Abrupt Climate Change around 4 ka BP:Role of the Thermohaline Circulation as Indicated by a GCM Experiment

A great deal of palaeoenvironmental and palaeoclimatic evidence suggests that a predominant temperature drop and an aridiflcation occurred at ca. 4.0 ka BP. Palaeoclimate studies in China support this dedution. The collapse of ancient civilizations at ca. 4.0 ka BP in the Nile Valley and Mesopotamia has been attributed to climate-induced aridification. A widespread alternation of the ancient cultures was also found in China at ca. 4.0 ka BP in concert with the collapse of the civilizations in the Old World. Palaeoclimatic studies indicate that the abrupt climate change at 4.0 ka BP is one of the realizations of the cold phase in millennial scale climate oscillations, which may be related to the modulation of the Thermohaline Circulation (THC) over the Atlantic Ocean. Therefore, this study conducts a numerical experiment of a GCM with SST forcing to simulate the impact of the weakening of the THC. Results show a drop in temperature from North Europe, the northern middle East Asia, and northern East Asia and a significant reduction of precipitation in East Africa, the Middle East, the Indian Peninsula, and the Yellow River Valley. This seems to support the idea that coldness and aridification at ca. 4.0 ka BP was caused by the weakening of the THC.

Abrupt Climate Changes of Holocene

This paper is a review of studies of abrupt climate changes(ACCs) during the Holocene published during the past ten years.North Atlantic cold events are indicators of ACCs.As indicated by North Atlantic ice-rafted debris(IRD),there were nine confirmed cold events during the Holocene,occurring at 11.1 kyr,10.3 kyr,9.4 kyr,8.1 kyr,5.9 kyr,4.2 kyr,2.8 kyr,1.4 kyr,and 0.4 kyr respectively according to most representative results from Bond et al.(1997).However,the identification of chronology has been made with some uncertainties.Considerable climatic proxy data have shown that,during the cold events,substantial climate abnormalities have occurred widely across the globe,particularly in the areas surrounding the North Atlantic.These abnormalities were in the form of high-latitude cold in the both hemispheres,expansion of the Westerlies to low latitudes,drought in the monsoon regions,recession of summer monsoons,and intensification of the winter monsoons.Studies have indicated that the four ACCs occurring in the early Holocene may be related to freshwater pulses from ice melting in the northern part of the North Atlantic,and the other five ACCs that occurred during the middle and late Holocene may be related to the decreased solar activity.

Detection and attribution of abrupt climate changes in the last one hundred years

Based on physical backgrounds, the four time series of the Guliya （Tibetan plateau） ice core （GIC） 5180, and three natural factors, i.e. the rotation rate of earth, sunspots, and E1 Nino-Southern Oscillation （ENSO） signals, are decomposed into two hierarchies, i.e. more and less than 10-year hierarchies respectively, and then the running t-test is used to reanalyse the data before and after filtering with the purpose of investigating the contribution of natural factors to the abrupt climate changes in the last one hundred years. The results show that the GIC 5180 evolved with a quasi-period of 7-9 years, and the abrupt climate changes in the early 1960s and in the period from the end of the 1970s to the beginning of the 1980s resulted from the joint effect of the two hierarchies, in other words, the two interdecadal abrupt changes of climate in the last one hundred years were global. The interannual variations of ENSO and sunspots were the important triggering factors for the abrupt climate changes in the last one hundred years. At the same time, the method of Information Transfer （IT） is employed to estimate the contributions of ENSO signals and sunspots activities to the abrupt climate changes, and it is found that the contribution of the interannual variation of ENSO signals is relatively large.

Climate Changes and Sustainability

Climate change is the phrase used to describe long-term changes in temperatures and weather patterns. Changes in the atmosphere and their interactions with diverse geologic, chemical, biological, and geographic variables are the main contributors to this cyclical adjustment of the Earth’s climate. Such changes may be induced purposefully, because of burning fossil fuels, clearing forests, and raising animals, or they may be natural, brought on by significant volcanic eruptions or variations in the sun’s activity. By significantly increasing the amount of greenhouse gases already in the atmosphere, this heightens the greenhouse effect and contributes to global warming. This work includes several additional theoretical and practical explanations of sustainable development. The theoretical work encompasses hundreds of researches that identify requirements for how development routes might satisfy sustainable development (SD) criteria using economic theory, complex systems approach, ecological science, and other techniques. The agreements made by the Parties in various nations across the world will consider a wide range of perspectives about what would be considered undesirable effects on the environment, the climate system, sustainability, economic growth, or food production.

