Out of the chamber of the South cometh the storm,
and cold out of the North.
THE BOOK OF JOB
WHEN THE BUILDING of the Panama Canal was first suggested, the project was severely criticized in Europe. The French, especially, complained that such a canal would allow the waters of the Equatorial Current to escape into the Pacific, that there would then be no Gulf Stream, and that the winter climate of Europe would become unbearably frigid. The alarmed Frenchmen were completely wrong in their forecast of oceanographic events, but they were right in their recognition of a general principle—the close relation between climate and the pattern of ocean circulation.
There are recurrent schemes for deliberately changing—or attempting to change—the pattern of the currents and so modifying climate at will. We hear of projects for diverting the cold Oyashio from the Asiatic coast, and of others for controlling the Gulf Stream. About 1912 the Congress of the United States was asked to appropriate money to build a jetty from Cape Race eastward across the Grand Banks to obstruct the cold water flowing south from the Arctic. Advocates of the plan believed that the Gulf Stream would then swing in nearer the mainland of the northern United States and would presumably bring us warmer winters. The appropriation was not granted. Even if the money had been provided, there is little reason to suppose that engineers then—or later—could have succeeded in controlling the sweep of the ocean’s currents. And fortunately so, for most of these plans would have effects different from those popularly expected. Bringing the Gulf Stream closer to the American east coast, for example, would make our winters worse instead of better. Along the Atlantic coast of North America, the prevailing winds blow eastward, across the land toward the sea. The air masses that have lain over the Gulf Stream seldom reach us. But the Stream, with its mass of warm water, does have something to do with bringing our weather to us. The cold winds of winter are pushed by gravity toward the low-pressure areas over the warm water. The winter of 1916, when Stream temperatures were above normal, was long remembered for its cold and snowy weather along the east coast. If we could move the Stream inshore, the result in winter would be colder, stronger winds from the interior of the continent—not milder weather.
But if the eastern North American climate is not dominated by the Gulf Stream, it is far otherwise for the lands lying ‘down-stream.’ From the Newfoundland Banks, as we have seen, the warm water of the Stream drifts eastward, pushed along by the prevailing westerly winds. Almost immediately, however, it divides into several branches. One flows north to the western shore of Greenland; there the warm water attacks the ice brought around Cape Farewell by the East Greenland Current. Another passes to the southwest coast of Iceland, and, before losing itself in arctic waters, brings a gentling influence to the southern shores of that island. But the main branch of the Gulf Stream or North Atlantic Drift flows eastward. Soon it divides again. The southernmost of these branches turns toward Spain and Africa and re-enters the Equatorial Current. The northernmost branch, hurried eastward by the winds blowing around the Icelandic ‘low,’ piles up against the coast of Europe the warmest water found at comparable latitudes anywhere in the world. From the Bay of Biscay north its influence is felt. And as the current rolls northeastward along the Scandinavian coast, it sends off many lateral branches that curve back westward to bring the breath of warm water to the arctic islands and to mingle with other currents in intricate whirls and eddies. The west coast of Spitsbergen, warmed by one of these lateral streams, is bright with flowers in the arctic summer; the east coast, with its polar current, remains barren and forbidding. Passing around the North Cape, the warm currents keep open such harbors as Hammerfest and Murmansk, although Riga, 800 miles farther south on the shores of the Baltic, is choked with ice. Somewhere in the Arctic Sea, near the island of Novaya Zemlya, the last traces of Atlantic water disappear, losing themselves at last in the overwhelming sweep of the icy northern sea.
