资源环境科技发展态势分析平台

The degree of physical-biogeochemical equilibration of the climate system determines for how long global warming will continue after anthropogenicCO2 emissions have ceased. The physical part of this equilibration process is quantified by the realized warming fraction (RWF), butRWFestimates differ strongly between different climate models. Here we analyze theRWFspread and its physical causes in three model ensembles: 1. an ensemble of comprehensive climate models, 2. an ensemble of reduced-complexity models, and 3. an observationally constrained parameter ensemble of the Bern3D-LPX reduced-complexity model. Weshow thatRWFis generally lower in models with higher equilibrium climate sensitivity. TheRWFuncertainty from applying different extrapolation methods for climate sensitivity is substantial, but smaller than the inter-model spread in the three ensembles. Wedecompose the inter-model spread ofRWFusing a diagnostic global energy balance model, to compare the spread contribution by the climate sensitivity to contributions by other physical quantities: the efficiency and efficacy of ocean heat uptake, and the effective radiative forcing. In the ensembles of the comprehensive climate models and the Bern3D-LPX model, the spread of theRWF is mostly determined by the spread of the climate sensitivity; for the reduced-complexity models, the spread contribution by the ocean heat uptake efficiency is dominant. Compared to the comprehensive models, the reduced-complexity models have a lower range of climate sensitivities and lower, more unitary ocean heat uptake efficacies, resulting in higher RWF. However, by tuning such models to higher climate sensitivities, they can also achieveRWFvalues in the lower range of comprehensive models, as demonstrated for Bern3D-LPX. This suggests that reduced-complexity models remain useful tools for future climate change projections, but should employ a range of climate sensitivity tunings to account for the uncertainty in both the long-term warming and the RWF.