The mid-Miocene (15.98 to 13.82 Ma) was characterized by substantially warmer temperatures than today and atmospheric CO222
Holocene flood reconstructions from western and southern Norway indicate a non-stationary behaviour through time, with a major regime shift around 4000 years ago. Under the influence of global warming, flood frequency, seasonality, and magnitude are changing worldwide. The full range of natural variability in flood frequency and seasonality remains poorly constrained, underscoring the need for ultra-high-resolution records to place recent changes in a long-term context. This study presents an 8000-year flood record from Lake Vangsvatnet, Western Norway, that combines high-resolution computed tomography (CT) scanning, X-ray fluorescence (XRF), grain-size analysis, and radiocarbon dating to differentiate between seasonal flood deposits (spring snowmelt versus autumn rainfall). The 11 m sediment core reveals distinct flood layers (n = 230), linked to varying hydrological conditions, and validated by historical discharge data (1892–2016 CE). The record shows fluctuating flood frequencies, with peaks at 6000–5300 and 1400 cal yr BP to present. A seasonal shift from rainfall-dominated to snowmelt-dominated floods occurred around 3100 cal yr BP, coinciding with regional cooling. The last 500 years exhibit the highest flood frequency of the entire record. These findings highlight the sensitivity of flood regimes to climatic and, in the most recent centuries, human influence. Under future warming, reduced snowpack may diminish spring floods, while intensified autumn and winter rainfall could increase flood risks.
Quantitative reconstructions of terrestrial climate conditions typically rely on biological proxies such as pollen. Despite their widespread use, these proxies exhibit inherent limitations such as low taxonomic resolution and complex taphonomies. Sedimentary ancient DNA (sedaDNA), particularly plant metabarcoding using chloroplast markers (trnL-gh), has emerged as a promising alternative offering enhanced taxonomic precision and local origin. Here, we present the framework for quantitative reconstruction of summer temperatures from sedaDNA assemblages applying methods that rely on surface samples for calibration (weighted-averaging partial least squares (WA-PLS), modern analogue technique (MAT)) and introducing a framework that combines modern plant occurrences and species distribution modeling (SDM) to derive taxon-specific probability density functions (PDFs) for calibration. Applying these approaches to sedaDNA data from 203 lake sediment-surface samples across Siberia, we obtained highly accurate reconstructions with median biases as low as 0.5 °C and a strong correlation with observed temperatures. Our method shows a low reconstruction bias when compared to those from other proxy calibration studies. Applied to a Lake Billyakh sediment core in eastern Siberia, our sedaDNA-based reconstructions using various approaches show similar trends and successfully reproduce regional climate changes over the past 32 000 years, aligning closely with independent pollen-based records. We also reveal that higher taxonomic resolution results in a more precise reconstruction due to narrower tolerance ranges with higher taxonomic resolution. The demonstrated reliability, low bias, and superior taxonomic resolution underscore the significant potential of sedaDNA as a robust and sensitive new terrestrial proxy for quantitative paleoclimatic research.
The climatic response to the weakening of the Atlantic Meridional Overturning Circulation (AMOC) is investigated under glacial conditions representative of Heinrich Stadial 5 using a fully coupled Earth System Model (ACCESS-ESM1.5). We find that the climatic response to an AMOC slowdown or shutdown, respectively representing Dansgaard–Oeschger (D–O) and Heinrich stadials, is non-linear. Global mean temperature and precipitation anomalies increase linearly with an AMOC slowdown; however, crossing the threshold of AMOC shutdown results in non-linear and more complex atmospheric circulation and climate responses. The atmosphere partially compensates for the significantly reduced oceanic energy transport due to AMOC shutdown through alterations in the cross-equatorial Hadley Cell (HC), with pronounced changes in boreal winter season. The northern winter HC is enhanced and expanded, while the southern winter HC is weakened but increased in width due to a northward shift of the ascending branch resulting from the AMOC shutdown. This drives seasonal climate variability in the tropical and subtropical regions via changes in the subtropical high pressure systems, subtropical jet, Southern Hemisphere mid-latitude westerly winds and other climate features such as the monsoon systems, with significant impacts on Australasian hydroclimate. The study demonstrates the potential location of a threshold in the climate system between linear slowdown and nonlinear shutdown of the AMOC, with differing climate impacts being broadly consistent with available proxy records for Heinrich and D–O stadials. This further highlights the importance of not crossing the threshold of AMOC shutdown in the future.