It is always a warm-water current, but the temperature of the Gulf Stream nevertheless varies from year to year, and a seemingly slight change profoundly affects the air temperatures of Europe. The British meteorologist, C. E. P. Brooks, compares the North Atlantic to ‘a great bath, with a hot tap and two cold taps.’ The hot tap is the Gulf Stream; the cold taps are the East Greenland Current and the Labrador Current. Both the volume and the temperature of the hot-water tap vary. The cold taps are nearly constant in temperature but vary immensely in volume. The adjustment of the three taps determines surface temperatures in the eastern Atlantic and has a great deal to do with the weather of Europe and with happenings in arctic seas. A very slight winter warming of the eastern Atlantic temperatures means, for example, that the snow cover of northwestern Europe will melt earlier, that there will be an earlier thawing of the ground, that spring plowing may begin earlier, and that the harvest will be better. It means, too, that there will be relatively little ice near Iceland in the spring and that the amount of drift ice in the Barents Sea will diminish a year or two later. These relations have been clearly established by European scientists. Someday long-range weather forecasts for the continent of Europe will probably be based in part on ocean temperatures. But at present there are no means for collecting the temperatures over a large enough area, at frequent enough intervals.*
For the globe as a whole, the ocean is the great regulator, the great stabilizer of temperatures. It has been described as ‘a savings bank for solar energy, receiving deposits in seasons of excessive insolation and paying them back in seasons of want.’ Without the ocean, our world would be visited by unthinkably harsh extremes of temperature. For the water that covers three-fourths of the earth’s surface with an enveloping mantle is a substance of remarkable qualities. It is an excellent absorber and radiator of heat. Because of its enormous heat capacity, the ocean can absorb a great deal of heat from the sun without becoming what we would consider ‘hot,’ or it can lose much of its heat without becoming ‘cold.’
Through the agency of ocean currents, heat and cold may be distributed over thousands of miles. It is possible to follow the course of a mass of warm water that originates in the trade-wind belt of the Southern Hemisphere and remains recognizable for a year and a half, through a course of more than 7000 miles. This redistributing function of the ocean tends to make up for the uneven heating of the globe by the sun. As it is, ocean currents carry hot equatorial water toward the poles and return cold water equator-ward by such surface drifts as the Labrador Current and Oyashio, and even more importantly by deep currents. The redistribution of heat for the whole earth is accomplished about half by the ocean currents, and half by the winds.
At that thin interface between the ocean of water and the ocean of overlying air, lying as they do in direct contact over by far the greater part of the earth, there are continuous interactions of tremendous importance.
The atmosphere warms or cools the ocean. It receives vapors through evaporation, leaving most of the salts in the sea and so increasing the salinity of the water. With the changing weight of that whole mass of air that envelops the earth, the atmosphere brings variable pressure to bear on the surface of the sea, which is depressed under areas of high pressure and springs up in compensation under the atmospheric lows. With the moving force of the winds, the air grips the surface of the ocean and raises it into waves, drives the currents onward, lowers sea levels on windward shores, and raises it on lee shores.
But even more does the ocean dominate the air. Its effect on the temperature and humidity of the atmosphere is far greater than the small transfer of heat from air to sea. It takes 3000 times as much heat to warm a given volume of water 1° as to warm an equal volume of air by the same amount. The heat lost by a cubic meter of water on cooling 1° C. would raise the temperature of 3000 cubic meters of air by the same amount. Or to use another example, a layer of water a meter deep, on cooling .1° could warm a layer of air 33 meters thick by 10°. The temperature of the air is intimately related to atmospheric pressure. Where the air is cold, pressure tends to be high; warm air favors low pressures. The transfer of heat between ocean and air therefore alters the belts of high and low pressure; this profoundly affects the direction and strength of the winds and directs the storms on their paths.
There are six more or less permanent centers of high pressure over the oceans, three in each hemisphere. Not only do these areas play a controlling part in the climate of surrounding lands, but they affect the whole world because they are the birthplaces of most of the dominant winds of the globe. The trade winds originate in high-pressure belts of the Northern and Southern hemispheres. Over all the vast extent of ocean across which they blow, these great winds retain their identity; it is only over the continents that they become interrupted, confused, and modified.
In other ocean areas there are belts of low pressure, which develop, especially in winter, over waters that are then warmer than the surrounding lands. Traveling barometric depressions or cyclonic storms are attracted by these areas; they move rapidly across them or skirt around their edges. So winter storms take a path across the Icelandic ‘low’ and over the Shetlands and Orkneys into the North Sea and the Norwegian Sea; other storms are directed by still other low-pressure areas over the Skagerrak and the Baltic into the interior of Europe. Perhaps more than any other condition, the low-pressure area over the warm water south of Iceland dominates the winter climate of Europe.
And most of the rains that fall on sea and land alike were raised from the sea. They are carried as vapor in the winds, and then with change of temperature the rains fall. Most of the European rain comes from evaporation of Atlantic water. In the United States, vapor and warm air from the Gulf of Mexico and the tropical waters of the western Atlantic ride the winds up the wide valley of the Mississippi and provide rains for much of the eastern part of North America.
