Global aridification in the second half of the 20th century and its relationship to large-scale climate background

The variation in surface wetness index (SWI), which was derived from global gridded monthly precipi- tation and monthly mean surface air temperature datasets of Climatic Research Unit (CRU), from 1951― 2002 over global land was analyzed in this paper. The characteristics of the SWI variation in global continents, such as North America, South America, Eurasia, Africa, and Australia, were compared. In addition, the correlation between the SWI variation of each continent (or across the globe) and the large-scale background closely related to SST variations, which affects climate change, was analyzed. The results indicate that the SWI variation shows distinct regional characteristics in the second half of the 20th century under global warming. A drying trend in the last 52 years occurred in Africa, Eurasia, Australia and South America, most obviously in Africa and Eurasia. North America shows a wetting trend after 1976. A 30-year period of dry-wet oscillation is found in South America and Australia; the latest is in a drying period in two regions. The results also revealed that global warming has changed the dry-wet pattern of the global land. South America and Australia have a drying trend despite in- creases in precipitation. This indicates that increases in surface air temperature cannot be ignored in aridification studies. Global dry-wet variation is closely related to large-scale SST variations: the drying trend in Africa and Eurasia and the wetting trend in North America are correlated with Pacific Decadal Oscillation (PDO); the interdecadal oscillation of SWI in South America and Australia is consistent with the interdecadal variation in Southern Oscillation Index (SOI).     

Relationship between sea surface salinity and ocean circulation and climate change

Based on Argo sea surface salinity(SSS) and the related precipitation(P), evaporation(E), and sea surface height data sets, the climatological annual mean and low-frequency variability in SSS in the global ocean and their relationship with ocean circulation and climate change were analyzed. Meanwhile, together with previous studies, a brief retrospect and prospect of seawater salinity were given in this work. Freshwater flux(E-P) dominated the mean pattern of SSS, while the dynamics of ocean circulation modulated the spatial structure and low-frequency variability in SSS in most regions. Under global warming, the trend in SSS indicated the intensification of the global hydrological cycle, and featured a decreasing trend at low and high latitudes and an increasing trend in subtropical regions. In the most recent two decades, global warming has slowed down, which is called the"global warming hiatus". The trend in SSS during this phase, which was different to that under global warming, mainly indicated the response of the ocean surface to the decadal and multi-decadal variability in the climate system, referring to the intensification of the Walker Circulation. The significant contrast of SSS trends between the western Pacific and the southeastern Indian Ocean suggested the importance of oceanic dynamics in the cross-basin interaction in recent decades. Ocean Rossby waves and the Indonesian Throughflow contributed to the freshening trend in SSS in the southeastern Indian Ocean, while the increasing trend in the southeastern Pacific and the decreasing trend in the northern Atlantic implied a long-term linear trend under global warming. In the future, higher resolution SSS data observed by satellites, together with Argo observations, will help to extend our knowledge on the dynamics of mesoscale eddies, regional oceanography, and climate change.     

21世纪以来泛北极湖泊水位变化时空特征及原因探讨

在全球气候变暖和极端气候事件增加的背景下,流域水文循环过程受到的影响越来越强烈,导致湖泊水位变化表现出复杂的时空特征。而泛北极地区是地球上湖泊数量与面积分布最为集中的区域之一,该地区湖泊对气候变化响应非常敏感。因此,了解这些湖泊近期水文变化特征十分必要。本研究共搜集了36个泛北极大型湖泊(>500 km²)基于遥感或站点观测的近20年水位数据,分析其时空变化特征。本文使用线性回归模型来估算湖泊水位的变化趋势,进而利用皮尔逊相关分析了其主要水文影响变量和大气环流机制,并运用Mann-Kendall突变检验法探讨了水位突变的原因。结果表明,泛北极湖泊的水位整体上呈现不同程度上升(平均速率为0.013 m/a),有23个(64%)湖泊的水位呈上升趋势;研究湖泊中有10个通过90%统计显著性检验。其中,水位上升速率最大的湖泊是位于哈萨克斯坦的腾吉兹湖,上升速率为0.078 m/a。泛北极湖泊水位的波动主要与径流有关,有19个(53%)湖泊的水位波动与径流的增加更为相关;相比而言,位于亚洲的极地湖泊水位的上升与流域蒸发的降低显著相关,尤其是库苏古尔湖。从区域大气环流影响来看,泛北极湖泊水位变化主要与厄尔尼诺-南方涛动有关,其次是北极涛动和北大西洋涛动。本研究有助于加深对泛北极湖泊近20年水位变化规律及气候影响特征的科学理解。     

