Density of near-extreme events

We provide a quantitative analysis of the phenomenon of crowding of near-extreme events by computing exactly the density of states (DOS) near the maximum of a set of independent and identically distributed random variables. We show that the mean DOS converges to three different limiting forms depending on whether the tail of the distribution of the random variables decays slower than, faster than, or as a pure exponential function. We argue that some of these results would remain valid even for certain {\em correlated} cases and verify it for power-law correlated stationary Gaussian sequences. Satisfactory agreement is found between the near-maximum crowding in the summer temperature reconstruction data of western Siberia and the theoretical prediction.Comment: 4 pages, 3 figures, revtex4. Minor corrections, references updated. This is slightly extended version of the Published one (Phys. Rev. Lett.

Eurasian Arctic greening reveals teleconnections and the potential for novel ecosystems

Arctic warming has been linked to observed increases in tundra shrub cover and growth in recent decades on the basis of significant relationships between deciduous shrub growth/biomass and temperature. These vegetation trends have been linked to Arctic sea ice decline and thus to the sea ice/albedo feedback known as Arctic amplification. However, the interactions between climate, sea ice and tundra vegetation remain poorly understood. Here we reveal a 50- year growth response over a >100,000 km2 area to a rise in summer temperature for alder (Alnus) and willow (Salix), the most abundant shrub genera respectively at and north of the continental treeline. We demonstrate that whereas plant productivity is related to sea ice in late spring, the growing season peak responds to persistent synoptic-scale air masses over West Siberia associated with Fennoscandian weather systems through the Rossby wave train. Substrate is important for biomass accumulation, yet a strong correlation between growth and temperature encompasses all observed soil types. Vegetation is especially responsive to temperature in early summer. These results have significant implications for modelling present and future Low Arctic vegetation responses to climate change, and emphasize the potential for structurally novel ecosystems to emerge fromwithin the tundra zone.Vertaisarviointia edeltävä käsikirjoitu

An 8768-year Yamal Tree-ring Chronology as a Tool for Paleoecological Reconstructions

Abstract—In recent years, the supra-long Yamal tree-ring chronology has been significantly extended and became much more reliable. This article characterizes the sample wood used to build the longest absolutely dated Siberian Larch tree-ring chronology of the Subarctic area, i.e. from 6748 BC to 2019 AD, for a total continuous period of 8768 years. The ecological value of the temporal and spatial distribution of the dated trees are presented, and their potential use for application in various field of natural sciences and humanities are discussed. © 2021, Pleiades Publishing, Ltd.This study was supported by the Russian Foundation for Basic Research (project no. 18-05-00575). P. Fonti thanks the Swiss Science Foundation for the financial support (project “CALDERA” no. CRSII5_183571)

Current Siberian heating is unprecedented during the past seven millennia

The Arctic is warming faster than any other region on Earth. Putting this rapid warming into perspective is challenging because instrumental records are often short or incomplete in polar regions and precisely-dated temperature proxies with high temporal resolution are largely lacking. Here, we provide this long-term perspective by reconstructing past summer temperature variability at Yamal Peninsula – a hotspot of recent warming – over the past 7638 years using annually resolved tree-ring records. We demonstrate that the recent anthropogenic warming interrupted a multi-millennial cooling trend. We find the industrial-era warming to be unprecedented in rate and to have elevated the summer temperature to levels above those reconstructed for the past seven millennia (in both 30-year mean and the frequency of extreme summers). This is undoubtedly of concern for the natural and human systems that are being impacted by climatic changes that lie outside the envelope of natural climatic variations for this region. © 2022, The Author(s).Natural Environment Research Council, NERC: NE/S015582/1; Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, SNF: 183571; Russian Foundation for Basic Research, РФФИ: 18-05-00575; Russian Science Foundation, RSF: 182398, 21-14-00330R.M.H., S.G.S., A.Y.S., and L.A.G. received funding from the Russian Foundation for Basic Research (no. 18-05-00575). M.S., C.C., S.G., and P.F. received funding from the SNF Sinergia project CALDERA (no. 183571). V.V.K. acknowledges support from the Russian Science Foundation (no. 21-14-00330). G.vA. acknowledges support from the SNF project XELLCLIM (no. 182398). T.J.O. acknowledges support from UK NERC project GloSAT (no. NE/S015582/1)

