ZEMBA v1.0: an energy and moisture balance climate model to investigate Quaternary climate

Abstract. The Zonally Averaged Energy and Moisture BAlance (ZEMBA) climate model is introduced as a simple and computationally efficient tool for studies of the glacial–interglacial cycles of the Quaternary. The model is based on an energy balance model comprising an atmospheric layer, a land component and a two-dimensional ocean transport model with sea ice. In addition, ZEMBA replaces temperature with moist static energy for calculations of diffusive heat transport in the atmospheric layer and includes a hydrological cycle for simulating precipitation and snowfall. Prior to coupling with an ice sheet model, we present and evaluate equilibrium simulations of the model for the pre-industrial period and the Last Glacial Maximum, using prescribed land ice fractions and elevation. In addition, we test the sensitivity of ZEMBA to a doubling of the atmospheric CO2 concentration and a 2 % increase in solar radiation at the top of the atmosphere. Compared to a global climate model (the Norwegian Earth System Model version 2, NorESM2) and reanalysis data (ERA5), ZEMBA reproduces the zonally averaged climate of the pre-industrial period with reasonable accuracy, capturing features such as surface temperature, precipitation, radiative fluxes, snow cover, sea ice cover and meridional heat transport. The response of ZEMBA to increasing CO2 concentrations is qualitatively similar to the observational record and climate models of higher complexity, including polar amplification over the Northern Hemisphere and during the winter months. The globally averaged rise in surface air temperature for a doubling in CO2 is 3.6 °C. Finally, ZEMBA shows success in emulating changes in surface temperature and precipitation during the Last Glacial Maximum when compared to reconstructions and global climate models.