地震和潮汐对气候波动变化的影响

2004年12月26日印尼地震海啸后,全球低温冻害和暴雪灾害频繁发生."潮汐调温说"和"深海巨震降温说"是一种合理的解释.根据"潮汐调温说"和"深海巨震降温说"理论,2005年以后全球气温将因为地震海啸和强潮汐南北震荡而降低.2009年11月至2010年1月低温暴雪袭击北半球,西方科学家也承认2000～2010年气候的...     

Climate change and global cycling of persistent organic pollutants: A critical review

Climate warming, one of the main features of global change, has exerted indelible impacts on the environment, among which the impact on the transport and fate of pollutants has aroused widespread concern. Persistent organic pollutants (POPs) are a class of pollutants that are transported worldwide. Determining the impact of climate warming on the global cycling of POPs is important for understanding POP cycling processes and formulating relevant environmental policies. In this review, the main research findings in this field over the past ten years are summarized and the effects of climate warming on emissions, transport, storage, degradation and toxicity of POPs are reviewed. This review also summarizes the primary POP fate models and their application. Additionally, research gaps and future research directions are identified and suggested. Under the influence of climate change, global cycling of POPs mainly shows the following responses. (1) Global warming directly promotes the secondary emission of POPs; for example, temperature rise will cause POPs to be re-released from soils and oceans, and melting glaciers and permafrost can re-release POPs into freshwater ecosystems. (2) Global extreme weather events, such as droughts and floods, result in the redistribution of POPs through intense soil erosion. (3) The changes in atmospheric circulation and ocean currents have significantly influenced the global transport of POPs. (4) Climate warming has altered marine biological productivity, which has changed the POP storage capacity of the ocean. (5) Aquatic and terrestrial food-chain structures have undergone significant changes, which could lead to amplification of POP toxicity in ecosystems. (6) Overall, warming accelerates the POP volatilization process and increases the amount of POPs in the environment, although global warming facilitates their degradation at the same time. (7) Various models have predicted the future environmental behaviors of POPs. These models are used to assist governments in comprehensively considering the impact of global warming on the environmental fate of POPs and therefore controlling POPs effectively. Future studies should focus on the synergistic effects of global changes on the cycling of POPs. Additionally, the interactions among global carbon cycling, water cycling and POP cycling will be a new research direction for better understanding the adaptation of ecosystems to climate change.     

C-Isotope stratigraphy,a monitor of paleoenvironmental change: A case study from the early cretaceous

Today's disturbance of the global carbon cycle induced by anthropogenic processes has raised new interest in the history of the global carbon cycle and its relationship to climate and other geochemical cycles. Carbon-isotope stratigraphy proves to be most useful as a monitor of the history of the carbon-cycle during the last 200 million years. In the introductory paragraphs of this review the mode of functioning of the global carbon-cycle is summarized and the connection between carbon-cycle and carbon isotope geochemistry is documented. A case study on the disturbance of the global carbon cycle during the Aptian-Albian is presented. The disturbance of the carbon cycle lasting up to millions of years is recorded in the carbon-isotope stratigraphy of pelagic sediments. It is superimposed on high frequency sedimentological cycles, related to climate and oceanographic cycles of 20, 40 or 100 ky duration. The data reviewed suggest that the change in the global carbon system was linked to a global acceleration of geochemical cycles triggered by a long-term change in atmospheric CO₂ controlled by the rate of sea-floor formation and by volcanic activity. Increased accumulation rates of terrestrial material and terrestrial organic matter in marine sediments may be used as an indicator of an intensified hydrological cycling resulting in higher water-discharge rates. An intensification of the Aptian-Albian water cycle is further reflected in continental sediments monitoring a period of elevated humidity. An increase in water discharge rates should have affected the transfer rate of dissolved nutrients from continents to oceans. Elevated concentrations of phosphorus may have led to an increase in Aptian-Albian oceanic productivity enhancing the transfer of marine organic matter from the oceanic into the sedimentary reservoir. Increased productivity, increased bulk sedimentation rates and poorly oxygenated deep-water led to increased preservation of marine and terrestrial organic matter in marine sediments. The accelerated output of marine organic carbon from the oceanic reservoir is ultimately registered in the positive carbon-isotope excursion of the marine carbonate carbon-isotope stratigraphy.     

