The expectation of future precipitation change over the Mediterranean region is different from what we observe

In this study we assess the role of anthropogenic forcing (greenhouse gases and sulphate aerosols, GS) in recently observed precipitation trends over the Mediterranean region. We investigate whether the observed precipitation trends (1966–2005 and 1979–2008) are consistent with what 22 models project as response of precipitation to GS forcing. Significance is estimated using 9,000-year control runs derived from the CMIP3 archive. The results indicate that externally forced changes are detectable in observed precipitation trends in winter, late summer and in autumn. Natural internal climate variability cannot explain these changes. However, the observed trends (derived from 3 sources) are markedly inconsistent with expected changes due to GS forcing. While the influence of GS signal is detectable in winter and early spring, observed changes are several times larger than the projected response to GS forcing. The most striking inconsistency, however, is the contradiction between projected drying and the observed increase in precipitation in late summer and autumn, irrespective of the data set used. Natural (internal) variability as estimated from the models cannot account for these inconsistencies, which are already present in the large scale circulation patterns (Geopotential height at 500 hPa). The obtained results are robust to the removal of the fingerprint of the North Atlantic Oscillation. The detection of an outright sign mismatch of observed and projected trends in autumn and late summer, leads us to conclude that the recently observed trends can not be used as an illustration of plausible future expected change in the Mediterranean region. These significant shortcomings in our understanding of recent observed changes complicate communication of future expected changes in Mediterranean precipitation.     

The identification of distinct patterns in California temperature trends

Regional changes in California surface temperatures over the last 80 years are analyzed using station data from the US Historical Climate Network and the National Weather Service Cooperative Network. Statistical analyses using annual and seasonal temperature data over the last 80 years show distinctly different spatial and temporal patterns in trends of maximum temperature (Tmax) compared to trends of minimum temperature (Tmin). For trends computed between 1918 and 2006, the rate of warming in Tmin is greater than that of Tmax. Trends computed since 1970 show an amplified warming rate compared to trends computed from 1918, and the rate of warming is comparable between Tmin and Tmax. This is especially true in the southern deserts, where warming trends during spring (March?CMay) are exceptionally large. While observations show coherent statewide positive trends in Tmin, trends in Tmax vary on finer spatial and temporal scales. Accompanying the observed statewide warming from 1970 to 2006, regional cooling trends in Tmax are observed during winter and summer. These signatures of regional temperature change suggest that a collection of different forcing mechanisms or feedback processes must be present to produce these responses.     

Trend analysis of air temperature time series in Greece and their relationship with circulation using surface and satellite data: 1955–2001

Summary In this study, trends of annual and seasonal surface air temperature time series were examined for 20 stations in Greece for the period 1955–2001, and satellite data for the period 1980–2001. Two statistical tests based on the least square method and one based on the Mann-Kendall test, which is also capable of detecting the starting year of possible climatic discontinuities or changes, were used for the analysis. Greece, in general, shows a cooling trend in winter for the period 1955–2001, whereas, summer shows an overall warming trend, however, neither is statistically significant. As a result, the overall trend of the annual values is nearly zero. Comparison with corresponding trends in the Northern Hemisphere (NH) shows that temperatures in Greece do not follow the intense warming trends. Satellite data indicate a remarkable warming trend in mean annual, winter and summer in Greece for the period 1980–2001, and a slight warming trend in annual, spring and autumn for the NH. Comparison with the respective trends detected in the surface air temperature for the same period (1980–2001) shows they match each other quite well in both Greece and the NH. The relationship between temperature variability in Greece and atmospheric circulation was also examined using correlation analysis with three circulation indices: the well-known North Atlantic Oscillation Index (NAOI), a Mediterranean Oscillation Index (MOI) and a new Mediterranean Circulation Index (MCI). The MOI and MCI indices show the most interesting correlation with winter temperatures in Greece. The behaviour of pressure and the height of the 500hPa surface over the Mediterranean region supports these results.     

