| 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. |
- Cohen, J., et al.
(författare)
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Divergent consensuses on Arctic amplification influence on midlatitude severe winter weather
- 2020
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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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| 3. |
- Liu, Y., et al.
(författare)
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Anthropogenic Aerosols Cause Recent Pronounced Weakening of Asian Summer Monsoon Relative to Last Four Centuries
- 2019
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 46:10, s. 5469-5479
-
Tidskriftsartikel (refereegranskat)abstract
- The Asian Summer Monsoon (ASM) affects ecosystems, biodiversity, and food security of billions of people. In recent decades, ASM strength (as represented by precipitation) has been decreasing, but instrumental measurements span only a short period of time. The initiation and the dynamics of the recent trend are unclear. Here for the first time, we use an ensemble of 10 tree ring-width chronologies from the west-central margin of ASM to reconstruct detail of ASM variability back to 1566 CE. The reconstruction captures weak/strong ASM events and also reflects major locust plagues. Notably, we found an unprecedented 80-year trend of decreasing ASM strength within the context of the 448-year reconstruction, which is contrary to what is expected from greenhouse warming. Our coupled climate model shows that increasing anthropogenic sulfate aerosol emissions over the Northern Hemisphere could be the dominant factor contributing to the ASM decrease. Plan Language Summary Monsoonal rainfall has a certain influence on agriculture and industry in the regions of Asian Summer Monsoon (ASM). An understanding of the spatial-temporal variability of the ASM and the associated dynamics is vital for terrestrial ecosystems, water resources, forests, and landscapes. We have developed a 448-year ASM reconstruction back to 1566 CE using 10 tree ring chronologies from the margin region of ASM. We find that historical severe droughts and locust plague disasters during weak ASM events. The recent decreasing ASM trend persisting for over 80 years is unprecedented over the past 448 years. Coupled climate models show that increasing anthropogenic aerosol emissions are the dominant underlying factor. Our aim is that the time series will find a wide range of utility for understanding past climate variability and for predicting future climate change.
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| 4. |
- Liu, Y., et al.
(författare)
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Recent enhancement of central Pacific El Nino variability relative to last eight centuries
- 2017
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- The far-reaching impacts of central Pacific El Nino events on global climate differ appreciably from those associated with eastern Pacific El Nino events. Central Pacific El Nino events may become more frequent in coming decades as atmospheric greenhouse gas concentrations rise, but the instrumental record of central Pacific sea-surface temperatures is too short to detect potential trends. Here we present an annually resolved reconstruction of NINO4 sea-surface temperature, located in the central equatorial Pacific, based on oxygen isotopic time series from Taiwan tree cellulose that span from 1190 AD to 2007 AD. Our reconstruction indicates that relatively warm Nino4 sea-surface temperature values over the late twentieth century are accompanied by higher levels of interannual variability than observed in other intervals of the 818-year-long reconstruction. Our results imply that anthropogenic greenhouse forcing may be driving an increase in central Pacific El Nino-Southern Oscillation variability and/or its hydrological impacts, consistent with recent modelling studies.
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| 5. |
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| 6. |
- Smerdon, J. E., et al.
(författare)
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Comparing proxy and model estimates of hydroclimate variability and change over the Common Era
- 2017
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 13:12, s. 1851-1900
-
Tidskriftsartikel (refereegranskat)abstract
- Water availability is fundamental to societies and ecosystems, but our understanding of variations in hydroclimate (including extreme events, flooding, and decadal periods of drought) is limited because of a paucity of modern instrumental observations that are distributed unevenly across the globe and only span parts of the 20th and 21st centuries. Such data coverage is insufficient for characterizing hydroclimate and its associated dynamics because of its multidecadal to centennial variability and highly regionalized spatial signature. High-resolution (seasonal to decadal) hydroclimatic proxies that span all or parts of the Common Era (CE) and paleoclimate simulations from climate models are therefore important tools for augmenting our understanding of hydroclimate variability. In particular, the comparison of the two sources of information is critical for addressing the uncertainties and limitations of both while enriching each of their interpretations. We review the principal proxy data available for hydroclimatic reconstructions over the CE and highlight the contemporary understanding of how these proxies are interpreted as hydroclimate indicators. We also review the available last-millennium simulations from fully coupled climate models and discuss several outstanding challenges associated with simulating hydroclimate variability and change over the CE. A specific review of simulated hydroclimatic changes forced by volcanic events is provided, as is a discussion of expected improvements in estimated radiative forcings, models, and their implementation in the future. Our review of hydroclimatic proxies and last-millennium model simulations is used as the basis for articulating a variety of considerations and best practices for how to perform proxy-model comparisons of CE hydroclimate. This discussion provides a framework for how best to evaluate hydroclimate variability and its associated dynamics using these comparisons and how they can better inform interpretations of both proxy data and model simulations. We subsequently explore means of using proxy-model comparisons to better constrain and characterize future hydroclimate risks. This is explored specifically in the context of several examples that demonstrate how proxy-model comparisons can be used to quantitatively constrain future hydroclimatic risks as estimated from climate model projections.
