a 352 year record of summer temperature reconstruction in the western tianshan mountains china as deduced from tree ring density three robust tree ring density chronologies were developed for the western tianshan mountains of northwestern china the chronologies were significantly correlated and form a regional chronology gld the gld had significant and positive correlations with temperature of warm seasons based on this relationship the mean minimum temperatures of may to august were reconstructed using the gld chronology for the period ad 1657 to 2008 the temperature reconstruction exhibited temperature patterns on interannual to centennial timescales and showed that the end of the 20th century is the warmest period in the past 352 years the reconstructed temperature variation has a teleconnection with large scale atmospheric oceanic variability and captures long and broad scale regional climatic variations

climate of the past 2500 years in the gulf of taranto central mediterranean sea a high resolution climate reconstruction based on δ18o and δ13c of globigerinoides ruber white we present a high resolution isotope stratigraphy based on globigerinoides ruber white over the past 2500 years in the gulf of taranto central mediterranean g ruber white reflects summer conditions in the gulf of taranto but is influenced by two major surface water masses the western adriatic current wac and the ionian surface water isw and their variations on a decadal to multicentennial scale our analysis of the 13c and 18o of g ruber white allows the distinction of several climatic periods the roman warm period rwp 450 0 bc with relatively wet and warm conditions and a higher influence of the wac the roman classical period rcp ad 1 200 characterized by salinity increase resulting from circulation changes the dark ages cold period dcp ad 500 750 where wetter conditions in the gulf of taranto region are coherent with an increase dominance of the wac the medieval warm period mwp with wet and warm conditions in the first and a gradual drying in the second half and finally the transition from the mwp to the little ice age lia which is characterized by continuing dry conditions

frost rings in trees as records of major volcanic eruptions new data about climatically effective volcanic eruptions during the past several thousand years may be contained in frost damage zones in the annual rings of trees there is good agreement in the timing of frost events and recent eruptions and the damage can be plausibly linked to climatic effects of stratospheric aerosol veils on hemispheric and global scales the cataclysmic proto historic eruption of santorini thera in the aegean is tentatively dated to 1628 26 bc from frost ring evidence

hydrological changes in the mediterranean sea over the last 30 000 years sea surface temperatures were reconstructed over the last 30 000 years from alkenone paleothermometry sst alk and planktonic foraminifera assemblages using the modern analog technique mat sst foram along two cores of the mediterranean sea md84 632 levantine basin and md04 2797 siculo tunisian strait oxygen isotope of planktonic foraminifera g bulloides for core md04 2797 and g ruber for core md84 632 were also determined sst alk in the levantine basin indicate colder values at the last glacial maximum lgm 14 c than earlier established from mat and a cooling amplitude of 6 7 c comparable to the central mediterranean sea climatic events such as the younger dryas yd and heinrich events 1 and 2 h1 and h2 were times of significant cooling in the two cores in the eastern basin values of local seawater oxygen isotope w indicate relatively saltier waters during the lgm and deglaciation than today with increasing w values higher salinity in the eastern basin and decreasing ones lower salinity in the central mediterranean sea during cold stadials the observed alterations of surface water properties t and w in the central and eastern mediterranean at the lgm are consistent with model experiments showing slightly lower evaporation in the mediterranean than today except for the eastern basin

annual climate variability in the holocene interpreting the message of ancient trees abstract over vast areas of the world s landmasses where climate beats out a strong seasonal rhythm tree growth keeps unerring time in their rings trees record many climate melodies played in different places and different eras recent years have seen a consolidation and expansion of tree ring sample collections across the traditional research areas of north america and europe and the start of major developments in many new areas of eurasia south america and australasia from such collections are produced networks of precisely dated chronologies records of various aspects of tree growth registered continuously year by year across many centuries their sensitivities to different climate parameters are now translated into ever more detailed histories of temperature and moisture variability across expanding dimensions of time and space with their extensive coverage high temporal resolution and rigid dating control dendroclimatic reconstructions contribute significantly to our knowledge of late holocene climates most importantly on timescales ranging from 1 to 100 years in special areas of the world where trees live for thousands of years or where subfossil remnants of long dead specimens are preserved work building chronologies covering many millennia continues apace very recently trees have provided important new information about major modes of general circulation dynamics linked to the el nino southern oscillation and the north atlantic oscillation and about the effect of large volcanic eruptions as for assessing the significance of 20th century global warming the evidence from dendroclimatology in general supports the notion that the last 100 years have been unusually warm at least within a context of the last two millennia however this evidence should not be considered equivocal the activities of humans may well be impacting on the natural growth of trees in different ways making the task of isolating a clear climate message subtly difficult

rapid alluvial sedimentation aided expansion of moissac during the high middle ages along the tarn river in southern france abstract we examine medieval urban expansion of moissac a town located at the outlet of the tarn river basin draining 15 400 km2 in southern france in order to understand the association of moissac s expansion to river position and sedimentation patterns in the river valley a chronostratigraphic framework was derived from three auger holes and an archaeological excavation using radiocarbon dating and standard field and laboratory characterization of sediments five radiocarbon dates were obtained from one auger hole along with particle size magnetic susceptibility organic matter and quantitative soil color analyses to augment field descriptions results indicate moissac spawned from the abbey of saint pierre on the apex of a small alluvial fan surrounded by backswamps ca 850 ce and urban growth radiated down the fan toward the river bottomlands throughout the following several centuries at ca 1000 1200 ce human induced soil erosion in the watershed caused very rapid aggradation of surrounding alluvial backswamps at long term average sedimentation rates of 20 30 mm y such rapid bottomland accretion probably was driven by rampant agricultural soil erosion linked with wet climatic periods and enhanced flooding this bottomland accretion enabled urban expansion and agricultural activities to cover the former backswamp and wetlands by the late middle ages ca 1300 1500 ce although we normally associate human induced soil erosion with negative consequences of ecosystem services the rapid bottomland accretion and resulting habitable and arable land can be viewed as a positive ecosystem service outcome resulting from human induced soil erosion

revising midlatitude summer temperatures back to a d 600 based on a wood density network annually resolved and millennium long reconstructions of large scale temperature variability are primarily composed of tree ring width trw chronologies changes in ring width however have recently been shown to bias the ratio between low and high frequency signals to overcome limitations in capturing the full spectrum of past temperature variability we present a network of 15 maximum latewood density mxd chronologies distributed across the northern hemisphere extratropics independent subsets of continental scale records consistently reveal high mxd before 1580 and after 1910 with below average values between these periods reconstructed extratropical summer temperatures reflect not only these long term trends but also distinct cooling pulses after large volcanic eruptions in contrast to trw dominated reconstructions this mxd based record indicates a delayed onset of the little ice age by almost two centuries the reduced memory inherent in mxd is likely responsible for the rapid recovery from volcanic induced cooling in the fourteenth century and the continuation of warmer temperatures until 1600

can climate variations be inferred from tree ring parameters and stable isotopes from larix decidua juvenile effects budmoth outbreaks and divergence issue abstract larch wood has been used for centuries as a building material hence the study of the tree ring width the latewood maximal density and the oxygen and carbon isotope composition of the cellulose of this tree provides potential and valuable insights when reconstructing past climate variability we explore the qualities and limitations of these proxies focusing on a forest standing the nevache valley french alps the analysis of 15 trees demonstrates a small intra tree variability in comparison with the inter tree variability of 13c and 18o and shows that 6 trees at least must be pooled to make a population representative sample our results show no juvenile effect for 13c unlike tree ring width and density 13c and 18o are not altered by budmouth outbreaks these two parameters therefore appear well suited for climate reconstructions and depict a strong correlation with july august temperature and relative humidity the 18o of larch cellulose is also strongly linked with the previous winter december march oxygen isotopic composition of the precipitation this is consistent with a winter water recharge of soil and ground the past variations of july august maximum temperature and relative humidity were established using two different combinations of the isotopic ratios uncertainties on the reconstructions are estimated respectively at 1 4 c and 3 6 inter annual variations of temperature and relative humidity are well reproduced however the reconstructed july august temperature series diverges from the instrumental one being lower after ca 1990 the effects of the variation through time of the depth of source water and of the ecophysiological response of trees to rising co2 on the isotope composition are discussed as possible causes of divergence this divergence problem strongly questions the possibility of producing appropriate isotope based temperature calibration the relationships between isotopes and the july august relative humidity are more stationary than those with temperature this may reflect the first order control of the relative humidity on 13c via the stomatal conductance and its influence on the evaporative enrichment of the oxygen of the leaf water our study suggests that past variations of relative humidity in the french alps can be accurately estimated using the stable isotope composition of larch cellulose

a 7000 year environmental history and soil erosion record inferred from the deep sediments of lake pavin massif central france a 14 m long sedimentary sequence core pav12 was collected in the deepest part of lake pavin a maar lake located in the french massif central the pav12 sedimentary sequence documents the lake s environmental evolution since its formation 7000 years ago the relationships between the catchment s vegetation cover erosion processes and changes in trophic status were shown using a multi proxy characterization of mineral and organic fractions supported by palynological data the record shows a succession of lithological units starting at the base with volcanoclastic material corresponding to the early stage of lake pavin the deposition of organic rich and diatomaceous sedimentary units above volcanoclastic material indicates an evolution toward a pristine lacustrine state the late holocene environmental history of this lake is marked by two tipping points reflecting major environmental disturbances at ca 4000 cal bp and after the deposition of erosive mass wasting deposits mwds at 1350 cal bp ce 600 and 650 cal bp ce 1300 the upper unit of core pav12 which corresponds to the past 700 years indicates that one of these mwds was likely the driving force behind a major limnological change marked by a shift in redox sensitive elements i e current meromictic lacustrine state the palynological diagram indicates a forested catchment where woodland clearances and agro pastoral activities have remained limited except over the last 700 years these findings suggest restricted human impact within the watershed compared to other regional archives the reconstruction of the lake pavin erosion record determined from titanium and red amorphous particle fluxes highlights phases of enhanced erosion at ca 6 5 5 5 4 1 3 8 3 5 2 8 2 6 1 6 1 4 cal kyr bp and during the little ice age lia a comparison between this erosion record palaeoenvironmental archives from western europe and palaeoclimatic data supports an atlantic signal driving precipitation patterns over lake pavin at centennial to millennial timescales the influence of local human activities even on a small scale cannot be completely discounted as their impact on erosional processes may be amplified in a steep catchment such as that found in lake pavin