鄱阳湖流域过去1000 a径流模拟以及对气候变化响应研究

为研究过去千年尺度径流变化及其对气候变化的响应,以长江中游鄱阳湖流域为研究区,运用气候模式CCSM4和ECHAM5模拟过去1000 a气候数据,空间降尺度后驱动水文模型模拟了鄱阳湖流域过去近千年流域径流序列.利用快速傅里叶变换、小波分析等手段,分析流域极端径流变化特征、周期和该流域旱涝事件发生频率.结果表明:2种气候模式均能反映出中世纪暖期及小冰期阶段的干湿交替变化,且小冰期内中干旱状态维持时间较长;径流的丰枯变化与降水量变化具有较好的对应关系.CCSM4和ECHAM5模式下发生旱涝灾害与极大极小降水事件发生频率基本相同,径流丰枯变化与降水变化周期相近,均具有30 a左右的主周期,10~15、7 a左右的子周期.小波系数模平方图中30 a左右显著的能量信号揭示了该周期与北太平洋气候的主要环流机制的太平洋年代际振荡周期相近,因此,大气环流涛动是造成气候-水文变化的主要原因.研究结果拓展了基于近代60 a观测记录的流域水文变化的认识,探讨了千年时间长度下流域干湿变化特征和水文对气候响应的动力机制,有助于全面系统认识长江中游在全球气候暖化背景下旱涝极端水文事件的发生机制与变化规律.     

On North Pacific circulation and associated marine debris concentration

Marine debris in the oceanic realm is an ecological concern, and many forms of marine debris negatively affect marine life. Previous observations and modeling results suggest that marine debris occurs in greater concentrations within specific regions in the North Pacific Ocean, such as the Subtropical Convergence Zone and eastern and western "Garbage Patches". Here we review the major circulation patterns and oceanographic convergence zones in the North Pacific, and discuss logical mechanisms for regional marine debris concentration, transport, and retention. We also present examples of meso- and large-scale spatial variability in the North Pacific, and discuss their relationship to marine debris concentration. These include mesoscale features such as eddy fields in the Subtropical Frontal Zone and the Kuroshio Extension Recirculation Gyre, and interannual to decadal climate events such as El Ni?o and the Pacific Decadal Oscillation/North Pacific Gyre Oscillation.     

华北降水年代际变化特征及相关的海气异常型

利用近50年华北地区26个站逐月降水观测资料和全球大气海洋分析资料,分析了华北降水的年代际变化特征及其和全球海气系统年代际变化的关系.对华北降水距平指数变化分析表明,近50年来华北降水具有减少的总体趋势,叠加在该趋势之上的是年代际变化,其中1965年和1980年发生了两次跃变,使得20世纪80年代干旱尤为严重.在对华北地区降水年代际变化特征分析的基础上,揭示了与华北降水年代际异常相伴随的大气环流和上层海洋热力异常型.结果表明,华北降水年代际异常与太平洋上层海洋热力状况异常有显著关系,主要表现为太平洋年代际振荡（PDO）与华北降水异常的相关.在年代际时间尺度上,华北干旱与上层海洋热力及大气环流异常的配置关系如下：当华北地区干旱时,则热带中东太平洋海温偏高,北太平洋中部海温偏低,即太平洋上主要表现为PDO暖位相,全球大部分地区（包括华北地区）气温偏高,青藏高原地区气温偏低,日本北部及东西伯利亚气压异常偏低,华北及其以南大片地区气压偏高,华北地区由异常西北风控制,不利于水汽向华北地区输送.     

