On the generation and interpretation of probabilistic estimates of climate sensitivity

The equilibrium climate response to anthropogenic forcing has long been one of the dominant, and therefore most intensively studied, uncertainties in predicting future climate change. As a result, many probabilistic estimates of the climate sensitivity (S) have been presented. In recent years, most of them have assigned significant probability to extremely high sensitivity, such as P(S?>?6C)?>?5%. In this paper, we investigate some of the assumptions underlying these estimates. We show that the popular choice of a uniform prior has unacceptable properties and cannot be reasonably considered to generate meaningful and usable results. When instead reasonable assumptions are made, much greater confidence in a moderate value for S is easily justified, with an upper 95% probability limit for S easily shown to lie close to 4°C, and certainly well below 6°C. These results also impact strongly on projected economic losses due to climate change.     

Sources of uncertainty in projections of twenty-first century westerly wind changes over the Amundsen Sea,West Antarctica,in CMIP5 climate models

The influence of changes in winds over the Amundsen Sea has been shown to be a potentially key mechanism in explaining rapid loss of ice from major glaciers in West Antarctica, which is having a significant impact on global sea level. Here, Coupled Model Intercomparison Project Phase 5 (CMIP5) climate model data are used to assess twenty-first century projections in westerly winds over the Amundsen Sea (U _AS ). The importance of model uncertainty and internal climate variability in RCP4.5 and RCP8.5 scenario projections are quantified and potential sources of model uncertainty are considered. For the decade 2090–2099 the CMIP5 models show an ensemble mean twenty-first century response in annual mean U _AS of 0.3 and 0.7 m s^?1 following the RCP4.5 and RCP8.5 scenarios respectively. However, as a consequence of large internal climate variability over the Amundsen Sea, it takes until around 2030 (2065) for the RCP8.5 response to exceed one (two) standard deviation(s) of decadal internal variability. In all scenarios and seasons the model uncertainty is large. However the present-day climatological zonal wind bias over the whole South Pacific, which is important for tropical teleconnections, is strongly related to inter-model differences in projected change in U _AS (more skilful models show larger U _AS increases). This relationship is significant in winter (r = ?0.56) and spring (r = ?0.65), when the influence of the tropics on the Amundsen Sea region is known to be important. Horizontal grid spacing and present day sea ice extent are not significant sources of inter-model spread.     

Tree rings and climate for the last 680 years in Wulan area of northeastern Qinghai-Tibetan Plateau

A 680-year ring-width chronology of Sabina przewalskii Kom. was developed for Wulan area of northeastern Qinghai-Tibetan Plateau, China. Response function and correlation analyses showed that spring precipitation (May–June) is the critical limiting factor for tree-ring growth, and temperature in prior November may also play a role in affecting tree-ring growth. Excessive spring precipitation occurred during AD 1380s–1390s, 1410s–1420s, 1520s–1560s and 1938 to present. Dry springs occurred during AD 1430s–1510s, 1640s–1730s and 1780s–1890s most of which generally coincided with cold intervals of the Little Ice Age (LIA) on the plateau, suggesting that the LIA climate on the northeastern Qinghai-Tibetan Plateau might be characterized by three episodes of dry spring and cold autumn. The relatively driest spring and probably coldest autumn occurred in AD 1710s–1720s, 1787–1797, 1815–1824, 1869–1879 and 1891–1895. The extreme drought in AD 1787–1797 might result from little monsoon precipitation due to the failure of Asian monsoon in this period. The tree-ring data produced in this study contribute to the spatial expansion of proxy climate records for the Qinghai-Tibetan Plateau.     

