Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 2 1 2002 10.5194/acpd-2-173-2002 http://www.atmos-chem-phys-discuss.net/2/173/2002/ http://www.atmos-chem-phys-discuss.net/2/173/2002/acpd-2-173-2002.html http://www.atmos-chem-phys-discuss.net/2/173/2002/acpd-2-173-2002.pdf 173 180 2002-02-14 Reply to: “Tropical cirrus and water vapor: an effective Earth infrared iris feedback?" M.-D. Chou R. S. Lindzen A. Y. Hou 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 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.