Analysis on the Climate Change Characteristics in Zhumadian in Recent 50 Years

By means of linear function and Mann-Kendall test method,the climate change characteristics of temperature and precipitation from Zhumadian meteorological station in recent 50 years were analyzed.The results revealed that annual mean temperature and extreme temperature showed increase trend,especially minimum temperature,and there was a slight increase in annual precipitation.Temperature increase was more obvious in spring than that in autumn and winter,while there was a decrease of temperature in summer.Meanwhile,precipitation went down in spring and autumn,particular in autumn,while the increase of summer precipitation was most obvious.Mann-Kendall test showed that temperature in Zhumadian had obvious increase trend in recent 50 years,while there was abrupt change in temperature in the late 1990s and fluctuation change in annual precipitation.

Early warning signals of abrupt temperature change in different regions of China over the past 50 years

In this paper, the early warning signals of abrupt temperature change in different regions of China are investigated. Seven regions are divided on the basis of different climate temperature patterns, obtained through the rotated empirical orthogonal function, and the signal-to-noise temperature ratios for each region are then calculated. Based on the concept of critical slowing down, the temperature data that contain noise in the different regions of China are preprocessed to study the early warning signals of abrupt climate change. First, the Mann-Kendall method is used to identify the instant of abrupt climate change in the temperature data. Second, autocorrelation coefficients that can identify critical slowing down are calculated. The results show that the critical slowing down phenomenon appeared in temperature data about 5-10 years before abrupt climate change occurred, which indicates that the critical slowing down phenomenon is a possible early warning signal for abrupt climate change, and that noise has less influence on the detection results of the early warning signals. Accordingly, this demonstrates that the model is reliable in identifying the early warning signals of abrupt climate change based on detecting the critical slowing down phenomenon, which provides an experimental basis for the actual application of the method.

A study of the early warning signals of abrupt change in the Pacific decadal oscillation

In recent years, the phenomenon of a critical slowing down has demonstrated its major potential in discovering whether a complex dynamic system tends to abruptly change at critical points. This research on the Pacific decadal oscillation(PDO) index has been made on the basis of the critical slowing down principle in order to analyze its early warning signal of abrupt change. The chaotic characteristics of the PDO index sequence at different times are determined by using the largest Lyapunov exponent(LLE). The relationship between the regional sea surface temperature(SST) background field and the early warning signal of the PDO abrupt change is further studied through calculating the variance of the SST in the PDO region and the spatial distribution of the autocorrelation coefficient, thereby providing the experimental foundation for the extensive application of the method of the critical slowing down phenomenon. Our results show that the phenomenon of critical slowing down, such as the increase of the variance and autocorrelation coefficient, will continue for six years before the abrupt change of the PDO index. This phenomenon of the critical slowing down can be regarded as one of the early warning signals of an abrupt change. Through calculating the LLE of the PDO index during different times, it is also found that the strongest chaotic characteristics of the system occurred between 1971 and 1975 in the early stages of an abrupt change(1976), and the system was at the stage of a critical slowing down, which proves the reliability of the early warning signal of abrupt change discovered in 1970 from the mechanism. In addition, the variance of the SST,along with the spatial distribution of the autocorrelation coefficient in the corresponding PDO region, also demonstrates the corresponding relationship between the change of the background field of the SST and the change of the PDO.

