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1.
  • Cohen, Judah, et al. (författare)
  • ARCTIC CHANGE AND POSSIBLE INFLUENCE ON MID-LATITUDE CLIMATE AND WEATHER - A US CLIVAR White Paper
  • 2018
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • The Arctic has warmed more than twice as fast as the global average since the mid 20th century, a phenomenon known as Arctic amplification (AA). These profound changes to the Arctic system have coincided with a period of ostensibly more frequent events of extreme weather across the Northern Hemisphere (NH) mid-latitudes, including extreme heat and rainfall events and recent severe winters. Though winter temperatures have generally warmed since 1960 over mid-to-high latitudes, the acceleration in the rate of warming at high-latitudes, relative to the rest of the NH, started approximately in 1990. Trends since 1990 show cooling over the NH continents, especially in Northern Eurasia. The possible link between Arctic change and mid-latitude climate and weather has spurred a rush of new observational and modeling studies. A number of workshops held during 2013-2014 have helped frame the problem and have called for continuing and enhancing efforts for improving our understanding of Arctic-mid-latitude linkages and its attribution to the occurrence of extreme climate and weather events. Although these workshops have outlined some of the major challenges and provided broad recommendations, further efforts are needed to synthesize the diversified research results to identify where community consensus and gaps exist. Building upon findings and recommendations of the previous workshops, the US CLIVAR Working Group on Arctic Change and Possible Influence on Mid-latitude Climate and Weather convened an international workshop at Georgetown University in Washington, DC, on February 1-3, 2017. Experts in the fields of atmosphere, ocean, and cryosphere sciences assembled to assess the rapidly evolving state of understanding, identify consensus on knowledge and gaps in research, and develop specific actions to accelerate progress within the research community. With more than 100 participants, the workshop was the largest and most comprehensive gathering of climate scientists to address the topic to date. In this white paper, we synthesize and discuss outcomes from this workshop and activities involving many of the working group members.
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2.
  • Edvardsson, Johannes, et al. (författare)
  • Old wood in a new light : an online dendrochronological database
  • 2023
  • Ingår i: International Journal of Wood Culture. - : Brill Academic Publishers. - 2772-3194 .- 2772-3186. ; 3:1-3, s. 442-463
  • Tidskriftsartikel (refereegranskat)abstract
    • The Old Wood in a New Light database project focuses on the digitization and accessibility of the results of dendrochronological samples analyzed and archived at four Swedish university-based tree-ring laboratories at Lund University, Stockholm University, University of Gothenburg, and the Swedish University of Agricultural Sciences. Collaboration with the Environmental Archaeology Laboratory and Humlab at Umeå University enables long-term open access to data, raw data, and metadata. In this project, we (1) systematically undertake large-scale entry and open access publication of results from wood samples scientifically analyzed and archived by Swedish laboratories and the associated metadata, into the Strategic Environmental Archaeology Database (SEAD; www.sead.se) research data infrastructure, and (2) actively promote the database as a resource for new and ongoing interdisciplinary research initiatives. Including dendrochronological data in SEAD infrastructure allows interdisciplinary studies that combine major scientific and societal questions. Building on a pilot study of construction timber from southern Sweden and adaptation of SEAD digitization workflows, more than 70 000 samples archived at the four dendrochronological laboratories are now being handled in the project. The broad coverage of research networks, stakeholder interaction, and strategic support from the cultural heritage community is guaranteed owing to the ongoing collaboration between laboratories and an established international and multidisciplinary reference group.
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3.
  • Edvardsson, Johannes, et al. (författare)
  • South Swedish bog pines as indicators of Mid-Holocene climate variability
  • 2012
  • Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865. ; 30:2, s. 93-103
  • Tidskriftsartikel (refereegranskat)abstract
    • Dendroclimatic investigations of subfossil Scots pine (Pinus sylvestris) from two raised bogs in southern Sweden yielded a continuous floating 1492-year long tree-ring record. By cross-dating with bog-pine chronologies from Lower Saxony, Germany, the South Swedish record was assigned an absolute age of 5219-3728 BC. The cross-match between ring-width chronologies from these two regions, separated by 500-700 km, is remarkably strong and the correlation positive, which indicates that large-scale climate dynamics had a significant impact on the growth of bog pines during the Holocene Thermal Maximum (HTM) when bog-pine distribution reached a maximum in both regions. However, local population dynamics were also influenced by peatland ontogeny and competition, as shown by differences in replication and mean tree age between the Swedish and German records. Comparisons with chronologies developed from modern bog pines in southern Sweden indicate that more coherent climate was controlling pine growth on natural peatlands during warm periods in the past. This study demonstrates the usefulness of Swedish subfossil bog-pine material as a climate proxy, with particular potential for decadal- to centennial-scale reconstructions of humidity fluctuations. (C) 2011 Istituto Italiano di Dendrocronologia. Published by Elsevier GmbH. All rights reserved.
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4.
  • Linderholm, Hans W., 1968, et al. (författare)
  • Age-dependent climate sensitivity of Pinus sylvestris L. in the central Scandinavian Mountains
  • 2004
  • Ingår i: Boreal Environmental Research. - 1239-6095. ; 9:4, s. 307-317
  • Tidskriftsartikel (refereegranskat)abstract
    • Twentieth century climate–radial growth relationships of Pinus sylvestris L. at the central Scandinavian Mountain tree line were analyzed. Some differences in growth responses to climate were evident among age classes, where the old pines (> 250 years old) retained their climate sensitivity throughout the analysed period better than the middle-aged pines (100–250 years old). However, the pines in the oldest age class responded less to unfavourable climate than the pines in younger age classes. The pines in all the age classes displayed significant changes in climate/radial growth relationships from the 1940s and onwards. From the 1970s, pines in the youngest age class (about 35 years old) displayed a higher climate sensitivity than the older pines, in addition to which they had high growth rates not previously seen in the past five centuries. Changes in climate/radial growth relationships were related to a twentieth-century climate change. Finally our results illustrated the importance of including trees of all ages when building a tree-ring chronology for climate research
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6.
  • Abraham, Nerilie, et al. (författare)
  • The third phase of the PAGES 2k network
  • 2017
  • Ingår i: Past Global Changes Magazine. - : Past Global Changes (PAGES). - 2411-605X .- 2411-9180. ; 25, s. 71-74
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The past 2000 years (the “2k” interval) provides critical context for our understanding of recent anthropogenic forcing of the climate, as well as baseline information about Earth’s natural climate variability. It also provides opportunities to improve the interpretation of paleoclimate proxy observations, and to perform out-of-sample evaluation of the climate and earth system models that are used to generate projections of future climate change
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7.
  • Abram, Nerilie, et al. (författare)
  • Understanding the climate of the past 2000 years: Phase 3of the PAGES 2k Network
  • 2017
  • Ingår i: Past Global Changes Magazine. - : Past Global Changes (PAGES). - 2411-605X .- 2411-9180. ; 25:2
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The PAGES 2k Network was created with the aim of reconstructing changes in regional and global surface climate over the past 2000 years. During Phases 1 (2008-2013) and 2 (2014-2016), regional and trans-regional groupings focused on building reconstructions for terrestrial regions and the oceans. The conclusion of Phase 2 coincided with the release of an open and transparent global database of temperature-sensitive proxies spanning the Common Era (Fig. 1; PAGES 2k Consortium 2017). This product will be followed up by a special issue of Climate of the Past, entitled “Climate of the past 2000 years: regional and trans-regional syntheses”
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8.
