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A fifth very serious impact of climate change may be on ocean
circulation. Palaeo-analogues and model simulations show
that the Meridional Overturning Circulation (MOC) can react
abruptly and with a hysteresis response, once a certain forcing
threshold is crossed. Discussion on the probability of the forc-
ing thresholds being crossed during this century lead to different
conclusions depending on the kind of model or analysis (Atmo-
sphere-Ocean General Circulation Models, Earth systemmodels
of intermediate complexity or expert elicitations) being used. Po-
tential impacts associated with MOC changes within the marine
SLOWING DOWN OF THERMOHALINE
CIRCULATION AND CONTINENTAL MARGIN
DENSE-WATER EXCHANGE MECHANISMS
Figure 20. The Meridional Overturning Circulation plays a crucial role for life in the oceans.
If this ocean conveyor belt slows down or
changes as a result of melting ice and increasing ocean temperatures, the impacts on marine life may become severe.