short term climate variability during roman classical period in the eastern mediterranean abstract to obtain insight into character and potential forcing of short term climatic and oceanographic variability in the southern italian region during the roman classical period 60 bc ad 200 climatic and environmental reconstructions based on a dinoflagelate cyst record from a well dated site in the gulf of taranto located at the distal end of the po river discharge plume have been established with high temporal resolution short term fluctuations in accumulation rates of the adriatic surface water species lingulodinium machaerophorum the freshwater algae concentricystes and species resistant to aerobic degradation indicate that fluctuations in the trophic state of the upper waters are related to river discharge of northern and eastern italian rivers which in turn are strongly related to precipitation in italy the dinoflagellate cyst association indicates that local sea surface temperatures which in this region are strongly linked to local air temperatures were slightly higher than today we reconstruct that sea surface temperatures have been relatively high and stable between 60 bc ad 90 and show a decreasing trend after ad 90 fluctuations in temperature and river discharge rates have a strong cyclic character with main cyclicities of 7 8 and 11 years we argue that these cycles are related to variations of the north atlantic oscillation climate mode a strong correlation is observed with global variation in 14c anomalies suggesting that solar variability might be one of the major forcings of the regional climate apart from cyclic climate variability we observed a good correlation between non cyclic temperature drops and global volcanic activity indicating that the latter forms an additional major forcing factor of the southern italian climate during the roman classical period

a robust equatorial pacific westerly response to tropical volcanism in multiple models after each of the 1963 agung 1982 el chichon and 1991 pinatubo eruptions an el nino was observed the increased likelihood of an el nino after a tropical eruption has also been found in long term reconstructed proxy data through examining simulations over the last millennium by 11 different models we show that a tropical volcano eruption can robustly excite a western to central equatorial pacific wcep westerly anomaly at 850 hpa in eight out of the 11 models such a westerly anomaly is favorable for el nino development under the volcanic forcing there are significant extratropical continent surface cooling and tropical drying with negative precipitation anomalies over the south south east asia ssea west african monsoon and intertropical convergence zone itcz regions this common precipitation suppression response occurs in most of the models sensitivity experiments show that a wcep westerly anomaly can be excited by the tropical land cooling especially the ssea cooling induced precipitation suppression rather than by the extratropical land surface cooling theoretical results show that a wcep westerly anomaly is excited due to a gill response to reduced precipitation over the ssea and west african monsoon regions and the ssea contributes more than the west african monsoon does the itcz weakening however excites an easterly wind anomaly the models with more sensitive convective feedback tend to simulate an el nino more easily while a failed simulation of an el nino after a robust westerly anomaly in some models calls for further studies on these models delayed responses to radiative forcing induced by volcano eruptions

simulated global mean sea level changes over the last half millennium simulations of the last 500 yr carried out using the third hadley centre coupled ocean atmosphere gcm hadcm3 with anthropogenic and natural solar and volcanic forcings have been analyzed globalmean surface temperature change during the twentieth century is well reproduced simulated contributions to global mean sea level rise during recent decades due to thermal expansion the largest term and to mass loss from glaciers and ice caps agree within uncertainties with observational estimates of these terms but their sum falls short of the observed rate of sea level rise this discrepancy has been discussed by previous authors a completely satisfactory explanation of twentieth century sea level rise is lacking the model suggests that the apparent onset of sea level rise and glacier retreat during the first part of the nineteenth century was due to natural forcing the rate of sea level rise was larger during the twentieth century than during the previous centuries because of anthropogenic forcing but decreasing natural forcing during the second half of the twentieth century tended to offset the anthropogenic acceleration in the rate volcanic eruptions cause rapid falls in sea level followed by recovery over several decades the model shows substantially less decadal variability in sea level and its thermal expansion component than twentiethcentury observations indicate either because it does not generate sufficient ocean internal variability or because the observational analyses overestimate the variability

