Long-term summer temperature reconstruction inferred from tree-ring records from the Eastern Carpathians

The first 1,000 year long Carpathian tree-ring width chronology was established based on living and subfossil stone pine (Pinus cembra L.) samples from an upper timberline forest located in Calimani Mts. (Romania). Tree-ring data were standardized using the regional curve standardization method in order to preserve the low and medium frequency climate signals. The de-trended index strongly correlates with summer mean temperature both at annual and decadal scales. The Calimani summer mean temperature anomalies were reconstructed for the period ad 1163-2005 applying the rescaling method. This new climate proxy from the Carpathians shows similar fluctuations to other North Hemispheric temperature reconstructions, but with periods of distinct differences. The fingerprint of Little Ice Age in the Calimani area is visible between ad 1370 and 1630 followed by lagged cold decades in ad 1820 and 1840. The recent warming is evident only after the 1980s in our reconstruction.     

A 1052-year tree-ring proxy for Alpine summer temperatures

A June–August Alpine temperature proxy series is developed back to AD 951 using 1,527 ring-width measurements from living trees and relict wood. The reconstruction is composed of larch data from four Alpine valleys in Switzerland and pine data from the western Austrian Alps. These regions are situated in high elevation Alpine environments where a spatially homogenous summer temperature signal exists. In an attempt to capture the full frequency range of summer temperatures over the past millennium, from inter-annual to multi-centennial scales, the regional curve standardization technique is applied to the ring width measurements. Correlations of 0.65 and 0.86 after decadal smoothing, with high elevation meteorological stations since 1864 indicate an optimal response of the RCS chronology to June–August mean temperatures. The proxy record reveals warm conditions from before AD 1000 into the thirteenth century, followed by a prolonged cool period, reaching minimum values in the 1820s, and a warming trend into the twentieth century. This latter trend and the higher frequency variations compare well with the actual high elevation temperature record. The new central Alpine proxy suggests that summer temperatures during the last decade are unprecedented over the past millennium. It also reveals significant similarities at inter-decadal to multi-centennial frequencies with large-scale temperature reconstructions, however, deviating during certain periods from H.H. Lamb‘s European/North Atlantic temperature history.     

Reconstructions of spring/summer precipitation for the Eastern Mediterranean from tree-ring widths and its connection to large-scale atmospheric circulation

This study represents the first large-scale systematic dendroclimatic sampling focused on developing chronologies from different species in the eastern Mediterranean region. Six reconstructions were developed from chronologies ranging in length from 115 years to 600 years. The first reconstruction (1885–2000) was derived from principal components (PCs) of 36 combined chronologies. The remaining five, 1800–2000, 1700–2000, 1600–2000, 1500–2000 and 1400–2000 were developed from PCs of 32, 18, 14, 9, and 7 chronologies, respectively. Calibration and verification statistics for the period 1931–2000 show good levels of skill for all reconstructions. The longest period of consecutive dry years, defined as those with less than 90% of the mean of the observed May–August precipitation, was 5 years (1591–1595) and occurred only once during the last 600 years. The longest reconstructed wet period was 5 years (1601–1605 and 1751–1755). No long term trends were found in May–August precipitation during the last few centuries. Regression maps are used to identify the influence of large-scale atmospheric circulation on regional precipitation. In general, tree-ring indices are influenced by May–August precipitation, which is driven by anomalous below (above) normal pressure at all atmospheric levels and by convection (subsidence) and small pressure gradients at sea level. These atmospheric conditions also control the anomaly surface air temperature distribution which indicates below (above) normal values in the southern regions and warmer (cooler) conditions north of around 40°N. A compositing technique is used to extract information on large-scale climate signals from extreme wet and dry summers for the second half of the twentieth century and an independent reconstruction over the last 237 years. Similar main modes of atmospheric patterns and surface air temperature distribution related to extreme dry and wet summers were identified both for the most recent 50 years and the last 237 years. Except for the last few decades, running correlation analyses between the major European-scale circulation patterns and eastern Mediteranean spring/summer precipitation over the last 237 years are non-stationary and insignificant, suggesting that local and/or sub-regional geographic factors and processes are important influences on tree-ring variability over the last few centuries.     