Tree-Rings Reveal Two Strong Solar Proton Events in 7176 and 5259 BCE

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. © 2022, The Author(s).The Laboratory of Ion Beam Physics is partially funded by its consortium partners PSI, EAWAG, and EMPA. N.B. is funded by the Swiss National Science Foundation (SNSF grant #SNF 197137). The establishment of the BRAMS Facility was jointly funded by the NERC, BBSRC and the University of Bristol and the measurements in this work were partly funded by an ERC Proof of Concept grant awarded to R.P.E. and financing E.C. postdoctoral contract (LipDat H2020 ERC-2018-PoC/812917). We thank Bisserka Gaydarska for sub-sampling the inter-laboratory replicates from M49, M234, Q2729 and Q2750, Cathy Tyers for reviewing the dating of the Irish and German samples, and Alexander Land for assistance in dating sample M49. P.F. received funding from the SNF Sinergia project CALDERA (no. 183571). R.H. is funded by Russian Science Foundation (grant № 21-14-00330). I.U. acknowledges the support from the Academy of Finland (grant 321882 ESPERA). C.L.P.’s and M.W.S.’s work on bristlecone pine was funded by the M.H. Wiener Foundation (ICCP Project). K.N. acknowledges the support provided by the Austrian Science Fund FWF (grant I-1183-N19)

Global wood anatomical perspective on the onset of the Late Antique Little Ice Age (LALIA) in the mid-6th century CE

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. © 2022 Science China PressFritz & Elisabeth Schweingruber FoundationNational Science Foundation, NSF, (1203749, 1902625, 2002454, 2112314, 2124885, RSF 18-14-00072P, RSF 21-14-00330)Engineering Research Centers, ERCEuropean Research Council, ERC, (AdG 882727, CZ.02.1.01/0.0/0.0/16_019/0000797)Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, SNF, (CRSII5 183571)Fondo Nacional de Desarrollo Científico y Tecnológico, FONDECYT, (1201411, 1221307)Vetenskapsrådet, VR, (2018-01272)Universität BielefeldRussian Science Foundation, RSF, (RSF 21-17-00006)Fondo de Financiamiento de Centros de Investigación en Áreas Prioritarias, FONDAP, (15110009, BASAL FB210018)Neurosciences Foundation, NSFAgencia Nacional de Investigación y Desarrollo, ANIDFunding text 1: Ulf Büntgen and Jan Esper received funding from the ERC Advanced Project MONOSTAR (AdG 882727). Ulf Büntgen, Jan Esper, and Mirek Trnka received funding from SustES: adaptation strategies for sustainable ecosystem services and food security under adverse environmental conditions (CZ.02.1.01/0.0/0.0/16_019/0000797). Ulf Büntgen, Jan Esper, and Clive Oppenheimer discussed many aspects of this study at the Center for Interdisciplinary Research (ZiF) at the University of Bielefeld, Germany. Alan Crivellaro received funding from the Fritz & Elisabeth Schweingruber Foundation. Duncan A. Christie and Carlos Le Quesne received funding from the ANID (FONDECYT 1201411, 1221307, FONDAP 15110009, BASAL FB210018). Olga V. Churakova (Sidorova) received funding from the Russian Science Foundation grant (RSF 21-17-00006). Rosanne D'Arrigo received funding from NSF Arctic Social Science 2112314 and NSF Arctic Natural Science 2124885, as well as the NSF P2C2 (Paleo Perspectives on Climatic Change) program (various grants). Rashit M. Hantemirov received funding from the Russian Science Foundation grant (RSF 21-14-00330). Alexander V. Kirdyanov received funding from the Russian Science Foundation grant (RSF 18-14-00072P). Fredrik C. Ljungqvist was supported by the Swedish Research Council (2018-01272). Patrick Fonti and Markus Stoffel received funding from the Swiss National Science Foundation through the SNSF Sinergia CALDERA project (CRSII5 183571). Matthew Salzer and Malcolm K. Hughes received funding from the National Science Foundation's P2C2 Program (1902625 and 1203749) and from the Malcolm H. Wiener Foundation. Greg Wiles was funded through NSF P2C2 Program (2002454). Ulf Büntgen designed the study and wrote the first draft of this manuscript with input from Jan Esper, Paul J. Krusic, and Clive Oppenheimer. Samples were processed and analysed by Alma Piermattei and Alan Crivellaro. All authors provided data and/or contributed to discussion and improving the article.Funding text 2: Ulf Büntgen and Jan Esper received funding from the ERC Advanced Project MONOSTAR (AdG 882727). Ulf Büntgen, Jan Esper, and Mirek Trnka received funding from SustES : adaptation strategies for sustainable ecosystem services and food security under adverse environmental conditions (CZ.02.1.01/0.0/0.0/16_019/0000797). Ulf Büntgen, Jan Esper, and Clive Oppenheimer discussed many aspects of this study at the Center for Interdisciplinary Research (ZiF) at the University of Bielefeld, Germany. Alan Crivellaro received funding from the Fritz & Elisabeth Schweingruber Foundation . Duncan A. Christie and Carlos Le Quesne received funding from the ANID ( FONDECYT 1201411 , 1221307, FONDAP 15110009 , BASAL FB210018). Olga V. Churakova (Sidorova) received funding from the Russian Science Foundation grant ( RSF 21-17-00006 ). Rosanne D’Arrigo received funding from NSF Arctic Social Science 2112314 and NSF Arctic Natural Science 2124885 , as well as the NSF P2C2 (Paleo Perspectives on Climatic Change) program (various grants). Rashit M. Hantemirov received funding from the Russian Science Foundation grant (RSF 21-14-00330). Alexander V. Kirdyanov received funding from the Russian Science Foundation grant (RSF 18-14-00072P). Fredrik C. Ljungqvist was supported by the Swedish Research Council (2018-01272). Patrick Fonti and Markus Stoffel received funding from the Swiss National Science Foundation through the SNSF Sinergia CALDERA project (CRSII5 183571). Matthew Salzer and Malcolm K. Hughes received funding from the National Science Foundation’s P2C2 Program (1902625 and 1203749) and from the Malcolm H. Wiener Foundation . Greg Wiles was funded through NSF P2C2 Program (2002454)

