Linearity of Climate Response to Increases in Black Carbon Aerosols

• DOI: 10.1175/jcli-d-12-00715.1
• Publication Date: 2013-06-18T03:03:08Z
• Authors: Salil Mahajan; Katherine J. Evans; James J. Hack; John E. Truesdale
• Keywords: Atmospheric models; Intertropical Convergence Zone; Forcing (mathematics)

Abstract The impacts of absorbing aerosols on global climate are not completely understood. This paper presents the results idealized experiments conducted with Community Atmosphere Model, version 4 (CAM4), coupled to a slab ocean model (CAM4–SOM) simulate response increases in tropospheric black carbon (BC) by direct and semidirect effects. CAM4-SOM was forced 0, 1×, 2×, 5×, 10× an estimate present day concentration BC while maintaining estimated spatial vertical distribution. top-of-atmosphere (TOA) radiative forcing these is positive (warming) linearly as burden increases. total effect for 1 × experiment but becomes increasingly negative higher concentrations. global-average surface temperature found be linear function TOA forcing. sensitivity from 0.42 K W−1 m2 when effects accounted 0.22 only considered. Global-average precipitation decreases increases, atmospheric absorption 0.4% m2. hemispheric asymmetry also causes increase southward cross-equatorial heat transport resulting northward shift intertropical convergence zone simulations at rate 4° PW−1. mid- high-level clouds decrease, whereas low-level BC. marine stratocumulus cloud fraction over southern tropical Atlantic caused increased BC-induced diabatic heating free troposphere.