Termination of global warmth at the Palaeocene/Eocene boundary through productivity feedback

The onset of the Palaeocene/Eocene thermal maximum (about 55 Myr ago) was marked by global surface temperatures warming by 5-7 degrees C over approximately 30,000 yr (ref. 1), probably because of enhanced mantle outgassing and the pulsed release of approximately 1,500 gigatonnes of methane carbon from decomposing gas-hydrate reservoirs. The aftermath of this rapid, intense and global warming event may be the best example in the geological record of the response of the Earth to high atmospheric carbon dioxide concentrations and high temperatures. This response has been suggested to include an intensified flux of organic carbon from the ocean surface to the deep ocean and its subsequent burial through biogeochemical feedback mechanisms. Here we present firm evidence for this view from two ocean drilling cores, which record the largest accumulation rates of biogenic barium--indicative of export palaeoproductivity--at times of maximum global temperatures and peak excursion values of delta13C. The unusually rapid return of delta13C to values similar to those before the methane release and the apparent coupling of the accumulation rates of biogenic barium to temperature, suggests that the enhanced deposition of organic matter to the deep sea may have efficiently cooled this greenhouse climate by the rapid removal of excess carbon dioxide from the atmosphere.     

Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation

The covariation of carbon dioxide (CO(2)) concentration and temperature in Antarctic ice-core records suggests a close link between CO(2) and climate during the Pleistocene ice ages. The role and relative importance of CO(2) in producing these climate changes remains unclear, however, in part because the ice-core deuterium record reflects local rather than global temperature. Here we construct a record of global surface temperature from 80 proxy records and show that temperature is correlated with and generally lags CO(2) during the last (that is, the most recent) deglaciation. Differences between the respective temperature changes of the Northern Hemisphere and Southern Hemisphere parallel variations in the strength of the Atlantic meridional overturning circulation recorded in marine sediments. These observations, together with transient global climate model simulations, support the conclusion that an antiphased hemispheric temperature response to ocean circulation changes superimposed on globally in-phase warming driven by increasing CO(2) concentrations is an explanation for much of the temperature change at the end of the most recent ice age.     

温室气体变化数值模拟试验中全球降水和温度变化的迟滞效应

利用耦合气候模式(GFDL-CM2.1)研究变动气候背景下全球平均降水和温度的变化。不同情景CO2 强迫试验表明, 降水变化存在明显的迟滞效应。全球平均降水与地表温度的变化存在显著的线性关系, 但是降水同时也受到CO2 浓度的直接影响。在CO2 增加又恢复的试验中, 降水变化滞后于地表温度变化, 出现降水 “迟滞效应”。在CO2 增加过程中, 温室效应增强会立即导致大气长波吸收增强, 大气获得的净辐射能量增加, 为维持大气能量收支平衡, 地面向上潜热通量受到抑制, 形成CO2 增加对降水的抑制效应。随之而来的温度上升则主要引起大气层顶出射长波辐射以及大气对地表的长波回辐射增加, 大气净辐射能量减少, 地面潜热通量增加, 从而引起降水的增加。在CO2 减少过程中, 情况正好相反, 温室效应减弱会增加降水, 而温度降低会减少降水。温度和CO2 对降水的不同影响决定了降水的迟滞效应。     

Vertical structure of recent Arctic warming

Near-surface warming in the Arctic has been almost twice as large as the global average over recent decades-a phenomenon that is known as the 'Arctic amplification'. The underlying causes of this temperature amplification remain uncertain. The reduction in snow and ice cover that has occurred over recent decades may have played a role. Climate model experiments indicate that when global temperature rises, Arctic snow and ice cover retreats, causing excessive polar warming. Reduction of the snow and ice cover causes albedo changes, and increased refreezing of sea ice during the cold season and decreases in sea-ice thickness both increase heat flux from the ocean to the atmosphere. Changes in oceanic and atmospheric circulation, as well as cloud cover, have also been proposed to cause Arctic temperature amplification. Here we examine the vertical structure of temperature change in the Arctic during the late twentieth century using reanalysis data. We find evidence for temperature amplification well above the surface. Snow and ice feedbacks cannot be the main cause of the warming aloft during the greater part of the year, because these feedbacks are expected to primarily affect temperatures in the lowermost part of the atmosphere, resulting in a pattern of warming that we only observe in spring. A significant proportion of the observed temperature amplification must therefore be explained by mechanisms that induce warming above the lowermost part of the atmosphere. We regress the Arctic temperature field on the atmospheric energy transport into the Arctic and find that, in the summer half-year, a significant proportion of the vertical structure of warming can be explained by changes in this variable. We conclude that changes in atmospheric heat transport may be an important cause of the recent Arctic temperature amplification.     

