Given that the Arctic could be ice-free in summer within the next ten to 20 years, accurately predicting low-ice states is of crucial importance. Paleo-evidence shows that the strong orbitally-induced high latitude insolation anomaly at 127 000 years ago (127 ky), of around +70 Wm-2 in the Arctic during spring-summer, led to warm conditions and an Arctic that was occasionally or often ice-free during summer. Building on two Coupled Model Intercomparison Projects (CMIPs): the Sea-Ice Model Intercomparison Project and the Paleoclimate Modelling Intercomparison Project, we propose an Assessment Fast Track experiment, abrupt-127k, focusing on this seasonally ice-free, or near ice-free, Arctic at 127 ky. The abrupt-127k experiment is initialised from a piControl simulation and abruptly imposes observed values for the insolation distribution and greenhouse gas forcing at 127 ky. It provides a new opportunity to evaluate models used to compute climate projections, both against paleo-evidence and each other, during a known low Arctic sea ice state. As CMIP models are not usually tuned to paleo observations, abrupt-127k represents a true “out-of-sample” test. The abrupt-127k experiment has four key scientific objectives, to: ascertain the simulated Arctic sea ice state, including the presence and characteristics of last-ice areas; evaluate the simulated climates using Arctic paleo-evidence; characterise the central Arctic surface energy budget; and analyse the ice budget including ice melt, growth, and transport. We show that a large Arctic ice response will manifest within the first 30 years of the simulation, thus a single 100-year long run is sufficient for these objectives. Modelling groups are requested to follow standard CMIP output protocol for analysis, including the use of standard “fixed-length” output. Given abrupt-127k is similar in setup to abrupt-2xCO2 and abrupt-4xCO2 CMIP7 experiments, combined analysis of these abrupt-experiments will facilitate understanding of the impacts of instantaneous radiative forcing in the Arctic.

This study investigates the impact of vegetation–climate feedback on the global land monsoon system during the Last Interglacial (LIG, 127 000 years BP) and the mid-Holocene (MH, 6000 years BP) using the earth system model EC-Earth3. Our findings indicate that vegetation changes significantly influence the global monsoon area and precipitation patterns, especially in the North African and Indian monsoon regions. The North African monsoon region experienced the most substantial increase in vegetation during both the LIG and MH, resulting in significant increases in monsoonal precipitation by 9.8% and 6.0%, respectively. The vegetation feedback also intensified the Saharan Heat Low, strengthened monsoonal flows, and enhanced precipitation over the North African monsoon region. In contrast, the Indian monsoon region exhibited divergent responses to vegetation changes. During the LIG, precipitation in the Indian monsoon region decreased by 2.2%, while it increased by 1.6% during the MH. These differences highlight the complex and region-specific impacts of vegetation feedback on monsoon systems. Overall, this study demonstrates that vegetation feedback exerts distinct influences on the global monsoon during the MH and LIG. These findings highlight the importance of considering vegetation–climate feedback in understanding past monsoon variability and in predicting future climate change impacts on monsoon systems.

Climate variability has profoundly influenced societies in the semiarid Eastern Mediterranean. Proxy records indicate progressive mid-Holocene drying culminating in severe droughts ∼1250 BCE, coincident with the Late Bronze Age collapse (1300 to 900 BCE). Using the EC-Earth3-Tr8K transient Holocene simulation, we reconstruct regional hydroclimate evolution and its underlying mechanisms. The model reproduces a gradual orbitally driven aridification, spatially heterogeneous across the region, with persistent drying in the Levant but enhanced effective moisture in parts of the Balkans and Anatolia due to cooling-induced evapotranspiration decline. Superimposed on this long-term trend are extreme drought events, which arise from the alignment of Atlantic internal variability across centennial to millennial timescales, amplifying drying on an already arid background state. These results provide model-based evidence of how evolving amplitude and phase structure of Atlantic internal variability reshaped Eastern Mediterranean hydroclimate through the mid-to-late Holocene. We demonstrate that oceanic variability can manifest as abrupt regional crises when ecological and societal thresholds are crossed.

