Ensemble projection of 1―3℃ warming in China

Studies on the influences of climate change on biogeochemical cycles and on the key vulnerabilities and the risk from climate change suggest that annual surface temperature rise of 1 ℃, 2℃ and 3℃ above the present level would lead to changes in extreme weather and climate events, food production, fresh water resources, biodiversity, human mortality, etc. Here two sets of simulations as performed with seventeen atmosphere-ocean general circulation models （AOGCMs） for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change （IPCC AR4）, i.e. the model outputs from the 20th Century Climate in Coupled Models （20C3M） and from the Special Report on Emissions Scenarios （SRES） emission scenarios B1, A1B and A2, are used to analyze spatial and temporal characteristics of the above values in China over the 21st century. The results indicate that the rate of warming varies from region to region. The above values are reached much later （earlier） when emission amount is lower （higher）, and spread of the time when the lower （higher） value is exceeded is narrower （wider） among the three scenarios. As far as the spatial pattern is concerned, the above values are crossed much earlier in northern China and the Tibetan Plateau with respect to the Yangtze-Huaihe River Valley and South China.     

Sea surface temperature record from the north of the East China Sea since late Holocene

Using the alkenone paleotemperature index U37^k, a high-resolution sea surface temperature （SST） record since 3600 a BP was reconstructed from the mud area in the north of the East China Sea. Combining with the grain size distribution curve of sensitive grain size group, which may reflect the East Asia Winter Monsoon activity, the palaeoenvironmental evolution cycle throughout the late Holocene in the area was obtained. The marine environment evolution during the last 3600 years displays a five-stage trend. （1） Temperature descending period from 0.85 cal. ka BP to present. The maximum temperature decrease amplitude is 2℃. The winter monsoon intensified and ＇Little Ice Age＇ were recorded in this period. （2） Warming period from 1.90 to 0.85 cal. ka BP. The mean temperature increase amplitude is 0.8℃. The Sui-Tang warming period was recorded at about 0.85--1.35 cal. ka BP and a prominent cooling event was recorded at 1.4 cal. ka BP in this period. （3） Temperature descending period from 2.55 to 1.90 cal. ka BP. Temperature cooling amplitude is 0.9℃. This period is coincident with an integrated temperature circle recorded in the Antarctic ice core, with the temperature changes from a slow cooling stage to a rapid warming stage. （4） Temperature comparatively stable with a little ascending period from 3.2 to 2.55 cal. ka BP. Temperature warming amplitude is 0.3℃. This period is coincident with the temperature fluctuant ascending period recorded in Antarctic ice core. （5） Temperature comparatively stable with little descending period from 3.6 to 3.2 cal. ka BP. This period corresponds with the temperature fluctuant cooling period recorded in Antarctic ice core. Basically, those five periods were coincident with the Antarctic ice core record. During the global cooling stage, the SST change in the continental shelf sea can be adjusted simultaneously.     

Sea surface temperature records of core ZY2 from the central mud area in the South Yellow Sea during last 6200 years and related effect of the Yellow Sea Warm Current

Sea surface temperature (SST) records in the South Yellow Sea during the last 6200 years are reconstructed by the unsaturation index of long-chain alkenones (K 37 U ’) in sediment core ZY2 from the central mud area.The SST records varied between 14.1 and 16.5°C (15.6°C on average),with 3 phases:(1) A high SST phase at 6.2-5.9 cal ka BP;(2) A low and intensely fluctuating SST phase at 5.9-2.3 cal ka BP;and (3) A high and stable SST phase since 2.3 cal ka BP.Variation of the SST records is similar to intensity of the Kuroshio Current (KC),and corresponds well in time to global cold climate events.However,the amplitude of the SST response to cooling events was significantly different in different phases.The SST response to global cooling event was weak while the KC was strong;and the SST response was strong while the KC was weak.The difference in amplitude of the SST response is possibly caused by the modulation effect of the Yellow Sea Warm Current which acts as a shelf branch of the KC and a compensating current induced by the East Asia winter monsoon.The warm waters brought by the Yellow Sea Warm Current cushion the SST decrease induced by climate cooling,and both the Kuroshio and East Asian winter monsoon play important roles in the modulation mechanism.The SST records display a periodicity of 1482 years.The same period was found in the KC records,indicating that variation of the SST records in the central South Yellow Sea is strongly affected by KC intensity.The same period was also found in Greenland ice cores and North Atlantic and Arabian Sea sediment cores,showing a regional response of marine environmental variability in the East China Seas to that in the global oceans.     

