| 1. |
- Buntgen, U., et al.
(författare)
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Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- McCarroll, D., et al.
(författare)
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A 1200-year multiproxy record of tree growth and summer temperature at the northern pine forest limit of Europe
- 2013
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Ingår i: Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 23:4, s. 471-484
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Tidskriftsartikel (refereegranskat)abstract
- Combining nine tree growth proxies from four sites, from the west coast of Norway to the Kola Peninsula of NW Russia, provides a well replicated (> 100 annual measurements per year) mean index of tree growth over the last 1200 years that represents the growth of much of the northern pine timberline forests of northern Fennoscandia. The simple mean of the nine series, z-scored over their common period, correlates strongly with mean June to August temperature averaged over this region (r = 0.81), allowing reconstructions of summer temperature based on regression and variance scaling. The reconstructions correlate significantly with gridded summer temperatures across the whole of Fennoscandia, extending north across Svalbard and south into Denmark. Uncertainty in the reconstructions is estimated by combining the uncertainty in mean tree growth with the uncertainty in the regression models. Over the last seven centuries the uncertainty is < 4.5% higher than in the 20th century, and reaches a maximum of 12% above recent levels during the 10th century. The results suggest that the 20th century was the warmest of the last 1200 years, but that it was not significantly different from the 11th century. The coldest century was the 17th. The impact of volcanic eruptions is clear, and a delayed recovery from pairs or multiple eruptions suggests the presence of some positive feedback mechanism. There is no clear and consistent link between northern Fennoscandian summer temperatures and solar forcing.
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| 3. |
- Balouet, J-C, et al.
(författare)
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Applied Dendroecology and Environmental Forensics. Characterizing and Age Dating Environmental Releases: : Fundamentals and Case Studies.
- 2007
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Ingår i: Environmental Forensics. - : Informa UK Limited. - 1527-5922 .- 1527-5930. ; 8:1-2, s. 1-17
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Tidskriftsartikel (refereegranskat)abstract
- Dendroecology, or the use of ring patterns to assess the age of trees and environmental factors controlling their growth, is a well-developed method in climatologic studies. This method holds great potential as a forensic tool for age dating, contamination assessment, and characterization of releases. Moreover, the method is independent of the physical presence of contamination at the time of sampling because it is focused on the effect rather than the cause. This review is one of the very few articles published to date exploring the forensic applicability of dendroecology. This article is organized in two parts: Part I describes the method principles and proposes a practical procedure for forensic applications; Part II exemplifies and validates the method through six case studies of successful forensic application (related to petroleum products and chlorinated solvent spills).
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| 4. |
- Briffa, KR, et al.
(författare)
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Trends in recent temperature and radial tree growth spanning 2000 years across northwest Eurasia.
- 2008
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Ingår i: Philos Trans R Soc Lond B Biol Sci. - : The Royal Society. - 0962-8436. ; 363, s. 2271-2284
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Büntgen, U, et al.
(författare)
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Eight centuries of Pyrenees summer temperatures from tree-ring density
- 2008
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 31, s. 615-631
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Tidskriftsartikel (refereegranskat)abstract
- Two hundred and sixty one newly measured tree-ring width and density series from living and dry-dead conifers from two timberline sites in the Spanish Pyrenees were compiled. Application of the regional curve standardization method for tree-ring detrending allowed the preservation of inter-annual to multi-centennial scale variability. The new density record correlates at 0.53 (0.68 in the higher frequency domain) with May–September maximum temperatures over the 1944–2005 period. Reconstructed warmth in the fourteenth to fifteenth and twentieth century is separated by a prolonged cooling from ∼1450 to 1850. Six of the ten warmest decades fall into the twentieth century, whereas the remaining four are reconstructed for the 1360–1440 interval. Comparison with novel density-based summer temperature reconstructions from the Swiss Alps and northern Sweden indicates decadal to longer-term similarity between the Pyrenees and Alps, but disagreement with northern Sweden. Spatial field correlations with instrumental data support the regional differentiation of the proxy records. While twentieth century warmth is evident in the Alps and Pyrenees, recent temperatures in Scandinavia are relatively cold in comparison to earlier warmth centered around medieval times, ∼1450, and the late eighteenth century. While coldest summers in the Alps and Pyrenees were in-phase with the Maunder and Dalton solar minima, lowest temperatures in Scandinavia occurred later at the onset of the twentieth century. However, fairly cold summers at the end of the fifteenth century, between ∼1600–1700, and ∼1820 were synchronized over Europe, and larger areas of the Northern Hemisphere.
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| 6. |
- Campbell, R, et al.
(författare)
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Blue intensity in Pinus sylvestris tree-rings: developing a new palaeoclimate proxy
- 2007
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 17:6, s. 821-828
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Tidskriftsartikel (refereegranskat)abstract
- Minimum blue intensity measurements of resin-extracted Pinus sylvestris (L.) samples, conducted using a flat-bed scanner and commercially available software, are shown to provide a robust and reliable surrogate for maximum latewood density. Blue intensity data from 15 trees, from three stands, are reported relative to a standard blue-scale in a manner similar to grey-scale calibration in x-ray densitometry. The resulting time series are highly correlated with x-ray densitometry data generated from the same samples and preserve the same high level of signal strength. Sensitivity to summer climate variables is similar to that identified in the relative density record, demonstrating that minimum blue intensity can also be used for the study of climate change. While not a replacement for the powerful range of x-ray densitometry techniques, blue intensity provides an inexpensive and accessible alternative for accessing palaeoclimatic information.