Connection of sea level variability between the tropical western Pacific and the southern Indian Ocean during recent two decades

Based on the merged satellite altimeter data and in-situ observations,as well as a diagnosis of linear baroclinic Rossby wave solutions,this study analyzed the rapidly rise of sea level/sea surface height(SSH)in the tropical Pacific and Indian Oceans during recent two decades.Results show that the sea level rise signals in the tropical west Pacific and the southeast Indian Ocean are closely linked to each other through the pathways of oceanic waveguide within the Indonesian Seas in the form of thermocline adjustment.The sea level changes in the southeast Indian Ocean are strongly influenced by the low-frequency westward-propagating waves originated in the tropical Pacific,whereas those in the southwest Indian Ocean respond mainly to the local wind forcing.Analyses of the lead-lag correlation further reveal the different origins of interannual and interdecadal variabilities in the tropical Pacific.The interannual wave signals are dominated by the wind variability along the equatorial Pacific,which is associated with the El Ni?o-Southern Oscillation;whereas the interdecadal signals are driven mainly by the wind curl off the equatorial Pacific,which is closely related to the Pacific Decadal Oscillation.     

气候变化对湖库水环境的潜在影响研究进展

本文着重归纳气候变化对湖库热力特性、冰期、溶解氧、营养盐、浮游植物和水生植物等方面的影响规律,探讨气候变化对湖库水环境潜在影响的区域差异,讨论现有研究方法的优缺点和发展前景.研究表明,气候变暖对湖库物理过程的影响最为显著;热带草原气候和温带海洋性气候对于气候变暖和降雨变化的响应较其他气候类型突出;气候变化对湖库水环境的影响效果具有两面性.通过分析各气候类型中气候变暖对磷水平的潜在影响差异表明,亚热带季风气候的湖库更可能受气候变暖的影响趋于富营养状态.在今后研究中,建议深入开展各气候类型中区域性气候变化对湖库水环境影响的实例研究.     

The Barents Sea impact study (BASIS): methodology and first results

Global and climate changes are subject to scientific, societal and political debates. Recent observational evidence and results of global climate models have identified the circumpolar North as a region particularly susceptible to future climate change. To understand and assess the consequences of these changes for environmental and societal components of the European Arctic, the Barents Sea Impact Study (BASIS), an EU-funded integrated regional impact study (IRIS) has been carried out (ENV4-CT-97-0637). In common with global integrated assessments (IAs), IRISs also take a holistic view on climate change and its impact. Contrary to IAs, however, IRISs adopt a regional to sub-regional spatial scale. BASIS was carried out by an interdisciplinary team of specialists from 13 institutions in 6 countries. Major results pertain to impacts of possible climate change on marine and terrestrial ecosystems, freshwater hydrology, marine trace gas budgets, forestry and fishery. However, in this paper we focus on the major methodological aspects of an IRIS in general and on methods applied in BASIS in particular.     

Downscaling IPCC control run and future scenario with focus on the Barents Sea

Global atmosphere-ocean general circulation models are the tool by which projections for climate changes due to radiative forcing scenarios have been produced. Further, regional atmospheric downscaling of the global models may be applied in order to evaluate the details in, e.g., temperature and precipitation patterns. Similarly, detailed regional information is needed in order to assess the implications of future climate change for the marine ecosystems. However, regional results for climate change in the ocean are sparse. We present the results for the circulation and hydrography of the Barents Sea from the ocean component of two global models and from a corresponding pair of regional model configurations. The global models used are the GISS AOM and the NCAR CCSM3. The ROMS ocean model is used for the regional downscaling of these results (ROMS-G and ROMS-N configurations, respectively). This investigation was undertaken in order to shed light on two questions that are essential in the context of regional ocean projections: (1) How should a regional model be set up in order to take advantage of the results from global projections; (2) What limits to quality in the results of regional models are imposed by the quality of global models? We approached the first question by initializing the ocean model in the control simulation by a realistic ocean analysis and specifying air-sea fluxes according to the results from the global models. For the projection simulation, the global models’ oceanic anomalies from their control simulation results were added upon initialization. Regarding the second question, the present set of simulations includes regional downscalings of the present-day climate as well as projected climate change. Thus, we study separately how downscaling changes the results in the control climate case, and how scenario results are changed. For the present-day climate, we find that downscaling reduces the differences in the Barents Sea between the original global models. Furthermore, the downscaled results are closer to observations. On the other hand, the downscaled results from the scenario simulations are significantly different: while the heat transport into the Barents Sea and the salinity distribution change modestly from control to scenario with ROMS-G, in ROMS-N the heat transport is much larger in the scenario simulation, and the water masses become much less saline. The lack of robustness in the results from the scenario simulations leads us to conclude that the results for the regional oceanic response to changes in the radiative forcing depend on the choice of AOGCM and is not settled. Consequently, the effect of climate change on the marine ecosystem of the Barents Sea is anything but certain.     

