Abstract
AbstractThe equilibrium climate sensitivity (ECS) in the latest version of CNRM climate model, CNRM‐CM6‐1, and in its high‐resolution counterpart, CNRM‐CM6‐1‐HR, is significantly larger than in the previous version (CNRM‐CM5.1). The traceability of this climate sensitivity change is investigated using coupled ocean‐atmosphere model climate change simulations. These simulations show that the increase in ECS is the result of changes in the atmospheric component. A particular attention is paid to the method used to decompose the equilibrium temperature response difference, by using a linearized decomposition of the individual radiative agents diagnosed by a radiative kernel technique. The climate sensitivity increase is primarily due to the cloud radiative responses, with a predominant contribution of the tropical longwave response (including both feedback and forcing adjustment) and a significant contribution of the extratropical and tropical shortwave feedback changes. A series of stand‐alone atmosphere experiments is carried out to quantify the contributions of each atmospheric development to this difference between CNRM‐CM5.1 and CNRM‐CM6‐1. The change of the convection scheme appears to play an important role in driving the cloud changes, with a large effect on the tropical longwave cloud feedback change.
Highlights
The global temperature changes in response to an externally imposed radiative perturbation or climate sensitivity is an important feature of the climate system
The change in atmospheric and oceanic horizontal resolutions has a small effect on the model response, consistent with the small dependence of climate sensitivity to horizontal resolution in the
This study highlights the evolution of equilibrium temperature response to a quadrupling of atmospheric CO2 concentration in the CNRM suite of climate models from version 5, CNRM-CM5.1 (6.5 K) to version 6, CNRM-CM6-1 (9.8 K) and its high-resolution counterpart, CNRM-CM6-1-HR (8.8 K)
Summary
The global temperature changes in response to an externally imposed radiative perturbation or climate sensitivity is an important feature of the climate system. The surface temperature response to a radiative forcing causes radiative feedbacks within the system that can amplify or dampen the temperature response (e.g., Hansen et al, 1984; Wetherald & Manabe, 1988) These radiative agents include air temperature, water vapor, surface albedo, and clouds (e.g., Soden & Held, 2006). They can change at fast time scales, adding a fast adjustment component to the instantaneous radiative forcing A commonly used method to decompose the effect of each radiative agent consists in using radiative kernels (Shell et al, 2008; Soden & Held, 2006) Using this technique, the climate sensitivity can be broken down into the sum of the different contributions associated with each radiative agent. The method used for the decomposition can significantly impact the SAINT-MARTIN ET AL
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