Qinghua Ding

Antarctic mass loss has been a major contributor to global sea-level rise for most of the last few decades, mainly driven by West Antarctica ¹ . During 2021–2023, however, a sharp increase in surface mass balance over Queen Mary Land and Wilkes Land in East Antarctica offset West Antarctic loss and slowed the rate of total ice mass loss ^2,3 . Although this slowdown is consistent with the expected long-term precipitation response to global warming through poleward-shifted storm tracks and Antarctic moistening ⁴ , our results point to a different mechanism. Here we show that the recent ice mass gain was linked to a recurrent atmospheric teleconnection driven by sea surface temperature anomalies in the tropical warm pool, which experienced unusually persistent warming from 2021 to 2023 relative to the previous two decades. On the basis of observations and model experiments, we find that tropical warm pool warming excites a poleward-propagating Rossby-wave train that induces a high-pressure anomaly over East Antarctica, enhancing Queen Mary Land and Wilkes Land precipitation and driving the observed mass gain, with moisture primarily sourced from the mid-latitude Indian Ocean. Similar multiyear warming in the tropical warm pool recurs about once per decade in observations and historical simulations, and its influence on precipitation is distinct from the effects of global warming. Therefore, the recent Antarctic Ice Sheet mass gain is probably temporary and does not yet reflect a sustained, global-warming-driven moistening of Antarctica.

Arctic sea ice has declined at sharply contrasting rates over the past four decades—modest before 2000 and rapid thereafter. Using observational and model evidence, we show that large tropical volcanic eruptions can trigger decade‐long Arctic sea ice recoveries, and that without the 1982 El Chichón and 1991 Pinatubo eruptions, Arctic sea ice would have declined approximately 1.5 times faster before 2000. We further show a model's sensitivity to volcanic aerosol forcing scales with its sensitivity to GHG forcing across CMIP6 models, offering a new strategy to identify models with realistic climate response to radiative forcing. Following this, a selected subgroup of models that accurately simulate long‐term warming trend and decade‐long post‐Pinatubo recovery project ice‐free Arctic summer up to 20 years earlier than the full ensemble. These findings underscore the critical, yet underappreciated, importance of evaluating climate models against anthropogenic and volcanic forcing when projecting the future of Arctic sea ice.

As the global climate has warmed anthropogenically over the past decades, the atmosphere across most of the globe has experienced significant moistening, except for a “moistening hole” (MH) -like change over the Western U.S. This regional anomaly since 1980 is at odds with the forced response of climate models to global warming in this region. Here, through analysis of a wide array of observations and water-tagging enabled simulations, we find that atmospheric forcing originating from the North Pacific contributes to the MH. A barotropic high-pressure circulation trend over the North Pacific, driven by observed sea surface temperature cooling in the tropical Eastern Pacific, enhances atmospheric sinking over the Western U.S. through equatorward cold air advection. This intensified atmospheric descent suppresses precipitation and weakens land-sourced evaporation, which are critical for replenishing atmospheric moisture in the region. We suggest that focusing on low-frequency changes of atmospheric vertical motion may offer insights into assessing and projecting climate stress and drought risks posed by long-term atmospheric moisture deficits in arid regions.

We present the first results of the Water Isotope Model Intercomparison Project (WisoMIP), with Phase 1 focused on modern simulations (1979–2023) from a suite of isotope-enabled atmospheric general circulation models nudged to ERA5 reanalyses. Water sources, mixing, and rainout history influence the isotopic composition of vapor and precipitation, making these simulations powerful tools for tracing the global water cycle. By prescribing identical winds, sea surface temperatures, and sea ice conditions, we isolate differences in water isotope behavior across models, controlling for variability in atmospheric dynamics and mean climate. Our analyses show that the ensemble mean best matches observations, as individual model errors cancel out to yield a more accurate representation of Earth's isotope distributions. We also evaluate trends and responses to major climate modes during the recent warming period, highlighting regional and temporal sensitivities in the isotope signals. These diagnostics extend beyond traditional model evaluation metrics (e.g., temperature, precipitation) to reveal uncertainties in physical processes and guide improvements in model parameterizations. The resulting modern nudged ensemble dataset serves as a benchmark for isotope-enabled model development, satellite product comparison, and understanding of water cycle changes in a warming climate. Given its standardized design and broad participation, WisoMIP provides a valuable "isotope reanalysis" product for applications ranging from paleoclimate reconstruction to model tuning. Our work demonstrates the importance of coordinated isotope model evaluation in advancing the use of water isotopes as a diagnostic tool in climate science.

