What governs the spread in shortwave forcings in the transient IPCC AR4 models?
Article first published online: 13 JAN 2009
Copyright 2009 by the American Geophysical Union.
Geophysical Research Letters
Volume 36, Issue 1, January 2009
How to Cite
2009), What governs the spread in shortwave forcings in the transient IPCC AR4 models? Geophys. Res. Lett., 36, L01806, doi:10.1029/2008GL036069., , and (
- Issue published online: 13 JAN 2009
- Article first published online: 13 JAN 2009
- Manuscript Accepted: 2 DEC 2008
- Manuscript Revised: 16 NOV 2008
- Manuscript Received: 19 SEP 2008
- aerosol indirect effect;
- radiative forcings;
- transient simulations
 The coupled global atmospheric-ocean models used for transient simulations in the IPCC AR4 report differences in the present-day shortwave forcing of more than 2 W/m2. We show here that about 1.3 W/m2 of this spread could be explained by the different methods used to calculate cloud droplet number concentration (CDNC) from aerosol mass concentrations. Although we cannot rule out that other forcing agents could yield comparable uncertainties, this strongly points to the aerosol indirect effect as the main contributor to the wide spread in the shortwave forcing reported in IPCC AR4.