对喜马拉雅山脉中段6个台站的气候变化分析

利用喜马拉雅山脉中段南、北两侧6个气象站1971-2007年逐月气温、降水资料,分析了该地区气候变化趋势、异常及突变特征。结果表明：喜马拉雅山脉中段南、北两侧年、季平均气温均呈明显上升趋势,冬半年升温幅度大于夏半年。年及夏半年平均气温均为随年代升高趋势,而冬半年气温在20世纪80年代较70年代略偏低,90年代后又逐渐升高。21世纪前7 a升温最为显著,较20世纪70年代升高0.6～1.1℃。1997年该地区南侧年平均气温发生突变,突变后增温趋势更加明显。20世纪90年代末以来,异常偏暖年份出现的几率明显增加,且南侧多于北侧。喜马拉雅山脉中段北侧年及冬夏半年降水均呈增多趋势。南侧年和夏半年降水呈减少趋势,冬半年为增多趋势。降水异常出现在20世纪80、90年代,21世纪后降水出现异常的概率明显减少。近40 a,北侧气候具有暖湿化趋势;南侧冬半年与之类似,但夏半年及全年呈暖干化趋势。     

Variations and trends in annual and seasonal air temperatures in Greece determined from ground and satellite measurements

Summary The variations and trends in annual and seasonal air temperatures in Greece were examined on the basis of ground measurements for 25 stations during the period 1951–1993, and satellite measurements for the south eastern Mediterranean during the period 1979–1991. Data were smoothed using a 5-year running mean and were thereafter examined by regression analysis to define trends in the long duration time series. Data were also examined to detect abrupt changes and trends in the long duration annual, winter and summer series of mean maximum, mean minimum and mean temperatures. An overall cooling trend was detected for the majority of stations in winter over the entire period; the same cooling trend was also recognised for the annual and summer mean values, although a reverse warming trend was detected around the mid-70s at several stations. Satellite measurements indicate a slight warming trend, although this is not statistically significant. Considering the results of the regression analysis and the statistical tests applied to the 25 stations, it may be concluded that annual mean temperatures are dominated by an overall cooling trend, with the exception of stations in urban areas where urbanisation effects may have resulted in a warming trend. Summer temperatures, however, exhibit a warming trend roughly after 1975 at most stations.With 5 Figures     

Assessment of climate extremes in the Eastern Mediterranean

Summary Several seasonal and annual climate extreme indices have been calculated and their trends (over 1958 to 2000) analysed to identify possible changes in temperature- and precipitation-related climate extremes over the eastern Mediterranean region. The most significant temperature trends were revealed for summer, where both minimum and maximum temperature extremes show statistically significant warming trends. Increasing trends were also identified for an index of heatwave duration. Negative trends were found for the frequency of cold nights in winter and especially in summer. Precipitation indices highlighted more regional contrasts. The western part of the study region, which comprises the central Mediterranean and is represented by Italian stations, shows significant positive trends towards intense rainfall events and greater amounts of precipitation. In contrast, the eastern half showed negative trends in all precipitation indices indicating drier conditions in recent times. Significant positive trends were revealed for the index of maximum number of consecutive dry days, especially for stations in southern regions, particularly on the islands.Current affiliation: National Observatory of Athens, Athens, Greece.     

气候变暖背景下清远气温变化特征

根据1957—2007年清远站的年和月平均气温资料,采用线性倾向的最小二乘法估计分析季及年平均气温的变化趋势。结果表明:在气候变暖背景下,近50 a清远年平均气温存在与全球、中国及广东省同步的增暖趋势,增暖幅度(平均气温线性增暖速率为0.17℃/10 a)高于近50 a全球平均线性增暖速率,低于近50 a中国及广东省平均线性增暖速率。四季及年平均气温在变暖趋势上基本同步,只有冬季稍落后。且在气候变暖背景下,清远异常冷、暖冬事件出现频繁,暖冬明显。应用Mann-Kendall法检测气候的突变性,表明清远冬季平均气温于1968年前后存在由低向高的突变。     

