Summer sea-surface temperatures and climate events on the North Icelandic shelf through the last 3000 years

Diatom data from core MD992271 on the North Icelandic shelf record a cooling trend through the last 3000 years. This is indicated by a general decrease in warm water species and an increase in cold water taxa. The relative abundance of these two diatom groups changed periodically, suggesting that the climate also fluctuated within this time period. The results of diatom-based transfer function calculation show that the summer sea-surface temperatures (SSTs) before 1400 cal. a BP were generally higher than the mean value for the last 3000 years and the summer SSTs fluctuated around the mean between 1400 and 700 cal. a BP, and dropped to the values below the mean after 700 cal. a BP. Four cooling events were distinguished, centered at around 2600, 1900, 1300 and 600 cal. a BP respectively. The results are not only consistent with the data from neighbouring cores HM107-03 and MD992275, but also comparable with those from the GISP2 ice core and from other marine sediment records in the North Atlantic. This suggests that changes in the summer SSTs reflect regional climate variations in the North Atlantic. On the North Icelandic shelf, the summer SST variation is a result of changes in the in-teraction between the cold and the warm currents in the area.     

A biomass burning record from the Lingtai Loess Section during the last 370 ka and implication for climate and environment

Every moment of every day somewhere on Earth a wildfire burns. Generally three conditions are needed to cause such a wildfire: fuel, ignition, and favorable cli-mate characterized by certain critical temperature, hu- midity and oxygen content, etc. Occurr…     

Simulation of the future change of East Asian monsoon climate using the IPCC SRES A2 and B2 scenarios

In this paper, we applied the newest emission scenarios of the sulfur and greenhouse gases, i.e. Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A2 and B2 scenarios, to investigating the change of the East Asian climate in the last three decades of the 21st century with an atmosphere-ocean coupled general circulation model. The global warming enlarges the land-sea thermal contrast and, hence, enhances (reduces) the East Asian summer (winter) monsoon circulation. The precipitation from the Yangtze and Huaihe river valley to North China increases significantly. In particular, the strong rainfall increase over North China implies that the East Asian rainy area would expand northward. In addition, from the southeastern coastal area to North China, the rainfall would increase significantly in September, implying that the rainy period of the East Asian monsoon would be prolonged about one month. In July, August and September, the interannual variability of the precipitation enhances evidently over North China, meaning a risk of flooding in the future.     

Regional difference of aridity/ humidity conditions change over China during the last thirty years

Scientists have found that the global average surface temperature has increased by 0.6±0.2℃ since the late 19th century based on various evidence[1]. From the 1980s, temperature has experienced the most rapid warming to an extent of abrupt change statistically[2,3]. Global warming has attracted extensive attention from multiple depart-ments and has been an important issue related to global politics. Many scientific communities have made great efforts on climate change research and global env…     

Twenty-five years of change in scleractinian coral communities of Daya Bay （northern South China Sea） and its response to the 2008 AD extreme cold climate event

