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Atmospheric oscillations over the last millennium
JianBin Huang,ShaoWu Wang,DaoYi Gong,TianJun Zhou,XinYu Wen,ZiYin Zhang,JinHong Zhu
Chinese Science Bulletin , 2010, DOI: 10.1007/s11434-010-3210-8
Abstract: The variations of global atmospheric oscillations over the last millennium, including the North Atlantic Oscillation (NAO), the North Pacific Oscillation (NPO) highly associated with the Pacific Decadal Oscillation (PDO), the Southern Oscillation (SO) and the Antarctic Oscillation (AAO), are studied and compared in this paper based on observations and reconstructed data. The cross correlation analysis of AAO, NAO and NPO shows that there is no significant relationship on interannual variation among them. However, the consistency on decadal variability is prominent. During A.D.1920–1940 and A.D.1980–2000, the positive (strong) phase was dominant and the negative (weak) one noticeable during A.D.1940–1980. In addition, the reconstructed atmospheric oscillations series demonstrate that the positive phase existed in the early of the last millennium for NAO and in the late of the last millennium for AAO, respectively; while it occurred in the mid-late of the last millennium for PDO and ENSO.
Simulated climate variability in the region of Rapa Nui during the last millennium
C. Junk,M. Claussen
Climate of the Past (CP) & Discussions (CPD) , 2011,
Abstract: Rapa Nui, an isolated island in the Southeast Pacific, was settled by the Polynesians most likely around 1200 AD and was discovered by the Europeans in 1722 AD. While the Polynesians presumably found a profuse palm woodland on Rapa Nui, the Europeans faced a landscape dominated by grassland. Scientists have examined potential anthropogenic, biological and climatic induced vegetation changes on Rapa Nui. Here, we analyse observational climate data for the last decades and climate model results for the period 800–1750 AD to explore the potential for a climatic-induced vegetation change. A direct influence of the ENSO phenomenon on the climatic parameters of Rapa Nui could not be found in the model simulations. Furthermore, strong climatic trends from a warm Medieval Period to a Little Ice Age or rapid climatic fluctuations due to large volcanic eruptions were not verifiable for the Rapa Nui region, although they are detectable in the simulations for many regions world wide. Hence, we tentatively conclude that large-scale climate changes in the oceanic region around Rapa Nui might be too small to explain strong vegetation changes on the island over the last millennium.
Simulated climate variability in the region of Rapa Nui during the last millennium  [PDF]
C. Junk,M. Claussen
Climate of the Past Discussions , 2011, DOI: 10.5194/cpd-7-381-2011
Abstract: Easter Island, an isolated island in the Southeast Pacific, was settled by the Polynesians probably between 600 and 1200 AD and discovered by the Europeans in 1722 AD. While the Polynesians presumably found a profuse palm woodland on Easter Island, the Europeans faced a landscape dominated by grassland. Scientists have examined potential anthropogenic, biological and climatic induced vegetation changes on Easter Island. Here, we analyze observational climate data for the last decades and climate model results for the period 800–1750 AD to explore potential causes for a climatic-induced vegetation change. A direct influence of the ENSO phenomenon on the climatic parameters of Easter Island could not be found in the model simulations. Furthermore, strong climatic trends from a warm Medieval Period to a Little Ice Age or rapid climatic fluctuations due to large volcanic eruptions were not verifiable for the Easter Island region, although they are detectable in the simulations for many regions world wide. Hence we tentatively conclude that large-scale climate changes in the oceanic region around Easter Island might be too small to explain strong vegetation changes on the island over the last millennium.