paleoclimate changes of the last 1000 yr on the eastern qinghai tibetan plateau recorded by elemental isotopic and molecular organic matter proxies in sediment from glacial lake ximencuo abstract total organic carbon corg and nitrogen ntot concentrations and isotope compositions and n alkane and n alkan ol molecular biomarker compositions were measured in two parallel sediment cores from lake ximencuo a typical glacial lake on the eastern qinghai tibetan plateau qtp to reconstruct local climatic variations during the past 1000 yr concentrations of corg and ntot vary similarly with changes in precipitation recorded by tree rings in dulan northeastern qtp indicating their close relation to precipitation carbon preference index cpi values of c22 c33 n alkanes and c22 c28 n alkan 1 ols and average chain length acl values of c27 c33 n alkanes generally negatively correlate with 13corg and 15ntot and also vary comparably with the oxygen isotope temperature record from the dunde ice core northeastern qtp these patterns indicate that high cpi values and negative shifts of the 13corg and 15ntot correspond to warmer conditions that favor the growth of vascular land plants and that lower values and positive shifts correspond to cooler conditions in the lake ximencuo locality this observation contradicts previous interpretations from peat and modern soil studies that conclude that the cpi indices were controlled by microbial degradation under different climate conditions here we propose that the changes of organic matter sources under different climate regimes combined with physiological adjustments of vascular plants to different air temperatures might yield different cpi responses to climate changes in glacial plateau lakes air temperature and precipitation increases and decreases reconstructed in this 1000 yr study were generally independent of each other but they both occurred at centennial or multi centennial scales the interaction between subtropical asian monsoon and mid latitude westerly atmospheric circulation systems probably dominated the local precipitation variations in the lake ximencuo catchment whereas solar insolation volcanism and greenhouse gas variations were likely responsible for the air temperature changes that are recorded in the lake sediments and that are consistent with regional temperature variations in the eastern qtp

late quaternary erosion events in lowland and mid altitude tasmania in relation to climate change and first human arrival abstract the establishment of a chronology of landscape forming events in lowland and mid altitude tasmania essential for assessing the relative importance of climatic and human influences on erosion and for assessing present erosion risk has been limited by the small number of ages obtained and limitations of dating methods in this paper we critically assess previous tasmanian studies list published radiocarbon ages considered to be dependable present new radiocarbon and thermoluminescence tl ages for 25 sites around tasmania and consider the evidence for the hypotheses that erosion processes at low and mid altitudes have been 1 purely climatically controlled and 2 influenced both by climatic and anthropogenic increased fire frequency effects a total of 94 dependable finite ages calibrated for radiocarbon and as measured for tl and optically stimulated luminescence osl determinations are listed for deposits comprising dunes colluvium alluvium and loess like aeolian deposits two fall in the 100 ka period 15 fall in the period 65 35 ka and 77 fall in the period 35 0 3 ka there was a sustained increase in erosion recorded in the period 35 15 ka as reflected by a greater number of dated aeolian deposits during this period we considered three possible biases that may have affected the age distribution obtained the limitations of radiocarbon dating sampling bias and preservation bias sampling bias may have favoured more recent dune strata but radiocarbon dating and preservation biases are unlikely to have significantly distorted the age distribution obtained long but intermittent aeolian deposition is recorded at two sites southwood b c 59 28 ka and dunlin dune c 29 14 ka but there is no evidence of regional loess deposits such as found in new zealand the timing of increased erosion in tasmania between 35 and 30 ka approximately coincides with the intermittent ten fold increase of dust accumulation between 33 and 30 ka in the antarctic dome c ice core the absence of widespread erosion before 35 ka the abrupt increase of erosion around this time the frequent association of erosion products with charcoal the arrival of people in tasmania at c 40 cal ka and the known use of fires by aborigines to maintain areas of non climax vegetation suggest that ecosystem disturbance by anthropogenic fires in a drier climate than that presently prevailing may have contributed to erosion in lowland and mid altitude tasmania after 35 ka thus the tasmanian erosion record provides circumstantial support for the proposition that human dispersal in southeast australia was accompanied by significant ecological change

