| 1. |
- Büntgen, Ulf, et al.
(författare)
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New Tree-Ring Evidence from the Pyrenees Reveals Western Mediterranean Climate Variability since Medieval Times
- 2017
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Ingår i: Journal of Climate. - 0894-8755 .- 1520-0442. ; 30:14, s. 5295-5318
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Tidskriftsartikel (refereegranskat)abstract
- Paleoclimatic evidence is necessary to place the current warming and drying of the western Mediterranean basin in a long-term perspective of natural climate variability. Annually resolved and absolutely dated temperature proxies south of the European Alps that extend back into medieval times are, however, mainly limited to measurements of maximum latewood density (MXD) from high-elevation conifers. Here, the authors present the world's best replicated MXD site chronology of 414 living and relict Pinus uncinata trees found >2200 m above mean sea level (MSL) in the Spanish central Pyrenees. This composite record correlates significantly (p <= 0.01) with May-June and August-September mean temperatures over most of the Iberian Peninsula and northern Africa (r = 0.72; 1950-2014). Spanning the period 1186-2014 of the Common Era (CE), the new reconstruction reveals overall warmer conditions around 1200 and 1400, and again after around 1850. The coldest reconstructed summer in 1258 (-4.4 degrees C compared to 1961-90) followed the largest known volcanic eruption of the CE. The twentieth century is characterized by pronounced summer cooling in the 1970s, subsequently rising temperatures until 2003, and a slowdown of warming afterward. Little agreement is found with climate model simulations that consistently overestimate recent summer warming and underestimate preindustrial temperature changes. Interannual-multidecadal covariability with regional hydroclimate includes summer pluvials after large volcanic eruptions. This study demonstrates the relevance of updating MXD-based temperature reconstructions, not only back in time but also toward the present, and emphasizes the importance of comparing temperature and hydroclimatic proxies, as well as model simulations for understanding regional climate dynamics.
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| 2. |
- Büntgen, Ulf, et al.
(författare)
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Tree-Ring Amplification of the Early Nineteenth-Century Summer Cooling in Central Europe
- 2015
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Ingår i: Journal of Climate. - 0894-8755 .- 1520-0442. ; 28:13, s. 5272-5288
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Forskningsöversikt (refereegranskat)abstract
- Annually resolved and absolutely dated tree-ring chronologies are the most important proxy archives to reconstruct climate variability over centuries to millennia. However, the suitability of tree-ring chronologies to reflect the “true” spectral properties of past changes in temperature and hydroclimate has recently been debated. At issue is the accurate quantification of temperature differences between early nineteenth-century cooling and recent warming. In this regard, central Europe (CEU) offers the unique opportunity to compare evidence from instrumental measurements, paleomodel simulations, and proxy reconstructions covering both the exceptionally hot summer of 2003 and the year without summer in 1816. This study uses 565 Swiss stone pine (Pinus cembra) ring width samples from high-elevation sites in the Slovakian Tatra Mountains and Austrian Alps to reconstruct CEU summer temperatures over the past three centuries. This new temperature history is compared to different sets of instrumental measurements and state-of-the-art climate model simulations. All records independently reveal the coolest conditions in the 1810s and warmest after 1996, but the ring width–based reconstruction overestimates the intensity and duration of the early nineteenth-century summer cooling by approximately 1.5°C at decadal scales. This proxy-specific deviation is most likely triggered by inflated biological memory in response to reduced warm season temperature, together with changes in radiation and precipitation following the Tambora eruption in April 1815. While suggesting there exists a specific limitation in ring width chronologies to capture abrupt climate perturbations with increased climate system inertia, the results underline the importance of alternative dendrochronological and wood anatomical parameters, including stable isotopes and maximum density, to assess the frequency and severity of climatic extremes.
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| 3. |
- Esper, Jan, et al.