The decline of the Classic Maya civilisation (∼8th–10th centuries CE) occurred in part from drought stress induced by natural climate variability. Using the EC-Earth3 8K simulation, driven by time-varying orbital and greenhouse gas forcing, we show that the convergence of internal hydroclimatic rhythms alone, generated severe, prolonged droughts comparable to, or even greater than, observed extreme events. We identify the interaction of multi-centennial oscillations (∼600 years) and centennial (∼160 years) cycles, superimposed with robust sub-centennial oscillations (∼60–90 years) and persistent multi-decadal and inter-annual variability, created a shifting wet/dry regime over the Yucatán Peninsula. Severe droughts arose when different frequency modulations aligned in their dry phases. Our results provide the first model-based demonstration of how internal climate variability alone can trigger extreme events capable of reshaping societies, revealing key climatic drivers of societal vulnerability, with direct implications for how internal variability may interact with anthropogenic forcing to amplify future climate risks.

The Late Pliocene, particularly the Marine Isotope Stage KM5c (3.205 Ma BP) has been increasingly proposed as an analog to future climate change, especially considering changes in the hydrological cycle, monsoon systems, and atmospheric and ocean warming above Pre-Industrial (1850 CE) and historical levels. The Pliocene Modeling Intercomparison Project (PlioMIP), now in its third phase (PlioMIP3), seeks to explore climate of the Pliocene based on a combination of climate model simulations and proxy data reconstructions. One of its goals is also to assess the analogy between past and future climates and to quantify climate sensitivity to Pliocene boundary conditions. This work shall help to improve climate models and their application for both past and future warm climates and to provide a paleoclimate-informed assessment of uncertainties in modeled warm climates. With this manuscript we present the PlioMIP3 core simulations for the pre-industrial control (PI) and the Late Pliocene (LP) based on the AWI Climate Model, Version 3 (AWI-CM3). This represents the first application of AWI-CM3 at tectonic timescales which necessitates more extensive adjustment of model setups than the application for recent climate. We therefore take advantage of the opportunity to also document more generally the methods we devised to generate AWI-CM3 model setups for paleoclimate research under geographies that differ from the modern reference state. AWI-CM3 simulates a Late Pliocene climate that is about 4 °C warmer than the pre-industrial reference, with land warming exceeding ocean warming by a factor of 1.2. Polar amplification is particularly pronounced, with Antarctic surface air temperature anomalies exceeding 6 °C while Arctic anomalies reach 4 °C to 5 °C. In comparison to the previous PlioMIP2, this places AWI-CM3 among the warmer ensemble members, consistent with a relatively high equilibrium climate sensitivity of ~4 °C. Our simulations also display an intensified hydrological cycle, with global mean precipitation increasing by 0.31 mm d⁻¹. The ocean surface warms globally to about 3.06 °C, accompanied by contrasting salinity trends, with salinization of the North Atlantic (+3 PSU) and freshening of the Arctic (–2.5 PSU) and Indian (–1 PSU) Oceans. Additionally, the meridional overturning circulation (MOC) reorganizes, with the Atlantic MOC strengthening by about 8 Sv, the Pacific MOC remaining inactive, and the global Antarctic Bottom Water cell being substantially reduced (11 Sv weaker relative to PI). We find reduced global sea-ice extent, that is halved with respect to PI in the Southern Hemisphere, and enhanced northward ocean heat transport in the North Atlantic. Overall, AWI-CM3 reproduces the large-scale climate features of the Late Pliocene inferred from proxy records and the PlioMIP2 ensemble, while highlighting key ocean–atmosphere feedbacks shaping this warm climate.

