CO2 forcing induces semi-direct effects with consequences for climate feedback interpretations
Article first published online: 16 FEB 2008
Copyright 2008 by the American Geophysical Union.
Geophysical Research Letters
Volume 35, Issue 4, February 2008
How to Cite
2008), CO2 forcing induces semi-direct effects with consequences for climate feedback interpretations, Geophys. Res. Lett., 35, L04802, doi:10.1029/2007GL032273., and (
- Issue published online: 16 FEB 2008
- Article first published online: 16 FEB 2008
- Manuscript Accepted: 9 JAN 2008
- Manuscript Revised: 30 NOV 2007
- Manuscript Received: 6 OCT 2007
- tropospheric adjustment;
- semi-direct effects;
- cloud feedbacks
 Climate forcing and feedbacks are diagnosed from seven slab-ocean GCMs for 2 × CO2 using a regression method. Results are compared to those using conventional methodologies to derive a semi-direct forcing due to tropospheric adjustment, analogous to the semi-direct effect of absorbing aerosols. All models show a cloud semi-direct effect, indicating a rapid cloud response to CO2; cloud typically decreases, enhancing the warming. Similarly there is evidence of semi-direct effects from water-vapour, lapse-rate, ice and snow. Previous estimates of climate feedbacks are unlikely to have taken these semi-direct effects into account and so misinterpret processes as feedbacks that depend only on the forcing, but not the global surface temperature. We show that the actual cloud feedback is smaller than what previous methods suggest and that a significant part of the cloud response and the large spread between previous model estimates of cloud feedback is due to the semi-direct forcing.