不同平均强度热盐环流的年代际波动特征

基于美国国家大气研究中心的CCSM3(community climate system model version 3)模式,对淡水扰动试验下不同平均强度热盐环流(thermohline circulation,THC)的年代际波动特征及北大西洋气候响应特征进行研究。结果表明,百年以上尺度的THC变化对其年代际尺度波动产生显著影响,高平均强度下THC的年代际波动周期更长、更显著。对不同平均强度下北大西洋海、气要素与THC在年代际尺度上的相关分布进行分析,发现在高平均强度下,THC与海表温度(sea surface temperature,SST)的相关呈现为经向三核型分布,与海平面气压(sea lever pressure,SLP)的相关呈现为类NAO(North Atlantic oscillation)分布,而在低平均强度下,则不存在这2种模态分布;同时,在不同平均强度下,THC与各要素间的相关程度也不同,高平均强度下相关程度更高。     

Arctic sea ice bordering on the North Atlantic and interannual climate variations

Variations of winter Arctic sea ice bordering on the North Atlantic are closely related to climate variations in the same region. When winter North Atlantic Oscillation (NAO) index is positive (negative) anomaly phase, Icelandic Low is obviously deepened and shifts northwards (southwards). Simultaneously, the Subtropical High over the North Atlantic is also intensified, and moves northwards (southwards). Those anomalies strengthen (weaken) westerly between Icelandic Low and the Subtropical High, and further result in positive (negative) sea surface temperature (SST) anomalies in the mid-latitude of the North Atlantic, and increase (decrease) the warm water transportation from the mid-latitude to the Barents Sea, which causes positive (negative) mixed-layer water temperature anomalies in the south part of the Barents Sea. Moreover, the distribution of anomaly air temperature clearly demonstrates warming (cooling) in northern Europe and the subarctic regions (including the Barents Sea) and cooling (warming) in Baffin Bay/Davis Strait. Both of distributions of SST and air temperature anomalies directly result in sea ice decrease (increase) in the Barents/Kara Seas, and sea ice increase (decrease) in Baffin Bay/Davis Strait. :     

Weak response of the Atlantic thermohaline circulation to an increase of atmospheric carbon dioxide in IAP／LASG Climate System Model

Response of the Atlantic thermohaline circulation (THC) to global warming is examined by using the climate system model developed at IAP/LASG. The evidence indicates that the gradually warming climate associated with the increased atmospheric carbon dioxide leads to a warmer and fresher sea surface water at the high latitudes of the North Atlantic Ocean, which prevents the down-welling of the surface water. The succedent reduction of the pole-toequator meridional potential density gradient finally results in the decrease of the THC in intensity. When the atmospheric carbon dioxide is doubled, the maximum value of the Atlantic THC decreases approximately by 8%. The associated poleward oceanic heat transport also becomes weaker. This kind of THC weakening centralizes mainly in the northern part of the North Atlantic basin, indicating briefly a local scale adjustment rather than a loop oscillation with the whole Atlantic “conveyor belt” decelerating.     

Changes in mean and extreme climates over China with a 2°C global warming

Based on a 153-year (1948-2100) transient simulation of East Asian climate performed by a high resolution regional climate model (RegCM3) under the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A1B scenario, the potential future changes in mean and extreme climates over China in association with a global warming of 2℃ with respect to pre-industrial times are assessed in this study. Results show that annual temperature rises over the whole of China, with a greater magnitude of around 0.6℃ compared to the global mean increase, at the time of a 2℃ global warming. Large-scale surface warming gets stronger towards the high latitudes and on the Qinghai-Tibetan Plateau, while it is similar in magnitude but somewhat different in spatial pattern between seasons. Annual precipitation increases by 5.2%, and seasonal precipitation increases by 4.2%-8.5% with respect to the 1986-2005 climatology. At the large scale, apart from in boreal winter when precipitation increases in northern China but decreases in southern China, annual and seasonal precipitation increases in western and southeastern China but decreases over the rest of the country. Nationwide extreme warm (cold) temperature events increase (decrease). With respect to the 1986-2005 climatology, the country-averaged annual extreme precipitation events R5d, SDII, R95T, and R10 increase by 5.1 mm, 0.28 mm d -1 , 6.6%, and 0.4 d respectively, and CDD decreases by 0.5 d. There is a large spatial variability in R10 and CDD changes.     