人类影响引起全球变暖的证据

 按照归因分析的研究方法和工具，综述了近些年有关人类影响引起全球变暖证据的科学研究成果。利用全球气候模式考虑人类影响，采用指纹法检测和归因证实，发现人类影响几乎肯定是引起近百年特别是近50年全球变暖的主因。地球系统5个圈层（大气、海洋、陆地、冰雪、生物）与全球变暖有关的证据，如热浪增加、寒潮减弱、低层大气变暖、陆地和海洋变暖、受海水热膨胀和冰融化引起全球海平面上升、冰雪和永冻土融化加速、海洋酸度增加、植物生长季延长等，都与人类影响有密切联系。     

Warming magnitude of Indonesian Throughflow during the penultimate deglaciation (Termination II) and its relationship with climate change in high-latitude regions

The tropical oceans are important source areas for global heat and water vapor transport, and changes in tropical sea surface tem-perature (SST) will have important impacts on high-latitude and global climate change. It is crucial to establish the precise phase relationship between tropical and high-latitude climate variability to gain insight into the mechanisms of global climate change. Here, we present multi-proxy records across the penultimate deglaciation (Termination II) from sediment Core SO18459, which is located in the outflow area of the Indonesian Throughflow (ITF) of the Timor Sea. These proxy records include planktonic and benthic foraminifera δ¹⁸O, planktonic foraminifera G. ruber Mg/Ca-derived SST, and δ¹⁸O_w of sea surface water. The Mg/Ca-SST records indicate a warming of 4.1°C in the Timor Sea over Termination II, which is in phase with decrease in planktonic and benthic δ¹⁸O. Our results suggest that at millennial timescales, climate change of the tropical oceans is synchronous with high-latitude ice volume changes. Furthermore, warming of the Timor Sea is almost simultaneous with warming of the Antarctic, suggesting a rapid heat transfer from the tropics to the Antarctic via the atmosphere and/or ocean circulations. The G. ruber δ¹⁸O and SST records of Core SO18459 show a marked YD-like event during Termination II, which is probably caused by decrease in Australian rainfall or strengthening of the Western Pacific Warm Pool. However, a similar YD-like event is not observed in East Asian rainfall records. This discrepancy indicates that different tropical climate systems may have different responses to the same forcing, such as El Niño Southern Oscillation. A similar YD-like event is observed in the global benthic foraminiferal δ¹⁸O records during Termination II, implying teleconnection of millennial scale climate change between the tropical regions and high latitudes.     

碳捕获与封存技术专利分析

碳捕获与封存（CCS）是在不需要降低化石燃料使用量的情况下,减少温室气体排入大气的一种手段。为了达到这种效果,必须使用技术从排放气体中分离和捕获二氧化碳,并把二氧化碳转化为甲醇等资源或者把二氧化碳封存到地质沉积物中。随着温室气体排放与气候变暖问题的加剧,国际上对CCS技术的关注日益加强,这也反映在专利申请的发展趋势上。利用Thomson Data Analyzer分析工具和Aureka分析平台对Derwent Innovations Index（DII）专利文献进行分析,表明CCS专利主要涉及化学、工程、仪器、能源与燃料、高分子科学等学科领域。CCS技术经历了起步阶段、波动增长阶段和快速增长阶段。DII收录的CCS专利主要来自日本、美国、德国、中国、法国等。各国研究的重点有所不同,德国用催化剂从废气等中脱除氮氧化物的比例比其他国家高,法国通过液化或固化分离气体的比例较高,荷兰一般化合碳方面所占比例高。最近3Af-加拿大、中国、韩国申请专利的数量增长速度最快,表明这些国家近期在该技术领域创新比较活跃。对CCS技术的关注在今后一段时间内将持续上升,我国需继续支持该领域的研发创新工作。     

Reconstruction of surface ocean water <Emphasis Type="Italic">p</Emphasis>CO<Subscript>2</Subscript>(aq) in Nansha area,the South China Sea during the last 30 ka