区域气候模式REMO对中国气温和降水模拟能力的评估

采用泰勒图和偏差分析等统计方法,评估分析了德国区域气候模式（REMO）对中国1989-2008年气温和降水的模拟能力。结果表明：REMO气温模拟值与观测值空间相关系数为0.94,降水空间相关系数较低（0.42）,气温模拟结果明显优于降水;从空间偏差上看,在中国大部分地区,REMO模拟的气温高于观测值,偏差在±4℃以内,青藏高原整体有明显的-4～-2℃的冷偏差;模拟的降水值则高于观测值,空间偏差分布较均匀,中国大部分地区偏差在±300 mm之内;除青藏高原、华南和西南地区外,REMO能较准确地反映出中国气温和降水的空间分布特征,其中华北和东北地区模拟效果最好;REMO对夏季气温和冬季降水的模拟能力相对较好;REMO在地形起伏较大地区的模拟能力有待提高。     

Temperature variations and rice yields in China: historical contributions and future trends

Temperature is the principal factor that determines rice growth, development and ultimately grain yield. In this study, normal growing-degree-days (NGDD) and killing growing-degree-days (KGDD) were used to capture the different effects of normal and extreme temperatures on rice yields, respectively. Based on these indexes, we assessed the contributions of temperature variations to county-level rice yields across China during the historical period (1980–2008), and estimated the potential exposure of rice to extreme temperature stress in the near future (2021–2050). The results showed that historical temperature variations had measurable impacts on rice yields with a distinct spatial pattern: for different regions, such variations had contributed much to the increased rice yields in Northeast China (Region I) (0.59 % yield year^?1) and some portions of the Yunnan-Guizhou Plateau (Region II) (0.34 % yield year^?1), but seriously hindered the improvements of rice yields in the Sichuan Basin (SB) (?0.29 % yield year^?1) and the southern cultivation areas (Region IV) (?0.17 % yield year^?1); for the entire country, half of the contributions were positive and the other half were negative, resulting in a balance pattern with an average of 0.01 % yield year^?1. Under the RCP8.5 scenario, climate warming during 2021–2050 would substantially reduce cold stress but increase heat stress in the rice planting areas across China. For the future period, Region I, II and eastern China would be continually exposed to more severe cold stress than the other regions; Region III (including SB and the mid-lower reaches of Yangtze River (MLRYR)) would be the hot spot of heat stress.     

Relative humidity history on the Batang–Litang Plateau of western China since 1755 reconstructed from tree-ring δ18O and δD

We measured the annual variation in the stable isotopes of oxygen (δ¹⁸O) and hydrogen (δD) in tree rings of Abies georgei on the Batang–Litang Plateau of western China. Although correlations between tree-ring δ¹⁸O and δD are relatively weak in semi-arid regions, we found a strong correlation between the δ¹⁸O and δD time series from 1755 to 2009 under the wetter environment. Tree-ring δ¹⁸O and δD time series are both significantly and negatively correlated with moisture conditions from June to August, including relative humidity and total precipitation, respectively, from 1960 to 2009. Considering the difference in low-frequency domain between the two isotopes, the relative humidity histories from June to August, reconstructed separately from the tree-ring δ¹⁸O and δD data with instrumental climate data, reveal a persistent drying trend since 1850s, especially since the early 1970s. There is an obvious offset of reconstructed relative humidity from tree-ring δ¹⁸O and δD in the period 1755–1820, despite the strong similarity in their 21-year moving averages. The decreased relative humidity since the 1850s may be associated with the thermal contrast between the sea surface temperature of the Indian Ocean and the Qinghai-Tibetan Plateau, which determines the strength of moisture transfer via the Indian summer monsoon.     

Evaluation of Agricultural Climatic Resource Utilization During Spring Maize Cultivation in Northeast China Under Climate Change

Agricultural climatic resources （such as light,temperature,and water） are environmental factors that affect crop productivity.Predicting the effects of climate change on agricultural climatic resource utilization can provide a theoretical basis for adapting agricultural practices and distributions of agricultural production.This study investigates these effects under the IPCC （Intergovernmental Panel on Climate Change） scenario A1B using daily data from the high-resolution RegCM3 （0.25° ×0.25°） during 1951-2100.Model outputs are adjusted using corrections derived from daily observational data taken at 101 meteorological stations in Northeast China between 1971 and 2000.Agricultural climatic suitability theory is used to assess demand for agricultural climatic resources in Northeast China during the cultivation of spring maize.Three indices,i.e.,an average resource suitability index （Isr）,an average efficacy suitability index （Ise）,and an average resource utilization index （K）,are defined to quantitatively evaluate the effects of climate change on climatic resource utilization between 1951 and 2100.These indices change significantly in both temporal and spatial dimensions in Northeast China under global warming.All three indices are projected to decrease in Liaoning Province from 1951 to 2100,with particularly sharp declines in Isr,Ise,and K after 2030,2021,and 2011,respectively.In Jilin and Heilongjiang provinces,Isr is projected to increase slightly after 2011,while Ise increases slightly and K decreases slightly after 2030.The spatial maxima of all three indices are projected to shift northeastward.Overall,warming of the climate in Northeast China is expected to negatively impact spring maize production,especially in Liaoning Province.Spring maize cultivation will likely need to shift northward and expand eastward to make efficient use of future agricultural climatic resources.     