Sea surface temperature and subtropical front movement in the South Tasman Sea during the last 800 ka

Southern Hemisphere mid-latitude westerlies contribute to the ventilation of the deep Southern Ocean (SO), and drive changes in atmospheric carbon dioxide (CO₂) and the global climate. As the westerlies control directly oceanic fronts, the movement of the subtropical front (STF) reflects the westerlies migration. Thus it is important to understand the relationships between STF movement and the weaterlies, ventilation of the deep SO, ice volume and atmospheric CO₂. To this end, we use two new high-resolution records from early Marine Isotope Stage (MIS) 20 (~800 ka) of sea surface temperature (SST) based on Uk’ 37 paleo-thermometer and benthic oxygen isotope (δ¹⁸OB) at Ocean Drilling Program (ODP) Site 1170B in the southern Tasman Sea (STS), to construct linkages between the marine records and atmospheric proxies from Antarctic ice-cores. During the last 800 ka, the average SST (10.2°C) at Site 1170B is 1.8°C lower than today (annual average 12°C). The highest average SST of 11.6°C occurred during MIS 1, and the lowest average SST of 7.8°C occurred during MIS 2. The warmest and coldest records of 14.7°C and 6.2°C occurred in the MIS 5 and MIS 2, respectively. In the glacial-interglacial cycles of the last 800 ka, variability of reconstructed SST shows that the STF moved northward or southward more than 3° of latitude compared with its present location. In the warmest stage MIS 5, the STF shifted to its southernmost location of ~49°S. In contrast, in the coldest stage MIS 2, the STF moved to its northernmost location of ~43°S. In response to orbital cycles, the westerlies movement led ice volume and atmospheric CO₂ changes, but it was in phase with change in Antarctic atmospheric temperature. Ice volume only preceded atmospheric CO₂ only a little at the 23-ka precession band, lagged the atmospheric CO₂ at the 100-ka eccentricity band, and was in phase with atmospheric CO₂ at the 40-ka obliquity band.     

The high-resolution climate recorded in the δ18O ofPorites lutea from the Nansha Islands of China

A Porites lutea core from Yongshu Reef of Nansha Islands covering 50 years growth history was analyzed for oxygen isotopic composition with monthly and seasonally resolution. The calibration of the δ ¹⁸O with the instrumental temperature indicated that the coral δ ¹⁸O is a good indicator for sea surface temperature (SST) and air temperature ( t ). It can be used to reconstruct the SST and air temperature of the Yongshu Reef sea area. In addition, the coral δ ¹⁸O provides signatures for the intensity of the East Asia monsoon and it is a record for the activities of El Niño events. With the calibrated SST and air temperature formulas, the most recent fifty years SST and air temperature were reconstructed based on the coral δ ¹⁸O, thus back up the understanding of the climate of Nansha Islands to 1950, far beyond the limit of the instrumental recording since September 1988. It was found that, in general, increasing 1℃ air temperature results in 0.24‰ decrease in skeletal δ ¹⁸O.     

Signals of Antarctic Circum-polar Wave over the Southern Indian Ocean as recorded in an Antarctica ice core

Oxygen stable isotopic and ionic records, covering a period of 1745--1996, are recovered in DT001 ice core drilled in Princess Elizabeth Land, East Antarctica.Using empirical orthogonal function (EOF) analysis of the annually resolved glaciochemical time series, we find the first EOF (EOFI) represents sea-salt aerosols and is the proxy of sea level pressure (SLP) over a quasi-stationary low in the Southern Indian Ocean (SIO). δ^18O represents the sea surface temperature (SST) of the same ocean area. In the past two decades, four climatic waves as represented by SLP and SST proxies are found in the DT001 ice core, which in coincident with four Antarctic Circum-polar Waves (ACW) as revealed by NCEP/NCAR reanalysis. The phase difference between SST and SLP in the ice core is also coincident with that in ACW. Both ice-core record and reanalysis suggestthat there were no signals of ACW during 1958--1980, none during the overall recording period between 1745--1996, as there is no regular phase difference between SST and SLP.The ACW signal after early 1980s is probably attributable to the climate shift occurring over Antarctic Peninsula-Drake Passage region.     

Sea surface temperature and terrestrial biomarker records of the last 260 ka of core MD05-2904 from the northern South China Sea

This paper reports high-resolution biomarker records of the last 260 ka for core MD05-2904 from the northern South China Sea （SCS）. The sea surface temperature （SST） record using the U37^k＇, index reveals a minimum of 21.5℃（MIS 2） and a maximum of 28.3℃（MIS 5.5）, for a temperature difference of almost 7℃, and provides the longest high-resolution U37^k＇ SST record in northern SCS. The content of odd-number long chain n-alkanes and several n-alkanes indexes such as the CPI, ACL and the C31/C27 ratio, all reveal generally higher values during the glacials and lower values during the interglaclals. Terrestrial input as Indicated by n-alkane content was mostly controlled by sea-level changes： During the glacials, lower sea-level exposed the continental shelf to enable rivers to transport more terrestrial materials to the slope; and the situation reverses during the interglacials. The n-alkane indexes changes reveal more n-alkanes from contemporary vegetation during glacials as a result of the proximity of the core site to the source region, while the increases in ACL and C81/C27 ratio during glaclals indicate a change to more grassy vegetation. However, the highest values for CPI, ACL and the C81/C27 ratio all occurred during late MIS 3, and it was suggested that this period was characterized by a strong summer monsoon-dominated humid climate which resulted in a denser vegetation for the exposed continental shelf region.     

