Energy budgets and transports: global evolution and spatial patterns during the twentieth century as estimated in two AMIP-like experiments

Abstract

This study describes characteristics and evolution of the residual of the Earth energy budget (EB) individual components and the implied meridional transports during the twentieth century. This analysis considers two ensembles of AMIP-like experiments (Atmospheric Model Intercomparison Project) with prescribed evolution of sea surface temperature and sea ice concentration (SST-SIC), greenhouse gases (GHG), anthropogenic and volcanic aerosols over the entire twentieth century: ERA-20CM and ECHAM5-HAM model simulations. With the latter, additional sensitivity experiments are carried out by constraining either SST-SIC or aerosols to climatological values. The two models provide compatible estimates of the EBs and implied transport absolute values in recent decades. They are not in agreement in terms of global scale evolution: in the 1970s ERA-20CM shows a fast transition from negative to positive EBs at top of atmosphere (TOA) that is not found in ECHAM5-HAM. Climatological SST-SIC sensitivity experiments evidence that the aerosol forcing affects TOA and surface EBs by setting up an inter-hemispheric gradient after 1960. This is also reflected by an increased total transport in the Northern Hemisphere, while decreased in the Southern Hemisphere. ERA-20CM shows no evidence of a similar aerosol forcing. Sensitivity experiments with fixed pre-industrial aerosols show that transient SST are responsible for irregular spatio-temporal anomalies of surface and atmospheric EBs and transports. Surface and atmospheric anomalies oppose each other, and transient SSTs do not influence the EB changes at TOA. Impact of transient SST and GHG forcing on EBs and implied transports are robust across the two models.