Sea-level pressure variability around Antarctica since A.D. 1750 inferred from subantarctic tree-ring records

 A tree-ring chronology network recently developed from the subantarctic forests provides an opportunity to study long-term climatic variability at higher latitudes in the Southern Hemisphere. Fifty long (1911–1985), homogeneous records of monthly mean sea-level pressure (MSLP) from the southern latitudes (15–65^°S) were intercorrelated on a seasonal basis to establish the most consistent, long-term Trans-Polar teleconnections during this century. Variations in summer MSLP between the South America-Antarctic Peninsula and the New Zealand sectors of the Southern Ocean are significantly correlated in a negative sense (r=−0.53, P<0.001). Climatically sensitive chronologies from Tierra del Fuego (54–55^°) and New Zealand (39–47^°) were used to develop verifiable reconstructions of summer (November to February) MSLP for both sectors of the Southern Ocean. These reconstructions, which explain between 37 and 43% of the instrumentally recorded pressure variance, indicate that inverse trends in MSLP from diametrically opposite sides of Antarctica have prevailed during the past two centuries. However, the strength of this relationship varies over time. Differences in normalized MSLP between the New Zealand and the South America-Antarctic Peninsula sectors were used to develop a Summer Trans-Polar Index (STPI), which represents an index of sea-level pressure wavenumber one in the Southern Hemisphere higher latitudes. Tree-ring based reconstructions of STPI show significant differences in large-scale atmospheric circulation between the nineteenth and the twentieth centuries. Predominantly-negative STPI values during the nineteenth century are consistent with more cyclonic activity and lower summer temperatures in the New Zealand sector during the 1800s. In contrast, cyclonic activity appears to have been stronger in the mid-twentieth than previously for the South American sector of the Southern Ocean. Recent variations in MSLP in both regions are seen as part of the long-term dynamics of the atmosphere connecting opposite sides of Antarctica. A detailed analysis of the MSLP and STPI reconstructions in the time and frequency domains indicates that much of the interannual variability is principally confined to frequency bands with a period around 3.3–3.6 y. Cross spectral analysis between the STPI reconstruction and the Southern Oscillation Index suggests that teleconnections between the tropical ocean and extra-tropical MSLP variations may be influencing climate fluctuations at southern latitudes. Received: 18 December 1996/Accepted: 10 January 1997     

Early summer temperature reconstruction in the eastern Tibetan plateau since ad 1440 using tree-ring width of Sabina tibetica

Long climate records are scarce on the Tibetan Plateau for understanding the climate variability on long-term context. Here we presented an early summer (May?CJune) temperature reconstruction since ad 1440 for Qamdo area using tree rings of Sabina tibetica. The reconstruction accounted for 64% of the variance in the instrumental record. It showed warm periods during 1501?C1514, 1528?C1538, 1598?C1609, 1624?C1636, 1650?C1668, 1695?C1705, 1752?C1762, 1794?C1804, 1878?C1890, 1909?C1921, 1938?C1949, and 1979?C1991. Cool early summer occurred during 1440?C1454, 1482?C1500, 1515?C1527, 1576?C1597, 1610?C1621, 1669?C1679, 1706?C1716, 1782?C1793, 1863?C1873, 1894?C1908, and 1922?C1937. Comparison with other proxy or meteorological records suggested that there is obvious spatial variability in the May?CJune temperature variations along the eastern margin of the Tibetan Plateau.     