climatic evolution in the australian region over the last 94 ka spanning human occupancy and unveiling the last glacial maximum abstract the quaternary is well known for being a period of the geological record that saw significant and alternating climatic fluctuations here we concentrate on the last 94 millennia that saw australia and its surrounding seas undergo significant environmental changes importantly also it is during that this period of time includes the arrival and settlement of humans in australia following on from marine isotopic stage 4 mis4 that saw over the period of 71 59 ka bp a significant eustatic sea level drop 100 m low sea surface temperatures as well as glacial conditions on land australia experienced wet conditions again but eventually progressively entered into a glacial phase by then humans had arrived on this large continent and later the megafauna progressively became extinct this paper describes in detail the climate over this period based principally on the high resolution record of two marine sediment cores located offshore of the southern australian margin and that are then compared with known events on land as well as other deep sea cores particular emphasis is placed on the period that spans the last glacial maximum lgm the extent of which thus far had been poorly defined in the australian region emphasis is placed on the period from 34 to 14 ka to demonstrate that 1 the lgm defined here as the period 24 to 18 ka was not always extremely dry and cold and 2 that people were able to live in inland australia as water existed in places despite generally cold conditions we also show using a series of ten maps at 2 ka intervals over the 34 14 ka period the waxing and waning of oceanic fronts such as the subtropical and subantarctic fronts link sea surface temperatures sst with periods of glacial expansion in the australian alps and tasmania as well as the south island of new zealand and the extent of the leeuwin current down to south of australia aeolian dust was transported at sea over the main core site from 26 to 18 ka period pointing to arid conditions in australia but this period was punctuated by two significant reductions in dust transport to both core sites coinciding with a retreat of the subantarctic front away from the australian southern coastline and slight sst shifts for a few centuries at 24 and 22 21 ka bp at the peak of the cold phase from 23 to 18 4 ka summer sst were of the order of 9 c below that experienced during the middle of the holocene at about 6 ka bp a similar temperature drop was also experienced offshore the northwestern corner of western australia periglacial activity dates for the australian mainland and tasmania pool around 22 ka on either side of the 24 ka event the chain of lakes in the willandra lakes retained water and human activity was registered in the area elsewhere in australia water was present to sustain human populations during the cold and dry times it is postulated here that northern australia was at times quite wet especially during mis4 the cessation of the lgm is set on 18 4 ka from offshore southern australia as confirmed for the deep sea cores by several proxies and more likely at 18 ka inland finally we document that it took two millennia for glacial conditions to end in the australian region as registered in our deep sea core records well after the lowest global sea level 20 6 and 20 ka respectively started to rise there is also evidence of another very cold period determined on the australian mainland tasmania and the south island of new zealand centred around 27 ka after which time warmer conditions occurred before the start of the lgm this is matched with our deep sea records with very cold conditions and changes in oceanographic conditions

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

organic geochemical records of environmental variability in lake malawi during the last 700 years part i the tex86 temperature record abstract we have applied the tex86 paleothermometer to produce a surface water temperature record for lake malawi spanning the past 700 years over much of the record temperature fluctuates from 24 27 c with a mean of 25 c however there has been a substantial increase in temperature of 2 0 c during the past 100 years the tex86 temperature record reveals a strong similarity to the instrumental record both records demonstrate warming 0 7 1 4 c over the past 50 years as well as a cooling anomaly around 1959 comparison of the tex86 temperature record with the proxy records of primary productivity suggests that wind induced upwelling and or precipitation have a strong influence on the surface temperature of lake malawi

