Evaluation of the Arctic Surface Radiation Budget in CMIP5 Models

The Arctic region is warming at a rate more than double the global average. This trend is predicted to continue in the coming decades as simulated in the Coupled Model Intercomparison Project 5 (CMIP5) climate projections. Despite the consistency in the projected Arctic warming rate relative to the globe, significant inter-model spread is found in the simulated present-day Arctic surface temperature and the warming response to increased CO2. The representation of the surface radiation budget is a key factor in the simulation of the Arctic climate system. The goal of this paper is to evaluate the representation of the Arctic surface radiation budget in CMIP5 and investigate the influence of these biases on the simulated present-day Arctic climate. First, the Arctic surface radiation budget CMIP5 Historical-forcing scenario for 17 models is evaluated against Cloud and Earth's Radiant Energy System (CERES) surface radiative fluxes for the annual mean and seasonal cycle. The CMIP5 multi-model ensemble is found to simulate longwave surface fluxes well during the sunlit months but produce wintertime values that are less than observations. Shortwave fluxes show substantial across-model spread during summer. Second, the independent column approximation (ICA) is used to attribute the radiative flux biases to clear-sky, cloudy-sky, and cloud fraction contributions. Lastly, the surface radiation budget biases are used to explain the biases in simulated present day Arctic surface temperature