Whether any place will know the harsh extremes of a continental climate or the moderating effect of the sea depends less on its nearness to the ocean than on the pattern of currents and winds and the relief of the continents. The east coast of North America receives little benefit from the sea, because the prevailing winds are from the west. The Pacific coast, on the other hand, lies in the path of the westerly winds that have blown across thousands of miles of ocean. The moist breath of the Pacific brings climatic mildness and creates the dense rain forests of British Columbia, Washington, and Oregon; but its full influence is largely restricted to a narrow strip by the coast ranges that follow a course parallel to the sea. Europe, in contrast, is wide open to the sea, and ‘Atlantic weather’ carries hundreds of miles into the interior.
By a seeming paradox, there are parts of the world that owe their desert dryness to their nearness to the ocean. The aridity of the Atacama and Kalahari deserts is curiously related to the sea. Wherever such marine deserts occur, there is found this combination of circumstances: a western coast in the path of the prevailing winds, and a cold coastwise current. So on the west coast of South America the cold Humboldt streams northward off the shores of Chile and Peru—the great return flow of Pacific waters seeking the equator. The Humboldt, it will be remembered, is cold because it is continuously being reinforced by the upwelling of deeper water. The presence of this cold water offshore helps create the aridity of the region. The onshore breezes that push in toward the hot land in the afternoons are formed of cool air that has lain over a cool sea. As they reach the land they are forced to rise into the high coastal mountains—the ascent cooling them more than the land can warm them. So there is little condensation of water vapor, and although the cloud banks and the fogs forever seem to promise rain, the promise is not fulfilled so long as the Humboldt rolls on its accustomed course along these shores. On the stretch from Arica to Caldera there is normally less than an inch of rain in a year. It is a beautifully balanced system—as long as it remains in balance. What happens when the Humboldt is temporarily displaced is nothing short of catastrophic.
At irregular intervals the Humboldt is deflected away from the South American continent by a warm current of tropical water that comes down from the north. These are years of disaster. The whole economy of the area is adjusted to the normal aridity of climate. In the years of El Niño, as the warm current is called, torrential rains fall—the downpouring rains of the equatorial regions let loose upon the dust-dry hillsides of the Peruvian coast. The soil washes away, the mud huts literally dissolve and collapse, crops are destroyed. Even worse things happen at sea. The cold-water fauna of the Humboldt sickens and dies in the warm water, and the birds that fish the cold sea for a living must either migrate or starve.
Those parts of the coast of Africa that are bathed by the cool Benguela Current also lie between mountains and sea. The easterly winds are dry, descending winds, and the cool breezes from the sea have their moisture capacity increased by contact with the hot land. Mists form over the cold waters and roll in over the coast, but in a whole year the rainfall is the meagerest token. The mean rainfall at Swakopmund in Walvis Bay is 0.7 inches a year. But again this is true only as long as the Benguela holds sway along the coast, for there are times when the cold stream falters as does the Humboldt, and here also these are years of disaster.
The transforming influence of the sea is portrayed with beautiful clarity in the striking differences between the Arctic and Antarctic regions. As everyone knows, the Arctic is a nearly landlocked sea; the Antarctic, a continent surrounded by ocean. Whether this global balancing of a land pole against a water pole has a deep significance in the physics of the earth is uncertain; but the bearing of the fact on the climates of the two regions is plainly evident.
The ice-covered Antarctic continent, bathed by seas of uniform coldness, is in the grip of the polar anticyclone. High winds blow from the land and repel any warming influence that might seek to penetrate it. The mean temperature of this bitter world is never above the freezing point. On exposed rocks the lichens grow, covering the barrenness of cliffs with their gray or orange growths, and here and there over the snow is the red dust of the hardier algae. Mosses hide in the valleys and crevices less exposed to the winds, but of the higher plants only a few impoverished stands of grasses have managed to invade this land. There are no land mammals; the fauna of the Antarctic continent consists only of birds, wingless mosquitoes, a few flies, and microscopic mites.