  • Alonso Aller, Elisa, et al. (författare)
  • Monitoring of a protected multi-specific tropical seagrass meadow reveals a pattern of decline and recovery
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • In a changing environment, there is an increasing interest to monitor ecosystems to understand their responses to environmental change. Seagrass meadows are highly important ecosystems, but at the same time they are under a constant threat from human activities, as well as climate impacts, and marked declines have been observed worldwide. Despite increasing efforts, monitoring of multi-specific tropical seagrass meadows is scarce, particularly in developing regions. Here we analysed data from the first 10 years of a monitoring programme in a marine protected area in Zanzibar (Tanzania) to assess temporal changes in seagrass cover and species composition and to detect potential drivers of change. The seagrass meadow experienced a strong gradual decline in seagrass cover and changes in species composition, followed by a period of recovery. However, the timing and length of these temporal patterns varied in space (between transects). Of the climate variables considered, cloud cover, temperature, storm occurrence, sunspot activity and the height of the diurnal low tide seemed to influence seagrass cover, although only to a small extent, suggesting that the monitored seagrass meadow may be influenced by other unmeasured factors. Considering our results, seagrass meadows seem to be highly dynamic at small spatial scales even in the absence of major local anthropogenic impacts. Further monitoring programmes should be developed in the region to gain a better understanding of seagrass temporal variability and causes of change.
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9.
  • Alonso Aller, Elisa, et al. (författare)
  • Temporal variability of a protected multispecific tropical seagrass meadow in response to environmental change
  • 2019
  • Ingår i: Environmental Monitoring and Assessment. - : Springer Science and Business Media LLC. - 0167-6369 .- 1573-2959. ; 191
  • Tidskriftsartikel (refereegranskat)abstract
    • In a changing environment, there is an increasing interest to monitor ecosystems to understand their responses to environmental change. Seagrass meadows are highly important ecosystems that are under constant pressure from human activities and climate impacts, with marked declines observed worldwide. Despite increasing efforts, monitoring of multispecific tropical seagrass meadows is scarce, particularly in low-income regions. Based on data from a monitoring programme in a marine protected area in Zanzibar (Tanzania), we assessed temporal changes in seagrass cover and species composition during a 10-year period in relation to local variability in environmental variables. We observed a strong, gradual decline in seagrass cover and changes in species composition, followed by a period of recovery. However, the timing and length of these temporal patterns varied in space (between transects). Multiple environmental variables—cloud cover, temperature, storm occurrence, sunspot activity, and tidal amplitude and height—influenced seagrass cover, although only to a minor extent, suggesting that the monitored seagrass meadow may be influenced by other unmeasured factors (e.g. water currents and sediment movement). Our results show that seagrass meadows can be highly dynamic at small (10–50m) spatial scales, even in the absence of major local anthropogenic impacts. Our findings suggest that high-resolution monitoring programmes can be highly valuable for the detection of temporal changes in multispecific seagrass meadows; however, to understand the causes of change, there is a need of long-term (> 10years) data series that include direct measurements of environmental variables and extreme events.
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10.
  • Anchukaitis, Kevin, et al. (författare)
  • Last millennium Northern Hemisphere summer temperatures from tree rings: Part II, spatially resolved reconstructions
  • 2017
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 163, s. 1-22
  • Tidskriftsartikel (refereegranskat)abstract
    • Climate field reconstructions from networks of tree-ring proxy data can be used to characterize regionalscale climate changes, reveal spatial anomaly patterns associated with atmospheric circulation changes, radiative forcing, and large-scale modes of ocean-atmosphere variability, and provide spatiotemporal targets for climate model comparison and evaluation. Here we use a multiproxy network of tree-ring chronologies to reconstruct spatially resolved warm season (MayeAugust) mean temperatures across the extratropical Northern Hemisphere (40-90N) using Point-by-Point Regression (PPR). The resulting annual maps of temperature anomalies (750e1988 CE) reveal a consistent imprint of volcanism, with 96% of reconstructed grid points experiencing colder conditions following eruptions. Solar influences are detected at the bicentennial (de Vries) frequency, although at other time scales the influence of insolation variability is weak. Approximately 90% of reconstructed grid points show warmer temperatures during the Medieval Climate Anomaly when compared to the Little Ice Age, although the magnitude varies spatially across the hemisphere. Estimates of field reconstruction skill through time and over space can guide future temporal extension and spatial expansion of the proxy network.
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11.
  • Antoine, Emma, et al. (författare)
  • Legacy of last millennium timber use on plant cover in Central Europe: Insights from tree rings and pollen
  • 2024
  • Ingår i: SCIENCE OF THE TOTAL ENVIRONMENT. - 0048-9697 .- 1879-1026. ; 922
  • Tidskriftsartikel (refereegranskat)abstract
    • Throughout history, humans have relied on wood for constructions, tool production or as an energy source. How and to what extent these human activities have impacted plant abundance and composition over a long-term perspective is, however, not well known. To address this knowledge gap, we combined 44,239 precisely dated tree -ring samples from economically and ecologically important tree species (spruce, fir, pine, oak) from historical buildings, and pollen -based plant cover estimates using the REVEALS model from 169 records for a total of 34 1(degrees) x 1(degrees) grid cells for Central Europe. Building activity and REVEALS estimates were compared for the entire study region (4-15(degrees)E, 46-51(degrees)N), and for low (<500 m asl) and mid/high elevations (>= 500 m asl) in 100year time windows over the period 1150-1850. Spruce and oak were more widely used in wooden constructions, amounting to 35 % and 32 %, respectively, compared to pine and fir. Besides wood properties and species abundance, tree diameters of harvested individuals, being similar for all four species, were found to be the most crucial criterion for timber selection throughout the last millennium. Regarding land use changes, from the 1150-1250's onwards, forest cover generally decreased due to deforestation until 1850, especially at lower elevations, resulting in a more heterogeneous landscape. The period 1650-1750 marks a distinct change in the environmental history of Central Europe; increasing agriculture and intense forest management practices were introduced to meet the high demands of an increasing population and intensifying industrialization, causing a decrease in palynological diversity, especially at low elevations. Likely the characteristic vegetation structure and composition of contemporary landscapes originated from that period. We further show that land use has impacted vegetation composition and diversity at an increasing speed leading to a general homogenization of landscapes through time, highlighting the limited environmental benefits of even -aged plantation forestry.
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12.
  • Asplund, Maria. E., 1970, et al. (författare)
  • Dynamics and fate of blue carbon in a mangrove-seagrass seascape : influence of landscape configuration and land-use change
  • 2021
  • Ingår i: Landscape Ecology. - : Springer. - 0921-2973 .- 1572-9761. ; 36, s. 1489-1509
  • Tidskriftsartikel (refereegranskat)abstract
    • Context Seagrass meadows act as efficient natural carbon sinks by sequestering atmospheric CO2 and through trapping of allochthonous organic material, thereby preserving organic carbon (C-org) in their sediments. Less understood is the influence of landscape configuration and transformation (land-use change) on carbon sequestration dynamics in coastal seascapes across the land-sea interface. Objectives We explored the influence of landscape configuration and degradation of adjacent mangroves on the dynamics and fate of C-org in seagrass habitats. Methods Through predictive modelling, we assessed sedimentary C-org content, stocks and source composition in multiple seascapes (km-wide buffer zones) dominated by different seagrass communities in northwest Madagascar. The study area encompassed seagrass meadows adjacent to intact and deforested mangroves. Results The sedimentary C-org content was influenced by a combination of landscape metrics and inherent habitat plant- and sediment-properties. We found a strong land-to-sea gradient, likely driven by hydrodynamic forces, generating distinct patterns in sedimentary C-org levels in seagrass seascapes. There was higher C-org content and a mangrove signal in seagrass surface sediments closer to the deforested mangrove area, possibly due to an escalated export of C-org from deforested mangrove soils. Seascapes comprising large continuous seagrass meadows had higher sedimentary C-org levels in comparison to more diverse and patchy seascapes. Conclusion Our results emphasize the benefit to consider the influence of seascape configuration and connectivity to accurately assess C-org content in coastal habitats. Understanding spatial patterns of variability and what is driving the observed patterns is useful for identifying carbon sink hotspots and develop management prioritizations.