Sea surface temperature variations recorded on coralline Sr／Ca ratios during Mid-Late Holocene in Leizhou Peninsula

High-resolution Sr/Ca ratios of two Porites corals from Leizhou Peninsula were measured using inductively coupled plasma atomic spectrometry (ICP-AES). TIMS U-Th dating reveals that the life-spans of the two corals are 489-500 AD and 539-530 BC, respectively. Monthly sea surface temperatures (SSTs) during these two periods can be reconstructed from their skeletal Sr/Ca ratios. The results reveal that SSTs during 539-530 BC were roughly the same as those during 1990-2000 AD in this area, indicating a relative warm climate period. However, the period of 489-500 AD was significantly cooler, with annual mean SST, the 10-a average of minimum monthly winter SSTs and the 10-a average of maximum monthly summer SSTs being about 2, 2.9 and 1℃ lower than that in the 1990s, respectively. Such climate patterns agree well with the phenological results recorded in the historic documents in other areas of China.     

卫星多通道观测揭示的东北冷涡异常特征

利用美国气象卫星OLR，HIRS-Tb12,ERB,VIS,SSMR和SSM/I多通道的观测资料，分析了东北冷涡异常年的全球大气环流特征及其关键地区的先兆特征；对于东北冷涡异常，发现了有一个由北半球的海冰，赤道东太平洋的海温，亚洲的季风以及东北地区地气系统辐射收支组成的影响链存在。由此讨论了影响链上的各因子对东北冷涡异常的作用。结果表明多通道卫星观测资料的综合应用在气候变化的研究和预测中有着重要的意义。     

卫星多通道观测揭示的东北冷涡异常特征（OLR,HIRS-Tb12, ERB,VIS, SSMR和SSM/I的观测研究）

利用美国气象卫星OLR, HIRS-Tb12, ERB, VIS, SSMR和SSM/I多通道的观测资料,分析了东北冷涡异常年的全球大气环流特征及其关键地区的先兆特征;对于东北冷涡异常,发现了有一个由北半球的海冰,赤道东太平洋的海温,亚洲的季风以及东北地区地气系统辐射收支组成的影响链存在。由此讨论了影响链上的各因子对东北冷涡异常的作用。结果表明多通道卫星观测资料的综合应用在气候变化的研究和预测中有着重要的意义。     

Melt-Water-Pulse （MWP） events and abrupt climate change of the last deglaciation

The last deglaciation is characterized by massive ice sheet melting, which results in an average sea-level rise of -120-140m. At least three major Melt-Water-Pulse （MWP） events （19ka-MWP, MWP-1A and MWP-1B） are recognizable for the last deglaciation, of which MWP-1A event lasting from -14.2 to -13.7 ka B.P. is of the most significance. However, the accurate timing and source of MWP-1A event remain debatable and controversial. It has long been postulated that meltwater of the last deglaciaUon pouring into the North Atlantic resulted in a slowdown or even a shutdown of the thermohaline circulation （THC） which subsequently affected the global climate change. Accordingly, the focus of this debate consists in establishing a reasonable relationship between MWP events and abrupt climate change. Here we summarize a variety of geological and model results for the last deglaciation, reaching a conclusion that the major MWP events did not correspond with the rigorous stadials, nor always happened within climate reversal intervals. MWP events of the last deglaciation had very weak influences on the intensity of the THC and were not able to trigger a collapse of the global climate. We need to reevaluate the influences of the temporal meltwater variability on the global climate system.     

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.     

Changes in sea surface temperature in western South China Sea over the past 450 ka

Sea surface temperature over the past 450 ka was obtained by the unsaturation of molecular fossil-long chain alkenone with a resolution of about 1 ka from the western South China Sea. This is the longest temperature profile in the South China Sea at such high resolution. The U37^κ-SST results revealed similar glacial-interglacial cycles as the δ^18O profile of planktonic foraminifera, with SST variability of 23-25.5℃ for glacial and 25-28℃ for interglacial periods. The highest SST （28.4℃） was recorded at MIS5.5 and lowest SST （22.6℃） during MIS2. The SST record preceded the planktonic foraminiferal δ^18O on five glacial-interglacial transitions. Comparison of temperature records from the Southern and Northern Hemispheres indicated a more Southern Hemisphere-like pattern for the temperature variation in the SCS. Strong precession and semiprecession signals in the spectra of our SST record manifest the tropical phenomena.     

