Origin of the Greenland Ice Sheet 
Gerald R. North 
NASA/Goddard Space Flight Center, Greenbelt, MD 20771 
A climate model resolving the seasonal cycle and the two horizontal dimensions has been 
developed at GSFC over the last few years and applied to several problems of current interest. 
Models of this type are useful when for various reasons a general circulation model experiment 
is not warranted or not feasible. For example, in cases where the signal to natural variability 
is small it may be advantageous to first consider such a statistical dynamical model because 
extremely long runs may be necessary in the application. In this case the simpler statistical 
dynamical model serves as a pilot study device. 
The model developed at GSFC is a thermodynamic model whose solution yields the 
equilibrium seasonal cycle for the surface temperature field over the globe. The model is 
essentially a statement of the conservation of heat energy for individual columns of the earth 
atmosphere system. Various terms such as the infrared radiation flux to space are parame- 
terized with earth radiation budget data from satellites such as Nimbus 6. The primary agent 
modulating the seasonal cycle amplitude is the heat capacity per unit area which is a strong func- 
tion of surface type -- ocean surface can store 60 times more heat per unit time than land. By 
adjusting its few empirical parameters the model can be brought into remarkable agreement with 
the observed seasonal cycle. The model is described in detail elsewhere (North et al., 1983). 
The model is then very useful for looking at the dependence of the seasonal cycle of the 
temperature on such externally defined variables as the earth's orbital elements (eccentricity, 
tilt, precession of equinoxes) or the configuration of land-sea geography which can be changed 
by continental drift. Geological observations imply that the first effect appears to be the cause 
of the major periodic glaciations which have occurred over the last few million years. Studies 
with the GSFC energy balance model support this hypothesis further by suggesting the growth of 
large continental ice sheets especially in North America when orbital elements favor cooler sum- 
mers which was the case about 125 thousand years ago when the last great glaciation began 
(North et al., 1983). 
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Fig. 1. Polar projection of the July surface temperature distribution as computed by the model, 
which does not employ an increased albedo over the Greenland ice sheet. In other words the 
minimum over the Norwegian Sea is induced solely by land-sea configuration. 
