| 1. |
- Cook, Edward R., et al.
(författare)
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Tree-ring reconstructed summer temperature anomalies for temperate East Asia since 800 CE
- 2013
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 41:11-12, s. 2957-2972
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Tidskriftsartikel (refereegranskat)abstract
- We develop a summer temperature reconstruction for temperate East Asia based on a network of annual tree-ring chronologies covering the period 800-1989 C.E. The East Asia reconstruction is the regional average of 585 individual grid point summer temperature reconstructions produced using an ensemble version of point-by-point regression. Statistical calibration and validation tests indicate that the regional average possesses sufficient overall skill to allow it to be used to study the causes of temperature variability and change over the region. The reconstruction suggests a moderately warm early medieval epoch (ca. 850-1050 C.E.), followed by generally cooler 'Little Ice Age' conditions (ca. 1350-1880 C.E.) and 20th century warming up to the present time. Since 1990, average temperature has exceeded past warm epochs of comparable duration, but it is not statistically unprecedented. Superposed epoch analysis reveals a volcanic forcing signal in the East Asia summer temperature reconstruction, resulting in pulses of cooler summer conditions that may persist for several years. Substantial uncertainties remain, however, particularly at lower frequencies, thus requiring caution and scientific prudence in the interpretation of this record.
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| 2. |
- Ahmed, Moinuddin, et al.
(författare)
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Continental-scale temperature variability during the past two millennia
- 2013
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Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 6:5, s. 339-346
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Tidskriftsartikel (refereegranskat)abstract
- Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between ad 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period ad 1971–2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years.
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| 3. |
- Björklund, Jesper, 1979, et al.
(författare)
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Advances towards improved low-frequency tree-ring reconstructions, using an updated Pinus sylvestris L. MXD network from the Scandinavian Mountains
- 2013
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Ingår i: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 113:3-4, s. 697-710
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Tidskriftsartikel (refereegranskat)abstract
- The dendrochronological use of the parameter maximum density (MXD) in Pinus Sylvestris L., at high latitudes, has provided valuable insights into past summer temperature variations. Few long MXD chronologies, from climatically coherent regions, exist today, with the exception being in northern Europe. Five, 500-year-long, Fennoscandian, MXD chronologies were compared with regard to their common variability and climate sensitivity. They were used to test Signal-free standardization techniques, to improve inferences of low-frequency temperature variations. Climate analysis showed that, in accordance with previous studies on MXD in Fennoscandia, the summer temperature signal is robust (R (2) > 50 %) and reliable over this climatically coherent region. A combination of Individual standardization and regional curve standardization is recommended to refine long-term variability from these MXD chronologies and relieve problems arising from low replication and standardization end-effects.
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| 4. |
- Charpentier Ljungqvist, Fredrik, 1982-, et al.
(författare)
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Northern Hemisphere temperature patterns in the last 12 centuries
- 2012
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 8, s. 227-249
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Tidskriftsartikel (refereegranskat)abstract
- We analyse the spatio-temporal patterns of temperature variability over Northern Hemisphere land areas, on centennial time-scales, for the last 12 centuries using an unprecedentedly large network of temperature-sensitive proxy records. Geographically widespread positive temperature anomalies are observed from the 9th to 11th centuries, similar in extent and magnitude to the 20th century mean. A dominance of widespread negative anomalies is observed from the 16th to 18th centuries. Though we find the amplitude and spatial extent of the 20th century warming is within the range of natural variability over the last 12 centuries, we also find that the rate of warming from the 19th to the 20th century is unprecedented in the context of the last 1200 yr. The positive Northern Hemisphere temperature change from the 19th to the 20th century is clearly the largest between any two consecutive centuries in the past 12 centuries. These results remain robust even after removing a significant number of proxies in various tests of robustness showing that the choice of proxies has no particular influence on the overall conclusions of this study.
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| 5. |
- Esper, Jan, et al.