The reconstruction of pCO2 in the tropic ocean is one of the most important issues to understand global climatic changes.In this study,the high-resolution stratigraphic analysis of core 17962 was conducted,which is Iocated in the southern South China Sea(SCS).The contents of sedimentary organic matter,the stable carbon isotopic composition of sedimentary organic matter,and the δ^13C values of black carbon and terrigenons n-alkanes were determined.And the δ^13Cwc value of carbon derived from aquatic was calculated.On the basis of δ^13Corg-pCO2equation proposed by Popp et al.(1989),we estimated the pCO2 in the Nansha area,SCS,since the last glaciation using δ^13Cwc instead of δ^13Corg.The results show that the average pCO2 was estimated at 240 ppm V during the last glaciation,and at 320ppm V in the Holocene.A comparison of surface sea pCO2 with the atmosphere CO2 recorded in the Vostok ice core,indicates that CO2 in surface water of the southern SCS could emit into atmosphere during the last 30ka.     

A carbon isotope record of CO2 levels during the late Quaternary

Analyses of gases trapped in continental ice sheets have shown that the concentration of CO2 in the Earth's early atmosphere increased from 180 to 280 p.p.m. during the most recent glacial-interglacial transition. This change must have been driven by an increase in the concentration of CO2 dissolved in the mixed layer of the ocean. Biochemical and physiological factors associated with photosynthetic carbon fixation in this layer should lead to a relationship between concentrations of dissolved CO2 and the carbon isotopic composition of phytoplanktonic organic material, such that increased atmospheric CO2 should enhance the difference in 13C content between dissolved inorganic carbon and organic products of photosynthesis. Here we show that a signal related to atmospheric CO2 levels can be seen in the isotope record of a hemipelagic sediment core, which we can correlate with the CO2 record of the Vostok ice core. Calibration of the relationship between isotope fractionation and CO2 levels should permit the extrapolation of CO2 records to times earlier than those for which ice-core records are available.     

Magnitude and timing of temperature change in the Indo-Pacific warm pool during deglaciation

Ocean-atmosphere interactions in the tropical Pacific region have a strong influence on global heat and water vapour transport and thus constitute an important component of the climate system. Changes in sea surface temperatures and convection in the tropical Indo-Pacific region are thought to be responsible for the interannual to decadal climate variability observed in extra-tropical regions, but the role of the tropics in climate changes on millennial and orbital timescales is less clear. Here we analyse oxygen isotopes and Mg/Ca ratios of foraminiferal shells from the Makassar strait in the heart of the Indo-Pacific warm pool, to obtain synchronous estimates of sea surface temperatures and ice volume. We find that sea surface temperatures increased by 3.5-4.0 degrees C during the last two glacial-interglacial transitions, synchronous with the global increase in atmospheric CO2 and Antarctic warming, but the temperature increase occurred 2,000-3,000 years before the Northern Hemisphere ice sheets melted. Our observations suggest that the tropical Pacific region plays an important role in driving glacial-interglacial cycles, possibly through a system similar to how El Ni?o/Southern Oscillation regulates the poleward flux of heat and water vapour.     

Arctic warming aloft is data set dependent

Arctic sea ice and snow on land have retreated polewards at an alarming pace in the past few decades. Such retreat locally amplifies surface warming through a positive feedback, which causes the Arctic surface to warm faster than the rest of the globe. In contrast, ice and snow retreat causes little warming in the atmosphere above when the stable winter atmosphere inhibits vertical heat exchange. We therefore find surprising the recent report by Graversen et al. in which they claim that recent Arctic atmospheric warming extends far deeper into the atmosphere than expected, and can even exceed the surface warming during the polar night. Using a different data set, we show that there is much less warming aloft in winter, consistent with the recent retreat of ice and snow, as well as recent changes in atmospheric heat transport.     