Natural disasters in the history of the eastern Turk empire

This article analyzes the effect of climate extremes on the historical processes that took place (AD 536, 581, 601, 626 and 679) in the Eastern Turk Empire (AD 534–745) in Inner Asia. Climate extremes are sharp, strong and sometimes protracted periods of cooling and drought caused by volcanic eruptions that in this case resulted in a negative effect on the economy of a nomadic society and were often accompanied by famine and illness. In fact, many of these natural catastrophes coincided with the Black Death pandemics among the Eastern Turks and the Chinese living in the north of China. The Turk Empire can be split into several chronological periods during which significant events that led to changes in the course of history of the nomadic state took place: AD 534–545—the rise of the Turk Empire; AD 581–583—the division of the Turk Empire into theWestern and the Eastern Empires; AD 601–603—the rise of Qimin Qaghan; AD 627–630—the Eastern Turks are conquered by China; AD 679–687—the second rise of the Eastern Turk Empire. The research shows that there is clearly-discernable interplay between important historical events and climate extremes in the history of the Turk Empire. This interplay has led us to the conclusion that the climatic factor did have an impact on the historical processes that took place in the eastern part of Inner Asia, especially on the territories with a nomadic economy. © The Author(s) 2019

Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE

This study was funded by the WSL-internal COSMIC project (5233.00148.001.01), the ETHZ (Laboratory of Ion Beam Physics), the Swiss National Science Foundation (SNF Grant 200021L_157187/1), and as the Czech Republic Grant Agency project no. 17-22102s.Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the 14C content in 484 individual tree rings formed in the periods 770–780 and 990–1000 CE. Distinct 14C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved 14C measurements are needed.Publisher PDFPeer reviewe

Trends in recent temperature and radial tree growth spanning 2000 years across northwest Eurasia

This paper describes variability in trends of annual tree growth at several locations in the high latitudes of Eurasia, providing a wide regional comparison over a 2000-year period. The study focuses on the nature of local and widespread tree-growth responses to recent warming seen in instrumental observations, available in northern regions for periods ranging from decades to a century. Instrumental temperature data demonstrate differences in seasonal scale of Eurasian warming and the complexity and spatial diversity of tree-growing-season trends in recent decades. A set of long tree-ring chronologies provides empirical evidence of association between inter-annual tree growth and local, primarily summer, temperature variability at each location. These data show no evidence of a recent breakdown in this association as has been found at other high-latitude Northern Hemisphere locations. Using Kendall's concordance, we quantify the time-dependent relationship between growth trends of the long chronologies as a group. This provides strong evidence that the extent of recent widespread warming across northwest Eurasia, with respect to 100- to 200-year trends, is unprecedented in the last 2000 years. An equivalent analysis of simulated temperatures using the HadCM3 model fails to show a similar increase in concordance expected as a consequence of anthropogenic forcing