Temporal and Spatial Characteristics of Climate Changes in the Urumqi River Basin of Tianshan Mountain over 50 years

Based on the meteorological data during 1959-2008 from five representative weather stations in the Urumqi River Basin and surrounding areas,the regional characteristics of temperature and precipitation in the basin featuring multi-climatic zones were studied by means of some methods including wavelet analysis.As was shown in the results,the temperature in the whole Urumqi River Basin demonstrated a significant upward trend.The temperature increase particularly in autumn and winter made the greatest contribution to the marked ascent.The interdecadal temperature in the basin showed a tendency to decline before the period during 1970s-1980s while it was on the rise after 1990s on the whole.The most concentrated period of temperature mutations was in the late 1990s.At the same time,the precipitation also showed an escalating trend,which experienced a stage of unanimous upward trend after 1990s.The most concentrated period of precipitation mutations was in the early 1990s.

EVIDENCE FOR ABRUPT CLIMATIC CHANGES ON NORTHWESTERN MARGIN OF EAST ASIAN MONSOON REGION DURING LAST DEGLACIATION

Based on investigations of the Zhongwei Nanshan aeolian section situated in the southeastern margin of Tengger Desert, carbon-14 and TL (thermoluminescence) dating results and paleoclimatic proxies such as magnetic susceptibility and grain size, we inferred that the northwestern margin of East Asian monsoon region experienced abrupt climatic changes during the last deglaciation. Six oscillation events were identified: Oldest Dryas, Bolling, Older Dryas, Allerod, Intra-Allerod Cold Period (IACP) and Younger Dryas (YD). The summer monsoon was weaker during Oldest Dryas and Younger Dryas when the winter monsoon was stronger. However, during the B/A (Bolling/Allerod) period, the summer monsoon strengthened, reflected by magnetic susceptibility, when the winter monsoon also became strong, which is different from the paleoclimatic pattern established in the East Asian monsoon region. Furthermore, the summer monsoon was nearly in phase with the climate changes inferred from the oxygen isotopic records of Greenland ice cores. It could be speculated that the variations of the sea ice cover in the high latitudes of the North Hemisphere affected the high pressure of Asian continent and the changes of the winter monsoon inland. On the other hand, the sea ice cover variations might have indirectly caused the occurrence of ENSO events that has tightly been related to the summer monsoon in northwest margin of East Asian monsoon region.

The Interdecadal Changes of South Pacific Sea Surface Temperature in the Mid-1990s and Their Connections with ENSO

The characteristic changes of South Pacific sea surface temperature anomalies （SSTAs） for the period January 1979 to December 2011, during which the 1990s Pacific pan-decadal variability （PDV） interdecadal regime shifts occurred, were examined. Empirical Orthogonal Function （EOF） analysis was applied to the monthly mean SSTA for two sub-periods： January 1979 to December 1994 （P 1） and January 1996 to December 2011 （P2）. Both the spatial and temporal features of the leading EOF mode for P1 and P2 showed a remarkable difference. The spatial structure of the leading EOF changed from a tripolar pattern for P 1 （EOF-P 1） to a dipole-like pattern for P2 （EOF-P2）. Besides, EOF-P 1 （EOF-P2） had significant spectral peaks at 4.6 yr （2.7 yr）. EOF-P2 not only had a closer association with E1 Nifio-Southern Oscillation （ENSO）, but also showed a faster response to ENSO than EOF-P1 based on their lead-lag relationships with ENSO. During the development of ENSO, the South Pacific SSTA associated with ENSO for both PI and P2 showed a significant eastward propagation. However, after the peak of ENSO, EOF-P1 showed a stronger persistence than EOF-P2, which still showed eastward propagation. The variability of the SSTA associated with the whole process of ENSO evolution during P1 and the SSTA associated with the development of ENSO during P2 support the existence of ocean-to-atmosphere forcing, but the SSTA associated with the decay of ENSO shows the phenomenon of atmosphere-to-ocean forcing.

