Although recognized as Asia’s “Water Tower”, our understanding of past natural and recent anthropogenic enforced climate change is limited for much of the Himalayas. The main contributing factors for that are sparse and short meteorological observations, seasonally restricted and often imprecise proxy archives, and spatially heterogeneous and temporally unstable climate dynamics. Here we present a network of five maximum latewood density (MXD) chronologies from 135 living fir (Abies spectabilis) trees from sites near the upper treeline between 3220 and 3750 m a.s.l. in Nepal. Individual series were processed to preserve interannual, decadal, and centennial-scale variability. The resulting composite chronology was calibrated against April–September (AMJJAS) temperatures over the period 1951–2022 CE (rs = 0.64; p < 0.001), enabling the first MXD network-based temperature reconstruction for the Central Himalayas. Despite the relatively short reconstruction coverage (1775–2022 CE), it by far surpasses any regional instrumental record and explains more than 40

Briffa et al. (1998), https://doi.org/10.1038/35596 published a seminal paper on the reduced sensitivity of annual tree growth to temperature across Northern Hemisphere treeline stands. By averaging tree-ring chronologies to sub-continental means, they found decade-long trends in maximum latewood density (MXD) progressively diverging from observed warming temperatures since the 1960s. This divergence challenges the reliability of the proxy, but the lack of an intercontinental network of up-to-date MXD chronologies extending into the 21st century hindered large-scale evaluations of the phenomenon, leaving it unresolved. Here, we introduce nine new MXD chronologies along the North American Rocky Mountains between 38 degrees and 69 degrees N and analyze their trends after applying novel approaches to preserve low-frequency variability. When following the original Briffa et al. (1998), https://doi.org/10.1038/35596 methodology, the divergence between increasing temperatures and MXD chronologies reaches offset values greater than 1 degrees C by 2020 CE. However, divergence markedly decreases and even disappears entirely when MXD chronologies are (a) based on high-replication data sets including differently old trees, (b) detrended using signal-free age-dependent splines instead of Hugershoff curves, and (c) calibrated against optimum season instead of April-September temperatures. MXD chronologies north of 60 degrees N exhibit stable relationships with regional summer temperatures on interannual to multi-decadal timescales, but at the southern sites, a lack of high-frequency proxy-target coherency is evident starting in the second half of the 20th century. This study emphasizes the importance of careful site and target selection, sampling design, and chronology development for overcoming the divergence problem and reconstructing summer temperatures from MXD data in North America.

The Asian Water Towers play a crucial role by storing and releasing vast amounts of freshwater, thereby sustaining the base flow of major Asian rivers and water security for billions of people at sub-continent to hemispheric scales. Instrumental records, though spatially and temporally limited, indicate rapid warming in High Asia. However, the sensitivity and long-term resilience of these Water Towers remain uncertain. Here, we use an 814-year-long tree-ring record (including tree-ring width and maximum latewood density) from Picea likiangensis on the eastern Tibetan Plateau to develop a summer (June-September) temperature reconstruction. Our reconstruction reveals that the series has warmed by 1.5 °C during the modern observational period (1970–2023), which is 0.5 ± 0.4 °C above the pre-industrial baseline (1210–1850 or 1850-1900), making the summer of 2024 the warmest in the past eight centuries. This unprecedented warming amplifies winter runoff in the Brahmaputra, Indus, and Salween headwaters through a cascade of atmosphere-cryosphere feedbacks: enhanced meltwater and spring soil-moisture persistence promote earlier and lusher vegetation growth, which reduces summer albedo and further accelerates regional warming. Detection and attribution analyses identify volcanic and solar forcing as the main drivers of natural, pre-industrial variability before 1850 CE, whereas anthropogenic forcing is detected with high confidence (exceeding the 99