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| 7. |
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| 8. |
- Gagen, Mary, et al.
(författare)
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Cloud response to summer temperatures in Fennoscandia over the last thousand years
- 2011
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 38, s. L05701-
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Tidskriftsartikel (refereegranskat)abstract
- Cloud cover is one of the most important factors controlling the radiation balance of the Earth. The response of cloud cover to increasing global temperatures represents the largest uncertainty in model estimates of future climate because the cloud response to temperature is not well-constrained. Here we present the first regional reconstruction of summer sunshine over the past millennium, based on the stable carbon isotope ratios of pine treerings from Fennoscandia. Comparison with the regional temperature evolution reveals the Little Ice Age (LIA) to have been sunny, with cloudy conditions in the warmest periods of the Medieval at this site. A negative shortwave cloud feedback is indicated at high latitude. A millennial climate simulation suggests that regionally low temperatures during the LIA were mostly maintained by a weaker greenhouse effect due to lower humidity. Simulations of future climate that display a negative shortwave cloud feedback for high-latitudes are consistent with our proxy interpretation. Citation: Gagen, M., E. Zorita, D. McCarroll, G. H. F. Young, H. Grudd, R. Jalkanen, N. J. Loader, I. Robertson, and A. Kirchhefer (2011), Cloud response to summer temperatures in Fennoscandia over the last thousand years, Geophys. Res. Lett., 38, L05701, doi:10.1029/2010GL046216.
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| 9. |
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| 10. |
- Grudd, H
(författare)
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Torneträsk tree-ring width and density AD 500 – 2004 : A test of climatic sensitivity and a new 1500-year reconstruction of north Fennoscandian summers
- 2008
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 31, s. 843-857
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents updated tree-ring width(TRW) and maximum density (MXD) from Tornetra¨sk innorthern Sweden, now covering the period AD 500–2004. Byincluding data from relatively young trees for the most recentperiod, a previously noted decline in recent MXD is eliminated.Non-climatological growth trends in the data areremoved using Regional Curve Standardization (RCS), thusproducingTRWandMXDchronologies with preserved lowfrequencyvariability. The chronologies are calibrated usinglocal and regional instrumental climate records. A bootstrappedresponse function analysis using regional climatedata shows that tree growth is forced by April–August temperaturesand that the regression weights for MXD are muchstronger than for TRW. The robustness of the reconstructionequation is verified by independent temperature data andshows that 63–64% of the instrumental inter-annual variationis captured by the tree-ring data. This is a significantimprovement compared to previously published reconstructionsbased on tree-ring data from Tornetra¨sk. Adivergence phenomenon around AD 1800, expressed as anincrease in TRW that is not paralleled by temperature andMXD, is most likely an effect of major changes in the densityof the pine population at this northern tree-line site. The biasintroduced by this TRW phenomenon is assessed by producinga summer temperature reconstruction based onMXDexclusively. The new data show generally higher temperatureestimates than previous reconstructions based onTornetra¨sk tree-ring data. The late-twentieth century, however,is not exceptionally warm in the new record: Ondecadal-to-centennial timescales, periods around AD 750,1000, 1400, and 1750 were equally warm, or warmer. The200-year long warm period centered on AD 1000 was significantlywarmer than the late-twentieth century (p\0.05)and is supported by other local and regional paleoclimatedata. The new tree-ring evidence from Tornetra¨sk suggeststhat this ‘‘Medieval WarmPeriod’’ in northern Fennoscandiawas much warmer than previously recognized.
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| 11. |
- Larsen, LB, et al.
(författare)
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New ice core evidence for a volcanic cause of the A.D. 536 dust veil
- 2008
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Ingår i: Geophysical Research Letters. ; 35:L04708
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Tidskriftsartikel (refereegranskat)abstract
- New and well-dated evidence of sulphate deposits in Greenland and Antarctic ice cores indicate a substantial and extensive atmospheric acidic dust veil at A.D. 533–534 ± 2 years. This was likely produced by a large explosive, near equatorial volcanic eruption, causing widespread dimming and contributing to the abrupt cooling across much of the Northern Hemisphere known from historical records and tree-ring data to have occurred in A.D. 536. Tree-ring data suggest that this was the most severe and protracted short-term cold episode across the Northern Hemisphere in the last two millennia, even surpassing the severity of the cold period following the Tambora eruption in 1815.
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| 12. |
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| 13. |
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| 14. |
- Loader, N. J., et al.