LOW FREQUENCY VARIABILITY OF INTERANNUAL CHANGE PATTERNS FOR GLOBAL MEAN TEMPERATURE DURING THE RECENT 100 YEARS

The TEEOF method that expands temporally is used to conduct a diagnostic study of the variation patterns of 1, 3, 6 and 10 years with regard to mean air temperature over the globe and Southern and Northern Hemispheres over the course of 100 years. The results show that the first mode of TEEOF takes up more than 50% in the total variance, with each of the first mode in the interannual oscillations generally standing for annually varying patterns which are related with climate and reflecting long-term tendency of change in air temperature. It is particularly true for the first mode on the 10-year scale, which shows an obvious ascending trend concerning the temperature in winter and consistently the primary component of time goes in a way that is very close to the sequence of actual temperature. Apart from the first mode of all time sections of TEEOF for the globe and the two hemispheres and the second mode of the 1-year TEEOF, interannual variation described by other characteristic vectors are showing various patterns, with corresponding primary components having relation with long-term variability of specific interannual quasi-periodic oscillation structures. A 2T test applied to the annual variation pattern shows that the abrupt changes for the Southern Hemisphere and the globe come closer to the result of a uni-element t test for mean temperature than those for the Northern Hemisphere do. It indicates that the 2Ttest, when carried out with patterns of multiple variables, seems more reasonable than the t test with single elements.

The Characteristics of Changes in Sunshine Hours of Jimusi Region in Sanjiang Plain

Based on the data of sunshine hours from the four stations in Jiamusi region in Sanjiang Plain from 1961 to 2011, we analysed the changing tend and the abnormal year of sunshine hours in this region. The results showed that annual sunshine hours reduced extremely significantly in three stations of Jiamusi region in Sanjiang Plain in recent 50 years, especially in spring and winter, and the decrease of annual sunshine hours was the largest in the middle of Jiamusi region, followed by the west, while it was the smallest in the east. On the contrary, annual sunshine hours increased extremely significantly in Fuyuan in the northeast. Monthly sunshine hours of this area changed from 134.1 to 246.0 h, and the maximum data appeared in March, and the next was June, while the minimum one appeared in December. Total monthly sunshine hours reached the maximum in Tangyuan in the west, followed by middle Jiamusi and Fujin in the east, while the minimum appeared in Fuyuan in the northeast. Sunshine hours showed an increasing tendency only in July and August. From 2001 to 2011, annual sunshine hours showed a decreasing tendency in Jiamusi, while there was an obvious increase in Tangyuan, Fujin and Fuyuan; in the 20th century, annual average sunshine hours from the 1980s to 1990s decreased by 267.7 h compared with that from 1960s to 1970s. Among them, sunshine hours were the fewest in the 1990s. In recent 50 years, there was an abnormal increase in annual sunshine hours in Jiamusi in 1975 and 1982; while there were abnormal decreases in Tangyuan and Fujin in 1993, Fujin in 1995, and Fuyuan in 1982 and 1987.

Climatic Analysis of Continuous Rain in Southwest of Shandong

The continuous rain data from 1961 to 2007 in Heze city was analyzed in this paper.The results showed that continuous rain increased from north to south.Continuous rain processes took place most frequently in summer,next in autumn,and the least in winter.Using wavelet to analyze the sequence of seasonal and annual continuous rain,it had a 5 years cycle oscillation at 2Y(year) level and a 20 years cycle oscillation at 10Y level.An abrupt climate change of continuous rain took place in 1986.Continuous rain was in a more period from 2001 to 2010 and would decrease gradually within the period.

多种代用资料和模型模拟得到的亚洲季风在8.2ka显著气候影响的证据（英文）

Given the likelihood of future reductions in the strength of the Atlantic Meridional Overturning Circulation(AMOC),it is important to document how changes in the AMOC have altered climate patterns in the past and to assess the skill of coupled climate models in reproducing these teleconnections.Of past abrupt changes in the AMOC,the 8.2 ka event provides a particularly useful case study because its duration,magnitude of AMOC reduction and background climate state are closest to conditions expected in the future.In this research,we present an expanded proxy synthesis of the 8.2 ka event in monsoonal Asia,including new high-resolution lake and bog records,more sites from the East Asia monsoon region and proxies of winter monsoon strength.We compare proxy evidence with a new simulation of the 8.2 ka event using the Community Climate System Model version 3(CCSM3) and prescribing North Atlantic freshwater forcing according to the latest reconstructions.We find clear and objectively-determined evidence for 8.2 ka climate anomalies at nearly all of the fourteen proxy sites,emphasizing the strong and widespread impacts of the event in monsoonal Asia during both summer and winter seasons.The model simulation corroborates that these anomalies,described generally as a weakening of the summer monsoon and strengthening of the winter monsoon,were likely caused by a reduction of the AMOC.Examination of regional anomalies in East Asia reveals some spatial heterogeneity,however,that in the model simulation is caused by contraction of the seasonal migration of the subtropical monsoon front.The duration of climate anomalies at 8.2 ka in monsoonal Asia,both in proxy records and the model simulation,generally matches the duration of the event in Greenland ice core δ^(18)O,further supporting a tight connection to the North Atlantic.

