Weakening climatic signal since mid-20th century in European larch tree-ring chronologies at different altitudes from the Adamello-Presanella Massif (Italian Alps)

Tree rings from temperature-limited environments are highly sensitive climate proxies, widely used to reconstruct past climate parameters for periods prior to the availability of instrumental data and to analyse the effect of recent global warming on tree growth. An analysis of the climatic signal in five high-elevation tree-ring width chronologies of European larch (Larix decidua Mill.) from the tops of five different glacial valleys in the Italian Central Alps revealed that they contain a strong summer-temperature signal and that tree-ring growth is especially influenced by June temperatures. However, a moving correlation function analysis revealed a recent loss of the June temperature signal in the tree-ring chronologies. This signal reduction primarily involves the two lowest-altitude chronologies. It is probable that the observed increasing importance of late-summer temperature for tree-ring growth over the past 50 yr is an effect of the lengthening growing season and of the variations in the climate/tree-ring relationship over time. All the chronologies considered, especially those at the highest altitudes, show an increasing negative influence of June precipitation on tree-ring growth. The climatic signal recorded in tree-ring chronologies from the Italian Central Alps varies over time and is also differentially influenced by climatic parameters according to site elevation.     

Spatial and temporal stability of the climatic signal in northern Fennoscandian pine tree-ring width and maximum density

The spatial and temporal stability of the climatic signal in pine tree - ring width and maximum density is examined using data from four sites in northern Sweden and Finland. Moving-window multiple linear regression, using monthly and daily climate data, indicates that ring widths at all sites have been strongly controlled by July temperatures throughout the past century. The relationship between maximum density and temperature is stronger but much less stable across both space and time. Shifts in the hottest part of the summer do not explain large shifts in the period most strongly influencing density. It is concluded that palaeoclimate reconstructions based on northern Fennoscandian pine tree - ring width chronologies should be restricted to the temperature of midsummer (July), whereas maximum density should be used to reconstruct the temperature of a longer growth season (June to August). They thus provide different and compl e mentary palaeoclimate signals. At all four sites, the correlation between maximum density and June to August mean temperature is lowest in the latter half of the 20th century, but split sample tests with strong verification statistics (RE and CE) show that this represents a quantitative change in the strength of the correlation with climate, rather than a qualitative change in the nature of that relationship, and thus does not invalidate climate reconstructions.     

Spatial reconstruction of summer temperatures in Central Europe for the last 500 years using annually resolved proxy records: problems and opportunities

Most palaeoclimate studies in Central Europe, utilizing annually resolved proxies such as tree-ring and documentary sources to reconstruct past temperatures, have focused mainly upon single sites or regional studies. The combined information of published summer temperature reconstructions from the Alpine region show a generally coherent picture of cool conditions for the periods c. 1450-1475, 1575-1610, 1660-1710, 1800-1850 and 1875-1925. These reconstructed cool periods can be partly explained by external forcing (e.g. low solar activity and volcanic events). However, these reconstructions, in their present form, cannot be used to comparatively assess spatial summer temperature variability through the region due to methodological differences in their development and the fact that many of them were not originally developed to emphasize spatial patterns. We propose that a network of tree-ring chronologies which have been processed in a consistent way would allow the robust reconstruction of spatial summer temperature variability for high elevations in Central Europe. Unfortunately, most living tree-ring chronologies only go back into the 18th century - so restricting the length of reconstruction. As a possible solution, we introduce a historical database of ring-width series, measured from string instruments, that could be used to extend high elevation spruce chronologies in Central Europe back for at least 500 years.     

Late Holocene climatic variability reconstructed from incremental data from pines and pearl mussels – a multi‐proxy comparison of air and subsurface temperatures

