Title: Radiative Forcing by Aerosols as Derived from the AeroCom Present-day and Pre-Industrial Simulations
Authors: SCHULZ MichaelSCHULZ M.TEXTOR ChristianeKINNE StephanBALKANSKI YvesBAUER S.BERNTSEN T.BERGLEN T.BOUCHER OlivierDENTENER FRANCISCUSGUIBERT S.ISAKSEN I.s.a.IVERSEN T.KOCH D.KIRKEVAG A.LIU X.MONTANARO V.MYHRE G.PENNER J.e.PITARI G.REDDY S.SELAND O.STIER PHILIPTAKEMURA T.
Citation: ATMOSPHERIC CHEMISTRY AND PHYSICS vol. 6 p. 5225-5246
Publisher: EUROPEAN GEOSCIENCES UNION
Publication Year: 2006
JRC Publication N°: JRC34513
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC34513
Type: Articles in Journals
Abstract: Nine different global models with detailed aerosol modules have independently produced instantaneous direct radiative forcing due to anthropogenic aerosols. The anthropogenic impact is derived from the difference of two model simulations with iden- 5 tically prescribed aerosol emissions, one for present-day and one for pre-industrial conditions. The difference in the energy budget at the top of the atmosphere (ToA) yields a new harmonized estimate for the aerosol direct radiative forcing (RF) under all-sky conditions. On a global annual basis RF is −0.2Wm−2, with a standard deviation of ±0.2Wm−2. Anthropogenic nitrate and dust are not included in this estimate. 10 No model shows a significant positive all-sky RF. The corresponding clear-sky RF is −0.6Wm−2. The cloud-sky RF was derived based on all-sky and clear-sky RF and modelled cloud cover. It was significantly different from zero and ranged between −0.16 and +0.34Wm−2. A sensitivity analysis shows that the total aerosol RF is influenced by considerable diversity in simulated residence times, mass extinction coeffi15 cients and most importantly forcing efficiencies (forcing per unit optical depth). Forcing efficiency differences among models explain most of the variability, mainly because all-sky forcing estimates require proper representation of cloud fields and the correct relative altitude placement between absorbing aerosol and clouds. The analysis of the sulphate RF shows that differences in sulphate residence times are compensated 20 by opposite mass extinction coefficients. This is explained by more sulphate particle humidity growth and thus higher extinction in models with short-lived sulphate present at lower altitude and vice versa. Solar absorption within the atmospheric column is estimated at +0.85Wm−2. The local annual average maxima of atmospheric forcing exceed +5Wm−2 confirming the regional character of aerosol impacts on climate. The 25 annual average surface forcing is −1.03Wm−2
JRC Institute:Institute for Environment and Sustainability

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