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Controls on the Activation and Strength of a High-Latitude Convective Cloud Feedback DORIAN S. ABBOT
 

Summary: Controls on the Activation and Strength of a High-Latitude Convective Cloud Feedback
DORIAN S. ABBOT
School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts
ELI TZIPERMAN
School of Engineering and Applied Sciences, and Department of Earth and Planetary Science, Harvard University, Cambridge,
Massachusetts
(Manuscript received 23 May 2008, in final form 31 July 2008)
ABSTRACT
Previous work has shown that a convective cloud feedback can greatly increase high-latitude surface
temperature upon the removal of sea ice and can keep sea ice from forming throughout polar night. This
feedback activates at increased greenhouse gas concentrations. It may help to explain the warm ``equable
climates'' of the late Cretaceous and early Paleogene eras (;100 to ;35 million years ago) and may be
relevant for future climate under global warming. Here, the factors that determine the critical threshold CO2
concentration at which this feedback is active and the magnitude of the warming caused by the feedback are
analyzed using both a highly idealized model and NCAR's single-column atmospheric model (SCAM) run
under Arctic-like conditions. The critical CO2 is particularly important because it helps to establish the
relevance of the feedback for past and future climates.
Both models agree that increased heat flux into the high latitudes at low altitudes generally decreases the
critical CO2. Increases in oceanic heat transport and in solar radiation absorbed during the summer should
cause a sharp decrease in the critical CO2, but the effect of increases in atmospheric heat transport depends

  

Source: Abbot, Dorian Schuyler - Department of Geophysical Sciences, University of Chicago
Tziperman, Eli - Departments of Earth and Planetary Sciences & School of Engineering and Applied Sciences, Harvard University

 

Collections: Environmental Sciences and Ecology; Geosciences