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.     

Site-aspect influence on climate sensitivity over time of a high-altitude Pinus cembra tree-ring network

Recently a divergence between tree-ring parameters from temperature-limited environments and temperature records has been observed worldwide but comprehensive explanations are still lacking. From a dendroclimatic analysis performed on a high-altitude tree-ring network of Pinus cembra (L.) in the Central Italian Alps we found that site aspect influences non-stationary growth-climate relationships over time. A general increasing divergence between ring width and the summer temperature record (J–A) has been observed especially for chronologies from SW-facing slopes, whereas chronologies from N-facing sites showed stable relationships over time. The monthly analysis revealed that the decrease in sensitivity was mostly accounted for by the changes in the relationships with June temperature (decreasing correlations especially for S- and W-facing site chronologies), whereas trees from N-facing sites showed an increasing sensitivity to July temperatures. Our data suggest that at high altitudes, low temperatures at the beginning of the growing season no longer limit growth. We also found that our temperature-sensitive trees did not linearly respond in radial growth to the extreme heat event of summer 2003, and formed an annual ring of average width, resulting in a strong divergence from the temperature record. Our findings underline the importance of site ecology for tree-ring based climate reconstructions using temperature-sensitive ring-width chronologies, and may help in solving the ‘divergence problem’.     

Five millennia of paleotemperature from tree-rings in the Great Basin,USA

The instrumental temperature record is of insufficient length to fully express the natural variability of past temperature. High elevation tree-ring widths from Great Basin bristlecone pine (Pinus longaeva) are a particularly useful proxy to infer temperatures prior to the instrumental record in that the tree-rings are annually dated and extend for millennia. From ring-width measurements integrated with past treeline elevation data we infer decadal- to millennial-scale temperature variability over the past 4,500 years for the Great Basin, USA. We find that twentieth century treeline advances are greater than in at least 4,000 years. There is also evidence for substantial volcanic forcing of climate in the preindustrial record and considerable covariation between high elevation tree-ring widths and temperature estimates from an atmosphere–ocean general circulation model over much of the last millennium. A long-term temperature decline of ~?1.1 °C since the mid-Holocene underlies substantial volcanic forcing of climate in the preindustrial record.     

A millennial long March–July precipitation reconstruction for southern-central England

We present a millennial long dendroclimatic reconstruction of spring/summer precipitation for southern-central England. Previous research identified a significant moisture stress signal in ring-width data measured from oak trees growing in southern England. In this study, we build upon this earlier work, specifically targeting south-central England, to derive a well replicated oak ring-width composite chronology using both living and historical material. The data-set includes 352 living trees (AD 1629–2009) and 1540 individual historical series (AD 663–1925). The period expressed by at least 50 trees in any year is AD 980–2009. Calibration experiments identify the optimal seasonal predictand target as March–July precipitation (1901–2007: r² = 0.33). However, comparison with the long Kew Gardens precipitation record indicates a weakening in tree-growth/climate response from ~1800 to 1920 which we speculate may be related to smoke and sulphur dioxide (SO₂) emissions at that time which may have also contributed to a decrease in tree productivity. The time-series derived using the regional curve standardisation method to capture lower frequency information shows a mediaeval period with alternating multi-decade-long dry and wet periods, with AD 1153–1172 being the wettest reconstructed 20-year period in the whole record. Drier conditions are prevalent from ~1300 to the early sixteenth century followed by a period of increasing precipitation levels. The most recent four centuries of the record appear similar to the mediaeval period with multiple decade-long dry and wet periods. The late twentieth century is the second reconstructed wettest period. These centennial hydroclimatic trends are in broad agreement with independent regional scale hydroclimatic reconstructions from tree-ring (East Anglia), historical, speleothem and peat water level proxy archives in the United Kingdom and appear coupled with reconstructed sea surface temperature changes in the North Atlantic which in turn influence the Atlantic meridional overturning circulation and westerly airflow across the UK.     