In sharp contrast are the arctic summers, where the tundra is bright with many-colored flowers. Everywhere except on the Greenland icecap and some of the arctic islands, summer temperatures are high enough for the growth of plants, packing a year’s development into the short, warm, arctic summer. The polar limit of plant growth is set not by latitude, but by the sea. For the influence of the warm Atlantic penetrates strongly within the Arctic Sea, entering, as we have seen, through the one large break in the land girdle, the Greenland Sea. But the streams of warm Atlantic water that enter the icy northern seas bring the gentling touch that makes the Arctic, in climate as well as in geography, a world apart from the Antarctic.
So, day by day and season by season, the ocean dominates the world’s climate. Can it also be an agent in bringing about the long-period swings of climatic change that we know have occurred throughout the long history of the earth—the alternating periods of heat and cold, of drought and flood? There is a fascinating theory that it can. This theory links events in the deep, hidden places of the ocean with the cyclic changes of climate and their effects on human history. It was developed by the distinguished Swedish oceanographer, Otto Pettersson, whose almost century-long life closed in 1941. In many papers, Pettersson presented the different facets of his theory as he pieced it together, bit by bit. Many of his fellow scientists were impressed, others doubted. In those days few men could conceive of the dynamics of water movements in the deep sea. Now the theory is being re-examined in the light of modern oceanography and meteorology, and only recently C. E. P. Brooks said, ‘It seems that there is good support for Pettersson’s theory as well as for that of solar activity, and that the actual variations of climate since about 3000 B.C. may have been to a large extent the result of these two agents.’
To review the Pettersson theory is to review also a pageant of human history, of men and nations in the control of elemental forces whose nature they never understood and whose very existence they never recognized. Pettersson’s work was perhaps a natural outcome of the circumstances of his life. He was born—as he died 93 years later—on the shores of the Baltic, a sea of complex and wonderful hydrography. In his laboratory atop a sheer cliff overlooking the deep waters of the Gulmarfiord, instruments recorded strange phenomena in the depths of this gateway to the Baltic. As the ocean water presses in toward that inland sea it dips down and lets the fresh surface water roll out above it; and at that deep level where salt and fresh water come into contact there is a sharp layer of discontinuity, like the surface film between water and air. Each day Pettersson’s instruments revealed a strong, pulsing movement of that deep layer—the pressing inward of great submarine waves, of moving mountains of water. The movement was strongest every twelfth hour of the day, and between the 12-hour intervals it subsided. Pettersson soon established a link between these submarine waves and the daily tides. ‘Moon waves,’ he called them, and as he measured their height and timed their pulsing beat through the months and years, their relation to the ever-changing cycles of the tides became crystal clear.
Some of these deep waves of the Gulmarfiord were giants nearly 100 feet high. Pettersson believed they were formed by the impact of the oceanic tide wave on the submarine ridges of the North Atlantic, as though the waters moving to the pull of the sun and moon, far down in the lower levels of the sea, broke and spilled over in mountains of highly saline water to enter the fiords and sounds of the coast.
From the submarine tide waves, Pettersson’s mind moved logically to another problem—the changing fortunes of the Swedish herring fishery. His native Bohuslan had been the site of the great Hanseatic herring fisheries of the Middle Ages. All through the thirteenth, fourteenth, and fifteenth centuries this great sea fishery was pursued in the Sund and the Belts, the narrow passageways into the Baltic. The towns of Skanor and Falsterbo knew unheard-of prosperity, for there seemed no end of the silvery, wealth-bringing fish. Then suddenly the fishery ceased, for the herring withdrew into the North Sea and came no more into the gateways of the Baltic—this to the enrichment of Holland and the impoverishment of Sweden. Why did the herring cease to come? Pettersson thought he knew, and the reason was intimately related to that moving pen in his laboratory, the pen that traced on a revolving drum the movements of the submarine waves far down in the depths of Gulmarfiord.
He had found that the submarine waves varied in height and power as the tide-producing power of the moon and sun varied. From astronomical calculations he learned that the tides must have been at their greatest strength during the closing centuries of the Middle Ages—those centuries when the Baltic herring fishery was flourishing. The sun, moon, and earth came into such a position at the time of the winter solstice that they exerted the greatest possible attracting force upon the sea. Only about every eighteen centuries do the heavenly bodies assume this particular relation. But in that period of the Middle Ages, the great underwater waves pressed with unusual force into the narrow passages to the Baltic, and with the ‘water mountains’ went the herring shoals. Later, when the tides became weaker, the herring remained outside the Baltic, in the North Sea.
