Global Warming and Northern Hemisphere Sea Ice Extent

Surface and satellite-based observations show a decrease in Northern Hemisphere sea ice extent during the past 46 years. A comparison of these trends to control and transient integrations (forced by observed greenhouse gases and tropospheric sulfate aerosols) from the Geophysical Fluid Dynamics Laboratory and Hadley Centre climate models reveals that the observed decrease in Northern Hemisphere sea ice extent agrees with the transient simulations, and both trends are much larger than would be expected from natural climate variations. From long-term control runs of climate models, it was found that the probability of the observed trends resulting from natural climate variability, assuming that the models' natural variability is similar to that found in nature, is less than 2 percent for the 1978-98 sea ice trends and less than 0.1 percent for the 1953-98 sea ice trends. Both models used here project continued decreases in sea ice thickness and extent throughout the next century.     

Simulation of recent global temperature trends

Observations show that global average tropospheric temperatures have been rising during the past century, with the most recent portion of record showing a sharp rise since the mid-1970s. This study shows that the most recent portion of the global temperature record (1970 to 1992) can be closely reproduced by atmospheric models forced only with observed ocean surface temperatures. In agreement with a diverse suite of controversial observational evidence from the past 40 years, the upward trend in simulated tropospheric temperatures is caused by an enhancement of the tropical hydrologic cycle driven by increasing tropical ocean temperatures. Although it is possible that the observed behavior is due to natural climate variability, there is disquieting similarity between these model results, observed climate trends in recent decades, and the early expressions of the climatic response to increased atmospheric carbon dioxide in numerical simulations.     

Potential magnitude of future vegetation change in eastern north america: comparisons with the past

Increases in atmospheric trace gas concentrations could warm the global average temperature 1.5 degrees to 4.5 degrees C by the end of the next century. Application of climate-pollen response surfaces to three climate model simulations of doubled preindustrial atmospheric CO(2) levels shows that the change in the equilibrium distribution of natural vegetation over eastern North America over the next 200 to 500 years could be larger than the overall change during the past 7,000 to 10,000 years and equivalent to the change that took place over the 1,000- to 3,000-year period of most rapid deglaciation. Some plant ranges and abundance maxima could shift as much as 500 to 1000 km during the next 200 to 500 years; such changes would have dramatic impacts on silvicultural and natural ecosystems. Although unprecedented vegetation change is likely if climate changes as predicted, forecasting the exact timing and patterns of change will be difficult.     

Causes of climate change over the past 1000 years

Recent reconstructions of Northern Hemisphere temperatures and climate forcing over the past 1000 years allow the warming of the 20th century to be placed within a historical context and various mechanisms of climate change to be tested. Comparisons of observations with simulations from an energy balance climate model indicate that as much as 41 to 64% of preanthropogenic (pre-1850) decadal-scale temperature variations was due to changes in solar irradiance and volcanism. Removal of the forced response from reconstructed temperature time series yields residuals that show similar variability to those of control runs of coupled models, thereby lending support to the models' value as estimates of low-frequency variability in the climate system. Removal of all forcing except greenhouse gases from the approximately 1000-year time series results in a residual with a very large late-20th-century warming that closely agrees with the response predicted from greenhouse gas forcing. The combination of a unique level of temperature increase in the late 20th century and improved constraints on the role of natural variability provides further evidence that the greenhouse effect has already established itself above the level of natural variability in the climate system. A 21st-century global warming projection far exceeds the natural variability of the past 1000 years and is greater than the best estimate of global temperature change for the last interglacial.     

External control of 20th century temperature by natural and anthropogenic forcings

A comparison of observations with simulations of a coupled ocean-atmosphere general circulation model shows that both natural and anthropogenic factors have contributed significantly to 20th century temperature changes. The model successfully simulates global mean and large-scale land temperature variations, indicating that the climate response on these scales is strongly influenced by external factors. More than 80% of observed multidecadal-scale global mean temperature variations and more than 60% of 10- to 50-year land temperature variations are due to changes in external forcings. Anthropogenic global warming under a standard emissions scenario is predicted to continue at a rate similar to that observed in recent decades.     

