The iris hypothesis was a hypothesis proposed by Richard Lindzen and colleagues 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.

Other scientists have found this work to be "gravely flawed and its results wrong on multiple fronts."[2]: 92 [3] It no longer plays a role in the current scientific consensus on climate change.

Scientific discussion

Scientists subsequently tested the hypothesis. Some concluded that there was no evidence supporting the hypothesis.[4] 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.[5][6]

A later 2007 study conducted by Roy Spencer et al. using updated satellite data potentially supported the iris hypothesis.[7] In 2011, Lindzen published another paper on this topic.[8] This work has been described as "gravely flawed and its results wrong on multiple fronts. Their choice of observational periods distorted the results and underscored the defective nature of their analysis."[2]: 92 

In his memoirs in 2023, Kevin E. Trenberth rebutted the Iris hypothesis in strong words:[2]: 92 

"On the science front, Lindzen made great waves with a widely touted paper on possibilities that might nullify global warming (Lindzen et al. 2001) hyping an iris effect that would allow more longwave radiation escape to space as more widespread subsidence occurred as a consequence of stronger convection with increased heating. The idea of the iris effect was reasonable in of itself, but it focused only on the role of the areal extent of tropical cirrus on the outgoing infrared radiation, with no accounting for the huge and largely compensating effects on incoming solar radiation, or changes in altitude. In terms of SST response, the solar effects are greater!"

In 2015, a paper was published which again suggested the possibility of an "Iris Effect".[9] It also proposed what it called a "plausible physical mechanism for an iris effect." In 2017, a paper was published which found that "tropical anvil cirrus clouds exert a negative climate feedback in strong association with precipitation efficiency".[10]

See also

References

  1. ↑ Lindzen, R.S., M.-D. Chou, and A.Y. Hou (2001). "Does the Earth have an adaptive infrared iris?" (PDF). Bull. Amer. Meteor. Soc. 82 (3): 417–432. Bibcode:2001BAMS...82..417L. doi:10.1175/1520-0477(2001)082<0417:DTEHAA>2.3.CO;2. hdl:2060/20000081750.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  2. 1 2 3 Trenberth, Kevin E. (2023). A personal tale of The Development of Climate Science. The life and times of Kevin Trenberth. Auckland, New Zealand: Published by Kevin E Trenberth. ISBN ISBN 978-0-473-68694-9 (paperback), ISBN 978-0-473-68696-3 (pdf), ISBN 978-0-473-68695-6 (epub). {{cite book}}: Check |isbn= value: invalid character (help)
  3. ↑ Trenberth, Kevin E.; Fasullo, John T.; O'Dell, Chris; Wong, Takmeng (2010). "Relationships between tropical sea surface temperature and top‐of‐atmosphere radiation". Geophysical Research Letters. 37 (3). doi:10.1029/2009GL042314. ISSN 0094-8276.
  4. ↑ Hartman, D.L.; M.L. Michelsen (2002). "No evidence for iris". Bull. Amer. Meteor. Soc. 83 (2): 249–254. Bibcode:2002BAMS...83..249H. doi:10.1175/1520-0477(2002)083<0249:NEFI>2.3.CO;2.
  5. ↑ Fu, Q., Baker, M., and Hartman, D. L. (2002). "Tropical cirrus and water vapor: an effective Earth infrared iris feedback?" (PDF). Atmos. Chem. Phys. 2 (1): 31–37. doi:10.5194/acp-2-31-2002.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  6. ↑ 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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ↑ 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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  8. ↑ Lindzen R.S.; Y.-S. Choi (2011). "On the observational determination of climate sensitivity and its implications" (PDF). Asia-Pacific J. Atmos. Sci. 47 (4): 377–390. Bibcode:2011APJAS..47..377L. CiteSeerX 10.1.1.167.11. doi:10.1007/s13143-011-0023-x. S2CID 9278311. Archived from the original (PDF) on 2019-01-04. Retrieved 2014-01-11.
  9. ↑ Mauritsen T.; Stevens B. (2015). "Missing iris effect as a possible cause of muted hydrological change and high climate sensitivity in models". Nature Geoscience. 8 (5): 346–351. Bibcode:2015NatGe...8..346M. doi:10.1038/ngeo2414.
  10. ↑ Choi, Yong-Sang; Kim, WonMoo; Yeh, Sang-Wook; Masunaga, Hirohiko; Kwon, Min-Jae; Jo, Hyun-Su; Huang, Lei (2017). "Revisiting the iris effect of tropical cirrus clouds with TRMM and A-Train satellite data". Journal of Geophysical Research: Atmospheres. 122 (11): 2016JD025827. Bibcode:2017JGRD..122.5917C. doi:10.1002/2016JD025827. ISSN 2169-8996. S2CID 134384103.
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