1951—2010年大连市气温变化特征

利用1951—2010年大连市气温资料,采用气候趋势系数和气候倾向率、Mann-Kendal1突变分析等方法对年和季平均气温、最高最低气温变化特征进行了分析和突变检验。结果表明：大连市年和季平均气温呈上升趋势,进入21世纪,升温趋势有所减缓;大连市年平均气温的增温速率为0.33/10 a,明显高于近50 a中国平均增温速率0.22/10 a,更高于近50 a全球平均0.13/10 a的增温速率。大连市平均气温的升高主要发生在春季和冬季;年平均最低气温的升温幅度大于年平均最高气温的升温幅度;年、季平均气温存在突变,突变始于1987—1990年前后,突变前后平均气温均值相差较大;年、季平均最高气温和最低气温大都存在突变,但秋季平均最高气温无突变。     

北极平流层冬季早期变暖的GCM模拟研究

观测表明北极平流层自20世纪70年代末以来在冬季早期 (11～12月) 存在变暖的趋势。为了验证该趋势是否是由于海面温度 (SST) 升高造成的, 我们使用观测的全球SST强迫一个全球大气环流模式 (AGCM)。集合模拟的结果表明, 在SST强迫下, 北极平流层呈现统计显著的变暖趋势, 极地对流层也有相对较弱的变暖趋势, 但统计显著性较低。通过对模拟的位势高度进行经验正交函数 (EOF) 分析, 我们发现北半球位势高度第一模态 (EOF1) 的空间结构非常类似于北极涛动 (AO) 或北半球环状模 (NAM), 其平流层主分量时间序列在冬季早期呈现统计显著的负趋势。与负的AO趋势相对应的是, 对流层高纬度和平流层中高纬度波动增强, 说明极区变暖是由于波动增强产生的极区绝热加热增强造成的。另外, 模拟的结果还表明北极平流层不仅在冬季早期出现变暖的趋势, 在冬季晚期 (2～3月) 北极平流层低层也出现弱的变暖趋势。SST强迫导致北极平流层冬季变暖不利于异相臭氧化学反应的发生, 这对极地平流层臭氧恢复有着重要意义。     

Attribution of twentieth century temperature change to natural and anthropogenic causes

  We analyse possible causes of twentieth century near-surface temperature change. We use an “optimal detection” methodology to compare seasonal and annual data from the coupled atmosphere-ocean general circulation model HadCM2 with observations averaged over a range of spatial and temporal scales. The results indicate that the increases in temperature observed in the latter half of the century have been caused by warming from anthropogenic increases in greenhouse gases offset by cooling from tropospheric sulfate aerosols rather than natural variability, either internal or externally forced. We also find that greenhouse gases are likely to have contributed significantly to the warming in the first half of the century. In addition, natural effects may have contributed to this warming. Assuming one particular reconstruction of total solar irradiance to be correct implies, when we take the seasonal cycle into account, that solar effects have contributed significantly to the warming observed in the early part of the century, regardless of any relative error in the amplitudes of the anthropogenic forcings prescribed in the model. However, this is not the case with an alternative reconstruction of total solar irradiance, based more on the amplitude than the length of the solar cycle. We also find evidence for volcanic influences on twentieth century near-surface temperatures. The signature of the eruption of Mount Pinatubo is detected using annual-mean data. We also find evidence for a volcanic influence on warming in the first half of the century associated with a reduction in mid-century volcanism. Received: 24 January 2000 / Accepted: 20 April 2000     

1951—2010年大连市气温变化特征

利用1951—2010年大连市气温资料,采用气候趋势系数和气候倾向率、Mann-Kendal1突变分析等方法对年和季平均气温、最高最低气温变化特征进行了分析和突变检验。结果表明：大连市年和季平均气温呈上升趋势,进入21世纪,升温趋势有所减缓;大连市年平均气温的增温速率为0.33/10 a,明显高于近50 a中国平均增温...     