Long-term summer temperature variations in the Pyrenees

Two hundred and sixty one newly measured tree-ring width and density series from living and dry-dead conifers from two timberline sites in the Spanish Pyrenees were compiled. Application of the regional curve standardization method for tree-ring detrending allowed the preservation of inter-annual to multi-centennial scale variability. The new density record correlates at 0.53 (0.68 in the higher frequency domain) with May–September maximum temperatures over the 1944–2005 period. Reconstructed warmth in the fourteenth to fifteenth and twentieth century is separated by a prolonged cooling from ∼1450 to 1850. Six of the ten warmest decades fall into the twentieth century, whereas the remaining four are reconstructed for the 1360–1440 interval. Comparison with novel density-based summer temperature reconstructions from the Swiss Alps and northern Sweden indicates decadal to longer-term similarity between the Pyrenees and Alps, but disagreement with northern Sweden. Spatial field correlations with instrumental data support the regional differentiation of the proxy records. While twentieth century warmth is evident in the Alps and Pyrenees, recent temperatures in Scandinavia are relatively cold in comparison to earlier warmth centered around medieval times, ∼1450, and the late eighteenth century. While coldest summers in the Alps and Pyrenees were in-phase with the Maunder and Dalton solar minima, lowest temperatures in Scandinavia occurred later at the onset of the twentieth century. However, fairly cold summers at the end of the fifteenth century, between ∼1600–1700, and ∼1820 were synchronized over Europe, and larger areas of the Northern Hemisphere.     

Fading temperature sensitivity of Alpine tree growth at its Mediterranean margin and associated effects on large-scale climate reconstructions

A millennium-long tree-ring width chronology of living and dead larch (Larix decidua Mill.) specimens from the Maritime French Alps was introduced 35?years ago. This record has been included in various large-scale temperature reconstructions, though recent analyses revealed only weak associations with regional summer temperatures. Calibration and verification trials against instrumental measurements were, however, limited by the original record’s early ending in 1974. Here we introduce an update of this widely considered chronology until 2007 and back into medieval times. A total of 297 new larch samples from high-elevation settings in the southern French Alps were included, and the combined 398 measurement series allowed effects of tree-ring detrending and chronology development to be explored. Comparisons with meteorological temperature, precipitation and drought indices revealed weak and temporally inconsistent climate sensitivity. To further place these local findings in a biogeographic context, we used >3,000 larch trees from 61 locations across the Alpine arc. This unique network approach confirmed fading temperature sensitivity with decreasing latitude, and thus questioned the overall reliability of ring width-based temperature reconstructions in the Mediterranean region. Our results further emphasize the pending need to develop chronologies from maximum latewood densities and stable isotope ratios across the lower latitudes, and to carefully evaluate ecological site conditions and methodological data restrictions prior to compiling local data into global networks.     

RECONSTRUCTING MIDDLE-TIBET CLIMATE DURING THE LAST 600 YEARS BY DENDROCLIMATOLOGICAL METHOD*

Based on four tree-ring chronologies which was analyscd with appropriate collection and accurate dating in the middle Tibetan Plateau,an essential procedure on reconstruction of past climate has been pointed out in this paper.First,the response function of each dendrochronology has been built and used to estimate how ring-width growth responds to variations in monthly climatic change.Second,the climate factors which could be produced with different tree-ring series have been selected.Then,the transfer function equation,including a new set of orthogonal variables,can be used to reconstruct local past temperature or precipitation.It should be emphasized that prior growth has been considered in the relationship between climate factor and tree-ring chronology,Besides,some different periods for calibration and verification have been divided.And some statistics and other kinds of proxy data have been adopted as test approaches.As a result,the variations of air temperature during the last 600 years and precipitation during the last 340 years were reconstructed by combining the same types of tree-ring series in the middle Tibet.     

Temperature variability over the past millennium inferred from Northwestern Alaska tree rings

We describe a new tree-ring width data set of 14 white spruce chronologies for the Seward Peninsula (SP), Alaska, based on living and subfossil wood dating from 1358 to 2001 AD. A composite chronology derived from these data correlates positively and significantly with summer temperatures at Nome from 1910 to 1970, after which there is some loss of positive temperature response. There is inferred cooling during periods within the Little Ice Age (LIA) from the early to middle 1600s and late 1700s to middle 1800s; and warming from the middle 1600s to early 1700s. We also present a larger composite data set covering 978–2001 AD, utilizing the SP ring-width data in combination with archaeological wood measurements and other recent collections from northwestern Alaska. The Regional Curve Standardization (RCS) method was employed to maximize potential low-frequency information in this data set. The RCS chronology shows intervals of persistent above-average growth around the time of the Medieval Warm Period (MWP) early in the millennium, which are comparable to growth levels in recent centuries. There is a more sustained cold interval during the LIA inferred from the RCS record as compared to the SP ring-width series. The chronologies correlate significantly with Bering and Chukchi Sea sea surface temperatures and with the Pacific Decadal Oscillation index. These atmosphere–ocean linkages probably account for the differences between these records and large-scale reconstructions of Arctic and Northern Hemisphere temperatures based largely on continental interior proxy data.     