Simulated and reconstructed winter temperature in the eastern China during the last millennium
Jian Liu,H. Storch,Xing Chen,E. Zorita,Jingyun Zheng,Sumin Wang
Chinese Science Bulletin , 2005, DOI: 10.1360/982004-856
Abstract: The reconstructed temperature anomalies in the eastern China were compared with the output from a 1000-year model simulation in an attempt to evaluate the model’s regional simulation skills and to understand the causes of climate change in China over the last millennium. The reconstructed data are the winter half-year temperature anomalies in the central region of eastern China (25°–40°N, east of 105°E) for the last 1000 years with a 30-year resolution. The model used is the global atmosphere-ocean coupled climate model, ECHO-G, which was driven by time-varying external forcings including solar radiation, volcanic eruptions, and greenhouse gas concentrations (CO2 and CH4) for the same period. The correlation coefficient between the simulated and reconstructed time series is 0.37, which is statistically significant at a confidence level of 97.5%. The Medieval Warm Period (MWP) during 1000–1300 A.D., the Little Ice Age (LIA) during 1300–1850 A.D. and the modern warming period after 1900 A.D. are all recognizable from both the simulated and reconstructed temperatures. The anomalies associated with the LIA and the modern warming simulated by the model are in good consistency with the reconstructed counterpart. In particular during the Maunder sun-spot minimum (1670–1710 A.D.), both the simulated and reconstructed temperature anomalies reach their minima without any phase difference. But in the earlier MWP, significant discrepancies exist between the simulation and the reconstruction, which might reflect the degrading quality of the reconstruction data. The range of the simulated anomalies (1.62 K) is comparable with that of reconstructed (2.0 K). Diagnosis of the model results indicates that, during the last millennium, variations in solar radiation and volcanic activity are the main controlling factors on regional temperature change, while in the recent 100 years, the change of the concentration of greenhouse gases plays most important role in explaining the rapid temperature rising.
The climate in the Baltic Sea region during the last millennium simulated with a regional climate model
S. Schimanke, H. E. M. Meier, E. Kjellstr m, G. Strandberg,R. Hordoir
Climate of the Past (CP) & Discussions (CPD) , 2012,
Abstract: Variability and long-term climate change in the Baltic Sea region is investigated for the pre-industrial period of the last millennium. For the first time dynamical downscaling covering the complete millennium is conducted with a regional climate model in this area. As a result of changing external forcing conditions, the model simulation shows warm conditions in the first centuries followed by a gradual cooling until ca. 1700 before temperature increases in the last centuries. This long-term evolution, with a Medieval Climate Anomaly (MCA) and a Little Ice Age (LIA), is in broad agreement with proxy-based reconstructions. However, the timing of warm and cold events is not captured at all times. We show that the regional response to the global climate anomalies is to a strong degree modified by the large-scale circulation in the model. In particular, we find that a positive phase of the North Atlantic Oscillation (NAO) simulated during MCA contributes to enhancing winter temperatures and precipitation in the region while a negative NAO index in the LIA reduces them. In a second step, the regional ocean model (RCO-SCOBI) is used to investigate the impact of atmospheric changes onto the Baltic Sea for two 100 yr time slices representing the MCA and the LIA. Besides the warming of the Baltic Sea, the water becomes fresher at all levels during the MCA. This is induced by increased runoff and stronger westerly winds. Moreover, the oxygen concentrations in the deep layers are slightly reduced during the MCA. Additional sensitivity studies are conducted to investigate the impact of even higher temperatures and increased nutrient loads. The presented experiments suggest that changing nutrient loads may be more important determining oxygen depletion than changes in temperature or dynamic feedbacks.