Analyses of summer lightning activity and precipitation in the Central and Eastern Mediterranean

The lightning activity and precipitation in two 3-hour time intervals in the grid boxes of 0.25 × 0.25° over East and Central Mediterranean during the summer of 2005 and 2006 are analysed. The results show that the frequency distribution of the precipitation amount is shifted towards larger values for the cases with lightning as compared with the cases without lightning. It was found that the number of cases with 3-hour accumulated rainfall greater than 10 mm was bigger when lightning occurred (65%) than when it was absent (35%). Investigation of diurnal and spatial distributions of lightning shows that the afternoon flash density peak is associated mainly with lightning over the land, which is in accordance with the results of earlier works. The early morning flash density peak is associated mainly with flashes over the sea. High correlation coefficients (0.89 during the morning hours and 0.98 during afternoon) were found between rain rate (mm/h) and average flash density (fl/km²) when flash density is averaged in logarithmic intervals of rain rate.     

Reconstructed Northern Hemisphere annual temperature since 1671 based on high-latitude tree-ring data from North America

Annual Northern Hemisphere surface temperature departures for the past 300 yr were reconstructed using eleven tree-ring chronologies from high-latitude, boreal sites in Canada and Alaska, spanning over 90 degrees of longitude. This geographic coverage is believed to be adequate for a useful representation of hemispheric-scale temperature trends, as high northern latitudes are particularly sensitive to climatic change. We also present a reconstruction of Arctic annual temperatures. The reconstructions show a partial amelioration of the Little Ice Age after the early 1700's, an abrupt, severe renewal of cold in the early 1800's and a prolonged wanning since approximately 1840. These trends are supported by other proxy data. Similarities and differences between our Northern Hemisphere reconstruction and other large-scale proxy temperature records depend on such factors as the data sources, methods, and degree of spatial representation. Analyses of additional temperature records, as they become available, are needed to determine the degree to which each series represents fluctuations for the entire hemisphere. There appear to be relationships between trends observed in our Northern Hemisphere reconstruction and certain climatic forcing functions, including solar fluctuations, volcanic activity and atmospheric CO₂. In particular, our reconstruction supports the hypothesis that the global warming trend over the past century of increasing atmospheric CO₂ has exceeded the recent level of natural variability of the climate system.Of Columbia University Department of Geological Sciences.     

Trans-Tasman Sea climate variability since ad 1740 inferred from middle to high latitude tree-ring data

The limited length and spatial coverage of instrumental climate data for many areas of the Southern Hemisphere impedes the study of atmosphere-ocean dynamics prior to the past century. Such analyses are important for understanding interannual to decadal variation of the Southern Hemisphere circulation and whether recent changes are related to anthropogenic effects rather than natural variability. We use a middle- to high-latitude tree-ring width data set (from Tasmania, New Zealand and Tierra del Fuego) to reconstruct sea-level pressure (SLP) variability spanning the Tasman Sea and vicinity since ad 1740. The variables reconstructed are austral summer (November–March) SLP for Hobart, Tasmania (43°S, 147°E) and the Chatham Islands, New Zealand (44°S, 177°E), as well as a meridional circulation index (Hobart-Chatham Islands index) which measures the pressure gradient between these two stations. The three reconstructions are well verified statistically and capture between 40 and 48% of the variance in the SLP data. The instrumental and estimated SLP show similar spatial patterns of correlation with the sea surface temperature (SST) field for the Pacific. Statistically significant (above 95% level) 3–3.5 year spectral peaks are identified in the three reconstructions using multitaper spectral analysis, and a significant 4–5 year peak is found in both the Chatham Islands and Hobart-Chatham Islands SLP reconstructions. These two modes are within the bandwidth of the El Nino-Southern Oscillation. Although very speculative, they may also correspond to a proposed Antarctic circumpolar wave of SLP, SST, wind and sea-ice extent, believed to play a key role in atmosphere-ocean circulation for the Southern Hemisphere. Received: 30 November 1998 / Accepted: 13 December 1999     