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| 7. |
- Chen, F., et al.
(författare)
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Juniper Tree-Ring Data from the Kuramin Range (Northern Tajikistan) Reveals Changing Summer Drought Signals in Western Central Asia
- 2019
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Ingår i: Forests. - : MDPI AG. - 1999-4907. ; 10:6
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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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| 8. |
- Cohen, Judah, et al.
(författare)
-
ARCTIC CHANGE AND POSSIBLE INFLUENCE ON MID-LATITUDE CLIMATE AND WEATHER - A US CLIVAR White Paper
- 2018
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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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| 9. |
- Cook, ER, et al.
(författare)
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Old World megadroughts and pluvials during the Common Era
- 2015
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 1:10
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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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| 10. |
- Cunningham, LK, et al.
(författare)
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Reconstructions of surface ocean conditions from the North East Atlantic and Nordic Seas during the last Millennium
- 2013
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 23:7, s. 921-935
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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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| 11. |
- Emile-Geay, J., et al.
(författare)
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Data Descriptor: A global multiproxy database for temperature reconstructions of the Common Era
- 2017
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Ingår i: Scientific Data. - : Springer Science and Business Media LLC. - 2052-4463. ; 4
-
Tidskriftsartikel (refereegranskat)abstract
- Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850-2014. Global temperature composites show a remarkable degree of coherence between high-and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python. Since the pioneering work of D'Arrigo and Jacoby1-3, as well as Mann et al. 4,5, temperature reconstructions of the Common Era have become a key component of climate assessments6-9. Such reconstructions depend strongly on the composition of the underlying network of climate proxies10, and it is therefore critical for the climate community to have access to a community-vetted, quality-controlled database of temperature-sensitive records stored in a self-describing format. The Past Global Changes (PAGES) 2k consortium, a self-organized, international group of experts, recently assembled such a database, and used it to reconstruct surface temperature over continental-scale regions11 (hereafter, ` PAGES2k-2013'). This data descriptor presents version 2.0.0 of the PAGES2k proxy temperature database (Data Citation 1). It augments the PAGES2k-2013 collection of terrestrial records with marine records assembled by the Ocean2k working group at centennial12 and annual13 time scales. In addition to these previously published data compilations, this version includes substantially more records, extensive new metadata, and validation. Furthermore, the selection criteria for records included in this version are applied more uniformly and transparently across regions, resulting in a more cohesive data product. This data descriptor describes the contents of the database, the criteria for inclusion, and quantifies the relation of each record with instrumental temperature. In addition, the paleotemperature time series are summarized as composites to highlight the most salient decadal-to centennial-scale behaviour of the dataset and check mutual consistency between paleoclimate archives. We provide extensive Matlab code to probe the database-processing, filtering and aggregating it in various ways to investigate temperature variability over the Common Era. The unique approach to data stewardship and code-sharing employed here is designed to enable an unprecedented scale of investigation of the temperature history of the Common Era, by the scientific community and citizen-scientists alike.
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| 12. |
- Linderholm, Hans W., 1968, et al.
(författare)
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Age-dependent climate sensitivity of Pinus sylvestris L. in the central Scandinavian Mountains
- 2004
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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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| 13. |
- Liu, Y, et al.
(författare)
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Tree-ring-based annual precipitation reconstruction in Kalaqin, Inner Mongolia for the last 238 years
- 2011
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Ingår i: Chinese Science Bulletin. ; 56:28-29, s. 2995-3002
-
Tidskriftsartikel (refereegranskat)abstract
- A tree-ring-width chronology of Pinus tabulaeformis from Kalaqin, Inner Mongolia was developed using modern dendrochronological techniques. Based on the results of correlation function analysis, the total precipitation from the previous August to current July was reconstructed for 1771–2008 AD with an explained variance of 49.3%. The reconstruction correlated well with the dryness/ wetness series derived from historical documents, as well as the precipitation reconstruction of the Chifeng-Weichang region. There were eight intervals with greater precipitation than the average (associated with the strong East Asian summer monsoon) and seven intervals lower than the average (weak monsoon). A power spectrum analysis showed that there were 120 a, 80 a, 8 a and 2 a periodicities.