Over the last 20 000 years, Northern Hemisphere vegetation underwent major shifts in response to orbital changes, rising CO2, and ice sheet retreat. Using the large-scale pollen-based tree cover reconstruction by Schild et al. (2025), we evaluate the performance of the MPI-ESM Earth System Model in simulating tree cover dynamics from the Last Glacial Maximum to the present. Although the model reproduces the broad increase in tree cover during deglaciation and decrease throughout the Holocene, it fails to simulate the mid-Holocene maximum observed in the reconstructions. The model does capture the shift from energy-limited conditions during deglaciation to water-limited conditions in the early to mid-Holocene, and then back to energy-limited conditions in the late Holocene, but regional discrepancies remain substantial. MPI-ESM simulates too much forest in sparsely forested areas and too little forest in densely forested areas, particularly in mid- and high-latitude regions. Statistical analyses indicate that summer temperature dominates simulated high-latitude forests, while precipitation is critical in most other regions, contrasting with reconstructions that highlight cold-season temperature in temperate and boreal forests. Areas of model-data agreement show largely linear responses to climate drivers, whereas regions of disagreement exhibit non-linear dynamics to the temperature of the warmest month and over-sensitivity of the plant-physiological CO2
Ice cores contain stratified layers of impurities scavenged from the atmosphere, which are a vital tool for investigating the Earth system. Reconstructing past eruption records by way of ice core tephrochronology can help us understand ash dispersal, atmospheric circulation processes, and the impacts of volcanic eruptions on climate. This study presents the coastal East Antarctic Mount Brown South (MBS, 69.11° S, 86.31° E; 2084 meter above sea level (m a.s.l.)) ice core as an untapped tephrochronological archive. We utilize a customized cryptotephra sampling plan, integrating ice core data, HYSPLIT air parcel trajectories, and known eruption records, and identify two distinct cryptotephra horizons at ∼13.3∼17.9 m
The northern South China Sea (SCS) is a critical region for understanding East Asian Monsoon dynamics. However, integrated, multi-proxy records elucidating long-term climatic and vegetation changes in this region remain fragmented, with a notable scarcity of coherent land-ocean interaction data during the Last Glacial Maximum (LGM). This gap has impeded progress in elucidating the mechanisms underpinning monsoon variability and in rigorously evaluating the performance of palaeoclimate models. To address this, we conducted a multi-proxy analysis combining palynological, organic- and inorganic-geochemical methods on a marine sediment core from the northern SCS to reconstruct environmental and oceanic dynamics at millennial-scale resolution that spans the last 33 ka. Our results reveal a clear contrast between glacial and interglacial regimes. The glacial period, especially the LGM, was characterized by higher sedimentation rates, elevated marine primary productivity, cooler and drier conditions, herb-dominated vegetation, and intensified fire activity. This regime was dominantly forced by low sea level and glacial aridity, which together promoted open terrestrial vegetation and enhanced nutrient input to the ocean. The deglaciation was characterized by pronounced warming, reduced productivity, increased moisture availability, a shift to pine-dominated vegetation, and reduced fire activity. A key finding is the ocean warming which began around 1.3 ka earlier than major terrestrial changes, indicating that tropical ocean-atmosphere interactions initiated the deglacial transition. The overall findings highlight a fundamental transition in climatic controls, from a glacial regime dominated by sea-level-driven shelf exposure and arid climate to an interglacial regime governed by tropical ocean-atmosphere dynamics. This study underscores the sensitivity of the northern SCS to both high- and low-latitude forcing and the value of integrated land-sea proxies in deciphering complex climate interactions.
