Abstract
Inquiry into the climate response to external forcing perturbations has been the central interest of climate dynamics. But the understanding of two important aspects of climate change response—nonlinearity and regionality—is still lacking. Here a Green’s function approach is developed to estimate the linear response functions (LRFs) for both the linear and quadratic nonlinear response to ocean thermal forcing in a climate model, whereby the most excitable temperature modes, aka the neutral modes, can be identified for the current Earth climate. The resultant leading mode of the nonlinear response is characterized by a polar-amplified global cooling pattern, unveiling an intrinsic inclination of the modern climate towards cooling. Moreover, optimal forcing patterns are identified to most efficiently excite the corresponding neutral mode patterns. The forcing-response framework developed herein can be utilized to determine the optimal forcing patterns to inform solar geoengineering experiments and to interpret regional climate response and feedback in general.
Highlights
Equilibrium climate sensitivity concerning how much the global mean surface temperature increases in response to a doubling of the concentration of carbon dioxide (CO2) has been the central focus of climate research
Published in partnership with CECCR at King Abdulaziz University energy convergence induced by ocean circulation, and the same amplified pattern for the linear and nonlinear response is strongly amount of energy is passed to the overlying atmosphere as the implicative of a mode behavior intrinsic to the climate system
The approach used here for estimating the linear response functions (LRFs) is empirical, the resultant neutral modes reflect the deterministic physical and dynamical constraints built into the climate model
Summary
Equilibrium climate sensitivity concerning how much the global mean surface temperature increases in response to a doubling of the concentration of carbon dioxide (CO2) has been the central focus of climate research. Climate change response is not uniform, exhibiting considerable regional heterogeneity even if the forcing is uniform[1]. Predicting regional climate change response is one of the grand challenges to the climate community[1,4,5], while confidence in regional climate projection is sorely needed for climate mitigation and adaptation planning. The climate community is only beginning to tackle the challenge of regionality from the perspective of dynamical system[6,7] to understand and quantify the systematic relationships between the response and the forcing, each being geographically varying, to improve climate projection and confidence therein. This study stands as a pilot effort towards systematically linking the regional thermal forcing around globe to the global temperature through building linear response relationships and performing neutral mode analysis. As to be demonstrated later, such an effort may potentially be beneficial for exploring geoengineering experiments[8,9] for achieving the optimal cooling effect
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