4.7 Article

Sources of Intermodel Spread in the Lapse Rate and Water Vapor Feedbacks

Journal

JOURNAL OF CLIMATE
Volume 31, Issue 8, Pages 3187-3206

Publisher

AMER METEOROLOGICAL SOC
DOI: 10.1175/JCLI-D-17-0674.1

Keywords

Climate change; Climate sensitivity; Climate models

Funding

  1. National Science Foundation [AGS-1624881]
  2. UW IGERT Program on Ocean Change (NSF) [1068839]
  3. NASA [NNX13AN49G]
  4. NSF [PLR-1341497]
  5. U. S. Department of Energy (DOE) by LLNL [DE-AC52-07NA27344]
  6. LLNL-LDRD Program [18-ERD-054]
  7. Regional and Global Climate Modeling Program of the DOE Office of Science
  8. Direct For Education and Human Resources
  9. Division Of Graduate Education [1068839] Funding Source: National Science Foundation
  10. Office of Polar Programs (OPP)
  11. Directorate For Geosciences [1341497] Funding Source: National Science Foundation

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Sources of intermodel differences in the global lapse rate (LR) and water vapor (WV) feedbacks are assessed using CO2 forcing simulations from 28 general circulation models. Tropical surface warming leads to significant warming and moistening in the tropical and extratropical upper troposphere, signifying a nonlocal, tropical influence on extratropical radiation and feedbacks. Model spread in the locally defined LR and WV feedbacks is pronounced in the Southern Ocean because of large-scale ocean upwelling, which reduces surface warming and decouples the surface from the tropospheric response. The magnitude of local extratropical feedbacks across models and over time is well characterized using the ratio of tropical to extratropical surface warming. It is shown that model differences in locally defined LR and WV feedbacks, particularly over the southern extratropics, drive model variability in the global feedbacks. The cross-model correlation between the global LR and WV feedbacks therefore does not arise from their covariation in the tropics, but rather from the pattern of warming exerting a common control on extratropical feedback responses. Because local feedbacks over the Southern Hemisphere are an important contributor to the global feedback, the partitioning of surface warming between the tropics and the southern extratropics is a key determinant of the spread in the global LR and WV feedbacks. It is also shown that model Antarctic sea ice climatology influences sea ice area changes and southern extratropical surface warming. As a result, model discrepancies in climatological Antarctic sea ice area have a significant impact on the intermodel spread of the global LR and WV feedbacks.

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