ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-1-221-2001 Tropical cirrus and water vapor: an effective Earth infrared iris feedback? Fu Q. 1 Baker M. 1 Hartmann D. L. 1 Department of Atmospheric Sciences, Box 351640, University of Washington, Seattle, Washington 98195, USA 03 09 2001 1 1 221 238 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/1/221/2001/acpd-1-221-2001.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/1/221/2001/acpd-1-221-2001.pdf

We revisit a model of feedback processes proposed by Lindzen et al. (2001), in which an assumed 22% reduction in the area of tropical high clouds per degree of sea surface temperature increase produces negative feedbacks associated with upper tropospheric water vapor and cloud radiative effects. We argue that the water vapor feedback is overestimated in Lindzen et al. (2001) by at least 60%, and that the high cloud feedback should be small. Although not mentioned by Lindzen et al, tropical low clouds make a significant contribution to their negative feedback, which is also overestimated. Using more realistic parameters in the model of Lindzen et al., we obtain a feedback factor in the range of −0.15 to −0.51, compared to their larger negative feedback factor of −0.45 to −1.03.