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GEOPHYSICAL RESEARCH LETTERS, VOL. 28, NO. 22, PAGES 4223–4226, 2001

Atlantic Thermohaline Circulation and its Response to Increasing CO₂ in a Coupled Atmosphere-Ocean Model

Shan Sun

NASA Goddard Institute for Space Studies, New York, New York

Rainer Bleck

Los Alamos National Laboratory, Los Alamos, New Mexico

Abstract

We discuss aspects of the Atlantic thermohaline circulation (THC) and its response to increased greenhouse gas concentration, using a coupled atmosphere-ocean general circulation model (AOGCM) whose oceanic component is a new hybrid-isopycnal model. Two 200-year model integrations are carried out - a control run assuming fixed atmospheric composition and a perturbation run assuming gradual doubling of CO₂. We employ no flux corrections at the air-sea interface, nor do we spin up the ocean prior to coupling. The surface conditions in the control run stabilize after several decades. When doubling CO₂ at the rate of 1% per year, the model responds with a 2°C increase in global mean surface air temperature (SAT) after 200 years and a virtually unchanged Atlantic meridional overturning circulation. The latter is maintained by a salinity increase that counteracts the effect of global warming on the surface buoyancy.

Received 20 April 2001; accepted 31 July 2001.

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Citation: Sun, S., and R. Bleck (2001), Atlantic Thermohaline Circulation and its Response to Increasing CO₂ in a Coupled Atmosphere-Ocean Model, Geophys. Res. Lett., 28(22), 4223–4226.

Copyright 2001 by the American Geophysical Union.