254 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1958 
sheet like the atmosphere, but is broken up by the relatively dry areas 
we call continents. Fourth, like an invisible pousse-café, the atmos- 
phere is stratified in thin layers that do not mix readily with each 
other, and each of these layers has to a considerable extent a separate 
behavior of its own. The same is true of the ocean but with the 
marked difference that while the temperatures of the different layers 
of the atmosphere are alternatively lower and higher as we go up- 
ward, the temperature of the ocean decreases continuously nearly 
to the freezing point at great depths. It increases slightly near the 
bottom because of the heat coming from the interior of the earth. 
The energy needed to drive the sea-air circulation is only a small 
portion of the incoming solar radiation, but it is still enormous on 
a human scale. The winds of the earth have a total kinetic energy 
estimated to equal 7 million atomic bombs, or more electric power 
than all the powerplants in the United States could produce in a 
hundred years. This energy must be replenished every 9 to 12 days 
because of the loss by friction between the winds and the earth’s 
surface. 
Although there is a general agreement about the foregoing generali- 
zations, our mental model of the sea-atmosphere system is so inade- 
quate in many essentials that meteorologists are unable to predict 
anything very useful for more than a few days in advance about the 
circulation of the atmosphere. 
CLIMATIC CHANGES 
Even more fundamentally, we do not know the factors that deter- 
mine the average conditions. Consequently, we are quite unable to 
forecast changes in climate. Yet we know that such changes have 
occurred in the relatively recent past. Only about 10,000 years ago 
the earth emerged from a dark age of snow and ice; less than 5,000 
years ago, Greenland offered a fair and pleasant habitation for human 
beings. Within the last 50 years, the climate over eastern North 
America and northern Europe has again become slightly warmer 
and the Arctic wastes are perhaps again becoming accessible to human 
beings, while elsewhere prolonged droughts are destroying the work 
and hopes of decades. For the farmer, the strategist, and the states- 
man, an accurate forecast of climatic change over the next 50 years 
would be of immeasurable value. But such a forecast is completely 
beyond our present ability. Ability to forecast depends on under- 
standing, and this comes in two interrelated ways: by constructing 
small models in our heads of the two great earth fluids, and by testing 
and refining these models through observations. This second method 
is one of the major objectives of the International Geophysical Year. 
In particular, we are concerned with measurements in areas that have 