A low-latitude, high-altitude Alpine ice core record was obtained in 2011 from the glacier Alto dell'Ortles (3859 m, Eastern Alps, Italy). A preliminary timescale (TC2016) based on absolute time markers such as a peak in 3H activity, from 210Pb dating, and 14C dating of carbonaceous particles and organic remains provided evidence of one of the oldest Alpine ice core records, extending back to the last Northern Hemisphere Climatic Optimum and spanning the last ∼ 7000 years. Here we present additional time markers that corroborate the multimillennial nature of the Alto dell'Ortles ice cores and significantly reduce the uncertainty of the chronology. First, 14C dating of an additional organic fragment (a charred spruce needle) discovered next to the basal ice provided an age (232 ± 126 BCE) which agrees with previous 14C dates in the oldest part of the record. Second, novel seasonally resolved pollen records from the upper firn/ice portion of the Alto dell'Ortles cores were combined with δ18O and dust annual variations to refine the dating for the 20th century by means of an automatic algorithm (Straticounter; between 1927 and 2011 CE) and visual counting (from 1900 to 1926 CE). The new and previous time markers were combined into a revised intermediate timescale (CP2025/1) by fitting with Markov chain Monte Carlo simulation (COPRA model). CP2025/1 then served as the basis for temporal synchronization of a novel Pb concentration record obtained from the Alto dell'Ortles cores to a well-dated (±5 years) Pb record from an array of Arctic ice cores (AN), with synchronisation performed for the period from 175 BCE to 1755 CE. Possible ties for matching the two Pb records were thereby constrained by the requirement that resulting age shifts remained within the range of overlap between the 1–2σσ, in the ancient part; 1σ, in the recent part). The correlation obtained after synchronization is 0.44 (Pearson's r, p < 0.001), demonstrating that these two distant atmospheric Pb records share a large portion of their variability back to 200 BCE. Most importantly for this study, the synchronization resulted in a further refined, final timescale with a strongly reduced dating uncertainty (CP2025/2). Investigation of CP2025/2 using a simple 1-D ice flow model suggests that non-steady-state conditions, particularly changes in net accumulation rates,
The alkenone-derived
The Devonian period, spanning from 419 to 359 million years ago, was marked by a warmer-than-present climate and recurring ocean anoxic events, with evidence increasingly suggesting a link between these events and astronomical forcing. Here, we explore how astronomical forcing influences ocean oxygenation by modulating the continental weathering flux of phosphate within a Late Devonian climate framework. To investigate this, we performed transient simulations spanning 1.1 Myr, crossing a 2.4 Myr eccentricity node using the cGENIE Earth system model. These simulations were driven by spatially resolved fluxes of reactive phosphorus from continents, computed using the emulator developed by Sablon et al.2025), trained on GEOCLIM and HadSM3 outputs. Our results provide new evidence supporting eccentricity maxima as a driver of Late Devonian anoxic events. Additionally, global analysis reveals that obliquity variations can leave an imprint on global ocean oxygen levels via their influence on biological productivity, suggesting a potential pathway for obliquity-driven anoxia under greenhouse conditions. Regional analysis revealed pronounced spatial heterogeneity in the biogeochemical response to astronomical forcing. Local ocean circulation emerged as a critical factor in shaping these patterns. The simulations indicate that astronomical forcing can, through its impact on continental weathering fluxes, exert a dominant influence on ocean oxygenation, with regional oxygen concentrations varying by up to 35 % and driving changes in regional anoxic volume of up to 19 %. Finally, these findings help explain why proxy records from different locations may show divergent expressions of astronomical signals, potentially leading to contrasting interpretations of their role in driving ocean anoxia.
The Caucasus occupies a unique climatic region influenced by European, Mediterranean, and Asian circulation systems, yet it remains underrepresented in tree ring-based Northern Hemisphere temperature proxy networks. Here, we present the first summer temperature reconstruction for the Caucasus region based on maximum latewood density (MXD). We used X-ray micro-computed tomography of tree-ring samples from Pinus sylvestris
Life on Earth has been capitalizing on the C34δ13C soil carbonate record from the Eastern Mediterranean region (Anatolia) to reconstruct long-term geographic distributions of C3443–C44434pCO2. However, the Anatolian paleoecosystem patterns are unique due to a rapid and permanent return to C334-dominated floodplains and the open-environment adapted Pikermian chronofauna at the Eurasian-African crossroads.
