HR: 1340h
AN: A23B-0796    [Abstracts]
TI: Behavior of the Thermohaline Circulation as a Function of Climate Sensitivity for Various Increased CO$_{2}$ Scenarios
AU: * Scott, J R
EM: jscott@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139 United States
AU: Sokolov, A P
EM: sokolov@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139 United States
AU: Stone, P H
EM: phstone@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139 United States
AU: Webster, M D
EM: mort@email.unc.edu
AF: The University of North Carolina at Chapel Hill, Dept. of Public Policy, Chapel Hill, NC 27599 United States
AB: Using a global coupled model of intermediate complexity (2D atmosphere, 3D ocean), the behavior of the thermohaline circulation is explored for various increased CO$_{2}$ scenarios. A novel feature of the model is our ability to adjust the model's sensitivity to CO$_{2}$ increases by changing the strength of the cloud feedback. By varying the rate and duration of increases in atmospheric CO$_{2}$, the model's sensitivity, and the river runoff scheme for perturbations in freshwater forcing, we are able to obtain and analyze a spectrum of behaviors, ranging from little change in the thermohaline circulation to a full shutdown of sinking in the North Atlantic. Although the initial decrease in overturning strength (i.e., over a centennial time scale) is primarily a function of the rate of CO$_{2}$ increase, whether the North Atlantic sinking ultimately shuts down is governed by the product of the model's prescribed climate sensitivity and the stabilization CO$_{2}$. However, if the rate of increase (for a given stabilization level) is sufficiently slow (e.g., over several hundred years), a recovery can occur for a model sensitivity/stabilization combination that collapses given a more rapid increase. Over a portion of phase space a weak, meta-stable overturning circulation exists; once the circulation crosses this threshold, a collapse rapidly occurs.
DE: 4532 General circulation
DE: 1620 Climate dynamics (3309)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting