Abstract

The climate sensitivity question is examined from the viewpoint of surface energy balance considerations. This approach clarifies the role of ocean-atmosphere interactions in determining the surface warming to an increase in CO2. The study uses a one-dimensional, 17-layer, coupled ocean-atmosphere model. The primary contribution to the surface warming is from the enhanced tropospheric IR emission, which is an order of magnitude greater than the direct CO2 radiative heating at the surface. The source for this enhancement is the increased H2O evaporation from the warmer oceans in the CO2 rich atmosphere and, hence, ocean-atmosphere interactions play a crucial role in determining the magnitude of the surface warming as well as its transient response.

This ocean-atmosphere feedback is implicitly included in model studies, but past analysts of model results have not highlighted this aspect of the problem. Consequently, published empirical approaches based on surface energy balance considerations (unaware of the ocean-atmosphere feedbacks that contribute to surface warming) have obtained results differing significantly from climate model results. Several experiments are performed with the coupled one-dimensional model to identify the various sources of the discrepancy between the modeling and empirical approaches. The paper also examines the influence of ocean-atmospheric interactions on the transient response of the climate system, which reveals the deficiencies in present schemes of asynchronously coupling the ocean and the atmosphere in three-dimensional climate models.

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