Papers on the iris hypothesis of Lindzen

This is a list of papers on the iris hypothesis of Lindzen. The list contains only papers that concentrate on the iris hypothesis, so there’s no such papers that study related matters but only mention the hypothesis in passing. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (November 18, 2009): Earth Observatory article added to the “closely related” section, thanks to Paul Middents for pointing it out (see the comment section below).

Papers of others

An Evaluation of the Proposed Mechanism of the Adaptive Infrared Iris Hypothesis Using TRMM VIRS and PR Measurements – Rapp et al. (2005) “This [iris] hypothesis assumes that increased precipitation efficiency in regions of higher sea surface temperatures will reduce cirrus detrainment. Tropical Rainfall Measuring Mission (TRMM) satellite measurements are used here to investigate the adaptive infrared iris hypothesis. … The current analysis does not show any significant SST dependence of the ratio of cloud area to surface rainfall for deep convection in the tropical western and central Pacific.” [Link to PDF]

Examination of the Decadal Tropical Mean ERBS Nonscanner Radiation Data for the Iris Hypothesis – Lin et al. (2004) “In this study, the ERBS decadal observations are compared with the predictions of the Iris hypothesis using 3.5-box model. … On the decadal time scale, the predicted tropical mean radiative flux anomalies are generally significantly different from those of the ERBS measurements, suggesting that the decadal ERBS nonscanner radiative energy budget measurements do not support the strong negative feedback of the Iris effect.” [Link to PDF]

The decadal tropical mean radiation data and the Iris hypothesis – Lin et al. (2003) A conference paper. “This study examines the evidence of the strong negative climate feedback of the Iris hypothesis using decadal satellite observations of tropical mean radiative energy budget anomalies, and finds that the decadal satellite measurements do not support the Iris effect.”

Examination of New CERES Data for Evidence of Tropical Iris Feedback – Chambers et al. (2002) “New data products from the Clouds and the Earth’s Radiant Energy System (CERES) instrument on the Tropical Rainfall Measuring Mission Satellite have been examined in the context of the recently proposed adaptive tropical infrared Iris hypothesis. … Regardless of definition, the radiative properties are found to be different from those assigned in the original Iris hypothesis. As a result, the strength of the feedback effect is reduced by a factor of 10 or more. Contrary to the initial Iris hypothesis, most of the definitions tested in this paper result in a small positive feedback. Thus, the existence of an effective infrared iris to counter greenhouse warming is not supported by the CERES data.”

New CERES Data Examined for Evidence of Tropical Iris Feedback – Chambers et al. (2002) A conference paper. “New data products are available from the CERES instrument, a part of the NASA Earth Observing System. … Regardless, the current results show that the proposed Iris feedback is very much weaker when objectively-determined radiative properties are used in the model.” [Link to PDF]

Reply – Chambers et al. (2002) “Chou et al. (2002, hereinafter CLH) argue in their comment that the way in which Lin et al. (2002) analyzed the Clouds and the Earth’s Radiant Energy System (CERES) data (Wielicki et al. 1996) is not appropriate. … The analysis in the Lin et al. paper exactly followed the original iris idea, as presented by Lindzen et al. (2001, hereinafter LCH), yet obtained significantly different results. We have repeated the analysis with some additional thresholds as illustrated in the CLH comment, and our basic conclusion remains: the difference between the net radiative fluxes of the cloudy-moist and clear-moist regions should be small. Thus, the radiative forcing resulting from a change in tropical high cloud amount is still about 1/10 of that found in LCH.” [Link to PDF]

Climatic Properties of Tropical Precipitating Convection under Varying Environmental Conditions – Del Genio & Kovari (2002) “A clustering algorithm is used to define the radiative, hydrological, and microphysical properties of precipitating convective events in the equatorial region observed by the Tropical Rainfall Measuring Mission (TRMM) satellite. … The adaptive iris hypothesis (clouds thinning with warming) is clearly not supported by the TRMM data. … Several flaws in reasoning lead Lindzen et al. (2001) to their conclusion.” [Link to PDF]

