reconstructing the mediaeval low stands of mono lake sierra nevada california usa palaeosimulations of mono lake covering the past 2 kyr have been conducted using a water balance model forced with tree ring derived inflow estimates the results show two low stands during the ninth to tenth and twelfth to thirteenth centuries that agree well in timing and magnitude with those described by stine 1987 1990 1994 on the basis of geomorphic evidence and relict trees and shrubs exposed on mono lake s artifi cially exposed shorelands the lake simulation provides independent corroboration of the timing and magni tude of stine s drought induced low stands and supports the accuracy of tree ring derived estimates of mediaeval precipitation and runoff reductions in the central sierra nevada specifically we estimate that dur ing the two mediaeval droughts centennial average precipitation and river runoff in the central sierra nevada reached as low as 75 of the twentieth century values with multidecade averages as low as 60 65 in both magnitude and duration these droughts far exceed anything experienced in the region during modern times an analysis of the spatial patterns of reconstructed drought indices shows that the particular two drought mono lake low stand signal was focused over central and southern california indicating the dominant role of boreal winter precipitation deficits in this respect the great sierra nevada droughts were somewhat distinct from the more general great basin far western plains pattern of mediaeval aridity over the western usa

tree ring reconstructed hydroclimate of the upper klamath basin summary this work presents the first tree ring reconstructions of hydroclimate for the upper klamath river basin which stretches from northern california into southern oregon the extended record provides a centuries long perspective on the region s hydroclimatic variability and context for water related political issues that have erupted in recent years reconstructions of water year precipitation for klamath falls oregon extending 1564 2004 and 1000 2010 ce were developed to compare past drought severity with drought severity of the instrumental record extending 1896 2011 the reconstructions suggest that variability exhibited during the instrumental period captures extremes of moderate to long duration 6 10 and 20 year droughts but not of short single year and 3 year and very long 50 year droughts which were more severe during the 11th 13th centuries the late 16th century mega drought is present in the klamath river basin though with less strength than in the neighboring sacramento river basin cool season storm tracks appear to be a direct driver of hydroclimatic variability leading to instances of see saw like relationships with neighboring regions such as in the mid 14th century in contrast the larger area of drought in the 12th century is suggestive of a long term northward shift in cool season storm tracks

annually resolved late holocene paleohydrology of the southern sierra nevada and tulare lake california here we present 2000 year long annually resolved records of streamflow for the kings kaweah tule and kern rivers in the southwestern sierra nevada of california and consequent lake level fluctuations at tulare lake in the southern san joaquin valley the integrated approach of using moisture sensitive tree ring records from the living blended drought atlas to reconstruct annual discharge and then routing this discharge to an annual tulare lake water balance model highlights the differences between these two types of paleoclimate records even when subject to the same forcing factors the reconstructed streamflow in the southern sierra responded to yearly changes in precipitation and expressed a strong periodicity in the 2 8 year range over most of the reconstruction the storage capacity of tulare lake caused it to fluctuate more slowly masking the 2 8 year streamflow periodicity and instead expressing a strong periodicity in the 32 64 year range over much of the record although there have been longer droughts the 2015 water year represents the driest in the last 2015 years and the 2012 2015 drought represents the driest 4 year period in the record under natural conditions simulated tulare lake levels would now be at about 60 m which is not as low as what occurred multiple times over the last 2000 years this long term perspective of fluctuations in climate and water supply suggests that different drought scenarios that vary in terms of severity and duration can produce similar lake level responses in closed lake basins

age and paleoclimatic significance of late holocene lakes in the carson sink nv usa abstract new dating in the carson sink at the termini of the humboldt and carson rivers in the great basin of the western united states indicates that lakes reached elevations of 1204 and 1198 m between 915 and 652 and between 1519 and 1308 cal yr b p respectively these dates confirm morrison s original interpretation lake lahontan geology of the southern carson desert professional paper 40 u s geol survey 1964 that these shorelines are late holocene features rather than late pleistocene as interpreted by later researchers paleohydrologic modeling suggests that discharge into the carson sink must have been increased by a factor of about four and maintained for decades to account for the 1204 m lake stand the hydrologic effects of diversions of the walker river to the carson sink were probably not sufficient by themselves to account for the late holocene lake level rises the decadal long period of increased runoff represented by the 1204 m lake is also reflected in other lake records and in tree ring records from the western united states