Temporal and Spatial Characteristics of Extreme Hourly Precipitation over Eastern China in the Warm Season

Based on hourly precipitation data in eastern China in the warm season during 1961-2000,spatial distributions of frequency for 20 mm h 1 and 50 mm h 1 precipitation were analyzed,and the criteria of short-duration rainfall events and severe rainfall events are discussed.Furthermore,the percentile method was used to define local hourly extreme precipitation;based on this,diurnal variations and trends in extreme precipitation were further studied.The results of this study show that,over Yunnan,South China,North China,and Northeast China,the most frequent extreme precipitation events occur most frequently in late afternoon and/or early evening.In the Guizhou Plateau and the Sichuan Basin,the maximum frequency of extreme precipitation events occurs in the late night and/or early morning.And in the western Sichuan Plateau,the maximum frequency occurs in the middle of the night.The frequency of extreme precipitation (based on hourly rainfall measurements) has increased in most parts of eastern China,especially in Northeast China and the middle and lower reaches of the Yangtze River,but precipitation has decreased significantly in North China in the past 50 years.In addition,stations in the Guizhou Plateau and the middle and lower reaches of the Yangtze River exhibit significant increasing trends in hourly precipitation extremes during the nighttime more than during the daytime.     

Projected Shifts in Kppen Climate Zones over China and Their Temporal Evolution in CMIP5 Multi-Model Simulations

Previous studies have examined the projected climate types in China by 2100. This study identified the emergence time of climate shifts at a 1?scale over China from 1990 to 2100 and investigated the temporal evolution of K o¨ppen–Geiger climate classifications computed from CMIP5 multi-model outputs. Climate shifts were detected in transition regions(7%–8% of China's land area) by 2010, including rapid replacement of mixed forest(Dwb) by deciduous forest(Dwa) over Northeast China, strong shrinkage of alpine climate type(ET) on the Tibetan Plateau, weak northward expansion of subtropical winterdry climate(Cwa) over Southeast China, and contraction of oceanic climate(Cwb) in Southwest China. Under all future RCP(Representative Concentration Pathway) scenarios, the reduction of Dwb in Northeast China and ET on the Tibetan Plateau was projected to accelerate substantially during 2010–30, and half of the total area occupied by ET in 1990 was projected to be redistributed by 2040. Under the most severe scenario(RCP8.5), sub-polar continental winter dry climate over Northeast China would disappear by 2040–50, ET on the Tibetan Plateau would disappear by 2070, and the climate types in 35.9%and 50.8% of China's land area would change by 2050 and 2100, respectively. The results presented in this paper indicate imperative impacts of anthropogenic climate change on China's ecoregions in future decades.     

CMIP5多模式预估的1.5℃升温背景下中国气温和降水变化

本文使用国际耦合模式比较计划第五阶段（CMIP5）中39个全球气候模式的试验数据,预估了相对于工业革命前期全球1.5℃升温背景下中国气温和降水变化。根据多模式中位数预估结果,在不同典型浓度路径（RCPs）情景下,相对于工业革命前期全球1.5℃升温分别发生在2034年（RCP2.6）、2033年（RCP4.5）和2029年（RCP8.5）。全球升温1.5℃时,中国年和季节气温平均上升1.8℃和1.6～2.1℃,其中冬季最强。增温总体上由南向北加强,青藏高原为高值中心。年和各季节增温均超过其自然内部变率,区域平均的信噪比分别为3.4和1.6～2.7。年和季节降水整体上在中国北方增加、华南减少;区域平均的年降水增加1.4%,季节降水增加0.1%～5.1%,冬季增幅最大。年和季节降水变化要远小于其自然内部变率,区域平均的信噪比仅为0.1和0.01～0.2。总体上,模式对气温预估的不确定性较小,对降水的偏大,其中对季节尺度预估的不确定性要高于年平均结果。     

