| 1. |
- Yang, Bao, et al.
(author)
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Long-term decrease in Asian monsoon rainfall and abrupt climate change events over the past 6,700 years
- 2021
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In: Proceedings of the National Academy of Sciences of the United States of America. - Washington : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 118:30
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Journal article (peer-reviewed)abstract
- Asian summer monsoon (ASM) variability and its long-term ecological and societal impacts extending back to Neolithic times are poorly understood due to a lack of high-resolution climate proxy data. Here, we present a precisely dated and well-calibrated treering stable isotope chronology from the Tibetan Plateau with 1- to 5-y resolution that reflects high- to low-frequency ASM variability from 4680 BCE to 2011 CE. Superimposed on a persistent drying trend since the mid-Holocene, a rapid decrease in moisture availability between similar to 2000 and similar to 1500 BCE caused a dry hydroclimatic regime from similar to 1675 to similar to 1185 BCE, with mean precipitation estimated at 42 +/- 4% and 5 +/- 2% lower than during themid-Holocene and the instrumental period, respectively. This second-millennium-BCE megadrought marks the mid-to late Holocene transition, during which regional forests declined and enhanced aeolian activity affected northern Chinese ecosystems. We argue that this abrupt aridification starting similar to 2000 BCE contributed to the shift of Neolithic cultures in northern China and likely triggered human migration and societal transformation.
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| 2. |
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| 3. |
- Wang, Jianglin, et al.
(author)
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Recent weakening of seasonal temperature difference in East Asia beyond the historical range of variability since the 14th century
- 2023
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In: Science China. Earth Sciences. - 1674-7313 .- 1869-1897. ; :66, s. 1133-1146
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Journal article (peer-reviewed)abstract
- Seasonal differences of temperature are crucial components of the Earth’s climate system. However, the relatively short observational record, especially for East Asia, has limited progress in understanding seasonal differences. In this study, we identify ten tree-ring chronologies separately correlated with local winter (December–February) temperatures and twelve different tree-ring chronologies separately correlated with summer (June–August) temperatures across East Asia. Using these discrete seasonal tree-ring chronologies, we develop two independent winter and summer temperature reconstructions covering the period 1376–1995 CE for East Asia, and compare them with model simulations. Our reconstructions show a more significant volcanic cooling and earlier onset of modern warming in summer than in winter. The reconstructed summer-minus-winter temperature decreased since as early as the late 19th century, which has driven the current state of seasonal temperature difference to out of the natural variability since the 1370s. Climate models could generally reproduce the variability and trends in seasonal reconstructions, but might largely underestimate seasonal differences due to the fact that seasonal expressions on external forcing and modes of internal variability are too small. Our study highlights the importance of using proxy-based seasonal reconstructions to evaluate the performance of climate models, and implies a substantial weakening of seasonal temperature differences in the future.
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| 4. |
- Büntgen, Ulf, et al.
(author)
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The influence of decision-making in tree ring-based climate reconstructions
- 2021
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12
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Journal article (peer-reviewed)abstract
- Tree-ring chronologies underpin the majority of annually-resolved reconstructions of Common Era climate. However, they are derived using different datasets and techniques, the ramifications of which have hitherto been little explored. Here, we report the results of a double-blind experiment that yielded 15 Northern Hemisphere summer temperature reconstructions from a common network of regional tree-ring width datasets. Taken together as an ensemble, the Common Era reconstruction mean correlates with instrumental temperatures from 1794–2016 CE at 0.79 (p < 0.001), reveals summer cooling in the years following large volcanic eruptions, and exhibits strong warming since the 1980s. Differing in their mean, variance, amplitude, sensitivity, and persistence, the ensemble members demonstrate the influence of subjectivity in the reconstruction process. We therefore recommend the routine use of ensemble reconstruction approaches to provide a moreconsensual picture of past climate variability.
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| 5. |
- He, Minhui, et al.