Self-sustained multicentennial variability of the Atlantic Meridional Overturning Circulation (AMOC) has been previously demonstrated in one‐hemisphere box models. In this study, we extend our earlier work by developing a two‐hemisphere box model that incorporates both thermohaline and wind‐driven components. Our analysis reveals that a robust, weakly damped multicentennial eigenmode persists in the two‐hemisphere framework, with the salinity advection feedback in the North Atlantic remaining the dominant control mechanism, while the South Atlantic plays a minor role. Compared to the one‐hemisphere model, the self-sustained multicentennial oscillation in the two-hemisphere box model is much easier to occur and less sensitive to changes in basin geometry. A further simplified box model is developed to reproduce the key eigenmode of the original model. This simplified model provides analytical insights showing that the oscillation period is primarily controlled by basin geometry and mean AMOC strength. Moreover, the inclusion of wind‐driven circulation acts to weaken the oscillation amplitude, with negligible impact on the oscillation period. Finally, we further demonstrate that the thermohaline component of the AMOC is a necessary and sufficient condition for the multicentennial oscillation in this model, as the shallow wind-driven overturning cannot exhibit multicentennial oscillations. Overall, these findings demonstrate the robustness of multicentennial AMOC oscillations and clarify the essential role of thermohaline processes in shaping their dynamics across varying oceanic configurations.

古气候数据同化能够有效融合气候模式模拟与代用资料，已成为重建过去气候场的重要方法。作为基础的先验数据集对同化结果具有重要影响，但现有研究多采用单一模式场作为同化先验，缺乏针对不同模式输出作为先验的系统对比框架以及同化效果的定量评估。基于离线古气候数据同化框架，系统评估了13个耦合气候模式输出作为先验数据集对北半球过去千年年均温度场重建的影响。对1880—2000年观测时期重建的结果显示，同化后的重建数据质量在时空维度上均获提升：时间相关系数由0.54~0.88提高至0.86~0.89，泰勒技巧评分由0.31~0.78提升至0.71~0.80，且不同重建结果间的离散程度缩小；空间维度上，同化有效提升了北半球年际变率的同步性并校正了多数区域的平均态冷暖偏差，但改善幅度呈现区域差异特征，主要受代用资料覆盖密度与先验场初始质量的共同约束，模式固有偏差是制约特定区域功效系数提升的关键因素。通过多维度秩评分体系，将重建结果划分为高、中、低性能组进行评估后发现，各组均能清晰捕捉中世纪暖期、小冰期和现代暖期的演变特征，并反映出了极地放大效应及强火山事件冷却响应，其中高性能组表现较为稳健。研究证实了耦合模式比较计划的标准输出作为同化先验数据集的可行性，也为先验优选提供了定量依据，以期为理解过去千年气候演变特征提供数据基础。

Paleoclimate data assimilation effectively integrates climate model simulations with proxy records and has emerged as a key approach for reconstructing past climate. The prior strongly influences assimilation results. However, the literature lacks a systematic comparative framework across diverse model prior and a rigorous quantitative assessment of assimilation efficacy. We applied an offline paleoclimate data assimilation framework to systematically evaluate the influence of prior datasets derived from 13 coupled climate models on annual mean temperature field reconstructions across the Northern Hemisphere over the past millennium. Evaluation over the 1880-2000 observational period revealed consistent improvements in reconstruction quality across both temporal and spatial dimensions: temporal correlation coefficients increased from 0.54~0.88 to 0.86~0.89, Taylor skill scores rose from 0.31~0.78 to 0.71~0.80, and the spread across reconstructions narrowed substantially. Spatially, assimilation enhanced the coherence of interannual variability across the Northern Hemisphere and corrected mean-state biases in most regions. The magnitude of improvement varied regionally, primarily reflecting the combined constraints of proxy network density and prior field quality, with model-inherent biases constituting a key limiting factor for efficiency coefficient gains in specific regions. A multidimensional rank scoring system classified all reconstructions into high-, medium-, and low-performance groups. All groups clearly captured the Medieval Warm Period, the Little Ice Age, and the Modern Warm Period, and reproduced both polar amplification and the cooling signatures of major volcanic eruptions, with the high-performance group demonstrating the greatest robustness. This study confirms that standard Coupled Model Intercomparison Project (CMIP) outputs serve as viable prior datasets for paleoclimate data assimilation, provide a quantitative basis for prior selection, and offer a data foundation for advancing our understanding of climate variability over the past millennium.