late holocene sedimentary environments and lake level fluctuations at walker lake nevada usa walker lake is a terminal lake located at the end of the walker river in western nevada lake level lowering of 50 m during the past 100 yr has led to deep incision by the walker river into the former lake bed this incision has exposed a sedimentary record of lake level fluctuations spanning at least the past 4000 yr fourteen new radiocarbon dates on plant material collected from diverse sedimentary environments including fluvial deltaic beach and offshore settings have led to the refinement of the late holocene lake level curve for this basin this new curve documents at least four highstands that have occurred since ca 3500 cal yr b p between elevations of 1245 and 1255 m the lake has also experienced several lowstands during this same period comparison of this outcrop based record to existing lake level curves and to an oxygen isotope curve for the past 1200 yr reveals many similarities between the records but also some differences therefore research should be conducted to integrate outcrop studies where absolute water depth and lake volume can be estimated with isotopic or other types of proxies from cored sediments that may have higher temporal resolution the extensive and nearly continuous outcrops along the lower walker river also provide valuable information on the relationships between various sedimentary features and their formative water depths in clastic dominated lacustrine systems the paleo water depth relationships deciphered here can be applied in other basins where outcrops are typically more limited to arrive at better constrained lake level records

hydrologic variability and the onset of modern el nino southern oscillation a 19 250 year record from lake elsinore southern california there are very few terrestrial palaeoclimate archives spanning the last glacial maximum through the holocene from coastal southern california yet knowledge of past climate dynamics is critical for assessing present and future constraints on the region s dwindling freshwater resources we present initial results from two drill cores extracted from the present day edge of lake elsinore southern california s largest natural lake using a multiproxy approach including lithologic description mass magnetic susceptibility loi 550 c total organic matter and loi 950 c total carbonate we infer first order long term climate change over the past 19 250 calendar years furthermore we suggest possible first order forcing mechanisms that drive this change which include presence absence of continental ice sheets insolation and complex ocean atmosphere interactions our results indicate four distinct millennial scale climate modes over the past 19 250 calendar years these modes include a wet last glacial maximum 19 250 17 120 cal yr bp a relatively dry late glacial holocene transition 17 120 9450 cal yr bp a wet early holocene 9450 7670 cal yr bp and a highly variable mid to late holocene climate i e alternating wet dry cycles 7670 cal yr bp present we attribute the mid to late holocene climate interval to the onset of el nino southern oscillation ca 7000 cal yr bp and a more vigorous hydrologic system these results are supported by a variety of regional terrestrial and marine palaeoclimate archives copyright 2005 john wiley sons ltd

short duration holocene lakes in the mojave river drainage basin southern california stratigraphic sedimentologic and pedologic studies of beach ridge and lacustrine deposits indicate that up to five times during the holocene shallow lakes covered silver lake playa in southeastern california for periods of years to decades the two youngest lacustrine events at about 390 90 yr b p and 3620 70 yr b p coincide with the early and late neoglacial episodes of north america increasing evidence in recent years from other nonglaciated areas leads us to conclude that the effects of these climatic episodes were much more widespread than previously thought the climate during these episodes was characterized by an increased frequency of winter storms in the southwestern united states causing wetter conditions that affected diverse hyperarid environments in the mojave desert and adjacent regions we propose that this wide areal coverage was caused by large scale winter atmospheric circulation patterns which are probably related to changes in sea surface temperatures and oceanic circulation in the eastern north pacific ocean

atmospheric circulation during holocene lake stands in the mojave desert evidence of regional climate change it is commonly thought that the climate conditions that supported lakes over a period of years in the mojave desert in southern california only existed before 8 000 yr bp and that the environment has been arid since1 2 here we look at a drill core in the silver lake playa at the terminus of the mojave river and find holocene lake deposits which indicate that shallow lakes existed for at least a few decades these deposits were radiocarbon dated at 3620 70 and 390 90 yr bp corresponding to the early neo glacial and the little ice age respectively3 to identify the conditions necessary to produce these holocene lake events we have examined the modern climate and hydrological patterns that produce ephemeral lakes in this usually arid watershed available data indicate that there is a link between anomalous winter atmospheric conditions over the north pacific and mojave river floods that produced ephemeral lakes in the silver lake playa and that the mojave river filters out small to medium floods and allows only the extreme floods to reach the terminal playa and leave a record of the anomalous conditions we suggest that the late holocene lakes may have resulted from persistent similar atmospheric circulation patterns and winter floods