Raw measurements of maximum latewood density (MXD) typically decline with cambial age. This small but persistent trend may diminish or even reverse in living trees under global warming. We here present such a dataset from the Harz mountains in northern Germany that is characterized by an overall positive age trend retained in 92 MXD series of differently old Picea abies trees spanning the period from 1809 to 2020 CE. The positive age trend creates a new situation in which the identification of a temperature signal based on deviations from a horizontal line (e.g. by disabling positive slopes in ARSTAN; Cook, 1985) results in an underestimation of anthropogenic warming, because the residual between the horizontal line and presumed negative age trend remains unconsidered. We approach this problem by testing a range of detrending methods including classic curve fits, signal free (SF), and regional curve standardization (RCS). While none of the methods produces a chronology that perfectly depicts anthropogenic warming, the smallest offset is found when applying RCS to a trimmed MXD dataset. However, the selection of detrending methods based on the fit with instrumental target data, without prior understanding of their suitability, reduces the independency of the proxy record and causes statistical overfitting of the calibration model. Awareness of this problem is important in a rapidly warming world, in which positive age trends in MXD and other temperature-sensitive proxies are likely to increase.

The East Asian Monsoon Transition Zone is highly sensitive to hydroclimatic variability, making it essential to systematically investigate its hydrological dynamics from both historical and future perspectives. However, the scarcity of long-term hydrological observations hampers robust assessments of whether recent extreme events exceed the bounds of natural variability. Here, we reconstructed a 260-year streamflow record for a representative watershed in this transition zone using tree-ring chronologies. The reconstruction reveals that, relative to the East Asian Summer Monsoon, the regulatory influence of the upper-jet stream on regional streamflow variability has become increasingly prominent. To investigate the recent rise in extreme hydrological events, we integrate machine learning models with Shapley additive planation (SHAP)-based interpretability analysis. Results indicate that precipitation is the dominant control on runoff variability, while leaf area index and potential evapotranspiration emerge as particularly sensitive indicators of hydrological change. Furthermore, a comprehensive assessment combining the Budyko framework with CMIP6 multi-model ensemble projections suggests that future increases in runoff will be primarily governed by land surface processes, which account for approximately 59.5% of the total projected change. Overall, this study provides a long-term perspective and forward-looking assessment of hydrological evolution in the East Asian monsoon transition zone, offering critical insights into the mechanisms regulating regional water resources under ongoing climate change.

Although it is generally accepted today that climate and other environmental factors affected past human societies at different spatiotemporal scales, direct linkages are difficult to determine, and correlation should not be confused with causation. Here, we use a tree-ring width network of multimillennial chronologies from inner Eurasia to reconstruct annual changes in Net Primary Productivity (NPP) back to 200 BCE. Our findings reveal that episodes of reduced NPP around the 70s-100s, 360s-380s, and 470s-560s CE likely contributed to the westward and southward migration of nomadic people from their homelands in northwestern China and Mongolia. Although prolonged multidecadal periods of climate-induced low NPP served as tipping points for agricultural and pastoral subsistence systems, the inherent mobility of nomadic communities not only enabled them to adapt to adverse environmental conditions but also facilitated a widespread dispersal of ethnic groups.

Anthropogenic climate change affects regional hydrological cycles and poses significant challenges to the sustainable supply of freshwater. The Central China water tower (CCWT) is the key source region feeding the Yangtze and Yellow Rivers, and its runoff is indispensable for the surrounding mega-city clusters. Here we present a reconstruction of CCWT runoff depth (RD) back to 1595 CE, based on a new dendrochronological network including 100 tree-ring sampling sites and an ensemble averaging approach that combines multiple regression models. Comparison of this reconstruction with similar records from six water tower regions along the Pacific Rim (Mongolian Plateau, Tibetan Plateau TP, Great Dividing Range, Southern and Northern Rocky Mountains, Andes Mountains) revealed that the CCWT provide the most stable water supply, while the TP to be most susceptible to extreme runoff events. Twenty-first century projections indicate generally increasing runoff across most Pacific Rim water towers, whereas the Northern Rocky Mountains are projected to decline substantially. We attribute the differences in runoff variability and projected trends across Pacific Rim water towers to their distinct geographies and synoptic climatic conditions. The long-term runoff reconstructions and projected changes highlighted in this study provide insights for adaptive management strategies in China and all other regions relying on supply from mountain water towers.

