Black carbon indirect radiative effects in a climate model

Ribu Cherian,Johannes Quaas,Marc Salzmann,Lorenzo Tomassini

doi:10.1080/16000889.2017.1369342

Abstract

The aerosol–cloud interactions due to black carbon (BC) aerosols, as well as the implied climate responses, are examined using an aerosol module in the coupled atmosphere–ocean general circulation model MPI-ESM. BC is simulated to enhance cloud droplet number concentration (CDNC) by 10–15% in the BC emission source regions, especially in the Tropics and mid-latitudes. Higher CDNC and reduced auto-conversion from cloud water to rain water explains the increased cloud water path over the tropical regions (30S–30N) in the model. In the global mean, the cloud water– as well as precipitation changes are negligibly small. The global-mean effective radiative forcing due to aerosol–cloud interactions for BC is estimated at , which is attributable to the increase in CDNC burden and (regionally) cloud water in the model. Global mean temperature and rainfall response were found to be and , respectively, with significantly larger regional changes mainly in the downwind regions from BC sources.

Highlights

The global-mean effective radiative forcing due to aerosol–cloud interactions for black carbon (BC) is estimated at −0.13 ± 0.1 W m−2, which is attributable to the increase in cloud droplet number concentration (CDNC) burden and cloud water in the model
The largest anthropogenic BC emissions are over India, China and African regions
The climate responses from the BC indirect effect are examined using an ocean-coupled aerosol climate model (MPI-ESM)

Summary

Introduction

Aerosol cloud indirect effects have been extensively studied, only few studies isolate the cloud effects of BC aerosols alone (Koch et al, 2011). The BC indirect radiative effects have previously been found to exert a negative forcing (Kristjánsson, 2002; Hansen et al, 2005), discernible mainly over the most prominent BC emission source regions. BC could have a substantial influence on the clouds due to its large contribution to aerosol number concentration even at low mass owing to the small average size (Andrews et al, 2010; Bond et al, 2013). BC has more complex effects on precipitation, which are dependent on the vertical structure and the source regions (Andrews et al, 2010)

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