(author)
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Recent advances in dendroclimatology in China
- 2019
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In: Earth-Science Reviews. - : Elsevier BV. - 0012-8252 .- 1872-6828. ; 194, s. 521-535
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Research review (peer-reviewed)abstract
- Considerable progress has been made in dendroclimatological research in China during the period 2000-2017, including a significant increase in the spatial coverage of tree-ring chronologies developed for paleoclimatic research. New tree-ring sampling sites have been established across the Tibetan Plateau, as well as the north-eastern and sub-tropical eastern parts of China. Most of the studies use coniferous trees, although different plant functional types (e.g., broadleaf species and shrubs) have also been increasingly investigated. Tree-ring chronologies longer than 600 years, however, are mostly found on the Tibetan Plateau, with the longest one extending back to 2637 BCE (before Common Era). Most tree-ring records in the eastern parts of China are < 400 years long. Tree-ring width is the most commonly studied parameter, although stable isotope ratios and wood density data have also been obtained for specific sites. Stable oxygen isotope data frequently shares a common hydroclimate signal, whereas the climate or environmental signals remain inconsistent for the few available stable carbon isotope records. In general, tree-ring width-based temperature reconstructions originate from higher elevation sites (i.e., treeline) compared to hydroclimate reconstructions. Precipitation or drought reconstructions are mainly obtained from regions with an annual precipitation of < 800 mm. Most of the tree-ring reconstructions are based on individual site or local-scale chronologies, although a limited number of regional-scale and field reconstructions have been produced. The most prominent identified characteristics of the recent advances in dendroclimatological research for China have manifested in aspects such as an expanded network of sampling sites, improved climate reconstruction methodology, and improved uncertainty estimations in the latter. Furthermore, the traditional statistical-based tree growth climate relationships have been supplemented by monitoring and modeling approaches. Based on the progress from 2000 to 2017, and on the research potential of the country in this field, we expect additional widening of the dendroclimatological investigations in China during the coming years.
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| 6. |
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| 7. |
- Song, Miao, et al.
(author)
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Tree-ring-based winter temperature reconstruction for East Asia over the past 700 years
- 2021
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In: Science China. Earth Sciences. - : Springer Science and Business Media LLC. - 1674-7313 .- 1869-1897. ; 64:6, s. 872-889
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Journal article (peer-reviewed)abstract
- Almost all proxy-based temperature reconstructions for East Asia have hitherto been designed to resolve summer or annual temperature variability. Reconstruction for the winter temperature is still lacking. Here, we report an annually resolved, winter-season (December-February, DJF) temperature field reconstruction for East Asia covering the period 1300-2000 CE, based on 260 temperature-sensitive tree-ring records. The most striking feature of our new reconstruction is a significant long-term warming trend since the 14th century, which is associated with winter solar insolation at mid-latitudes of the Northern Hemisphere and the global anthropogenic impact. The amplitude of reconstructed winter temperature change over the study period was similar to 4.7 times greater than that for summer temperature, and the rate of winter temperature increase was similar to 6 times as much as that of summer temperature. The results from climate model simulations were consistent with the reconstruction, showing that the amplitude and rate of temperature change in winter were greater than that in summer. The reconstruction also suggests the possible influence of volcanic eruptions, anthropogenic activities and winter solar insolation on the winter temperature variations. Our result also suggests a long-term decrease in summer-to-winter temperature difference occurred in 1625 (+/- 24 years) CE.
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| 8. |
- Wang, Feiyue, et al.
(author)
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Surface properties of natural aquatic sediments
- 1997
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In: Water Research. - 0043-1354 .- 1879-2448. ; 31:7, s. 1796-1800
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Journal article (peer-reviewed)abstract
- Eleven geographically and hydrologically diverse sediment samples were collected from major rivers of China and determined for the surface properties. The results indicate the sediments have a large variation in surface area (6.9-16.0 m(2)/g of SSA(N2), 35.6-73.2 m(2)/g Of SSA(CPB), surface site density (10.3-149.8 mu mol/g) and surface acidity constants (1.56-2.50 of pK(s.a1)(int), and 3.75-5.58 of pK(s.a2)(int)) but a small difference in PZSE (3.0-4.0). Within the pH range 3.0-9.0, all sediments present negative surface charges. Their surface charge distribution curves with pH extend between these of SiO2, montmorillonite. kaolinite, alpha-MnO2, calcite and gamma-Al2O3;. Correlation analysis reveals that surface area and surface site density of the sediments are correlated strongly with reactive and amorphous iron oxides, total aluminum, clay and total organic carbon, while surface acidity constants, PZSE and the permanent structural charge only show a weak correlation with total aluminum in the sediments.
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| 9. |
- Wang, Jianglin, et al.