pollen climate calibration based on a near annual peat sequence from the swiss alps the objective of this study was to develop a high resolution pollen based climate inference model using calibration in time for the mire mauntschas se swiss alps 1818 m above sea level we focused on 11 types of pollen and spores referred to as pollen for simplicity for which we produced 150 year a time series of accumulation rates and percentages dating of these series was based on 29 14c dates from pure sphagnum spheroidal carbonaceous particles larch bud moth events and an age depth model that took into account probabilities of calibrated 14c ages the degree of curvature of the age depth line and changes in concentrations of all major pollen types time resolution was 1 5 a we first smoothed the series using a 3 a triangular filter thus removing time resolution dependent changes in variability and minimising effects of potential dating uncertainties using redundancy analysis we then studied the simultaneous response of the selected pollen to 288 different combinations of monthly temperature or precipitation data measured at sils maria 1798 m above sea level located 9 km from mauntschas from ad 1954 to 2002 mean may august air temperature from the same year explained most 18 1 of the variation in pollen accumulation rates the amount of explained variation dropped to 9 9 after detrending all data with a 50 a high pass filter which possibly removed non climatic trends temperature explained more variation among par than among pollen percentages however during the verification period ad 1864 1953 the former were potentially affected by dating uncertainties and could not be used for developing a pollen based temperature inference model we tested ordinary least squares regression time series regression ridge regression principal components regression and partial least squares regression during the well dated calibration period ad 1954 2002 ordinary least squares regression based on percentages of six pollen types turned out to be the most parsimonious model having a cross validated root mean square error of prediction of 0 23 c for mean april november temperature a comparison of reconstructed with measured temperature from sils maria during the verification period showed that the model best reflected long term at least decadal scale temperature changes copyright 2009 john wiley sons ltd

frequency dependent signals in multi centennial oak vessel data article i nfo article history this work evaluates whether vessel size data contain a coherent spring precipitation signal over different frequency domains and how this climatic information varies from the signal encoded in radial growth the study was conducted at a forest site dominated by old oak trees quercus petraea mattuschka liebl located in the southern part of the swiss alps measurements of earlywood vessel size of 27 cores from 12 oak trees were performed in order to build an unprecedented multi centennial vessel size chronology age independent long term growth changes and climatic responses in the high mid and low frequency domains of differently composed chronologies are explored to test the stability of the signals results are compared with analyses of tree ring width measurements from the same material to gain a deeper understanding of physiological processes we find that mean vessel size data in contrast to tree ring width carry a frequency dependent signal although the signal of both parameters is similar in the low frequency domain the climate response in the high frequency domain differs vessel size responds negatively to wet spring conditions whereas ring width mainly responds positively to water availability during the summer we hypothesize that the processes responsible for signal registration in the specific frequencies are different the differing high frequency signals appear to be directly linked to dissimilar responses to weather conditions driving ring and vessel formation in contrast the long term response is related to conditions that affect tree vigour and due to a positive feedback on growth is indirectly reflected in the vessels and ring width characteristics due to the change in the frequency related response observed in this pioneering study it appears that the mean earlywood vessel size of oak is not an adequate proxy for long term reconstruction of spring precipitation

multiple stable isotopes from oak trees in southwestern scotland and the potential for stable isotope dendroclimatology in maritime climatic regions across much of europe eurasia and n america there exist networks of long tree ring chronologies which under favourable circumstances may be used to provide a record of palaeoclimate information a proportion of these tree ring archives primarily those collected for archaeological dating purposes represent a significant and largely untapped palaeoenvironmental archive such records may be unsuitable for palaeoclimatic reconstruction based solely upon their physical characteristics ring width and density owing to weak or poorly expressed climatic forcing this is especially true of oak chronologies from maritime regions this study explores the potential for extracting a climate signal from such chronologies by comparing the stable isotope ratios of c h and o from the rings of common oak quercus robur trees in southwestern scotland with local and regional meteorological data summer growing season climate influences all three isotopes and the relationships identified are consistent with published empirical and mechanistic studies the climate signal appears strongest in o and weakest in h the c and o series in combination explain 31 of the variance in july august mean temperature measured locally and 26 when compared with a homogenised gridded dataset for the period ad1957 2002 over longer timescales the combination of c and o isotopes may also preserve a significant low frequency signal july august r 2 0 57 9 year running mean ad1879 1998 these findings demonstrate the potential of stable isotope dendroclimatology for investigating climatic change from oak chronologies in maritime regions 2008 published by elsevier b v

paleo sea surface temperature calculations in the equatorial east atlantic from mg ca ratios in planktic foraminifera a comparison to sea surface temperature estimates from u37k oxygen isotopes and foraminiferal transfer function we present two 270 kyr paleo sea surface temperature sst records from the equatorial divergence and the south equatorial current derived from mg ca ratios in the planktic foraminifer globigerinoides sacculifer the present study suggests that the magnesium signature of g sacculifer provides a seasonal sst estimate from the upper 50 m of the water column generated during upwelling in austral low latitude fall winter common to both down core records is a glacial interglacial amplitude of 3 3 5 c for the last climatic changes and lower holocene and glacial oxygen isotope stage 2 temperatures compared with interglacial stage 5 5 and glacial stage 6 temperatures respectively the comparison to published sst estimates from alkenones oxygen isotopes and foraminiferal transfer function from the same core material pinpoints discrepancies and conformities between methods

improving a tree ring reconstruction from west central scandinavia 900 years of warm season temperatures dendroclimatological sampling of scots pine pinus sylvestris l has been made in the province of jamtland in the west central scandinavian mountains since the 1970s the tree ring width trw chronology spans several thousand years and has been used to reconstruct june august temperatures back to 1632 bc a maximum latewood density mxd dataset covering the period ad 1107 1827 with gap 1292 1315 was presented in the 1980s by fritz schweingruber here we combine these historical mxd data with recently collected mxd data covering ad 1292 2006 into a single reconstruction of april september temperatures for the period ad 1107 2006 regional curve standardization rcs provides more low frequency variability than non rcs and stronger correlation with local seasonal temperatures 51 variance explained the mxd chronology shows a stronger relationship with temperatures than the trw data but the two chronologies show similar multi decadal variations back to ad 1500 according to the mxd chronology the period since ad 1930 and around ad 1150 1200 were the warmest during the last 900 years due to large uncertainties in the early part of the combined mxd chronology it is not possible to conclude which period was the warmest more sampling of trees growing near the tree line is needed to further improve the mxd chronology

a last millennium temperature reconstruction using chironomids preserved in sediments of anoxic seebergsee switzerland consensus at local regional and central european scales determining if temperatures of the last century exceed natural variability necessitates the use of high resolution paleo reconstructions extending beyond the instrumental data i e 150 years although syntheses using tree ring stalagmite and borehole based reconstructions are available biological proxies preserved in lake sediments have been neglected as a source of high resolution information on climate change here we present a decadal scale mean july air temperature reconstruction covering the past millennium from varved seebergsee switzerland this reconstruction is compared to instrumental data at local regional and european scales to another high resolution chironomid inferred temperature reconstruction from lake silvaplana switzerland to a composite of paleo climate reconstructions from the greater alpine region and to various millennial scale climate reconstructions from the northern hemisphere when compared to local and regional instrumental records since ca 1760 ad significant p 0 5 are obtained suggesting that chironomids accurately register the changes in temperature for the past ca 250 years at european scale the seebergsee reconstruction correlates rpearson 0 40 p 0 01 with instrumental and early instrumental data back to 1500 ad on the millennial time scale the chironomid reconstruction of seebergsee provides a pattern of temperature changes mirrored by the chironomid reconstruction from silvaplana rpearson 0 44 p 0 01 and the greater alpine region composite of reconstructions rpearson 0 40 p 0 01 this includes warmer than the last century mean july air temperatures 1 2 c on average during the end of the medieval climate anomaly mca and colder than the last century temperatures 0 5 c on average during the little ice age both chironomid reconstructions inferred a warming during the last decades but this chironomid inferred warming does not exceed the mca temperatures this result is not singular as many millennial temperature reconstructions in the northern hemisphere do not show unprecedented warming of the last century at local regional scale however the chironomid assemblages found in seebergsee and silvaplana since ca 1950 ad seem to be unique i e they show unprecedented assemblage compositions for the past 1000 years

last millennium summer temperature variations in western europe based on proxy data we present a method of multiproxy reconstruction of the climate of europe during the last millennium the proxies used comprise long tree ring width series grape harvest dates greenland ice oxygen isotope series and temperature indices based on historical documents the proxies are calibrated using gridded april to september mean temperatures for western europe i e between 10 degrees w and 20 degrees e and between 35 degrees n and 55 degrees n they are calibrated also using the long instrumental summer temperature series of the marseilles observatory of longchamp which begins in the mid eighteenth century the method is a combination of an analogue technique which is able to deal with missing data an artificial neural network technique for an optimal non linear calibration and a bootstrap technique for calculating error bars on the reconstruction about 70 of the temperature variance is reconstructed the amplitude of the past temperature variations is particularly well reconstructed which is important when considering whether the recent temperature trend is or is not within the natural variability it appears that the temperature of the last decade of the twentieth century was reached only 14 times during the last millennium the reconstruction is discussed with respect to other multiproxy and borehole temperature reconstructions we conclude that a reconstruction such ours with a specific regional focus as opposed to the larger northern hemisphere is more reliable and is in better agreement with borehole results even allowing for the fact that only a part of the long term variance is reconstructed little ice age c ad 1560 1930 summers were 0 2 0 5 degrees c cooler than the 1961 1990 period borehole temperatures indicate a cooling of 0 4 degrees c which falls in the 95 confidence interval of our reconstructions

