About one quarter of the Arctic pack melts each summer,although the percentage varies widely.Unlike other ocean,the Arctic Ocean is almost landlocked,but warm,Gulf Stream water flows into it from the Atlantic and a lesser amount of heat is also carried in from the Pacific through the Bering Strait.Hence the Arctic Ocean,at depths below 500 feet,is underlaid by a layer of warm water 2,500 feet thick.tis surface would also be warmer,were it not for its covering of ice,which on the average is a few yards thick.The North Pole region receives more solar heat in the summer months than do the tropics,since the sun shines on it night and day.
Such specialists as Dr.Mikhail I. Budyko,director of the main Geophysical Observatory in Leningrad,and Dr.Henri Bader of the University of Miami,believe that the ocean would not freeze again,even in the winter,once the pack had disappeared.In fact,Dr.budyko argues that an ice-free Arctic Ocean is the "normal" situation.He thinks that throughout the 70 million years preceding the ice ages of the last million years the ocean was ice-free.There is a strong suspicious on both sides of the Atlantic that the ages-which may continue to recur-represent some kind of cyclic behavior related to the presence or absence of ice on the Arctic Ocean.
If the ocean were free of ice,storm paths,it is thought,would move further north,depriving the plains of North American and of central Eurasia of rainfall.Winds blowing off the Arctic Ocean would become moist,and snowfall on mountains in the path of those winds would be almost continuous.This would start the formation of sheets such as those the several times south across North American and Eurasia.
The warning sounded by Colonel Balchen has stirred up enough excitement in Washington for the Navy to ask Dr.Norbert Untersteiner of the University of Washington to prepare an assessment of trends in the pack.His report will appear shortly in Naval Research Reviews.Dr.Untersteiner,who has spent a good part of his professional career living on or studying the Arctic pack summarized his report in a telephone interview.In essence, he believes not only that the climatic trend in the Arctic has turned toward cooling,but that the evidence for swift and dramatic thinning of the pack is unreliable.
Until recently there was a suspicion that the warming trend of the century preceding 1940 was a by-product of the industrial revolution.Carbon dioxide,produced by combustion,makes the atmosphere less transparent to infra-red radiation,thus trapping the earth's heat like the roof of a greenhouse.There is evidence that the carbon dioxide content of the world's air has risen from10 to 15 percent during the last century.However,the cooling trend of recent years indicates that other factors are at work,including perhaps the volume of dust and smog in the air.this tends to reduce the solar heat reaching the surface.According to Dr.Reid A. bryson,professor of meteorology at the University of Wisconsin,transparency of the atmosphere above the highest summit of the Hawaiian Islands has been decreasing at a rate of 30 percent each decade.In view of the summit's remoteness from industrial areas,thus is taken as an index of global air pollution.