1975年以来珠峰北坡地区水环境变化研究

喜马拉雅山高大的山体和特殊的局地环流系统大大加强了该地区地面环境与区域尺度乃至全球大气过程的联系.本文采用1975年以来珠峰北坡绒布河水样品,对该地区30年来水环境变化过程进行研究.对绒布河水中12种化学元素含量的研究结果表明,珠峰北坡地区的水环境受到全球大气环境事件的影响,同时也受到该地区逐渐增加的人类活动的影响.1992年中东石油大火排放的污染物使得珠峰地区绒布河水中的12种化学元素总体含量达到30年研究期间中的极大值;2004年以后人类无序活动的不断增加,使得珠峰北坡绒布河水环境不断恶化,2006年12种化学元素总体含量达到近30年研究区间中的第二大值.     

树轮最大密度记录的吉尔吉斯斯坦天山山区公元1650年以来的7-8月温度变化

利用吉尔吉斯斯坦天山山区3个采样点的雪岭云杉树轮最大密度数据建立区域树轮最大密度年表（RC）。气候响应分析发现,区域树轮最大密度年表与7-8月平均温度显著相关。在此基础上,利用区域树轮最大密度年表重建了吉尔吉斯斯坦天山山区自1650年以来的7-8月温度变化,重建方程的方差解释量高达45．3％（Radj^2=44．7％,N=95,F=77．029）。重建结果显示,在过去的346a中吉尔吉斯斯坦天山山区7-8月平均温度的异常高温年份为40a,异常低温年份为46a,且存在11个低温时段（16501654,1662-1678,1693-1703,1779-1794,1801-1805,1811-1819,1834-1854,1882-1910,1917-1923,1952-1975和1986-1992年）和11个高温时段（1655-1661,1679-1692,1704-1778,1795-1800,1806-1810,1820-1833,1855-1881,1911-1916,1924-1951,1976-1985和1994-至今）。突变和周期分析揭示该地区的温度变化受到了火山、太阳活动和海陆气交互作用的共同影响。此外,在过去的346a来气候以暖干／冷湿为主,近20a来出现了明显暖湿化趋势。     

Increasing prevalence of extreme summer temperatures in the U.S.

Human-caused climate change can affect weather and climate extremes, as well as mean climate properties. Analysis of observations and climate model results shows that previously rare (5th percentile) summertime average temperatures are presently occurring with greatly increased frequency in some regions of the 48 contiguous United States. Broad agreement between observations and a mean of results based upon 16 global climate models suggests that this result is more consistent with the consequences of increasing greenhouse gas concentrations than with the effects of natural climate variability. This conclusion is further supported by a statistical analysis based on resampling of observations and model output. The same climate models project that the prevalence of previously extreme summer temperatures will continue to increase, occurring in well over 50% of summers by mid-century.     

Tree-ring reconstructed summer temperature anomalies for temperate East Asia since 800 C.E.

We develop a summer temperature reconstruction for temperate East Asia based on a network of annual tree-ring chronologies covering the period 800–1989 C.E. The East Asia reconstruction is the regional average of 585 individual grid point summer temperature reconstructions produced using an ensemble version of point-by-point regression. Statistical calibration and validation tests indicate that the regional average possesses sufficient overall skill to allow it to be used to study the causes of temperature variability and change over the region. The reconstruction suggests a moderately warm early medieval epoch (ca. 850–1050 C.E.), followed by generally cooler ‘Little Ice Age’ conditions (ca. 1350–1880 C.E.) and 20th century warming up to the present time. Since 1990, average temperature has exceeded past warm epochs of comparable duration, but it is not statistically unprecedented. Superposed epoch analysis reveals a volcanic forcing signal in the East Asia summer temperature reconstruction, resulting in pulses of cooler summer conditions that may persist for several years. Substantial uncertainties remain, however, particularly at lower frequencies, thus requiring caution and scientific prudence in the interpretation of this record.     

