Iris hypothesis
Encyclopedia
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 cloud
s 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. 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. Others found evidence suggesting that increased sea surface temperature in the tropics did indeed reduce cirrus cloud
s but found that the effect was nonetheless a positive feedback rather than the negative feedback that Lindzen had hypothesized. A later 2007 study conducted by Roy Spencer, et al. using updated satellite data supported the iris hypothesis.
Richard Lindzen
Richard Siegmund Lindzen is an American atmospheric physicist and Alfred P. Sloan Professor of Meteorology at the Massachusetts Institute of Technology. Lindzen is known for his work in the dynamics of the middle atmosphere, atmospheric tides and ozone photochemistry. He has published more than...
in 2001 that suggested increased sea surface temperature
Sea surface temperature
Sea surface temperature is the water temperature close to the oceans surface. The exact meaning of surface varies according to the measurement method used, but it is between and below the sea surface. Air masses in the Earth's atmosphere are highly modified by sea surface temperatures within a...
in the tropics
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
would result in reduced cirrus cloud
Cirrus cloud
Cirrus clouds are atmospheric clouds generally characterized by thin, wispy strands, giving them their name from the Latin word cirrus meaning a ringlet or curling lock of hair...
s and thus more infrared radiation leakage from Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
's atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
. His study of observed changes in cloud coverage and modeled effects on infrared radiation released to space as a result supported the hypothesis. 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. Others found evidence suggesting that increased sea surface temperature in the tropics did indeed reduce cirrus cloud
Cirrus cloud
Cirrus clouds are atmospheric clouds generally characterized by thin, wispy strands, giving them their name from the Latin word cirrus meaning a ringlet or curling lock of hair...
s but found that the effect was nonetheless a positive feedback rather than the negative feedback that Lindzen had hypothesized. A later 2007 study conducted by Roy Spencer, et al. using updated satellite data supported the iris hypothesis.