Sarah M. Kang

While extratropical forcing has far‐reaching effects through teleconnections, the Intertropical Convergence Zone (ITCZ) has been shown to partly block the propagation of extratropical perturbations to the opposite hemisphere. However, the influence of the ITCZ location on the tropical response and the blocking effect remain poorly understood. We investigate this using aquaplanet slab‐ocean simulations in MPI‐ESM, by imposing a southern hemispheric extratropical cooling on five control states with different background ITCZ locations. Results show that the cross‐equatorial atmospheric energy transport sensitively depends on the mean ITCZ position, with cloud radiative effects dominating this sensitivity. We also demonstrate that the ITCZ blocks the propagation of sea surface temperature anomalies to the opposite hemisphere through changes in latent heat flux, which originate from the wind response to the imposed extratropical forcing. Our findings suggest that model biases in the ITCZ location may alter the modeled climate response to high‐latitude perturbations.

Global storm‐resolving models (GSRMs) provide new opportunities to investigate the climate response to warming with explicitly resolved deep convection. However, the limited number of existing studies has so far precluded the systematic assessment of similarities and differences across GSRMs. Here, we compare the Cess sensitivity (the climate sensitivity estimated from the response of atmospheric radiation budget to uniform surface warming) of the ICOsahedral Nonhydrostatic (ICON) model with three other GSRMs and CMIP5/6 models, using AMIP and aquaplanet model experiments under uniform warming (+4 K). We find that the Cess sensitivity across GSRMs at their finest horizontal resolution ranges from 2.2 to 3.3 K, comparable to that of CMIP6 models. In ICON, the negative net climate feedback parameter and its longwave component both decrease with finer resolution, while the positive shortwave component increases. The resolution dependence of the longwave and shortwave components originates primarily from the tropics and the Northern Hemisphere extratropics, respectively.

A robust proportionality between radiative forcing and global-mean temperature has been established for most climate drivers. However, land-surface changes are considered an exception due to their potential to alter surface hydrology, introducing non-radiative effects that may rival those from surface albedo changes. Here, comparing Earth-system-model simulations with large-scale perturbations of surface albedo and water availability, we find that the spatially integrated biophysical climate impact is similarly dominated by radiative processes and scales approximately linearly with the resulting shifts in planetary albedo, implying a ~ 0.4 K surface temperature response per W m ⁻² change in top-of-atmosphere net short-wave radiation. Thus, while non-radiative effects strongly influence local temperatures, their net contribution to the global-mean signal is negligible. The planetary-albedo response is primarily governed by regional cloud-cover characteristics, resulting in a substantially stronger temperature response to land-surface change in mid- and high-latitude regions than in the tropics and subtropics.

Cloud processes constitute one of the key uncertainties for climate change projections. The fourth iteration of the Cloud Feedback Model Intercomparison Project, CFMIP4, contributes to the Coupled Model Intercomparison Project phase 7 (CMIP7), by providing a set of global climate model experiments aiming to enhance our understanding of clouds, circulation and climate sensitivity, thereby informing improved projections of future climate change. CFMIP4 targets four knowledge gaps: (1) Physical mechanisms of cloud feedback and adjustment; (2) Dependence of cloud feedback and adjustment on climate base state and on the nature of the forcing; (3) Coupled mechanisms of the sea-surface temperature “pattern effect”; and (4) Coupling of clouds with circulation and precipitation. CFMIP4 contributes four CMIP7 Assessment Fast Track experiments that are central to the quantification of climate feedback and sensitivity in past, present and future climates, essential for process understanding and model evaluation. Furthermore, CFMIP4 supports the joint analysis of models and observations through a data request that includes process and satellite simulator output.

Climate models robustly project an El Niño–like warming under rising CO ₂ , yet recent observations show the opposite with enhanced zonal SST gradients. Whether the long‐term projection is relevant for interpreting historical trends remains questionable. Using a large‐ensemble of abrupt 4xCO ₂ experiment, we identify a two‐phase transition in equatorial Pacific warming: an initial gradient strengthening followed by long‐term weakening. To isolate the underlying mechanisms, we prescribe CO ₂ forcing over discrete latitudinal bands in a model hierarchy that varies the degree to which ocean dynamics are represented. While the initial strengthening is commonly attributed to ocean dynamical thermostat associated with climatological upwelling, our equatorial forcing experiment highlights the role of ocean circulation changes. We further reveal another mechanism involving atmospheric feedbacks via Hadley cell shifts under remote Northern Hemisphere off‐equatorial forcing. These fast responses transition to weakened gradients through slow ocean adjustments. In contrast, Southern Hemisphere forcing induces a persistent gradient weakening. Our results suggest that observed SST trends may reflect a fast, forced response to CO ₂ .