(författare)
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Eastern Mediterranean summer temperatures since 730 CE from Mt. Smolikas tree-ring densities
- 2020
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 54:3-4, s. 1367-1382
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Tidskriftsartikel (refereegranskat)abstract
- The Mediterranean has been identified as particularly vulnerable to climate change, yet a high-resolution temperature reconstruction extending back into the Medieval Warm Period is still lacking. Here we present such a record from a high-elevation site on Mt. Smolikas in northern Greece, where some of Europe's oldest trees provide evidence of warm season temperature variability back to 730 CE. The reconstruction is derived from 192 annually resolved, latewood density series from ancient living and relict Pinus heldreichii trees calibrating at r(1911-2015) = 0.73 against regional July-September (JAS) temperatures. Although the recent 1985-2014 period was the warmest 30-year interval (JAS Twrt.1961-1990 = + 0.71 degrees C) since the eleventh century, temperatures during the ninth to tenth centuries were even warmer, including the warmest reconstructed 30-year period from 876-905 (+ 0.78 degrees C). These differences between warm periods are statistically insignificant though. Several distinct cold episodes punctuate the Little Ice Age, albeit the coldest 30-year period is centered during high medieval times from 997-1026 (- 1.63 degrees C). Comparison with reconstructions from the Alps and Scandinavia shows that a similar cold episode occurred in central Europe but was absent at northern latitudes. The reconstructions also reveal different millennial-scale temperature trends (NEur = - 0.73 degrees C/1000 years, CEur = - 0.13 degrees C, SEur = + 0.23 degrees C) potentially triggered by latitudinal changes in summer insolation due to orbital forcing. These features, the opposing millennial-scale temperature trends and the medieval multi-decadal cooling recorded in Central Europe and the Mediterranean, are not well captured in state-of-the-art climate model simulations.
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| 4. |
- Esper, Jan, et al.
(författare)
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LONG-TERM SUMMER TEMPERATURE VARIATIONS IN THE PYRENEES FROM DETRENDED STABLE CARBON ISOTOPES
- 2015
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Ingår i: Geochronometria. - : Walter de Gruyter GmbH. - 1733-8387 .- 1897-1695. ; 42:1, s. 53-59
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Tidskriftsartikel (refereegranskat)abstract
- Substantial effort has recently been put into the development of climate reconstructions from tree-ring stable carbon isotopes, though the interpretation of long-term trends retained in such timeseries remains challenging. Here we use detrended delta C-13 measurements in Pinus uncinata tree-rings, from the Spanish Pyrenees, to reconstruct decadal variations in summer temperature back to the 13th century. The June-August temperature signal of this reconstruction is attributed using decadally as well as annually resolved, 20th century delta C-13 data. Results indicate that late 20th century warming has not been unique within the context of the past 750 years. Our reconstruction contains greater amplitude than previous reconstructions derived from traditional tree-ring density data, and describes particularly cool conditions during the late 19th century. Some of these differences, including early warm periods in the 14th and 17th centuries, have been retained via d13C timeseries detrending - a novel approach in tree-ring stable isotope chronology development. The overall reduced variance in earlier studies points to an underestimation of pre-instrumental summer temperature variability derived from traditional tree-ring parameters.
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| 5. |
- Esper, Jan, et al.
(författare)
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Ranking of tree-ring based temperature reconstructions of the past millennium
- 2016
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 145, s. 134-151
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Tidskriftsartikel (refereegranskat)abstract
- Tree-ring chronologies are widely used to reconstruct high-to low-frequency variations in growing season temperatures over centuries to millennia. The relevance of these timeseries in large-scale climate reconstructions is often determined by the strength of their correlation against instrumental temperature data. However, this single criterion ignores several important quantitative and qualitative characteristics of tree-ring chronologies. Those characteristics are (i) data homogeneity, (ii) sample replication, (iii) growth coherence, (iv) chronology development, and (v) climate signal including the correlation with instrumental data. Based on these 5 characteristics, a reconstruction-scoring scheme is proposed and applied to 39 published, millennial-length temperature reconstructions from Asia, Europe, North America, and the Southern Hemisphere. Results reveal no reconstruction scores highest in every category and each has their own strengths and weaknesses. Reconstructions that perform better overall include N-Scan and Finland from Europe, E-Canada from North America, Yamal and Dzhelo from Asia. Reconstructions performing less well include W-Himalaya and Karakorum from Asia, Tatra and S-Finland from Europe, and Great Basin from North America. By providing a comprehensive set of criteria to evaluate tree-ring chronologies we hope to improve the development of large-scale temperature reconstructions spanning the past millennium. All reconstructions and their corresponding scores are provided at www.blogs.uni-mainz.de/fb09climatology.
