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Clouds play an important role in the earth's energy budget, and changes in their properties can remarkably impact the amount of warming in response to greenhouse gas increases. In this study, we applied the Coupled Feedback Response Analysis Method (CFRAM) to estimate the contributions of cloud property changes to the magnitude of the annual mean-surface temperature response in a transient simulation where CO2 increases at rate 1% yr-1 , using the NCAR Community Climate System Model, version 4 (CCSM4). To examine closely the contributions of changes in cloud properties to the annual mean-surface temperature, the full-cloud level is divided into three levels in terms of the cloud-top pressure (CTP). This study found that the annual and global mean-surface temperature response is a warming of (+0.175 oK) due to the net cloud feedback that comes mainly from the positive SW cloud feedback. The medium (400 < CTP < 700 mb) clouds changes are the dominant contributors (+0.175 oK) to the surface warming due to their magnificent positive SW cloud feedback (+0.33 oK). High (CTP < 400 mb) clouds changes cause a weak negative contribution (-0.0218 oK) to the surface warming because of the close cancellation between their large negative SW and large positive LW high-cloud feedbacks. Low (CTP > 700 mb) cloud changes are the least contributors to SW and LW cloud feedbacks (positive SW and negative LW); however, they still contribute positively (+0.0217 oK) to the net cloud feedback with an absolute magnitude that is almost equal to the contribution of the high-cloud changes. Furthermore, this study found that the annual mean-surface temperature increases in the Polar Regions (60o-90o in both hemispheres) are due to the positive LW cloud feedback from the changes in the three cloud levels, mostly due to positive LW medium-cloud feedback. However, the annual mean surface warming for the region covered between (60o S-60o N) is due to the positive SW low- and medium-cloud feedbacks.
A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science.
Includes bibliographical references.
Ming Cai, Professor Directing Thesis; Guosheng Liu, Committee Member; Zhaohua Wu, Committee Member.
Florida State University
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