The wanning of the Arctic is presumed to be the cause of the rise 

 in sea level which is noted over most seacoasts. The ice is gradually- 

 melting, not only from the glaciers and ice caps, but from the Arctic 

 basin as well, and the voliime of the oceans is gradually increasing. 

 Complete melting of all ice of land and sea origin would raise the sea 

 level at least 50 feet, thus causing great changes in land area along 

 the Arctic coasts and reducing the source region of the coldest conti- 

 nental air. The long-range forecast for the Arctic basin is therefore 

 to be ice-free and warmer. 



E. FORECASTING AND THE POUR PACK 



The problems of ice forecasting of the polar pack may be divided 

 into those connected with short- and long-range forecasts. Since short- 

 range ice forecasting Is prjmarlly related to the meteorological situ- 

 ation, it will not be discussed here. The problem of long-range ice 

 forecasting for periods of from 5 days to several months may be attacked 

 through analysis of the upper-air structure and use of long-range mete- 

 orological forecasts, through analysis of the thermohaline stinicture and 

 the water masses, and through calculation of the ice potential. This 

 paper discusses only the implications of the theory of polar pack history 

 upon the forecasting problem. 



In forecasting the movements and extent of the polar pack, the fore- 

 cast may be made in general and specific terms. By general is mesLnt the 

 characterization of the coming summer or winter as a light, normal, or 

 heavy ice season. It is sufficient to predict the general extent of the 

 shore lead, the concentration, and the relative proportions of winter and 

 polar ice in the pack. For more specific forecasts it is necessary to 

 forecast the thickness of the ice, the amount of surface melting, spe- 

 cific concentrations in the various portions of the pack, the breakup 

 and freezeup conditions, the hardness, topography, rafting, pressure 

 ridging and relief of the winter and polar ice, and similar factor -, 



The polar pack ice in summer is made up of from 10 to 20 percent 

 winter ice and 75 to 85 percent polar ice. Melting proceeds more 

 rapidly in the winter ice, as about 20 to 50 percent of the area of 

 winter ice melts during the summer, while melting of the polar ice 

 amounts to only about 1 to 2 percent of the area. The major loss of 

 polar ice comes in the East. Greenland drift, in which almost 10 percent 

 of the polar ice leaven the polar basin annually. Thus, the average 

 age of the polar ice is about 8 or 9 years, although some floes are 

 much older than this and merit the name of paleocrystic ice. In fact, 

 by postulating a unifonn coverage from year to year the relative pro- 

 portions of ice of all ages can be determined. For example, with a total 

 surface coverage of 95 percent made up of 85 percent polar ice and 10 

 percent winter ice and with melting of the polar ice amounting to 1 per- 

 cent of its total area, the mean age of the polar ice is 8,7 years. Of 

 the polar ice, 10,5 percent is one year old, 19,8 percent is two years 

 old or less, etc. More than half of the ice (53,6 percent) is seven 

 years old or less, while 11,3 percent is more than 20 years old. The 

 composition of the polar ice reveals that most of it is only a few years 



8 