We present the first results of the Water Isotope Model Intercomparison Project (WisoMIP), with Phase 1 focused on modern simulations (1979–2023) from a suite of isotope‐enabled atmospheric general circulation models nudged to ERA5 reanalyses. Water sources, mixing, and rainout history influence the isotopic composition of vapor and precipitation, making these simulations powerful tools for tracing the global water cycle. By prescribing identical winds, sea surface temperatures, and sea ice conditions, we isolate differences in water isotope behavior across models, controlling for variability in atmospheric dynamics and mean climate. Our analyses show that the ensemble mean best matches observations, as individual model errors cancel out to yield a more accurate representation of Earth's isotope distributions. We also evaluate trends and responses to major climate modes during the recent warming period, highlighting regional and temporal sensitivities in the isotope signals. These diagnostics extend beyond traditional model evaluation metrics (e.g., temperature, precipitation) to reveal uncertainties in physical processes and guide improvements in model parameterizations. The resulting modern nudged ensemble data set serves as a benchmark for isotope‐enabled model development, satellite product comparison, and understanding of water cycle changes in a warming climate. Given its standardized design and broad participation, WisoMIP provides a valuable “isotope reanalysis” product for applications ranging from paleoclimate reconstruction to model tuning. Our work demonstrates the importance of coordinated isotope model evaluation in advancing the use of water isotopes as a diagnostic tool in climate science.

The primary sources of recent summer Arctic moistening trends in reanalysis are uncertain, hindering attribution of observed Arctic warming due to radiative effects from water vapor changes. Here, we use a combined online numerical water tracer and circulation nudging approach in the Community Earth System Model to track the sources of water vapor beyond its initial sources. Trends in boreal summer large-scale circulation have driven moistening of the Arctic over recent decades, having a large impact on the Arctic radiative budget, accounting for 94% of the strengthening water vapor radiative feedback. We identify two key regions supplying the Arctic water vapor feedback: Northeast North America and western/central Eurasia. In both regions, anticyclonic circulations over the southwest Atlantic and eastern Europe move moisture from the tropical oceans poleward to high latitude land through precipitation in winter and spring. During summer, evapotranspiration over land releases this water vapor, and it is transported by winds into the Arctic. We refer to this sequence of terrestrial moisture storage and release as the land capacitor effect. Thus, the impacts of circulation changes on poleward moisture transport and land-atmosphere interactions over high latitudes represent the underlying mechanisms of the recent moistening and warming in the Arctic.

The Arctic is a prime example of global climate change, experiencing shifts on an unparalleled scale. This review summarizes the current state of knowledge on long-term changes and variations—both historical and projected—in the oceanic and sea ice components of the Arctic climate system. Using observations and modeling results, it examines the role of climate variability modes, from multidecadal to seasonal time scales, in shaping the Arctic climate. Emphasis is placed on the interconnectivity between Arctic system components, with a focus on feedbacks (including newly emerging ones), pathways, and processes that link long-term changes and variations in the oceanic and sea ice systems. The review also explores the relationships of Arctic climate change and variability with atmospheric forcing and sub-Arctic regions. It provides a critical assessment of the roles of natural variability and human-induced climate change, as well as projections for the future. Understanding these changes and their drivers is crucial for assessing the Arctic’s role in the global climate system.