The article presents a description of a newly discovered, unique series of meteorological measurements in SW Greenland (Godthåb [now Nuuk]) from the beginning of the 19th century (1 November 1806 to 16 August 1813), for scientific climatological research. The series is the longest available from before 1840, not only for Greenland but also for the entire Arctic. The handwritten meteorological register was found in the archives of the Royal Society in London (MA/154). The meteorological observations were carried out by the German mineralogist Dr. Charles Lewis Giesecke. The observations include measurements, taken two to three times per day, of air temperature, atmospheric pressure and wind direction. In addition, the meteorological register briefly describes the weather conditions for each day. In the article, we present a detailed analysis of thermal conditions for the period covered by a complete series of measurements (August 1807–July 1813). The analysis of air temperature clearly shows that the study period was one of the coldest periods (possibly the coldest) in the past two millennia. A cooling of this severity in the first decades of the 19th century for the study region, encompassing the whole of Greenland and the entire Arctic, has also been previously reconstructed by other scientists using different proxy data and models. Among the available reconstructions that use different proxy data or that use climate models for this purpose, most of the reconstructions of air temperature are almost fully consistent with the available results of meteorological observations for this period.
High-resolution ice core records from the Greenland ice sheet provide critical insights into past climate variability across seasonal to multidecadal timescales. A key proxy in these reconstructions is the concentration of stable oxygen isotopes (δ18O), which reflects both regional climatic conditions, such as temperature, as well as atmospheric and oceanic circulation patterns. While some studies have linked δ18Oδ18Oδ18Oδ18Oδ18O
The North Atlantic region is a key component of the climate system via large-scale atmosphere and ocean circulation. Climate field reconstructions can provide a long-term context for ongoing climate change and contribute to our understanding of climate dynamics, impact of external forcings, and act as references for model evaluation and baseline for natural variability. There are distinct differences in North Atlantic climate variability between the seasons in terms of climate modes and amplitude of the variance. Constraining long-term climate variability in sub-annual resolution is therefore needed for a more complete understanding of the governing processes. In this study, we present reconstructed climate in annual and seasonal resolution based on a small high-quality network of proxy data combined with output from an isotope enabled climate model. Compared to earlier work, we have improved the methodology to obtain better skill across a larger area and more realistic variance of the reconstructed variables which include 2 m temperature (T2m), sea surface temperature (SST), sea level pressure (SLP) and precipitation amount. Here we validate the reconstructions against reanalysis data, observed SST and eight long-term records of observed temperature. The reconstructed temperature correlates with up to 0.71 for seasonal data and 0.68 for annual data compared to reanalysis data. The skill for SLP shows the imprint of large-scale circulation for winter with more local patterns dominating for summer. This is also mirrored in the skill for precipitation. In addition, the reconstructed annual mean SST shows basin-wide skill for the North Atlantic, indicating relevance of the reconstruction to studies of atmosphere-ocean interaction. A comparison to other climate field reconstructions show that our new reconstruction has comparable properties, and is unique in offering long-term seasonal SLP, temperature and precipitation. This comparison also underlines the importance of consistency in choice of assimilated proxy data, which influences the long-term performance of the reconstruction. In summary, the results show the potential of assimilating a small high-quality network of proxy records.
The Arctic during the Last Interglacial period (LIG) was considered warmer than it is today. The previous study points to a large difference in the degree of simulated annual-mean Arctic warming among models. While recent reconstructions suggest the disappearance of summer sea ice in the Arctic at the LIG, many climate models fail to capture this feature. It is thus essential to investigate sources of uncertainty in climate models. The current study examines the impact of the temperature-cloud phase relationship. Sensitivity studies are conducted for the first time to explore the potential importance of this relationship in simulating the LIG climate. Two different cloud parameter sets are used for an atmosphere-ocean general circulation model with and without the dynamic vegetation feedback. The model with cloud parametrization that permits liquid water at lower temperatures and a larger fraction of supercooled liquid water at the same temperature simulates a warmer preindustrial (PI) climate, greater annual-mean Arctic warming at the LIG, and substantially reduced summer sea ice cover at the LIG. It is demonstrated that the low-level clouds play a crucial role in controlling the Arctic response via the greenhouse effect. The result indicates the importance of the temperature-cloud phase relationship in simulating the Arctic climate at the LIG. It also highlights the importance of accurately simulating modern sea ice thickness and representing the processes that affect the fraction of supercooled liquid water in clouds.