Simulated analysis of summer climate on centennial time scale in eastern China during the last millennium
HongLi Wang,Jian Liu,ZhiYuan Wang,SuMin Wang,XueYuan Kuang
Chinese Science Bulletin , 2011, DOI: 10.1007/s11434-011-4548-2
Abstract: Using Lanczos filtered simulation results from the ECHO-G coupled ocean-atmosphere model, this study analyzes the spatiotemporal structure of temperature and precipitation on centennial time scale to examine how climate change in eastern China responded to external forcing during the last millennium. The conclusions are (1) eastern China experienced a warm-cold-warm climate transition, and the transition from the warm period to the cold period was slower than the cold to warm transition which followed it. There was more rainfall in the warm periods, and the transitional peak and valley of precipitation lag those of temperature. The effective solar radiation and solar irradiance have significant impacts on the temporal variation of both temperature and precipitation. Volcanic activity plays an important role in the sudden drop of temperature before the Present Warm Period (PWP). There is a positive correlation between precipitation and volcanic activity before 1400 A.D., and a negative relationship between the two thereafter. The concentration of greenhouse gases increases in the PWP, and the temperature and precipitation increase accordingly. (2) The spatial pattern of the first leading empirical orthogonal function (EOF) mode of temperature on centennial time scale is consistent with that on the inter-annual/inter-decadal (IA-ID) time scales; namely, the entirety of eastern China is of the same sign. This pattern has good coherence with effective solar radiation and the concentrations of greenhouse gases. The first leading EOF mode of precipitation on centennial time scale is totally different from that on the IA-ID time scales. The first leading mode of centennial time scale changes consistently over the entirety of eastern China, while the middle and lower reaches of the Yangtze and Yellow Rivers are the opposite to the rest of eastern China is the leading spatial pattern on IA-ID time scale. The distribution of precipitation on centennial time scale is affected by solar irradiance and greenhouse gas concentrations.
COMPARISON OF SIMULATED AND RECONSTRUCTED TEMPERATURE IN CHINA DURING THE LAST MILLENNIUM
近千年来中国气温模拟与重建资料的对比分析

Kuang Xueyuan,Liu Jian,Wang Hongli,Ti Ruyuan,
况雪源
,刘健,王红丽,提汝媛

第四纪研究 , 2011,
Abstract: With more and more effects of human activities on natural climate variability,the climate change becomes enormously complex in the past 1000 years,which is the key period for linking the proxy data and instrumental observation periods.It is crucial to further reveal the role and mechanism of climate change in this special period despite the fact it is quite difficult due to scarcity and uncertainty of proxy data.To compensate for the deficiency of the proxy data,climate model is used as an important tool in paleoclimate research areas with the advantage in revealing the internal mechanism and response to external forcing factors of climate change.The sea-atmospheric coupled climate model ECHO-G has been proved to be an efficient climate model for both paleoclimate and modern climate research,but its simulation performance in China region needs to be further examined.In this paper,the simulated annual mean temperature series averaged in China region in last 1000 years is compared with two reconstructed proxy series,which was processed by Yang et al.18](named Y series)and Wang et al.19](W series)respectively,to validate the performance of the global climate coupled model ECHO-G in simulating the climate of China.The results indicate that the model successfully reproduces the medieval warm period(MWP)from 11th to 14th century,little ice age(LIA)from 15th to 19th century and present warm period(PWP),and the transition times from one period to another are also well corresponding to the reconstruction of Y series.Moreover,the features of simulated temperature in various areas of Eastern China are consistent with that in W series.It means that the model captures the essence characteristics of the temperature change in China during last millennium.Further study on the simulation shows that the West China can be divided into two parts based on the simulated temperature: North West China and Tibetan Plateau.The climate change in the former is well consistent with the East China but the latter is different in various seasons.There exists significant difference in temperature change between Tibetan Plateau and other regions in winter while the similarity prevails in other seasons.Temperature of Tibetan Plateau in winter is characterized by obvious upward trend in the last millennium,implying that it was cold in WMP in Plateau in winter.