Coral reefs worldwide are becoming increasingly and detrimentally impacted upon by a variety of factors including significant climate changes, such as global warming and increased El Nino-Southern Oscillation activity. Generally, the persistence of coral reefs, especially at low-latitudes, is governed, in part, by sea surface temperatures not exceeding the critical limit （-30℃） at which mass mortality can occur. Thus, it is thought that corals living at high-latitudes （i.e., currently cooler sea surface temperatures） will likely respond more favourably to hypothesized future temperature increases than corals living at low-latitudes （i.e., currently warmer sea surface temperatures）. Consequently, high-latitude coral communities may have the potential to act as regions of refugia for many coral species in the face of potential future global warming. The Daya Bay （22°31′--22°50′N）, northern South China Sea, contains several high-latitude non-reefal coral communities and represents one of the most northerly distributions of scleractinian corals within the region. Significantly, Daya Bay has experienced dramatic warming in both air and sea surface temperatures throughout the past 50 years. In this paper, we analyze 25 years of change in the Daya Bay coral communities, based both on historic surveys and our latest 2006--2008 regional ecological surveys. Our results suggest that, contrary to predictions, there have been significant declines in coral cover within the Daya Bay during the past 25 years （i.e., 76.6% coral cover in 1983/1984 to only 15.3% coral cover by 2008）. Such changes also reflect a significant shift in the most abundant coral species, from Acropora pruinosa to Favites abdita. Most of the modern coral communities became established between 15 and 30 years ago, corresponding to a period of increased winter sea surface temperature. However, very few colonies have become established within the last 15 years, despite a more intense period of warming. By taking into account additional factors, we hypothesize that direct anthropogenic impacts, rather than climatic events, have both restricted the development, and drove the decline, of Daya Bay coral communities in the last 15 years. The Daya Bay has also been subjected to occasional extreme cold events during the past 50 years, with the most recent occurring in early 2008 （13 January-13 February）. During the 2008 cold event, the lowest air temperature reaches only 6.6℃, and the mean sea surface temperature for February fall to 〈 14℃, including six continuous days at 12.3℃. Significantly, the sea surface temperatures fall below the hypothesized critical lower temperature threshold （-13℃） that commonly leads to mass mortality in scleractinian coral communities. Surprisingly, our coral community surveys, conducted both before （August 2007） and after （late February 2008） the extreme 2008 cold event, demonstrate that the Daya Bay coral ecosystems are barely impacted upon during the cold period. Those observations suggest that the Daya Bay scleractinian coral communities have developed adaptations to low sea surface temperatures. Overall, our data support the hypothesis that high-latitude coral communities, such as Daya Bay, have the potential to act as areas of refugia for scleractinian corals in the advent of potential future global warming.     

Hierarchy and nonstationarity in climate systems： Exploring the prediction of complex systems

The prediction theories for complex systems with a hierarchial structure and their applications to the climate process are a significant and forward-looking field of research.However,up to the present,they are yet not known and understood very well. This paper presents a preliminary theoretical frame for them.As a normal example,the basic behaviors and the dynamic strructure of the climate system are discussed in detail.The conclusions indicate that the climate system may be considered as a cascade of several subsystems located in different hierarchies.Such a dynamic structure is just the cause resulting in the nonstationarity.The conclusions also indicate that the main barrier of the climate prediction in theory derives from the contrary between the stationarity hypothesis for the current prediction theory and the nonstationary behavior of the real climate process.In addition,some work is disussed for detecting the nonstationarity in climate and other geophysical data and predicting the nonstationary process developed in recent years.These works may construct a preliminary base for applying to the climate predictions.     

Coupling controls of neotectonism and paleoclimate on the Quaternary sediments of the Yangtze （Changjiang） coast

1 Introduction The Quaternary sediments of the Yangtze coast, re-garding their distribution and origin, have been intensively discussed over the last decades since they are deeply in-volved into many aspects of Quaternary study, such as sea-level fluctuations, paleoclimate change and sediment facies evolution[1―6]. A painstaking effort has been made on the sediment study, which tends to elucidate what the primary control on sediment deposition and sedimentary facies formation is. Of note, nu…     

Change of bacterial community in the Malan Ice Core and its relation to climate and environment

In order to understand the relationship between the community structure of bacteria in ice core and the past climate and environment, we initiated the study on the microorganisms in the three selected ice samples from the Malan ice core drilled from the Tibetan Plateau. The 16S ribosomal DNA (rDNA) molecules were directly amplified from the melt water samples, and three 16S rDNA clone libraries were established. Among 94 positive clones, eleven clones with unique restriction pattern were used for partial sequence and compared with eight reported sequences from the same ice core. The phylotypes were divided into 5 groups: alpha, beta, gamma proteobacteria; CFB, and other eubacteria group. Among them, there were many “typical Malan glacial bacteria“ pertaining to psychrophilies and new bacteria found in the ice core. At a longer time scale, the concentration distribution of “typical Malan glacial bacteria“ with depth showed negative correlation with temperature variations and was coincident with dirty layer. It implied the influence of temperature on the microbial record through impact on the concentrations of the “typical Malan glacial bacteria“. In addition, the nutrition contained in ice was another important factor controlling the distribution of microbial population in ice core section. Moreover, the result displayed an apparent layer distribution of bacterial community in the ice core section, which reflected the microbial response to the past climatic and environmental conditions at the time of deposition.     

