Journal of Quantitative Spectroscopy & Radiative Transfer 93 (2005) 447–460 Resolution of the uncertainties in the radiative forcing of HFC-134a Piers M. de F. Forster a,b,Ã , J.B. Burkholder b , C. Clerbaux c,d , P.F. Coheur d , M. Dutta e , L.K. Gohar a , M.D. Hurley f , G. Myhre g , R.W. Portmann b , K.P. Shine a , T.J. Wallington f , D. Wuebbles e a Department of Meteorology, The University of Reading, P.O. Box 243, Earley Gate, Reading, RG6 6BB, UK b NOAA Aeronomy Laboratory, 325 Broadway, Boulder, CO 80305-3328, USA c Service d’Ae´ronomie/CNRS, Institut Pierre-Simon Laplace, Paris, France d Service de Chimie Quantique et Photophysique, Universite´Libre de Bruxelles, Bruxelles, Belgium e University of Illinois, Urbana, IL, USA f Ford Motor Company, Dearborn, MI, USA g University of Oslo, Oslo, Norway Received 30 January 2004; received in revised form 25 August 2004; accepted 25 August 2004 Abstract HFC-134a (CF 3 CH 2 F) is the most rapidly growing hydrofluorocarbon in terms of atmospheric abundance. It is currently used in a large number of household refrigerators and air-conditioning systems and its concentration in the atmosphere is forecast to increase substantially over the next 50–100 years. Previous estimates of its radiative forcing per unit concentration have differed significantly 25%. This paper uses a two-step approach to resolve this discrepancy. In the first step six independent absorption cross section datasets are analysed. We find that, for the integrated cross section in the spectral bands that contribute most to the radiative forcing, the differences between the various datasets are typically smaller than 5% and that the dependence on pressure and temperature is not significant. A ‘‘recommended’’ HFC- 134a infrared absorption spectrum was obtained based on the average band intensities of the strongest bands. In the second step, the ‘‘recommended’’ HFC-134a spectrum was used in six different radiative transfer models to calculate the HFC-134a radiative forcing efficiency. The clear-sky instantaneous ARTICLE IN PRESS www.elsevier.com/locate/jqsrt 0022-4073/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jqsrt.2004.08.038 Ã Corresponding author. Department of Meteorology, The University of Reading, P.O. Box 243, Earley Gate, Reading, RG6 6BB, UK. Tel.: +44 118 378 6020; fax: +44 118 378 8905. E-mail address: piers@met.rdg.ac.uk (P.M. de F. Forster).