The Intertropical Convergence Zone (ITCZ) strongly shapes tropical rainfall and global circulation, yet its response to carbon dioxide (CO ₂ ) forcing remains uncertain. Climate models project a long-term narrowing of the ITCZ under warming, but recent decades instead show a poleward expansion linked to eastern tropical Pacific cooling. Using a 30-member ensemble of abruptly quadrupled CO ₂ experiments, we identify a two-phase evolution: a fast expansion over the first decade, driven by basin-wide relative cooling in the equatorial Pacific, followed by a slow contraction as equatorial warming strengthens. Applying this framework to a 1%-per-year CO ₂ scenario reveals that the slow phase dominates only after ∼80 years, when the CO ₂ levels more than double relative to preindustrial, suggesting that present-day conditions are still dominated by the fast response. This potentially reconciles recent ITCZ expansion with long-term projections of contraction, underscoring the importance of accounting for timescale-dependent processes when interpreting past trends and projecting near-term climate change.

The Walker Circulation is commonly understood as driven by oceanic upwelling that cools the eastern Pacific and establishes the equatorial zonal sea-surface temperature gradient. Here we test this canonical view using an atmospheric general circulation model coupled to a slab ocean with prescribed ocean heat uptake. Contrary to this view, removing the zonal asymmetry of ocean heat uptake weakens the Walker Circulation by only 10%. In contrast, removing American land or flattening American orography strongly weakens the Walker circulation. American land and orography seed its eastern, subsiding branch by anchoring subtropical highs, promoting equatorward cold advection, and cooling the eastern Pacific. Equatorial water-vapor and cloud radiative feedbacks amplify this land-forced asymmetry. Our results identify land as a fundamental driver of the Walker Circulation and reframe it as an atmosphere-ocean-land system rather than an air-sea phenomenon alone.

Recent decades have seen persistent sea surface temperature (SST) cooling in the Southeast Pacific (SEP) and Southern Ocean (SO), contrasting with broad ocean warming expected under anthropogenic forcing. Using an interpretable machine‐learning attribution framework applied to multi‐source observations and reanalyses, we focus on monthly SST variations beyond intrinsic oceanic persistence and relate them to physical predictors. Cooling in each region is associated with distinct combinations of physical predictors. In the SO, enhanced sea‐ice variability and lower‐tropospheric circulation anomalies account for a substantial fraction of the post‐2000 cooling. In the SEP, cooling is associated with a strengthened subtropical high, thermodynamic and cloud–radiative feedbacks. A moving‐window analysis indicates asymmetric coupling, with strengthening SO‐to‐SEP association in SST variability and a relative decline in local SEP feedbacks. These results show how high‐latitude–subtropical interactions can modulate regional SST trends under global warming through circulation, sea ice, and air–sea coupling.

The unresolved recent multidecadal cooling of the eastern Pacific and its uncertain future remain key puzzles in climate dynamics. We propose the land-sea heating contrast as a potential driver of this phenomenon. To test this, we amplify the land-sea contrast by quadrupling carbon dioxide (CO ₂ ) only over land in a global coupled climate model. We show that this causes a pronounced transient cooling of the eastern and equatorial Pacific. A transient 1%-per-year CO ₂ increase over land produces decadal cooling, suggesting relevance to the observed eastern Pacific cooling. Targeted simulations with locally increased CO ₂ concentrations over different land regions reveal three drivers of this cooling: a northward intertropical convergence zone shift, a westward convection shift over the western Pacific, and strengthened subtropical highs from Rossby waves. These insights recast the commonly used ocean dynamical thermostat mechanism as a feedback rather than a driver of transient cooling and contribute to understanding and predicting Pacific temperature patterns.