Then Pettersson realized another fact of extreme significance—that those centuries of great tides had been a period of ‘startling and unusual occurrences’ in the world of nature. Polar ice blocked much of the North Atlantic. The coasts of the North Sea and the Baltic were laid waste by violent storm floods. The winters were of ‘unexplained severity’ and in consequence of the climatic rigors political and economic catastrophes occurred all over the populated regions of the earth. Could there be a connection between these events and those moving mountains of unseen water? Could the deep tides affect the lives of men as well as of herring?
From this germ of an idea, Pettersson’s fertile mind evolved a theory of climatic variation, which he set forth in 1912 in an extraordinarily interesting document called Climatic Variations in Historic and Prehistoric Time.* Marshalling scientific, historic, and literary evidence, he showed that there are alternating periods of mild and severe climates which correspond to the long-period cycles of the oceanic tides. The world’s most recent period of maximum tides, and most rigorous climate, occurred about 1433, its effect being felt, however, for several centuries before and after that year. The minimum tidal effect prevailed about A.D. 550, and it will occur again about the year 2400.
During the latest period of benevolent climate, snow and ice were little known on the coast of Europe and in the seas about Iceland and Greenland. Then the Vikings sailed freely over the northern seas, monks went back and forth between Ireland and ‘Thyle’ or Iceland, and there was easy intercourse between Great Britain and the Scandinavian countries. When Eric the Red voyaged to Greenland, according to the Sagas, he ‘came from the sea to land at the middle glacier—from thence he went south along the coast to see if the land was habitable. The first year he wintered on Erik’s Island …’ This was probably in the year 984. There is no mention in the Sagas that Eric was hampered by drift ice in the several years of his exploration of the island; nor is there mention of drift ice anywhere about Greenland, or between Greenland and Wineland. Eric’s route as described in the Sagas— proceeding directly west from Iceland and then down the east coast of Greenland—is one that would have been impossible during recent centuries. In the thirteenth century the Sagas contain for the first time a warning that those who sail for Greenland should not make the coast too directly west of Iceland on account of the ice in the sea, but no new route is then recommended. At the end of the fourteenth century, however, the old sailing route was abandoned and new sailing directions were given for a more southwesterly course that would avoid the ice.
The early Sagas spoke, too, of the abundant fruit of excellent quality growing in Greenland, and of the number of cattle that could be pastured there. The Norwegian settlements were located in places that are now at the foot of glaciers. There are Eskimo legends of old houses and churches buried under the ice. The Danish Archaeological Expedition sent out by the National Museum of Copenhagen was never able to find all of the villages mentioned in the old records. But its excavations indicated clearly that the colonists lived in a climate definitely milder than the present one.
But these bland climatic conditions begin to deteriorate in the thirteenth century. The Eskimos began to make troublesome raids, perhaps because their northern sealing grounds were frozen over and they were hungry. They attacked the western settlement near the present Ameralik Fiord, and when an official mission went out from the eastern colony about 1342, not a single colonist could be found—only a few cattle remained. The eastern settlement was wiped out some time after 1418 and the houses and churches destroyed by fire. Perhaps the fate of the Greenland colonies was in part due to the fact that ships from Iceland and Europe were finding it increasingly difficult to reach Greenland, and the colonists had to be left to their own resources.
The climatic rigors experienced in Greenland in the thirteenth and fourteenth centuries were felt also in Europe in a series of unusual events and extraordinary catastrophes. The seacoast of Holland was devastated by storm floods. Old Icelandic records say that, in the winters by the early 1300’s, packs of wolves crossed on the ice from Norway to Denmark. The entire Baltic froze over, forming a bridge of solid ice between Sweden and the Danish islands. Pedestrians and carriages crossed the frozen sea and hostelries were put up on the ice to accommodate them. The freezing of the Baltic seems to have shifted the course of storms originating in the low-pressure belt south of Iceland. In southern Europe, as a result, there were unusual storms, crop failures, famine, and distress. Icelandic literature abounds in tales of volcanic eruptions and other violent natural catastrophes that occurred during the fourteenth century.