近30 a华北地区高空温度时空演变特征

根据华北地区12个探空站近30 a(1979-2008年)的各标准等压面月平均气温资料,对该地区高空年、季气温时空演变特征进行了分析.结果表明:华北地区高空年、季平均气温变化均具有非常高的空间一致性,其中冬季的一致性特征最明显;华北地区高空年、季平均气温大致以150-100 hPa层为界,以上(平流层下层)和以下(对流层)的气温存在着不同的变化特征:从近地面到200 hPa冬(夏)季最低(高),但在年平均气温最低的100-70 hPa,气温季节变化位相与对流层相反,50 hPa层以上气温的年变化不大;近30 a来华北地区对流层中下层的年、季平均气温变化以上升为主,而对流层上层至平流层下层则以下降为主.低层的变暖始于20世纪80年代后期,高层的变冷普遍始于20世纪90年代.     

The relative contributions of radiative forcing and internal climate variability to the late 20th Century winter drying of the Mediterranean region

The roles of anthropogenic climate change and internal climate variability in causing the Mediterranean region’s late 20th Century extended winter drying trend are examined using 19 coupled models from the Intergovernmental Panel on Climate Change Fourth Assessment Report. The observed drying was influenced by the robust positive trend in the North Atlantic Oscillation (NAO) from the 1960s to the 1990s. Model simulations and observations are used to assess the probable relative roles of radiative forcing, and internal variability in explaining the circulation trend that drove much of the precipitation change. Using the multi-model ensemble we assess how well the models can produce multidecadal trends of realistic magnitude, and apply signal-to-noise maximizing EOF analysis to obtain a best estimate of the models’ (mean) sea-level pressure (SLP) and precipitation responses to changes in radiative forcing. The observed SLP and Mediterranean precipitation fields are regressed onto the timeseries associated with the models’ externally forced pattern and the implied linear trends in both fields between 1960 and 1999 are calculated. It is concluded that the radiatively forced trends are a small fraction of the total observed trends. Instead it is argued that the robust trends in the observed NAO and Mediterranean rainfall during this period were largely due to multidecadal internal variability with a small contribution from the external forcing. Differences between the observed and NAO-associated precipitation trends are consistent with those expected as a response to radiative forcing. The radiatively forced trends in circulation and precipitation are expected to strengthen in the current century and this study highlights the importance of their contribution to future precipitation changes in the region.     

Historical Trend in River Ice Thickness and Coherence in Hydroclimatological Trends in Maine

We analyzed long-term records of ice thickness on the Piscataquis River in central Maine and air temperature in Maine to determine whether there were temporal trends that were associated with climate warming. The trend in ice thickness was compared and correlated with regional time series of winter air temperature, heating degree days (HDD), date of river ice-out, seasonal center-of-volume date (SCVD) (date on which half of the stream runoff volume during the period 1 Jan. to 31 May has occurred), water temperature, and lake ice-out date. All of these variables except lake ice-out date showed significant temporal trends during the 20th century. Average ice thickness around 28 February decreased by about 23 cm from 1912 to 2001. Over the period 1900 to 1999, winter air temperature increased by 1.7 °C and HDD decreased by about 7.5%.Final ice-out date on the Piscataquis River occurred earlier (advanced), by 0.21 days yr^–1 over the period 1931 to 2002, and the SCVD advancedby 0.11 days yr^–1 over the period 1903 to 2001. Ice thickness was significantly correlated (P-value <0.01) with winter air temperature, HDD, river ice-out, and SCVD. These systematic temporal trends in multiple hydrologic indicator variables indicate a coherent response to climate forcing.     