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13.
  • Bao, Guang, et al. (författare)
  • April–September mean maximum temperature inferred from Hailar pine (Pinus sylvestris var. mongolica) tree rings in the Hulunbuir region, Inner Mongolia, back to 1868 AD
  • 2012
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 313-314, s. 162-172
  • Tidskriftsartikel (refereegranskat)abstract
    • Two robust tree-ring width chronologies were developed for the Hulunbuir region, Inner Mongolia, northeast China. Both chronologies were significantly correlated with each other and were arithmetically averaged to build a regional chronology (NBSTD). NBSTD showed significant and negative correlations with the growing season maximum temperature from April to September. Based on this relationship, the mean maximum temperature of April to September was reconstructed for the period from 1868 to 2008. The percentage of variance in the data explained by the reconstruction was 40.3% during the calibration period of 1953–2008. Five severe warm events of two years or more were found in 1905–1909, 1996–1997, 2000–2001, 2003–2005 and 2007–2008. Five cold events occurred during the periods 1880–1881, 1897–1900, 1948–1949, 1955–1960 and 1962–1964. On a decadal scale, several warm intervals (above the 1868–2008 mean) were 1904–1913, 1920–1933, 1968–1975 and 1990–2003. Cold intervals (below the mean) were 1893–1901, 1950–1963 and 1976–1989. Warmer events and intervals corresponded to dry periods. Colder events and intervals coincided with wet or moist conditions in and near the study region. Spatial correlation patterns revealed that our reconstruction represents a regional temperature and drought signal for the central and eastern Mongolian Plateau. Comparison with other tree ring-based temperature reconstructions from surrounding areas provides a high degree of confidence in our reconstruction. Power spectrumandwavelet analyses suggest that the reconstructed mean maximum temperature variation may be related to large-scale atmospheric–oceanic variability such as the Pacific Decadal Oscillation (PDO), El Niño–Southern Oscillation (ENSO) and sunspot activity.
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14.
  • Bao, G, et al. (författare)
  • Drought variability in eastern Mongolian Plateau and its linkages to the large‑scale climate forcing
  • 2015
  • Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 44:3-4, s. 717-733
  • Tidskriftsartikel (refereegranskat)abstract
    • A robust regional tree-ring chronology with a span of 1819–2009 was developed for the Hulun Buir steppe, China, a region in the eastern edge of the Mongolian Plateau. This chronology exhibited significantly positive correlation with precipitation in June, and negative correlations with temperature from April to September except for May. Highest correlation was found between tree rings and the average April–August standardized precipitation evapotranspiration index (SPEI), suggesting that pines growth strongly respond to the seasonal drought conditions. Accordingly, the average April–August SPEI reconstruction was performed for the period 1854–2009, explaining 45.5 % variance of the calibration period 1953–2009. New reconstruction shows some synchrony with regional-scale events found in other reconstructions to the west Mongolian Plateau. The recent droughts in late 1990 to present are not unusual in the context of the past several centuries. Spectrum analyses suggested that the average April–August SPEI variations, especially severe droughts in the late 1870s-early 1880s, 1920s and since the late 1990s could be associated with large-scale climate forcing, such as the El Niño-Southern Oscillation, the Pacific Decadal Oscillation and the summer North Atlantic Oscillation. Significant teleconnections indicated drought variability during the past several centuries in eastern Mongolian Plateau existed close connections with large-scale synoptic features.
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15.
  • Bartolino, Valerio, et al. (författare)
  • Forecasting fish stock dynamics under climate change: Baltic herring (Clupea harengus) as a case study
  • 2014
  • Ingår i: Fisheries Oceanography. - : Wiley. - 1054-6006 .- 1365-2419. ; 23:3, s. 258-269
  • Tidskriftsartikel (refereegranskat)abstract
    • Climate change and anthropogenic disturbances may affect marine populations and ecosystems through multiple pathways. In this study we present a framework in which we integrate existing models and knowledge on basic regulatory processes to investigate the potential impact of future scenarios of fisheries exploitation and climate change on the temporal dynamics of the central Baltic herring stock. Alternative scenarios of increasing sea surface temperature and decreasing salinity of the Baltic Sea from a global climate model were combined with two alternative fishing scenarios, and their direct and ecosystem-mediated effects (i.e., through predation by cod and competition with sprat) on the herring population were evaluated for the period 2010-2050. Gradual increase in temperature has a positive impact on the long-term productivity of the herring stock, but it has the potential to enhance the recovery of the herring stock only in combination with sustainable fisheries management (i.e., F-msy). Conversely, projections of herring spawning stock biomass (SSB) were generally low under elevated fishing mortality levels (F-high), comparable with those experienced by the stock during the 1990s. Under the combined effects of long-term warming and high fishing mortality uncertainty in herring SSB projections was higher and increasing for the duration of the forecasts, suggesting a synergistic effect of fishery exploitation and climate forcing on fish populations dynamics. Our study shows that simulations of long-term fish dynamics can be an informative tool to derive expectations of the potential long-term impact of alternative future scenarios of exploitation and climate change.
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16.
  • Bartolino, Valerio, 1979, et al. (författare)
  • Historical spatiotemporal dynamics of eastern North Sea cod
  • 2012
  • Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - : Canadian Science Publishing. - 0706-652X .- 1205-7533. ; 69:5, s. 833-841
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent analyses of historical data of fish abundance and distribution have shown the importance of a long temporal perspective in the evaluation of the current status of fish populations, but pose numerous difficulties such as fragmentation and inhomogeneities in the amount of available information in space and time. Using mixed-effects models in a multiscale analysis, we identified an appropriate spatiotemporal scale of investigation of a high-quality, spatially explicit historical data set, and we reconstructed the long-term spatial dynamics of Atlantic cod (Gadus morhua) in the Kattegat– Skagerrak along the 20th century. We identified a northern and southern main aggregation of adult cod in the study area, corresponding to the Skagerrak portion of the North Sea and the Kattegat cod stocks, respectively. The stocks showed specificities in their spatial dynamics, but common extensive loss of coastal aggregations during the last decades when only 13% (Kattegat) and 35% (Skagerrak) of the estimated early century cod biomass was left. Our reconstruction showed that the collapse of the cod stocks in the area followed the peak in landings in the 1960s–1970s, suggesting that the postwar development of the industrial fisheries played a major role in the decrease of local abundances and disappearance of local adult cod aggregations.
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18.
  • Björklund, Jesper, 1979, et al. (författare)
  • Advances towards improved low-frequency tree-ring reconstructions, using an updated Pinus sylvestris L. MXD network from the Scandinavian Mountains
  • 2013
  • Ingår i: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 113:3-4, s. 697-710
  • 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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19.
  • Björklund, Jesper, 1979, et al. (författare)
  • Blue intensity and density from Northern Fennoscandian tree rings, exploring the potential to improve summer temperature reconstructions with earlywood information
  • 2014
  • Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 10, s. 877-885
  • Tidskriftsartikel (refereegranskat)abstract
    • Here we explore two new tree-ring parameters, derived from measurements of wood density and blue intensity (BI). The new proxies show an increase in the interannual summer temperature signal compared to established proxies, and present the potential to improve long-term performance. At high latitudes, where tree growth is mainly limited by low temperatures, radiodensitometric measurements of wood density, specifically maximum latewood density (MXD), provides a temperature proxy that is superior to that of tree-ring widths. The high cost of developing MXD has led to experimentation with a less expensive method using optical flatbed scanners to produce a new proxy, herein referred to as maximum latewood blue absorption intensity (abbreviated MXBI). MXBI is shown to be very similar to MXD on annual timescales but less accurate on centennial timescales. This is due to the fact that extractives, such as resin, stain the wood differentially from tree to tree and from heartwood to sapwood. To overcome this problem, and to address similar potential problems in radiodensitometric measurements, the new parameters 1blue intensity (1BI) and 1density are designed by subtracting the ambient BI/density in the earlywood, as a background value, from the latewood measurements. As a case-study, based on Scots pine trees from Northern Sweden, we show that 1density can be used as a quality control of MXD values and that the reconstructive performance of warm-season mean temperatures is more focused towards the summer months (JJA – June, July, August), with an increase by roughly 20% when also utilising the interannual information from the earlywood. However, even though the new parameter 1BI experiences an improvement as well, there are still puzzling dissimilarities between 1density and 1BI on multicentennial timescales. As a consequence, temperature reconstructions based on 1BI will presently only be able to resolve information on decadalto- centennial timescales. The possibility of trying to calibrate BI into a measure of lignin content or density, similarly to how radiographic measurements are calibrated into density, could be a solution. If this works, only then can 1BI be used as a reliable proxy in multicentennial-scale climate reconstructions.