improved dendroclimatic calibration using blue intensity in the southern yukon in north western north america the so called divergence problem dp is expressed in tree ring width rw as an unstable temperature signal in recent decades maximum latewood density mxd from

a six hundred year annual minimum temperature history for the central tibetan plateau derived from tree ring width series the recent unprecedented warming found in different regions has aroused much attention in the past years how temperature has really changed on the tibetan plateau tp remains unknown since very limited high resolution temperature series can be found over this region where large areas of snow and ice exist herein we develop two juniperus tibetica kom tree ring width chronologies from different elevations we found that the two tree ring series only share high frequency variability correlation response function and partial correlation analysis indicate that prior year annual january december minimum temperature is most responsible for the higher belt juniper radial growth while more or less precipitation signal is contained by the tree ring width chronology at the lower belt and is thus excluded from further analysis the tree growth climate model accounted for 40 of the total variance in actual temperature during the common period 1957 2010 the detected temperature signal is further robustly verified by other results consequently a six century long annual minimum temperature history was firstly recovered for the yushu region central tp interestingly the rapid warming trend during the past five decades is identified as a significant cold phase in the context of the past 600 years the recovered temperature series reflects low frequency variability consistent with other temperature reconstructions over the whole tp region furthermore the present recovered temperature series is associated with the asian monsoon strength on decadal to multidecadal scales over the past 600 years

quantitative summer temperature reconstruction derived from a combined biogenic si and chironomid record from varved sediments of lake silvaplana south eastern swiss alps back to ad 1177 abstract high resolution quantitative temperature records are needed for placing the recent warming into the context of long term natural climate variability in this study we present a quantitative high resolution 9 year summer june august temperature reconstruction back to ad 1177 for the south eastern swiss alps this region is a good predictor for summer temperatures in large parts of western and central europe our reconstruction is based on a combination of the high frequency component of annually resolved biogenic silica bsi flux data and the low frequency component of decadal chironomid inferred temperatures from annually laminated well dated sediments varves from proglacial lake silvaplana eastern swiss alps for the calibration period ad 1760 1949 we assess systematically the effects of six different regression methods type i regressions inverse regression ir inverse prediction ip generalised least squares gls type ii regressions major axis ma ranged major axis rma and standard major axis sma with regard to the predicted amplitude and the calibration statistics such as root mean square error of prediction rmsep reduction of error re and coefficient of efficiency ce we found a trade off in the regression model choice between a good representation of the amplitude and good calibration statistics the band pass filtered bsi flux record is in close agreement both in the structure and the amplitude with two fully independent reconstructions spanning back to ad 1500 and ad 1177 respectively all known pulses of negative volcanic forcing are represented as cold anomalies in the bsi flux record volcanic pulses combined with low solar activity sporer and maunder minimum are seen as particularly cold episodes around ad 1460 and ad 1690 the combined chironomid and bsi flux temperature record rmsep 0 57 c is in good agreement with the glacier history of the alps the warmest ad 1190 and coldest decades 17th century 1680 1700 of our reconstruction coincide with the largest anomalies in the alpine tree ring based reconstruction both records show in the decadal variability an amplitude of 2 8 c between ad 1180 and 1950 which is substantially higher than the amplitude of hemispheric reconstructions our record suggests that the current decade is slightly warmer than the warmest decade in the pre industrial time of the past 800 years

10 be exposure dating of the timing of neoglacial glacier advances in the ecrins pelvoux massif southern french alps alpine glacier variations are known to be reliable proxies of holocene climate here we present a terrestrial cosmogenic nuclide tcn based glacier chronology relying on 24 new be 10 exposure ages which constrain maximum neoglacial positions of four small to mid sized glaciers rateau lautaret bonnepierre and etages in the ecrins pelvoux massif southern french alps glacier advances marked by mainly lateral moraine ridges that are located slightly outboard of the little ice age lia c 1250 1860 ad maximum positions were dated to 4 25 0 44 ka 3 66 0 09 ka 2 09 0 10 ka c 1 31 0 17 ka and to 0 92 0 02 ka the 4 2 ka advance albeit constrained by rather scattered dates is to our knowledge exposure dated here for the first time in the alps it is considered as one of the first major neoglacial advance in the western alps in agreement with other regional paleoclimatological proxies we further review alpine and northern hemisphere mid to high latitude evidence for climate change and glacier activity concomitant with the 4 2 ka event the 2 1 ka advance was not extensively dated in the alps and is thought to represent a prominent advance in early roman times other neoglacial advances dated here match the timing of previously described alpine neoglacial events our results also suggest that a neoglacial maximum occurred at etages glacier 0 9 ka ago i e during the medieval climate anomaly mca c 850 1250 ad at rateau glacier discordant results are thought to reflect exhumation and snow cover of the shortest moraine boulders overall this study highlights the need to combine several sites to develop robust neoglacial glacier chronologies in order to take into account the variability in moraine deposition pattern and landform obliteration and conservation

dynamic winter climate response to large tropical volcanic eruptions since 1600 1 we have analyzed the mean climate response pattern following large tropical volcanic eruptions back to the beginning of the 17th century using a combination of proxy based reconstructions and modern instrumental records of cold season surface air temperature warm anomalies occur throughout northern eurasia while cool anomalies cover northern africa and the middle east extending all the way to china in north america the northern portion of the continent cools with the anomalies extending out over the labrador sea and southern greenland the analyses confirm that for two years following eruptions the anomalies strongly resemble the arctic oscillation northern annular mode ao nam or the north atlantic oscillation nao in the atlantic eurasian sector with our four century record the mean response is statistically significant at the 95 confidence level over much of the northern hemisphere land area however the standard deviation of the response is larger than the mean signal nearly everywhere indicating that the anomaly following a single eruption is unlikely to be representative of the mean both the mean response and the variability can be successfully reproduced in general circulation model simulations driven by the solar heating induced by the stratospheric aerosols these models produce enhanced westerlies from the lower stratosphere down to the surface the climate response to volcanic eruptions thus strongly suggests that stratospheric temperature and wind anomalies can affect surface climate by forcing a shift in the ao nam or nao

european summer temperature response to annually dated volcanic eruptions over the past nine centuries the drop in temperature following large volcanic eruptions has been identified as an important component of natural climate variability however due to the limited number of large eruptions that occurred during the period of instrumen tal observations the precise amplitude of post volcanic cooling is not well constrained here we present new evidence on summer temperature cooling over europe in years following volcanic eruptions we compile and analyze an updated net work of tree ring maximum latewood density chronologies spanning the past nine centuries and compare cooling sig natures in this network with exceptionally long instru mental station records and state of the art general circu lation models results indicate post volcanic june august cooling is strongest in northern europe 2 years after an eruption 0 52 0 05 c whereas in central europe the temperature response is smaller and occurs 1 year after an eruption 0 18 0 07 c we validate these estimates by comparisonwith the shorter instrumental network and evaluate the statistical significance of post volcanic summer tempera ture cooling in the context of natural climate variability over the past nine centuries finding no significant post volcanic temperature cooling lasting longer than 2 years our results question the ability of large eruptions to initiate long term temperature changes through feedback mechanisms in the climate system we discuss the implications of these findings with respect to the response seen in general circulation models and emphasize the importance of considering well documented annually dated eruptions when assessing the

tracing the origin of arctic driftwood 1 arctic environments where surface temperatures increase and sea ice cover and permafrost depth decrease are very sensitive to even slight climatic variations placing recent environmental change of the high northern latitudes in a long term context is however complicated by too short meteorological observations and too few proxy records driftwood may represent a unique cross disciplinary archive at the interface of marine and terrestrial processes here we introduce 1445 driftwood remains from coastal east greenland and svalbard macroscopy and microscopy were applied for wood anatomical classification a multi species subset was used for detecting fungi and information on boreal vegetation patterns circumpolar river systems and ocean current dynamics was reviewed and evaluated four conifer pinus larix picea and abies and three deciduous populus salix and betula genera were differentiated species specific identification also separated pinus sylvestris and pinus sibirica which account for 40 of all driftwood and predominantly originate from western and central siberia larch and spruce from siberia or north america represents 26 and 18 of all materials respectively fungal colonization caused different levels of driftwood staining and or decay our results demonstrate the importance of combining wood anatomical knowledge with insight on boreal forest composition for successfully tracing the origin of arctic driftwood to ultimately reconstruct spatiotemporal variations in ocean currents and to better quantify postglacial uplift rates we recommend consideration of dendrochronologically dated material from many more circumpolar sites

fennoscandian summers from ad 500 temperature changes on short and long timescales quantitative estimates of 1480 years of summer temperatures in northern fennoscandia have previously been derived from continuous treering records from northern sweden here we show the results of spectral analyses of these data only a few peaks in the spectra are consistently significant when the data are analyzed over a number of sub periods relatively timestable peaks are apparent at periods of 2 1 2 5 3 1 3 6 4 8 32 33 and for a range between 55 100 years these results offer no strong evidence for solar related forcing of summer temperatures in these regions our previously published reconstruction was limited in its ability to represent long timescale temperature change because of the method used to standardize the original tree ring data here we employ an alternative standardization technique which enables us to capture temperature change on longer timescales considerable variance is now reconstructed on timescales of several centuries in comparison with modern normals 1951 70 generally extended periods when cool conditions prevailed prior to the start of the instrumental record include 500 700 790 870 1110 1150 1190 1360 1570 1750 a d with the most significant cold troughs centred on about 660 800 1140 1580 1620 and 1640 predominantly warm conditions occurred in 720 790 870 1110 and 1360 1570 with peaks of warmth around 750 930 990 1060 1090 1160 1410 1430 1760 and 1820

