从地球系统的观点看气候突变

在地球的气候史中,经历了许多次气候突变事件。这些突变对地球表层系统的演变与进化产生了巨大影响。随着全球气候变暖的持续发展,人类赖以生存的气候环境正在经历重大变化。如何科学地理解和认识这些变化,尤其是气候突变。是人类寻求对策,应对气候变化,保护自己持续发展的科学基础。文中从地球系统的角度对气候突变的科学问题进行了探讨,认为对气候突变的研究不应仅局限于大气圈,而应该对地球系统的整体变化进行研究。     

气候变化及其未来情景

论述了百余年来气候变化的事实及对未来情景的预估。1861年以来,全球平均温度升高了0.6±0.2℃。20世纪90年代是20世纪最暖的10a。近百年来,降水分布也发生了变化,大陆地区尤其是中高纬地区降水增加,非洲等一些地区降水减少。气候模式模拟表明:全球平均地表气温到2100年时将比1990年上升1.4￣5.8℃。21世纪全球平均降水将会增加,但大部分年平均降水增加的区域很可能同时出现大的年际变化。全球平均海平面到2100年时将比1990年上升0.09￣0.88m。北半球雪盖和海冰范围将进一步缩小。未来,若干极端事件发生的频率会增加。     

全球变暖与地球“三极”气候变化

北极、南极和青藏高原分别是地球的最北端、最南端和海拔最高的高原,被称为地球“三极”。地球三极是全球气候变化的关键区与敏感区,在区域及全球气候系统中的重要性日益凸显。本文回顾了该领域的最新研究成果,重点阐述了地球三极气候年代际变化的基本特征及其对区域气候的影响,探究了在全球气候变暖背景下地球三极气候变化之间的潜在联系,讨论并展望了未来地球三极气候变化研究所面临的挑战。     

近54年中国地面气温变化

采用国家基准气候站和基本气象站地面月平均气温资料,在严格质量控制和非均一性订正的基础上,分析了1951年以来中国大陆地区近地表年和季节平均气温演化的时间与空间特征.结果表明,我国近54年来年平均地表气温变暖幅度约为1.3℃,增温速率接近0.25℃/10 a,比全球或半球同期平均增温速率高得多.全国大范围增暖主要发生在近20余年.气温变化的季节差异和空间特征与前人分析结论基本一致,冬季增温速率高达0.39℃/10 a,春季为0.28℃/10 a,秋季0.20℃/10 a,夏季增温速率最小,但也达到0.15℃/10 a.我国20世纪80年代初期开始的明显增暖主要表现在冷季,但进入90年代以来夏季增暖也日趋明显.从区域上看,中国大陆地区最明显的增温发生在北方和青藏高原地区,而西南的四川盆地和云贵高原北部仍维持弱的降温趋势.值得提出的是,作者给出的结果尚未考虑城镇化对地面气温观测记录的影响.     

大连地区近44 a冬季气温的变化特征

利用大连地区1960-2004年的气温资料，应用一元线性回归、小波分析、气候趋势系数等方法，对大连地区气温的季节一年际变化特征进行了研究，着重分析了该地区冬季气温年际、年代际变化的时空特征。结果发现，大连四季都有增暖的变化趋势，其中春、冬两季增暖的速度最快；20世纪60年代大连地区的冬季气温呈下降趋势，从70年代以后，冬季气温呈明显的增暖趋势，特别是90年代以后这种增暖趋势十分显著，而且增暖的幅度全区分布不均匀；大连地区冬季气温与全国冬季气温年代际变化的步调基本一致。     

1.5℃增暖对全球和区域影响的研究进展

《巴黎协定》明确提出将全球平均升温控制在相对于工业化前水平2℃以内,并努力将其控制在1.5℃以内,以降低气候变化的风险与影响。随后,《联合国气候变化框架公约》（UNFCCC）邀请IPCC筹备关于1.5℃增暖影响及温室气体排放途径的特别报告,为UNFCCC谈判提供科学依据。通过回顾近期发表的一些成果发现,在1.5℃到2℃的不同升温条件下,很多极端天气事件发生的概率将增加。2℃条件下一些易受威胁的系统,如生态系统和农业系统,将承受全球变暖带来的严重后果;海平面明显上升,珊瑚礁锐减,季风降水减弱等影响将进一步加强。同时,不同地区对全球不同程度增暖的响应也存在很大差异。总的说来,相较于2℃增暖而言,将增暖控制在1.5℃以内能进一步减小气候变化影响的风险。然而,要把全球增暖控制在1.5℃内具有极大的挑战性,并且目前对1.5℃增暖的影响认识仍然十分不足。定量分析2℃和1.5℃增暖对不同区域自然和人类系统造成的影响差异,需要更高分辨率的模式以及更多针对2℃和1.5℃增暖影响而设计的专门试验支持。     

