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    Atmospheric and hydrospheric sciences

    201607201607

    A review of progress towards understanding the transient global mean surface temperature response to radiative perturbation

    Yoshimori M, Watanabe M, Shiogama H, Oka A, Abe-Ouchi A, Ohgaito R, Kamae Y

    Transient climate response, Equilibrium climate sensitivity, Climate feedback, Ocean heat uptake efficacy, Efficacy of forcing

    Relation between global mean surface air temperature and top-of-the-atmosphere net radiation changes from the preindustrial control simulation in the MIROC3.2 (medres) atmosphere-ocean general circulation model experiments. Black crosses: 1pctCO2 experiment (every year for 1-140 years); blue crosses: abrutp4xCO2 experiment (every year for 1-150 years), red crosses: const4xCO2 experiment (every 20-year average for 141-3680 years); blue line: linear regression for the 150-year abrupt4xCO2 experiment; Blue circles: equilibrium temperature response to 4xCO2 estimated by Gregory’s method for 10 abrupt4xCO2 20-year-long ensemble experiments (that start from different initial conditions in the preindustrial control simulation).

    The correct understanding of the transient response to external radiative perturbation is important for the interpretation of observed climate change, the prediction of near-future climate change, and committed warming under climate stabilization scenarios, as well as the estimation of equilibrium climate sensitivity based on observation data. It has been known for some time that the radiative damping rate per unit of global mean surface temperature increase varies with time, and this inconstancy affects the transient response. Knowledge of the equilibrium response alone is insufficient, but understanding the transient response of the global mean surface temperature has made rapid progress. The recent progress accompanies the relatively new concept of the efficacies of ocean heat uptake and forcing. The ocean heat uptake efficacy associates the temperature response induced by ocean heat uptake with equilibrium temperature response, and the efficacy of forcing compares the temperature response caused by non-CO2 forcing with that by CO2 forcing.

    In this review article, recent studies on these efficacies are discussed, starting from the classical global feedback framework and basis of the transient response. An attempt is made to structure different studies that emphasize different aspects of the transient response and to stress the relevance of those individual studies. The implications on the definition and computation of forcing and on the estimation of the equilibrium response in climate models are also discussed. Along with these discussions, examples are provided with MIROC climate model multi-millennial simulations