The construction of oxygen isotope chronologies from tree-ring series sampled at different temporal resolution and its use as climate proxies: statistical aspects

Tree-ring oxygen stable isotope data series from conifers growing on the Dachstein Plateau (Austrian Alps) were selected to demonstrate the applicability of the serial pooling method using shifted 5-year tree-ring blocks for summer temperature reconstruction. The addressed method allows the construction of long isotope chronologies with significant climate correlation and well preserved climate sensitivity applying the irreducible sample replication of five trees. The linear regression model for temperature reconstruction is verifiable and the predicted data are well correlated with instrumental data, especially reproducing the long-term temperature trend. However, the reduced mean variance leads to loss of extreme years, which can be regulated by the combination of one data series in annual resolution with five shifted 5-year block data series. This significantly improves the variance of the mean chronology, sufficiently to identify extremes. Therefore, we recommend the use of mixed data sets as a compromise between essential sample replication and economic considerations.     

Detection of climate signal in dendrochronological data analysis: a comparison of tree-ring standardization methods

Summary Tree-ring standardization methods were compared. Traditional methods along with the recently introduced approaches of regional curve standardization (RCS) and power-transformation (PT) were included. The difficulty in removing non-climatic variation (noise) while simultaneously preserving the low-frequency variability in the tree-ring series was emphasized. The potential risk of obtaining inflated index values was analysed by comparing methods to extract tree-ring indices from the standardization curve. The material for the tree-ring series, previously used in several palaeoclimate predictions, came from living and dead wood of high-latitude Scots pine in northernmost Europe. This material provided a useful example of a long composite tree-ring chronology with the typical strengths and weaknesses of such data, particularly in the context of standardization. PT stabilized the heteroscedastic variation in the original tree-ring series more efficiently than any other standardization practice expected to preserve the low-frequency variability. RCS showed great potential in preserving variability in tree-ring series at centennial time scales; however, this method requires a homogeneous sample for reliable signal estimation. It is not recommended to derive indices by subtraction without first stabilizing the variance in the case of series of forest-limit tree-ring data. Index calculation by division did not seem to produce inflated chronology values for the past one and a half centuries of the chronology (where mean sample cambial age is high). On the other hand, potential bias of high RCS chronology values was observed during the period of anomalously low mean sample cambial age. An alternative technique for chronology construction was proposed based on series age decomposition, where indices in the young vigorously behaving part of each series are extracted from the curve by division and in the mature part by subtraction. Because of their specific nature, the dendrochronological data here should not be generalized to all tree-ring records. The examples presented should be used as guidelines for detecting potential sources of bias and as illustrations of the usefulness of tree-ring records as palaeoclimate indicators.     

Tree-ring inferred annual mean temperature variations on the southeastern Tibetan Plateau during the last millennium and their relationships with the Atlantic Multidecadal Oscillation

We present two tree-ring chronologies for the southeastern Tibetan Plateau (TP), established by applying the signal-free regional curve standardization and standard dendrochronological methodologies to a set of ring-width series of Tibetan juniper. The relationship between tree growth and climate shows that temperature variability in the previous year is the primary factor controlling tree growth at the upper portion of the forest belt. Accordingly, we developed a mean annual temperature reconstruction covering the period A.D. 984–2009 and explaining 50 % of the instrumental variance. The spatial correlation patterns suggest that our temperature reconstruction is a reasonable proxy for temperature change over the TP. At long time scales, the temperature reconstruction shows similar warm-cold patterns to those in temperature records from other regions of the TP, indicating that decadal and multidecadal temperature variations were generally synchronous across the TP during the past millennium. The periods 1140–1350 and 1600–1800 were common warm and cold episodes over the TP, respectively. Comparison of our reconstruction with four Northern Hemisphere (NH) temperature series indicates that temperature changes on the southeastern TP have generally followed the NH temperature patterns during the past millennium. Our results also suggest that temperature variability over the TP is affected by the Atlantic Multidecadal Oscillation (AMO), with the warm (cool) phases of the AMO associated with above-average (below-average) temperatures over the TP.     

