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Constraining the Intermodel Spread in Cloud and Water Vapor Feedback
  • Haozhe He,
  • Ryan J Kramer,
  • Brian Soden
Haozhe He
University of Miami

Corresponding Author:haozhe.he@rsmas.miami.edu

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Ryan J Kramer
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Brian Soden
Univ. Miami, Miami
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Uncertainty in climate feedbacks is the primary source of spread in model projections of surface temperature response to anthropogenic forcing. Cloud feedback persistently appears as the main source of disagreement in future projections while the combined lapse-rate plus water vapor (LR+WV) feedback is a smaller (~30%), but non-trivial source of uncertainty in climate sensitivity. Here observation-based emergent constraints are adopted to evaluate the intermodel spread in these feedbacks. The observed interannual variation provides a useful constraint on the long-term cloud feedback as evidenced by the consistency between their global-mean values as well as their similar regional contributions to the intermodel spread. However, internal variability does not serve to constrain the long-term LR+WV feedback spread, which we find is mostly associated with the relative humidity response over the tropics. Model differences in hemispheric warming asymmetries, induced primarily by ocean heat uptake differences, also contribute to the spread in water vapor feedback.