Understanding the spatial distribution of tree growth sensitivity in response to climate change is essential for developing effective adaptive forest management strategies, particularly in vulnerable ecotones and transitional zones. Here, we present a network of 70 tree ring width chronologies from 12 tree species to systematically investigate the radial growth responses to key climatic factors, including temperature, precipitation, and drought (scPDSI), across the North-South transitional zone in China (NSTZ). Our analysis indicates that precipitation in the previous September (r = 0.005 - 0.503), January of the current year (r = 0.001 - 0.297), and late spring to early summer (April to June, r = 0.003 - 0.535) exerts a positive influence on the growth of most trees (chronologies > 50), whereas temperature suppresses tree growth in May (r = -0.443 - -0.004) and December (r = -0.396 - -0.026) of the current year. Further redundancy (RDA) and GeoDetector (GD) analysis indicates that the spatial variability of growth sensitivity is primarily governed by combined geographic, aridity gradients, and species, with local microclimatic variables such as vapor pressure deficit (VPD) and soil moisture exerting comparatively weaker influences. Multi-model projections under the SSP2-4.5 and SSP5-8.5 scenarios suggest that the transitional zone is likely to experience a drier and increasingly heterogeneous eco-climatic regime (the mean coefficient of variation > 0.25). Such changes may intensify the spatial divergence and potential destabilization of tree growth-climate relationships, posing challenges for forest ecosystem long-term sustainability.

Pollarded trees – traditionally pruned and maintained for centuries near rural settlements – represent an untapped resource for climate reconstruction in Mediterranean lowlands. In this study, we evaluate the potential of 102 pollarded deciduous oaks from two communal woodlands (dehesas) in northcentral Spain as proxies for past hydroclimatic variability. Using the correlation between latewood and November–June precipitation, we reconstruct regional precipitation variability from 1649 to 2023, achieving calibration/validation correlations of 0.84–0.71 against regional and large-scale instrumental datasets. The reconstruction reveals pronounced interannual to multidecadal variability, with precipitation ranging from 257 to 838 mm. The longest dry spell lasted 25 years (1818–1842), while the wettest sustained period extended over 21 years (1719–1739). We identify 8 extremely dry years and 19 extremely wet years consistently detected across the three threshold criteria considered. Pre-instrumental drought extremes are further supported by historical evidence, including Catholic pro pluvia rogations – ceremonies traditionally held in response to agricultural drought. Our findings demonstrate that pollarded trees, when sampled from sites with asynchronous management, preserve robust climate signals and provide reliable high-resolution information on precipitation variability across Mediterranean dehesas.

The temperature sensitivity of maximum latewood density measurements in pine trees from a high-elevation site in the Spanish Pyrenees increases with tree age. Detrending modulates the intensity of the effect. Tree-rings are the prime archive for high-resolution climate information over the past two millennia. However, the accuracy of annually resolved reconstructions from tree-rings can be constrained by what is known as climate signal age effects (CSAE), encompassing changes in the sensitivity of tree growth to climate over their lifespans. Here, we evaluate CSAE in Pinus uncinata from an upper tree line site in the Spanish central Pyrenees, Lake Gerber, which became a key location for reconstructing western Mediterranean summer temperatures at annual resolution. We use tree-ring width (TRW) and maximum latewood density (MXD) measurements from 50 pine trees with individual ages ranging from 7 to 406 years. For MXD, temperature sensitivity increases significantly (p < 0.01) with tree age from r = 0.31 in juvenile rings with a cambial age < 100 years to r = 0.49 in adult rings > 100 years. Similar CSAE are not detected in TRW, likely affected by the overall lower temperature signal (rTRW = 0.45 vs. rMXD = 0.81 from 1951 to 2020). The severity of CSAE is influenced by the approach used to remove ontogenetic trends, highlighting the need to assess and consider potential biases during tree-ring standardization. Our findings reveal CSAE to add uncertainty in MXD-based climate reconstructions in the Mediterranean. We recommend studying CSAE by sampling diverse age classes in dendroclimatic field campaigns.