Climate impact of increasing atmospheric carbon dioxide

The global temperature rose by 0.2 degrees C between the middle 1960's and 1980, yielding a warming of 0.4 degrees C in the past century. This temperature increase is consistent with the calculated greenhouse effect due to measured increases of atmospheric carbon dioxide. Variations of volcanic aerosols and possibly solar luminosity appear to be primary causes of observed fluctuations about the mean trend of increasing temperature. It is shown that the anthropogenic carbon dioxide warming should emerge from the noise level of natural climate variability by the end of the century, and there is a high probability of warming in the 1980's. Potential effects on climate in the 21st century include the creation of drought-prone regions in North America and central Asia as part of a shifting of climatic zones, erosion of the West Antarctic ice sheet with a consequent worldwide rise in sea level, and opening of the fabled Northwest Passage.     

Perspectives on the Arctic's shrinking sea-ice cover

Linear trends in arctic sea-ice extent over the period 1979 to 2006 are negative in every month. This ice loss is best viewed as a combination of strong natural variability in the coupled ice-ocean-atmosphere system and a growing radiative forcing associated with rising concentrations of atmospheric greenhouse gases, the latter supported by evidence of qualitative consistency between observed trends and those simulated by climate models over the same period. Although the large scatter between individual model simulations leads to much uncertainty as to when a seasonally ice-free Arctic Ocean might be realized, this transition to a new arctic state may be rapid once the ice thins to a more vulnerable state. Loss of the ice cover is expected to affect the Arctic's freshwater system and surface energy budget and could be manifested in middle latitudes as altered patterns of atmospheric circulation and precipitation.     

Interannual variability of temperature at a depth of 125 meters in the north atlantic ocean

Analyses of historical ocean temperature data at a depth of 125 meters in the North Atlantic Ocean indicate that from 1950 to 1990 the subtropical and subarctic gyres exhibited linear trends that were opposite in phase. In addition, multivariate analyses of yearly mean temperature anomaly fields between 20 degrees N and 70 degrees N in the North Atlantic show a characteristic space-time temperature oscillation from 1947 to 1990. A quasidecadal oscillation, first identified at Ocean Weather Station C, is part of a basin-wide feature. Gyre and basin-scale variations such as these provide the observational basis for climate diagnostic and modeling studies.     

黄河流域极端气候事件的时空变异特征研究

以黄河流域为例,充分考虑降水要素的空间异质性,将其划分为8个子区域;选定持续干燥指数（CDD）、持续湿润指数（CWD）、强降水日数（R10）和5 d最大降水量（RX5）4个极端降水指标,采用数理统计、一元线性回归等方法对各子区域极端降水特征进行趋势性分析;并采用基于贝叶斯理论的可逆跳跃马尔科夫蒙特卡洛算法（RJMCMC）,识别并量化了各子区域不同极端降水指标的突变位置及其变异程度。结果表明:1）黄河流域暖干化趋势明显,流域北部尤为突出。2）CDD、CWD、R10和RX5指数空间上趋势变化较大,但相邻区域之间存在相似的分布规律。3）不同子区域不同极端气候指数的突变年份不同,但多集中于90年代。研究结果可有效提高极端气候预测的准确性和可靠性。识别并量化气候时空变异特征对防洪、抗旱布控工作的顺利开展具有现实意义。     

Anthropogenic influence on the autocorrelation structure of hemispheric-mean temperatures

It is shown that lagged correlations for and cross-correlations between observed hemispheric-mean temperature data differ markedly from those for unforced (control-run) climate model simulations. The differences can be explained adequately by assuming that the observed data contain a significant externally forced component involving both natural (solar) and anthropogenic influences and that the global climate sensitivity is in the commonly accepted range. Solar forcing alone cannot reconcile the differences in autocorrelation structure between observations and model control-run data.     

1953～2008年辽宁本溪地区气候异常年分析

对1953～2008年本溪地区温度和降水资料进行统计分析。利用Mann-Kendall方法对年平均气温和年降水量进行突变年检测;应用气温降水异常指标,分析确定异常年。结果表明,本溪地区气候变化特点是温度上升,降水呈减少趋势。气温增加幅度各季差异较大,对气候变暖贡献最大的是冬季,平均最低气温升高幅度明显高于平均最高气温;年平均气温1988年为突变年。1953～2008年,本溪地区降水量呈减少趋势,阶段性较明显;1974年为突变年,之前为降水偏多时段,之后为降水偏少时段。     

张家口地区气候特征及其对玉米生产的影响

基于张家口地区近50年(1965-2014)的气温和降水等气象资料,以及近34年(1981-2014)玉米产量资料,研究了张家口地区气候变化特征,并分析了气候变化对张家口玉米生产的影响。结果表明,近50年平均气温呈上升趋势,并在1986/1987年发生突变,降水量变化表现为年际间波动性大,存在稳定的9年左右变化周期。干旱具有明显变化特征,自气温发生突变后,夏季干旱的空间范围、持续时间和干旱程度均有所增加。各县玉米产量变化与气候要素变化具有很强的相关性,其中降水是影响产量变化的主要因素,玉米产量与降水量呈正相关关系。     