late pleistocene holocene alluvial stratigraphy of southern baja california mexico abstract a late pleistocene to holocene alluvial stratigraphy has been established for the basins of la paz and san jose del cabo in the southern tip of the baja california peninsula mexico six discrete alluvial units qt1 through qt6 were differentiated across the region using a combination of geomorphologic mapping sedimentological analysis and soil development these criteria were supported using radiocarbon optically stimulated luminescence and cosmogenic depth profile geochronology major aggradation started shortly after 70 ka qt2 and buildup of the main depositional units ended at 10 ka qt4 after deposition of qt4 increasing regional incision of older units and the progressive development of a channelized alluvial landscape coincide with deposition of qt5 and qt6 units in a second incisional phase all units consist of multiple 1 3 m thick alluvial packages deposited as upper flow stage beds that represent individual storms main aggradational units qt2 qt4 occurred across broad 2 km channels in the form of sheetflood deposition while incisional stage deposits are confined to channels of 0 5 2 km width continuous deposition inside the thicker 10 m pre qt5 units is demonstrated by closely spaced dates in vertical profiles in a few places disconformities between these major units are nevertheless evident and indicated by partly eroded buried soils the described units feature sedimentological traits similar to historical deposits formed by large tropical cyclone events but also include characteristics of upper regime flow sedimentation not shown by historical sediments like long 10 m wavelength antidunes and transverse ribs we interpret the whole sequence as indicating discrete periods during the late pleistocene and holocene when climatic conditions allowed larger and more frequent tropical cyclone events than those observed historically these discrete periods are associated with times when insolation at the tropics was higher than the present day conditions determined by precessional cycles and modulated by the presence of el nino like conditions along the tropical and northeastern pacific the southern baja california alluvial record is the first to document a precession driven alluvial chronology for the region and it constitutes a strong benchmark for discrimination of direct tropical influence on any other alluvial record in southwestern north america

tree ring and summer temperature response to volcanic aerosol forcing at the northern tree line kola peninsula russia potential linkages between volcanic activity and a 403 year record of pinus sylvestris l scots pine growth and summer temperatures estimated from tree ring widths are evaluated from an arctic tree line site on the kola peninsula northwestern russia the joint occurrence of volcanic eruptions and severe negative ring width values is more than four times that expected by chance a composite average of temperatures indicates that a 0 72 c temperature reduction is typical for the year immediately following volcanic eruptions while tree growth is reduced for up to two decades the greenland ice sheet project 2 gisp2 volcanic sulphate record shows a small but significant correlation with summer temperatures volcanic aerosols originating at low and middle latitudes appear to cause the greatest ring width reduction and cooling

late holocene summer temperature reconstruction from chironomid assemblages of lake anterne northern french alps we present a chironomid based reconstruction of late holocene temperature from lake anterne 2060 m a s l in the northern french alps chironomid assemblages were studied in 49 samples along an 8 m long sediment core covering the last 1800 years july air temperatures were inferred using an inference model based on the distribution of chironomid assemblages in 100 swiss lakes the transfer function has a leave one out cross validated coefficient of determination r of 0 88 a root mean square error of prediction rmsep of 1 40 c despite possible biases induced by methodological aspects and the ecological complexity of the chironomid response to both climate and environmental changes the concordance of the lake anterne temperature reconstruction with other alpine records suggests that the transfer function has successfully reconstructed past summer temperature during the last two millennia the twentieth century is the only section of the record which shows a poor agreement with other climate recons

proxy based northern hemisphere surface temperature reconstructions sensitivity to method predictor network target season and target domain abstract results are presented from a set of experiments designed to investigate factors that may influence proxy based reconstructions of large scale temperature patterns in past centuries the factors investigated include 1 the method used to assimilate proxy data into a climate reconstruction 2 the proxy data network used 3 the target season and 4 the spatial domain of the reconstruction estimates of hemispheric mean temperature are formed through spatial averaging of reconstructed temperature patterns that are based on either the local calibration of proxy and instrumental data or a more elaborate multivariate climate field reconstruction approach the experiments compare results based on the global multiproxy dataset used by mann and coworkers with results obtained using the extratropical northern hemisphere nh maximum latewood tree ring density set used by briffa and coworkers mean temperature reconstructions are compared for the full nh tropics and extratropics land and ocean and ext

five hundred years of gridded high resolution precipitation reconstructions over europe and the connection to large scale circulation we present seasonal precipitation reconstructions for european land areas 30 w to 40 e 30 71 n given on a 0 5 0 5 resolved grid covering the period 1500 1900 together with gridded reanalysis from 1901 to 2000 mitchell and jones 2005 principal component regression techniques were applied to develop this dataset a large variety of long instrumental precipitation series precipitation indices based on documentary evidence and natural proxies tree ring chronologies ice cores corals and a speleothem that are sensitive to precipitation signals were used as predictors transfer functions were derived over the 1901 1983 calibration period and applied to 1500 1900 in order to reconstruct the large scale precipitation fields over europe the performance quality estimation based on unresolved variance within the calibration period of the reconstructions varies over centuries seasons and space highest reconstructive skill was found for winter over central europe and the iberian peninsula precipitation variability over the last half millennium reveals both large interannual and decadal fluctuations applying running correlations we found major non stationarities in the relation between large scale circulation and regional precipitation for several periods during the last 500 years we identified key atmospheric modes for southern spain northern morocco and central europe as representations of two precipitation regimes using scaled composite analysis we show that precipitation extremes over central europe and southern spain are linked to distinct pressure patterns due to its high spatial and temporal resolution this dataset allows detailed studies of regional precipitation variability for all seasons impact studies on different time and space scales comparisons with high resolution climate models as well as analysis of connections with regional temperature reconstructions

a millennial long record of warm season precipitation and flood frequency for the north western alps inferred from varved lake sediments implications for the future abstract the recent warming of the global climate is well recognized however does a warmer climate also mean a moister climate does dry get drier and wet get wetter there are important questions as they relate to changes in the water cycle and impacts the water resources as well as the frequency and intensity of storms and floods in the near future in europe regional climate models do not show consistent and robust results for future hydroclimatic changes and how extreme events will evolve in response to future climate change paleo hydroclimatic data from natural archives are one of the few means to assess such changes in the longer context here we present an annually resolved record of warm season mjja precipitation and summer flood frequency from the varved annually laminated sediments of proglacial lake oeschinen 46 30 n 7 44 e 1580 m nw swiss alps back to ad 884 these data sets are inferred from the thickness of annual sediment deposits and the occurrence of flood event layers in the sediments the chronology of the sediment record is based on multiple varve counts and validated with historical floods chronicled in written documents back to the 14th century and 14c ams dates the precipitation record shows pronounced interannual to centennial variability with humid warm season phases between ad 920 950 ad 1100 1180 ad 1300 1400 ad 1590 1650 ad 1700 1790 ad 1820 1880 and ad 1960 2008 driest conditions are reconstructed for ad 960 1080 ad 1250 1300 and for ad 1880 1900 our precipitation record is consistent with the few multi centennial warm season precipitation records available for europe we did not find a persistent relationship between warm season precipitation and temperature in contrast results show that the relation between precipitation and temperature has oscillated between positive correlations warmer gets wetter cooler gets drier and negative correlations warmer gets drier cooler gets wetter with a highly significant 2 99 multidecadal 60 70 yrs periodicity over the last millennium possible explanations for this phenomenon are changes in the weather type statistics or the within weather type variability which influence the combinations between precipitation and temperature over continental central europe and operate at multidecadal scales such multidecadal effects might also be important for precipitation scenarios in the alpine area under future warming our record of flood frequency suggests more frequent floods under cool and humid climate during the warm seasons this picture is consistent with other studies from small and medium size catchments at mid and high elevations in the alpine area however the 13th century reveals a period with high flood frequency during warm and moderately dry average precipitation conditions this anomalous situation is currently not understood nonetheless this is also one out of several possible scenarios for the future from the different combinations found in our record we conclude that the relation between floods precipitation and temperature and in consequence future projections remain poorly constrained

frequency and intensity of high altitude floods over the last 3 5 ka in northwestern french alps lake anterne in central western europe several studies have shown that colder holocene periods such as the little ice age also correspond to wet periods however in mountain areas which are highly sensitive to erosion processes and where precipitation events can be localized past evolution of hydrological activity might be more complicated to assess these past hydrological changes a paleolimnological approach was applied on a 13 4 m long sediment core taken in alpine lake anterne 2063 m asl and representing the last 3 5 ka lake sedimentation is mainly composed of ood deposits triggered by precipitation events sedimentological and geochemical analyses show that oods were more frequent during cold periods while high intensity ood events occurred preferentially during warmer periods in mild temperature conditions both ood patterns are present this underlines the complex relationship between ood hazards and climatic change in mountain areas during the warmer and or dryer times of the end of iron age and the roman period both the frequency and intensity of oods increased this is interpreted as an effect of human induced clearing for grazing activities and reveals that anthropogenic interferences must be taken into account when reconstructing climatic signals from natural archives

reconstructing holocene climate from tree rings the potential for a long chronology from the scottish highlands despite promising research in the 1980s showing the potential of scots pine pinus sylvestris l for the reconstruction of past summer temperatures in the scottish highlands little dendroclimatic work has been attempted in this region since this reflects in part the limited number of sparsely distributed remnant natural semi natural pine woodlands in the scottish highlands and the lack of old growth forest therein on average most of the pine trees dated in this region are around 225 years in age here we present the first results of an ongoing interdisciplinary initiative to develop a long scottish chronology through the acquisition of modern historical and subfossil pine material from the native pinewoods historic structures and lakes of the scottish highlands radiocarbon dating of 25 subfossil pine timbers recovered from lake sediments identified the presence of preserved material covering the last 8000 years with initial clusters focused on the last two millennia and early mid holocene alth