冰冻圈变化及其对中国气候的影响

The cryosphere is a prominent factor in and an indicator of global climate change. It serves one of the most direct and sensitive feedbacks in the climate system, and plays an important role in the earth＇s climate system. Cryospheric research has attracted unprecedented attention in the context of global warming, and is now one of the most active areas in studies of global change, sustainable development, and the climate system. This paper addresses recent and potential future changes in the cryosphere both globally and within China under the background of global warming. Particular attention is paid to progress toward understanding the impacts of the Tibetan Plateau and Eurasian snow cover, Arctic and Antarctic sea ice, and permafrost and glaciers on Chinese climate. The future development of cryospheric research in China is also discussed.     

雅鲁藏布江流域气温变化特征及趋势分析

通过分析1980～2005年间雅鲁藏布江流域7个气象台站平均的气温变化趋势和气候系数变化,并进一步分析了1960～2005年间该流域中游日喀则站和下游林芝站气温的变化趋势,研究了该流域气温变化对全球变暖的响应.结果表明,1980～2005年间雅鲁藏布江流域的气温呈现逐渐升高的趋势,尤其是夜间气温和冬、春季气温的升高更显著,而且该流域变暖幅度高于整个高原的平均增幅,因此该流域对全球变暖的响应程度也较整个高原更为显著;而该流域中游地区的增温幅度要明显高于下游地区的,即该流域中游地区的增暖较下游地区的更为显著.     

The response of currents in Trinity Bay,Newfoundland, to local wind forcing

Abstract

Analysis of current measurements taken between June and October 1984 at four moorings in Trinity Bay, Newfoundland, is discussed. The alongshore component of current exhibits baroclinic fluctuations coherent with the along‐bay component of wind stress at periods between 3 and 7 days. A two‐layer model of internal Kelvin waves propagating around the perimeter of an elongated bay and forced by a spatially uniform wind stress is presented. The observations support several features of the model response to wind forcing. Along the side of the bay on which Kelvin waves are incoming, the amplitude of the response increases into the bay and decreases with increasing frequency. Along the outgoing side of the bay the amplitude of the response generally shows a maximum at a frequency between 0.2 and 0.3 cpd. The phase lag between current and wind is consistent with a forced response. An example is given of upwelling and downwelling on opposite sides of the bay in agreement with the model behaviour.     

全球变暖背景下西太平洋副热带高压变化的探讨

为去除全球变暖等压面抬升的影响、客观地反映西太平洋副热带高压的真实变化,本研究使用了1951~2017年NCEP/NCAR的月平均500hPa高度场再分析资料以及国家气候中心提供6~8月的大气环流指数,基于去除全球变暖影响的西太平洋副热带高压表征线,研究探讨了全球变暖背景下西太平洋副热带高压的变化。研究表明,去除全球变暖影响前(后)西太平洋副热带高压有面积指数增大(减小)、强度指数增强(减弱)和西伸脊点指数西伸(东退)的演变特征。可见,全球变暖可能是西太平洋副热带高压面积、强度和东西位置发生变化的原因之一。     

The potential impacts of warmer-continent-related lower-layer equatorial westerly wind on tropical cyclone initiation

Global climate models predict that the increasing Amazonian-deforestation rates cause rising tempera- tures (increases of 1.8℃ to 8℃ under different conditions) and Amazonian drying over the 21st century. Observations in the 20th century also show that over the warmer continent and the nearby western South At- lantic Ocean, the lower-layer equatorial westerly wind (LLEWW) strengthens with the initiation of tropical cyclones (TCs). The warmer-continent-related LLEWW can result from the Coriolis-force-induced deflection of the cross-equatorial flow (similar to the well-known heat-island effect on sea breeze) driven by the enhanced land-sea contrast between the warmer urbanized continents and relatively cold oceans. This study focuses on the processes relating the warmer-continent-related LLEWW to the TC initiation and demonstrates that the LLEWW embedded in trade easterlies can directly initiate TCs by creating cyclonic wind shears and forming the intertropical convergence zone. In addition to this direct effect, the LLEWW combined with the rotating Earth can boost additional updraft vapor over the high sea-surface temperature region (factor 1), facilitating a surface-to-midtroposphere moist layer (factor 2) and convective instability (factor 3) followed by diabatic processes. According to previous studies, the diabatic heating in a finite equatorial region also activates TCs (factor 4) on each side of the Equator with weak vertical shear (factor 5). Factors 1-5 are favorable conditions for the initiation of severe TCs. Statistical analyses show that the earliest signal of sustained LLEWW not only leads the earliest signal of sustained tropical depression by >3 days but also explains a higher percentage of total variance.     

