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Yet Another Climate Model Flip-Flop
Latif, M., Roeckner, E., Mikolajewicz, U. and Voss, R.  2000.  Tropical stabilization of the thermohaline circulation in a greenhouse warming simulation.  Journal of Climate 13: 1809-1813.

What was done
The authors investigated the sensitivity of the global ocean's thermohaline circulation (THC) to greenhouse warming using a state-of-the-art global climate model.

What was learned
Whereas most other contemporary climate models have tended to predict a weakening of the North Atlantic THC in response to greenhouse warming, due to both surface warming and the reduced surface salinity that results from enhanced freshwater riverine inputs in a high-CO2 world of intensified hydrologic cycle, the current model predicts a stabilized thermohaline circulation, due to large-scale air-sea interactions that produce anomalously high salinities in the tropical Atlantic that are subsequently advected into the region of North Atlantic Deep Water formation.

What it means
The original climate model studies that initiated the global warming hysteria all predicted, in fairly straightforward fashion, a worldwide temperature increase of catastrophic proportions.  A few years later, however, a number of "new-and-improved" climate models suggested that the global ocean's THC could be significantly weakened by a warming-induced reduction in the rate of North Atlantic Deep Water formation and that this phenomenon could significantly mute the warming.  Some of these models even simulated a complete breakdown of the THC at sufficiently strong forcing, suggesting the possibility of dramatic cooling.

We have discussed this subject at some length in two editorials - Why Worry About CO2? and What Consensus? - where we have noted the significant change in ultimate consequence predicted by these two suites of models, old and new.  We now merely call attention to the latest change elicited by the newest-and-even-more-improved model, concluding that whether or not the climate is in a state of oscillatory flux, the climate modeling enterprise sure seems to be, and at a much finer scale of temporal resolution.

The take-home message of all this?  Take all climate model predictions with a grain of salinity.  The next generation is apt to produce a very different result.

Reviewed 1 July 2000