Although orbital signal is widely identified in Miocene proxy records, the climate mechanisms linking insolation changes to regional temperature within this warm, low-ice period remains not well known. Here we use fully coupled climate model simulations to assess temperature response to maximum and minimum boreal summer insolation under Miocene and pre-industrial (PI) conditions. Under both conditions, temperature exhibits broadly anti-phased responses to increased and decreased insolation, but the Miocene response is overall weaker, with regionally dependent contrasts and reduced symmetry between two orbital cases. Three notable Miocene-PI differences emerge: (1) reduced boreal continental sensitivity in the Miocene due to dampened albedo, water-vapor and cloud feedbacks in a warmer, low-ice climate; (2) stronger Miocene cooling over tropical North Africa under high insolation, driven by intensified hydrological and moisture-feedbacks supported by a wider Tethys Sea; (3) reversed Southern Ocean anomalies under low insolation, where poleward-restricted Miocene sea ice enables winter insolation changes to trigger positive ice-albedo feedbacks. These results demonstrate that background climate state strongly modulates orbital-scale responses and provide important context for interpreting Miocene proxy records and long-term changes in Earth's climate sensitivity through the Neogene.
Studies of the Late Pliocene have frequently been used as a means to improve our understanding of the climate system in a warmer state. Large scale features of Late Pliocene climate, such as Arctic Amplification, will impact global circulation including the jet stream. To date, the majority of Late Pliocene studies have focused on long term mean climate. However, considering interannual variability is important to fully understand the response of the climate system to different forcings. Using data from the Pliocene Model Intercomparison Project Phase 2, we find a more poleward, yet weaker jet stream in the North Pacific during winter months, and increased interannual jet stream variability in the Late Pliocene compared to the pre-industrial control. This result is consistent across the majority of models, although there is variation in the magnitude of change across the ensemble. Using new simulations from the Hadley Centre Climate Model Version 3 (HadCM3), we find that changes in jet stream variability are due to orographic boundary conditions and are correlated with sea ice feedbacks. Carbon dioxide has little impact on the interannual variability in HadCM3 suggesting that the Late Pliocene is not an analogue for future jet stream variability. This change in jet stream variability in the Late Pliocene could lead to a change in the distribution of temperature and precipitation which could have implications for how proxy data and model simulations are compared.
It has been hypothesized that the Earth may have experienced snowball events in the past, during which its surface became completely covered with ice. Previous studies used general circulation models to investigate the onset and climate of such snowball events. Using the MIROC4m coupled atmosphere–ocean climate model, this study examined the changes in the oceanic circulation during the onset of a modern snowball Earth and elucidated their evolution to steady states under the snowball climate. Abruptly changing the solar constant to 94 % of its present-day value caused the modern Earth climate to turn into a snowball state after ∼ 1300 years and initiated rapid increase in sea ice thickness. During onset of the snowball, extensive sea ice formation and melting of sea ice in the mid-latitudes caused substantial freshening of surface waters and salinity stratification. By contrast, such salinity stratification was absent if the duration between the change in the solar flux and the snowball onset was short. After snowball onset, the global sea ice cover and the buildup of salinity stratification caused drastic weakening in the deep ocean circulation. However, the meridional overturning circulation resumed within several hundred years after the snowball onset because the density flux by sea ice production weakens the salinity stratification. While the evolution of the oceanic circulation would depend on the continental distribution and the evolution of continental ice sheets, our results highlight the gradual growth of sea ice and associated brine rejection are essential factors for the transient evolution of the oceanic circulation in the snowball events.
The last deglaciation featured abrupt climate shifts driven by interactions among Earth system components, notably retreating ice sheets and meltwater input. While globally detected, the magnitude, timing, and sequence of North Atlantic meltwater events remain uncertain. We present a Uranium-Thorium-dated stalagmite from northwestern Iberia spanning 24–12 ka BP, capturing both the impact of North Atlantic meltwater on surface ocean chemistry and regional air temperature changes. Our record reveals primarily gradual meltwater inflow during the Last Glacial Maximum and early deglaciation (about 20.8–18.2 ka BP), followed by abrupt increases during Heinrich Stadial 1. The first abrupt cooling is decoupled from the first meltwater pulse, appearing around 810 years