Energy-balance and circulation controls of consistent large-scale temperature responses in warm and cold climates

The Coupled Modelling Intercomparison Project Phase 5 (CMIP5), which requires the same version of models for paleo, historical, and future simulations, combined with large-scale paleoclimatic data syntheses (e.g., the Multiproxy Approach for the reconstruction of Glacial Ocean (MARGO) project, and the quantitative climate reconstructions based on the pollen and plant macrofossil data) allow diagnostic analyses of the mechanisms responsible for the large-scale spatial patterns of temperature that consistently occur in simulations of warm and cold climates. Comparison with the large-scale temperature changes shown by historical observations and by paleoclimate reconstructions also allows us to determine the realism of these responses. We have examined temperature responses in several CMIP5 experiments (lgm, midHolocene, historical, 1pctCO2, and abrupt4xCO2), and used six models (IPSL-CM5A-LR, MPI-ESM-P, MIROC-ESM, CCSM4, MRI-CGCM3, and GISS-E2-R). The simulations show major patterns of past and modern climates changes including 1) the differential response of land-ocean to warming/cooling, 2) the tendency for temperature changes in the higher latitudes to be more extreme than changes in the tropics, and 3) the amplification of seasonality in both warmer/cooler climates. The consistency among simulated and observed large-scale temperature responses shows that these are features of the real climate system that are simulated successfully by models. Moreover, consistency in the simulated patterns of past (e.g., lgm) and future (e.g., abrupt4xCO2) temperature changes implies that a small set of common mechanisms controls the response of the climate system across multiple states. In this study, we explore the key controls for the three large-scale temperature responses in both warmer and cooler climates using a simple energy balance model and analyses of atmospheric circulation changes. Overall, across the range of simulations, variations in clear-sky downward longwave radiation are responsible for the patterns in large-scale temperature anomalies, and in the lgm simulation, this mechanism is augmented by surface albedo feedback.