Climatic Impact of a Change in North Atlantic Deep Water Formation 
David Rind 
NASA/Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025 
The response of the ocean to climate changes is one of the most uncertain questions 
regarding the impact of increasing CO, on climate and society. North Atlantic deep water for- 
mation apparently depends on a complex confluence of different water masses originating in dif- 
ferent areas, all of which will presumably be affected by changes in wind, evaporation, etc. as 
the atmosphere warms. To analyze from first principles what the effect will be on NADW for- 
mation is a task which requires an ocean modeling capability not yet available. 
As a substitute, one can investigate past climates and see if there is any evidence for 
alterations in NADW formation. In addition, one can then explore the possible impact of such 
changes on climate. Such a study allows for an estimate of NADW sensitivity (at least in the 
past) and of the climatic consequences. 
As reported by Ruddiman and Mix, reconstructions of the North Atlantic surface water tem- 
peratures indicate a substantial cooling between 11,000 and 10,000 years B.P. Were NADW for- 
mation to have ceased, it would have resulted in cooler surface waters; whether the 
reconstructed temperatures were due to this or some other effect cannot be determined at this 
time. Nevertheless, it was decided that it would be useful to see what the effect these colder 
temperatures would have had on the climate. 
In a joint study involving Drs. Ruddiman, McIntyre, Broecker and Alan Mix from Lamont 
and Drs. Rind, Peteet, Russell and Hansen from GISS, a GISS GCM run was made with the North 
Atlantic surface water temperatures reduced to the Ice Age value from approximately 30-70°N, 
values consistent with the 11 to 10k B.P. temperature reconstructions. Sea ice was kept at 
current values, as there is no direct evidence for sea ice changes during this interval. The 
model was integrated with all other parameters initially identical to those for the current cli- 
mate, and run for several years. The change in surface air temperature between the second 
year of the experiment and a five year control run of the current climate is shown in Fig. 1. 
Strong cooling is indicated downwind from the Atlantic, maximizing over Britian and western 
Europe, with some effect seen as far inland as central Asia. Little effect is seen upstream, 
over North America. 
90 A Surface Temperature (Deg C), Annual N.A. SST- Control 
Rese Pe 
BIS SREY 
ok _| 
-180 -120 -60 60 120 180 
eee 
Fig. 1. Change in annual average atmospheric surface air temperature between 
the experiment with cold North Atlantic surface waters and the control run. 
Latitude (degrees) 