Helama, S., Läänelaid, A., Tietäväinen, H., Macias Fauria, M., Kukkonen, I. T., Holopainen, J., Nielsen, J. K. & Valovirta, I. 2010: Late Holocene climatic variability reconstructed from incremental data from pines and pearl mussels – a multi‐proxy comparison of air and subsurface temperatures. Boreas, Vol. 39, pp. 734–748. 10.1111/j.1502‐3885.2010.00165.x. ISSN 0300‐9483. Dendrochronological and sclerochronological records are mean series of arboreal and molluscan increments that are correctly aligned in time by rigorous dating. These records of tree rings and annual shell‐growth increments exhibit climate signals that can be used to reconstruct fluctuations and trends in past climates. Here we present a multi‐proxy reconstruction of temperature histories using a combination of dendrochronological and sclerochronological evidence. Regional curve standardization (RCS) was used to remove the non‐climatic variations from dendrochronological and sclerochronological series prior to palaeoclimatic interpretation. Conventional and signal‐free methods of RCS were compared. It was found that the signal‐free methods produced more reliable chronologies and systematically higher climate–proxy correlations. Consequently, the temperature reconstructions were derived using the chronologies constructed by this method. Proxy‐based histories of summer (July–August) temperatures were reconstructed from AD 1767 onwards. The compound use of proxies resulted in reconstructions that were of higher quality than single‐proxy reconstructions. Further improvement of reconstructions was accomplished by the inclusion of lagging increment values in the transfer functions. The final multi‐proxy model explained 58% of the temperature variance over the instrumental period. The multi‐proxy temperature reconstruction correlated well with the long records of instrumental temperatures from Tornedalen, St. Petersburg, Uppsala and Stockholm. Overall, the reconstruction for the past 250 years agreed reasonably well with borehole temperature reconstructions obtained in northern Finland. In general, this study demonstrates the benefits of the compound use of several proxies in reconstructing climate histories. In particular, the study emphasizes the so far largely unexploited advantages of multi‐proxy data sets obtained by rigorously cross‐dated incremental chronologies to produce more robust palaeoclimatic reconstructions.     

Stable isotope coherence in the earlywood and latewood of tree-line conifers

Annually resolved and replicated tree-ring stable isotope series have the potential to reconstruct growing season environmental parameters over multi-millennial timescales. As this archive may require only minimal statistical detrending, it has the potential to preserve a large portion of low frequency climate signals. To date, many studies have utilised only the latewood portion of the tree ring, in an attempt to minimize carry-over effects from previous year reserves and maximise the annual nature of the climate signal preserved. However, the old trees from tree-line locations, necessary to build long chronologies, often display narrow ring-widths (< 0.5 mm), making accurate earlywood–latewood separation difficult and particular time consuming. The resulting samples may also be too small for efficient cellulose purification or multiple isotopic determinations. As photosynthates from the current year are predominantly used in conifer ring formation at marginal sites with short growing seasons, latewood separation may not be especially advantageous in determining a useful climate signal and therefore unnecessary where resources are limited. To test this hypothesis, Scots pine from Northern Norway and European larch from the Swiss Alps are used. Both sites are tree-line locations where growth is predominantly temperature limited. Tree rings were cut and extracted to cellulose for both the earlywood and latewood of each annual growth ring and stable carbon isotope ratios were measured. Our results demonstrate a very high common carbon isotope signal between earlywood and latewood in both species (r_larch = 0.68 and r_pine = 0.79), which also show high correlations with summer temperature over the investigated period (AD 1980–2004 for larch and AD 1929–1978 for pine). High turnover rates and small reserve pools at these tree-line locations may account for these high common signals. These results suggest that for European tree-line conifers, the separation of earlywood from latewood is unnecessary to resolve an annual isotopic signal and make a reliable climate calibration. Using the whole ring may provide additional analytical advantages and consequently even improve climate calibrations.     

Central Scandinavian winter precipitation variability during the past five centuries reconstructed from Pinus sylvestris tree rings

Using Scots pine ( Pinus sylvestris L.) tree-ring data, winter (September-April) precipitation variability in west central Scandinavia was reconstructed for the past five centuries. The main growth-limiting factor for pine growing in the studied area is summer temperature, but there is an additional influence of precipitation. Using principal components analysis on three tree-ring-width chronologies, a time series was yielded that contained information on winter precipitation (P_w). Using tree rings, only a small part (20%) of the interannual P_w variability could be explained. However, better agreement between the modelled and measured P_w data on semi-decadal time scales (45% variance explained) suggests that tree-ring data from the west-central part of Scandinavia contain useful information on those time scales. The driest winters, disregarding the absolute beginning of the record, were found at the beginning of the 18th century; the last half of the 20th century seems to be the wettest, at least for the past 400 years. Since our precipitation reconstruction agrees fairly well with previously published precipitation proxies, it is suggested that tree rings may add useful information to future multi-proxy reconstructions.     

