1 Is a Shutdown of the Thermohaline Circulation Irreversible?
The thermohaline circulation (THC) in the North Atlantic plays a vital role in explaining past abrupt climate changes and in maintaining the current climate. Its remarkable nonlinear dynamics, first demonstrated by Stommel, has been supported by various types of climate models. This has led to sever...
| Main Authors: | , , , , |
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.418.478 http://www.agci.org/dB/PDFs/05S1_MSchlesinger_THC=JGR paper.pdf |
| Summary: | The thermohaline circulation (THC) in the North Atlantic plays a vital role in explaining past abrupt climate changes and in maintaining the current climate. Its remarkable nonlinear dynamics, first demonstrated by Stommel, has been supported by various types of climate models. This has led to severe concerns that global warming may shut down the THC irreversibly, with consequent catastrophic climate changes, particularly for Europe. Here we use a suite of models to investigate the nonlinear response of the THC to freshwater perturbation in the northern North Atlantic. We find that the THC shuts down irreversibly in the uncoupled ocean general circulation model (OGCM) simulations, but reversibly in the coupled atmosphere/ocean general circulation model (AOGCM) simulation. This occurs because of a crucial negative feedback in the AOGCM simulation that cannot occur in the OGCM simulations. This negative feedback results from complex air-sea interactions and its operation needs detailed and comprehensive simulation about the climate system. Analysis of Stommel’s 2-box ocean model supports this finding. The simulations from the uncoupled OGCM and AOGCM correspond to different parameter regimes of the 2-box model. Thus, the irreversible shutdown of the THC caused by freshwater addition appears to be a model artifact rather than a likely outcome of global warming. 2 1. |
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