Tree-ring reconstruction of summer temperature for A.D. 1475–2003 in the central Hengduan Mountains, Northwestern Yunnan, China

Development of long tree-ring records is an important task in paleoclimate studies. Here we presented a five-century long reconstruction of summer (June to August) temperature based on a tree ring-width chronology of Picea brachytyla var. complanata originating from the Hengduan Mountains of China. Climate-growth response analysis showed that summer temperature was the main climatic factor limiting tree-ring growth in the study area. The reconstructed summer temperature accounted for 47.6% of the variance in actual temperature during their common period A.D. 1958–2002. Analysis of the temperature reconstruction showed that major warm periods occurred in the A.D. 1710s–1750s, 1850s, 1920s–1950s and 1990s to present, whereas cold intervals occurred in the A.D. 1630s–1680s, 1790s–1800s, 1860s–1880s and 1950s–1980s, respectively. The low-frequency variation of the reconstruction agreed fairly well with tree-ring reconstructed temperature from nearby regions and with records of glacier fluctuations in the surrounding high mountains, suggesting that our reconstructed summer temperature was reliable, and could aid in the evaluation of regional climate variability.     

吉尔吉斯斯坦西天山上下林线树轮对气候的响应差异

利用2012年10月采自吉尔吉斯斯坦西天山chon-kyzyl-suu附近的森林上线和下线两个采样点的雪岭云杉树轮样本,建立了上下线树轮宽度年表,结合近百年CRU（0.5?.5）气温和降水资料,分析该地区森林上下线树轮对气候响应的异同。研究表明,森林上下线树轮年表一致性较好,尤其是窄轮出现年份基本相同;对气温响应方面,森林上线树轮年表与春季尤其是4-5月份平均温度显著负相关;而森林下线树轮年表与夏季尤其是6-7月平均气温显著相关。降水方面,树轮年表与上年7月到当年6月降水相关最好,森林下线年表与上年7月到当年6月的降水量相关系数超过0.61;上线也达到了0.49。与中国境内雪岭云杉对气候响应基本相同,位于吉尔吉斯斯坦的西天山北坡树轮宽度同样对降水的响应更为敏感,尤其在森林下线;降水可能是该地区树木生长的主要限制性因子,降水对森林下线树轮径向生长起决定性作用。空间相关分析表明,树轮年表能较好的代表西天山大部分区域上年7月到当年6月的降水量,尤其是西天山北坡吉尔吉斯斯坦境内。     

The historical temperature series of Bologna (Italy): 1716–1774

The Bologna meteorological record is one of the oldest and most complete among the series already collected for Europe. Data from the regions south of the Alps being extremely sparse, this station is of great importance for all climatic reconstructions dating as far back as the beginning of the 18th century. The focus here is on the temperature series, because it presents some a priori problems with respect to the series analysis itself. These problems relate to the homogeneity of the temperature record, which is affected by the use of different thermometers within the record, the statistical reconstruction of the thermometric scales, and the drift in calibration of one of these instruments. After correcting for these heterogeneities, the temperature series indicate a thermal behaviour in agreement with other historical European sources. The Bologna series is characterised by a warm period during the first decades of the 18th century, with large decreases in temperature in 1740 and 1742, and a positive trend from 1742 to the end of the record. The behaviour of the Bologna temperature series is in good agreement with the series for Central England, De Bilt (Netherlands) and Padua (Italy).     

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.     

An efficient forward model of the climate controls on interannual variation in tree-ring width

We present a simple, efficient, process-based forward model of tree-ring growth, called Vaganov–Shashkin-Lite (VS-Lite), that requires as inputs only latitude and monthly temperature and precipitation. Simulations of six bristlecone pine ring-width chronologies demonstrate the interpretability of model output as an accurate representation of the climatic controls on growth. Ensemble simulations by VS-Lite of two networks of North American ring-width chronologies correlate with observations at higher significance levels on average than simulations formed by regression of ring width on the principal components of the same monthly climate data. VS-Lite retains more skill outside of calibration intervals than does the principal components regression approach. It captures the dominant low- and high-frequency spatiotemporal ring-width signals in the network with an inhomogeneous, multivariate relationship to climate. Because continuous meteorological data are most widely available at monthly temporal resolution, our model extends the set of sites at which forward-modeling studies are possible. Other potential uses of VS-Lite include generation of synthetic ring-width series for pseudo-proxy studies, as a data level model in data assimilation-based climate reconstructions, and for bias estimation in actual ring-width index series.     

