Clouds, Radiation, and Atmospheric Circulation in the Present‐Day Climate and Under Climate Change
By interacting with radiation, clouds modulate the flow of energy through the Earth system, the circulation of the atmosphere, and regional climate. This paper reviews the impact of cloud‐radiation interactions for the atmospheric circulation in the present‐day climate, its internal variability, and its response to climate change. Cloud‐controlling factors and cloud‐radiative effects are summarized, and the Clouds On‐Off Klimate Model Intercomparison Experiment (COOKIE) and cloud‐locking modeling methods and their limitations are described.
This paper provides the first comprehensive review of our understanding of the role that cloud-radiative effects play in present-day climate, climate variability, and climate change. While many individual studies have broached these topics over the years, the past decade has provided a new understanding of the coupling between clouds and circulation. This has been aided by the COOKIE and cloud-locking methodologies, which are presented in detail, and which are compared and contrasted for the first time. This paper is also able to synthesize results from cloud-locking experiments across several models for the first time. The review provides insights into the strengths and weaknesses of the modeling approaches, including the role of variability and structural uncertainties.
Experiments using the COOKIE approach show that the presence of cloud‐radiative effects shapes the circulation in the present‐day climate in many important ways, including the width of the tropical rain belts and the position of the extratropical storm tracks. Cloud locking, in contrast, has identified how clouds affect internal variability and the circulation response to global warming. Examples include strong, but model‐dependent, shortwave and longwave cloud impacts on the El Niño-Southern Oscillation, and the finding that most of the poleward circulation expansion in response to global warming can be attributed to radiative changes in clouds. The review highlights the circulation impact of shortwave changes from low‐level clouds and longwave changes from rising high‐level clouds and the contribution of cloud changes to model differences in the circulation response to global warming. Attention is drawn to the role of cloud‐radiative heating within the atmosphere. Some open questions are raised, including the need for studying the cloud impact on regional scales and opportunities created by the next generation of global storm‐resolving models.