黄山地区春夏季气溶胶离子组分及其对云微物理特征的影响

利用2009年5-8月在华东地区高山——黄山顶取得的气溶胶和云微物理参数观测资料以及同期气溶胶离子成分数据,结合多种化学组分气溶胶绝热气块分档云模式,研究了黄山地区多化学组分气溶胶对云凝结核和云微物理特征的影响.气团轨迹和气溶胶离子成分的分析结果表明,3种气团影响着黄山地区气溶胶的化学组分,即北方大陆气团气溶胶富含CaCO3,局地污染气团气溶胶以可水溶性无机盐((NH4)2SO4、NH4 NO3)为主,而变性混合海洋性气团气溶胶中NaCl较多.数值模拟结果显示,在气溶胶谱一定时,不同天气形势下黄山气溶胶的化学组分的差异会对云微物理特征产生不同的影响.同一上升速度下实际多组分气溶胶模拟的云滴数浓度大于纯硫酸铵,主要体现在云滴谱第1个峰值3.3 μm之前;气块上升速度低于0.7 m/s时,含有较多不可水溶物质的混合气溶胶对云滴数浓度的影响较大;上升速度大于0.7 m/s时,气块中可凝结水增多,海盐对云滴数浓度增加的效果更显著.多组分气溶胶模拟云滴谱较纯硫酸铵窄,其中,北方气团方案造成云滴谱变窄的程度高于混合气团方案;而模拟的云滴数目增多,造成云滴有效半径减小,云光学厚度和反照率增加,将会对暖云降水及辐射效应产生不同的影响.     

Comparison of instrumental and interpolated meteorological data-based summer temperature reconstructions on Mt. Taibai in the Qinling Mountains,northwestern China

Theoretical and Applied Climatology - Previous dendroclimatical studies have been based on the relationship between tree growth and instrumental climate data recorded at lower land meteorological...     

Spring-summer temperatures since AD 1780 reconstructed from stable oxygen isotope ratios in white spruce tree-rings from the Mackenzie Delta,northwestern Canada

High-latitude δ¹⁸O archives deriving from meteoric water (e.g., tree-rings and ice-cores) can provide valuable information on past temperature variability, but stationarity of temperature signals in these archives depends on the stability of moisture source/trajectory and precipitation seasonality, both of which can be affected by atmospheric circulation changes. A tree-ring δ¹⁸O record (AD 1780–2003) from the Mackenzie Delta is evaluated as a temperature proxy based on linear regression diagnostics. The primary source of moisture for this region is the North Pacific and, thus, North Pacific atmospheric circulation variability could potentially affect the tree-ring δ¹⁸O-temperature signal. Over the instrumental period (AD 1892–2003), tree-ring δ¹⁸O explained 29 % of interannual variability in April–July minimum temperatures, and the explained variability increases substantially at lower-frequencies. A split-period calibration/verification analysis found the δ¹⁸O-temperature relation was time-stable, which supported a temperature reconstruction back to AD 1780. The stability of the δ¹⁸O-temperature signal indirectly implies the study region is insensitive to North Pacific circulation effects, since North Pacific circulation was not constant over the calibration period. Simulations from the NASA-GISS ModelE isotope-enabled general circulation model confirm that meteoric δ¹⁸O and precipitation seasonality in the study region are likely insensitive to North Pacific circulation effects, highlighting the paleoclimatic value of tree-ring and possibly other δ¹⁸O records from this region. Our δ¹⁸O-based temperature reconstruction is the first of its kind in northwestern North America, and one of few worldwide, and provides a long-term context for evaluating recent climate warming in the Mackenzie Delta region.     