reconstructing 800 years of summer temperatures in scotland from tree rings this study presents a summer temperature reconstruction using scots pine tree ring chronologies for scotland allowing the placement of current regional temperature changes in a longer term context living tree chronologies were extended using subfossil samples extracted from nearshore lake sediments resulting in a composite chronology 800 years in length the north cairngorms ncairn reconstruction was developed from a set of composite blue intensity high pass and ring width low pass filtered chronologies with a range of detrending and disturbance correction procedures calibration against july august mean temperature explains 56 4 of the instrumental data variance over 1866 2009 and is well verified spatial correlations reveal strong coherence with temperatures over the british isles parts of western europe southern scandinavia and northern parts of the iberian peninsula ncairn suggests that the recent summer time warming in scotland is likely not unique when compared to multi decadal warm periods observed in the 1300s 1500s and 1730s although trends before the mid sixteenth century should be interpreted with some caution due to greater uncertainty prominent cold periods were identified from the sixteenth century until the early 1800s agreeing with the so called little ice age observed in other tree ring reconstructions from europe with the 1690s identified as the coldest decade in the record the reconstruction shows a significant cooling response 1 year following volcanic eruptions although this result is sensitive to the datasets used to identify such events in fact the extreme cold and warm years observed in ncairn appear more related to internal forcing of the summer north atlantic oscillation

methods to merge overlapping tree ring isotope series to generate multi centennial chronologies abstract stable isotopes ratios in tree rings are increasingly used to assess long term environmental variation as with conventional tree ring investigations crossdating overlapping sequences of wood material allows chronologies longer than the lifespans of individual trees to be developed we measured data from four overlapping cohorts of recent ad 1650 2004 and historic ad 1100 1198 ad 1150 1325 ad 1256 1700 wood to yield millennial length 13 c d and 18 o chronologies however we found that offsets in absolute isotopic values between overlapping segments challenge the preservation of low frequency climate signals in this paper we describe the development of these records signal strength assessments and present the problems associated with overcoming these offsets and preserving low frequency variance we then propose and evaluate four different solutions to link the cohorts these methods include various types of transformations of mean and variance all present potential advantages and drawbacks inflated variance loss of absolute isotope values and the loss of low frequency signals are major problems only one method is capable of fully preserving low frequency trends but this method may also risk inducing long term artifacts while the various solutions we propose may be useful to help overcome such biases the challenges described here if typical for other isotopic series will best be solved by additionally modifying sampling and measurement procedures we recommend avoiding pooling of tree rings in the overlap period and to increase the replication in order to extract the original signal and to maintain low frequency signals

atmospheric circulation variability in the north atlantic european area since the mid seventeenth century based on monthly mean sea level pressure grids objectively reconstructed by luterbacher et al variations of dynamical modes of the atmospheric circulation for january and july are described by novel indices for running 31 year periods between 1659 and 1999 these indices reflect the continuous evolution of the atmospheric circulation not only with regard to frequency changes of major dynamical modes but also in terms of internal changes within each mode concerning both dynamic vorticity intensity and climatic properties central european temperature and precipitation during occurrence of each mode respectively results indicate the great importance of within mode variations the zonal circulation mode in january varying in frequency with long term cycles primarily changed its dynamic and climatic properties towards higher indices during the transition from the little ice age to modern conditions between 1800 and 1930 within the russian high mode of january a change in preference from easterly to westerly patterns above central europe occurred around 1850 for july a striking frequency maximum of the westerly mode at the end of the eighteenth century coincided with a period of marked summer warmth in central europe due to negative positive deviations in vorticity temperature during occurrence of this mode the long term evolution in july indicates a general increase of anticyclonic conditions strengthening during the last 50 years towards a unique phenomenon within the last centuries the strong increase in the winter time westerly circulation during the last decades however does not appear extraordinary in view of the low frequency variations of this mode

on smoothing potentially non stationary climate time series 1 a simple approach to the smoothing of a potentially non stationary time series is presented which provides an optimal choice among three alternative readily motivated and easily implemented boundary constraints this method is applied to the smoothing of the instrumental northern hemisphere nh annual mean and cold season north atlantic oscillation nao time series yielding an objective estimate of the smoothed decadal scale variations in these series including long term trends

tree ring recorded may august temperature variations since a d 1585 in the gaoligong mountains southeastern tibetan plateau abstract high resolution proxy data are still scarce in the southeastern tibetan plateau which limit our understanding of climatic variability before instrumental records in this study we developed 595 year tree ring width chronology from larix speciosa near the timberlines of the gaoligong mountains southeastern tibetan plateau ring width site chronologies and a well replicated regional chronology rc showed significant positive correlations with warm season temperatures from may to august using rc as predictor we reconstructed mean may august temperature for the study region that extends back to a d 1585 cold conditions prevailed during the periods 1600s 1620 30 1640 50s 1700s 1730 40s 1760s 1810 20s 1850s 1900 10s and 1955 70 warm episodes occurred during 1610s 1660 1680s 1710 20s 1750s 1780 90s 1820 40 1920 50 and 1980 present spatial correlations with gridded land surface temperatures revealed that our reconstruction represents regional temperature signal for the southern tibetan plateau comparison with other tree ring based temperature reconstructions from surrounding areas implies a high degree of confidence for our reconstruction

a synthetic pollen record of the eastern mediterranean sapropels of the last 1 ma implications for the time scale and formation of sapropels abstract the quaternary climate of southern europe south italy and greece is investigated by pollen analysis of the sapropels which were deposited in the deep eastern mediterranean sea during the last 1 million year ma the time scale of core kc01b in the ionian sea has been established by tuning its oxygen isotopic record to the ice volume model of imbrie and imbrie 1980 for the last 250 000 year 250 ka the previous pollen studies and astronomical tuning have been confirmed sapropels were deposited under a large range of mediterranean climates fully interglacial fully glacial and intermediary as revealed mainly by the balance between the respective pollen abundances of oak quercus and sage brush artemisia the high value of the oak reveals the warm and wet climate of an interglacial and the high value of the sage brush the dry and cold climate of a glacial whereas the mediterranean climate is directly related to the variation of the high latitude ice sheets the deposition of sapropels is not so in contrast with the wide climatic range sapropels were deposited only when summer insolation in the low latitudes reached its highest peaks however between 250 ka and 1 ma that stable pattern is not yet established only six sapropels are observed many expected ones do not appear even as ghosts signalled by peaks of barium abundance that remain after the post deposition oxidation of organic matter the pattern of sapropel formation in stable and direct relationship to highest insolation does not seem to apply for five of those sapropels neither climate extremes are observed they mainly formed during intermediary types of mediterranean climate in contrast one sapropel and one ghost relates to a relatively low peak of insolation and its climate is of a unique composite type not seen later this might suggest an unsuspected more complex pattern linking the formation of mediterranean sapropels to the astronomical configuration

ice core evidence for an explosive tropical volcanic eruption 6 years preceding tambora high resolution analyses of ice cores from antarctica and greenland reveal an explosive volcanic eruption in the tropics in a d 1809 which is not reflected in the historical record a comparison in the same ice cores of the sulfate flux from the a d 1809 eruption to that from the tambora eruption a d 1815 indicates a near equatorial location and a magnitude roughly half that of tambora thus this event should be considered comparable to other eruptions producing large volumes ofsulfur rich gases such as coseguina krakatau agung and el chichtn the increase in the atmospheric concentration of sulfuric acid may have contributed to the northern hemisphere cooling observed in the early nineteenth century and may account partially for the decline in surface temperatures which preceded the eruption of tamborn in a d 1815

a well verified multiproxy reconstruction of the winter north atlantic oscillation index since a d 1400 abstract a new well verified multiproxy reconstruction of the winter north atlantic oscillation nao index is described that can be used to examine the variability of the nao prior to twentieth century greenhouse forcing it covers the period a d 1400 1979 and successfully verifies against independent estimates of the winter nao index from european instrumental and noninstrumental data as far back as 1500 the best validation occurs at interannual timescales and the weakest at multidecadal periods this result is a significant improvement over previous proxy based estimates which often failed to verify prior to 1850 and is related to the use of an extended reconstruction model calibration period that reduced an apparent bias in selected proxies associated with the impact of anomalous twentieth century winter nao variability on climate teleconnections over north atlantic sector land areas although twentieth century nao variability is somewhat unusual comparable periods of persistent positive phase

high resolution palaeoclimatology of the last millennium a review of current status and future prospects this review of late holocene palaeoclimatology represents the results from a pages clivar intersection panel meeting that took place in june 2006 the review is in three parts the principal high resolution proxy disciplines trees corals ice cores and documentary evidence emphasizing current issues in their use for climate reconstruction the various approaches that have been adopted to combine multiple climate proxy records to provide estimates of past annual to decadal timescale northern hemisphere surface temperatures and other climate variables such as large scale circulation indices and the forcing histories used in climate model simulations of the past millennium we discuss the need to develop a framework through which current and new approaches to interpreting these proxy data may be rigorously assessed using pseudo proxies derived from climate model runs where the answer is known the article concludes with a list of recommendations first more raw proxy data are required from the diverse disciplines and from more locations as well as replication for all proxy sources of the basic raw measurements to improve absolute dating and to better distinguish the proxy climate signal from noise second more effort is required to improve the understanding of what individual proxies respond to supported by more site measurements and process studies these activities should also be mindful of the correlation structure of instrumental data indicating which adjacent proxy records ought to be in agreement and which not third large scale climate reconstructions should be attempted using a wide variety of techniques emphasizing those for which quantified errors can be estimated at specified timescales fourth a greater use of climate model simulations is needed to guide the choice of reconstruction techniques the pseudo proxy concept and possibly help determine where given limited resources future sampling should be concentrated

recurrent climate winter regimes in reconstructed and modelled 500 hpa geopotential height fields over the north atlantic european sector 1659 1990 recurrent climate winter regimes are examined from statistically reconstructed and modelled 500 hpa geopotential height fields over the north atlantic european sector for the period 1659 1990 we investigate the probability density function of the state space spanned by the first two empirical orthogonal functions of combined winter data regimes are detected as patterns that correspond to areas of the state space with an unexpected high recurrence probability using a monte carlo approach the reconstruction and the model reveal four recurrent climate regimes they correspond to the two phases of the north atlantic oscillation and two opposite blocking patterns complemented by the investigation of the temporal evolution of the climate regimes this leads to the conclusion that the reconstructed and the modelled data for this geographic sector reproduce low frequency atmospheric variability in the form of regime like behaviour the overall evidence for recurrent climate regimes is higher for the model than for the reconstruction however comparisons with independent data sources for the period 1659 1990 revealed a more realistic temporal evolution of the regimes for the reconstructed data