(författare)
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European summer temperature response to annually dated volcanic eruptions over the past nine centuries
- 2013
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Ingår i: Bulletin of Volcanology. - : Springer Science and Business Media LLC. - 0258-8900 .- 1432-0819. ; 75:7, s. 736-
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Tidskriftsartikel (refereegranskat)abstract
- The drop in temperature following large volcanic eruptions has been identified as an important component of natural climate variability. However, due to the limited number of large eruptions that occurred during the period of instrumental observations, the precise amplitude of post-volcanic cooling is not well constrained. Here we present new evidence on summer temperature cooling over Europe in years following volcanic eruptions. We compile and analyze an updated network of tree-ring maximum latewood density chronologies, spanning the past nine centuries, and compare cooling signatures in this network with exceptionally long instrumental station records and state-of-the-art general circulation models. Results indicate post-volcanic June-August cooling is strongest in Northern Europe 2 years after an eruption (-0.52 +/- 0.05 degrees C), whereas in Central Europe the temperature response is smaller and occurs 1 year after an eruption (-0.18 +/- 0.07 degrees C). We validate these estimates by comparison with the shorter instrumental network and evaluate the statistical significance of post-volcanic summer temperature cooling in the context of natural climate variability over the past nine centuries. Finding no significant post-volcanic temperature cooling lasting longer than 2 years, our results question the ability of large eruptions to initiate long-term temperature changes through feedback mechanisms in the climate system. We discuss the implications of these findings with respect to the response seen in general circulation models and emphasize the importance of considering well-documented, annually dated eruptions when assessing the significance of volcanic forcing on continental-scale temperature variations.
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| 6. |
- Esper, Jan, et al.
(författare)
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Northern European summer temperature variations over the Common Era from integrated tree-ring density records
- 2014
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 29:5, s. 487-494
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Tidskriftsartikel (refereegranskat)abstract
- Tree-ring chronologies of maximum latewood density are most suitable to reconstruct annually resolved summer temperature variations of the late Holocene. The two longest such chronologies have been developed in northern Europe stretching back to the 2nd century BC, and the 5th century AD. We show where similarities between the two chronologies exist, and combine portions of both into a new summer temperature reconstruction for the Common Era. To minimize the transfer of potential biases, we assess the contribution of the candidate reconstructions' measurements, and exclude data (i) from exceptionally young and old trees, and (ii) produced by different laboratory technologies. Our new composite reconstruction reveals warmer conditions during Roman, Medieval and recent times, separated by prolonged cooling during the Migration period and Little Ice Age. Twentieth century warmth, as indicated in one of the existing density records, is reduced in the new reconstruction, also affecting the overall, millennial-scale, cooling trend over the late Holocene (-0.30 degrees C per 1000 years). Due to the reduced biological memory, typical for tree-ring density measurements, the new reconstruction is most suitable for evaluating the rate and speed of abrupt summer cooling following large volcanic eruptions.
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| 7. |
- Esper, Jan, et al.
(författare)
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Testing the hypothesis of post-volcanic missing rings in temperature sensitive dendrochronological data
- 2013
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Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865 .- 1612-0051. ; 31:3, s. 216-222
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Tidskriftsartikel (refereegranskat)abstract
- The precise, annual dating control, inherent to dendrochronology, has recently been questioned through a combined analysis of tree-growth and coupled climate models (Mann et al. (2012; hereafter MAN12)) suggesting single tree-rings in temperature limited environments are missing following large volcanic events. We test this hypothesis of missing, post-volcanic rings by using a compilation of maximum late-wood density (MXD) records that are typically used for reconstructing temperature and the detection of volcanic events, together with a unique set of long instrumental station data from Europe reaching back into the early 18th century. We investigate the temporal coherence between tree-ring MXD and observed summer temperatures before and after the most significant, precisely dated, volcanic event of the past 1000 years, the 1815 Tambora eruption widely known as the cause for the 1816 year without a summer. Comparison of existing and newly developed MXD chronologies from cold environments in Northern Scandinavia ((r) over bar North = 0.70, N=3) and the European Alps, including the Pyrenees, ((r) over bar central = 0.46, N=4) reveals significant interseries correlations over the 1722-1976 common period, suggesting coherence among these independently developed timeseries. Comparisons of these data with observed JJA temperatures - from 1722 to 1976, a 94-year pre-Tambora (1722-1815), and a 94-year post-Tambora (1817-1910) period - reveals significant and temporally stable correlations ranging from 0.32 to 0.68. However, if we assume the 1816 ring is missing in the MXD chronologies (i.e., shift the pre-Tambora data by one year), all proxy/instrumental correlations fall apart approaching zero. Results from an additional experiment, where the long instrumental record is replaced by an annually resolved, 500-year, summer temperature reconstruction derived from documentary evidence, corroborates the findings from the first experiment: significant positive correlations with the unmolested chronologies and zero correlation with the perturbed chronologies back to 1500 AD. These elementary analyses indicate that either the tree-ring chronologies are correctly dated, i.e., no is ring missing in the year without a summer, or that both the long instrumental and documentary records contain dating uncertainties. As the latter is unlikely, we conclude the MAN12 hypothesis on post-volcanic missing rings can be rejected based on simple comparisons of tree-ring, instrumental and documentary data over the past 300-500 years from Central and Northern Europe.
