Seasonal distribution of radiative contributions to climate feedback strengths

Description

The 2xCO2 climate sensitivity is controlled by the strength of climate feedbacks, which can act to amplify or dampen the CO2 forcing. Traditionally, model climate feedback sensitivity parameters are defined in terms of global annual mean TOA net flux radiative perturbations driven by model climate responses: water vapor, temperature, cloud properties, and surface albedo. Little attention has been given to the distributions of these radiative perturbations throughout the annual cycle. Therefore, the annual cycle of radiative contributions to climate feedbacks will be investigated here using the partial radiative perturbation (PRP) methodology. Monthly mean model output was generated from a simulation of the NCAR CCSM3.0 forced with the SRESA1B emissions scenario. It was found that the TOA radiative perturbations show significant month-to-month variability with different annual cycle structures for each feedback. In addition, it was found that April and December are the least and most sensitive months, respectively, indicating that the simulated annual cycle influences the final climate sensitivity. The representativeness of model-derived annual cycle of climate feedback radiative perturbation to the expected climate system response is contingent on the model’s ability reproduce the observed annual cycle. As a result, the annual cycle of various NCAR CCSM3.0 radiative quantities will be compared against satellite radiometric observations from the Clouds and Earth Radiative Energy System (CERES) instrument in conjunction with radiative flux measurements from the ARM SGP site. Comparing observations with model annual cycle in conjunction with radiative perturbations and feedback strengths allows for the investigation of possible links between monthly variability, climate feedbacks, and climate sensitivity.