holocene landscape response to seasonality of storms in the mojave desert abstract new optically stimulated and radiocarbon ages for alluvial fan and lake deposits in the mojave desert are presented which greatly improves the temporal resolution of surface processes the new mojave desert climate landscape record is particularly detailed for the late holocene evidence from ephemeral lake deposits and landforms indicates times of sustained stream flow during a wet interval of the latter part of the medieval warm period at ca ad 1290 and during the little ice age at ca ad 1650 the former lakes postdate megadroughts of the medieval warm period whereas the latter match the maunder minimum of the little ice age periods of alluvial fan aggradation across the mojave desert are 14 9 cal ka and 6 3 cal ka this timing largely correlates to times of increased sea surface temperatures in the gulf of california and enhanced warm season monsoons this correlation suggests that sustained alluvial fan aggradation may be driven by intense summer season storms these data suggest that the close proximity of the mojave desert to the pacific ocean and the gulf of california promotes a partitioning of landscape process responses to climate forcings that vary with seasonality of the dominant storms cool season pacific frontal storms cause river flow ephemeral lakes and fan incision whereas periods of intense warm season storms cause hillslope erosion and alluvial fan aggradation the proposed landscape process partitioning has important implications for hazard mitigation given that climate change may increase sea surface temperatures in the gulf of california which indirectly could increase future alluvial fan aggradation

a fan dam for tulare lake california and implications for the wisconsin glacial history of the sierra nevada historic fluctuations and late quaternary deposits of tulare lake in the southern san joaquin valley indicate that maximum lake size has depended chiefly on the height of a frequently overtopped spillway this dependence gives tulare lake a double record of paleoclimate climate in the tulare lake region has influenced the degree to which the lake fills its basin during dry seasons and dry years during the past 100 000 130 000 yr incidence of desiccation of tulare lake inferred from stiffness mud cracks and other hand specimen properties has been broadly consistent with the lake9s salinity and depth inferred from diatoms and ostracodes and with regional vegetation inferred from pollen climate however also appears to control basin capacity itself tulare lake becomes large as a consequence of glacial outwash aggradation of its alluvial fan dam late wisconsin enlargement of tulare lake probably resulted from the last major glaciation of the sierra nevada the lake9s spillway coincides with the axis of the glacial outwash fan of a major sierra nevada stream moreover sediment deposited in the transgressive lake resembles glacial rock flour from the sierra nevada differential tectonic subsidence and deposition by a coast range creek facilitated the building of tulare lake9s fan dam during the late wisconsin but were less important than deposition of sierra nevada outwash four stratigraphically consistent 14 c dates on peat and wood give an age of 26 000 yr b p for the start of tulare lake9s late wisconsin transgression the last major sierra nevada glaciation tioga glaciation thus may have begun about 26 000 yr b p provided that vigorous glacial outwash deposition began early in the glaciation onset of the tioga glaciation about 26 000 yr b p is consistent with new stratigraphic and radiocarbon data from the northeastern san joaquin valley these data suggest that the principal episode of glacial outwash deposition of wisconsin age began in the san joaquin valley after 32 000 yr b p rather than at least 40 000 yr b p as previously believed an earlier enlargement of tulare lake probably resulted from a fan dam produced by the penultimate major tahoe glaciation of the sierra nevada average sedimentation rates inferred from depths to a 600 000 yr old clay and from radiocarbon dates indicate that this earlier lake originated no later than 100 000 yr b p the tahoe glaciation therefore is probably pre wisconsin

