affected by dating uncertainties increasing with age, the fragmentary nature of most of the available records, which typically only incorporate a fraction of the time interval of interest, and the limited replication of records within and between regions. Furthermore, there have been few attempts to cross-validate different approaches across this time interval to confirm reconstructed patterns of climatic change by several independent lines of evidence. Based on our review we identify a number of developments that would provide major advances for palaeoclimate reconstruction for the period 60-8 ka in the Alps and their forelands. These include (1) the compilation of individual, fragmentary records to longer and continuous reconstructions, (2) replication of climate records and the development of regional reconstructions for different parts of the Alps, (3) the cross-validation of different proxy-types and approaches, and (4) the reconstruction of past variations in climate gradients across the Alps and their forelands. Furthermore, the development of downscaled climate model runs for the Alpine region 60-8 ka, and of forward modelling approaches for climate proxies would expand the opportunities for quantitative assessments of climatic conditions in Europe within this time-interval.
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| 10. |
- Tegel, Willy, et al.
(författare)
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Higher groundwater levels in western Europe characterize warm periods in the Common Era
- 2020
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Hydroclimate, the interplay of moisture supply and evaporative demand, is essential for ecological and agricultural systems. The understanding of long-term hydroclimate changes is, however, limited because instrumental measurements are inadequate in length to capture the full range of precipitation and temperature variability and by the uneven distribution of high-resolution proxy records in space and time. Here, we present a tree-ring-based reconstruction of interannual to centennial-scale groundwater level (GWL) fluctuations for south-western Germany and north-eastern France. Continuously covering the period of 265-2017 CE, our new record from the Upper Rhine Valley shows that the warm periods during late Roman, medieval and recent times were characterized by higher GWLs. Lower GWLs were found during the cold periods of the Late Antique Little Ice Age (LALIA; 536 to similar to 660 CE) and the Little Ice Age (LIA; between medieval and recent warming). The reconstructed GWL fluctuations are in agreement with multidecadal North Atlantic climate variability derived from independent proxies. Warm and wet hydroclimate conditions are found during warm states of the Atlantic Ocean and positive phases of the North Atlantic Oscillation on decadal scales.
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| 11. |
- Trachsel, Mathias, et al.
(författare)
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Multi-archive summer temperature reconstruction for the European Alps, AD 1053-1996
- 2012
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Ingår i: Quaternary Science Reviews. - : Elsevier. - 0277-3791 .- 1873-457X. ; 46, s. 66-79
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Tidskriftsartikel (refereegranskat)abstract
- We present a multi-archive, multi-proxy summer temperature reconstruction for the European Alpscovering the period AD 1053-1996 using tree-ring and lake sediment data. The new reconstruction isbased on nine different calibration approaches and errors were estimated conservatively. Summertemperatures of the last millennium are characterised by two warm (AD 1053-1171 and 1823-1996) andtwo cold phases (AD 1172-1379 and 1573-1822). Highest pre-industrial summer temperatures of the12th century were 0.3 degC warmer than the 20th century mean but 0.35 degC colder than proxy derivedtemperatures at the end of the 20th century. The lowest temperatures at the end of the 16th centurywere ~1 degC lower than the 20th century mean.
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