Millennial and orbital variations of El Niño/Southern Oscillation and high-latitude climate in the last glacial period

The El Ni?o/Southern Oscillation (ENSO) phenomenon is believed to have operated continuously over the last glacial-interglacial cycle. ENSO variability has been suggested to be linked to millennial-scale oscillations in North Atlantic climate during that time, but the proposals disagree on whether increased frequency of El Ni?o events, the warm phase of ENSO, was linked to North Atlantic warm or cold periods. Here we present a high-resolution record of surface moisture, based on the degree of peat humification and the ratio of sedges to grass, from northern Queensland, Australia, covering the past 45,000 yr. We observe millennial-scale dry periods, indicating periods of frequent El Ni?o events (summer precipitation declines in El Ni?o years in northeastern Australia). We find that these dry periods are correlated to the Dansgaard-Oeschger events--millennial-scale warm events in the North Atlantic climate record--although no direct atmospheric connection from the North Atlantic to our site can be invoked. Additionally, we find climatic cycles at a semiprecessional timescale (approximately 11,900 yr). We suggest that climate variations in the tropical Pacific Ocean on millennial as well as orbital timescales, which determined precipitation in northeastern Australia, also exerted an influence on North Atlantic climate through atmospheric and oceanic teleconnections.     

Abrupt climate change and collapse of ancient civilizations at 2200BC-2000BC

Plentiful evidence of historical, archaeological and palaeoclimatic studies proved that an abrupt change from wetter to drier climate occurred over the Nile Valley, the Mesopotamia, the Indus Valley and Huanghe River Valley at 2200BC-2000BC. The abrupt change was developed based on the general lowering of temperature in the middle latitudes, and was a strong cold event since the beginning of the Megathermal (8.5-3.0 kaBP). Collapse of Nile civilization appeared at the First Intermediate Period (2181BC-2040BC). Civilization of Mesopotamia began collapse following the disintegration of Akkadian Empire. This process lasted to the foundation of Babylon Kingdom from 2200BC to 1900BC. Indus civilization abruptly fell off at 1800BC. A widespread alternation of archaeological cultures happened in China at ca. 2000BC except only in its central part. Longsheng culture was replaced by the Erlitou culture, which is now acknowledged in China as Xia Culture. Foundation of Xia Dynasty at 2070BC opened a new chapter in the development of Chinese civilization. Studies indicated that abrupt climate change may be caused by the weakening of the Thermohaline Circulation (THC).     

温盐环流对气候突变的影响

由于全球气候变暖的一个负反馈机制——温盐环流的存在,使得气候在变暖过程中有可能出现突然变冷事件．地质历史时期气候突变事件的研究表明：这种潜在的突然变冷事件可能会持续几百年甚至上千年．加强对温盐环流强度变化的监测研究对于预测未来的气候变化,制定防灾减灾措施具有重要意义．     

Evidence for cold events in the early Holocene from the Guliya ice core, Tibetan Plateau, China

Evidence for the “8.2 ka cold event” has been provided mostly from the circum-North Atlantic area. However, whether this cold event occurred in other places is a key to understanding its cause. Here, we provide the evidence for the “8.2 ka cold event” from the Guliya ice core in the northwest Tibetan Plateau, and it was found that the peak cooling (~8.3—8.2 ka) in this ice core was about 7.8—10℃, which was larger than the cooling in the North Atlantic region. The primary causes for this episode were diminished solar activity and weakened thermohaline circulation. Moreover, another weak cold event, centered about 9.4 ka, was also recorded in the Guliya ice core record. These two cold events were concurrent with the ice-rafting episodes in the North Atlantic during the early Holocene, which implies that the millennial-scale climatic cyclicity might exist in the Tibetan Plateau as well as in the North Atlantic.     

The relationship between the thermohaline circulation and climate variability

The long-term integration with the Global Ocean-Atmosphere-Land System model of the State Key Laboratory of Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics(IAP), Chinese Academy of Sciences has been used in the investigations on the relationship between the thermohaline circulation and climate variability. The results show that the strength of the North Atlantic Thermohaline circulation (THC) is negatively correlated with the North Atlantic Oscillation (NAO). Based on this kind of relationship, and also the instrument-measured climate record such as air pressure and sea surface temperature, the activity of the thermohaline circulation during the 20th century has been evaluated. The inferred variations of the strength of the THC is that, during two multi-decadal periods of 1867–1903 and 1934–1972, the THC is estimated to have been running stronger, whereas during the two periods of 1904–1933 and 1973–1994, it appears to have been weaker.     