Latest Advances in Climate Change Detection Techniques

In recent years,the global warming and its influences on people and social economy have received increasing attention from international communities.Determining the current trend of global temperature variation has become one of the critical issues in climate change research.Obviously,it is rather important to develop new climate change detection technology in order to identify new characteristics of the global warming.This review introduces the latest advances and past achievements on the climate change detection technology in China with emphases on new detection methods in the following five aspects：（1） abrupt climate change detection,（2） signal separation and extraction from observed data,（3） intrinsic complexity of the climate system,（4） recognition of the dynamical characteristics of the climate system,and（5） definitions and detection of extreme events.At last,some cruxes and key problems in the current climate change detection technology research are briefly discussed.

Temperature Variation of Jiamusi Region in Sanjiang Plain

[Objective] The study aimed at analysing the change characteristics of temperature in Jiamusi region of Sanjiang Plain.[Method] Based on temperature data of Jiamusi region in Sanjiang Plain from 1961 to 2010,including Jiamusi,Huanan,Fujin and Fuyuan station,we studied the change trends,abrupt climate change and abnormal years of temperature in Jiamusi region.[Result] Annual average temperature of Jiamusi region in Sanjiang Plain showed increasing trend,with the increase of 0.249-0.412 ℃/10 a.The order of annual average temperature in Jiamusi region was east> south> north> west.In addition,abrupt climate change of annual average temperature occurred in the early 1980s.Abrupt climate change of annual average temperature appeared in 1981 in Jiamusi,Huanan and Fujin,but in 1984 in Fuyuan.Annual average temperature in the mid-1960s and late 1960s was abnormally low in Jiamusi,Fujin and Huanan,while it was abnormally high in Huanan,Fuyuan and Jiamusi from 2007 to 2008,but Fujin in the early 1990s.Meanwhile,anomalies of seasonal average temperature in distinct regions appeared in various years.[Conclusion] The research could provide references for the prediction of temperature in Jiamusi region of Sanjiang Plain in furture.

Orbital and Millennial-Scale Climate Variability over the Past 76 ka in the Western Tarim Basin, Northwest China

Paleoclimate changes during the last glacial in the arid central Asia are not as well understood as the monsoon-dominated areas of Asia. Here we report a 75-m-long sediment core over past 120 kyr based on astronomical tuning combined with the optically stimulated luminescence(OSL) dating in the Kashi depression of the western Tarim Basin, Northwest China. Analysis of grain size and highresolution gamma ray(GR) logs from the KT11 borehole across the last glacial period yields a climate history for the Tarim Basin which reflects the variations of its temperature and the hydrological cycles. Comparison of these records with north hemisphere summer insolation, the Greenland ice core temperature, stalagmites and the loess from the nearby region indicates that the deposits in the fluvio-lacustrine system of the Kashi depression responded to climate change at the Younger Dryas(YD), six Heinrich cooling events and the Dansgaard-Oeschger cycles. Our work indicates that the alternations between warm-humid and cold-dry climates were prevalent in the western Tarim Basin during the last glacial period, showing an in-phase pattern with the climate variations of the East Asian Monsoon, controlled ultimately by precession and North Atlantic Ocean climate variability on orbital-millennial time scales.