Shelf wave dispersion in a geophysical ocean

We consider subinertial, free waves trapped along three coastlines (i.e., shelf waves) in an ocean governed by a geophysical model in which stratification is explicitly obtained by taking the Vaisala frequency N much greater than the inertial frequency f. The behavior is generalized in terms of the parameter S = (N/f)a where a is the bottom slope of the trapping region. Only when $\text{S}\text{\$}\text{?}\text{0.2}$, are the predicted shelf waves like those predicted by Laplace's tidal equations (LTE) on an f-plane. When 0.2 ? S < 1, LTE are inappropriate because the shelf waves are only qualitatively like those predicted by LTE, and when S 1, the shelf waves are like baroclinic Kelvin waves in that they can occur at any subinertial frequency up to f (in qualitative disagreement with the predictions of LTE). Since N/f is usually a large number in the real ocean (of order 50–250), S is likely to be large unless the bottom slope is very gentle throughout the trapping region. Some applications to coastal current observations are discussed.     

Characteristics of the atmospheric heat source and moisture sink over the Qinghai-Tibetan Plateau during the second TIPEX of summer 1998 and their impact on surrounding monsoon

Summary ?Using the data of 6 automatic heat balance observation (AWS) stations and a data set of 52 surface observation stations over the Qinghai-Tibetan Plateau (“the Plateau”) and surroundings, the horizontal distribution is studied of “apparent atmospheric heat sources” 〈Q ₁〉 and of “apparent atmospheric moisture sinks” 〈Q ₂〉. The AWS stations were established during the period May to August 1998 of the Tibetan Plateau Meteorological Experiment (second TIPEX) by a cooperation of China and Japan. For this period the Plateau mean of 〈Q ₁〉 is positive. Its value of 74 W/m² is a little greater than a climate value and than values from MONEX and the first TIPEX in 1979, respectively. Also the corresponding 〈Q ₂〉 is positive. Hence during that time the Plateau is a heat source and a moisture sink. A day-to-day change of 〈Q ₁〉 and 〈Q ₂〉 is more pronounced over the middle and east part of the Plateau than over the west part. Diagnostics accompanied by numerical simulations are used to study the daily relationship between 〈Q ₁〉 over the Plateau and the weather over China and Asia for this summer. The results suggest that 〈Q ₁〉 may affect precipitation over northern China and position of the west Pacific subtropical high. Abnormal southward retreat of this Pacific high seems to have caused the second flood over the middle and lower Yangtse river basin in July. Received May 20, 2001; revised February 2, 2002     

A Study of Surface Humidity Changes in China During the Recent 50 Years

This paper analyzes in detail the characteristics of surface humidity changes in China under the background of global warming in the recent 50 years by using the observation data compiled by the National Meteorological Information Center of China. The results reveal that (1) with the increase of temperature,surface saturation specific humidity (qs) shows basically an exponential growth, according to the Clausius-Clapeyron equation. The nationwide average moistening rate in winter is obviously less than the annual average rate and the summer rate. There are some regional differences in qstrends in different regions of China. For example, qsin central and eastern parts of China exhibits a reducing trend in summer, consistent with the weakening trend of temperature in these areas; (2) except parts of South China and Jianghuai Region in eastern China, unanimously increasing trends of annual and winter specific humidity (q) are found in most of China, especially in western China. In summer, except parts of Northeast China, Northwest China, and some areas over the Qinghai-Tibetan Plateau, the decreasing and drying trends are significant in most of China, which is not consistent with the global mean situation; (3) the surface relative humidity(RH) in most of China shows a reducing trend. One of the major reasons for the reduction of RH is that the increasing rates of q are smaller than those of qs. Nonetheless, upward trends of RH in central and eastern China mainly due to the cooling temperature and rising q in these regions are observed in summer, leading to more precipitation. From about 2003 or so, qshas remarkably increased while q has sharply decreased in most parts of China; therefore, RH has reduced to a great extent. This may be closely related to the persistent growth of drought areas in China in the recent 10 years.     

