SUN, SEA, AND AIR—REVELLE 257 
it is also necessary to attempt to determine the nature of simultaneous 
climatic changes in different latitude zones. 
The great ice caps of Antarctica and Greenland and the mountain 
glaciers throughout the world are remarkable indicators of climatic 
change. During periods of warming or reduced precipitation the gla- 
ciers retreat ; when the atmosphere is cooled or snowfall increases, they 
thicken and rapidly advance. Moreover, the layers of ice laid down 
in successive years constitute an unrivaled record of events on earth 
during past millennia. 
Many aspects of glaciers will be studied during the IGY. Among 
the most significant from the standpoint of the heat and water budget 
of the earth will be the thickness of the ice. This will be measured by 
the seismic techniques used in prospecting for oil. Bore holes and 
cores will also be taken to study the frozen record of the past. 
Ice caps now cover about 3 percent of the earth’s surface. A melt- 
ing of 2 feet per year over these surfaces seems quite possible from 
present data. This would result in a rise of sea level of about an inch 
per year or roughly 10 feet in 100 years. Even such a rise as this 
would bring serious consequences to many thickly populated coastal 
areas. 
The sediments of the deep sea floor, like the ice caps, contain a de- 
tailed climatic record extending back over many thousands of years. 
For example, variations in the numbers of limy shells of the tiny ani- 
mals called Foraminifera reflect variations in the oceanic circulation 
near the surface. The ratios of oxygen isotopes in these shells tell us 
something about past ocean temperatures. At least part of the pres- 
ent temperature differences we can measure between different layers 
in deep sea sediments may be the result not of heat flow from the 
earth’s interior but of warmer temperature of the deep ocean waters 
a few hundreds or thousands of years ago. Studies of these sediments 
and their significance for climatic change will be an important part of 
the series of oceanographic expeditions to be conducted during the 
International Geophysical Year. 
The meteorologist and the oceanographer can seldom use that peer- 
less tool of the laboratory scientist—controlled experiment. As sub- 
stitutes for experiment they must attempt to make comparative inves- 
tigations of the behavior of the earth fluids under different conditions. 
For this reason a major part of the IGY meterological program will be 
focused on comparisons between the Southern and the Northern 
Hemispheres. 
Because the earth is closer to the sun in January than in July, 
the Southern Hemisphere receives about 6 percent more radiation in 
summer than does the Northern. The geometry of the two hemi- 
spheres is also quite different. In the north, the Polar Sea with its 
thin, cracked skin of ice is surrounded by continents; in the south a 