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| 6. |
- Klippel, Lara, et al.
(författare)
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A 1200+year reconstruction of temperature extremes for the northeastern Mediterranean region
- 2019
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 39:4, s. 2336-2350
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Tidskriftsartikel (refereegranskat)abstract
- Proxy evidence is necessary to place current temperature and hydroclimatic changes in a long-term context and to assess the full range of natural and anthropogenic climate forcings. Here, we present the first millennium-length reconstruction of late summer (August-September) temperature variability for the Mediterranean region. We compiled 132 maximum latewood density (MXD) tree-ring series of living and relict Pinus heldreichii trees from a network of four high-elevation sites in the Pindus Mountains of Greece. Forty series reach back into the first millennium and the oldest sample dates to 575 CE. At annual to decadal scales, the record correlates significantly with August-September temperatures over the Balkan Peninsula and northeastern Mediterranean (r1950-2014 = 0.71, p < 0.001). We produce two reconstructions emphasizing interannual and decadal scale variance over the past millennium. Analysis of temperature extremes reveals the coldest summers occurred in 1035, 1117, 1217, 1884 and 1959 and the coldest decades were 1061-1070 and 1811-1820. The warmest summers occurred in 1240 and 1474, and the warmest decades were 1141-1150 and 1481-1490. Comparison of this new reconstruction with MXD-based summer temperature reconstructions across Europe reveals synchronized occurrences of extreme cool summers in the northeastern Mediterranean, and an antiphase-relationship with warm summer temperatures over the British Isles and Scandinavia. This temperature dipole is related to anomalies in the latitudinal position of the North Atlantic Jet. Despite the representation of common atmospheric forcing patterns, the occurrence of warm extremes is limited to few events, suggesting potential weaknesses of MXD to record warm temperature anomalies. In addition, we acknowledge problems in the observational data to capture local temperature variability due to small scale topographic differences in this high-elevation landscape. At a broader geographical scale, the occurrence of common cold summer extremes is restricted to years with volcanically induced changes in radiative forcing.
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| 7. |
- Konter, Oliver, et al.
(författare)
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Climate sensitivity and parameter coherency in annually resolved delta C-13 and delta O-18 from Pinus uncinata tree-ring data in the Spanish Pyrenees
- 2014
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 377, s. 12-19
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Tidskriftsartikel (refereegranskat)abstract
- We explore the 20th century climate sensitivity of annually resolved carbon and oxygen isotope ratios in five Pinus uncinata individuals from the upper treeline in similar to 2400 m asl of the Spanish Pyrenees. Time series of delta C-13 and delta O-18 are calibrated against temperature, precipitation, and drought indices over the period 1901-2009. Negative correlations of delta C-13 with summer precipitation and drought indices, as well as positive correlations with summer temperatures, confirm previous evidence from similar habitats in the Pyrenees. In contrast to this summer climate signal in the carbon isotopes, the delta O-18 record reveals mainly negative correlations with spring precipitation and drought. We explore the coherence between delta C-13 and delta O-18 time series derived from individual trees and assess the influence of widely applied delta C-13 correction procedures on the climate signal strength. Spatial correlation patterns and decomposition of the time series into high-and low-frequency components are used to develop a calibration setup for carbon and oxygen isotope ratios, which will improve long-term climate reconstructions in a region, where classical tree-ring width and density data are limited.
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