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20.
  • Björklund, Jesper, 1979, et al. (författare)
  • Using adjusted Blue Intensity data to attain high-quality summer temperature information : A case study from Central Scandinavia
  • 2015
  • Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 25:3, s. 547-556
  • Tidskriftsartikel (refereegranskat)abstract
    • The inexpensive Blue Intensity proxy has been considered a complement or surrogate to maximum latewood density (MXD), but is associated with biases from differential staining between sapwood and heartwood and also between deadwood samples and living-wood samples that compromise centennial-scale information. Here, we show that, with some minor adjustments, Blue Intensity (BI) is comparable with MXD or Density (=the difference or contrast between latewood and earlywood density) in dendroclimatological reconstructions of summer temperatures in the Central Scandinavian region, using Pinus sylvestris L. (Scots pine), on annual and multi-centennial timescales. By using BI, this bias is significantly reduced, but the contrast between earlywood and latewood in BI is altered with degree of staining, while for density it is not. Darker deadwood samples have a reduced contrast compared with the lighter living-wood samples that make BI and Density chronologies diverge. Here, we quantify this behaviour in BI and offer an adjustment that can reduce this bias. The adjustment can be derived on independent samples, so in future work on BI, parallel density measurements are not necessary. We apply this methodology to two Central Scandinavian Scots pine chronologies that averaged into a composite is able to reconstruct summer temperatures with an explained variance in excess of 60% in each verification period using a split sample calibration verification procedure. Although the amount of data used to derive this contrast adjustment produces desirable results, more tests are needed to confirm its performance, and we suggest that future work on the BI proxy should aim for a small subset of parallel BI and density measurements while the bulk of the data is only measured with the BI technique. This is to ensure that the adjustment is continuously updated with new data and that the conclusions derived here are robust.
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21.
  • Bonow, Johan M., et al. (författare)
  • Editorial
  • 2020
  • Ingår i: Geografiska Annaler: Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 102:4, s. 331-332
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Another year has passed, and indeed it has been turbulent for many of us. Despite the hardship in many aspects of life, our Associated Editors have made tremendous effort and thus, Geografiska Annaler: Series A, Physical Geography have successfully published volume 102 with 4 issues, including a special issue on different aspects of dendrochronology in Asia.
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22.
  • Bonow, Johan M., et al. (författare)
  • Editorial
  • 2020
  • Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 102:4, s. 331-332
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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23.
  • Büntgen, Ulf, et al. (författare)
  • Prominent role of volcanism in Common Era climate variability and human history
  • 2020
  • Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865 .- 1612-0051. ; 64
  • 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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24.
  • Buntgen, U., et al. (författare)
  • Recognising bias in Common Era temperature reconstructions
  • 2022
  • Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865 .- 1612-0051. ; 74
  • Tidskriftsartikel (refereegranskat)abstract
    • A steep decline in the quality and quantity of available climate proxy records before medieval times challenges any comparison of reconstructed temperature and hydroclimate trends and extremes between the first and second half of the Common Era. Understanding of the physical causes, ecological responses and societal consequences of past climatic changes, however, demands highly-resolved, spatially-explicit, seasonally-defined and absolutely-dated archives over the entire period in question. Continuous efforts to improve existing proxy records and reconstruction methods and to develop new ones, as well as clear communication of all uncertainties (within and beyond academia) must be central tasks for the paleoclimate community.
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25.
  • Buntgen, U., et al. (författare)
  • Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE
  • 2018
  • Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
  • 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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26.
  • Cardinale, M, et al. (författare)
  • CES. 2009. Report of the Workshop on Combining Climatic Scenarios and Medium‐Term Predictions for Baltic Herring and Sprat stocks (WKCSMPB), 13–16 October 2009, Ponza, Italy. ICES CM 2009/BCC:03. : ICES WKCSMPB REPORT 2009
  • 2009
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • The direct and indirect effects of density dependence (i.e. parental stock effects) and climate‐induced hydrographic change on five different Baltic herring stocks and on Baltic sprat, investigated by WKHRPB and WKSSRB (ICES 2007b and 2008) to develop stock specific recruitment‐environment relationships, were revisited and updated. The predictors to be included in the final recruitment models were selected on the basis of the parsimonious principle, statistical significance of the predictors and the ecological criterion being fulfilled simultaneously (Cardinale et al. 2009). In previous work, temperature was detected to be an important predictor for several stocks of clupeids. Weight at age (WAA) was the major factor explaining recruitment for Main Basin herring (MBH) while spawning stock biomass (SSB) was important for Baltic sprat (BS) and Gulf of Riga herring (GRH). For MBH, food supply was also a significant predictor, suggesting that a part of the changes in climate and hydrographic conditions may affect herring indirectly via prey availability. The best recruitment model for Baltic sprat (BS) linked recruitment success to its spawning stock biomass (SSB), sea surface temperature in August (NASA8), predation mortality by cod (PM), and Bottom Depth Anomaly (BDA) which is a proxy of drift/retention of sprat larvae (ICES 2008). The final recruitment models provided by Cardinale et al. (2009) were tested with updated data series only for MBH, GRH and BS as no satisfactory final model was found for the other stocks (Cardinale et al. 2009). Further, as the main aim was to include climatic scenarios for recruitment predictions, number of recruits (thereafter referred also as recruitment) was used for all stocks instead of recruitment success. Thus, models developed for MBH, GRH and BS were re‐fitted with updated input data and with number of recruits as response variable using both a linear and a GAM model to allow for medium‐term recruitment predictions under different climatic scenarios. SSB time series were generated using the BALMAR food‐web model (Lindegren et al. 2009), a linear state‐space model based on a theoretical approach for predicting longterm responses of populations to environmental change (Ives 1995; Ives et al. 2003). SSB time series were generated assuming two different levels of fishing mortalities (Fmed, Fmsy or Fmp). Predictions of SST were generated using higher resolution Regional Climate Models (RCMs). The results show that in the next 30 years recruitment of herring stocks will generally increase or stay relatively stable at values observed in the last decade for any of the scenarios considered. This is likely to be mainly an effect of a predicted increase in SST. On the other hand, the effect of SSB is small for MBH mainly due to the narrow range of predicted SSB values over the next 3 decades. In the case of GRH, a similar pattern was observed although the increase in recruitment is not as large as for MBH. For sprat, a satisfactory model was not found for predicting recruitment and further analysis are needed.
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27.