An 810‐year history of cold season temperature variability for northern Poland

Scots pine (Pinus sylvestris L.) is a widely used tree species in European dendroclimatology studies due to its common distribution across much of the continent. Almost all studies find radial growth strongly related to summer temperature, a result reflecting site selection at high elevation/latitude environments where trees grow at their ecophysiological limits. Due to the amount of attention spent on these sites there is a geographical and seasonal bias in temperature reconstructions based upon tree‐ring proxies in Europe. To overcome the limited availability of tree‐ring data in temperate lowlands, we present a northern Poland ring‐width chronology developed from living and historic Scots pine material with a strong common growth signal going back to AD 1200. Investigations into climate‐growth relationships found year‐to‐year ring‐width variability to be more strongly correlated to cold season temperature (November to April) prior to the growing season than summer temperatures during tree‐ring formation. Based on this relationship it was possible to reconstruct cold season temperature conditions for the last 810 years. Spatial field correlations with gridded instrumental records indicated that the reconstruction provides relevant cold season temperature information across the land regions bordering the North Atlantic Ocean and Baltic Sea, lowlands and uplands of western and central Europe, and the eastern and central interior of Russia. Despite an unsuccessful attempt to find a stationary relationship with the North Atlantic Oscillation, comparisons with several cold season temperature reconstructions confirmed the long‐term connection between our reconstructed temperature series for northern Poland and the wider area.     

Estimates of uncertainty in the prediction of past climatic variables

Fitting a regression line to a set of measurements to investigate the relationship between a proxy estimate of past climate and known climatic parameters is a routine procedure. It is generally accepted that the higher the correlation between parameters, the more reliable the reconstruction. However, there is a lack of published work upon what correlation is the minimum acceptable value. Simulated data was used to demonstrate that the relationship between proxy values and the climatic data are adversely affected by falling correlation, to the point where, in a training set consisting of 100 pairs of temperature and tree-ring proxies, the mean 95% confidence interval width for the reconstructed temperature exceeds the total range of temperatures in the training set at or below r = 0.65. This correlation is typical of that used in many climate-proxy reconstructions, and it suggests that understanding of past climate variability may be somewhat constrained.     

Exploring the potential of tree-ring chronologies from the Trafoi Valley (Central Italian Alps) to reconstruct glacier mass balance

Two tree-ring chronologies of stone pine ( Pinus cembra L.) and two of Norway spruce ( Picea abies Karst.) were constructed on the basis of data from three high-altitude sites in the Trafoi Valley (Central Alps, Italy) to test tree species sensitivity to climate at different sites and to explore the potential of the two species for reconstructing the mass balance of two glaciers in the same region (the Careser and Hintereis glaciers). Influence of climate on tree-ring growth and on glacier mass variations was tested by means of Pearson's correlation and response functions. At highest altitude sites, both species appeared to be sensitive to July temperatures, while stone pine also showed higher sensitivity than Norway spruce to previous winter precipitation. Comparing the dendrochronological and glaciological series, stone pine showed higher negative correlations with glacier mass balance series than Norway spruce. These different relationships reflect different species responses to climate, and stone pine is potentially useful in reconstructing past glacier mass balance in the Central Alps. Extreme climatic events induce different and even contrasting responses of tree-ring growth and glacier mass variations and may therefore bias tree-ring-based glacier mass balance reconstructions.     

Regional tree growth and inferred summer climate in the Winnipeg River basin, Canada, since AD 1783

A network of 54 ring-width chronologies is used to estimate changes in summer climate within the Winnipeg River basin, Canada, since AD 1783. The basin drains parts of northwestern Ontario, northern Minnesota and southeastern Manitoba, and is a key area for hydroelectric power production. Most chronologies were developed from Pinus resinosa and P. strobus, with a limited number of Thuja occidentalis, Picea glauca and Pinus banksiana. The dominant pattern of regional tree growth can be recovered using only the nine longest chronologies, and is not affected by the method used to remove variability related to age or stand dynamics from individual trees. Tree growth is significantly, but weakly, correlated with both temperature (negatively) and precipitation (positively) during summer. Simulated ring-width chronologies produced by a process model of tree-ring growth exhibit similar relationships with summer climate. High and low growth across the region is associated with cool/wet and warm/dry summers, respectively; this relationship is supported by comparisons with archival records from early 19th century fur-trading posts. The tree-ring record indicates that summer droughts were more persistent in the 19th and late 18th century, but there is no evidence that drought was more extreme prior to the onset of direct monitoring.     