1956～2007年河北地区气候变化时空特征研究

[目的]研究1956～2007年河北地区气候变化时空特征。[方法]选取河北地区(包括京津)均匀分布的23个气象站点1956～2007年数据,采用统计分析方法,对该地区气温、降水等主要气象要素的时空变化特征进行分析,探讨该地区52年来的气候变化事实和演变规律。[结果]1956～2007年河北地区年和四季气温均表现为波动上升趋势,冬季增温幅度最大,对该地区年气温的上升贡献率最大;全区气温均为升高趋势,其变化差异具有规律性。年和四季降水量的波动幅度均较大,且呈现不同的线性变化趋势,年降水量总体呈波动减少的趋势;降水量变化的空间差异性较显著,全区降水量均呈减少趋势,且其减少幅度由东北到西南基本呈现低—高—低的形态。全区潜在蒸发量20世纪60年代达到最大,之后其并没有随着升温而继续增大,相反的是呈明显下降趋势;各季节潜在蒸发量也呈下降趋势;全区除丰宁、蔚县等个别站蒸发量呈微弱上升趋势外,其余站均为下降趋势。相对湿度的变化趋势总体为缓慢减小;全区相对湿度仅有承德、秦皇岛、南宫等站呈上升趋势,其他站均呈减少趋势。日照时数具有明显的下降趋势。[结论]该研究为实现区域的可持续发展、改善生态环境和提高人民生活质量提供科学依据。     

Radiosonde daytime biases and late-20th century warming

The temperature difference between adjacent 0000 and 1200 UTC weather balloon (radiosonde) reports shows a pervasive tendency toward cooler daytime compared to nighttime observations since the 1970s, especially at tropical stations. Several characteristics of this trend indicate that it is an artifact of systematic reductions over time in the uncorrected error due to daytime solar heating of the instrument and should be absent from accurate climate records. Although other problems may exist, this effect alone is of sufficient magnitude to reconcile radiosonde tropospheric temperature trends and surface trends during the late 20th century.     

Dynamics of recent climate change in the Arctic

The pattern of recent surface warming observed in the Arctic exhibits both polar amplification and a strong relation with trends in the Arctic Oscillation mode of atmospheric circulation. Paleoclimate analyses indicate that Arctic surface temperatures were higher during the 20th century than during the preceding few centuries and that polar amplification is a common feature of the past. Paleoclimate evidence for Holocene variations in the Arctic Oscillation is mixed. Current understanding of physical mechanisms controlling atmospheric dynamics suggests that anthropogenic influences could have forced the recent trend in the Arctic Oscillation, but simulations with global climate models do not agree. In most simulations, the trend in the Arctic Oscillation is much weaker than observed. In addition, the simulated warming tends to be largest in autumn over the Arctic Ocean, whereas observed warming appears to be largest in winter and spring over the continents.     

沈阳沈北新区气候变暖对农业的影响

[目的]研究近38年沈阳沈北新区气候变暖对农业的影响。[方法]利用沈阳沈北新区1971~2008年气温资料,采用常规统计方法,分析了在气候变暖的环境下沈北新区气温、活动积温的变化趋势,并讨论了气候变暖对农业的影响。[结果]近38年来沈北新区年平均气温、年平均最高气温、年平均最低气温和稳定通过≥0℃、≥10℃活动积温均呈现明显的升高趋势,气候倾向率分别为0.4、0.3、0.1℃/10a和79.1、76.7（℃.d）/10a。最寒冷的12和1月呈下降趋势,其他各月均呈上升趋势。最高气温大于最低气温的升温幅度,夏季升温幅度大于冬季,这一分析结果与很多学者研究的结果有所不同。气温升高、热量资源增加农业复种指数提高,中晚熟品种栽培界限北移,设施农业迅速发展,同时也增加了旱涝灾害的风险和促进了病虫害的加重。[结论]该研究为提高气候变暖对农业生产影响的认识和增强当地农业生产适应气候变化的应变能力提供科学依据。     