What of the previous era of cold and storms, which should have occurred about the third or fourth century B.C., according too the tidal theory? There are shadowy hints in early literature and folklore. The dark and brooding poetry of the Edda deals with a great catastrophe, the Fimbul-winter or Götterdämmerung, when frost and snow ruled the world for generations. When Pytheas journeyed to the seas north of Iceland in 330 B.C., he spoke of the mare pigrum, a sluggish, congealed sea. Early history contains striking suggestions that the restless movements of the tribes of northern Europe—the southward migrations of the ‘barbarians’ who shook the power of Rome—coincided with periods of storms, floods, and other climatic catastrophes that forced their migrations. Large-scale inundations of the sea destroyed the homelands of the Teutons and Cimbrians in Jutland and sent them southward into Gaul. Tradition among the Druids said that their ancestors had been expelled from their lands on the far side of the Rhine by enemy tribes and by ‘a great invasion of the ocean.’ And about the year 700 B.C. the trade routes for amber, found on the coasts of the North Sea, were suddenly shifted to the east. The old route came down along the Elbe, the Weser, and the Danube, through the Brenner Pass to Italy. The new route followed the Vistula, suggesting that the source of supply was then the Baltic. Perhaps storm floods had destroyed the earlier amber districts, as they invaded these same regions eighteen centuries later.
All these ancient records of climatic variations seemed to Pettersson an indication that cyclic changes in the oceanic circulation and in the conditions of the Atlantic had occurred. ‘No geologic alteration that could influence the climate has occurred for the past six or seven centuries,’ he wrote. The very nature of these phenomena—floods, inundations, ice blockades—suggested to him a dislocation of the oceanic circulation. Applying the discoveries in his laboratory on Gulmarfiord, he believed that the climatic changes were brought about as the tide-induced submarine waves disturbed the deep waters of polar seas. Although tidal movements are often weak at the surface of these seas, they set up strong pulsations at the submarine boundaries, where there is a layer of comparatively fresh, cold water lying upon a layer of salty, warmer water. In the years or the centuries of strong tidal forces, unusual quantities of warm Atlantic water press into the Arctic Sea at deep levels, moving in under the ice. Then thousands of square miles of ice that normally remain solidly frozen undergo partial thawing and break up. Drift ice, in extraordinary volume, enters the Labrador Current and is carried southward into the Atlantic. This changes the pattern of surface circulation, which is so intimately related to the winds, the rainfall, and the air temperatures. For the drift ice then attacks the Gulf Stream south of Newfoundland and sends it on a more easterly course, deflecting the streams of warm surface water that usually bring a softening effect to the climate of Greenland, Iceland, Spitsbergen, and northern Europe. The position of the low-pressure belt south of Iceland is also shifted, with further direct effect on European climate.
Although the really catastrophic disturbances of the polar regime come only every eighteen centuries, according to Pettersson, there are also rhythmically occurring periods that fall at varying intervals—for example, every 9, 18, or 36 years. These correspond to other tidal cycles. They produce climatic variations of shorter period and of less drastic nature.
The year 1903, for instance, was memorable for its outbursts of polar ice in the Arctic and for the repercussions on Scandinavian fisheries. There was ‘a general failure of cod, herring, and other fish along the coast from Finmarken and Lofoten to the Skagerrak and Kattegat. The greater part of the Barents Sea was covered with pack ice up to May, the ice border approaching closer to the Murman and Finmarken coasts than ever before. Herds of arctic seals visited these coasts, and some species of the arctic whitefish extended their migrations to the Christiana Fiord and even entered into the Baltic.’ This outbreak of ice came in a year when earth, moon, and sun were in a relative position that gives a secondary maximum of the tide-producing forces. The similar constellation of 1912 was another great ice year in the Labrador Current—a year that brought the disaster of the Titantic.
Now in our own lifetime we are witnessing a startling alteration of climate, and it is intriguing to apply Otto Pettersson’s ideas as a possible explanation. It is now established beyond question that a definite change in the arctic climate set in about 1900, that it became astonishingly marked about 1930, and that it is now spreading into sub-arctic and temperate regions. The frigid top of the world is very clearly warming up.