青海湖地区环境变化对动物区系演变影响的探讨

青海湖地区近百年来由于气候干暖化趋势增强,湖周植被、土地退化,人类经济活动加剧,湖区青藏高原动物成分的种类和数量减少,但蒙新及华北动物区系成分则有增加趋势,致使该区动物区系成分发生显著变化。从青海湖地区动物区系形成来看,决定动物区系演变的原因主要是气候、生物等生态因子的综合作用,人为因子影响仅在近30年来才日益突出。     

Conceptual model about the interaction between El Nio/Southern Oscillation and Quasi-Biennial Oscillation in far west equatorial Pacific

In the tropical Pacific region, El Ni?o/Southern Os- (COADS SST from 1945 to 1993) in the eastern cillation (ENSO) and the Quasi-Biennial Oscillation in (150°W-90°W, 5°S-5°N) and the observed SST far west equatorial Pacific (QBOWP) are two most and zonal wind in the far western equatorial Pacific prominent interannual variation phenomena. The for- (120°-140°E, 0°-10°N) (Fig.1), in the eastern Pa- mer is characterized by coupled SST-wind variability cific the period of S…     

Conceptual model about the interaction between El Ni?o/Southern Oscillation and Quasi-Biennial Oscillation in far west equatorial Pacific

Interaction between the Quasi-Biennial Oscillation in far west equatorial Pacific (QBOWP) and the El Ni?o/Southern Oscillation (ENSO) is studied using a new conceptual model. In this conceptual model, the QBOWP effects on ENSO are achieved through two ways: (1) the oceanic Kelvin wave along equatorial Pacific, and (2) the Atmospheric Walker Circulation anomaly, while ENSO effects on QBOWP can be accomplished by the atmospheric Walker Circulation anomaly. Diagnosis analysis of the model results shows that the Atmospheric bridge (Walker circulation) plays a more important role in interaction between the ENSO and QBOWP than the oceanic bridge (oceanic Kelvin wave along equatorial Pacific); It is found that by the interaction of the ENSO and QBOWP, a free ENSO oscillation with 3–5 years period could be substituted by a oscillation with the quasi-biennial period, and the dominant period of SST anomaly and wind anomaly in the far west equatorial Pacific tends to be prolonged with enhanced ENSO forcing. Generally, the multi-period variability in the coupled Atmosphere-Ocean System in the Tropical Pacific can be achieved through the interaction between ENSO and QBOWP.     

由TOPEX/Poseidon和Jason-1/2探测的1993—2012中国海海平面时空变化

海平面变化是社会经济发展和科学研究的重要内容.利用1993年1月至2012年12月共20年的TOPEX/Poseidon、Jason-1和Jason-2卫星测高数据,研究中国海海平面的时空变化.首先通过三颗卫星伴飞阶段数据得到三颗卫星之间的逐点海面高系统偏差,进行逐点海面高改正,建立了20年的中国海海面高异常时间序列.分析了中国海海面高异常空间分布,给出了1月到12月月均平均海平面异常的空间变化规律.分析了中国海海面高异常的时变规律,分别给出了年、季度和月的海面上升速率.利用小波分析研究了中国海海面高异常周期变化规律,分别给出了渤海、黄海、东海和南海的海面高变化周期.讨论了ENSO对海面高异常的影响.     

