ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-2-31-2002 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, University of Washington, Seattle, Washington, USA 30 01 2002 2 1 31 37 Copyright: © 2002 Q. Fu et al. 2002 This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 Generic License. To view a copy of this licence, visit https://creativecommons.org/licenses/by-nc-sa/2.5/ This article is available from https://acp.copernicus.org/articles/2/31/2002/acp-2-31-2002.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/2/31/2002/acp-2-31-2002.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 increase in sea surface temperature 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 is small. Although not mentioned by Lindzen et al. (2001), 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. (2001), 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. It is noted that our feedback factor could still be overestimated due to the assumption of constant low cloud cover in the simple radiative-convective model.