Variations Trend of Soil Temperature at Deep Layers in Xining from 1961 to 2010

[Objective] The aim was to analyze the changes trend of mean earth temperature at 0.8, 1.6 and 3.2 m deep to the ground in Xining from 1961 to 2010. [Method] Using the data of monthly mean soil temperatures at 0.8,1.6 and 3.2 m in Xining from 1961 to 2010, the linear trend, climatic anomalous and climate abrupt of deep soil temperature during recent 50 years were analyzed by using of linear trend analysis, accumulated variance and signal noise ratio methods. [Result] In terms of linear trend, the annual mean soil temperatures at 0.8 m in recent 50 years, as well as 1.6 and 3.2 m in recent 45 years displayed a weak increasing trend in Xining. Comparing with the average air temperature in the same period, the rising range of deep soil temperature is obvious less. The average soil temperatures at 0.8 m was the highest in 1980s, but it was the lowest in the 1960s. In spring, autumn and winter in the 1980s, the average soil temperature was a little higher than many other years at 1.6 m. In four seasons in the 1980s, the average soil temperature was obvious higher at 3.2 m. The annual soil temperatures at 0.8 m were anomalous warm in 1991, and from 1987 to 1992, as well as in 1994, 2007 and 2009. The annual soil temperatures at 3.2 m were anomalous warm. In the 1990s, there were four years which were anomalous warm at 3.2 m, as well as five years at 0.8 m and five years at 1.6 m. [Conclusion] The study provided theoretical basis for the development of climate changes in Xining.

青藏高原冰芯记录揭示早-中全新世发生多次融水事件

Understanding the impact of meltwater discharge during the final stage of the Laurentide Ice Sheet(LIS)has important implications for predicting sea level rise and climate change.Here we present a highresolution ice-core isotopic record from the central Tibetan Plateau(TP),where the climate is sensitive to the meltwater forcing,and explore possible signals of the climate response to potential LIS meltwater discharges in the early to mid-Holocene.The record shows four abrupt large fluctuations during the 7–9 ka BP(kiloannum before present),reflecting large shifts of the mid-latitude westerlies and the Indian summer monsoon(ISM)over this period,and they corresponded to possible LIS freshwater events documented in other paleoclimate records.Our study suggests that multiple rapid meltwater discharge events might have occurred during the final stage of LIS.The finding implies the possibility of rapid sea level rise and unstable climate in the transition zone between the mid-latitude westerlies and the ISM due to fast polar ice retreat under the anthropogenic global warming.

An Analysis of Interdecadal Variations of the Asian-African Summer Monsoon

The response of the Asian-African summer monsoon （AASM） to the fast global warming in the 1980s is studied based on several datasets, which span a long time period of nearly 100 yr, with two special periods 1980-1985 and 1990-1995 being focused on. Wavelet analyses are employed to explore the interdecadal variations of the AASM. It is found that after the mid 1980s, the global annual mean surface temperature rises more significantly and extensively over most parts of the African Continent, north of the Indian Ocean, and the Eurasian Continent excluding the Tibetan Plateau. Correspondingly, the global precipitation pattern alters with in- creased rainfall seen over the Sahel and North China in 1990-1995, though it is not recovered to the level of the rainy period before the mid-1960s. Changes of monsoonal circulations between the pre- and post-1980s periods display that, after the fast global warming of the 1980s, the African summer monsoon intensifies distinctly, the Indian summer mon- soon weakens a little bit, and the East Asian summer monsoon remains almost unchanged. The summer precipitation over the Asian-African Monsoon Belt （AAMB） does not change in phase coherently with the variations of the monsoonal circulations. Wavelet analyses of the land-sea thermal contrast and precipitation over North China and the Sahel indicate that interdecadal signals are dominant and in positive phases in the 1960s, leading to an overall enhanced interdecadal variation of the AASM, although the 1960s witnesses a global cooling. In the 1980s, however, in the context of a fast global warming, interdecadal signals are in opposite phases, and they counteract with each other, leading to a weakened interdecadal variation of the AASM. After the mid-1960s, the AASM weakened remarkably, whereas after the mid-1980s, the AASM as a whole did not strengthen uniformly and synchronously, because it is found that the interannual variations of the AASM in the 1980s are stronger than those in the 1960s, and they superimposed on the counteracting interdecadal signals, causing different regions of the AAMB behaving differently. Therefore, the response of the AASM to the accelerated global warming post the mid-1980s is not simply out-of-phase with that after the mid-1960s; it may involve more complicated multiscale physical elements.