ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-2-173-2002 Reply to: “Tropical cirrus and water vapor: an effective Earth infrared iris feedback?" Chou M.-D. 1 Lindzen R. S. 2 Hou A. Y. 1 Laboratory for Atmospheres, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA Dept. of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA 14 02 2002 2 1 173 180 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/2/173/2002/acpd-2-173-2002.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/2/173/2002/acpd-2-173-2002.pdf

In assessing the iris effect suggested by Lindzen et al. (2001), Fu et al. (2001, 2002) found that the response of high-level clouds to the sea surface temperature had an effect of reducing the climate sensitivity to external radiative forcing, but the effect was not as strong as Lindzen et al. (2001) found. The approach of Fu et al. (2001, 2002) to specifying longwave emission and cloud albedos appears to be inappropriate, and the derived cloud optical properties may not have real physical meaning. The cloud albedo calculated by Fu et al. (2001, 2002) is too large for cirrus clouds and too small for boundary layer clouds, which underestimates the iris effect.