1959～2008年辽宁省浅层地温变化趋势分析

利用1959～2008年辽宁省0、5、15、20cm各层逐月平均地温,采用气候倾向率和累积距平气候统计方法,分析辽宁省各浅层地温年、月变化趋势及气候异常等特征。结果表明：各层年平均地温以0.171～0.823℃/10a的升温率显著上升。年代变化趋势存在共同的特征：20世纪60年代前期至中期变化平稳,20世纪60年代末期至70年代初期处于50年以来的低温期。20世纪70年代中期至21世纪初,尤其80年代以后,各浅层地温增温显著,其中21世纪初期处于50年以来的高温期。辽宁省近50年浅层5、10、15、20cm月平均地温4～10月异常年份较多,且异常偏暖年份明显多于异常偏冷年份。就年平均温度而言：异常年份较少。     

Multidecadal changes in the vertical temperature structure of the tropical troposphere

Trends in global lower tropospheric temperature derived from satellite observations since 1979 show less warming than trends based on surface meteorological observations. Independent radiosonde observations of surface and tropospheric temperatures confirm that, since 1979, there has been greater warming at the surface than aloft in the tropics. Associated lapse-rate changes show a decrease in the static stability of the atmosphere, which exceeds unforced static stability variations in climate simulations with state-of-the-art coupled ocean-atmosphere models. The differential temperature trends and lapse-rate changes seen during the satellite era are not sustained back to 1960.     

气温变化背景下中国黄淮旱地冬小麦农艺性状的变化特征 ——以山西临汾为例

【目的】作物品种选育是在气候变化背景下的自然选择和人工选择的结果。黄淮麦区是中国最大的麦区,在保障中国小麦生产和粮食安全中有重要作用。研究过去30年黄淮旱地冬小麦品种农艺性状和气温要素变化规律,为旱地小麦育种适应未来气候变化提供理论依据和技术支撑。【方法】利用近30年来国家黄淮旱地冬小麦区域试验典型代表临汾点的对照品种农艺性状及该市的气温资料,研究对照品种农艺性状、生育期平均气温和≥0℃积温的变化规律,并进行农艺性状和气象要素的相关、多元回归和通径分析。【结果】小麦生育期的平均气温、≥0℃积温、最低和最高温度在逐年呈缓慢增加。小麦生育期平均气温平均每年上升0.05℃,≥0℃积温平均每年上升21.9℃,且二者呈正相关关系。≥0℃积温变化更能深入反映小麦生育期的温度变化情况。小麦生育期最高气温平均每年上升0.02℃、最低气温平均每年上升0.16℃。播种至越冬前的平均气温和≥0℃积温增加最多,营养生长阶段平均气温和≥0℃积温增加明显,生殖生长阶段平均气温增加较少且≥0℃积温有下降趋势。随着气候变暖,分蘖多的强冬性品种逐渐被分蘖适中的冬性和弱冬性品种替代。1986-1996年对照品种农艺性状变化幅度不大,1997-2007年期间变化较大,2007-2014年变化幅度最大;这和小麦生育期平均气温变化趋势基本相同。黄淮旱地对照品种千粒重和穗粒数逐年缓慢上升,分别每年平均增加1.57%和3.39%。有效穗数和产量及株高缓慢下降,分别每年平均下降0.16%和1.29%。产量与株高（0.684^**）、有效穗（0.531^**）和千粒重（0.541^**）均极显著正相关。株高、起身至拔节期≥0℃积温和平均气温是决定小麦产量的3个主要因子,分别决定了小麦产量的46.73%、26.17和3.26%的变异。在黄淮旱地小麦适应气候变化中,起身至拔节期≥0℃积温和株高对产量贡献较大且为正效应;起身至拔节期平均气温为负效应。【结论】气候变暖对黄淮旱地冬小麦农艺性状变化趋势有较强的影响,选育株高和有效穗数适中、穗粒数较多、千粒重较大的中高产抗旱品种是黄淮旱地小麦适应未来气候变化的育种改良方向。     

Evidence for large decadal variability in the tropical mean radiative energy budget

It is widely assumed that variations in Earth's radiative energy budget at large time and space scales are small. We present new evidence from a compilation of over two decades of accurate satellite data that the top-of-atmosphere (TOA) tropical radiative energy budget is much more dynamic and variable than previously thought. Results indicate that the radiation budget changes are caused by changes in tropical mean cloudiness. The results of several current climate model simulations fail to predict this large observed variation in tropical energy budget. The missing variability in the models highlights the critical need to improve cloud modeling in the tropics so that prediction of tropical climate on interannual and decadal time scales can be improved.