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Abstract Climate models predict a slowing of the atmospheric overturning circulation with warming. In models, this slowing manifests primarily as a weakening of the Walker Circulation (WC). However, observational studies indicate a strengthened Pacific WC over the past several decades, raising questions about the models' ability to represent critical energetic and hydrologic constraints responsible for the predicted weakening. This discrepancy is closely tied to differences in the warming pattern over the Pacific during this period. We show that model simulations with either observed or model‐projected warming patterns predict a robust weakening of atmospheric overturning circulation, despite having opposing changes in the Pacific WC strength. This weakening occurs in the zonally asymmetric circulation, rather than in the zonal‐mean Hadley cell. Weakening inferred from satellite observations is reproduced in coupled models only when anthropogenic forcing is included, suggesting that a human‐induced weakening of the global atmospheric circulation is already detectable in observations.

Abstract This study investigates how climate sensitivity depends upon the spatial pattern of radiative forcing. Sensitivity experiments using a coupled ocean‐atmosphere model were conducted by adding anomalous incoming solar radiation over the entire globe, Northern Hemisphere mid‐latitudes, Southern Ocean, and tropics. The varied forcing patterns led to highly divergent climate sensitivities. Specifically, the climate is nearly twice as sensitive to Southern Ocean forcing as tropical forcing. Strong coupling between the surface and free troposphere in the tropics increases the inversion strength, leading to smaller cloud feedback in the tropical forcing experiments. In contrast, the extratropics exhibit weaker coupling, a decrease or near‐zero change in the inversion strength, and strong positive cloud feedback. These results contrast with the conventional SST‐pattern effect in which tropical surface temperature changes regulate climate sensitivity. They also have important implications for other potentially asymmetric forcings, such as those from geoengineering, volcanic eruptions, and paleoclimatic changes.

Abstract Ocean heat uptake (OHU) plays an important role in determining the rate of surface warming under CO2 forcing. We examined the transient response to CO2 forcing in a set of 30 climate models from Coupled Model Intercomparison Project Phase 6 (CMIP6) and found that the intermodel spread in OHU efficiency largely depends on the base‐state ocean stratification, especially in the Southern Ocean. This dependence is primarily traced to ocean salinity rather than ocean temperature. Models with weaker ocean stratification primarily due to higher upper‐ocean salinity tend to sequester heat into the deeper ocean, leading to a lower rate of surface warming, a primary reason for higher OHU efficiency; the stratification impact on total OHU is secondary. We applied the relationship between salinity and OHU efficiency for an emergent constraint on OHU efficiency, suggesting an OHU efficiency higher than the CMIP6 multimodel average and arguing against models with extremely low efficiency.

Abstract It is widely believed that precipitation extremes will increase in response to a warming climate, as inferred from both observations and numerical simulations. In the absence of changes in atmospheric circulations, extreme precipitation is expected to increase in already‐moist regions along a thermodynamical Clausius‐Clapeyron scaling. However, within the tropics, the sensitivities inferred from observations of interannual variability are roughly twice as large, implying an unknown contribution from atmospheric dynamics. In this paper, we use satellite observations and climate model simulations to investigate the relationship between convective aggregation and precipitation and the role that convective aggregation plays in amplifying the response of tropical precipitation extremes to interannual surface warming. We find that the occurrence of heavier precipitation coincides with a higher degree of convective aggregation. Extreme precipitation events and convective aggregation tend to increase during warm, El Niño events compared to colder, La Niña events. Although both the frequency and intensity of heavy to extreme precipitation can increase with increased aggregation during El Niño, the changes in frequency are more consistent among the observations and models than changes in intensity. In both the observations and models, increases in large‐scale convective aggregation contribute to roughly one third of the increase in extreme precipitation frequency due to interannual warming by shifting moderate‐to‐heavy precipitation events to more extreme precipitation intensities. The linkages between convective aggregation and precipitation extremes considered here offer insights into their potential response to anthropogenic warming.