我国强降雪气候特征及其变化

基于全国气象台站逐日地面降雪观测数据,对我国25°N以北不同气候区强降雪事件的地理分布和年内旬、月变化等气候特征进行分析,并探讨1961—2008年其时间序列演变特征,及1961—2008年和1981—2008年 (气候变暖后) 气候变化趋势。结果表明:强降雪量和强降雪日数在青藏高原东部、新疆和东北北部最多;强降雪强度高值中心出现在云南。东北北部、华北、西北、青藏高原东部强降雪事件多发生于初冬和初春,年内分布呈双峰型;新疆和黄淮地区年内分布呈单峰型,前者多发生在隆冬时节,后者多发生于晚冬;1961—2008年东北北部、新疆、青藏高原东部平均强降雪量和强降雪日数呈明显增加趋势;气候变暖后我国大部年强降雪量增多,强降雪日数增加,强降雪强度增强。     

The ratio of land to ocean temperature change under global warming

The result in climate simulations, supported in the observation-based record, is that the ratio $\phi = T_{L} /T_{O} $ of land-average to ocean-average temperature change is greater than one and varies comparatively modestly as climate changes. This is investigated in results from the CMIP3 data archive of climate change simulations following the B1 and more strongly forced A1B scenarios as well as in 2×CO₂ integrations. The associated precipitation ratio $ \psi = P_{L} /P_{O} $ is also considered briefly. The behaviour of ? is analyzed in terms of a forcing-response view of the energy balance over land and ocean regions. The analysis indicates that the value of ??>?1 is not maintained by separate local balances over land and ocean but by an energetic balance that also involves a change in transport between the regions. The transport change does not restrain the land warming by exporting energy to the ocean region but, rather, the reverse. The anomalous transport is from the ocean to the land region even though the ocean warms less than the land does. Feedbacks in the ocean region, especially in the equatorial Pacific, do not sufficiently counteract the forcing and the result is an excess of energy that is transported to the land. The land warms in order to radiate away both the energy from the forcing over land but also the extra energy imported from the ocean region, thereby maintaining ??>?1. This situation can be understood to parallel the SST-forced case in model studies where ??>?1 despite the forcing being confined to the ocean area. The climate system is effective in redistributing forcing so that it is the local feedbacks, rather than the pattern of the forcing, that determine the temperature response. Land and ocean averaged quantities and budgets behave in a consistent manner to provide a simplified representation of the changes in temperature and energetic processes that are occurring. The geographical distributions of the terms do not, however, display a strong land/ocean demarcation. The land/ocean average budgets and balances are the residual of processes that vary considerably within the land and ocean boundaries.     

An evaluation of ice nuclei characteristics from the long-term measurement data over North China

An attempt was made to delineate the characteristics of ice nuclei (IN) over North China using the ground-based measurement data from 1963?C2003. The results show that: (1) the IN concentrations increased during the period from 1963?C1996, but decreased after 2000; (2) the average IN concentrations range from 1.0 to 26.3, 3.6 to 78.9, 19.2 to 627.3, and 92.9 to 5285.0 L^?1 at temperature ?15, ?20, ?25, and ?30°C, with the overall average of 7.8, 20.6, 167.7, and 890.6 L^?1, respectively; and (3) the number concentration of active IN increased nearly exponentially with decreasing temperature, with the slope (ranging from 0.11 to 0.42°C^?1) being of a narrow range in a log-linear coordinate; the regression equations for the western central China and the eastern central China can be expressed as N(T) = 0.0396 exp (?0.317 ??T) and N(T) = 0.1496 exp (?0.299??T), respectively. The present study may be useful toward applications in models for predicting IN effects on the cloud, precipitation and climate over North China.     