extracting a climate signal from 169 glacier records i constructed a temperature history for different parts of the world from 169 glacier length records using a first order theory of glacier dynamics i related changes in glacier length to changes in temperature the derived temperature histories are fully independent of proxy and instrumental data used in earlier reconstructions moderate global warming started in the middle of the 19th century the reconstructed warming in the first half of the 20th century is 0 5 kelvin this warming was notably coherent over the globe the warming signals from glaciers at low and high elevations appear to be very similar

high resolution chironomid inferred temperature history since ad 1580 from varved lake silvaplana switzerland comparison with local and regional reconstructions chironomids were used to reconstruct mean july air temperatures between c ad 1580 and 2001 at lake silvaplana a varved lake located in the engadine eastern swiss alps the goal of this study was to reconstruct temperature changes at near annual resolution and validate the reconstruction by comparison with records based on early instrumental data documentary proxy evidence dendrochronology geochemical biogenic silica bsi and mineralogical data quartz mica ratios at local and regional scales warmer than the climate normal ad 1961 1990 mean july air temperatures were inferred between c ad 1610 and 1662 ad 1710 and 1740 ad 1790 and 1866 ad 1940 and 1960 and ad 1990 and 2001 colder than the climate normal july air temperatures were reconstructed between c ad 1662 and 1710 ad 1740 and 1790 ad 1866 and 1919 and ad 1970 and 1990 the 420 year chironomid inferred mean july air temperature record was significantly p 0 01 related to june september jjas temperatures reconstructed from e

last millennium northern hemisphere summer temperatures from tree rings part i the long term context abstract large scale millennial length northern hemisphere nh temperature reconstructions have been progressively improved over the last 20 years as new datasets have been developed this paper and its companion part ii anchukaitis et al in prep details the latest tree ring tr based nh land air temperature reconstruction from a temporal and spatial perspective this work is the first product of a consortium called n trend n orthern hemisphere tre e ring n etwork d evelopment which brings together dendroclimatologists to identify a collective strategy for improving large scale summer temperature reconstructions the new reconstruction n trend2015 utilises 54 records a significant expansion compared with previous tr studies and yields an improved reconstruction with stronger statistical calibration metrics n trend2015 is relatively insensitive to the compositing method and spatial weighting used and validation metrics indicate that the new record portrays reasonable coherence with large scale summer temperatures and is robust at all time scales from 918 to 2004 where at least 3 tr records exist from each major continental mass n trend2015 indicates a longer and warmer medieval period 900 1170 than portrayed by previous tr nh reconstructions and by the cmip5 model ensemble but with better overall agreement between records for the last 600 years future dendroclimatic projects should focus on developing new long records from data sparse regions such as north america and eastern eurasia as well as ensuring the measurement of parameters related to latewood density to complement ring width records which can improve local based calibration substantially

reconstructing palaeoprecipitation from an active cave flowstone several drill cores were obtained from a laminated actively forming flowstone from a shallow cave in austria highly resolved petrographic and geochemical analyses combined with multi annual cave monitoring reveal a distinct sensitivity of flowstone growth and composition to late holocene meteoric precipitation the regular sub millimetre scale lamination consists of thicker translucent laminae and thinner organic inclusion rich laminae there is also a macroscopic millimetre scale banding of darker and lighter bands comprising several laminae stable isotope analyses of drill cores and modern calcite precipitates show a pronounced positive covariation of 13c and 18o values indicative of kinetic isotope effects comparing the isotope values with petrography shows gradual changes across several of the annual laminae i e changes of several per mille on a multi annual to decadal timescale the stable isotope and trace element composition as well as the flowstone petrography are mainly controlled by the variable drip water discharge controlling the water film thickness and water residence time on the flowstone surface and consequently the intensity of co2 degassing kinetic isotope enrichment and concomitant calcite precipitation drill core pfu6 provides an isotope record of the last ca 3000 years at near annual resolution a distinct phase of low c and o isotope values interpreted as increased discharge and hence higher meteoric precipitation occurred from ca 300 to 140 a b2k second half of the little ice age and another wet interval occurred around 700 a corresponding to reported medieval glacier advances the roman warm period was also dominated by relatively wet conditions although significant decadal variability prevailed increased precipitation further characterized the intervals from ca 2480 to 2430 and 2950 to 2770 a dry conditions persisted during the medieval climate anomaly although this trend towards reduced precipitation started earlier the highest c isotope values of the last 2 ka are recorded around 750 a and another dry phase is centred at 1480 a this new record shows that inter annual to decadal oscillations are a dominant mode of variation during the last 3 ka in the alps copyright 2011 john wiley sons ltd

abrupt temperature changes in the western mediterranean over the past 250 000 years a continuous high resolution western mediterranean sea surface temperature sst alkenone record spanning the past 250 000 years shows that abrupt changes were more common at warming than at cooling during marine isotope stage mis 6 sst oscillated following a stadial interstadial pattern but at lower intensities and rates of change than in the dansgaard oeschger events of mis 3 some of the most prominent events occurred over miss 5 and 7 after prolonged warm periods of high stability climate during the whole period was predominantly maintained in interglacial interstadial conditions whereas the duration of stadials was much shorter

climatic variability during the last 90 ka of the southern and northern levantine basin as evident from marine records and speleothems abstract the influence of the northern atlantic and tropical monsoonal systems as recorded by the river nile on the climate variability of the southeastern mediterranean was studied in two cores taken by the r v marion dufresne one core taken se of cyprus representing the northern levantine basin core 9501 980 m water depth and the other located 380 km further south represents the southeastern levantine basin in an area influenced by the river nile plume core 9509 884 m water depth the study was performed at relatively high resolution using several proxies 18o of globigerinoides ruber sediment characteristics and index colour parameters in core sections representing the last 86 ka a low resolution alkenone sea surface temperature record was also measured the time frame in both cores was mostly constrained by wiggle matching with the nearby well dated 18o and 13c record of the soreq cave which is mainly influenced by the eastern mediterranean water vapor the sedimentary record of the southern core is strongly influenced by the river nile contribution throughout the last 86 ka as evidenced by the higher sedimentation rates compared with the northern core 20 cm ka vs 5 cm ka continuously darker sediment colour and higher toc values 0 6 0 9 vs 0 25 wt not including sapropels during sapropels s1 and s3 present in both cores the influence of the river nile became more widespread reaching as far as cyprus yet the influence of the river nile remained stronger in the south as evident by the higher toc values in the southern core throughout the entire 90 ka period and the longer duration of s1 in the southern core an anomalous low 18o interval that is not recorded in western mediterranean occurred between 58 and 49 ka in the levantine basin and is more developed in the northern core this period correlates with d o interstadial 14 and maximum northern hemisphere insolation during the lastglacial cycle suggesting that the warming mainly impacted the northern levant the eastern mediterranean sea and land area was considerably warmer than the western mediterranean throughout the lgm holocene transition and the 18og ruber drop of 4 5 is significantly greater than the 3 shift found for the western mediterranean 18og bulloides both differences reflecting an increased continental effect from the western to eastern mediterranean comparison between the marine and the land 18o records suggests that the origin of rain over the land is composed of mixed signal from the southern and northern levantine basin the study of 18osea land variations demonstrates that various factors have influenced the sea land relationship during the last 90 ka the amount effect has an important influence on rainfall 18o during interglacial periods particularly sapropel periods whereas during glacial periods increased land distances and elevation differences arising from decrease in sea level may have brought about decrease in 18o of rainfall due to rayleigh distillation processes these influences were superimposed on those of sea surface water 18o changes brought about by continental ice melting and the strong effects felt in the southern levantine basin of the high river nile input during periods of enhanced monsoonal activity

on the long term context for late twentieth century warming 1 previous tree ring based northern hemisphere temperature reconstructions portray a varying amplitude range between the medieval warm period mwp little ice age lia and present we describe a new reconstruction developed using largely different methodologies and additional new data compared to previous efforts unlike earlier studies we quantify differences between more traditional std and regional curve standardization rcs methodologies concluding that rcs is superior for retention of low frequency trends continental north american versus eurasian rcs series developed prior to merging to the hemispheric scale cohere surprisingly well suggesting common forcing although there are notable deviations e g fifteenth to sixteenth century results indicate clear mwp warm lia cool and recent warm episodes direct interpretation of the rcs reconstruction suggests that mwp temperatures were nearly 0 7c cooler than in the late twentieth century with an amplitude difference of 1 14c from the coldest 1600 1609 to warmest 1937 1946 decades however we advise caution with this analysis although we conclude as found elsewhere that recent warming has been substantial relative to natural fluctuations of the past millennium we also note that owing to the spatially heterogeneous nature of the mwp and its different timing within different regions present palaeoclimatic methodologies will likely flatten out estimates for this period relative to twentieth century warming which expresses a more homogenous global fingerprint therefore we stress that presently available paleoclimatic reconstructions are inadequate for making specific inferences at hemispheric scales about mwp warmth relative to the present anthropogenic period and that such comparisons can only still be made at the local regional scale

tree ring derived little ice age temperature trends from the central british columbia coast mountains canada abstract most glaciers in the british columbia coast mountains reached their maximum holocene extent during the little ice age early and late little ice age intervals of expansion and retreat fluctuations describe a mass balance response to changing climates although existing dendroclimatic records provide insights into these climatic fluctuations over the last 400 yr their short durations prohibit evaluation of early little ice age climate variability to extend the duration of these records submerged coarse woody debris salvaged from a high elevation lake was cross dated to living chronologies the resulting chronology provides the opportunity to reconstruct a regional june july air temperature anomaly record extending from ad 1225 to 2010 the reconstruction shows that the intervals ad 1350 1420 1475 1550 1625 1700 and 1830 1940 characterized distinct periods of below average june july temperature followed by periods of above average temperature our reconstruction provides the first annually resolved insights into high elevation climates spanning the little ice age in this region and indicates that little ice age moraine stabilization corresponds to persistent intervals of warmer than average temperatures we conclude that coarse woody debris submerged in high elevation lakes has considerable potential for developing lengthy proxy climate records and we recommend that researchers focus attention on this largely ignored paleoclimatic archive