Warm-season temperatures since 1600 BC reconstructed from Tasmanian tree rings and their relationship to large-scale sea surface temperature anomalies

We describe an improved tree-ring reconstruction of mean warm-season (November–April) temperatures for Tasmania from Huon pine. This record extends back to 1600 BC and is based on a tree-ring chronology that was processed to retain as much low-frequency variance as possible. The resulting reconstruction explains 46.6% of the variance and verifies significantly when compared to withheld instrumental data. Cross-spectral analysis of actual and estimated temperatures over the 1886–1991 common period indicates that most of the unexplained variance is at periods < 12 years in length. At periods > 12 years, the squared coherency ranges between 0.6–0.8, and the cross-spectral gain indicates that the amplitude of the reconstruction is a nearly unbiased estimate of the true temperature amplitude. Therefore, this reconstruction should be especially useful for studying multi-decadal temperature variability in the Tasmanian sector of the Southern Hemisphere over the past 3592 years. To this end, we examined the time evolution of low-frequency temperature amplitude fluctuations and found evidence for a 35% amplitude reduction after AD 100 that persisted until about AD 1900. Since that time, the low-frequency temperature amplitude has systematically increased. We also show how this reconstruction is related to large-scale sea surface temperatures (SST) in the Indian Ocean and eastward to the dateline. Pointwise correlations between the Tasmanian record and SSTs reveal a relationship that extends across the southern Indian Ocean and towards the Arabian Sea. This pattern is largely determined by inter-decadal temperature variability, with correlations in this > 10-year bandwidth commonly exceeding 0.6 over most of the southern Indian and southwestern Pacific sectors. A rotated empirical orthogonal function analysis reveals that the pattern of pointwise correlations found between the temperature reconstruction and SSTs is largely explained by the linear combination of three orthogonal modes of SST variability. Received: 12 January 1999 / Accepted: 31 July 1999     

新疆西北部萨吾尔山西伯利亚落叶松树轮宽度的气候响应特征

树木生长对气候变化的响应研究不仅能为全球变化背景下森林生态系统的响应提供关键参数,也是树轮气候学研究的基础。本文利用位于新疆西北部萨吾尔山南坡的西伯利亚落叶松树木年轮宽度资料,建立了不同海拔高度的4个树轮宽度年表,采用相关分析和冗余分析法分析了树轮年表特征及其对气候的响应特征。结果表明：（1）不同海拔西伯利亚落叶松树轮宽度年表均具有较高的敏感度和一致性,可能包含较为丰富的气候信息。树轮年表参数有较一致的规律性：平均敏感度、标准差和信噪比随海拔高度降低逐渐增大;反映树轮对环境要素响应滞后效应的一阶自相关系数随海拔高度降低而减小。（2）随着海拔高度的降低,树轮宽度年表与生长季温度（5—9月）的正相关逐渐减弱,直至变为负相关;与反映水分状况的气象要素（降水量、相对湿度和水汽压）由不显著相关变为显著正相关（P<0.01）。萨吾尔山南坡海拔2000~2100m是西伯利亚落叶松树轮宽度对气候响应关系发生转折的关键高度。（3）位于下树线区域西伯利亚落叶松树轮宽度受年降水量（上年7月至当年6月）和当年生长季（5—7月）最高气温共同影响,具备开展区域干旱指数重建的潜力。     

Reconstruction of seasonal temperatures in Central Canada since A.D. 1700 and detection of the 18.6- and 22-year signals

This paper presents an attempt to summarize various sparse proxy series into continuous and exhaustive climatic data. Freeze-up and break-up dates, early meteorological records and tree-ring data have been combined for the Hudson Bay region and 22 continuous proxy series extending from 1700 to 1979 have been deduced. These new series in term provided the basis for a regressive reconstruction of six seasonal temperature series. Verification tests are successful mainly for the high frequencies components. The low frequencies variability is better estimated by a best analogues method. Both kinds of reconstructions have been combined to improve the results. The main characteristic of the reconstructions is a warming trend beginning at the end of the 19th century. Evidence for a beat wave resulting from 22-year solar and 18.6-year lunar nodal tidal cycles is presented. A phase analysis showed results consistent with other studies of summer temperature variability: temperature maxima correspond to sunspot minima ending an even cycle and are emphasized by the lunar maxima. Different phenomena are pointed out for autumn and winter temperatures: their maxima coincide to sunspot even maxima amplified by lunar minima. In spring, the transition season, these signals are not apparent.