Abstract The Atlantic Niño/Niña is a leading mode of tropical climate variability with profound global environmental and socioeconomic impacts. Conventionally, its variability is projected to weaken under greenhouse warming, primarily attributed to suppressed basin‐scale air–sea interactions. However, the modulating role of sub‐basin‐scale ocean dynamical processes remains largely unexplored. Here, using an ensemble of high‐resolution climate simulations, we show that submesoscale ocean eddies substantially dampen Atlantic Niño/Niña variability by regulating vertical heat transport. Under greenhouse warming, this eddy‐induced damping is projected to diminish due to the suppressed Atlantic cold tongue and enhanced upper‐ocean stratification. Consequently, this attenuation of damping buffers approximately one‐third of the variability weakening driven by basin‐scale processes. This mechanism is corroborated by comparison with standard‐resolution climate simulations, which fail to resolve submesoscale eddies, and is further supported by CMIP6 model outputs. These findings highlight the critical importance of resolving fine‐scale ocean processes to improve the fidelity of future climate projections.

The ocean is in constant motion, containing eddies across a wide spectrum of scales. Outside the equatorial region, nonlinear interactions of ocean mesoscale eddies, ranging in scales from tens to hundreds of kilometers, drive a universal upscale kinetic energy (KE) transfer. This transfer is fundamental to sustaining large-scale flows and shaping the ocean kinetic energy spectrum, consequently maintaining an equilibrium state of the ocean. Yet, how this upscale KE transfer will respond to greenhouse warming remains poorly understood. By applying a spatial coarse-graining approach to a state-of-the-art high-resolution climate simulation, we reveal an overall weakening of the upscale KE transfer outside the equatorial region, predominantly in the deep ocean. This weakened upscale KE transfer is primarily caused by a diminished conversion from available potential energy to KE at mesoscales, due to enhanced stratification. Our findings suggest significant shifts in the ocean energy cycle in response to anthropogenic climate changes.

Wind power on oceanic near-inertial internal waves () is one of the major energy sources to sustain ocean turbulent diapycnal mixing. However, its response to global warming remains poorly understood. Using a high-resolution climate simulation that simulates reasonably well, we show that under a high-emission scenario, the quasi-globally (5 degrees-60 degrees latitudes) integrated exhibits a significant negative trend of per century during 2001-2100, decreasing by about 13% by the end of the 21st century compared to its present level. This decline is driven by reduced near-inertial wind stress variance, primarily due to weakened mid-latitude storm activities resulting from a poleward shift of storm tracks in both hemispheres and weakening of storm tracks in the Northern Hemisphere. Our findings suggest that near-inertial internal waves should likely weaken in a warming climate, with important implications for ocean turbulent diapycnal mixing.

The Atlantic Ni & ntilde;o/Ni & ntilde;a, akin to the Pacific El Ni & ntilde;o-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), is a dominant mode of interannual climate variability, exerting profound impacts on the global climate. Previous studies show reversed changes in ENSO and IOD variability before and after 2100. However, the projected evolution of the Atlantic Ni & ntilde;o/Ni & ntilde;a beyond 2100 remains unknown. Here, we find that the Atlantic Ni & ntilde;o/Ni & ntilde;a variability displays a sustained weakening toward the 23rd century under high- and low- emission scenarios. On the one hand, atmospheric stratification is stabilized in the equatorial Atlantic, reducing the sensitivity of zonal wind to the anomalous sea surface temperature (SST) gradient. On the other hand, weakened equatorial upwelling decreases SST sensitivity to thermocline anomalies. These changes suppress the Bjerknes feedback in the tropical Atlantic, leading to a sustained weakening of Atlantic Ni & ntilde;o/Ni & ntilde;a variability under persistent greenhouse warming, in sharp contrast to ENSO and the IOD. Such weakening in variability may further influence the predictability and global impacts of the Atlantic Ni & ntilde;o/Ni & ntilde;a, with potentially far-reaching ramifications.