Although anthropogenic greenhouse gas emissions are widely regarded as the major cause of ongoing global climate change, isolating anthropogenic impacts on climate is difficult due to the internal variability of the climate system and the brevity of the observational record. Here we attempt to discern a human signal in recent climate change using a 400-year reconstruction of the self-calibrating Palmer Drought Severity Index for the southeastern Tibetan Plateau, where current warming is more pronounced than most other places. Our results highlight a trend towards progressively drier conditions, while the most recent drought and wetness events are ranked as the second most severe throughout the entire reconstruction. We conclude that anthropogenic influence on climate in this region, which is clearly detected at the end of the 20th century, will become stronger in the foreseeable future.

Increasing drought pressure under anthropogenic climate change may jeopardize the potential of tropical forests to capture carbon in woody biomass and act as a long-term carbon dioxide sink. To evaluate this risk, we assessed drought impacts in 483 tree-ring chronologies from across the tropics and found an overall modest stem growth decline (2.5% with a 95% confidence interval of 2.2 to 2.7%) during the 10% driest years since 1930. Stem growth declines exceeded 10% in 25% of cases and were larger at hotter and drier sites and for gymnosperms compared with angiosperms. Growth declines generally did not outlast drought years and were partially mitigated by growth stimulation in wet years. Thus, pantropical forest carbon sequestration through stem growth has hitherto shown drought resilience that may, however, diminish under future climate change.

Tree-ring stable isotopes and wood anatomical traits emerged as powerful proxies for paleoclimate reconstructions, providing information beyond traditional ring width and wood density chronologies. However, comprehensive comparisons of these state-of-the-art tree-ring proxies derived from the same trees have yet to be performed to identify and differentiate their full paleoclimatic skill. Here, we assess covariance and climate signals in tree-ring width (TRW), maximum latewood density (MXD), cellulose stable carbon (S13Cc) and oxygen (S18Oc) isotopes, lignin methoxy carbon (S13Cm) and hydrogen (S2Hm) isotopes, radial cell lumen diameter (Drad), and radial and tangential cell wall thickness (CWTrad/CWTtan) of ten Bosnian pines (Pinus heldreichii) from a treeline site on Mt. Smolikas, Greece. Proxy cross-comparison over the period 1861-2020 CE reveals strong covariance between detrended S13Cc and S13Cm (r >= 0.81). S13Cc and S18Oc exhibit the highest inter-series correlations (r >= 0.61) among all proxies. S13Cc, S13Cm, S18Oc, together with Drad, show considerable skill for reconstructing summer precipitation, whereas MXD and S2Hm may be used for summer temperature reconstructions. Enhanced inter-series and hydroclimate correlations, along with a prolonged seasonality are significant advances of the isotopic and wood anatomical measurements compared to TRW. Our findings highlight the importance of integrating new isotopic, particularly S13Cc, and xylem anatomical data into existing TRW networks to enhance our understanding of past hydroclimate variability and contextualize the recent aridification of the Mediterranean region.

Heatwaves and summer droughts across Europe are likely to intensify under anthropogenic global warming thereby affecting ecological and societal systems. To place modern trends and extremes in the context of past natural variability, annually resolved and absolutely dated climate reconstructions are needed. Here, we present a network of 153 yew (Taxus baccata L.) tree-ring width (TRW) series from 22 sites in southern England that cover the past 310 years. Significant positive correlations were found between TRW chronologies and both April–July precipitation totals (r > 0.7) and July drought indices (r > 0.59) back to 1901 CE (p < 0.05). We used a suite of residual and standard TRW chronologies to reconstruct interannual to multi-decadal spring–summer precipitation and mid-summer drought variability over western Europe, respectively. Our yew hydroclimate reconstructions capture the majority of reported summer droughts and pluvials back to 1710 CE. Clusters of severe drought spells occurred in the second half of the 18th and mid-twentieth century. Our study suggests that the frequency and intensity of recent hydroclimate extremes over western Europe are likely still within the range of past natural variability.