climate model comparison of gondwanan and laurentide glaciations geologic studies indicate that the carboniferous glaciation on gondwanaland was approximately as extensive as the ice sheets during the pleistocene however there is one major difference between the climate boundary conditions for the two ice sheets the gondwanan ice sheet was located on a supercontinent three different levels of sensitivity experiments were conducted to examine the effect of the large landmass on the magnitude of summer warming over the ice sheets 1 simulations with present solar luminosity and present orbital forcing resulted in summer temperatures over the gondwanan ice sheet 12 17 c greater than over the pleistocene laurentide ice sheet 2 lowering the solar constant 3 or modifying the seasonal insolation cycle to a cold summer orbit reduced the warming but still led to significant differences between gondwanan and pleistocene simulations and 3 the combined effect of lowering the solar constant and modifying the seasonal insolation cycle to a cold summer orbit resulted in temperature patterns over the gondwanan ice sheet similar to the pleistocene model simulations also predict tropical sea surface temperatures about 4 c less than at present as a result of reduced solar luminosity these results suggest that conditions necessary to explain gondwanan ice sheet stability may be known but required boundary conditions would be more extreme than in the pleistocene although a number of uncertainties remain in these calculations they help to better define critical conditions for glaciation for one of the most prolonged periods of continuous glaciation in earth history

skillful prediction of multidecadal variations in volcanic forcing stratospheric sulfate injections from explosive volcanic eruptions are a primary natural climate forcing improved statistical models can now capture and simulate dynamical relationships in temporal variations of binary data leveraging these new techniques the presented analysis clearly indicates that the number of large eruptions in the most recent records of explosive volcanism cannot be considered to be fully random including dynamical dependence in our models improves their ability to reproduce the historical record and thus forms a strong basis for skill in statistical prediction possible geophysical mechanisms behind the identified multi decadal variations are discussed including variations in the observed length of day

late pleistocene vegetation and climate history of lake selina western tasmania analysis of pollen nrm intensity of sediments and dating of a 397 cm core from lake selina in western tasmania provides a detailed record of vegetation and climate changes for the last interglacial last glacial cycle the vegetation record shows that cool temperate rainforest was present during isotope substage 5e and during the holocene wet montane forest and subalpine shrublands dominated the early last glacial interstades subalpine alpine heathlands and herbfield the stadials stages 4 2 mainly had grassland herbland and heath vegetation there is close correlation between phases of maximum magnetic intensity in the sediments with pollen zones indicating presence of herbaceous vegetation this suggests erosion of the catchment was greater in the absence of forest or woodland climate may have been slightly cooler than present during substage 5e but the evidence is not definitive climate was colder at all times during the last glacial stage until after ca 14 kyr bp maximum temperature depression from present during stage 2 was 3 5 c at lake selina but probably as much as 6 5 c in the west coast range holocene climate was cool and wet comparison of the lake selina record with others in western tasmania and victoria indicate that variations in vegetation during the last interglacial last glacial cycle were primarily responses to temperature changes in western tasmania and to precipitation changes particularly summer drought in western victoria

effects of syn pandemic fire reduction and reforestation in the tropical americas on atmospheric co2 during european conquest abstract a new reconstruction of late holocene biomass burning in the tropical americas is consistent with the expansion of fire use by mesoamerican and amazonian agriculturalists and a subsequent period of fire reduction beginning 500 years bp the marked reduction of biomass burning after 500 years bp a unique feature of the fire history of the tropical americas relative to other regions of the globe is synchronous with the collapse of the american indigenous population during pandemics accompanying european conquest we predict that fire reduction contemporaneous with pandemics in the tropical americas was associated with massive forest regeneration on 5 105 km2 of land and sequestration of 5 10 gt c into the terrestrial biosphere which contributed to the 2 global reduction in atmospheric co2 levels and the 0 1 increase in 13c of atmospheric co2 from 1500 to 1750 a d this study 1 builds upon prior fire history reconstructions by synthesizing a substantially greater number of stratigraphic charcoal accumulation records and soil charcoal 14c dates to resolve features of the late holocene biomass burning record in the tropical americas and 2 corroborates the hypothesis advanced by ruddiman ruddiman w f 2003 the anthropogenic era began thousands of years ago climatic change 61 261 293 ruddiman w f 2005 plows plagues and petroleum princeton university press princeton new jersey that biospheric carbon sequestration via reforestation of cropland abandoned during pandemics contributed to changes in atmospheric co2 concentration during the past millennium

