Neutral Mode Dominates the Forced Global and Regional Surface Temperature Response in the Past and Future. Issue 15 (6th August 2022)

• Record Type: Journal Article
• Authors: Liu, Fukai; Lu, Jian; Leung, L. Ruby
• Is Part Of: Geophysical research letters. Volume 49:Issue 15(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-06
• Subjects: global warming -- climate sensitivity -- neutral mode -- optimal forcing; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL098788
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Using a large suite of Green's function perturbation experiments, we construct the emergent dynamical operator for surface temperature and extract the most excitable mode. The leading mode turns out to be the most dominant mode excited by the climate forcing of doubling CO2, alone capturing 56% of the total spatial variances of the surface temperature response. The pattern of the leading mode is partly organized by the atmospheric annular modes in both hemispheres, and further modulated by the feedbacks from ocean circulations. Though derived from a single model, the leading mode can capture the spatio‐temporal variabilities of the global mean surface temperature over the past century in both the CMIP6 model simulations and observations. Moreover, the leading mode is most efficiently excited by radiative forcings from the midlatitude bands centered around 45°N and 25°S, where most human activities take place, suggesting the potency of human influence on the climate change. Plain Language Summary: Confidence in the regional features of climate change projections is a prized commodity for climate adaptation and mitigation. This study strives to decipher the pattern of the forced climate response using a dynamical mode‐based framework such that certain confidence may be established for regional climate projections. The dynamical modes, also known as the neutral modes, are extracted through singular value decomposition of the linear response function of a coupled climate model using a large suite of Green's function perturbation experiments. The leading mode turns out to be the most dominant mode excited by anthropogenic climate forcing, capturing the global mean surface temperature evolution over the past century in both observations and multi‐model simulations, lending confidence to the regional climate change features captured by the leading mode. Coincidentally, the leading mode is most efficiently excited by radiative forcings from the midlatitude bands centered around 45°N and 25°S where human activities are most prominent. Key Points: Green's function experiments are used to extract the most excitable modes and optimal forcing of surface temperature variability The leading mode can capture the spatial‐temporal structure of the surface temperature variability over the past century Midlatitude radiative forcings due prominently to the human activities are effective in inducing global‐scale surface temperature changes