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More Evidence for Future CO2-Induced Global Cooling
Barber, D.C., Dyke, A., Hillaire-Marcel, C., Jennings, A.E., Andrews, J.T., Kerwin, M.W., Bilodeau, G., McNeely, R., Southon, J., Morehead, M.D. and Gagnon, J.-M. 1999. Forcing of the cold event of 8,200 years ago by catastrophic drainage of Laurentide lakes. Nature 400: 344-348.

What was done
The authors studied a large number of different data sets in an attempt to derive a reason for the dramatic cooling event that occurred approximately 8200 years ago: a temperature drop of 4-8C in central Greenland and drops of 1.5-3C at marine and terrestrial sites around the northeastern North Atlantic Ocean.

What was learned
The available evidence argued strongly for the catastrophic release of more than 1014 m3 of freshwater into the Labrador Sea via the final outburst drainage of glacial lakes Agassiz and Ojibway. This sudden increase in freshwater flux from the waning Laurentide ice sheet is believed by the authors to have reduced the formation rates of Labrador Sea Intermediate Water and North Atlantic Deep Water sufficiently to have strongly altered oceanic heat transport. This shock to the thermohaline oceanic "conveyor belt" system then dramatically reduced northward heat transport in this region of the world and consequently led to the observed dramatic cooling event.

What it means
This well-reasoned and data-supported analysis provides further support for the idea that CO2-induced global warming (if it is real) likely has a well-defined upper limit beyond which it cannot pass, due to the fact that nearly all models of this phenomenon predict an intensification of the hydrological cycle that would ultimately bring more freshwater outflow from the continents into this critical region of the North Atlantic, thereby slowing the rate of North Atlantic Deep Water formation, reducing the magnitude of the global thermohaline circulation, and stalling the warming that initiated the whole process.

See our Vol. 2, No. 15 Editorial Commentary What Consensus? for more detail on this topic, especially the fact that many scientists believe that this phenomenon could actually lead to dramatic global cooling.

Reviewed 1 September 1999