Rapid oscillations of Chinese monsoon climate since the last deglaciation and its comparison with GISP2 record

The geographic extent of the climate oscillations during the last deglaciation is an open question in the world. Here a high resolution climate record from a 16 000 C-14 a loess sequence in the northwestern margin of the Chinese Loess Plateau is reported. Comparison with GISP2 record shows that all major climate oscillation (e. g. Oldest Dryas/ Boiling/ Older Dryas/ Allerod/ Younger Dryas) in the North Atlantic region also registered in the record. In addition, the sequence also contains some other distinctive strengthened winter monsoon periods. It is suggested that a coupling mechanism operate between the two areas, and climate oscillations in the North Atlantic region may not be a local phenomenon.     

Abrupt climate change：Debate or action

Global abrupt climate changes have been documented by various climate records, including ice cores, ocean sediment cores, lake sediment cores, cave deposits, loess deposits and pollen records. The climate system prefers to be in one of two stable states, i.e. interstadial or stadial conditions, but not in between. The transition between two states has an abrupt character. Abrupt climate changes are, in general, synchronous in the northern hemisphere and tropical regions. The timescale for abrupt climate changes can be as short as a decade. As the impacts may be potentially serious, we need to take actions such as reducing CO2 emissions to the atmosphere.     

武汉近百年来气温变化的多时间尺度分析

用墨西哥帽小波变换分析了武汉１９０５～１９９８年逐月气温资料,揭示了气候变化的多时间尺度结构,分析了其中存在的主要周期振荡和突变点。结果表明：武汉气候在２０世纪主要经历了冷－暖－冷－暖４个阶段,目前处于相对暖期;气温存在准２ａ、２１ａ和６５左右的周期振荡;不同时间尺度下具有不同的冷暖结构和气候突变点。     

1960-2007年无定河流域径流情势变化及其归因分析

在气候变化和人类活动的双重影响下,流域径流过程会发生显著改变.利用M-K法、有序聚类法、Yamamoto法对无定河流域径流量进行水文变异诊断,利用IHA/RVA法对变异前后径流情势进行对比分析,并量化分析气候变化和人类活动对径流改变的影响.结果显示:1)1970-2007年无定河流域径流量呈现显著减小趋势,并在1971年发生减小突变;2)突变后径流情势发生改变,径流量年内分配、极端流量及其发生时间、频率、平均延时等均具有较高改变程度;3)枯水期平均流量、最小90日平均流量和高流量平均延时可作为识别无定河流域径流量突变的关键指标;4)无定河流域径流量的减少受到气候变化和人类活动的综合影响,且气候变化和人类活动对径流量减少的贡献率分别为36.57%和63.43%.      

近50ａ来南疆气候变化对可利用降水量的影响

选择1951~2006年逐月降水和温度资料,计算出南疆年平均蒸发量及可利用降水量.在详细分析了50 a来南疆地区降水、气温、蒸发及可利用降水量变化特征的基础上,采用逐步回归周期分析法对降水、气温和可利用降水量进行了模拟,并对未来5 a上述要素进行了预测.结果表明,20世纪70年代以后南疆地区的温度、降水和蒸发变化基本呈上升态势,可利用降水量却呈现出偏多和偏少交替的波状变化特征.这说明气候变暖,可利用降水量不一定增多,未来5 a南疆地区可利用降水量将可能减少.     

酒泉市肃州区近55a的气候变化特征、突变与周期分析

利用1951-2005年酒泉市肃州区气象观测站平均气温和降水量资料,运用多年趋势线、5a滑动趋势线、Mann-Kendall突变检验、滑动t检验和小波分析等方法对肃州区气候变化的主要特征、突变特点和周期特征进行分析.结果表明:近55a来,肃州区年平均气温呈明显上升趋势,年降水量呈微弱减少趋势.年平均气温和年平均降水量均有明显的突变,前者突变年份在1992年,后者突变年份较多,以1995年最显著.Morlel小波及其功率谱分析表明,年平均气温和年平均降水量的变化周期具有多尺度、多层次和多分辨的特性结构.其中,年平均气温存在21a和7.14 a(P≤0.16)的优势周期,年降水量存在21a,10.87a,9.09a和6.41a(P≤0.1)的显著周期,且中长期优势周期一致,中短周期不同.