- Iris hypothesis
The iris hypothesis is a theory proposed by Prof.
Richard Lindzenin 2001 [ [http://eaps.mit.edu/faculty/lindzen/adinfriris.pdf R.S. Lindzen, M.-D. Chou, and A.Y. Hou (2001) Does the Earth have an adaptive infrared iris? Bull. Amer. Met. Soc. 82, 417-432] ] that suggested increased sea surface temperature in the tropics would result in reduced cirrus clouds and thus more infrared radiationleakage from Earth's atmosphere. This suggested infrared radiationleakage was hypothesized to be a negative feedback which would have an overall cooling effect. The consensus view is that increased sea surface temperature would result in increased cirrus clouds which would have the effect of warming the sea surface further and thus there would be positive feedback.
Other scientists have since tested the hypothesis. Some concluded that that there was simply no evidence supporting the hypothesis [ [http://ams.allenpress.com/archive/1520-0477/83/2/pdf/i1520-0477-83-2-249.pdf Hartman, D.L., and M.L. Michelsen, 2002. No evidence for iris. Bulletin of the American Meteorological Society, 83, 249-254.] ] . Others found evidence suggesting that increased sea surface temperature in the tropics did indeed reduce
cirrus clouds but found that the effect was nonetheless a positive feedback rather than the negative feedback that Lindzen had hypothesized [ [http://www.atmos-chem-phys-discuss.net/1/221/2001/acpd-1-221-2001-print.pdf Fu, Q., Baker, M., and Hartman, D. L.: Tropical cirrus and water vapor: an effective Earth infrared iris feedback? Atmos. Chem. Phys., 2, 31–37, 2002.] ] [ [http://langley.atmos.colostate.edu/at722/references/Lin-etal-IRIS-Jclim-Letter.pdf The Iris Hypothesis: A Negative or Positive Cloud Feedback? Bing Lin, Bruce Wielicki, Lin Chambers, Yongxiang Hu, and Kuan-Man Xu Atmospheric Sciences Research, NASA Langley Research Center, Hampton, VA] ] . However, there has been some relatively recent evidence potentially supporting the hypothesis [ [http://www.agu.org/pubs/crossref/2007/2007GL029698.shtml Spencer, R.W., Braswell, W.D., Christy, J.R., Hnilo, J., 2007. Cloud and radiation budget changes associated with tropical intraseasonal oscillations. Geophysical Research Letters, 34, L15707, doi:10.1029/2007/GL029698.] ] .
* [http://earthobservatory.nasa.gov/Study/Iris/ NASA summary of Global Warming and Iris Hypothesis]
* [http://earthobservatory.nasa.gov/Study/Iris/iris2.html Evidence against the Iris Hypothesis]
* [http://earthobservatory.nasa.gov/Study/Iris/iris3.html New satellites to resolve Hypothesis]
* [http://www.nasa.gov/pdf/133608main_cloudsat-calipso-launch.pdf Cloudsat and CALIPSO satellite summary]
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