Trend analysis of precipitation time series in Greece and their relationship with circulation using surface and satellite data: 1955–2001

Summary In this study, the trends of annual and seasonal precipitation time series were examined on the basis of measurements of 22 surface stations in Greece for the period 1955–2001, and satellite data during the period 1980–2001. For this purpose, two statistical tests based on the least square method and one based on the Mann-Kendall test, which is also capable of detecting the starting year of possible climatic discontinuities or changes, are applied. Greece, in general, presents a clear significant downward trend in annual precipitation for the period 1955–2001, which is determined by the respective decreasing trend in winter precipitation. Both winter and annual series exhibit a downward trend with a starting year being 1984. Satellite-derived precipitation time series could be an alternative means for diagnosing the variability of precipitation in Greece and detecting trends provided that they have been adjusted by surface measurements in the wider area of interest. The relationship between precipitation variability in Greece and atmospheric circulation was also examined using correlation analysis with three circulation indices: the well-known North Atlantic Oscillation Index (NAOI), a Mediterranean Oscillation Index (MOI) and a new Mediterranean Circulation Index (MCI). NAOI is the index that presented the most interesting correlation with winter, summer and annual precipitation in Greece, whereas the MOI and MCI were found to explain a significant proportion of annual and summer precipitation variability, respectively. The observed downward trend in winter and annual precipitation in Greece is linked mainly to a rising trend in the hemispheric circulation modes of the NAO, which are connected with the Mediterranean Oscillation Index.     

North-Atlantic SST amplified recent wintertime European land temperature extremes and trends

Europe has been warming over the past 30?years. In particular all seasonal temperature records have been broken since 2003, which altered socio-economic and environmental systems. Since we expect this trend in both mean and extreme temperatures to continue along the twenty first century under enhanced radiative forcing, it is crucial to understand the underlying mechanisms of such climate variations to help in considering adaptation or mitigation strategies to reduce the impacts of a warmer climate. From a statistical analysis we show that the inter-annual variability of European seasonal temperatures can be reconstructed from North-Atlantic atmospheric circulation only, but not their recent trends and extreme seasons. Adding North-Atlantic sea-surface temperature (SST) as a predictor helps improving the reconstruction, especially in autumn and winter. Sensitivity experiments with the MM5 regional model over 2003?C2007 suggest that the anomalous SST enhance European land temperatures through the upper-air advection of heat and water vapor, interacting with radiative fluxes over the continent. This mechanism is pronounced in autumn and winter, where estimates of SST influence as obtained from MM5 are in agreement with those obtained from statistical regressions. We find a lesser SST influence in spring and summer, where local surface and radiative feedbacks are the main amplifiers of recent extremes.     

An assessment and interpretation of the observed warming of West Antarctica in the austral spring

We synthesize variability and trends in multiple analyses of Antarctic near-surface temperature representing several independent source datasets and spatially complete reconstructions, and place these into the broader context of the behavior of other components of the climate system during the past 30–50?years. Along with an annual-mean trend during the past 50?years of about 0.1°C/decade averaged over Antarctica, there is a distinct seasonality to the trends, with insignificant change (and even some cooling) in austral summer and autumn in East Antarctica, contrasting with warming in austral winter and spring. Apart from the Peninsula, the seasonal warming is largest and most significant in West Antarctica in the austral spring since the late 1970s. Concurrent trends in sea ice are independent evidence of the observed warming over West Antarctic, with the decrease in sea ice area in the Amundsen and Bellingshausen Seas congruent with at least 50% of the inland warming of West Antarctica. Trends in near surface winds and geopotential heights over the high-latitude South Pacific are consistent with a role for atmospheric forcing of the sea ice and air temperature anomalies. Most of the circulation trend projects onto the two Pacific South American (PSA) modes of atmospheric circulation variability, while the Southern Annular Mode lacks a positive trend in spring that would otherwise cause a cooling tendency. The largest circulation trend is associated with the PSA-1 mode, a wave-train extending from the tropics to the high Southern latitudes. The PSA-1 mode is significantly correlated with SSTs in the southwestern tropical and subtropical Pacific. The increased SSTs in this region, together with the observed increase in rainfall, suggest that anomalous deep convection has strengthened or increased the occurrence of the Rossby wave-train associated with PSA-1. This hypothesis is supported by results from two ensembles of SST-forced atmospheric general circulation model simulations. Finally, the implications of the seasonality, timing, and spatial patterns of Antarctic temperature trends with respect to interpreting the relative roles of stratospheric ozone depletion, SSTs and increased atmospheric concentrations of greenhouse gasses are discussed.     

