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Modeling abrupt change in the thermohaline circulation


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Image of sea surface temperature in the North Atlantic

Measured sea surface temperature in the North Atlantic, in degrees Celsius.
Paleoclimate records give an abundance of information about how climate changed in the past. Why climate changed is more difficult to answer. Unfortunately, the resolution and dating of paleoclimate records are sometimes insufficient for examining leads and lags in the climate system. Also, scientists are able to reconstruct only certain climate variables at certain locations, which give an incomplete picture of past events. To test ideas about causation, scientists have turned to computer climate models.

Climate models are computer programs that apply physical laws to calculate how climate has changed in the past and may change in the future. Models range from relatively simple ones, which represent only the most essential processes at a coarse spatial resolution, to complex ones, which include many additional important interactions between the atmosphere, ocean, sea ice and land surface operating at regional scales. Models are not a perfect representation of the climate system. By necessity, some complex processes must be idealized or incompletely represented. That said, models do a remarkable job of reproducing most of the important aspects of our present climate system.

Climate models have been used to test the hypothesis that floods of freshwater entering the North Atlantic were responsible for past abrupt coolings in Europe and eastern North America. The effects of such a freshwater hosing can be examined using numerical (computer) models of the coupled ocean-atmosphere circulation. The model results shown below were completed by Ron Stouffer at the NOAA Geophysical Fluid Dynamics Laboratory, and are based on the work reported by Manabe and Stouffer (1997).

Animation of surface air temperature changeAnimation of surface air temperature change
Watch changes in annual surface air temperature through 200 years of model simulation.

Maps of surface air temperature Maps of surface air temperature
Map annual surface air temperature from the model simulation for any two user-specified years.


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Last Updated Wednesday, 20-Aug-2008 11:21:31 EDT by paleo@noaa.gov
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