the rotating hydraulics of the open channel flow between two basins the theory of rotating open channel flow between two basins is presented and experimentally verified for three cases the first case considered is the submerged weir flow i e the height of the channel floor is below the free surface height of the fluid in the lower basin flow for this case is found to depend on the fluid level in the downstream basin when the fluid level there is high and is independent of the fluid level downstream as soon as the level falls below a critical height at that point the flow in the channel becomes critical controlled the dependence of the flow on upstream potential vorticity and on rotation rate is also examined it is shown that transport of the flow decreases whenever rotation rate or upstream potential vorticity is increased the second case studied is controlled flow through a channel of irregular cross section the truncated channel transport of this flow is shown to increase at some moderate rotations if the channel floor has a cross channel slope similar to that of the surface of the current otherwise the transport always decreases with rotation rate the final case is concerned with supercritical separation of the current downstream of the control section i e the current separates from the left wall of the channel looking downstream visual evidence and measurements of formation of such a boundary current are obtained comparisons between the theory and the experiment for the three cases are generally reasonable except when flow separates in the control section the theory is found inapplicable to such separation

low frequency temperature variations from a northern tree ring density network we describe new reconstructions of northern extratropical summer temperatures for nine subcontinental scale regions and a composite series representing quasi northern hemisphere temperature change over the last 600 years these series are based on tree ring density data that have been processed using a novel statistical technique age band decomposition designed to preserve greater long timescale variability than in previous analyses we provide time dependent and timescale dependent uncertainty estimates for all of the reconstructions the new regional estimates are generally cooler in almost all precalibration periods compared to estimates obtained using earlier processing methods particularly during the 17th century one exception is the reconstruction for northern siberia where 15th century summers are now estimated to be warmer than those observed in the 20th century in producing a new northern hemisphere series we demonstrate the sensitivity of the results to the methodology used once the number of regions with data and the reliability of each regional series begins to decrease we compare our new hemisphere series to other published large regional temperature histories most of which lie within the 1 confidence band of our estimates over most of the last 600 years the 20th century is clearly shown by all of the palaeoseries composites to be the warmest during this period