近百年全球气候变暖的分析

本文对比分析了IPCC，Vinnikov，Jones及Hansen的北半球，南半球及全球共12个地面温度序列，以及中国的气温序列。资料为1880—1991年。近百年气候变暖的速度为0.5℃/100 a。温度的长期变化趋势占序列总方差60%以上。但气候变暖有突变性，在1890年代中，1920年代中及1970年代末有3次突然气候变暖。分析表明，总的变暖趋势与CO2浓度及太阳活动有密切关系。火山活动也可能有一定作用。但前两次突然变暖可能与火山活动沉寂有关。最后一次突然变暖则可能是温室效应加剧的结果。     

C‐band SAR backscatter characteristics of Arctic sea and land ice during winter

Abstract

Synthetic Aperture Radar (SAR) data has become an important tool for studies of polar regions, due to high spatial resolution even during the polar night and under cloudy skies. We have studied the temporal variation of sea and land ice backscatter of twenty‐four SAR images from the European Remote Sensing satellite (ERS‐1) covering an area in Lady Ann Strait and Jones Sound, Nunavut, from January to March 1992. The presence of fast ice in Jones Sound and glaciers and ice caps on the surrounding islands provides an ideal setting for temporal backscatter studies of ice surfaces. Sample regions for eight different ice types were selected and the temporal backscatter variation was studied. The observed backscatter values for each ice type characterize the radar signatures of the ice surfaces. This time series of twenty‐four SAR images over a 3‐month period provides new insights into the degree of temporal variability of each surface. Ice caps exhibit the highest backscatter value of ‐3.9 dB with high temporal variability. Valley glacier ice backscatter values decrease with decreasing altitude, and are temporally the most stable, with standard deviations of 0.08–0.10 dB over the 90‐day period.

First‐year ice and lead ice show a negative trend in backscatter values in time and a positive correlation of up to 0.59 with air temperature over the 90‐day period. For first‐year ice and lead ice, episodes of large temperature fluctuations (±12°C) are associated with rapid changes in backscatter values (±2 dB). We attribute the backscatter increase to a temperature‐induced increase in brine volume at the base of the snow pack. Multi‐year ice, conglomerate ice and shore ice are relatively stable over the 3‐month period, with a backscatter variation of only a few dBs. An observed lag time of up to three days between backscatter increase/decrease and air temperature can be attributed to the insulation effect of the snow cover over sea ice. The net range of the backscatter values observed on the most temporally stable surface, valley glacier ice, of about 0.30 dB indicates that the ERS‐1 SAR instrument exceeds the 1 dB calibration accuracy specified for the Alaska SAR Facility processor for the three winter months.     

全球变暖在继续

基于全球和中国的观测资料指出,无论全球还是中国,2001-2010年都是有仪器观测记录以来最暖的10年。虽然这10年内的温度上升趋势很弱,但并不意味着气候变暖已经停止。分季节来看,近10年（2001-2010年）冬季中国东北及新疆的气温低于前10年（1991-2000年）。然而,这种区域性和季节性的温度下降并没有影响全国、全年保持变暖的趋势。     

1.5～4℃升温阈值下亚洲地区气候变化预估

基于18个CMIP5模式在RCP情景下的模拟结果,综合分析了全球升温1.5～4℃阈值下亚洲地区平均温度和降水以及极端温度和降水的变化,并着重对比了1.5℃与2℃升温阈值下的异同。结果表明：相比工业化前,在全球升温1.5℃、2℃、3℃和4℃阈值下,亚洲区域平均温度将分别升高2.3℃、3.0℃、4.6℃和6.0℃,高纬度地区的响应大于中低纬地区;降水分别增加4.4%、5.8%、10.2%和13.0%,存在明显的区域差异。极热天气将增加,极冷天气将减少;极端降水量的变率将会加大。与2℃升温阈值相比：1.5℃阈值下亚洲平均温度的上升幅度将降低0.5～1.0℃以上,大部分地区的降水增幅减少5%～20%,但西亚和南亚西部的降水则偏多10%～15%;极端高温的增温幅度在亚洲地区均匀下降,而极端低温的增温幅度在亚洲中高纬地区降低显著;亚洲大部分地区极端降水的增加幅度减弱,但在西亚会增强。全球升温1.5℃和2℃时,亚洲发生非常热天气的概率相比基准期（1861-1900年）均将增加1倍以上,发生极热天气的概率普遍增加10%;发生极端强降水的概率增加10%。     

Major modes of short-term climate variability in the newly developed NUIST Earth System Model (NESM)