The East African uplift during the Miocene played a crucial role in reshaping regional climates, ecosystems, and faunal communities, contributing to a shift from forested landscapes to widespread grasslands. Here, we use the high-resolution Earth System Model EC-Earth3, coupled with a dynamic vegetation model, to simulate climate and vegetation responses to East African uplift across three key Miocene intervals (25, 20, and 15 Ma) under varying atmospheric CO₂ levels. Our results show that tectonic uplift, combined with declining CO₂ during the Middle Miocene Climate Transition, substantially reduced forest cover and promoted grassland expansion across East and Central Africa. These environmental transitions likely facilitated faunal dispersals and ecological turnover, including among large mammals and early crown hominoids. By integrating geodynamic reconstructions, paleoclimate modeling, and fossil data, this study provides insight into how large-scale Earth system processes shaped Miocene biodiversity and altered the environmental context for mammalian evolution in Africa.

Precipitation variability in the South African Monsoon Domain, which encompasses much of southern Africa and the adjoining Indian Ocean, is marked by a distinct dipole pattern, with one center over southeastern Africa and the other along a northwest-southeast-oriented belt that extends across tropical eastern Africa and the southwest Indian Ocean. However, the climatic mechanisms of this dipole pattern over timescales remain unclear. In this study, we integrate modern observations, reanalysis data, and regional paleoclimate proxy records spanning the past 8 ka to investigate hydroclimate variability in the eastern South African Monsoon Domain at interannual to millennial scales. While modern observations identify the Indian Ocean Basin Mode (IOB), Subtropical Indian Ocean Dipole (SIOD), and Indian Ocean Dipole (IOD) as key drivers, the shift from IOD- to IOB/SIOD-dominated SSTA patterns reflects both long-term Pacific forcing and strong Indian Ocean-Pacific coupling that critically shapes rainfall variability in the South African Monsoon Domain. The SIOD and IOB dominate hydroclimate fluctuations in tropical eastern Africa and the southwest Indian Ocean, while the interaction between SIOD and El Niño Southern Oscillation amplifies the southeastern Africa - the southwest Indian Ocean dipole pattern. On longer timescales, we find that multi-millennial and multi-centennial hydroclimate precipitation patterns broadly resemble the dipole pattern as observed today. However, comparisons lack support from western Indian Ocean SST reconstructions, necessitating further high-resolution SST records and model simulations to validate these relationships.

El Niño–Southern Oscillation (ENSO) events, whether in warm or cold phases, that persist for two or more consecutive years (multi-year), are relatively rare. Compared with single-year events, they create cumulative impacts and are linked to extended periods of extreme weather worldwide. Here we combine central Pacific fossil coral oxygen isotope reconstructions with a multimodel ensemble of transient Holocene global climate simulations to investigate the multi-year ENSO evolution during the Holocene (beginning ~11,700 years ago), when the global climate was relatively stable and driven mainly by seasonal insolation. We find that, over the past ~7,000 years, in proxies the ratio of multi-year to single-year ENSO events increased by a factor of 5, associated with a longer ENSO period (from 3.5 to 4.1 years). This change is verified qualitatively by a subset of model simulations with a more realistic representation of ENSO periodicity. More frequent multi-year ENSO events and prolonged ENSO periods are being caused by a shallower thermocline and stronger upper-ocean stratification in the Tropical Eastern Pacific in the present day. The sensitivity of the ENSO duration to orbital forcing signals the urgency of minimizing other anthropogenic influence that may accelerate this long-term trend towards more persistent ENSO damages.