temperature covariance in tree ring reconstructions and model simulations over the past millennium spatial covariance in the simulated temperature evolution over the past millennium has been reported to exceed that of multiproxy based reconstructions here we use tree ring based temperature reco

quantitative estimates of temperature and precipitation changes over the last millennium from pollen and lake level data at lake joux swiss jura mountains abstract this paper presents quantitative climate estimates for the last millennium using a multi proxy approach with pollen and lake level data from lake joux swiss jura mountains the climate reconstruction based on the modern analogue technique indicates warmer and drier conditions during the medieval warm period mwp mwp was preceded by a short lived cold humid event around ad 1060 and followed by a rapid return around ad 1400 to cooler and wetter conditions which generally characterize the little ice age lia around ad 1450 solar sporer minimum the lia attained a temperature minimum and a summer precipitation maximum the solar maunder minimum around ad 1690 corresponded at joux to rather mild temperatures but maximal annual precipitation these results generally agree with other records from neighbouring alpine regions however there are differences in the timing of the lia temperature minimum depending on the proxy and or the method used for the reconstruction as a working hypothesis the hydrological signal associated with the mwp and lia oscillations at lake joux may have been mainly driven by a shift around ad 1400 from positive to negative nao modes in response to variations in solar irradiance possibly coupled with changes in the atlantic meridional overturning circulation

multispectral analysis of northern hemisphere temperature records over the last five millennia aiming to describe spatio temporal climate variability on decadal to centennial time scales and longer we analyzed a data set of 26 proxy records extending back 1 000 5 000 years all records chosen were calibrated to yield temperatures the seven irregularly sampled series in the data set were interpolated to a regular grid by optimized methods and then two advanced spectral methods namely singular spectrum analysis ssa and the continuous wavelet transform were applied to individual series to separate significant oscillations from the high noise background this univariate analysis identified several common periods across many of the 26 proxy records a millennial trend as well as oscillations of about 100 and 200 years and a broad peak in the 40 70 year band to study common nh oscillations we then applied multichannel ssa temperature variations on time scales longer than 600 years appear in our analysis as a dominant trend component which shows climate features consistent with the medieval warm period and the little ice age statistically significant nh wide peaks appear at 330 250 and 110 years as well as in a broad 50 80 year band strong variability centers in several bands are located around the north atlantic basin and are in phase opposition between greenland and western europe

landslide inventories for climate impacts research in the european alps landslides present a geomorphological hazard in alpine regions threatening life infrastructure and property here we present the development of a new regional landslide inventory ri for the european alps this database provides a substantial temporal and spatial picture of landsliding in the alps with particular focus on the swiss and french alps we use segmented models to evaluate recording bias in the temporal record we use scaling relationships to calculate landslide area based on a given volume for similar types of landslide with the result of this being that 9 5 of the landslides recorded in the ri now have area data recorded these landslide area data are then used to examine the log linear trend which exists between landslide area and frequency in inventories we show that this relationship is present for this historical dataset however none of the individual databases nor a unification of these contain a complete record with the small and larger landslides being recorded more consistently the use of segmented models on the temporal distribution of landslides in the ri shows that the post 1970 portion of the database is more reliable highlighted through an improved power law relationship although the frequency of medium sized landslides is still underestimated we show that creating a unified database ri can increase the reliability of datasets and consistency in recording for the use by researchers for attribution and detection studies

scale dependent reconstruction of the nao index a method is presented to reconstruct decadal variations of the north atlantic oscillation nao the spectral characteristics of the nao on time scales of decades and longer are of particular interest for the understanding of north atlantic ocean atmosphere interactions the reconstruction is based on a transfer model calibration that uses bandpass filtered time series the maximum overlap discrete wavelet transform modwt is applied for decomposing the time series variance into different time scales a total of 43 proxies including greenland ice cores and european tree ring chronologies are selected and regionally grouped providing four independent reconstructions for the period 1700 1978 the mean reconstruction agrees well with two recently published reconstructions during most of the time period however there are considerable differences in the earliest part before 1750 running correlations between the reconstructions indicate that time dependent relations exist among the different nao reconstructions the results suggest that the geographical distribution of proxies strongly affects the reconstruction and could explain some of the apparent discrepancies among the reconstructions recently published in literature in the early eighteenth century external forcing solar volcanic seems to mask the nao signature within the proxies

summer temperatures in the canadian rockies during the last millennium a revised record we present a significant update to a millennial summer temperature reconstruction 1073 1983 that was originally published in 1997 utilising new tree ring data predominantly picea engelmannii the reconstruction is not only better replicated but has been extended 950 1994 and is now more regionally representative calibration and verification statistics were improved with the new model explaining 53 of may august maximum temperature variation compared to the original 39 of april august mean temperatures the maximum latewood density data which are weighted more strongly in the regression model than ringwidth were processed using regional curve standardisation to capture potential centennial to millennial scale variability the reconstruction shows warm intervals comparable to twentieth century values for the first half of the eleventh century the late 1300s and early 1400s the bulk of the record however is below the 1901 1980 normals with prolonged cool periods from 1200 to 1350 and from 1450 to the late 19th century the most extreme cool period is observed to be in the 1690s these reconstructed cool periods compare well with known regional records of glacier advances between 1150 and the 1300s possibly in the early 1500s early 1700s and 1800s evidence is also presented of the influence of solar activity and volcanic events on summer temperature in the canadian rockies over the last 1 000 years although this reconstruction is regional in scope it compares well at multi decadal to centennial scales with northern hemisphere temperature proxies and at millennial scales with reconstructions that were also processed to capture longer timescale variability this coherence suggests that this series is globally important for the assessment of natural temperature variability over the last 1 000 years

a multi proxy analysis of hydroclimate trends in an ombrotrophic bog over the last millennium in the eastern carpathians of romania abstract we describe an ombrotrophic bog profile from tinovul mohos eastern carpathians romania to quantitatively reconstruct the hydroclimate and the palaeoecological evolution over the past 1000 years findings are based on high resolution analyses of testate amoebae plant macrofossils pollen micro and macrocharcoal 13c stable carbon isotopes organic matter content and bulk density supported by ams radiocarbon dating we identify five major hydroclimatic intervals between ad 1050 and 1300 a wet period occurred associated with a time of reduced human population between ad 1300 and 1600 wet conditions continued to prevail but with tendency towards drier mire settings the third period from ad 1600 1680 revealed two abrupt disturbances in the local hydrology strong dry wet shifts the fourth period from ad 1680 1950 showed intermediate moist conditions with an increased humidity after ad 1950 mire conditions became dry and there was an intensification in disturbances activity forest clearance fire and peatland drainage our multi proxy reconstruction represents one of the few studies of the hydroclimate and palaeoecological evolution of the last millennium in the central eastern europe findings show good agreement with other hydroclimate reconstructions from this region but not with records from north western europe more high resolution multi proxy studies are needed to improve our understanding of the feedback mechanisms in peatlands and the factors behind these changes

use of paleo records in determining variability within the volcanism climate system abstract volcanic eruptions that inject large quantities of sulfur rich gases into the stratosphere have the capability of cooling global climate by 0 2 0 3 c for several years after the eruption equatorial eruptions will impact global climate whereas mid latitude eruptions can cool climate in the hemisphere of origin magnitude of cooling varies by latitude and it is possible for warming to occur in certain regions primarily during the winter although instrumental records have been used to quantify the volcanic impact on climate they are limited in their temporal and spatial coverage and the style and magnitude of eruptions occurring over the two centuries of instrumental records is limited a thorough evaluation of the range of variability in the volcanism climate system requires a multidisciplinary approach that includes the analysis of ice core records geological data atmospheric measurements and visual phenomena tree ring records and other proxy data evaluation of these longer time series indicates that multiple volcanic eruptions have the potential to force climate over decadal to multi decadal time frames especially when these eruptions enhance or extend pre existing cool conditions on the other hand a lack of climatically significant eruptions may result in warmer average temperatures over decadal time frames because the volcanic cooling component within the climate system is absent mega eruptions like the toba eruption of 71 000 73 000 yr ago may impact climate on centennial time frames through positive feedback mechanisms evidence exists which indicates that environmental changes associated with rapid climatic fluctuations such as crustal loading unloading with glaciation deglaciation and variability in glacial meltwater loading on ocean basins may cause an increase in volcanic activity

multi proxy reconstructions of northeastern pacific sea surface temperature data from trees and pacific geoduck abstract we demonstrate the potential for developing sea surface temperature sst reconstructions in the northeast pacific from combinations of tree ring and growth increment chronologies of the long lived marine bivalve the pacific geoduck six pacific geoduck chronologies developed from site along the washington british columbia coast are compared and combined with tree ring chronologies from california to alaska all chronologies are annually resolved and strongly relate to local to regional scale sst though differences in the response season as well as the spectral properties of the two proxies are observed both proxy types closely track sst and when used in combination yield a more robust sst reconstruction than tree ring or geoduck chronologies could provide alone in total variance explained in sst is 63 9 at the regional scale and 68 2 at a local scale providing sst estimates for more than 60 years prior to the start of continuous instrumental records in this region this study represents one of the few climate reconstructions where both proxies are annually resolved and is the first to integrate regional networks of geoduck chronologies and tree ring chronologies

an investigation of the common signal in tree ring stable isotope chronologies at temperate sites we observed a strong common high frequency interannual signal for thed 13 c chronologies whereas the low frequency decadal scale signal was more similar among thed 18 o chronologies for both carbon and oxygen isotopes we found significant positive relationships with annual and growing season temperatures and negative relationships with precipitation again of similar magnitude for all species except forfraxinus which contained only minor climatic information averaging of all chronologies resulted in an increase in the climatic signal of the mean chronology the combinedd 18 o record reflected decadal scale temperature variations remarkably well r 0 72 however the relationship between climate and carbon isotopes declined over the last 3 decades of the 20th century probably related to the steep increase in atmospheric co 2 concentrations resulting in strongly divergingd 13 c trends of the different chronologies our study indicates that combining chronologies from different species enhances the potential of isotope studies for extending climate reconstructions into areas of temperate climate