A chironomid-based reconstruction of late glacial summer temperatures in the southern Carpathians (Romania)

Late glacial and early Holocene summer temperatures were reconstructed based on fossil chironomid assemblages at Lake Brazi (Retezat Mountains) with a joint Norwegian–Swiss transfer function, providing an important addition to the late glacial quantitative climate reconstructions from Europe. The pattern of the late glacial temperature changes in Lake Brazi show both similarities and some differences from the NGRIP δ¹⁸O record and other European chironomid-based reconstructions. Our reconstruction indicates that at Lake Brazi (1740 m a.s.l.) summer air temperature increased by ~ 2.8°C at the Oldest Dryas/Bølling transition (GS-2/GI-1) and reached 8.1–8.7°C during the late glacial interstade. The onset of the Younger Dryas (GS-1) was characterized by a weak (< 1°C) decrease in chironomid-inferred temperatures. Similarly, at the GS-1/Holocene transition no major changes in summer temperature were recorded. In the early Holocene, summer temperature increased in two steps and reached ~ 12.0–13.3°C during the Preboreal. Two short-term cold events were detected during the early Holocene between 11,480–11,390 and 10,350–10,190 cal yr BP. The first cooling coincides with the Preboreal oscillation and shows a weak (0.7°C) temperature decrease, while the second is characterized by 1°C cooling. Both cold events coincide with cooling events in the Greenland ice core records and other European temperature reconstructions.     

Long‐term summer (AD751–2008) temperature fluctuation in the French Alps based on tree‐ring data

Corona, C., Edouard, J.‐L., Guibal, F., Guiot, J., Bernard, S., Thomas, A. & Denelle, N. 2010: Long‐term summer (AD751–2008) temperature fluctuation in the French Alps based on tree‐ring data. Boreas, 10.1111/j.1502‐3885.2010.00185.x. ISSN 0300‐9843. On the basis of a dense tree‐ring width network (34 unpublished multi‐centennial larch chronologies), this paper attempts to reconstruct, for the first time, the summer temperatures in the French Alps (44°–45.30°N, 6.30°–7.45°E) during the last millennium. The adaptative Regional Growth Curve standardization method is applied to preserve interannual to multi‐centennial variations in this high‐elevation proxy data set. The proxies are calibrated using the June to August mean temperatures from the last revised version of the HISTALP database spanning the period AD1760–2003 and adjusted to take into account the warm bias before 1850. About 45% of the temperature variance is reconstructed. Despite the use of the newly updated meteorological data set, the reconstruction still shows colder temperatures than early instrumental measurements between 1760 and 1840. The proxy record evidences a prolonged Medieval Warm Period persisting until 1500, with warm periods that resemble 20th century conditions but also cold phases before 1000 synchronous with Swiss glacier advances. The Little Ice Age is rather mild until 1660 if compared with other Alpine reconstructions. Thereafter, summers are 0.7 °C cooler than the 1961–1990 mean until 1920. The maximum temperature amplitude over the past 1250 years is estimated to be 3 °C between the warmest (810s, 1990s) and coldest (1810s) decades. Most of the 20th century is comparable with the Medieval Warm Period.     

树轮记录的过去384a乌鲁木齐河源7月温度变化

利用采自乌鲁木齐河源上树线跃进桥东采样点的雪岭云杉树轮样本,分析了其年表特征和气候响应特点.结果表明:采样点树轮早材密度标准化年表与和大西沟气象站7月份平均最高温度具有很好的正相关关系.用跃进桥东采样点的早材密度标准化年表序列,可较好地重建乌鲁木齐河源1623-2006年的7月平均最高温度,1959-2006年48 a...     