  • Cardinale, Massimiliano, et al. (författare)
  • Spatial and temporal depletion of haddock and pollack during the last century in the Kattegat-Skagerrak
  • 2012
  • Ingår i: Journal of Applied Ichthyology. - : Hindawi Limited. - 0175-8659 .- 1439-0426. ; 28:2, s. 200-208
  • Tidskriftsartikel (refereegranskat)abstract
    • By reconstructing a centennial time-series of stock spatio-temporal dynamics and commercial landings, the long-term erosion is shown of the spatial structure of haddock and pollack in the Skagerrak and Kattegat that resulted in their regional depletion in the area. The erosion occurred in parallel with the development of the industrial fisheries and the peak in landings was followed by a decline in adult biomass and individual size. Also found was that pollack adult biomass was significantly lower for elevated water temperatures, while the response for haddock was less clear. However the main decline of both stocks and the disappearance of their adult aggregations occurred several decades before the unprecedented warming trend, which started in the Skagerrak and Kattegat only in the mid-1980s. These findings also suggest that haddock in the study area is not responding to the scale on which the management of the neighbouring North Sea haddock stock is currently performed. These results illustrate the hazardous consequences of prolonged overfishing on the population structure of commercially exploited stocks and the lack of knowledge which ultimately leads to spurious assumptions on the recovery potential of many fish stocks. Also argued is that the continuation of commercial fishery at sustainable levels adjusted to the present stock productivity might hinder the recovery of these depleted stocks for a long period of time.
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28.
  • Cerrato, Riccardo, et al. (författare)
  • A Pinus cembra L. tree-ring record for late spring to late summer temperature in the Rhaetian Alps, Italy
  • 2019
  • Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865 .- 1612-0051. ; 53, s. 22-31
  • Tidskriftsartikel (refereegranskat)abstract
    • Ongoing climate change strongly affects high-elevation environments in the European Alps, influencing the cryosphere and the biosphere and causing widespread retreat of glaciers and changes in biomes. Nevertheless, high-elevation areas often lack long meteorological series, and global datasets cannot represent local variations well. Thus, proxy data, such as tree rings, provide information on past climatic variations from these remote sites. Although maximum latewood density (MXD) chronologies provide better temperature information than those based on tree-ring width (TRW), MXD series from the European Alps are lacking. To derive high-quality temperature information for the Rhaetian Alps, Pinus cembra L. trees sampled at approximately 2000 m a.s.l. were used to build one MXD chronology spanning from 1647 to 2015. The MXD data were significantly and highly correlated with seasonal May-September mean temperatures. The MXD chronology showed a generally positive trend since the middle of the 19th century, interrupted by short phases of climatic deterioration in the beginning of the 20th century and in the 1970s, conforming with the temperature trends. Our results underline the potential for using Pinus cembra L. MXD to reconstruct mean temperature variations, especially during the onset and latter part of the growing season, providing additional information on parts of the growing season not inferred from TRW. Future studies on MXD for this species will increase the availability of temporal and spatial data, allowing detailed climate reconstructions.
  •  
29.
  • Cerrato, Riccardo, et al. (författare)
  • Pinus cembra L. tree-ring data as a proxy for summer mass-balance variability of the Careser Glacier (Italian Rhaetian Alps)
  • 2020
  • Ingår i: Journal of Glaciology. - : Cambridge University Press (CUP). - 0022-1430 .- 1727-5652. ; 66:259, s. 714-726
  • Tidskriftsartikel (refereegranskat)abstract
    • Copyright © The Author(s), 2020. Published by Cambridge University Press. Glacial extent and mass balance are sensitive climate proxies providing solid information on past climatic conditions. However, series of annual mass-balance measurements of more than 60 years are scarce. To our knowledge, this is the first time the latewood density data (MXD) of the Swiss stone pine (Pinus cembra L.) have been used to reconstruct the summer mass balance (Bs) of an Alpine glacier. The MXD-based Bs well correlates with a Bs reconstruction based on the May to September temperature. Winter precipitation has been used as an independent proxy to infer the winter mass balance and to obtain an annual mass-balance (Bn) estimate dating back to the glaciological year 1811/12. The reconstructed MXD/precipitation-based Bn well correlates with the data both of the Careser and of other Alpine glaciers measured by the glaciological method. A number of critical issues should be considered in both proxies, including non-linear response of glacial mass balance to temperature, bedrock topography, ice thinning and fragmentation, MXD acquisition and standardization methods, and finally the 'divergence problem' responsible for the recently reduced sensitivity of the dendrochronological data. Nevertheless, our results highlight the possibility of performing MXD-based dendroglaciological reconstructions using this stable and reliable proxy.
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30.
  • Chen, Deliang, 1961, et al. (författare)
  • Recent Recovery of the Siberian High Intensity
  • 2011
  • Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116
  • Tidskriftsartikel (refereegranskat)abstract
    • This study highlights the fast recovery of the wintertime Siberian High intensity (SHI) over the last two decades. The SHI showed a marked weakening trend from the 1970s to 1980s, leading to unprecedented low SHI in the early 1990s according to most observational data sets. This salient declining SHI trend, however, was sharply replaced by a fast recovery over the last two decades. Since the declining SHI trend has been considered as one of the plausible consequences of climate warming, the recent SHI recovery seemingly contradicts the continuous progression of climate warming in the Northern Hemisphere. We suggest that alleviated surface warming and decreased atmospheric stability in the central Siberia region, associated with an increase in Eurasian snow cover, in the recent two decades contributed to this rather unexpected SHI recovery. The prominent SHI change, however, is not reproduced by general circulation model (GCM) simulations used in the IPCC AR4. The GCMs indicate the steady weakening of the SHI for the entire 21st century, which is found to be associated with a decreasing Eurasian snow cover in the simulations. An improvement in predicting the future climate change in regional scale is desirable.
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31.
  • Chen, Deliang, 1961, et al. (författare)
  • Summary of a workshop on extreme weather events in a warming world organized by the Royal Swedish Academy of Sciences
  • 2020
  • Ingår i: Tellus Series B-Chemical and Physical Meteorology. - : Stockholm University Press. - 1600-0889 .- 0280-6509. ; 72:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Climate change is not only about changes in means of climatic variables such as temperature, precipitation and wind, but also their extreme values which are of critical importance to human society and ecosystems. To inspire the Swedish climate research community and to promote assessments of international research on past and future changes in extreme weather events against the global climate change background, the Earth Science Class of the Royal Swedish Academy of Sciences organized a workshop entitled 'Extreme weather events in a warming world' in 2019. This article summarizes and synthesizes the key points from the presentations and discussions of the workshop on changes in floods, droughts, heat waves, as well as on tropical cyclones and extratropical storms. In addition to reviewing past achievements in these research fields and identifying research gaps with a focus on Sweden, future challenges and opportunities for the Swedish climate research community are highlighted.
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32.
  • Chen, Feng, et al. (författare)
  • Annual precipitation variation for the southern edge of the Gobi Desert (China) inferred from tree rings: linkages to climatic warming of twentieth century
  • 2016
  • Ingår i: Natural Hazards. - : Springer Science and Business Media LLC. - 0921-030X .- 1573-0840. ; 81:2, s. 939-955
  • Tidskriftsartikel (refereegranskat)abstract
    • We developed a new reconstruction of annual precipitation (August–July) for the Helan Mountains near the southern edge of the Gobi Desert, using a regional tree-ring width chronology. The reconstruction explained 52.1 % of the observed precipitation variance during the period 1953–2008. In addition to the new precipitation reconstruction for the Helan Mountains, two previously published annual precipitation reconstructions from the same region were also used to infer the large-scale precipitation signal of the southern edge of the Gobi Desert. Spatial correlation analyses with gridded precipitation data showed that the tree-ring records were indeed able to capture much of the regional interannual precipitation variability. Using principal component analyses on the precipitation reconstructions and documentary records, 29 large-scale dry events were found during the period AD 1760–2006. Many of these dry events have had profound impacts on the people of the study area over the past several centuries. A notably good agreement with a temperature reconstruction for Zhangye suggests that the precipitation of the Gobi Desert has the characteristics of monsoon rainfall variability (wet–warm and cold–dry). Our precipitation reconstruction exhibited a downward trend during the last two decades, a trend also found in northern and eastern China. It might be caused by a weakening of the Asian summer monsoon induced by global warming (especially increased sea surface temperature).
