Effective radiative forcing in the aerosol–climate model CAM5.3-MARC-ARG

Benjamin S. Grandey,Samuel Albani,Xiaohong Liu,Chien Wang,Daniel Rothenberg,Qinjian Jin,Zheng Lu,Alexander Avramov,Hsiang-He Lee

doi:10.5194/acp-18-15783-2018

Abstract

Abstract. We quantify the effective radiative forcing (ERF) of anthropogenic aerosols modelled by the aerosol–climate model CAM5.3-MARC-ARG. CAM5.3-MARC-ARG is a new configuration of the Community Atmosphere Model version 5.3 (CAM5.3) in which the default aerosol module has been replaced by the two-Moment, Multi-Modal, Mixing-state-resolving Aerosol model for Research of Climate (MARC). CAM5.3-MARC-ARG uses the ARG aerosol-activation scheme, consistent with the default configuration of CAM5.3. We compute differences between simulations using year-1850 aerosol emissions and simulations using year-2000 aerosol emissions in order to assess the radiative effects of anthropogenic aerosols. We compare the aerosol lifetimes, aerosol column burdens, cloud properties, and radiative effects produced by CAM5.3-MARC-ARG with those produced by the default configuration of CAM5.3, which uses the modal aerosol module with three log-normal modes (MAM3), and a configuration using the modal aerosol module with seven log-normal modes (MAM7). Compared with MAM3 and MAM7, we find that MARC produces stronger cooling via the direct radiative effect, the shortwave cloud radiative effect, and the surface albedo radiative effect; similarly, MARC produces stronger warming via the longwave cloud radiative effect. Overall, MARC produces a global mean net ERF of -1.79±0.03 W m−2, which is stronger than the global mean net ERF of -1.57±0.04 W m−2 produced by MAM3 and -1.53±0.04 W m−2 produced by MAM7. The regional distribution of ERF also differs between MARC and MAM3, largely due to differences in the regional distribution of the shortwave cloud radiative effect. We conclude that the specific representation of aerosols in global climate models, including aerosol mixing state, has important implications for climate modelling.

Highlights

Aerosol particles influence the earth’s climate system by perturbing its radiation budget
We focus on model output fields relating to different components of the effective radiative forcing (ERF), taking each component in turn: the direct radiative effect, the cloud radiative effect, and the surface albedo radiative effect
The low hygroscopicity of these pure organic carbon and pure black carbon modes leads to increased lifetimes of total organic carbon aerosol and total black carbon aerosol, influencing aerosol column burdens

Summary

Introduction

Aerosol particles influence the earth’s climate system by perturbing its radiation budget. Aerosols interact directly with radiation by scattering and absorbing solar and thermal infrared radiation (Haywood and Boucher, 2000). Aerosols interact indirectly with radiation by perturbing clouds, acting as the cloud condensation nuclei on which cloud droplets form and the ice nuclei that facilitate freezing of cloud droplets (Fan et al, 2016; Rosenfeld et al, 2014); for example, an aerosol-induced increase in cloud cover would lead to increased scattering of “shortwave” solar radiation and increased absorption of “longwave” thermal infrared radiation. Aerosols can influence the albedo of the earth’s surface; for example, the deposition of absorbing aerosol on snow reduces the albedo. Grandey et al.: Effective radiative forcing in the model CAM5.3-MARC-ARG of the snow, causing more solar radiation to be absorbed at the earth’s surface (Jiao et al, 2014)

Methods

Results

Conclusion