(author)
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A Millennial Summer Temperature Reconstruction for the Eastern Tibetan Plateau from Tree Ring Width
- 2015
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In: Journal of Climate. - 0894-8755 .- 1520-0442. ; 28:13, s. 5289-5304
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Journal article (peer-reviewed)abstract
- Although tree-ring-width-based temperature reconstructions of centennial-to-millennial length have previously been published for many parts of the eastern Tibetan Plateau (ETP), a millennium-long regional-scale composite reconstruction with annual resolution has so far been lacking. Here, the authors present a reconstruction of June–August (JJA) temperature variability over the ETP for the period AD 1000–2005 using a nested composite-plus-scale (CPS) approach to 12 temperature-sensitive tree-ring width chronologies, including 946 individual tree-ring width series. The composite reconstruction reveals warm episodes occurring during much of the sixteenth, nineteenth, and twentieth centuries and cold episodes during much of the eleventh, seventeenth, and eighteenth centuries. The period AD 1996–2005 is likely the warmest decade in the context of the past millennium. The authors explore the influence of possible forcings, finding only a weak direct relationship of temperature changes over the ETP with solar forcing at multidecadal time scales but a robust in-phase relationship with the Atlantic multidecadal oscillation (AMO) during the past millennium. This suggests that the AMO may play an important role in controlling summer temperature variability over the ETP at multidecadal time scales. A comparison with temperature reconstructions from the higher latitudes of East Asia, central-eastern China, and the whole of the Northern Hemisphere shows that the cold eleventh century and the warm nineteenth century prevailing over ETP are somewhat unique, suggesting regional specific characteristics of the temperature variability in this region. This result highlights the need to further increase the number of millennium-long, high-resolution temperature records from East Asia.
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| 10. |
- Wang, Jianglin, et al.
(author)
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Causes of East Asian Temperature Multidecadal Variability Since 850 CE
- 2018
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 45:24, s. 13485-13494
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Journal article (peer-reviewed)abstract
- The drivers of multidecadal- to centennial-scale variability in East Asian temperature, apparent in temperature reconstructions, are poorly understood. Here we apply a multivariate regression analysis to distinguish the influences of large-scale modes of internal variability (Atlantic Multidecadal Oscillation and Pacific Multidecadal Oscillation) and external natural (orbital, solar, and volcanic) and anthropogenic (greenhouse gas concentrations, aerosols, and land use changes) forcings on East Asian warm-season temperature over the period 850-1999 CE (Common Era). We find that similar to 80% of the temperature change on time scales longer than 30 years can be explained including all drivers over the full-length period. The Pacific Multidecadal Oscillation was the most important driver of multidecadal temperature variability during the Medieval Climate Anomaly (here 950-1250), while solar contribution was important during the Little Ice Age (here 1350-1850). Since 1850, two thirds of temperature change can be explained with anthropogenic forcing, whereas one third was related mainly to the Atlantic Multidecadal Oscillation and volcanic forcing. Plain Language Summary The Atlantic Multidecadal Oscillation (AMO) and Pacific Multidecadal Oscillation (PMO) are suggested to be key components of internal temperature variability globally and in the Northern Hemisphere. However, the contribution of the AMO and PMO to temperature at regional/continental scales in preindustrial times is still unclear. Here we use a multivariate regression analysis to distinguish the AMO and PMO contributions to the East Asian temperature multidecadal (> 30 years) changes from the influence of external (orbital solar, volcanic, and anthropogenic) forcings. We find that the contribution of the AMO and PMO is of similar magnitude as solar and volcanic forcing during the period 850-1999 CE (Common Era). We apply the same approach to three subperiods and find that the PMO, solar forcing, and anthropogenic forcing contributed most during the periods 950-1250, 1350-1850, and 1850-1999, respectively.
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| 11. |
- Wang, Jianglin, et al.
(author)
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Internal and external forcing of multidecadal Atlantic climate variability over the past 1,200 years
- 2017
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In: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 10:7, s. 512-517
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Journal article (peer-reviewed)abstract
- The North Atlantic experiences climate variability on multidecadal scales, which is sometimes referred to as Atlantic multidecadal variability. However, the relative contributions of external forcing such as changes in solar irradiance or volcanic activity and internal dynamics to these variations are unclear. Here we provide evidence for persistent summer Atlantic multidecadal variability from AD 800 to 2010 using a network of annually resolved terrestrial proxy records from the circum-North Atlantic region. We find that large volcanic eruptions and solar irradiance minima induce cool phases of Atlantic multidecadal variability and collectively explain about 30% of the variance in the reconstruction on timescales greater than 30 years. We are then able to isolate the internally generated component of Atlantic multidecadal variability, which we define as the Atlantic multidecadal oscillation. We find that the Atlantic multidecadal oscillation is the largest contributor to Atlantic multidecadal variability over the past 1,200 years. We also identify coherence between the Atlantic multidecadal oscillation and Northern Hemisphere temperature variations, leading us to conclude that the apparent link between Atlantic multidecadal variability and regional to hemispheric climate does not arise solely from a common response to external drivers, and may instead reflect dynamic processes.