climate signals in tree ring width density and δ13c from larches in eastern siberia russia abstract we present the first and longest 413 years dataset on stable carbon isotope ratios in tree ring cellulose 13c tree ring width trw and maximum latewood density mxd obtained from larch trees growing on permafrost under continental climate in the suntar khayata mountain ridge in eastern siberia russia with this first study we calibrate tree ring parameters against climate quantities and based on these results assess the potential added value of mxd and especially of 13c complementing trw analysis for future climate reconstruction purposes 13c chronologies were corrected for human induced changes in atmospheric co2 since ad 1800 two different approaches were compared i a correction referring merely to the decline in atmospheric 13c 13catm and ii a correction additionally accounting for the increase in atmospheric partial pressure of co2 13c chronologies are characterized by strong signal strength with only 4 trees representing the population signal at the site mean inter series correlation 0 71 and eps 0 90 13c variation shows low similarity to trw and mxd while correlation between trw and mxd is highly significant correlation analysis of tree ring parameters with gridded instrumental data climate research unit cru ts 2 1 over the ad 1929 2000 calibration period demonstrates that trw and mxd react as reported from other sites at cold and humid northern latitudes precipitation plays no significant role but strong dependencies on monthly mean maximum and minimum temperatures particularly of the current summer june to august are found up to r 0 60 p

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

temperature sensitive tien shan tree ring chronologies show multi centennial growth trends two millennia length juniper ring width chronologies processed to preserve multi centennial growth trends are presented for the alai range of the western tien shan in kirghizia the chronologies average the information from seven near timberline sampling sites and likely reflect summer temperature variation for comparison chronologies are also built using standard dendrochronological techniques we briefly discuss some qualities of these inter decadal records and show the low frequency components removed by the standardization process include a long term negative trend in the first half of the last millennium and a long term positive trend since about ad 1800 the multi centennial scale alai range chronologies where these trends are retained are both systematically biased but in an opposite sense in their low frequency domains nevertheless they represent the best constraints and estimates of long term summer temperature variation and reflect the medieval warm period the little ice age and a period of warming since about the middle of the nineteenth century

a 500 year record of summer near ground solar radiation from tree ring stable carbon isotopes tree ring stable carbon isotope ratios d13c in environments of low moisture stress are likely to be controlled primarily by photosynthetic rate therefore sunshine rather than temperature represents the more direct controlling factor temperature reconstructions based on tree ring d13c results thus rest on the assumption that temperature and sunshine are strongly coupled this assumption is tested using a d13c series from pine trees in nw norway where there are long 100 yr records of both summer temperature and cloud cover it is demonstrated that when summer temperature and d13c diverge summer temperature and cloud cover also diverge and that cloud cover sunshine may provide a stronger and more consistent parameter with which to calibrate tree ring d13c series in this area when a 500 year reconstruction of summer cloudiness is compared with a published reconstruction of summer temperatures in northern sweden based on tree ring maximum densities the two time series are largely parallel with

the little ice age signature in a 700 year high resolution chironomid record of summer temperatures in the central eastern alps despite the fact that the little ice age lia is well documented for the european alps substantial uncertainties concerning the regional spatio temporal patterns of temperature changes associated with the lia still exist especially for their eastern sector here we present a high resolution 4 10 years 700 year long mean july air temperature reconstruction based on subfossil chironomid assemblages from a remote lake in the austrian eastern alps to gain further insights into the lia climatic deterioration in the region the record provides evidence for a prolonged period of predominantly cooler conditions during ad 1530 1920 broadly equivalent to the climatically defined lia in europe the main lia phase appears to have consisted of two cold time intervals divided by slightly warmer episodes in the second half of the 1600s the most severe cooling occurred during the eighteenth century the lia temperature minimum about 1 5 c below the long term mean recorded in the mid 1780 s coincides with the strongest volcanic signal found in the greenland ice cores over the past 700 years and may be at least in part a manifestation of cooling that followed the long lasting ad 1783 1784 laki eruption a continuous warming trend is evident since ca ad 1890 1 1 c in 120 years the chironomid inferred temperatures show a clear correlation with the instrumental data and reveal a close agreement with paleotemperature evidence from regional high elevation tree ring chronologies a considerable amount of the variability in the temperature record may be linked to changes in the north atlantic oscillation

late holocene nao and oceanic forcing on high altitude proglacial sedimentation lake bramant western french alps comparison of glacially derived clastic inputs in high altitude proglacial lake bramant western french alps with measured north atlantic oscillation winter naow index reveals an inverse correlation between ad 1884 and 1968 at the pluridecadal timescale 20 25 years this reflects periodical variations in snow accumulation over lake bramant catchment area partly influencing the glacier mass balance in the watershed further comparisons with reconstructed naow index since ad 1500 highlight spatial and temporal variations of the pluridecadal naow influence on this alpine climate especially at the end of the little ice age in addition wavelet analysis of continuous proxies of clastic sedimentation over the last 4150 years indicates significant pluridecadal variability at frequencies compatible with the nao 30 years while periods centered at 60 70 years could also be linked to the north atlantic ocean atmosphere internal variability atlantic multidecadal oscillation amo the influence of the n

thousand years of climate change reconstructed from chironomid subfossils preserved in varved lake silvaplana engadine switzerland abstract fossil chironomids non biting midges from varved lake silvaplana switzerland were used to reconstruct climate mean july air temperatures during the last millennium at the beginning of the record corresponding to the last part of the medieval climate anomaly mca here the period between ca 1032 and 1262 ad the chironomid inferred mean july air temperatures were 1 c warmer p

volcanic cooling signal in tree ring temperature records for the past millennium the authors acknowledge the national science foundation for funding much of the research presented herein rw s scottish work is currently funded through the uk leverhulme trust and natural environment research council nerc projects relic reconstructing 8000 years of environmental and landscape change in the cairngorms f 00 268 bg and scot2k reconstructing 2000 years of scottish climate from tree rings ne k003097 1

reconstruction of the extratropical nh mean temperature over the last millennium with a method that preserves low frequency variability abstracta new multiproxy reconstruction of the northern hemisphere extratropical mean temperature over the last millennium is presented the reconstruction is performed with a novel method designed to avoid the underestimation of low frequency variability that has been a general problem for regression based reconstruction methods the disadvantage of this method is an exaggerated high frequency variability the reconstruction is based on a set of 40 proxies of annual to decadal resolution that have been shown to relate to the local temperature the new reconstruction shows a very cold little ice age centered around the 17th century with a cold extremum for 50 yr smoothing of about 1 1 k below the temperature of the calibration period ad 1880 1960 this cooling is about twice as large as corresponding numbers reported by most other reconstructions in the beginning of the millennium the new reconstruction shows small anomalies in agreement with previous studies however the new temperature reconstructi

effect of scaling and regression on reconstructed temperature amplitude for the past millennium 1 examination of large scale millennial long temperature reconstructions reveals a wide range of datasets and methods used for calibration proxy time series are commonly calibrated against overlapping instrumental records representing different seasons northern hemisphere latitudinal bands and including or excluding sea surface temperature data methodological differences include using scaling or regression the calibration time period and smoothing data before calibration we find that these various approaches alone can result in differences in the reconstructed temperature amplitude of about 0 5 c this magnitude is equivalent to the mean annual temperature change for the northern hemisphere reported in the last ipcc report for the 1000 1998 period a more precise assessment of absolute reconstructed temperature amplitudes is necessary to help quantify the relative influences of forcing mechanisms in climate models

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

summer temperature variations in the european alps a d 755 2004 abstract annually resolved summer temperatures for the european alps are described the reconstruction covers the a d 755 2004 period and is based on 180 recent and historic larch larix decidua mill density series the regional curve standardization method was applied to preserve interannual to multicentennial variations in this high elevation proxy dataset instrumental measurements from high low elevation grid boxes back to 1818 1760 reveal strongest growth response to current year june september mean temperatures the reconstruction correlates at 0 7 with high elevation temperatures back to 1818 with a greater signal in the higher frequency domain r 0 8 low elevation instrumental data back to 1760 agree with the reconstruction s interannual variation although a decoupling between warmer instrumental and cooler proxy data before 1840 is noted this offset is larger than during any period of overlap with more recent high elevation instrumental data even though the proxy time series

a matter of divergence tracking recent warming at hemispheric scales using tree ring data 1 no current tree ring tr based reconstruction of extratropical northern hemisphere enh temperatures that extends into the 1990s captures the full range of late 20th century warming observed in the instrumental record over recent decades a divergence between cooler reconstructed and warmer instrumental large scale temperatures is observed we hypothesize that this problem is partly related to the fact that some of the constituent chronologies used for previous reconstructions show divergence against local temperatures in the recent period in this study we compiled tr data and published local regional reconstructions that show no divergence against local temperatures these data have not been included in other large scale temperature reconstructions utilizing this data set we developed a new completely independent reconstruction of enh annual temperatures 1750 2000 this record is not meant to replace existing reconstructions but allows some degree of independent validation of these earlier studies as well as demonstrating that tr data can better model recent warming at large scales when careful selection of constituent chronologies is made at the local scale although the new series tracks the increase in enh annual temperatures over the last few decades better than any existing reconstruction it still slightly under predicts values in the post 1988 period we finally discuss possible reasons why it is so difficult to model post mid 1980s warming provide some possible alternative approaches with regards to the instrumental target and detail several recommendations that should be followed in future large scale reconstruction attempts that may result in more robust temperature estimates

stable isotope coherence in the earlywood and latewood of tree line conifers abstract 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

orbital ice sheet and possible solar forcing of holocene lake level fluctuations in west central europe a comment on bleicher bleicher 2013 discussed interpretations proposed by magny 2004 that holocene lake level fluctuations in west central europe suggest possible solar forcing of climate he pointed out that the me