Tropical cirrus and water vapor: an effective Earth infrared iris feedback? – Fu et al. (2002) “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.” [Link to PDF]

The Iris Hypothesis: A Negative or Positive Cloud Feedback? – Lin et al. (2002) “Using the Tropical Rainfall Measuring Mission (TRMM) satellite measurements over tropical oceans, this study evaluates the iris hypothesis recently proposed by Lindzen et al. that tropical upper-tropospheric anvils act as a strong negative feedback in the global climate system. … The observations show that the clouds have much higher albedos and moderately larger longwave fluxes than those assumed by Lindzen et al. As a result, decreases in these clouds would cause a significant but weak positive feedback to the climate system, instead of providing a strong negative feedback.” [Link to PDF]

Comments on “Does the Earth Have an Adaptive Infrared Iris?” – Harrison (2002) Finds much smaller value for fractional cloud-cover decrease per °C than Lindzen et al. (2001). [Link to PDF]

No Evidence for Iris – Hartmann & Michelsen (2002) “It is shown that the negative correlation between cloud-weighted sea surface temperature (SST) and high cloud fraction discussed recently by Lindzen et al. results from variations in subtropical clouds that are not physically connected to the deep convection near the equator. A negative correlation between cloud-weighted SST and average cloud fraction results from any variation in cloud fraction over the areas with lower SSTs within the domain of interest. Therefore, this correlation is not evidence that tropical cloud anvil area is inversely proportional to sea surface temperature and should not be used to infer the existence of a negative feedback in the climate system.” [Link to PDF]

Papers of Lindzen et al.

Comments on “Examination of the Decadal Tropical Mean ERBS Nonscanner Radiation Data for the Iris Hypothesis” – Chou & Lindzen (2005)

Further Results On The Iris Effect – Lindzen et al. (2002) A conference paper. “Our data set now extends to 4 full years rather than the 20 months used in the original study. … We have used CERES data in order to investigate how albedo varies with area of cirrus (scaled by cumulus activity) in order to separate the albedo change due to fluctuations of cirrus areas from mean albedos which are biased by the high albedos associated with thick anvils near cumulus cores. It is, of course, the former which are relevant to the feedback. Results from each of the above studies will be presented.”

Comment on “No Evidence for Iris” – Lindzen et al. (2002) “However, the points raised by HM hardly constitute challenges to the hypothesis.” [Link to PDF]

Comments on “The Iris Hypothesis: A Negative or Positive Cloud Feedback?” – Chou et al. (2002) “The difference in the feedback factor is due to a larger contrast in albedos and a smaller contrast in the outgoing longwave radiation (OLR) between the high-level cloudy region and the surrounding regions as derived by Lin et al. when compared with that specified in LCH. It appears that the approach taken by Lin et al. to estimate the albedo and OLR is not appropriate and that the inferred climate sensitivity is unreliable.” [Link to PDF]

Does the Earth Have an Adaptive Infrared Iris? – Lindzen et al. (2001) “Motivated by the observed relation between cloudiness (above the trade wind boundary layer) and high humidity, cloud data for the eastern part of the western Pacific from the Japanese Geostationary Meteorological Satellite–5 (which provides high spatial and temporal resolution) have been analyzed, and it has been found that the area of cirrus cloud coverage normalized by a measure of the area of cumulus coverage decreases about 22% per degree Celsius increase in the surface temperature of the cloudy region. … This new mechanism would, in effect, constitute an adaptive infrared iris that opens and closes in order to control the Outgoing Longwave Radiation in response to changes in surface temperature in a manner similar to the way in which an eye’s iris opens and closes in response to changing light levels.” [Link to PDF]

Closely related

Earth Observatory: Arbiters of Energy A lay people level review of the issue.