simple energy balance model resolving the seasons and the continents application to the astronomical theory of the ice ages a one level seasonal energy balance climate model which has explicit two dimensional land sea geography is introduced and its properties analyzed the model distinguishes land from sea surface strictly by the local thermal inertia employed the transport is governed by a smooth latitude dependent diffusion mechanism the model s seasonal cycle is solved for with and without ice feedback in each case good agreement with real data is accomplished with minimal tuning of the adjustable parameters the model sensitivity for small solar constant changes is in agreement with that of other accepted models however when the solar constant is lower a few percent the ice cap grows discontinuously from covering greenland and vicinity to a size three times larger and mostly into northern canada a similar discontinuous growth occurs when the orbital elements are changed to favor cool summers in the northern hemisphere this discontinuous sensitivity is discussed in the context of the milankovitch theory of the ice ages and the associated branch structure is shown to be analogous to the so called small ice cap instability known from simpler models although the discontinuity in sensitivity is somewhat conjectural both linear and nonlinear models have their largest sensitivity to orbital parameter changes in the northern portions of the large continents in the western hemisphere this also corresponds to the ice sheet boundary suggesting that the land sea configuration is crucial to large glacier growth irrespective of moisture budgets other experiments and implications are also discussed the remarkable paper by hays et al 1976 hereafter his presented compelling empirical evidence that continental ice sheet volume changes and sea surface temperature variations in the last 700 000 years are correlated with the changes in the earth s orbital elements theoretical arguments for such a connection date back to the last century but the most detailed and convincing arguments are due to milankovitch 1941 and the theory usually is associated with his name if the hypothesis is correct the theory and observations provide the cleanest experiment to determine the sensitivity of the earth s climate to truly external influences such a measure of climate sensitivity is of obvious importance considering the recent interest in estimating the change in climate due to other forcings such as the enhanced greenhouse effect due to increased levels of co2 in the atmosphere e g ramanathan 1981 hansen et al 1981 manabe and stouffer 1980 in effect climate models might be tested or calibrated by this natural experiment climate modeling has progressed dramatically in the last decade with the construction and testing of several general circulation models gcm s although some interesting ice age experiments have been done with these models gates 1976 manabe and hahn 1977 they still include only crude parameterizations of the slower components such as the oceans these numerical models are the ultimate tool that can be brought to bear upon the climate problem however they are almost as complicated as the climate itself hence experiments must be carefully designed and the interpretation is often difficult due to the expense of obtaining definitively long runs in parallel with gcm construction has been the development of x permanently at applied research corporation landover maryland 20785

comments on testing the fidelity of methods used in proxy based reconstructions of past climate abstract mann et el found that a version of the regularized expectation maximization regem method to reconstruct the temperatures of the last millennium showed similar results to previous reconstructions in one of their earlier papers they also tested the regem method in the surrogate climate of a simulation with the climate system model csm and found no attenuation of the pseudoreconstructed centennial variability of the northern hemisphere mean temperature compared to the one simulated by the model this is in contrast with the results by von storch et al who found in a simulation with echo g model that the earlier mann et al method underestimates the centennial temperature variability of the northern hemisphere temperature the newer paper by mann et al explains that this difference is in part due to the unrealistic character of the echo g simulation however it is shown here that similar results to those of von storch et al are also found in an echo g simulation that closely resembles th

glaciochemical evidence in an east antarctica ice core of a recent ad 1450 1850 neoglacial episode 1 chemical analysis of a shallow 82 5 m ice core from a location dt263 in the essentially unexplored area of princess elizabeth land east antarctica has been used to construct a continuous high resolution 780 year ad 1207 1996 glaciochemical record during the twentieth century snow accumulation rates and concentrations of chemical species in snow appear to be stable with short term variations indicating relatively stable and warm climatic conditions the period of ad 1450 1850 in this record is characterized by sharply reduced snow accumulation rates and decreased concentrations of several chemical species that suffer postdepositional losses linked to very low accumulation rates these characteristics are consistent with colder climatic conditions and suggest that this is likely a neoglacial episode the timing of this episode coincides with the little ice age lia a relatively cold period in the northern hemisphere between the beginning of the fifteenth century and the end of the nineteenth century evidence in ice core and sedimentary records also indicates neoglacial conditions in some southern hemisphere locations during the general time frame of lia the dt263 record along with a few published ice core records points to the existence of an lia type climatic episode in antarctica between the fifteenth century and the twentieth century however other antarctic ice core records show no such evidence together these records highlight the regional differences in holocene climate variations in antarctica the dt263 record suggests that colder and drier conditions prevailed during the lia time period at the eastern indian ocean sector of east antarctica

detection of volcanic solar and greenhouse gas signals in paleo reconstructions of northern hemispheric temperature 1 we apply a multiple regression method to estimate the response to anthropogenic and natural climate forcings simultaneously from a number of paleo reconstructions of northern hemispheric average temperature these long records 600 to 1000 years provide a unique opportunity to distinguish between different external influences on climate the response to volcanic forcing is reliably detected in all reconstructions and the simulated temperature response to volcanic eruptions compares favorably with observations the response to solar forcing is detected in hemispheric mean data only over some periods in some records and appears weak although most records can be used only to the middle of the 20th century the temperature response to co2 can be detected by this time in most records