The trend toward a milder climate in the Arctic is perhaps most strikingly apparent in the greater ease of navigation in the North Atlantic and the Arctic Sea. In 1932, for example, the Knipowitsch sailed around Franz Josef Land for the first time in the history of arctic voyaging. And three years later the Russian ice-breaker Sadko went from the northern tip of Novaya Zemlya to a point north of Severnaya Zemlya (Northern Land) and thence to 82° 41’ north latitude—the northernmost point ever reached by a ship under its own power.
In 1940 the whole northern coast of Europe and Asia was remarkably free from ice during the summer months, and more than 100 vessels engaged in trade via the arctic routes. In 1942 a vessel unloaded supplies at the west Greenland port of Upernivik (latitude 72° 43’ N) during Christmas week ‘in almost complete winter darkness.’ During the ’forties the season for shipping coal from West Spitsbergen ports lengthened to seven months, compared with three at the beginning of the century. The season when pack ice lies about Iceland became shorter by about two months that it was a century ago. Drift ice in the Russian sector of the Arctic Sea decreased by a million square kilometers between 1924 and 1944, and in the Laptev Sea two islands of fossil ice melted away completely, their position being marked by submarine shoals.
Activities in the nonhuman world also reflect the warming of the Arctic—the changed habits and migrations of many fishes, birds, land mammals, and whales.
Many new birds are appearing in far northern lands for the first time in our records. The long list of southern visitors—birds never reported in Greenland before 1920—includes the American velvet scoter, the greater yellowlegs, American avocet, black-browed albatross, northern cliff swallow, ovenbird, common crossbill, Baltimore oriole, and Canada warbler. Some high-arctic forms, which thrive in cold climates, have shown their distaste for the warmer temperatures by visiting Greenland in sharply decreasing numbers. Such abstainers include the northern horned lark, the grey plover, and the pectoral sandpiper. Iceland, too, has had an extraordinary number of boreal and even subtropical avian visitors since 1935, coming from both America and Europe. Wood warblers, skylarks, and Siberian rubythroats, scarlet grosbeaks, pipits, and thrushes now provide exciting fare for Icelandic bird watchers.
When the cod first appeared in Angmagssalik in Greenland in 1912, it was a new and strange fish to the Eskimos and Danes. Within their memory it had never before appeared on the east coast of the island. But they began to catch it, and by the 1930’s it supported so substantial a fishery in the area that the natives had become dependent upon it for food. They were also using its oil as fuel for their lamps and to heat their houses.
On the west coast of Greenland, too, the cod was a rarity at the turn of the century, although there was a small fishery, taking about 500 tons a year, at a few places on the southwest coast. About 1919 the cod began to move north along the west Greenland coast and to become more abundant. The center of the fishery has moved 300 miles farther north, and the catch is now about 15,000 tons a year.
Other fishes seldom or never before reported in Greenland have appeared there. The coalfish or green cod is a European fish so foreign to Greenland waters that when two of them were caught in 1831 they were promptly preserved in salt and sent to the Co-penhagen Zoological Museum. But since 1924 this fish has often been found among the cod shoals. The haddock, cusk, and ling, unknown in Greenland waters until about 1930, are now taken regularly. Iceland, too, has strange visitors—warmth-loving southern fishes, like the basking shark, the grotesque sunfish, the six-gilled shark, the swordfish, and the horse mackerel. Some of these same species have penetrated into the Barents and White seas and along the Murman coast.
As the chill of the northern waters has abated and the fish have moved poleward, the fisheries around Iceland have expanded enormously, and it has become profitable for trawlers to push on to Bear Island, Spitsbergen, and the Barents Sea. These waters now yield perhaps two billion pounds of cod a year—the largest catch of a single species by any fishery in the world. But its existence is tenuous. If the cycle turns, the waters begin to chill, and the ice floes creep southward again, there is nothing man can do that will preserve the arctic fisheries.
But for the present, the evidence that the top of the world is growing warmer is to be found on every hand. The recession of the northern glaciers is going on at such a rate that many smaller ones have already disappeared. If the present rate of melting continues others will soon follow them.
The melting away of the snowfields in the Opdal Mountains in Norway has exposed wooden-shafted arrows of a type used about A.D. 400 to 500. This suggests that the snow cover in this region must now be less than it has been at any time within the past 1400 to 1500 years.