tree ring record of streamflow and drought in the upper snake river 1 tree ring samples collected near the snake river headwaters were augmented with preexisting tree ring chronologies to create a 415 year reconstruction of upper snake river streamflow extending the short instrumental record and providing the first description of multicentury water supply variability in this river results indicate that the region s early 21st century drought is severe even in the context of long term climatic variability and that the instrumental record is representative of low flow individual years in terms of overall magnitude droughts of the recent past are eclipsed by a sustained low flow period lasting for over 30 years in the early to mid 1600s a comparison of reconstructed snake river flow with streamflow reconstructions of the colorado sacramento and verde rivers suggests that changes in the predominance of zonal versus meridional atmospheric flow may have influenced drought patterns in the western united states through time

a 9170 year record of decadal to multi centennial scale pluvial episodes from the coastal southwest united states a role for atmospheric rivers abstract a well dated 9170 calendar year before present cal yr bp paleohydrologic reconstruction is presented from lower bear lake in the san bernardino mountains of the coastal southwest united states this new multi proxy record is characterized by alternating organic rich carbonate rich sediment units interpreted to reflect hydrologically forced changes in the lake s depositional environment our interpretation of the proxy data indicates nine decadal to multi centennial pluvial episodes pe over the past 9170 cal yr bp of these nine inferred pluvials five are interpreted as more pronounced based on their combined proxy interpretations pe v 9170 8250 pe iv 7000 6400 pe iii 3350 3000 pe ii 850 700 and pe i 500 476 top of core cal yr bp the lower bear lake record indicates that the san bernardino mountains source region for the mojave river and its terminal playa was wet during the same periods within dating errors to several of the major pluvials proposed from the lakes in the sink of the mojave river our comparison extends north also to tulare lake which drains the southcentral western sierra nevada mountains this temporally and spatially coherent signal indicates that a similar climate forcing acted to increase regional wetness at various times during the past 9170 cal yr bp as originally proposed by enzel ely and colleagues e g enzel et al 1989 enzel 1992 ely et al 1994 enzel and wells 1997 we too contend that holocene pluvial episodes are associated with changing the frequency of large winter storms that track across a broad region at decadal to multi centennial timescales we build upon their hypothesis through the addition of new and better dated site comparisons recent advances in the understanding of atmospheric rivers and improved knowledge of the ocean atmosphere dynamics that caused the early 20th century western united states pluvial

the rambla highstand shoreline and the holocene lake level history of tulare lake california usa abstract the stratigraphy associated with a highstand wave cut shoreline and with sites farther out into the lake plain constrain the holocene lake level history of tulare lake california usa as follows seven to eight major fluctuations in lake level occurred during the past 11 500 yr lake level was generally higher during the early holocene prior to 6000 cal yr bp peaking in two highstands 65 70 masl at 9500 8000 cal yr bp and 6900 5800 cal yr bp thereafter it fluctuated at lower amplitude until reaching a major highstand during the most recent millennium between 750 and 150 cal yr bp two lake level rises of lower amplitude were centered on 3300 and 1600 cal yr bp at least three probably brief lowstands

updated streamflow reconstructions for the upper colorado river basin 1 updated proxy reconstructions of water year october september streamflow for four key gauges in the upper colorado river basin were generated using an expanded tree ring network and longer calibration records than in previous efforts reconstructed gauges include the green river at green river utah colorado near cisco utah san juan near bluff utah and colorado at lees ferry arizona the reconstructions explain 72 81 of the variance in the gauge records and results are robust across several reconstruction approaches time series plots as well as results of cross spectral analysis indicate strong spatial coherence in runoff variations across the subbasins the lees ferry reconstruction suggests a higher long term mean than previous reconstructions but strongly supports earlier findings that colorado river allocations were based on one of the wettest periods in the past 5 centuries and that droughts more severe than any 20th to 21st century event occurred in the past

a 2000 year tree ring record of annual temperatures in the sierra nevada mountains tree ring data have been used to reconstruct the mean late season june through january temperature at a timberline site in the sierra nevada california for each of the past 2000 years long term trends in the temperature reconstruction are indicative of a 125 year periodicity that may be linked to solar activity as reflected in radiocarbon and auroral records the results indicate that both the warm intervals during the medieval warm epoch a d 800 to 1200 and the cold intervals during the little ice age a d 1200 to 1900 are closely associated with the 125 year period significant changes in the phase of the 125 year temperature variation occur at the onset and termination of the most recent radiocarbon triplet and may indicate chaotic solar behavior