Variations of alkenone temperature in the Sea of Japan during the last 170 ka and its paleoceanographic implications

Two sediment cores, KCES1 and ODP797, which were recovered from the Sea of Japan （JS）, were measured for alkenone-derived sea surface temperatures （U37-SSTs）. Our results revealed that the SSTs closely follow the glacial-interglacial cycles during the last 170 ka, except in the last glacial maximum （LGM）, during which the SST was higher than in the Holocene. The anomalous high temperature in the LGM is considered as an effect of the intrusion of a low salinity water mass into the JS when the sea level was almost below 130 m. On the glacial- K interglacial to orbital timescale, the U37-SSTs record in the JS correlated well with the benthic foraminiferal SO record and solar insolation, which suggests the dominant control of solar insolation and its related sea ice develop- ment on the SST in the JS. On the sub-orbital/millennial timescale, reduced SST corresponds to an enhanced east asian winter monsoon （EAWM） during the last glacial period （MIS3 and MIS4）, indicating the dominant control of sea ice expansion due to the enhanced EAWM on the SST in the JS. In contrast, during the last interglacial period （MIS5）, the SST in the JS was controlled by variations in the east Asian summer monsoon. These results highlight the key role of solar insolation and associated glacial-interglacial conditions in the variations of the SST in the JS since the last 170 ka.     

Amplitude of climatic changes in Qinghai-Tibetan Plateau

On the basis of ice core and meteorological data from the Qinghai-Tibetan (Q-T) Plateau, this article focuses on the discussion of the problems related to the sensitivity of temporal and spatial changes of the climate in high-altitude regions, particularly in the Q-T Plateau. The features of abrupt climatic changes of the past 100 ka, 2 000 a and recent years indicate that the amplitude of these changes in the Q-T Plateau was obviously larger than that in low-altitude regions. The scope of temperature change above 6 000 m in the Q-T Plateau between glacial and interglacial stages could reach over 10°C, but only about 4°C in low-elevation regions close to sea level. During the last 2 000 a, the amplitude of temperature changes at Guliya (over 6 000 m a.s.l.) in the Q-T Plateau reached 7°C, in comparison with 2°C in eastern China at low altitude. In the present age, apparent differences of climatic warming have been observed in the Q-T Plateau, indicating that the warming in high-elevation regions is much higher than that in low-elevation regions. The temperature in over 3 500 m regions of the Q-T Plateau have been increasing at a rate of 0.25×10¹/a in recent 30 years, but almost no change has taken place in the regions below 500 m. Thus, we concluded that high-altitude regions are more sensitive to climatic changes than the low-altitude regions.     

Holocene Southern Ocean surface temperature variability west of the Antarctic Peninsula

The disintegration of ice shelves, reduced sea-ice and glacier extent, and shifting ecological zones observed around Antarctica highlight the impact of recent atmospheric and oceanic warming on the cryosphere. Observations and models suggest that oceanic and atmospheric temperature variations at Antarctica's margins affect global cryosphere stability, ocean circulation, sea levels and carbon cycling. In particular, recent climate changes on the Antarctic Peninsula have been dramatic, yet the Holocene climate variability of this region is largely unknown, limiting our ability to evaluate ongoing changes within the context of historical variability and underlying forcing mechanisms. Here we show that surface ocean temperatures at the continental margin of the western Antarctic Peninsula cooled by 3-4 °C over the past 12,000 years, tracking the Holocene decline of local (65° S) spring insolation. Our results, based on TEX(86) sea surface temperature (SST) proxy evidence from a marine sediment core, indicate the importance of regional summer duration as a driver of Antarctic seasonal sea-ice fluctuations. On millennial timescales, abrupt SST fluctuations of 2-4 °C coincide with globally recognized climate variability. Similarities between our SSTs, Southern Hemisphere westerly wind reconstructions and El Ni?o/Southern Oscillation variability indicate that present climate teleconnections between the tropical Pacific Ocean and the western Antarctic Peninsula strengthened late in the Holocene epoch. We conclude that during the Holocene, Southern Ocean temperatures at the western Antarctic Peninsula margin were tied to changes in the position of the westerlies, which have a critical role in global carbon cycling.