Rapid Cenozoic glaciation of Antarctica induced by declining atmospheric CO2

The sudden, widespread glaciation of Antarctica and the associated shift towards colder temperatures at the Eocene/Oligocene boundary (approximately 34 million years ago) (refs 1-4) is one of the most fundamental reorganizations of global climate known in the geologic record. The glaciation of Antarctica has hitherto been thought to result from the tectonic opening of Southern Ocean gateways, which enabled the formation of the Antarctic Circumpolar Current and the subsequent thermal isolation of the Antarctic continent. Here we simulate the glacial inception and early growth of the East Antarctic Ice Sheet using a general circulation model with coupled components for atmosphere, ocean, ice sheet and sediment, and which incorporates palaeogeography, greenhouse gas, changing orbital parameters, and varying ocean heat transport. In our model, declining Cenozoic CO2 first leads to the formation of small, highly dynamic ice caps on high Antarctic plateaux. At a later time, a CO2 threshold is crossed, initiating ice-sheet height/mass-balance feedbacks that cause the ice caps to expand rapidly with large orbital variations, eventually coalescing into a continental-scale East Antarctic Ice Sheet. According to our simulation the opening of Southern Ocean gateways plays a secondary role in this transition, relative to CO2 concentration.     

基于耦合气候模式的始新世全球季风数值模拟

全球一半以上人口生活在季风区。为了研究温室气候时期全球季风气候的特征,利用耦合气候数值模式(Community Earth System Model),模拟了距今最近的温室气候时期——始新世(40 Ma B.P.)的全球季风气候特征。该模式全面考虑了大气、海洋、陆地、陆冰、海冰、植被等气候子系统的耦合作用,大气CO2含量设为工业革命前的4倍。模拟结果表明,在始新世时期,全球季风的范围、强度与现今大体相当,但是区域上,各季风区的特征与现今有明显差异。     

Astronomical pacing of methane release in the Early Jurassic period

A pronounced negative carbon-isotope (delta13C) excursion of approximately 5-7 per thousand (refs 1-7) indicates the occurrence of a significant perturbation to the global carbon cycle during the Early Jurassic period (early Toarcian age, approximately 183 million years ago). The rapid release of 12C-enriched biogenic methane as a result of continental-shelf methane hydrate dissociation has been put forward as a possible explanation for this observation. Here we report high-resolution organic carbon-isotope data from well-preserved mudrocks in Yorkshire, UK, which demonstrate that the carbon-isotope excursion occurred in three abrupt stages, each showing a shift of -2 per thousand to -3 per thousand. Spectral analysis of these carbon-isotope measurements and of high-resolution carbonate abundance data reveals a regular cyclicity. We interpret these results as providing strong evidence that methane release proceeded in three rapid pulses and that these pulses were controlled by astronomically forced changes in climate, superimposed upon longer-term global warming. We also find that the first two pulses of methane release each coincided with the extinction of a large proportion of marine species.     

Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial drainage

Fluctuations in surface melting are known to affect the speed of glaciers and ice sheets, but their impact on the Greenland ice sheet in a warming climate remains uncertain. Although some studies suggest that greater melting produces greater ice-sheet acceleration, others have identified a long-term decrease in Greenland's flow despite increased melting. Here we use satellite observations of ice motion recorded in a land-terminating sector of southwest Greenland to investigate the manner in which ice flow develops during years of markedly different melting. Although peak rates of ice speed-up are positively correlated with the degree of melting, mean summer flow rates are not, because glacier slowdown occurs, on average, when a critical run-off threshold of about 1.4?centimetres a day is exceeded. In contrast to the first half of summer, when flow is similar in all years, speed-up during the latter half is 62?±?16 per cent less in warmer years. Consequently, in warmer years, the period of fast ice flow is three times shorter and, overall, summer ice flow is slower. This behaviour is at odds with that expected from basal lubrication alone. Instead, it mirrors that of mountain glaciers, where melt-induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient. A model of ice-sheet flow that captures switching between cavity and channel drainage modes is consistent with the run-off threshold, fast-flow periods, and later-summer speeds we have observed. Simulations of the Greenland ice-sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage; a simple model of basal lubrication alone misses key aspects of the ice sheet's response to climate warming.     

Links between climate and sea levels for the past three million years

The oscillations between glacial and interglacial climate conditions over the past three million years have been characterized by a transfer of immense amounts of water between two of its largest reservoirs on Earth -- the ice sheets and the oceans. Since the latest of these oscillations, the Last Glacial Maximum (between about 30,000 and 19,000 years ago), approximately 50 million cubic kilometres of ice has melted from the land-based ice sheets, raising global sea level by approximately 130 metres. Such rapid changes in sea level are part of a complex pattern of interactions between the atmosphere, oceans, ice sheets and solid earth, all of which have different response timescales. The trigger for the sea-level fluctuations most probably lies with changes in insolation, caused by astronomical forcing, but internal feedback cycles complicate the simple model of causes and effects.     