role of tropical pacific ssts in global medieval hydroclimate a modeling study 1 the role of tropical pacific ssts in driving global medieval hydroclimate is assessed using fossil coral records from palmyra atoll tropical pacific sea surface temperature sst boundary conditions are derived for the period 1320 1462 a d these boundary conditions consist of la nina like mean state conditions in the tropical pacific with inter annual and decadal variability about that altered state the reconstructed ssts in the tropical pacific are used to force a 16 member ensemble of atmospheric general circulation model agcm simulations coupled to a one layer ocean model outside of the tropical pacific the agcm simulations of medieval climate are compared with modern climate simulations for the period 1856 2005 a d and are shown to reproduce many aspects of medieval hydroclimate found in paleo proxy records for much of the western hemisphere northern eurasia and the northern tropics these results suggest that many features of global medieval hydroclimate changes can be explained by changes in tropical pacific ssts though the potential role for other oceans is also discussed

the use of total lake surface area as an indicator of climatic change examples from the lahontan basin abstract variation in the size of lakes in the lahontan basin is topographically constrained river diversion also has played a major role in regulating lake size in lahontan subbasins the proper gage of lake response to change in the hydrologic balance is neither lake depth level nor lake volume but instead lake surface area normalization of surface area is necessary when comparing surface areas of lakes in basins having different topographies to a first approximation normalization can be accomplished by dividing the paleosurface area of a lake by its mean historical reconstructed surface area

last glacial maximum and holocene lake levels of owens lake eastern california usa abstract stratigraphic investigations of fluvio deltaic and lacustrine sediments exposed in stream cuts quarry walls and deep trenches east of the sierra nevada in owens valley near lone pine california have enabled the reconstruction of pluvial owens lake level oscillations age control for these sediments is from 22 radiocarbon 14 c dates and the identification and stratigraphic correlation of a tephra which when plotted as a function of age versus altitude define numerous oscillations in the level of pluvial owens lake during the latest pleistocene and early holocene we have constructed a lake level altitude curve for the time interval 27 000 cal yr bp to present that is based on the integration of this new stratigraphic analysis with published surface stratigraphic data and subsurface core data pluvial owens lake regressed from its latest pleistocene highstands from 27 000 to 15 300 cal yr bp as recorded by 15 m of down cutting of the sill from the altitudes of 1160 to 1145 m by 11 600 cal yr bp the lake had dropped 45 m from the 1145 m sill this lowstand was followed by an early holocene transgression that attained a highstand near 1135 m before dropping to 1120 m at 7860 7650 cal yr bp that had not been recognized in earlier studies the lake then lowered another 30 m to shallow and near desiccation levels between 6850 and 4300 cal yr bp fluvial cut and fill relations north of lone pine and well preserved shoreline features at 1108 m indicate a minor lake level rise after 4300 cal yr bp followed by alkaline and shallow conditions during the latest holocene the new latest quaternary lake level record of pluvial owens lake offers insight to the hydrologic balance along the east side of the southern sierra nevada and will assist regional paleoclimatic models for the western basin and range

on the formation of deep seated subterranean peperite like magma sediment mixtures abstract in addition to large amounts of fragmented country rocks maar diatreme volcanoes commonly eject juvenile lapilli and cauliflower bombs containing many dispersed xenoliths and or xenocrysts derived from the country rocks surrounding the diatremes formation of these lapilli and bombs is attributed to thermohydraulic explosions in the root zones of the diatremes and their consequences the thermohydraulic explosions release shock waves which are capable of intensely fragmenting the surrounding country rocks vaporisation of water superheated during thermohydraulic explosions and its expansion to lower pressure causes ejection of major parts of the fragmented country rocks surviving sections of fragmented country rocks may collapse or slide into the partially evacuated root zone and thus form a mass flow deposit subsequent to each explosion when prior to a new explosion magma rises from the underlying feeder dyke into the root zone it intrudes this clastic debris inflates it and may mingle with the debris to form a peperite subsequent explosions can fragment and eject fragments of this peperite in the form of juvenile ash grains juvenile lapilli and bombs containing xenoliths or xenocrysts from the country rock debris lack of further explosions but continued rise and intrusion of magma will cause emplacement of such inflated peperite masses as plugs