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| 12. |
- Wang, Jianglin, et al.
(author)
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Moisture and Temperature Covariability over the Southeastern Tibetan Plateau during the Past Nine Centuries
- 2020
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In: Journal of Climate. - 0894-8755 .- 1520-0442. ; 33:15, s. 6583-6598
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Journal article (peer-reviewed)abstract
- Abstract Accurate projections of moisture variability across the Tibetan Plateau (TP) are crucial for managing regional water resources, ecosystems, and agriculture in densely populated downstream regions. Our understanding of how moisture conditions respond to increasing temperatures over the TP is still limited, due to the short length of instrumental data and the limited spatial coverage of high-resolution paleoclimate proxy records in this region. This study presents a new, early-summer (May–June) self-calibrating Palmer drought severity index (scPDSI) reconstruction for the southeastern TP (SETP) covering 1135–2010 CE using 14 tree-ring records based on 1669 individual width sample series. The new reconstruction reveals that the SETP experienced the longest period of pluvial conditions in 1154–75 CE, and the longest droughts during the periods 1262–80 and 1958–76 CE. The scPDSI reconstruction shows stable and significant in-phase relationships with temperature at both high and low frequencies throughout the past 900 years. This supports the hypothesis that climatic warming may increase moisture by enhancing moisture recycling and convective precipitation over the SETP; it is also consistent with climate model projections of wetter conditions by the late twenty-first century in response to global warming.
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| 13. |
- Wang, Jianglin, et al.
(author)
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The relationship between the Atlantic Multidecadal Oscillation and temperature variability in China during the last millennium
- 2013
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In: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 28:7, s. 653-658
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Journal article (peer-reviewed)abstract
- Using a large number of temperature-sensitive proxy records, we investigated the relationship between the Atlantic Multidecadal Oscillation (AMO) and temperature variability in China during the last millennium. The results indicate a relatively homogeneous pattern of cold/warm anomalies in East, West and the whole of China (EC, WC and WOC). The six major AMO cold phases coincided with cold conditions over EC, WC and WOC, while warm conditions across China occurred during the two major AMO warm phases. This close similarity between the AMO and multi-decadal temperature variability in China is supported by climate model simulations and emphasizes the critical role of surface heating over the Asian continent in linking the AMO and the Indian summer monsoon. The mid-latitude westerly anomalies and the propagation of Rossby waves related to the AMO may be two channels linking sea surface temperature anomalies in the North Atlantic and temperature variability over East Asia. Additionally, the Atlantic Meridional Overturning Circulation may play an important role in transmitting the AMO signal over the globe. We recommend further climate model studies on the mechanisms responsible for the connection between the AMO and regional to global climate changes.
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| 14. |
- Zhang, Huan, et al.
(author)
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East Asian warm season temperature variations over the past two millennia
- 2018
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
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Journal article (peer-reviewed)abstract
- East Asia has experienced strong warming since the 1960s accompanied by an increased frequency of heat waves and shrinking glaciers over the Tibetan Plateau and the Tien Shan. Here, we place the recent warmth in a long-term perspective by presenting a new spatially resolved warm-season (May-September) temperature reconstruction for the period 1-2000 CE using 59 multiproxy records from a wide range of East Asian regions. Our Bayesian Hierarchical Model (BHM) based reconstructions generally agree with earlier shorter regional temperature reconstructions but are more stable due to additional temperature sensitive proxies. We find a rather warm period during the first two centuries CE, followed by a multi-century long cooling period and again a warm interval covering the 900-1200 CE period (Medieval Climate Anomaly, MCA). The interval from 1450 to 1850 CE (Little Ice Age, LIA) was characterized by cooler conditions and the last 150 years are characterized by a continuous warming until recent times. Our results also suggest that the 1990s were likely the warmest decade in at least 1200 years. The comparison between an ensemble of climate model simulations and our summer reconstructions since 850 CE shows good agreement and an important role of internal variability and external forcing on multi-decadal time-scales.
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