The glaciologist Hans Ahlmann reports that most Norwegian glaciers ‘are living only on their own mass without receiving any annual fresh supply of snow’; that in the Alps there has been a general retreat and shrinkage of glaciers during the last decades, which became ‘catastrophic’ in the summer of 1947; and that all glaciers around the Northern Atlantic coasts are shrinking. The most rapid recession of all is occurring in Alaska, where the Muir Glacier receded about 10½ kilometers in 12 years.
At present the vast antarctic glaciers are an enigma; no one can say whether they also are melting away, or at what rate. But reports from other parts of the world show that the northern glaciers are not the only ones that are receding. The glaciers of several East African high volcanoes have been diminishing since they were first studied in the 1800’s—very rapidly since 1920—and there is glacial shrinkage in the Andes and also in the high mountains of central Asia.
The milder arctic and sub-arctic climate seems already to have resulted in longer growing seasons and better crops. The cultivation of oats has improved in Iceland. In Norway good seed years are now the rule rather than the exception, and even in northern Scandinavia the trees have spread rapidly above their former timber lines, and both pine and spruce are making a quicker annual growth than they have for some time.
The countries where the most striking changes are taking place are those whose climate is most directly under the control of the North Atlantic currents. Greenland, Iceland, Spitsbergen, and all of northern Europe, as we have seen, experience heat and cold, drought and flood in accordance with the varying strength and warmth of the eastward and northward-moving currents of the Atlantic. Oceanographers who have been studying the matter during the 1940’s have discovered many significant changes in the temperature and distribution of great masses of ocean water. Apparently the branch of the Gulf Stream that flows past Spitsbergen has so increased in volume that it now brings in a great body of warm water. Surface waters of the North Atlantic show rising temperatures; so do the deeper layers around Iceland and Spitsbergen. Sea temperatures in the North Sea and along the coast of Norway have been growing warmer since the 1920’s.
Unquestionably, there are other agents at work in bringing about the climatic changes in the Arctic and sub-Arctic regions. For one thing, it is almost certainly true that we are still in the warming-up stage following the last Pleistocene glaciation—that the world’s climate, over the next thousands of years, will grow considerably warmer before beginning a downward swing into another Ice Age. But what we are experiencing now is perhaps a climatic change of shorter duration, measurable only in decades or centuries. Some scientists say that there must have been a small increase in solar activity, changing the patterns of air circulation and causing the southerly winds to blow more frequently in Scandinavia and Spitsbergen; changes in ocean currents, according to this view, are secondary effects of the shift of prevailing winds.
But if, as Professor Brooks thinks, the Pettersson tidal theory has as good a foundation as that of changing solar radiation, then it is interesting to calculate where our twentieth-century situation fits into the cosmic scheme of the shifting cycles of the tides. The great tides at the close of the Middle Ages, with their accompanying snow and ice, furious winds, and inundating floods, are more than five centuries behind us. The era of weakest tidal movements, with a climate as benign as that of the early Middle Ages, is about four centuries ahead. We have therefore begun to move strongly into a period of warmer, milder weather. There will be fluctuations, as earth and sun and moon move through space and the tidal power waxes and wanes. But the long trend is toward a warmer earth; the pendulum is swinging.
*During the 1950’s enormous advances were made in the development of instruments for the recording of water temperatures. A continuous recording of water temperatures to a depth of several hundred feet may be obtained by towing a thermistor chain behind a vessel. The electronic bathythermograph is potentially capable of obtaining temperatures at any depth, depending on the length of cable available. It is a vast improvement over the original bathythermograph because a recorder on deck traces a continuous graph of the temperatures being registered while the vessel is under way. An even more revolutionary development in the study of sea temperatures is the airborne radiation thermometer which, while flown above the sea, registers the surface temperature with an accuracy of a fraction of a degree. Oceanographers regard this instrument as still in the developmental stage, with further refinement of accuracy possible. However, in such work as tracing the edge of the Gulf Stream these airborne thermometers have already proven themselves enormously useful. During a 1960 survey of the Gulf Stream conducted by the Woods Hold Oceanographic Institution, a low-flying plane covered some 30,000 miles, obtaining surface temperatures in various areas of the Stream.
* Svenska Hydrog.-Biol. Komm. Skrifter, No. 5, 1912.