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33.
  • Chen, F., et al. (författare)
  • Juniper Tree-Ring Data from the Kuramin Range (Northern Tajikistan) Reveals Changing Summer Drought Signals in Western Central Asia
  • 2019
  • Ingår i: Forests. - : MDPI AG. - 1999-4907. ; 10:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Coniferous forests cover the mountains in many parts of Central Asia and provide large potentials for dendroclimatic studies of past climate variability. However, to date, only a few tree-ring based climate reconstructions exist from this region. Here, we present a regional tree-ring chronology from the moisture-sensitive Zeravshan juniper (Juniperus seravschanica Kom.) from the Kuramin Range (Tajikistan) in western Central Asia, which is used to reveal past summer drought variability from 1650 to 2015 Common Era (CE). The chronology accounts for 40.5% of the variance of the June-July self-calibrating Palmer Drought Severity Index (scPDSI) during the instrumental period (1901 to 2012). Seven dry periods, including 1659-1696, 1705-1722, 1731-1741, 1758-1790, 1800-1842, 1860-1875, and 1931-1987, and five wet periods, including 1742-1752, 1843-1859, 1876-1913, 1921-1930, and 1988-2015, were identified. Good agreements between drought records from western and eastern Central Asia suggest that the PDSI records retain common drought signals and capture the regional dry/wet periods of Central Asia. Moreover, the spectral analysis indicates the existence of centennial (128 years), decadal (24.3 and 11.4 years), and interannual (8.0, 3.6, 2.9, and 2.0 years) cycles, which may be linked with climate forces, such as solar activity and El Nino-Southern Oscillation (ENSO). The analysis between the scPDSI reconstruction and large-scale atmospheric circulations during the reconstructed extreme dry and wet years can provide information about the linkages of extremes in our scPDSI record with the large-scale ocean-atmosphere-land circulation systems.
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34.
  • Chen, Tzu Tung, 1985, et al. (författare)
  • Can extreme weather trigger relapse to infectious diseases? A malaria case study in Sweden
  • 2019
  • Ingår i: TRACE 2019 (Tree Rings in Archaeology, Climatology and Ecology).
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Although previous studies have revealed the health impacts associated with inter-annual climate variability (such as El Niño) due to abnormal meteorological conditions, our understanding of climate change impacts on human health remains largely unknown. Malaria was one of the most common disease in the 1800’s in northern Europe, and it is still highly prevalent in many countries, posing a significant threat to the public health. The most severe year of malaria epidemic in Sweden, 1860, was reported as having approximately 3,000 malaria cases to total 30,000 inhabitants in Gothenburg. However, it is difficult to draw robust inferences about climate-related health impacts of malaria due to the complexity of many covarying social variables (e.g. housing conditions, war, population movement) and the lack of reliable data on diseases. The aim of this study is to assess the influence of climate change (warming and extreme weather) on the reoccurring frequency, time of onset, duration and intensity of malaria outbreaks during the 18th century in Sweden, using tree-ring based hydroclimate reconstruction OWDA (Old World Drought Atlas) network and reconstructed summer temperatures. Tree-ring data can be useful for investigating annual spatial and temporal variability in climate of the study area. Thus, it offers great possibilities to look at climate-disease correlations, to see if the change in humidity and temperature would have altered the catchiness or spreading pattern of such vector-borne disease.
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35.
  • Chen, Tzu Tung, 1985, et al. (författare)
  • The spatiotemporal distribution of historical malaria cases in Sweden : a climatic perspective
  • 2021
  • Ingår i: Malaria Journal. - : BioMed Central (BMC). - 1475-2875. ; 20:1
  • Tidskriftsartikel (refereegranskat)abstract
    • BackgroundUnderstanding of the impacts of climatic variability on human health remains poor despite a possibly increasing burden of vector-borne diseases under global warming. Numerous socioeconomic variables make such studies challenging during the modern period while studies of climate–disease relationships in historical times are constrained by a lack of long datasets. Previous studies have identified the occurrence of malaria vectors, and their dependence on climate variables, during historical times in northern Europe. Yet, malaria in Sweden in relation to climate variables is understudied and relationships have never been rigorously statistically established. This study seeks to examine the relationship between malaria and climate fluctuations, and to characterise the spatio-temporal variations at parish level during severe malaria years in Sweden 1749–1859.MethodsSymptom-based annual malaria case/death data were obtained from nationwide parish records and military hospital records in Stockholm. Pearson (rp) and Spearman’s rank (rs) correlation analyses were conducted to evaluate inter-annual relationship between malaria data and long meteorological series. The climate response to larger malaria events was further explored by Superposed Epoch Analysis, and through Geographic Information Systems analysis to map spatial variations of malaria deaths.ResultsThe number of malaria deaths showed the most significant positive relationship with warm-season temperature of the preceding year. The strongest correlation was found between malaria deaths and the mean temperature of the preceding June–August (rs = 0.57, p < 0.01) during the 1756–1820 period. Only non-linear patterns can be found in response to precipitation variations. Most malaria hot-spots, during severe malaria years, concentrated in areas around big inland lakes and southern-most Sweden.ConclusionsUnusually warm and/or dry summers appear to have contributed to malaria epidemics due to both indoor winter transmission and the evidenced long incubation and relapse time of P. vivax, but the results also highlight the difficulties in modelling climate–malaria associations. The inter-annual spatial variation of malaria hot-spots further shows that malaria outbreaks were more pronounced in the southern-most region of Sweden in the first half of the nineteenth century compared to the second half of the eighteenth century.
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36.
  • Cohen, J., et al. (författare)
  • Divergent consensuses on Arctic amplification influence on midlatitude severe winter weather
  • 2020
  • Ingår i: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 10, s. 20-29
  • Forskningsöversikt (refereegranskat)abstract
    • The Arctic has warmed more than twice as fast as the global average since the late twentieth century, a phenomenon known as Arctic amplification (AA). Recently, there have been considerable advances in understanding the physical contributions to AA, and progress has been made in understanding the mechanisms that link it to midlatitude weather variability. Observational studies overwhelmingly support that AA is contributing to winter continental cooling. Although some model experiments support the observational evidence, most modelling results show little connection between AA and severe midlatitude weather or suggest the export of excess heating from the Arctic to lower latitudes. Divergent conclusions between model and observational studies, and even intramodel studies, continue to obfuscate a clear understanding of how AA is influencing midlatitude weather.
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37.
  • Cook, ER, et al. (författare)
  • Old World megadroughts and pluvials during the Common Era
  • 2015
  • Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 1:10
  • Tidskriftsartikel (refereegranskat)abstract
    • Climate model projections suggest widespread drying in the Mediterranean Basin and wetting in Fennoscandia in the coming decades largely as a consequence of greenhouse gas forcing of climate. To place these and other “Old World” climate projections into historical perspective based on more complete estimates of natural hydroclimatic variability, we have developed the “Old World Drought Atlas” (OWDA), a set of year-to-year maps of tree-ring reconstructed summer wetness and dryness over Europe and the Mediterranean Basin during the Common Era. TheOWDAmatches historical accounts of severe drought and wetness with a spatial completeness not previously available. In addition, megadroughts reconstructed over north-central Europe in the 11th and mid-15th centuries reinforce other evidence from North America and Asia that droughts were more severe, extensive, and prolonged over Northern Hemisphere land areas before the 20th century, with an inadequate understanding of their causes. The OWDA provides new data to determine the causes of Old World drought and wetness and attribute past climate variability to forced and/or internal variability.
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38.
