How does rising atmospheric CO2 affect marine organisms?

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What Controls the Global Thermohaline Circulation?
Saenko, O.A., Weaver, A.J. and Schmittner, A.  2003.  Atlantic deep circulation controlled by freshening in the Southern Ocean.  Geophysical Research Letters 30: 10.1029/2003GL017681.

Many people fear - or at least claim they do - that global warming will lead to enhanced precipitation in high northern latitudes, which will lead to augmented freshwater runoff to the North Atlantic Ocean, which will lead to a precipitous decline in North Atlantic Deep Water formation, which will produce a swift reduction in the global ocean's thermohaline circulation, which will shut down the Gulf Stream and bring cold times to Europe [see Rapid Climate Change in our Subject Index].  Are their worries justified?

What was done
In exploring this hypothesis, the authors used "a coupled model which comprises an ocean general circulation model, a dynamic-thermodynamic sea ice model and an energy-moisture balance atmospheric model" to examine "the effect of meridional moisture transport in the Southern Hemisphere mid-latitudes on the meridional overturning circulation (MOC) and heat transport in the Atlantic."

What was learned
The authors purport to show that "the Atlantic MOC, northward oceanic heat transport, and the associated air-sea heat flux anomalies are all proportional to the southward moisture transport from subtropical to subpolar regions in the Southern Hemisphere."

What it means
In the words of the authors, "it has often been pointed out that in a warmer climate, an intensified hydrological cycle would weaken the MOC by transporting more moisture northward."  Their results, however, "suggest that the intensified hydrological cycle could also tend to stabilize the MOC by transporting more moisture southward."  The bottom line, as they thus remark, is that the various mechanisms that have been proposed for controlling deep water formation in the North Atlantic "remain controversial."

In view of these developments, it would appear to be way too early to even think of concluding, as many climate alarmists do, that there could soon be a warming-induced freezing of Europe of the "rapid climate change" type.

Reviewed 12 November 2003