On the persistent spread in snow-albedo feedback

Snow-albedo feedback (SAF) is examined in 25 climate change simulations participating in the Coupled Model Intercomparison Project version 5 (CMIP5). SAF behavior is compared to the feedback’s behavior in the previous (CMIP3) generation of global models. SAF strength exhibits a fivefold spread across CMIP5 models, ranging from 0.03 to 0.16 W m^?2 K^?1 (ensemble-mean = 0.08 W m^?2 K^?1). This accounts for much of the spread in 21st century warming of Northern Hemisphere land masses, and is very similar to the spread found in CMIP3 models. As with the CMIP3 models, there is a high degree of correspondence between the magnitudes of seasonal cycle and climate change versions of the feedback. Here we also show that their geographical footprint is similar. The ensemble-mean SAF strength is close to an observed estimate of the real climate’s seasonal cycle feedback strength. SAF strength is strongly correlated with the climatological surface albedo when the ground is covered by snow. The inter-model variation in this quantity is surprisingly large, ranging from 0.39 to 0.75. Models with large surface albedo when these regions are snow-covered will also have a large surface albedo contrast between snow-covered and snow-free regions, and therefore a correspondingly large SAF. Widely-varying treatments of vegetation masking of snow-covered surfaces are probably responsible for the spread in surface albedo where snow occurs, and the persistent spread in SAF in global climate models.     

Vegetation and climate of the Lop Nur area, China, during the past 7 million years

Lop Nur in Xinjiang, Northwest China, is located in the lowest part of the Tarim Basin at an altitude of 780?m and experiences an extremely dry climate with an annual precipitation of only 17?mm and a high evaporation rate of 2,728?mm. The pollen and spores from the Late Miocene strata of a borehole in Lop Nur were analyzed with a view to interpreting the paleoenvironmental evolution of Lop Nur. Main types of pollen such as Chenopodiaceae, Nitraria, Ephedra and Artemisia reflect an arid climate. By collating the palynological data in this area as recorded in other literature and by applying the method of Coexistence Analysis, we have obtained the paleoclimatic parameters from Late Miocene to Holocene in Lop Nur. These suggest that temperatures increased from the Late Miocene (10.2°C) to the Pliocene (13.4°C), decreased from Pliocene to Pleistocene (4.7°C), and were more stable from Holocene (12.1°C) until now (11.5°C). The precipitation was stable (about 900?mm) from Late Miocene to Early Pleistocene, then decreased markedly (to about 300?mm) in Middle and Late Pleistocene, and reached its lowest value (17.4?mm) in the Holocene. The changes in paleoclimate at Lop Nur provide new evidence for understanding the uplift of the Qinghai-Tibetan Plateau.     

Spatial and temporal changes in aridity index in northwest China: 1960 to 2010

Northwest China is the driest region in China and the regional climate fluctuated dramatically during the last century. Aridity index, as the ratio between potential evapotranspiration and precipitation, is a good indicator to represent regional climate character. In this study, the change and attribution of the aridity index was investigated in northwest China using the observed climate data from 80 national meteorological stations during 1960–2010. The spatial and temporal variabilities of the aridity index shows that the annual aridity index decreased significantly (P?<?0.05) by 0.048 year^?1, indicating that northwest China became wetter from 1960 to 2010. A differentiation equation method was used to attribute the change in aridity index to climate variables. The results indicate that the aridity index was most sensitive to the change in precipitation, followed by vapor pressure, solar radiation, wind speed, and air temperature. Increase in air temperature should have led to an increase in aridity index, but this effect had been offset by the increase in precipitation and vapor pressure and the decrease in wind speed. Increasing precipitation, which contributed 91.7 % of the decrease in the aridity index, was the dominant factor to the decrease in the aridity index in northwest China from 1960 to 2010.     

气候变化背景下中国小麦需水量的敏感性研究

利用CROPWAT作物模型模拟分析了过去50年（1961-2010年）及IPCC RCPs情景下未来2020年代（2020-2029年）中国小麦需水量的变化情况。在此基础上,以小麦需水量的变化率作为敏感性因子,对RCP4.5和RCP8.5排放情景下中国小麦需水量的敏感性进行了探讨。结果表明：中国小麦多年平均需水量约为1056.4亿m³,最高值位于黄淮海地区。小麦需水量对气候变化的敏感性存在空间差异,华北和西北地区是小麦需水量的重度和极度敏感区,东北地区以及云贵高原地带是小麦需水量的轻度敏感区,而中国中部及南方部分地区的小麦需水量对气候变化不敏感。不同RCP排放情景下小麦需水量的敏感性分布不同,RCP8.5高排放情景下的小麦需水量敏感性区域比RCP4.5中排放情景下明显扩大,轻度和中度敏感区域扩大尤为明显。