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| 8. |
- Martin-Benito, Dario, et al.
(författare)
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DENDROCHRONOLOGICAL DATING OF THE WORLD TRADE CENTER SHIP, LOWER MANHATTAN, NEW YORK CITY
- 2014
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Ingår i: Tree-ring research. - : Tree-Ring Society. - 1536-1098 .- 2162-4585. ; 70:2, s. 65-77
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Tidskriftsartikel (refereegranskat)abstract
- On July 2010, archaeologists monitoring excavation at the World Trade Center site (WTC) in Lower Manhattan found the remains of a portion of a ship's hull. Because the date of construction and origin of the timbers were unknown, samples from different parts of the ship were taken for dendrochronological dating and provenancing. After developing a 280-year long floating chronology from 19 samples of the white oak group (Quercus section Leucobalanus), we used 21 oak chronologies from the eastern United States to evaluate absolute dating and provenance. Our results showed the highest agreement between the WTC ship chronology and two chronologies from Philadelphia (r = 0.36; t = 6.4; p < 0.001; n = 280) and eastern Pennsylvania (r = 0.35; t = 6.3; p < 0.001; n = 280). The last ring dates of the seven best-preserved samples suggest trees for the ship were felled in 1773 CE or soon after. Our analyses suggest that all the oak timbers used to build the ship most likely originated from the same location within the Philadelphia region, which supports the hypothesis independently drawn from idiosyncratic aspects of the vessel's construction, that the ship was the product of a small shipyard. Few late-18th Century ships have been found and there is little historical documentation of how vessels of this period were constructed. Therefore, the ship's construction date of 1773 is important in confirming that the hull encountered at the World Trade Center represents a rare and valuable piece of American shipbuilding history.
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| 9. |
- Schollaen, Karina, et al.
(författare)
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Multiple tree-ring chronologies (ring width, delta C-13 and delta O-18) reveal dry and rainy season signals of rainfall in Indonesia
- 2013
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 73, s. 170-181
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Tidskriftsartikel (refereegranskat)abstract
- Climatic hazards, such as severe droughts and floods, affect extensive areas across monsoon Asia and can have profound impacts on the populations of that region. The area surrounding Indonesia, including large portions of the eastern Indian Ocean and Java Sea, plays a key role in the global climate system because of the enormous heat and moisture exchange that occurs between the ocean and atmosphere there. Here, we evaluate the influence of rainfall variability on multiple tree-ring parameters of teak (Tectona grandis) trees growing in a lowland rain forest in Central Java (Indonesia). We assess the potential of, annually resolved, tree-ring width, stable carbon (delta C-13) and oxygen (delta O-18) isotope records to improve our understanding of the Asian monsoon variability. Climate response analysis with regional, monthly rainfall data reveals that all three tree-ring parameters are significantly correlated to rainfall, albeit during different monsoon seasons. Precipitation in the beginning of the rainy season (Sep-Nov) is important for tree-ring width, confirming previous studies. Compared to ring width, the stable isotope records possess a higher degree of common signal, especially during portions of the peak rainy season (delta C-13: Dec-May; delta O-18: Nov-Feb) and are negatively correlated to rainfall. In addition, tree-ring delta O-18 also responds positively to peak dry season rainfall, although the delta O-13 rainy season signal is stronger and more time-stable. The correlations of opposite sign reflect the distinct seasonal contrast of the delta O-18 signatures in rainfall (O-18(Pre)) during the dry (O-18-enriched rain) and rainy (O-18-depleted rain) seasons. This difference in O-18(Pre) signal reflects the combination of two signals in the annual tree-ring delta O-18 record. Highly resolved intra-annual 8180 isotope analyses suggest that the signals of dry and rainy season can be distinguished clearly. Thereby reconstructions can improve our understanding of variations and trends of the hydrological cycle over the Indonesian archipelago.
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