A coupled earth system model(ESM) has been developed at the Nanjing University of Information Science and Technology(NUIST) by using version 5.3 of the European Centre Hamburg Model(ECHAM), version 3.4 of the Nucleus for European Modelling of the Ocean(NEMO), and version 4.1 of the Los Alamos sea ice model(CICE). The model is referred to as NUIST ESM1(NESM1). Comprehensive and quantitative metrics are used to assess the model's major modes of climate variability most relevant to subseasonal-to-interannual climate prediction. The model's assessment is placed in a multi-model framework. The model yields a realistic annual mean and annual cycle of equatorial SST, and a reasonably realistic precipitation climatology, but has difficulty in capturing the spring–fall asymmetry and monsoon precipitation domains. The ENSO mode is reproduced well with respect to its spatial structure, power spectrum, phase locking to the annual cycle, and spatial structures of the central Pacific(CP)-ENSO and eastern Pacific(EP)-ENSO; however, the equatorial SST variability,biennial component of ENSO, and the amplitude of CP-ENSO are overestimated. The model captures realistic intraseasonal variability patterns, the vertical-zonal structures of the first two leading predictable modes of Madden–Julian Oscillation(MJO), and its eastward propagation; but the simulated MJO speed is significantly slower than observed. Compared with the T42 version, the high resolution version(T159) demonstrates improved simulation with respect to the climatology, interannual variance, monsoon–ENSO lead–lag correlation, spatial structures of the leading mode of the Asian–Australian monsoon rainfall variability, and the eastward propagation of the MJO.     

一个地球系统模式模拟的气候变化对海洋碳循环的影响

使用维多利亚大学的地球系统模式进行模拟,选取1800-2500年间较高的CO₂浓度情景（RCP8.5）,分析由于CO₂增加引起的气候变化对海洋碳循环的影响。当气候敏感度为3.0 K时,相对于无气候变化,到2100年,由于大气CO₂增加造成的气候变化导致海表面温度升高2.7 K,北大西洋深水流量减少4.5 Sv,海洋对人为碳的年吸收减少0.8 Pg C;比较人为溶解无机碳在海洋中的垂直累积分布,发现气候变化对海洋吸收大气CO₂的影响在北大西洋区域最明显。1800-2500年,相对于不考虑气候变化的情景,模式模拟的气候变化导致整个海洋对人为碳的累积吸收总量减少23.1%,其中北大西洋减少32.0%。此外,比较不同气候敏感度（0～4.5 K,间隔为0.5 K）的模拟结果发现,气候敏感度越高,气候变化对海洋吸收CO₂能力的抑制作用越明显。     

气候变化减缓技术：国际现状与发展趋势

介绍了当前国际主要气候变化减缓技术,并以国际能源署（IEA）、世界自然基金会（WWF）、全球能源技术战略计划（GTSP）、世界资源研究所（WRI）和欧盟（EU）、美国等国际组织、机构与国家发布或拟议中的有关气候变化减缓技术的报告为框架,对全球的气候变化减缓技术部署进行了概述。在此基础上,分析了主要的气候变化减缓技术对减缓气候变化的预期贡献。最后,对减排技术的效果、安全性、对环境的影响以及公众的认可程度等进行了讨论。     

全球变暖对高原东北侧干旱气候影响的若干事实

应用西北地区８个代表站（１９７９￣１９８３年和１９８７￣１９９１年０１０年历年逐月５００、７００、８５０ｈＰａ的探空资料,分析了便于变暖对高原东北侧干旱气候的影响。结果指出：变暖使该区域夏季风减弱,８月偏南风分量减少,偏北风分量加强;并存在夏季变干的趋势。     

气候变暖背景下我国四季开始时间的变化特征

利用中国气象局国家气象信息中心提供的中国599个测站1961～2007年逐日温度资料,分析了我国近47年来四季开始日期的变化趋势。结果表明,四季开始日期在全国范围内主要表现为春季、夏季提早,秋季、冬季推迟的变化趋势,其中以夏季的变化最为明显,且在显著增温的21世纪初最为明显。这种趋势在空间分布上有所差异,北方比南方明显,东部比西部明显。东北最北部、华南最南部以及新疆局部区域春季推迟,青海东部以及内蒙古最北部的小范围地区夏季推迟,华南及西南局部地区冬季提早。此外,全国平均四季开始日期的年代际变化在20世纪并不是很明显,而在21世纪初非常明显。但年代际变化特征存在区域性差异,高原地区20世纪80年代和90年代春季提早,冬季推迟。而在21世纪初春季、冬季均推迟,但冬季的变化比春季明显得多。华南南部地区春季推迟、冬季提早。西南地区在21世纪初春季、夏季明显提早,秋季、冬季推迟,但之前这种趋势并不明显。