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

paleoclimate of the southern adriatic sea region during the medieval climate anomaly reflected by organic walled dinoflagellate cysts to obtain insight into the character and forcing of southern italian climate change during the medieval climate anomaly c ad 900 1200 marine sediments deposited between ad 990 and 1200 from t

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

exceptional ocean surface conditions on the se greenland shelf during the medieval climate anomaly diatom inferred 2900 year long records of august sea surface temperature asst and april sea ice concentration asic are generated from a marine sediment core from the se greenland shelf with a special focus on the interval ca 870 1910 common era c e reconstructed in subdecadal temporal resolution the medieval climate anomaly mca between 1000 and 1200 c e represents the warmest ocean surface conditions of the se greenland shelf over the late holocene 880 b c e before the common era to 1910 c e it was characterized by abrupt decadal to multidecadal changes such as an abrupt warming of 2 4 c in 55 years around 1000 c e temperature changes of these magnitudes are rare on the north atlantic proxy data compared to regional air temperature reconstructions our results indicate a lag of about 50 years in ocean surface warming either due to increased freshwater discharge from the greenland ice sheet or intensified sea ice export from the arctic as a response to atmospheric warming at the beginning of the mca a cool phase from 1200 1890 c e associated with the little ice age ends with the rapid warming of asst and diminished asic in the early twentieth century the results show that the periods of warm asst and asic minima are coupled with solar minima suggesting that solar forcing possibly amplified by atmospheric forcing have been behind the variability of surface conditions on the se greenland over the last millennium the results indicate that the se greenland shelf is a climatologically sensitive area where extremely rapid changes are possible and highlights the importance of the area under the present warming conditions

a chronology for the long pollen record from lake wangoom western victoria australia as derived from uranium thorium disequilibrium dating the chronology of a long pollen record from lake wangoom one of the few long palaeoenvironmental records from southeastern australia is discussed in light of the acquisition of new uranium thorium disequilibrium utd dates of crucial importance has been the estimation of ages for two major pre holocene phases of forest expansion recorded in the sequence with implications for the timing of periods of high effective precipitation in the region the new utd ages indicate that the oldest forest phase falls within the penultimate interglacial whereas the later phase corresponds with the last interglacial this is older than indicated by previously reported utd and radiocarbon dates but confirms a chronology based on direct correlation with the pollen record from marine core e55 6 the new chronology of the lake wangoom sequence provides evidence that phases of sustained forest development in southeast australia relate to interglacial periods in comparison interstadial periods appear to be characterised by only minor arboreal development marked differences in the pattern of vegetation development evident in each of the interglacials are thought to reflect varying climatic and anthropogenic influences copyright 2002 john wiley sons ltd

oxygen isotope evidence of little ice age aridity on the caribbean slope of the cordillera central dominican republic climate change during the so called little ice age lia of the 15th to 19th centuries was once thought to be limited to the high northern latitudes but increasing evidence reflects significant climate change in the tropics one of the hypothesized features of lia climate in the low latitudes is a more southerly mean annual position of the intertropical convergence zone itcz which produced more arid conditions through much of the northern tropics high resolution stable oxygen isotope data and other sedimentary evidence from laguna de felipe located on the caribbean slope of the cordillera central of the dominican republic support the hypothesis that the mean annual position of the itcz was displaced significantly southward during much of the lia placed within the context of regional paleoclimate and paleoceanographic records and reconstructions of global lia climate this shift in mean annual itcz position appears to have been induced by lower solar insolation and internal dynamical responses of the global climate system our results from hispaniola further emphasize the global nature of lia climate change and the sensitivity of circum caribbean climate conditions to what are hypothesized to be relatively small variations in global energy budgets