North Atlantic climate variability since AD 1350 recorded in δ 18O and skeletal density of Bermuda corals

The reconstruction of the climatic history during the past several hundred years requires a sufficient geographical coverage of combined climate proxy series. Especially in order to identify causal connections between the atmosphere and the ocean, inclusion of marine records into composite climate time series is of fundamental importance. We present two skeletal δ ¹⁸O chronologies of coral skeletons of Diploria labyrinthiformis from Bermuda fore-reef sites covering periods in the nineteenth and twentieth centuries and compare them with instrumental temperature data. Both time series are demonstrated to display sea-surface temperature (SST) variability on inter-annual to decadal time scales. On the basis of a specific modern δ ¹⁸O vs instrumental SST calibration we reconstruct a time series of SST anomalies between AD 1350 and 1630 covering periods during the Little Ice Age. The application of the coral δ ¹⁸O vs temperature relationship leads to estimates of past SST variability which are comparable to the magnitude of modern variations. Parallel to δ ¹⁸O chronologies we present time series of skeletal bulk density. Coral δ ¹⁸O and skeletal density reveal a strong similarity during Little Ice Age, confirming the reliability of both proxy climate indicators. The past coral records, presented in this study, share features with a previously published climate proxy record from Bermuda and a composite time series of reconstructed Northern Hemisphere summer temperatures. The coral proxy data presented here represent a valuable contribution to elucidate northern Atlantic subtropical climate variation during the past several centuries. Received: 9 November 1998 / Accepted: 13 September 1999     

Holocene peatland development and hydrological variability inferred from bog‐pine dendrochronology and peat stratigraphy – a case study from southern Sweden

Dendrochronological analysis was applied to subfossil remains of Scots pine (Pinus sylvestris L.) buried in a South Swedish peat deposit. In combination with peat stratigraphy, this approach was explored for its potential to provide information on the local hydrological and depositional history at the site, forming the basis for a regional palaeohydrological analysis. A 726‐year ring‐width chronology was developed and assigned an absolute age of 7233–6508 cal a BP (5284–4559 BC) through cross‐dating with German bog‐pine chronologies, whereas two short additional records of older ages were radiocarbon dated. Registration of growth positions of individual trees allowed assessment of the spatial dynamics of the pine population in response to hydrological changes and peatland ontogeny. Annually resolved growth variability patterns in the pine population reveal several establishment and degeneration phases, probably reflecting fluctuations in bog‐surface wetness. A major establishment phase at 7200–6900 cal a BP reflects the onset of a period of lowered groundwater level, also indicated by increased peat humification, and a development consistent with regional temperature and lake level reconstructions revealed from other proxies. This study demonstrates that subfossil bog‐pine populations may provide annually to decadally resolved reconstructions of local groundwater variability, which are highly relevant in a long‐term palaeoclimatic context. Copyright © 2012 John Wiley & Sons, Ltd.     

A critical evaluation of multi‐proxy dendroclimatology in northern Finland

Twentieth‐century summer (July–August) temperatures in northern Finland are reconstructed using ring widths, maximum density and stable carbon isotope ratios (δ¹³C) of Scots pine tree rings, and using combinations of these proxies. Verification is based on the coefficient of determination (r²), reduction of error (RE) and coefficient of efficiency (CE) statistics. Of the individual proxies, δ¹³C performs best, followed by maximum density. Combining δ¹³C and maximum density strengthens the climate signal but adding ring widths leads to little improvement. Blue intensity, an inexpensive alternative to X‐ray densitometry, is shown to perform similarly. Multi‐proxy reconstruction of summer temperatures from a single site produces strong correlations with gridded climate data over most of northern Fennoscandia. Since relatively few trees are required (<15) the approach could be applied to long sub‐fossil chronologies where replication may be episodically low. Copyright © 2010 John Wiley & Sons, Ltd.     

Ecological tree line history and palaeoclimate – review of megafossil evidence from the Swedish Scandes

The postglacial tree line and climate history in the Swedish Scandes have been inferred from megafossil tree remains. Investigated species are mountain birch (Betula pubescens ssp. czerepanovii), Scots pine (Pinus sylvestris) and grey alder (Alnus incana). Betula and Pinus first appeared on early deglaciated nunataks during the Lateglacial. Their tree lines peaked between 9600 and 9000 cal. a BP, almost 600 m higher than present‐day elevations. This implies (adjusted for land uplift) that early Holocene summer temperatures may have been 2.3°C above modern ones. Elevational tree line retreat characterized the Holocene tree line evolution. For short periods, excursions from this trend have occurred. Between c. 12 000 and 10 000 cal. a BP, a pine‐dominated subalpine belt prevailed. A first major episode of descent occurred c. 8200 cal. a BP, possibly forced by cooling and an associated shift to a deeper and more persistent snow pack. Thereafter, the subalpine birch forest belt gradually evolved at the expense of the prior pine‐dominated tree line ecotone. A second episode of pine descent took place c. 4800 cal. a BP. Historical tree line positions are viewed in relation to early 21st century equivalents, and indicate that tree line elevations attained during the past century and in association with modern climate warming are highly unusual, but not unique, phenomena from the perspective of the past 4800 years. Prior to that, the pine tree line (and summer temperatures) was consistently higher than present, as it was also during the Roman and Medieval periods, c. 1900 and 1000 cal. a BP, respectively.     