Eocene/Oligocene ocean de-acidification linked to Antarctic glaciation by sea-level fall

One of the most dramatic perturbations to the Earth system during the past 100 million years was the rapid onset of Antarctic glaciation near the Eocene/Oligocene epoch boundary (approximately 34 million years ago). This climate transition was accompanied by a deepening of the calcite compensation depth--the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution. Changes in the global carbon cycle, rather than changes in continental configuration, have recently been proposed as the most likely root cause of Antarctic glaciation, but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear. Here we use a global biogeochemical box model to test competing hypotheses put forward to explain the Eocene/Oligocene transition. We find that, of the candidate hypotheses, only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor. In our simulations, glacioeustatic sea-level fall associated with the growth of Antarctic ice sheets permanently reduces global calcium carbonate accumulation on the continental shelves, leading to an increase in pelagic burial via permanent deepening of the calcite compensation depth. At the same time, fresh limestones are exposed to erosion, thus temporarily increasing global river inputs of dissolved carbonate and increasing seawater delta13C. Our work sheds new light on the mechanisms linking glaciation and ocean acidity change across arguably the most important climate transition of the Cenozoic era.     

试论气候变化对中国生态、经济发展的影响

随着社会经济的发展和科学技术的进步,气候变暖的现实已对人类社会和自然生态系统构成了严重的威胁。世界经济的迅速发展和社会的进步,向大气排放的有害物质及化石能源消耗与日俱增,带来了日益严重的环境问题,导致全球平均气温逐年升高。中国是一个发展中国家,从能源方面入手采取减缓全球气候变化的措施,促进我国的能源利用水平,推进我国能源优质化的进程,加快我国实现经济增长方式从粗放型向集约型的根本性转变。     

Interhemispheric climate links revealed by late-glacial cooling episode in southern Chile

Understanding the relative timings of climate events in the Northern and Southern hemispheres is a prerequisite for determining the causes of abrupt climate changes. But climate records from the Patagonian Andes and New Zealand for the period of transition from glacial to interglacial conditions--about 14.6-10 kyr before present, as determined by radiocarbon dating--show varying degrees of correlation with similar records from the Northern Hemisphere. It is necessary to resolve these apparent discrepancies in order to be able to assess the relative roles of Northern Hemisphere ice sheets and oceanic, atmospheric and astronomical influences in initiating climate change in the late-glacial period. Here we report pollen records from three sites in the Lake District of southern Chile (41 degrees S) from which we infer conditions similar to modern climate between about 13 and 12.2 14C kyr before present (BP), followed by cooling events at about 12.2 and 11.4 14C kyr BP, and then by a warming at about 9.8 14C kyr BP. These events were nearly synchronous with important palaeoclimate changes recorded in the North Atlantic region, supporting the idea that interhemispheric linkage through the atmosphere was the primary control on climate during the last deglaciation. In other regions of the Southern Hemisphere, where climate events are not in phase with those in the Northern Hemisphere, local oceanic influences may have counteracted the effects that propagated through the atmosphere.     

Oceanic Cd/P ratio and nutrient utilization in the glacial Southern Ocean

During glacial periods, low atmospheric carbon dioxide concentration has been associated with increased oceanic carbon uptake, particularly in the southern oceans. The mechanism involved remains unclear. Because ocean productivity is strongly influenced by nutrient levels, palaeo-oceanographic proxies have been applied to investigate nutrient utilization in surface water across glacial transitions. Here we show that present-day cadmium and phosphorus concentrations in the global oceans can be explained by a chemical fractionation during particle formation, whereby uptake of cadmium occurs in preference to uptake of phosphorus. This allows the reconstruction of past surface water phosphate concentrations from the cadmium/calcium ratio of planktonic foraminifera. Results from the Last Glacial Maximum show similar phosphate utilization in the subantarctic to that of today, but much smaller utilization in the polar Southern Ocean, in a model that is consistent with the expansion of glacial sea ice and which can reconcile all proxy records of polar nutrient utilization. By restricting communication between the ocean and atmosphere, sea ice expansion also provides a mechanism for reduced CO2 release by the Southern Ocean and lower glacial atmospheric CO2.