Significant dynamical control of three seasonal-mean large-scale circulation modes, known as the Pacific–North American (PNA), West, and South modes, on winter precipitation over the contiguous United States (CONUS), through regulating atmospheric river (AR) frequency, is evident in reanalysis. The PNA mode affects changes in precipitation and the frequency of ARs over the Pacific Northwest, Midwest United States, and Florida, while the West and South modes influence the western and southern United States, respectively. The capability of operational seasonal forecast models to replicate these modes remains unclear, and evaluating their skill in this specific aspect is our primary goal. To achieve this, two operational model ensembles, the European Centre for Medium-Range Weather Forecasts’ fifth generation seasonal forecast system (SEAS5) and the National Centers for Environmental Prediction’s Climate Forecast System, version 2 (CFSv2), are assessed to gauge their overall skill in forecasting the observed compound effects of large-scale circulation and ARs on CONUS winter precipitation. We find that the two models, initialized on 1 December, are able to capture some spatial features of the observed modes during December–February (DJF). However, they fail to reproduce their temporal variations, especially those associated with the West mode, because in reality, it is directly driven by barotropic instability related to the subtropical jet stream over the North Pacific. This inherent limitation, arising from the West mode’s insensitivity to slowly varying sea surface temperature changes, constrains models’ skill in DJF precipitation forecasts over the western United States. Significance Statement: We evaluate the performance of two seasonal forecast systems in predicting the leading three large-scale circulation modes across the contiguous United States, given their crucial role in shaping winter precipitation variations by modulating atmospheric river activity. The West mode significantly impacts winter precipitation variability over the western United States (U.S.), while both models struggle to accurately forecast its observed variations and thus perform poorly in predicting western U.S. precipitation. This difficulty results from the internal origin of the West mode. These factors indicate that western U.S. precipitation may be highly unpredictable in the setting of current seasonal forecasts, reflecting both the inherently limited predictability of precipitation over the region and the models’ biases in simulating the internal characteristics of the West mode.

Atmospheric rivers (ARs) in winter can induce significant melting of sea ice as they approach the ice cover. However, due to the complex physical properties of sea ice, the specific processes within the ice pack that are responsible for its response to ARs remain poorly understood. This study aims to shed light on this question using a stand‐alone sea ice model forced by observed atmospheric boundary conditions. The findings reveal that the AR induced ice melt and hindered ice growth in the marginal seas are attributed to a combination of thermodynamic and dynamic processes. The AR‐wind transports ice floes from the marginal seas back to the central Arctic dynamically, resulting in a thickening of the ice cover in that region. Among the thermodynamic processes, reduced congelation growth (54%–56%), enhanced basal melting (17%–26%), and inhibited snow‐ice formation (11%–21%) play major roles in the sea ice loss in the marginal seas.

The hydrological cycle in South America during austral summer, including extreme precipitation and floods, is significantly influenced by northerly low-level jets (LLJs) along the eastern Andes. These synoptic weather events have been associated with three different types of LLJs (Central, Northern, and Andes) and are sensitive to remote large-scale forcings. This study investigates how tropical forcings related to El Niño/Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) regulate the duration and frequency of each LLJ type and their impacts on extreme precipitation. Our analysis reveals that ENSO and PDO are important in driving the variability of LLJs over the past 65 years. Specifically, the Central LLJ type is more prevalent during El Niño and Warm/Neutral PDO phases, leading to heightened extreme precipitation in southern South America. Conversely, La Niña years during Cold PDO phases tend to favor the Northern and Andes LLJs, which are associated with increased precipitation extremes in the western Amazon and southeastern South America. Central and Andes LLJs tend to persist longer during these favored conditions, causing more pronounced precipitation events in the areas under their influence. This study enhances our understanding of the influence of large-scale atmospheric forcings on the regional precipitation dynamics in South America.