1960-2009年咸宁市气候变化特征分析

利用1960-2009年咸宁市3个地面气象站气象资料,统计分析近50 a来该区域气温、降水等主要气候要素的年变化、四季变化及年代际变化的趋势特征。结果表明：近50 a研究区气温有上升趋势,气候倾向率为0.23℃/10a,年平均气温在20世纪90年代末发生突变。春秋季平均气温分别在2002年和1999年发生突变,夏季平均气温在2006年发生突变,冬季平均气温早在1990年发生突变。春季与秋季平均气温的变化比较一致,冬季平均气温对全球变暖响应最敏感,春秋与秋季对气候变暖的响应是比较敏感,而夏季对气候变暖的响应最为迟缓。近50 a年降水量呈波动但无明显增降的趋势,其中春夏两季变化趋势较为一致并有下降的趋势,且春夏降水量的变化主导着年降水量的变化;而冬季降水量有上升的趋势。通过对气温与降水变化趋势的比较,发现冬季对气候变化的响应最显著、其余季节无明显相关性。     

1960—2009年咸宁市气候变化特征

利用1960—2009年咸宁市3个地面气象站气象资料,统计分析近50 a来该区域气温、降水等主要气候要素的年变化、四季变化及年代际变化的趋势特征。结果表明：近50 a研究区气温有上升趋势,气候倾向率为0.23℃/10 a,年平均气温在20世纪90年代末发生突变。春秋季平均气温分别在2002年和1999年发生突变,夏季平均气温在2006年发生突变,冬季平均气温在1990年发生突变。春季与秋季平均气温的变化较一致,冬季平均气温对全球变暖响应最敏感,春季与秋季对气候变暖的响应较敏感,而夏季对气候变暖的响应最为迟缓。近50 a咸宁市年降水量呈波动但无明显增降的趋势,其中春夏两季变化趋势较为一致并有下降的趋势,且春夏降水量的变化主导着年降水量的变化;而冬季降水量有上升的趋势。通过对气温与降水变化趋势的比较,发现冬季对气候变化的响应最显著,其余季节无明显相关性。     

A stochastic model for the analysis of maximum daily temperature

Accurately predicting precipitation trends is vital in the economic development of a country. Ground observed data from the Nigeria Meteorological Agency (NIMET) was analyzed to study the long-term spatio-temporal trends of rainfall on annual and seasonal scales for 23 stations in Nigeria during a 40-year period spanning from 1974 to 2013. After testing the presence of autocorrelation, Mann–Kendall (modified Mann–Kendall) test was applied to non-autocorrelated (autocorrelated) series to detect the trends in rainfall data. Theil and Sen’s slope estimator test was used to find the magnitude of change over a time period. Pettitt’s test, Standard Normal Homogeneity Test, and Buishand’s test were further used to test the homogeneity of the rainfall series. The results show an increasing trend in annual rainfall; however, only nine stations have a significant increase during the period of study. On the seasonal time scale, a significant increasing trend was observed in the pre- and post-monsoon seasons, while only nine stations show a significant increasing trend in monsoon rainfall and a significant decreasing trend in the winter rainfall over the last 40 years. During the study period, 15.4 and 13.90 % increase were estimated for annual and monsoonal rainfall, respectively. Furthermore, seven stations exhibit changes in mean rainfall while majority of the stations considered (Eighteen stations) exhibit homogeneous trends in annual and seasonal rainfall over the country. The performance of the different tests used in this study was consistent at the verified significance level.