A tree-ring based precipitation reconstruction for the Mohe region in the northern Greater Higgnan Mountains,China, since AD 1724

August–July precipitation has been reconstructed back to AD 1724 for the Mohe region in the northern Greater Higgnan Mountains, China, using Pinus sylvestris var. mongolica tree-ring width. The reconstruction explains 39% of the variance in the precipitation observed from AD 1960–2008. Some droughts noted in historical documents are precisely captured in our reconstruction. Wet periods occurred during the periods of AD 1734–1785, AD 1805–1830, AD 1863–1880, AD 1922–1961, and AD 1983–1998; while the periods of AD 1786–1804, AD 1831–1862, AD 1881–1921, and AD 1962–1982 were relatively dry. Power spectral and wavelet analyses demonstrated the existence of significant 24-yr, 12-yr, and 2-yr cycles of variability. The results of the spatial correlations suggest that our reconstruction contains climatic signals for the southern Stanovoy Range and the northern Greater Higgnan Mountains. The positive correlations between the new reconstructed precipitation series and two precipitation reconstructions indicate that our precipitation reconstruction captures broad-scale regional climatic variations. A comparison between the weakening tendency of summer monsoon and the dry period of our reconstruction reveals that the annual precipitation in the Mohe region is partly influenced by the East Asian Summer Monsoon.     

Comparison of Simulated and Reconstructed Temperature in China during the past 2000 years

Studying climate changes over the past 2 000 years has important scientific significance in exploring climate variability on decadal to centennial timescales, assessing the natural and anthropogenic contribution to the climate warming, and understanding the effects of human activities in the past and future climate changes. Due to the scarcity of observation and uncertainty of reconstruction in this period, climate model is developed as a useful tool for studying paleoclimate.The Community Earth System Model (CESM) is one of the state-of-the-art climate models, but its performance in simulating the temperature in China has not been examined.The temperature datasets of observation/reanalysis (GHCN_CAMS) and reconstructions during the past 2000 years in China were used to examine the performance of CESM. The comparison between the annual average temperatures of GHCN_CAMS reanalysis and simulation showed that the model well reproduced the spatial distributions and upward trend of the annual average temperature in China, and the comparison with reconstructions in five sub-regions of China indicated that the simulation were in good consistent with the average temperature changes of reconstructionson decadal time scales. On the centennial time scale, the average temperature fluctuations of simulation in the regions of China were in accord with reconstructions generally except for Central East and Tibet.There existed three warm periods of simulated temperature variation in China over the past 2000 years, including 0-540AD, 800-1250AD and 1901-2000AD, and two cold periods involving the 551-721AD and 1400-1850AD, which had some discrepancies with reconstructions. And the discrepancies between simulation and reconstructions might be related to uncertainties of the resolution, external forcing and parameterization of the subgrid-scale process in the model.     

An inference model for mean summer air temperatures in the Southern Alps,New Zealand,using subfossil chironomids

Quantitative paleoclimate reconstructions from Southern Hemisphere mid-latitude sites are critical for identifying spatial and temporal patterns of abrupt climate change and for testing hypotheses about possible causal mechanisms. The analysis of chironomid distributions and environmental variables from 61 lakes was undertaken to develop a robust inference model for quantitative temperature reconstruction from sites in South Island, New Zealand. Detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) indicated that mean summer air temperature (SmT), chlorophyll a, conductivity, organic content of sediment as determined by loss-on-ignition, and mean annual precipitation account for a significant portion of variance in chironomid taxa distribution. SmT was the dominant variable. The strongest performing inference model, based on weighted averaging-partial least squares (WA-PLS), was developed from 60 lakes for SmT, having a root mean square error of prediction (RMSEP_jack) of 1.27 °C and a coefficient of determination of 0.80 (r²_jack). These results confirm that New Zealand chironomids may be used to provide robust estimates of mean summer air temperature and are a reliable method for quantitative paleoenvironmental reconstruction.