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

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

holocene hydrologic variation at lake titicaca bolivia peru and its relationship to north atlantic climate variation a growing number of sites in the northern hemisphere show centennial to millennial scale climate variation that has been correlated with change in solar variability or with change in north atlantic circulation however it is unclear how or whether these oscillations in the climate system are manifest in the southern hemisphere because of a lack of sites with suitably high sampling resolution in this paper we reconstruct the lake level history of lake titicaca using the carbon isotopic content of sedimentary organic matter to evaluate centennial to millennial scale precipitation variation and its phasing relative to sites in the northern hemisphere the pattern and timing of lake level change in lake titicaca is similar to the ice rafted debris record of holocene bond events demonstrating a possible coupling between precipitation variation on the altiplano and north atlantic sea surface temperatures ssts the cold periods of the holocene bond events correspond with periods of increased precipitation on the altiplano holocene precipitation variability on the altiplano is anti phased with respect to precipitation in the northern hemisphere monsoon region more generally the tropical andes underwent large changes in precipitation on centennial to millennial timescales during the holocene copyright 2005 john wiley sons ltd

modeling ocean heat content changes during the last millennium 1 observational studies show a significant increase in ocean heat content over the last half century herein we estimate heat content changes during the last millennium with a climate model whose forcing terms have been best fit to surface proxy data the model simulates the observed late 20th century ocean heat content increase and a comparable little ice age minimum when glacial advances are factored in these results imply a sea level fall after the middle ages that is consistent with some geologic data the present ocean heat content increase can be traced back to the mid 19th century with a near linear rate of change during the 20th century

are reconstructed pre instrumental hemispheric temperatures consistent with instrumental hemispheric temperatures 1 reconstructions of northern hemisphere near surface temperatures from climate proxy data such as tree rings ice cores and corals suggest that late 20th century northern hemisphere mean warmth is anomalous in the context of the past several centuries and likely at least the past two millennia though substantial uncertainties in the paleoclimate reconstructions exist these findings add to the evidence for a discernible human influence on climate here we use our simple climate model with six radiative forcing reconstructions and climate sensitivity determined from instrumental temperatures over 1861 to 1997 to simulate the forced pre instrumental hemispheric average temperatures from 1500 to 1895 the model simulated pre instrumental temperatures indicate that the proxy temperature reconstructions are consistent with the instrumental temperatures in the northern hemisphere but are too warm in the southern hemisphere

solar and volcanic fingerprints in tree ring chronologies over the past 2000 years abstract the sun is the main driver of earth s climate yet the sun s role in forcing decadal to centennial climate variations has remained controversial especially in the context of understanding contributions of natural climate forcings to continuing global warming to properly address long term fingerprints of solar forcing on climate long term very high resolution globally distributed climate proxy records are necessary in this study we compile and evaluate a near global collection of annually resolved tree ring based climate proxies spanning the past two millennia we statistically assess these records in both the time and frequency domains for solar forcing i e total solar irradiance tsi and climate variability with emphasis on centennial time scales analyses in the frequency domain indicate significant periodicities in the 208 year frequency band corresponding to the devries cycle of solar activity additionally results from superposed epoch analysis sea point toward a possible solar contribution in the temperature and precipitation series however solar climate associations remain weak with for example no clear linkage distinguishable in the southwestern united states drought records at centennial time scales other forcing factors namely volcanic activity appear to mask the solar signal in space and time to investigate this hypothesis we attempted to extract volcanic signals from the temperature proxies using a statistical modelling approach wavelet analysis of the volcanic contribution reveals significant periodicities near the devries frequency during the little ice age lia this remarkable and coincidental superposition of the signals makes it very difficult to separate volcanic and solar forcing during the lia nevertheless the volcano free temperature records show significant periodicities near the devries periodicity during the entire past 1500 years further pointing to solar mechanisms and emphasising the need for solar related studies in the absence of strong multi decadal volcanic forcing