Decreasing teleconnections with inter-site distance in monthly climatic data and tree-ring width networks in a mountainous Alpine area

Summary The similarities in time series recorded at sites which are distant from each other are called teleconnections. In this paper, the loss of such correlations with inter-site distance was investigated for both climatic and dendrochronological data sets, with 70 tree-ring chronologies. A dense network of weather stations was studied in the southeastern French Alps, covering complex climatic gradients over three departments. 78 sites with precipitation data (with a total of 48 756 monthly values), and 48 stations that recorded temperature (with 20 722 monthly mean values) were analysed. In the same area, four coniferous species (mountain pine and stone pine, European larch and Norway spruce) provided 37 ring-width chronologies for high elevation sites near the timberline. Both silver fir and Norway spruce provided a second tree-ring chronology network for 33 different sites at lower elevations. The teleconnections between precipitation series were found to be higher than those observed for temperature over short distances, but the maximum threshold distance was lower (193 km) compared to a positive correlation distance that exceeds 500 km for temperature. The maximum temperatures had stronger teleconnections than minimum values (522 km versus 476 km), since the latter are linked more with other site factors, such as slope, exposure and local topography. As expected, the tree-ring chronologies showed weaker teleconnections than the climatic series, with a threshold distance of 374 km obtained for all high elevation forests. The coniferous species with high intra-specific teleconnections over large distances were, in decreasing importance, Pinus uncinata (> 500 km), Picea abies (477 km), Pinus cembra (over 254 km) and Larix decidua (over 189 km only). The two former species showed the highest intra-specific correlations (with mean correlation R=0.625 and 0.666). The dendrochronological teleconnections were found to have a extent lesser for trees species that depend on rainfall (such as larch, and stone pine). They are enhanced, however, for temperature sensitive species such as spruce and mountain pine (a drought resistant tree). Therefore, these two latter conifers appear to be especially suitable for climatic reconstruction over large distances in mountainous areas. However, teleconnections within silver fir (Abies alba) and spruce chronologies were sharply reduced (over 131 km and 135 km) in lower elevation forests, underlining the interest of timberline forests for dendroclimatology. A better knowledge of the spatial correlations in climatic series and ring-width data may enable the optimisation of weather station networks. It may also permit a better choice of weather stations used for dendroclimatology, either for tree-ring and climate relationship calibration or for climate reconstructions. In dendrochronology, wood dating also requires the knowledge of to what extent remote ring-width chronologies can be used. Received September 11, 2000 Revised March 26, 2001     

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.     

Tree-ring evidence of recent abnormal warming on the southeast Tibetan Plateau

We developed four Georgei fir (Abies georgei var. smithii) tree-ring width chronologies at the timberline in the Sygera Mts. in southeast Tibet, China. All individual standard chronologies and a regional well-replicated ring-width composite chronology (RC) show significantly positive correlations with mean summer (June-August) temperature. Herein mean summer temperature was reconstructed for southeast Tibet back to A.D. 1765 based on RC. This reconstruction successfully captures recent warming observed in the instrumental record since 1961 with the last decade being the warmest period in the past 242 years. It agrees in general with other temperature reconstructions of the Tibetan Plateau and extratropical northern hemisphere. This study allows seeing recent warming on a longer time scale in southeast Tibet.     

Gulf of Alaska Atmosphere-Ocean Variability Over Recent Centuries Inferred from Coastal Tree-Ring Records

Eight tree-ring chronologies from coastal sites along the Gulf of Alaska (GOA) are used to develop a 227-year (1762–1988) reconstruction of spring/summer (March–September) coastal land temperatures for the region. This reconstruction explains 35% of the variance in the instrumental temperature data. The tree-ring records and reconstruction reflect the documented 1976 transition from cold to warm conditions in the North Pacific and are consistent with regional temperature compilations. Three of the eight ring-width series, from elevational timberline sites where trees are particularly stressed by temperature, extend back to A.D. 1600 and are used to identify additional occurrences of such transitions. The first principal component (PC) scores of these three longer records are positively correlated with spring (March–May) land and sea surface temperatures for the GOA region and are used to reconstruct land surface temperatures. Decadal-scale fluctuations in the reconstructions show agreement with decade-long changes in the intensity of the Aleutian Low pressure cell over the past century, suggesting that the tree-ring data may provide an index of past circulation changes for the northeast Pacific. Blackman-Tukey spectral analyses of both reconstructions indicate significant power at 7–11 years, with additional peaks at 3 years for the spring/summer reconstruction and 19 years for the longer spring temperature series. The modes of variation at about 3 and 7 years may correspond to those associated with the El Niño-Southern Oscillation bandwidth, whereas the 19-year term may relate to a proposed 20-year cycle of North Pacific circulation. The spring temperature series shows generally increased growth over the past century, coinciding with warmer spring temperatures in south coastal Alaska over this interval. Comparison with the entire spring series suggests that the recent warming exceeds temperature levels of prior centuries, extending back to A.D. 1600.