Central Asia, located in the innermost part of the Eurasian continent, has experienced “warming and humidification” in recent decades, with potentially important implications for tree growth in alpine forests, which are critical for regional water reserves. We use nested principal component analysis to assess tree radial growth patterns and reveal significant positive trends since the 20th century across Central Asian alpine forests (0.076 per decade during 1900–2021, p ​= ​0.003). Regional hydroclimatic variations affect the greening of these alpine forests, especially with extreme droughts being the most damaging. Growth acceleration is driven by low-latitude warming, which enhances regional temperatures and precipitation. The warming ocean centers alter atmospheric circulation patterns, leading to more moisture being transported to the Central Asian alpine forests, thereby increasing regional precipitation and promoting tree growth. Our model projections indicate that growth rates will continue to rise in the future. However, unprecedented warming may eventually lead to growth deterioration if negative effects, such as insufficient precipitation, occur due to breakdown signs of positive feedback mechanisms, such as moisture transport driven by low-latitude warming. Our study highlights the beneficial, but not unlimited, influences of climate warming on tree growth in Central Asian alpine forests, with implications for the sustainability of water resources. However, as urban and agricultural demands escalate, a holistic, long-term perspective is recommended to mitigate the adverse effects of temperature increases.

Our understanding of pre‐modern El Niño Southern Oscillation (ENSO) variability is reliant on proxy records, often distant from the center of ENSO activity in the equatorial Pacific Ocean. Here, we assess the relationship between reconstructed soil moisture in four distant ENSO‐influenced regions over the past 400 years. A major breakdown in the teleconnection of regional drought conditions in Asia, Eastern Australia, and North America is identified around 1700 CE. The statistically significant decline in inter‐series correlations ( p < 0.01) represents a previously unknown aspect of global hydroclimate dynamics. We hypothesize that the disruption was driven by ENSO weakening and/or by a large‐scale multi‐decadal reconfiguration of ocean‐atmosphere circulation. Data assimilation estimates of soil moisture from the same regions fail to produce results of the same magnitude, potentially due to an overreliance of ENSO influence on the boundaries of spatial covariance in the underlying climate models.

Climate sensitivity of Pinus sylvestris has changed in minimum density while maximum density remains mostly stable, suggesting the use of additional density parameters could help detect response changes. As one of Eurasia's most widely distributed conifer species, Pinus sylvestris L. is frequently used in dendroclimatological reconstructions based on tree-ring width (TRW) and maximum latewood density (MXD). However, the climatic signals of additional parameters such as earlywood/latewood density (EWD/LWD) or minimum density (MND) are often overlooked, leaving their skill unexplored. Here, we investigate the growth responses of multiple P. sylvestris tree-ring parameters to ongoing climate change at two sites with contrasting climatic conditions using well-replicated density data from Scotland and Sweden. Correlations with mean, minimum, and maximum temperatures are strongest for LWD and MXD at both sites, with coefficients ranging from 0.5 to 0.7 for July, August, and the June–August season (p < 0.05). A significant (p < 0.05) negative correlation between MND and July temperatures was identified in the Swedish Torneträsk (TOR) data (p < 0.05), which diminished since the late twentieth century. A comparable inverse MND temperature signal and change into the twenty-first century is not reflected in northern Scotland’s overall wetter and warmer site, suggesting a fundamental physiological change in tree-ring formation under global warming. A shift in the sensitivity of tree growth at northern European sites could reduce the effectiveness of proxies from such locations, posing implications for high-resolution climate reconstructions.