This study reviews the research of the past 20-years on the role of anvil cirrus in the Earth’s climate – research initiated by Lindzen et al. (Bull. Am. Meteor. Soc. 82:417-432, 2001). The original study suggested that the anvil cirrus would shrink with warming, which was estimated to induce longwave cooling for the Earth. This is referred to as the iris effect since the areal change hypothetically resembles the light control by the human eye’s iris. If the effect is strong enough, it exerts a significant negative climate feedback which stabilizes tropical temperatures and limits climate sensitivity. Initial responses to Lindzen et al. (Bull. Am. Meteor. Soc. 82:417-432, 2001) denied the existence and effectiveness of the iris effect. Assessment of the debatable issues in these responses will be presented later in this review paper. At this point, the strong areal reduction of cirrus with warming appears very clearly in both climate models and satellite observations. Current studies found that the iris effect may not only come from the decreased cirrus outflow due to increased precipitation efficiency, but also from concentration of cumulus cores over warmer areas (the so-called aggregation effect). Yet, different opinions remain as to the radiative effect of cirrus clouds participating in the iris effect. For the iris effect to be most important, it must involve cirrus clouds that are not as opaque for visible radiation as they are for infrared radiation. However, current climate models often simulate cirrus clouds that are opaque in both visible and infrared radiation. This issue requires thorough examination as it seems to be opposed to conventional wisdom based on explicit observations. This paper was written in the hope of stimulating more effort to carefully evaluate these important issues.

这项研究回顾了过去20年中有关铁砧卷云在地球气候中的作用的研究-Lindzen等人发起的研究。（Bull.Am.Meteor.Soc.82：417-432，2001）。原始研究表明，铁砧卷云会随着变暖而收缩，据估计，这会引起地球的长波冷却。这称为虹膜效果因为假设面积的变化类似于人眼虹膜的光控制。如果影响足够强烈，它将产生明显的负面气候反馈，从而稳定热带温度并限制气候敏感性。对Lindzen等人的初步回应。（Bull.Am.Meteor.Soc.82：417-432，2001）否认了虹膜效应的存在和有效性。这些回应中有争议的问题的评估将在本文的稍后部分进行介绍。在这一点上，气候模型和卫星观测都清楚地表明，随着气候变暖，卷云的面积明显减少。当前的研究发现，虹膜效应可能不仅是由于降水效率提高所导致的卷云流出减少所致，而且还可能是由于温暖地区积云核心的集中（所谓的聚集效应）所致。然而，关于卷云参与虹膜效应的辐射效应，仍存在不同意见。为了使虹膜效果最重要，它必须包含卷云，卷云对可见光的透明度要比对红外光的透明度高。但是，当前的气候模型通常会模拟在可见光和红外辐射中都是不透明的卷云。这个问题需要彻底检查，因为它似乎与基于显式观察的传统观点相反。撰写本文的目的是希望激发更多的努力来仔细评估这些重要问题。它必须包含卷云，卷云对可见辐射的透明度要比对红外辐射的透明度高。但是，当前的气候模型通常会模拟在可见光和红外辐射中都是不透明的卷云。这个问题需要彻底检查，因为它似乎与基于显式观察的传统观点相反。撰写本文的目的是希望激发更多的努力来仔细评估这些重要问题。它必须包含卷云，卷云对可见辐射的透明度要比对红外辐射的透明度高。但是，当前的气候模型通常会模拟在可见光和红外辐射中都是不透明的卷云。这个问题需要彻底检查，因为它似乎与基于显式观察的传统观点相反。撰写本文的目的是希望激发更多的努力来仔细评估这些重要问题。