This study develops an ensemble forecast system for Arctic sea ice with a horizontal resolution of similar to 2 km to resolve linear kinematic features (LKFs). The system is designed to run operationally on the Sunway computing architecture, which employs many-core processors with a distinct programming logic. The Parallel Data Assimilation Framework has been optimized for Sunway's architecture by leveraging fine-grained thread-level parallelism and restructuring memory hierarchies. Results from multiple process configurations show that the optimized analysis step achieves an average speedup of 9.19, while overall performance improves by an average of 3.66 compared to CPU-based architectures. To address the strong nonlinearity of LKFs, we employ ice strength parameter perturbations and a novel localized observation error function that preserves valuable LKF information from both the model and sea ice concentration observations. Compared to Synthetic Aperture Radar observations at 1-3-day lead times, the hindcast experiment yields a bidirectionally averaged minimum Hausdorff distance of 39.7-41.9 km for large-scale LKFs, and outperforms persistence forecasts in spatial maximum cross-correlation error within the 48 hr lead time. The probability density functions of LKF orientation and length largely follow the observed distributions. Results indicate that LKF predictability can be enhanced through model dynamics inherently from well-initialized sea ice states like concentration or thickness, despite only limited details of LKFs in the observations used during assimilation. With higher-frequency data assimilation, this system shows potential for operational LKF forecasting in support of practical Arctic navigation.

The Pacific Decadal Oscillation (PDO) profoundly influences marine ecosystems, fisheries, and global hydroclimate. Although traditionally interpreted as basin-scale oceanic responses to atmospheric stochastic forcing, whether its dynamics involve active ocean feedbacks remains unresolved. Using an unprecedented multicentury eddy-resolving global climate simulation, we find that mesoscale eddy-driven atmospheric anomalies in the Kuroshio Extension (KE) region are critical to PDO evolution. During the PDO cold phase, the northward-shifted meandering KE generates mesoscale sea surface temperature (SST) anomalies that intensify lateral diabatic heating gradient, driving deep updrafts that cool the mid-troposphere and weaken its northern baroclinicity. This suppresses transient eddy momentum flux and facilitates a basin-scale low-pressure anomaly, initiating transition to the warm phase. Concurrently, mesoscale eddy-induced vertical heat transport sustains SST anomalies, providing additional PDO memory. These coupled processes substantially enhance the PDO's predictability. Our findings highlight the previously underappreciated upscale effects of oceanic eddies, offering important insight into decadal climate variability.

The Kuroshio Extension (KE) exhibits pronounced decadal variability, influencing marine ecosystems, fisheries, and regional climate. However, how anthropogenic warming affects this variability remains uncertain due to limited satellite records and model resolution constraints. Based on an eddy-resolving historical-and-future transient climate simulation, we find that the KE decadal variability weakens significantly under a high-emissions scenario. This weakening likely results from a disruption of the coupled ocean-atmosphere delayed oscillation, which involves basin-scale atmospheric circulation both forcing and responding to KE variations. Specifically, warming-induced strengthening of atmospheric stratification likely suppresses the thermodynamic adjustment, including the deep-reaching updraft and associated mid-to-upper tropospheric responses, typically triggered by oceanic mesoscale warming during the KE stable state. Such suppression disrupts the coupled ocean-atmosphere delayed oscillation, contributing to the weakened KE decadal variability. Our findings imply that the KE system might be less predictable under future warming.

River flow seasonality (RFS) governs water availability for ecosystems and societies, but its response to future climate change remains poorly quantified at global scales. Here, we assess historical and future RFS trends across twenty major river basins using observational data (G-RUN Ensemble) and multi-model hydrological projections (RCP2.6 and RCP6.0). Our analysis shows declining historical RFS in snow-dominated high-latitude basins, contrasting with increases in tropical and temperate regions. Future projections show amplified river basin divergence: RFS weakens further in northern high latitudes but intensifies elsewhere, with RCP6.0 exacerbating these trends. Notably, over 30% of densely populated basins face co-occurring RFS intensification and population growth, compounding water stress. Our basin-scale analysis identifies hotspots where climate-driven RFS shifts intersect with rising water demand, providing actionable insights for adaptation planning.

The sea surface temperature (SST) in the Southern Ocean (SO) exerts widespread effects on the climate. Yet there is a persistent warm SST bias in the SO across generations of coupled global climate models (CGCMs). Existing literature blames such bias primarily on the deficiencies of model-simulated atmospheric processes or basin-scale ocean circulations. In this study, we show that the warm SST bias in the SO can be mitigated by parameterizing the vertical mixing induced by wind-driven near-inertial internal waves (NIWs) in the thermocline. By representing NIW-induced vertical mixing in the thermocline of an eddy-resolving CGCM, the warm SST bias in the SO is significantly reduced due to the enhanced downward heat flux from the surface boundary layer to the ocean interior. Our findings provide a new pathway to alleviate the warm SST bias in the SO, helping in improving the fidelity of model projected future climate changes.

