Iris hypothesis
The iris hypothesis is a hypothesis proposed by Professor Richard Lindzen in 2001 that suggested increased sea surface temperature in the tropics would result in reduced cirrus clouds and thus more infrared radiation leakage from Earth's atmosphere. His study of observed changes in cloud coverage and modeled effects on infrared radiation released to space as a result supported the hypothesis.[1] This suggested infrared radiation leakage was hypothesized to be a negative feedback in which an initial warming would result in an overall cooling of the surface. The consensus view is that increased sea surface temperature would result in increased cirrus clouds and reduced infrared radiation leakage and therefore a positive feedback.
Other scientists have since tested the hypothesis. Some concluded that there was simply no evidence supporting the hypothesis.[2] 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.[3][4] A later 2007 study conducted by Roy Spencer, et al. using updated satellite data supported the iris hypothesis.[5]
In 2012 scientists from the University of Auckland analyzed satellite data and found that the average height of clouds declined between 2000 and 2010. The decline was a result of a reduction in high altitude cirrus clouds. The average global cloud height is linked to the average global temperature—generally, the higher the average cloud height, the higher the average surface temperature, and vice versa.[6]
[edit] See also
[edit] References
- ^ Lindzen, R.S., M.-D. Chou, and A.Y. Hou (2001). "Does the Earth have an adaptive infrared iris?". Bull. Amer. Met. Soc. 82 (3): 417–432. Bibcode 2001BAMS...82..417L. doi:10.1175/1520-0477(2001)082<0417:DTEHAA>2.3.CO;2. http://eaps.mit.edu/faculty/lindzen/adinfriris.pdf.
- ^ Hartman, D.L., and M.L. Michelsen (2002). "No evidence for iris". Bull. Amer. Met. Soc. 83 (2): 249–254. doi:10.1175/1520-0477(2002)083<0249:NEFI>2.3.CO;2. http://journals.ametsoc.org/doi/pdf/10.1175/1520-0477%282002%29083%3C0249%3ANEFI%3E2.3.CO%3B2.
- ^ Fu, Q., Baker, M., and Hartman, D. L. (2002). "Tropical cirrus and water vapor: an effective Earth infrared iris feedback?". Atmos. Chem. Phys. 2 (1): 31–37. doi:10.5194/acp-2-31-2002. http://www.atmos-chem-phys-discuss.net/1/221/2001/acpd-1-221-2001-print.pdf.
- ^ Lin, B., B. Wielicki, L. Chambers, Y. Hu, and K.-M. Xu (2002). "The Iris Hypothesis: A Negative or Positive Cloud Feedback?". J. Clim. 15 (1): 3–7. Bibcode 2002JCli...15....3L. doi:10.1175/1520-0442(2002)015<0003:TIHANO>2.0.CO;2.
- ^ Spencer, R.W., Braswell, W.D., Christy, J.R., Hnilo, J. (2007). "Cloud and radiation budget changes associated with tropical intraseasonal oscillations". Geophys. Res. Lett. 34 (15): L15707. Bibcode 2007GeoRL..3415707S. doi:10.1029/2007GL029698. http://www.agu.org/pubs/crossref/2007/2007GL029698.shtml.
- ^ www.redorbit.com/news/science/1112479879/falling-clouds-may-combat-global-warming/
[edit] External links
- NASA summary of Global Warming and Iris Hypothesis
- Evidence against the Iris Hypothesis
- New satellites to resolve Hypothesis
- Cloudsat and CALIPSO satellite summary
