The Iris Hypothesis A Negative or Positive Cloud Feedback?

• Published in: Journal of climate Vol. 15; no. 1; pp. 3 - 7
• Main Authors: Lin, Bing, Wielicki, Bruce A., Chambers, Lin H., Hu, Yongxiang, Xu, Kuan-Man
• Format: Journal Article
• Language: English
• Published: Boston, MA American Meteorological Society 01-01-2002
• Subjects: Albedo; Ceres; Climate; Climate models; Climate system; Clouds; Earth, ocean, space; Exact sciences and technology; External geophysics; Global climate; LETTERS; Marine; Meteorology; Negative feedback; Oceans; Pollutant emissions; Positive feedback; Space research; Tropical climates; Tropical regions; Water in the atmosphere (humidity, clouds, evaporation, precipitation); World Tropical Regions; World Ocean; Rain; Albedo; Long wave; Clouds; Marine atmosphere; Feedback; Radiation flux; Troposphere; Satellite observation; Anvil cloud; Models; TRMM satellite
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/1520-0442(2002)015<0003:tihano>2.0.co;2

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 modeled radiative fluxes of Lindzen et al. are replaced by the Clouds and the Earth’s Radiant Energy System (CERES) directly observed broadband radiation fields. 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.