  • Cunningham, LK, et al. (författare)
  • Reconstructions of surface ocean conditions from the North East Atlantic and Nordic Seas during the last Millennium
  • 2013
  • Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 23:7, s. 921-935
  • Tidskriftsartikel (refereegranskat)abstract
    • We undertake the first comprehensive effort to integrate North Atlantic marine climate records for the last millennium, highlighting some key components common within this system at a range of temporal and spatial scales. In such an approach, careful consideration needs to be given to the complexities inherent to the marine system. Composites therefore need to be hydrographically constrained and sensitive to both surface water mass variability and three-dimensional ocean dynamics. This study focuses on the northeast (NE) North Atlantic Ocean, particularly sites influenced by the North Atlantic Current. A composite plus regression approach is used to create an inter-regional NE North Atlantic reconstruction of sea surface temperature (SST) for the last 1000 years. We highlight the loss of spatial information associated with large-scale composite reconstructions of the marine environment. Regional reconstructions of SSTs off the Norwegian and Icelandic margins are presented, along with a larger-scale reconstruction spanning the NE North Atlantic. The latter indicates that the ‘Medieval Climate Anomaly’ warming was most pronounced before ad 1200, with a long-term cooling trend apparent after ad 1250. This trend persisted until the early 20th century, while in recent decades temperatures have been similar to those inferred for the ‘Medieval Climate Anomaly’. The reconstructions are consistent with other independent records of sea-surface and surface air temperatures from the region, indicating that they are adequately capturing the climate dynamics of the last millennium. Consequently, this method could potentially be used to develop large-scale reconstructions of SSTs for other hydrographically constrained regions.
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39.
  • Dahl, Martin, 1984-, et al. (författare)
  • A 2,000-Year Record of Eelgrass (Zostera marina L.) : Colonization Shows Substantial Gains in Blue Carbon Storage and Nutrient Retention
  • 2024
  • Ingår i: Global Biogeochemical Cycles. - : John Wiley & Sons. - 0886-6236 .- 1944-9224. ; 38:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Assessing historical environmental conditions linked to habitat colonization is important for understanding long-term resilience and improving conservation and restoration efforts. Such information is lacking for the seagrass Zostera marina, an important foundation species across cold-temperate coastal areas of the Northern Hemisphere. Here, we reconstructed environmental conditions during the last 14,000 years from sediment cores in two eelgrass (Z. marina) meadows along the Swedish west coast, with the main aims to identify the time frame of seagrass colonization and describe subsequent biogeochemical changes following establishment. Based on vegetation proxies (lipid biomarkers), eelgrass colonization occurred about 2,000 years ago after geomorphological changes that resulted in a shallow, sheltered environment favoring seagrass growth. Seagrass establishment led to up to 20- and 24-fold increases in sedimentary carbon and nitrogen accumulation rates, respectively. This demonstrates the capacity of seagrasses as efficient ecosystem engineers and their role in global change mitigation and adaptation through CO2 removal, and nutrient and sediment retention. By combining regional climate projections and landscape models, we assessed potential climate change effects on seagrass growth, productivity and distribution until 2100. These predictions showed that seagrass meadows are mostly at risk from increased sedimentation and hydrodynamic changes, while the impact from sea level rise alone might be of less importance in the studied area. This study showcases the positive feedback between seagrass colonization and environmental conditions, which holds promise for successful conservation and restoration efforts aimed at supporting climate change mitigation and adaptation, and the provision of several other crucial ecosystem services. © 2024. The Authors.
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40.
  •  
41.
  • Dahl, Martin, et al. (författare)
  • Increased current flow enhances the risk of organic carbon loss from Zostera marina sediments: Insights from a flume experiment
  • 2018
  • Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 63:6, s. 2793-2805
  • Tidskriftsartikel (refereegranskat)abstract
    • Hydrodynamic processes are important for carbon storage dynamics in seagrass meadows, where periods of increased hydrodynamic activity could result in erosion and the loss of buried carbon. To estimate hydrodynamic impacts on the resuspension of organic carbon (Corg) in seagrass-vegetated sediments, we exposed patches (0.35 × 0.35 cm) of Zostera marina (with different biomass, shoot densities, and sediment properties) to gradually increased unidirectional (current) flow velocities ranging from low (5 cm s−1) to high (26 cm s−1) in a hydraulic flume with a standardized water column height of 0.12 m. We found that higher flow velocities substantially increased (by more than threefold) the proportion of Corg in the suspended sediment resulting in a loss of up to 5.5% ± 1.7% (mean ± SE) Corg from the surface sediment. This was presumably due to increased surface erosion of larger, carbon-rich detritus particles. Resuspension of Corg in the seagrass plots correlated with sediment properties (i.e., bulk density, porosity, and sedimentary Corg) and seagrass plant structure (i.e., belowground biomass). However, shoot density had no influence on Corg resuspension (comparing unvegetated sediments with sparse, moderate, and dense seagrass bed types), which could be due to the relatively low shoot density in the experimental setup (with a maximum of 253 shoots m−2) reflecting natural conditions of the Swedish west coast. The projected increase in the frequency and intensity of hydrodynamic forces due to climate change could thus negatively affect the function of seagrass meadows as natural carbon sinks. © 2018 The Authors. Limnology and Oceanography published by Wiley Periodicals, Inc. on behalf of Association for the Sciences of Limnology and Oceanography
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42.
  • Drobyshev, Igor, et al. (författare)
  • A 700-year record of large fire years in northern Scandinavia shows large variability and increased frequency during the 1800s
  • 2015
  • Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 30:3, s. 211-221
  • Tidskriftsartikel (refereegranskat)abstract
    • Years with climatically mediated increases in boreal forest fire activity, referred to as large fire years (LFYs), contribute to a disproportionally large portion of the burned area over centuries, and are important drivers of ecosystem processes by affecting forest structure, biodiversity, and carbon balance at regional and continental scales. We analysed changes in LFY return intervals in northern Sweden (the area above 60°N) over 1273-1960 using a network of 29 sites with dendrochronologically reconstructed fires, complemented by documentary records of fires available from forestry statistics. We observed large variability in return intervals of LFYs, an increase in LFY frequency during the 1800s, and consistent associations between LFY occurrence and 500-hPa pressure anomalies over the European sub-continent over 1800xps2#1960. An increase in LFY frequency during the 1800s might be climatically driven, and would thus long precede the period of likely human-induced climatic changes of the 1900s. Long-term variability in climatically driven LFYs may present a challenge in partitioning the effects of human-related and human-independent components of climatic forcing upon forest fire activity. © 2015 John Wiley & Sons, Ltd.
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43.
  • Drobyshev, Igor, et al. (författare)
  • Forest fire activity in Sweden: Climatic controls and geographical patterns in 20th century
  • 2012
  • Ingår i: Agricultural and Forest Meteorology. - : Elsevier BV. - 0168-1923 .- 1873-2240. ; 154-155, s. 174-186
  • Tidskriftsartikel (refereegranskat)abstract
    • We used Swedish county-scale forest fire statistics to quantify modern fire activity, identify its main temporal and geographical patterns, and evaluate statistical performance of six fire-related weather indices as proxy of fire activity in Sweden over 1942–1975 and 1996–2008, the periods with available countyscale fire statistics. The analyzed indices were monthly precipitation, SPI, MDC, PDSI, calibrated PDSI, and DI, a Drought Index calculated as a ratio between actual and equilibrium evapotranspiration. The modern fire cycle (FC) in the northern part of Sweden varies between 2 × 103 and 3 × 104 years, whereas in southern Sweden the FC is somewhat shorter (103–2 × 104 years). No temporal trend in average FC was evident at the country scale between the two periods. Significant and negative values of a Mantel test, obtained on county data for both periods (r = −0.494, p = 0.001 for 1942–1975 and r = −0.281 and p = 0.015 for 1996–2008) indicated the presence of a geographical pattern in annual forest fire activity. Over 1942–1975, PCA revealed that the central and northern counties formed one group with synchronized fire activity, and the southern and south–western counties formed another group. This pattern became less evident during the more recent period (1996–2008). Over 1996–2008, the analysis showed little synchronicity in annual fire activity across different parts of the country. The geographical position of a county had a clear effect on seasonal pattern of forest fires. In southern Sweden, the peak in the number of fires and the burnt area was in April–May, during a relatively short dry period immediately following the snowmelt. In northern Sweden, fires in the second half of fire season dominated the total annual area burnt. Analyzed indices differed considerably in their predictive power in respect to counties’ records of annual area burnt. Calibrated PDSI was a superior proxy of fire activity for the southern region (R2 = 60.8% in regression against total annual area burnt for respective provinces), and DIlate (Drought Index for the first half of the growing season) was superior for the northern counties (R2 = 73.3%). Predictive power of the indices was much higher for the recent period (1996–2002), with R2 values staying within 81.2 and 97.8%. Even if modern levels of forest fire activity in Sweden are very low from historical perspective, there is a strong spatiotemporal association between fire activity and climatic variability at regional scales, which provides a basis for modeling of the future fire hazard.
