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Symmetric and Antisymmetric Components of Polar-Amplified Warming
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2022
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Source: J. Climate, 35, 6757–6772
[PDF-2.36 MB]
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Journal Title:Journal of Climate
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Description:CO2-forced surface warming in general circulation models (GCMs) is initially polar amplified in the Arctic but not in the Antarctic—a largely hemispherically antisymmetric signal. Nevertheless, we show in CESM1 and 11 LongRunMIP GCMs that the hemispherically symmetric component of global-mean-normalized, zonal-mean warming (T∗sym) under 4 × CO2 changes weakly or becomes modestly more polar amplified from the first decade to near-equilibrium. Conversely, the antisymmetric warming component (T∗asym) weakens with time in all models, modestly in some including FAMOUS, but effectively vanishing in others including CESM1. We explore mechanisms underlying the robust T∗sym behavior with a diffusive moist energy balance model (MEBM), which given radiative feedback parameter (λ) and ocean heat uptake (O) fields diagnosed from CESM1 adequately reproduces the CESM1 T∗sym and T∗asym fields. In further MEBM simulations perturbing λ and O, T∗sym is sensitive to their symmetric components only, and more to that of λ. A three-box, two-time-scale model fitted to FAMOUS and CESM1 reveals a curiously short Antarctic fast-response time scale in FAMOUS. In additional CESM1 simulations spanning a broader range of forcings, T∗sym changes modestly across 2–16 × CO2, and T∗sym in a Pliocene-like simulation is more polar amplified but likewise approximately time invariant. Determining the real-world relevance of these behaviors—which imply that a surprising amount of information about near-equilibrium polar amplification emerges within decades—merits further study.
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Source:J. Climate, 35, 6757–6772
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