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| 14. |
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| 15. |
- 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
-
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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| 16. |
- Song, Yanling, et al.
(författare)
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Rain-season trends in precipitation and their effect in different climate regions of China during 1961–2008
- 2011
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 6:3, s. 1-8
-
Tidskriftsartikel (refereegranskat)abstract
- Using high-quality precipitation data from 524 stations, the trends of a set of precipitation variables during the main rain season (May–September) from 1961 to 2008 for different climate regions in China were analysed. However, different characteristics were displayed in different regions of China. In most temperate monsoon regions (north-eastern China), total rain-season precipitation and precipitation days showed decreasing trends; positive tendencies in precipitation intensity were, however, noted for most stations in this region. It is suggested that the decrease in rain-season precipitation is mainly related to there being fewer rain days and a change towards drier conditions in north-eastern China, and as a result, the available water resources have been negatively affected in the temperate monsoon regions. In most subtropical and tropical monsoon climate regions (south-eastern China), the rain-season precipitation and precipitation days (11–50, with > 50 mm) showed slightly positive trends. However, precipitation days with ≤ 10 mm decreased in these regions. Changes towards wetter conditions in this area, together with more frequent heavy rainfall events causing floods, have a severe impact on peoples' lives and socio-economic development. In general, the rain-season precipitation, precipitation days and rain-season precipitation intensity had all increased in the temperate continental and plateau/mountain regions of western China. This increase in rain-season precipitation has been favourable to pasture growth.
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| 17. |
- Song, Y., et al.
(författare)
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The negative impact of increasing temperatures on rice yields in southern China
- 2022
-
Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697. ; 820
-
Tidskriftsartikel (refereegranskat)abstract
- China is the main producer and consumer of rice in the world, and rice is a major staple food grain for more than half of the world's population. Reduced rice yields caused by climate factors not only affect the food security of China, but also has global repercussions. Thus, it is vital to assess the potential impact of climate warming on rice production. Using daily temperature and phenology records of double-cropping rice from agro-meteorological stations in southern China, the influence of increased temperatures on rice yields during the last several decades was investigated. Associated with an increase in average daily mean temperatures by 0.7 °C during 2009–2018 relative to 1961–1970, Killing Degree Days (KDD), an indicator for damaging high temperature, for early and late rice increased by 110% and 88.6% respectively. However, the negative influence of KDDs on yields was mainly evident for early rice, because high temperatures occurred frequently during the sensitive grain-filling period; early-rice yields showed a decrease of 8% per 1 °C increase in mean growing season air temperature. Late rice yields, on the other hand, were not as negatively influenced by increasing temperatures as early rice, because high temperature usually occurred during the vegetative growth stage, which was not so sensitive to high temperature. © 2022 The Authors
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| 18. |
- 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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| 19. |
- Abraham, Nerilie, et al.
(författare)
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The third phase of the PAGES 2k network
- 2017
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Ingår i: Past Global Changes Magazine. - : Past Global Changes (PAGES). - 2411-605X .- 2411-9180. ; 25, s. 71-74
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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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| 20. |
- Abram, Nerilie, et al.
(författare)
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Understanding the climate of the past 2000 years: Phase 3of the PAGES 2k Network
- 2017
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Ingår i: Past Global Changes Magazine. - : Past Global Changes (PAGES). - 2411-605X .- 2411-9180. ; 25:2
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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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| 21. |
- Alonso Aller, Elisa, et al.
(författare)
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Temporal variability of a protected multispecific tropical seagrass meadow in response to environmental change
- 2019
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Ingår i: Environmental Monitoring and Assessment. - : Springer Science and Business Media LLC. - 0167-6369 .- 1573-2959. ; 191
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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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| 22. |
- Anchukaitis, Kevin, et al.
(författare)
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Last millennium Northern Hemisphere summer temperatures from tree rings: Part II, spatially resolved reconstructions
- 2017
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 163, s. 1-22
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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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| 23. |
- Antoine, Emma, et al.
(författare)
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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
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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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| 24. |
- Asplund, Maria. E., 1970, et al.
(författare)
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Dynamics and fate of blue carbon in a mangrove-seagrass seascape : influence of landscape configuration and land-use change
- 2021
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Ingår i: Landscape Ecology. - : Springer. - 0921-2973 .- 1572-9761. ; 36, s. 1489-1509
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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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| 25. |
- Bao, Guang, et al.
(författare)
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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
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 313-314, s. 162-172
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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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