Large-Scale Temperature Changes across the Southern Andes: 20th-Century Variations in the Context of the Past 400 Years
Large-Scale Temperature Changes across the Southern Andes: 20th-Century Variations in the Context of the Past 400 Years
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安第斯山脉南部的大规模气温变化：过去 400 年背景下的 20 世纪变化
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
Alberto Ripalta
中科院分区：
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作者：
R. Villalba;A. Lara;J. Boninsegna;M. Masiokas;S. Delgado;J. Aravena;F. Roig;A. Schmelter;A. Wolodarsky;Alberto Ripalta
利用仪器和树木年轮记录的组合，研究了整个南安第斯山脉（37-55°S）温度变化的长期趋势。根据台站记录对南美洲南部20世纪的地表气温进行了批判性评估。在1930-1990年期间，确定了三种主要的温度趋势。在37°S至43°S之间的太平洋沿岸站的特点是年平均气温呈负趋势，1950年至1970年代中期有一个明显的降温期。在南站（46°S以南）观测到明显的变暖趋势，在高纬度地区加剧。45°s以北的大西洋沿岸站没有检测到温度趋势。北半球高纬度地区的年温度变化主要由冬季趋势主导，而南美洲南部的正趋势和负趋势主要是由于夏季（12月至2月）温度的变化。1976年前后太平洋年代际涛动（PDO）的变化体现在太平洋地区大多数站点的夏季气温上，开始了安第斯山脉南部和高纬度地区气温升高的时期。利用树木年轮记录重建了安第斯山脉南部两种主要模式的过去温度波动。这些重建可以追溯到1640年，基于复合树轮年表，这些年表经过处理以尽可能多地保留低频方差。对南安第斯山脉北部和南部的重建结果分别解释了1930-1989年间55%和45%的温度变化。对1930-1989年共同区间的实际温度和重建温度进行的交叉光谱分析表明，大部分可解释的变化发生在bbb10年的周期内。在> ~ 15年的周期内，两次重建的实际温度和重建温度的平方相干度在0.6 ~ 0.95之间。因此，这些重建对于研究过去360年来南半球南美洲部分的多年温度变化特别有用。因此，有可能表明，在20世纪，整个南安第斯山脉的温度异常温暖。1900-1990年期间，北半球和南半球的年平均气温分别比1640 - 1899年的平均值高0.53°C和0.86°C。这些发现将当前的变暖置于更长的历史角度，并为20世纪全球大部分地区出现前所未有的变暖提供了新的支持。1850年至1920年的温度上升速度是过去360年来最高的，这是北半球高纬度地区的几个代用记录中观察到的一个共同特征。局部温度制度受到行星环流变化的影响，而这些变化又与全球海表温度（SST）异常有关。因此，我们探讨了1856年以来南安第斯山脉的温度变化与南太平洋和南大西洋大尺度海温的关系。重建与海温的空间相关模式表明，南安第斯山脉北段的温度变化与热带和亚热带太平洋海温异常密切相关。这种空间相关模式与南太平洋海温变率的PDO模态的空间特征相似，并与南半球的太平洋-南美（PSA）大气模式有关。相反，南安第斯山脉南段的温度变化与南大西洋大部分地区的海温异常显著相关，副热带太平洋的海温异常程度较低。这种空间相关场对海温的回归类似于海温变率的“全球变暖”模式，而海温变率反过来又与南半球的主导环流模式有关。当然，重建中存在的部分温度信号可以表示为四个正交海温变率模态的线性组合。对南太平洋和南大西洋海温进行的旋转经验正交函数分析表明，海温变率的四种离散模态大约解释了南安第斯山脉温度波动总方差的三分之一。
Long-term trends of temperature variations across the southern Andes (37–55° S) are examined using a combination of instrumental and tree-ring records. A critical appraisal of surface air temperature from station records is presented for southern South America during the 20th century. For the interval 1930–1990, three major patterns in temperature trends are identified. Stations along the Pacific coast between 37 and 43° S are characterized by negative trends in mean annual temperature with a marked cooling period from 1950 to the mid-1970s. A clear warming trend is observed in the southern stations (south of 46°S), which intensifies at higher latitudes. No temperature trends are detected for the stations on the Atlantic coast north of 45° S. In contrast to higher latitudes in the Northern Hemisphere where annual changes in temperature are dominated by winter trends, both positive and negative trends in southern South America are due to mostly changes in summer (December to February) temperatures. Changes in the Pacific Decadal Oscillation (PDO) around 1976 are felt in summer temperatures at most stations in the Pacific domain, starting a period with increased temperature across the southern Andes and at higher latitudes.Tree-ring records from upper-treeline were used to reconstruct past temperature fluctuations for the two dominant patterns over the southern Andes. These reconstructions extend back to 1640 and are based on composite tree-ring chronologies that were processed to retain as much low-frequency variance as possible. The resulting reconstructions for the northern and southern sectors of the southern Andes explain 55% and 45% ofthe temperature variance over the interval 1930–1989, respectively. Cross-spectral analysis of actual and reconstructed temperatures over the common interval 1930–1989, indicates that most of the explained varianceis at periods >10 years in length. At periods >15 years, the squaredcoherency between actual and reconstructed temperatures ranges between 0.6 and 0.95 for both reconstructions. Consequently, these reconstructions are especially useful for studying multi-decennial temperature variations in the South American sector of the Southern Hemisphere over the past 360 years. As a result, it is possible to show that the temperatures during the 20thcentury have been anomalously warm across the southern Andes. The mean annual temperatures for the northern and southern sectors during the interval 1900–1990 are 0.53 °C and 0.86 °C above the1640–1899 means, respectively. These findings placed the current warming in a longer historical perspective, and add new support for the existence of unprecedented 20th century warming over much of the globe. The rate of temperature increase from 1850 to 1920 was the highest over the past 360 years, a common feature observed in several proxy records from higher latitudes in the Northern Hemisphere.Local temperature regimes are affected by changes in planetary circulation, with in turn are linked to global sea surface temperature (SST) anomalies. Therefore, we explored how temperature variations in the southern Andes since 1856 are related to large-scale SSTs on the South Pacific and South Atlantic Oceans. Spatial correlation patterns between the reconstructions and SSTs show that temperature variations in the northern sector of the southern Andes are strongly connected with SST anomalies in the tropical and subtropical Pacific. This spatial correlation pattern resembles the spatial signature of the PDO mode of SST variability over the South Pacific and is connected with the Pacific-South American (PSA) atmospheric pattern in the Southern Hemisphere. In contrast, temperature variations in the southern sector of the southern Andes are significantly correlated with SST anomalies over most of the South Atlantic, and in less degree, over the subtropical Pacific. This spatial correlation field regressed against SST resembles the `Global Warming' mode of SST variability, which in turn, is linked to the leading mode of circulation in the Southern Hemisphere. Certainly, part of the temperature signal present in the reconstructions can be expressed as a linear combination of four orthogonal modes of SST variability. Rotated empirical orthogonal function analysis, performed on SST across the South Pacific and South Atlantic Oceans, indicate that four discrete modes of SST variability explain a third, approximately, of total variance in temperature fluctuations across the southern Andes.