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

oceanography mixing with latitude measurements over a range of latitudes support a theory relating ocean turbulence to internal waves the upshot should be easier mapping of ocean mixing and eventually better climate models

abrupt onset of the little ice age triggered by volcanism and sustained by sea ice ocean feedbacks 1 northern hemisphere summer temperatures over the past 8000 years have been paced by the slow decrease in summer insolation resulting from the precession of the equinoxes however the causes of superposed century scale cold summer anomalies of which the little ice age lia is the most extreme remain debated largely because the natural forcings are either weak or in the case of volcanism short lived here we present precisely dated records of ice cap growth from arctic canada and iceland showing that lia summer cold and ice growth began abruptly between 1275 and 1300 ad followed by a substantial intensification 1430 1455 ad intervals of sudden ice growth coincide with two of the most volcanically perturbed half centuries of the past millennium a transient climate model simulation shows that explosive volcanism produces abrupt summer cooling at these times and that cold summers can be maintained by sea ice ocean feedbacks long after volcanic aerosols are removed our results suggest that the onset of the lia can be linked to an unusual 50 year long episode with four large sulfur rich explosive eruptions each with global sulfate loading 60 tg the persistence of cold summers is best explained by consequent sea ice ocean feedbacks during a hemispheric summer insolation minimum large changes in solar irradiance are not required

holocene glaciation of the central sierra nevada california abstract sediment cores from two bedrock dammed lakes in north fork big pine creek sierra nevada california preserve the most detailed and complete record of holocene glaciation yet recovered in the region the lakes are fed by outwash from the palisade glacier the largest 1 3 km 2 and presumably longest lived glacier in the range and capture essentially all of the rock flour it produces distinct late holocene matthes and late pleistocene recess peak moraines lie between the modern glacier and the lakes the lakes have therefore received continuous sedimentation from the basin since the retreat of the tioga glacier last glacial maximum and capture rock flour related to all post lgm advances a total of eight long cores up to 5 5 m sediment depth and one short surface sediment short core preserve a coherent record of fluctuating rock flour flux to the lakes through the holocene age constraints on rock flour spikes in first and second lakes based on 31 14c dated macrofossils indicate holocene glaciation began 3200 cal yr b p followed by a possible glacier maximum at 2800 cal yr b p and four distinct glacier maxima at 2200 1600 700 and 250 170 cal yr b p the most recent maximum being the largest reconstruction of the equilibrium line altitudes ela associated with each distinct advance recorded in the moraines recess peak matthes and modern indicates ela depressions relative to modern of 250 m and 90 m for recess peak and matthes advances respectively these differences represent decreases in summer temperatures of 1 7 2 8 c recess peak and 0 2 2 matthes and increases in winter precipitation of 22 34 cm snow water equivalent s w e recess peak and 3 26 cm s w e matthes compared to modern conditions although small these changes are significant and similar to those noted in the cascade range to the north and represent a significant departure from historical climate trends in the region

a 1000 year record of temperature and precipitation in the sierra nevada abstract tree ring data from subalpine conifers in the southern sierra nevada were used to reconstruct temperature and precipitation back to a d 800 tree growth of foxtail pine pinus balfouriana and western juniper juniperus occidentalis ssp australis is influenced by nonlinear interactions between summer temperature and winter precipitation reconstruction of the separate histories of temperature and precipitation is feasible by explicitly modeling species and site differences in climatic response using response surfaces the summer temperature reconstruction shows fluctuations on centennial and longer time scales including a period with temperatures exceeding late 20th century values from ca 1100 to 1375 a d corresponding to the medieval warm period identified in other proxy data sources and a period of cold temperatures from ca 1450 to 1850 corresponding to the little ice age precipitation variation is dominated by shorter period decadal scale oscillations the long term record presented here indicates that the 20th century is anomalous with respect to precipitation variation a tabulation of 20 and 50 yr means indicates that precipitation equaling or exceeding 20th century levels occurred infrequently in the 1000 yr record