Temperature response to external forcing in simulations and reconstructions of the last millennium  [PDF]
L. Fernández-Donado,J. F. González-Rouco,C. C. Raible,C. M. Ammann
Climate of the Past Discussions , 2012, DOI: 10.5194/cpd-8-4003-2012
Abstract: The understanding of natural climate variability and its driving factors is crucial to assess future climate change. Therefore, comparing proxy-based climate reconstructions with forcing factors as well as comparing these with paleoclimate model simulations is key to gain insights into the relative roles of internal versus forced variability. A review of the state of modeling of the last millennium climate previous to the CMIP5-PMIP3 coordinated effort is presented and compared to the available temperature reconstructions. Simulations and reconstructions broadly agree on reproducing the major temperature changes and suggest an overall linear response to external forcing on multidecadal or longer timescales. Internal variability is found to have an important influence at hemispheric and global scales. The spatial distribution of simulated temperature changes during the transition of the Medieval Climate Anomaly to the Little Ice Age disagrees with that found in the reconstructions, thus advocating for internal variability as a possible major player in shaping temperature changes through the millennium. A paleo transient climate response (PTCR) is defined to provide a quantitative framework for analysing the consistency between simulated and reconstructed climate. Beyond an overall agreement between simulated and reconstructed PTCR ranges, this analysis is able to single out specific discrepancies between some reconstructions and the ensemble of simulations. The disagreement is found in the cases where the reconstructions show reduced covariability with external forcings or when they present high rates of temperature change.
The climate in the Baltic Sea region during the last millennium  [PDF]
S. Schimanke,H. E. M. Meier,E. Kjellstr?m,G. Strandberg
Climate of the Past Discussions , 2012, DOI: 10.5194/cpd-8-1369-2012
Abstract: Variability and long-term climate change in the Baltic Sea region is investigated for the pre-industrial period of the last millennium. For the first time dynamical downscaling covering the complete millennium is conducted with a regional climate model in this area. As a result of changing external forcing conditions the model simulation shows warm conditions in the first centuries followed by a gradual cooling until c. 1700 before temperature increases in the last centuries. This long-term evolution, with a Medieval Climate Anomaly (MCA) and a Little Ice Age (LIA), is in broad agreement with proxy-based reconstructions. However, the timing of warm and cold events is not captured at all times. We show that the regional response to the global climate anomalies is to a strong degree modified by the large-scale circulation in the model. In particular, we find that a positive NAO-phase simulated during MCA contributes to enhancing winter temperatures and precipitation in the region while a negative NAO-anomaly in the LIA reduces them. In a second step, the regional ocean model RCO is used to investigate the impact of atmospheric changes onto the Baltic Sea for two 100 yr time slices representing the MCA and the LIA. Besides the warming of the Baltic Sea the water becomes fresher at all levels during the MCA. This is induced by increased runoff and stronger westerly winds. Moreover, the oxygen concentrations in the deep layers are slightly reduced during the MCA. Additional sensitivity studies are conducted to investigate the impact of even higher temperatures and increased nutrient loads. The presented experiments suggest that changing nutrient loads may be more important determining oxygen depletion than changes in temperature or dynamic feedbacks.
Volcanic impact on the Atlantic Ocean over the last millennium
J. Mignot, M. Khodri, C. Frankignoul,J. Servonnat
Climate of the Past (CP) & Discussions (CPD) , 2011,
Abstract: The oceanic response to volcanic eruptions over the last 1000 years is investigated with a focus on the North Atlantic Ocean, using a fully coupled AOGCM forced by a realistic time series of volcanic eruptions, total solar irradiance (TSI) and atmospheric greenhouse gases concentration. The model simulates little response to TSI variations but a strong and long-lasting thermal and dynamical oceanic adjustment to volcanic forcing, which is shown to be a function of the time period of the volcanic eruptions. The thermal response consists of a fast tropical cooling due to the radiative forcing by the volcanic eruptions, followed by a penetration of this cooling in the subtropical ocean interior one to five years after the eruption, and propagation of the anomalies toward the high latitudes. The oceanic circulation first adjusts rapidly to low latitude anomalous wind stress induced by the strong cooling. The Atlantic Meridional Overturning Circulation (AMOC) shows a significant intensification 5 to 10 years after the eruptions of the period post-1400 A.D., in response to anomalous atmospheric momentum forcing, and a slight weakening in the following decade. In response to the stronger eruptions occurring between 1100 and 1300, the AMOC shows no intensification and a stronger reduction after 10 years. This study thus stresses the diversity of AMOC response to volcanic eruptions in climate models and discusses possible explanations.
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