The observed Atlantic Ni & ntilde;o/Ni & ntilde;a displays robust variations at decadal timescale (decadal ATL), besides the well-known interannual variability. The underlying mechanisms, however, remain largely elusive. Analyzing observations and model outputs, we find the decadal ATL originates in the South Atlantic. During its positive phase, the cold tongue warming, triggering atmospheric Rossby wave train, weakens the St. Helena anticyclone, which enhances wind and cools sea surface temperature over the Southwestern Atlantic, leading to the positive phase of the South Atlantic Ocean Dipole. Meanwhile, the weakened anticyclone reduces the transport of the subtropical cell, suppressing the equatorial upwelling, which amplifies the initial cold tongue warming. The phase shift of the decadal ATL is attributed to an eastward propagation of thermocline displacements at 3 degrees S-15 degrees S, induced by a propagation of local wind stress curl anomalies in response to combined effects of the equatorial and mid-latitude air-sea coupling.

The Pacific El Niño‐Southern Oscillation and the Atlantic Niño/Niña change oppositely in the 21st century. Here, we find the weakened Atlantic Meridional Overturning Circulation (AMOC) plays a key role. Via reducing the equatorial Pacific trades and the Atlantic poleward heat transport, the weakened AMOC contributes to, at surface, a similar Niño‐like sea surface temperature (SST) warming and a strengthened atmospheric stratification in both basins, while, at subsurface, a western Pacific cooling in comparison to an intense Atlantic warming. The distinct subsurface changes induce strengthened Pacific oceanic stratification to enhance Bjerknes feedback, in contrast to an insignificant change in the Atlantic. Moreover, the similar surface changes exert different impacts, with a strengthened atmospheric stratification suppressing the Atlantic Bjerknes feedback, an influence offset in the Pacific by an eastward shift of deep convection due to Niño‐like SST warming. Such offset is absent in the Atlantic owing to the northern‐hemisphere‐located deep convection.

The ocean acts as a major buffer of global warming by absorbing approximately 90% of heat surplus over the past half century. An in‐depth knowledge of dynamical processes underpinning the ocean heat uptake (OHU) is crucial for accurately projecting anthropogenic climate changes. Mesoscale eddies contribute importantly to heat transport in the ocean, but their effects on the OHU remain poorly understood. Based on a high‐resolution climate simulation from a community earth system model, we find that mesoscale eddy vertical heat transport (EVHT), upward at the climatological mean state, is projected to weaken under global warming. This corresponds to an anomalous downward heat transport, facilitating the ocean absorption of heat surplus from the atmosphere and its storage in the deep ocean. Numerical sensitivity experiments suggest that the anthropogenic EVHT change could contribute to about 20% of the OHU by the end of the 21st century under a high carbon emission scenario.

Based on the high- and low-resolution Community Earth System Model, version 1 (CESM1), and corresponding simulations from phase 6 of the Coupled Model Intercomparison Project (CMIP6), we compare the interannual variability of the East Asian summer monsoon (EASM). The EASM interannual variability is characterized by the anomalous western North Pacific anticyclone (WNPAC) circulation and the dipole rainfall pattern with a negative southern lobe over the western North Pacific and a positive northern lobe along the Meiyu–Baiu region, which is better reproduced by the high-resolution models. The reason for the improvement in the high-resolution models has been attributed to the better simulation of the warm temperature advection from the wind anomalies on the climatological temperature gradient. Positive sea surface temperature (SST) anomalies over the tropical Indian Ocean are the key to the improved wind anomalies featuring a WNPAC in the high-resolution models. The warm SST anomalies over the tropical Indian Ocean strengthen the WNPAC by triggering a Kelvin-wave response to the enhanced heat release induced by the increased precipitation. Based on the mixed-layer heat budget analysis, the warm SST anomalies over the western Indian Ocean in the high-resolution CESM1 are tied to the anomalous easterly wind along the equator, which reduces surface evaporation and upwelling. Therefore, the better simulations of air–sea feedback and the oceanic mesoscale eddy over the western Indian Ocean are the key for the improved simulation of the EASM interannual variations in the high-resolution CESM1.