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44.
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45.
  • Drobyshev, Igor, et al. (författare)
  • Multi-century reconstruction of fire activity in Northern European boreal forest suggests differences in regional fire regimes and their sensitivity to climate
  • 2014
  • Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 102:3, s. 738-748
  • Tidskriftsartikel (refereegranskat)abstract
    • Forest fires are one of the main disturbance agents in boreal and temperate ecosystems. To decipher large-scale temporal and spatial patterns of past fire activity in Scandinavia, we analysed the synchronicity of dendrochoronologically reconstructed fire events in a large network of sites (n=62; 3296 samples, 392 individual fire years) covering a wide geographical gradient (56.5-67.0 degrees N and 9.3-20.5 degrees E) over AD 1400-1900. We identified large fire years (LFY) as years with regionally increased forest fire activity and located the geographical centres of climatic anomalies associated with synchronous LFY occurrence across the region, termed LFY centroids. The spatial pattern of LFY centroids indicated the presence of two regions with climatically mediated synchronicity of fire occurrence, located south and north from 60 degrees N. The return intervals of LFYs in Scandinavia followed a Weibull distribution in both regions. Intervals, however, differed: a period of 40years would carry a 0.93 probability of LFY occurrence in the southern region, but only a 0.48 probability of LFY occurrence in the northern region. Over 1420-1759, the northern region was characterized by significantly higher temporal variability in LFY occurrence than the southern region. Temporal correlation of LFYs with reconstructed average summer temperature and total precipitation was evident mainly for the northern region. LFYs in this region were associated with positive temperature and negative precipitation anomalies over Scandinavia and with colder and wetter conditions in more southern parts of the European subcontinent. Synthesis. Historical patterns of the occurrence of large fire years (LFY) in Scandinavia point towards the presence of two well-defined zones with characteristic fire activity, with the geographical division at approximately 60 degrees N. The northern and mid-boreal forests, although exhibiting lower LFY frequencies, appeared to be more sensitive to past summer climate, as compared to the southern boreal forests. This would imply that fire regimes across Scandinavia may show an asynchronous response to future climate changes.
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46.
  • Drobyshev, Igor, et al. (författare)
  • Reconstruction of a regional drought index in southern Sweden since AD 1750
  • 2011
  • Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 21:4, s. 667-679
  • Tidskriftsartikel (refereegranskat)abstract
    • We used a network of eight pedunculate oak (Quercus robur L.) sites (n(trees) = 70) and one Scots pine (Pinus sylvestris L.) site (n(trees) = 53) to develop drought-sensitive master chronologies for the two areas in southern Scandinavia: a SW-area centred on 57AN 12.7AE and a NE-area centred on 58.8AN 18.2AE. The ratio of actual to equilibrium evapotranspiration (AET/EET) was used as a measure of drought during the growing season defined as the period with average daily temperatures above 9 degrees C. Instrumental data were used to parameterize the relationship between tree-ring data and the drought index (DI) over 1922-2000 for the SW area and over 1922-1995 for the NE area. The DI reconstructions explained 29.7% (SW area) and 43.7% (NE area) of the variance in the observed DI index in the calibration period, and were extended back to AD 1770 for the SW area and to AD 1750 for the NE area. Reconstructed drought dynamics suggested strong decadal- and century-scale temporal variability and limited regional synchronicity over 1770-2000. Large variations in DI were observed in both regions in the second half of the 1700s. Dry conditions were synchronously reconstructed in both sub-regions during 1781-1784, 1853-1855, and, to a lesser degree, during 1974-1978. Over the 1945-1975 period the SW area exhibited a trend towards drier growing seasons, whereas no such trend could be identified for the NE area. Analysis of correlation maps indicated that regional DI dynamics reflected two different climate regimes, associated with the Kattegat area (SW reconstruction) and southeastern Swedish coast of the Baltic sea (NE reconstruction).
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47.
  • Drobyshev, I, et al. (författare)
  • Reconstruction of regional drought index in southern Sweden since 1750 AD
  • 2011
  • Ingår i: The Holocene. ; 21:4, s. 667-697
  • Tidskriftsartikel (refereegranskat)abstract
    • We used a network of eight pedunculate oak (Quercus robur L.) sites (ntrees = 70) and one Scots pine (Pinus sylvestris L.) site (ntrees = 53) to develop drought-sensitive master chronologies for the two areas in southern Scandinavia: a SW-area centred on 57°N 12.7°E and a NE-area centred on 58.8°N 18.2°E. The ratio of actual to equilibrium evapotranspiration (AET/EET) was used as a measure of drought during the growing season defined as the period with average daily temperatures above 9°C. Instrumental data were used to parameterize the relationship between tree-ring data and the drought index (DI) over 1922–2000 for the SW area and over 1922–1995 for the NE area. The DI reconstructions explained 29.7% (SW area) and 43.7% (NE area) of the variance in the observed DI index in the calibration period, and were extended back to ad 1770 for the SW area and to ad 1750 for the NE area. Reconstructed drought dynamics suggested strong decadal- and century-scale temporal variability and limited regional synchronicity over 1770–2000. Large variations in DI were observed in both regions in the second half of the 1700s. Dry conditions were synchronously reconstructed in both sub-regions during 1781–1784, 1853–1855, and, to a lesser degree, during 1974–1978. Over the 1945–1975 period the SW area exhibited a trend towards drier growing seasons, whereas no such trend could be identified for the NE area. Analysis of correlation maps indicated that regional DI dynamics reflected two different climate regimes, associated with the Kattegat area (SW reconstruction) and southeastern Swedish coast of the Baltic sea (NE reconstruction).
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48.
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49.
  • Edvardsson, Johannes, et al. (författare)
  • Periodicities in mid- to late-Holocene peatland hydrology identified from Swedish and Lithuanian tree-ring data
  • 2016
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 137, s. 200-208
  • Tidskriftsartikel (refereegranskat)abstract
    • Twenty-five tree-ring width (TRW) chronologies, developed from moisture sensitive peatland trees in Sweden and Lithuania, and representing eight periods during the mid-Holocene to present, were analysed regarding common periodicities (cycles). Periods of 13e15, 20e22, and 30e35 years were found in most chronologies, while 8e10, 18e19, and 60e65 year periodicities were observed as well, but less commonly. Similar periodicities, especially about 15 and 30 years in duration, were detected in both living and subfossil trees, indicating that the trees have responded to similar forcing mechanisms on those timescales through time. Some of the detected periods may be related to solar variability and lunar nodal tides, but most of the detected periodicities are more likely linked to hydrological changes in the peatlands associated to atmospheric patterns such as the North Atlantic Oscillation (NAO), or variations in sea surface temperatures (i.e. the Atlantic Multidecadal Oscillation, AMO). However, no significant relationships between tree growth, NAO and AMO could be formally established, possibly due to hydrological lag and feedback effects which are typical for peatlands but render in-depth assessments rather difficult.
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50.
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