(författare)
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Stable carbon isotopes from Tornetrask, northern Sweden provide a millennial length reconstruction of summer sunshine and its relationship to Arctic circulation
- 2013
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 62, s. 97-113
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents results from the first 1100 years of a long stable carbon isotope chronology currently in development from Scots Pine (Pinus sylvestris L.) trees growing in the Tornetrask region of northern Sweden. The isotope record currently comprises a total of 74 trees with a mean annual replication of >12, thereby enabling it to be compared directly with other tree-ring based palaeoclimate reconstructions from this region. In developing the reconstruction, several key topics in isotope dendroclimatology (chronology construction, replication, CO2 adjustment and age trends) were addressed. The resulting carbon isotope series is calibrated against instrumental data from the closest meteorological station at Abisko (AD1913-2008) to provide a record of June August sunshine for northern Fennoscandia. This parameter is closely linked to the direct control of assimilation rate; Photosynthetically Active Radiation (PAR) and the indirect measures; mean July August temperature and percent cloud cover. The coupled response of summer sunshine and temperature in this region permits a multiparameter comparison with a local reconstruction of past temperature variability based upon tree growth proxies to explore the stability of this coupling through time. Several periods are identified where the temperature (X-ray density) and sunshine (stable carbon isotope ratio) records diverge. The most significant and sustained of these occur between c AD1200-1380 and c AD1550-1780, providing evidence for a cool, sunny, two-phase Little Ice Age. Whilst summer sunshine reconstructed for the 20th century is significantly different from the mean of the last 1100 years (P < 0.01), conditions during the early medival period are similar to those experienced in northern Fennoscandia during the 20th century (P > 0.01), so it is the 17th-18th, and to a lesser extent, the 13th centuries rather than the early medival period that appear anomalous when viewed within the context of the last 1100 years. The observed departures between temperature and sunshine are interpreted as indicating a change in large-scale circulation associated with a southward migration of the Polar Front. Such a change, affecting the Northern Annular Mode (Arctic Oscillation) would result in more stable anticyclonic conditions (cool, bright, summers) over northern Fennoscandia, thus providing a testable mechanism for the development of a multi-phase, time-transgressive Little Ice Age across Europe.
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| 15. |
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| 16. |
- Saurer, Matthias, et al.
(författare)
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Spatial variability and temporal trends in water-use efficiency of European forests
- 2014
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 20:12, s. 3700-3712
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Tidskriftsartikel (refereegranskat)abstract
- The increasing carbon dioxide (CO2) concentration in the atmosphere in combination with climatic changes throughout the last century are likely to have had a profound effect on the physiology of trees: altering the carbon and water fluxes passing through the stomatal pores. However, the magnitude and spatial patterns of such changes in natural forests remain highly uncertain. Here, stable carbon isotope ratios from a network of 35 tree-ring sites located across Europe are investigated to determine the intrinsic water-use efficiency (iWUE), the ratio of photosynthesis to stomatal conductance from 1901 to 2000. The results were compared with simulations of a dynamic vegetation model (LPX-Bern 1.0) that integrates numerous ecosystem and land-atmosphere exchange processes in a theoretical framework. The spatial pattern of tree-ring derived iWUE of the investigated coniferous and deciduous species and the model results agreed significantly with a clear south-to-north gradient, as well as a general increase in iWUE over the 20th century. The magnitude of the iWUE increase was not spatially uniform, with the strongest increase observed and modelled for temperate forests in Central Europe, a region where summer soil-water availability decreased over the last century. We were able to demonstrate that the combined effects of increasing CO2 and climate change leading to soil drying have resulted in an accelerated increase in iWUE. These findings will help to reduce uncertainties in the land surface schemes of global climate models, where vegetation-climate feedbacks are currently still poorly constrained by observational data.
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| 17. |
- Treydte, Kerstin, et al.
(författare)
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Recent human-induced atmospheric drying across Europe unprecedented in the last 400 years
- 2024
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Ingår i: NATURE GEOSCIENCE. - 1752-0894 .- 1752-0908. ; 17, s. 58-65
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Tidskriftsartikel (refereegranskat)abstract
- The vapor pressure deficit reflects the difference between how much moisture the atmosphere could and actually does hold, a factor that fundamentally affects evapotranspiration, ecosystem functioning, and vegetation carbon uptake. Its spatial variability and long-term trends under natural versus human-influenced climate are poorly known despite being essential for predicting future effects on natural ecosystems and human societies such as crop yield, wildfires, and health. Here we combine regionally distinct reconstructions of pre-industrial summer vapor pressure deficit variability from Europe's largest oxygen-isotope network of tree-ring cellulose with observational records and Earth system model simulations with and without human forcing included. We demonstrate that an intensification of atmospheric drying during the recent decades across different European target regions is unprecedented in a pre-industrial context and that it is attributed to human influence with more than 98% probability. The magnitude of this trend is largest in Western and Central Europe, the Alps and Pyrenees region, and the smallest in southern Fennoscandia. In view of the extreme drought and compound events of the recent years, further atmospheric drying poses an enhanced risk to vegetation, specifically in the densely populated areas of the European temperate lowlands. The atmosphere has dried across most regions of Europe in recent decades, a trend that can be attributed primarily to human impacts, according to tree ring records spanning 400 years and Earth system model simulations.
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| 18. |
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| 19. |
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