Abstract Marine heatwaves (MHWs) are prolonged extreme warm water events, threatening marine ecosystems. Understanding drivers of MHWs over the global ocean is essential for their forecast. Here, we use an eddy‐resolving coupled global climate model with improved realism of MHWs to evaluate the drivers of MHWs at different spatial scales, that is, MHWs defined based on temperature anomalies at different spatial scales. The properties of MHWs are scale‐dependent, being generally weaker, less frequent, and longer with increasing spatial scales. The primary driver of MHWs shifts from local oceanic intrinsic advection to atmospheric forcing as their spatial scale becomes larger. The transition spatial scale between the ocean and atmosphere‐driven regimes varies geographically, being larger in eddy‐rich regions but smaller in gyre interior. This study suggests the complicated dynamics of MHWs at different spatial scales and provides guidance on improving their forecast capacity.

Subtropical western boundary currents (WBCs) are among the most energetic currents in the global circulation system and play an important role in the oceanic meridional heat transport (OHT). Based on nine high-resolution global coupled climate models, this study investigates the change of OHT by subtropical WBCs (WHT) under global warming. We found that WHT in both hemispheres depicts a weakening trend during 1950–2050, primarily caused by the transport change of WBCs. In the Northern Hemisphere, weakening of the Gulf Stream resulting from the slowing AMOC leads to the hemispheric WHT weakening. In the Southern Hemisphere, the WHT decrease is mainly induced by the sharp decline of Agulhas Current transport, associated with the change in wind field in the southern Indian Ocean and Indonesian Throughflow. Compared to the mean flow, the contribution of mesoscale eddies to OHT change is negligible along with WBCs but is important in their extension regions.

Abstract The response of upwelling in the eastern boundary upwelling systems (EBUSs) to anthropogenic climate change has attracted much scientific attention due to its core role in nourishing marine ecosystems. A decade‐old hypothesis suggests that greenhouse warming may intensify upwelling‐favorable winds and subsequently the upwelling in EBUSs, but the impact of greenhouse warming on the seasonal cycle of upwelling remains unknown. Using the recent generation of global climate simulations under a high carbon emission scenario, we show a universal weakening of the upwelling seasonal cycle in the major EBUSs. This is mainly ascribed to the projected weakened seasonal cycle of the upwelling‐favorable winds. In addition, long‐term changes in geostrophic transport exert a nonnegligible contribution to the changes in the upwelling seasonal cycle. Our study suggests that the upwelling in the EBUSs is likely to have a more complicated response to greenhouse warming than previously thought.

Extreme atmospheric rivers (EARs) are responsible for most of the severe precipitation and disastrous flooding along the coastal regions in midlatitudes. However, the current non-eddy-resolving climate models severely underestimate (~50%) EARs, casting significant uncertainties on their future projections. Here, using an unprecedented set of eddy-resolving high-resolution simulations from the Community Earth System Model simulations, we show that the models' ability of simulating EARs is significantly improved (despite a slight overestimate of ~10%) and the EARs are projected to increase almost linearly with temperature warming. Under the Representative Concentration Pathway 8.5 warming scenario, there will be a global doubling or more of the occurrence, integrated water vapor transport and precipitation associated with EARs, and a more concentrated tripling for the landfalling EARs, by the end of the 21st century. We further demonstrate that the coupling relationship between EARs and storms will be reduced in a warming climate, potentially influencing the predictability of future EARs.

Marine heatwaves (MHWs) exert devastating impacts on ecosystems and have been revealed to increase in their incidence, duration, and intensity in response to greenhouse warming. The biologically productive eastern boundary upwelling systems (EBUSs) are generally regarded as thermal refugia for marine species due to buffering effects of upwelling on ocean warming. However, using an ensemble of state-of-the-art high-resolution global climate simulations under a high carbon emission scenario, here we show that the MHW stress, measured as the annual cumulative intensity of MHWs, is projected to increase faster in the Southern Hemisphere EBUSs (Humboldt and Benguela current systems) than in their adjacent oceans. This is mainly because the additional warming caused by the weakened eastern boundary currents overwhelms the buffering effect of upwelling. Our findings suggest that the Southern Hemisphere EBUSs will emerge as local hotspots of MHWs in the future, potentially causing severe threats to the ecosystems.

Since the severe haze pollution events in early 2013 across China,strong actions have been taken to reduce anthropogenic emissions[1],leading to a subsequent decrease in fine particulate matter[2].In contrast,ozone concentrations in China have tended to increase in recent years[3].Elsewhere,elevated near-surface ozone pollutes many parts of the world,exerting consequential impacts on human health in ozone-prone regions[4],including eastern China,the eastern United States,and Europe.