Southern Ocean deglacial record supports global Younger Dryas

In Northern Hemisphere deglaciation records, the transition from the last glacial to the Holocene indicates a rapid return to near-glacial conditions during the Younger Dryas, whereas their Southern Hemisphere ice core counterparts record two separate cooling events: the Antarctic Cold Reversal and the Oceanic Cold Reversal. Spatial distribution and relative timing of these events in both hemispheres are central for our understanding of causes and mechanisms of abrupt climate change. To date, no marine record from the southern mid-latitudes conclusively demonstrates that the Younger Dryas was a significant event in the Southern Ocean. Here, we present high-resolution oxygen isotope and iron content records of a radiocarbon-dated sedimentary sequence from the Great Australian Bight, which constrains oceanic and atmospheric changes during the last deglaciation. Oxygen isotopes from planktonic foraminifera indicate two rapid cold reversals (between 13.1 and 11.1 kyr BP) separated by a brief warming. The sedimentary iron content, interpreted as a proxy for wind strength, indicates a simultaneous change in atmospheric circulation pattern. Both records demonstrate the existence of cooling events in the Southern Hemisphere, which are synchronous with the Northern Hemisphere Younger Dryas cold reversal (between 12.9 and 11.5 kyr BP). Such evidence for the spatial distribution and timing of abrupt climatic fluctuations is essential data for groundtruthing results derived from global climate models.     

太平洋年代际振荡与南北半球际大气质量振荡及东亚季风的联系

众多研究表明,太平洋年代际振荡(PDO)与东亚季风以及我国气候的年代际异常存在显著影响,然而其影响途径及机制仍不明确.本文分别分析了年代际尺度上的太平洋年代际振荡(PDO)、南北半球际大气质量振荡(IHO)以及东亚季风的变化特征,据此建立了三者之间的关系,并进一步分析了它们对我国东部冬夏两季年代际气候异常的影响,所得主要结果包括:(1)PDO与IHO以及东亚季风强度具有明显的年代际波动特征,三者之间存在较好联系,其中它们在70年代和90年代后期处于负位相,而在80年代至90年代中期均处于正位相期.PDO和IHO对全球大范围的低层气温异常,以及大气质量迁移尤其是东半球30°S-50°N区域的质量变化具有显著并且空间一致的影响;(2)当PDO为正位相时,整层大气质量年代际异常呈偶极型的自东半球向西半球太平洋区域输出,造成了南北半球际以及海陆间大气质量迁移,同时引起Walker环流的上升和下沉支位置变化,以及越赤道大气质量流的向北异常输送,并由此建立起东亚季风与PDO和IHO之间的联系;(3)PDO年代际异常与冬夏季节蒙古地区地表气压变动存在密切联系.当PDO指数增强时,冬夏季850hPa均出现显著反气旋风场异常,并在我国东部形成异常北风,从而显著影响东亚冬夏季风强度变化.与之对应,PDO指数与我国东部大部分地区的站点气温、降水的年代际分量保持显著的同期相关.     

全球变暖对淡水湖泊浮游植物影响研究进展

全球变暖对湖泊生态系统的影响已经成为近年来湖沼学领域的研究热点.本文首先列举了目前研究全球变暖对淡水湖泊浮游植物影响的常用方法:监测数据分析、时空转换、遥感信息提取、控制实验、模型预测和古湖沼学技术等.研究结果表明气候变暖导致的气温升高、湖泊热力分层提前破坏以及无冰期提前等因素可导致春季物候提前;在全球变暖大背景下浮游植物群落结构正朝着蓝藻占优的方向发展,但是不同地区以及不同物种对全球变暖的响应不一致.在营养盐充足的湖泊中,由于全球变暖延长了浮游植物生长季节等,从而能提高浮游植物初级生产力;但在贫营养湖泊中,浮游植物初级生产力与变暖趋势甚至可能呈负相关.由于生态系统往往是多因子的共同作用,这也使得全球变暖对浮游植物群落的影响效应复杂化,区分各因子的净影响份额是目前研究的一个难点;全球变暖引起的风场改变会促进浅水湖泊中营养盐从底泥的释放,同时也会增加水体中悬浮物的浓度而影响水下光场,因此开展气候变化对再悬浮及浮游植物群落结构的影响可能是将来研究的一个切入点.