The climate in the historical era is discussed in most detail in the monograph by A. S. Monin and Yu. A. Shishkov. Below is a brief description of the climate of the historical era according to these authors.
The end of the first and beginning of the second millennium AD in the history of Europe is known as the Viking Age. At this time, immigrants from Scandinavia - Swedes, Norwegians and Danes - made long trips, discovering and developing new lands. This expansion had political roots, but it was facilitated by the significant warming that ensued.
At this time, the Vikings conquered the Faroe Islands and Iceland, and later Greenland. The Faroe Islands, which means “Sheep” Islands in Norwegian, served as a springboard for the capture of Iceland. After the settlement of Iceland, the discovery and colonization of Greenland (Green Land) occurred.
Icelandic sagas indicate that the Normans repeatedly visited the islands of the Canadian Arctic archipelago. Although until recently their reliability was questioned, nevertheless, relatively recently, the remains of an ancient Norwegian settlement were discovered on the northern tip of Newfoundland. The layout of the house corresponds surprisingly closely to the layout of one of the houses, the ruins of which have been preserved in East Greenland. The widespread expansion of the Vikings into the northern countries was favored by climatic conditions; voyages at that time were not hampered by sea ice, the existence of which is not mentioned in the sagas. For a long time, regular communication was maintained between Greenland and Iceland. The voyage was carried out by the shortest route, along the 65th parallel. However, already in the middle of the 14th century. sea ice began to impede navigation along this route.
The inhabitants of modern Greenland are engaged in catching fish and sea animals, but at that time the villagers were mainly engaged in cattle breeding. This, in turn, indicates not only the absence of ice at that time, but also the wide distribution of meadow vegetation.
During the warming period, they also swam to the northeast. According to some data, it is assumed that they reached the mouth of the river. Ponoy on the Kola Peninsula, and on others - the Northern Dvina. The Normans discovered Spitsbergen, where at that time, as evidenced by spore-pollen analysis of sediments of this age, tundra existed.
According to various estimates, the average annual temperature in South Greenland was 2-4°C higher than at present. The waters of the Atlantic and southern Arctic Ocean were just as warmer. However, the warming of the Viking Age in Europe, due to its short duration, did not lead to large movements of plant zones. In the mountainous regions and Scandinavia, the height of distribution of woody vegetation increased by 100-200 m. At this time, grains were cultivated in Iceland, and the grape growing zone moved 4-5° to the north, and grapes were cultivated in the northern regions of the GDR and the Federal Republic of Germany, in Latvia and Southern England.
In North America, the period of the VIII-XIII centuries. had a favorable climate. Wild grapes, less demanding of heat, common in modern times up to 45° N. sh., at that time it grew at 50° N. w. Settlements were widespread throughout Southern Canada; the main occupation of their inhabitants was agriculture. The Upper Mississippi and Great Lakes regions were significantly warmer than in the modern era. The cooling that began in the 13th-14th centuries led to increased humidity in these areas and to aridity in the southwestern and western United States, which led to a sharp decline in agriculture.
Changes in the temperature regime in Greenland, Iceland and England, identified on the basis of variations in the heavy oxygen isotope by W. Dansgaard et al., occurred almost synchronously (6.3).
At the turn of the 1st and 2nd millennia AD, conditions were warmer than at present in Asia and on other continents. In the VII-X centuries. in the river valley On the Yellow River, tangerines and oranges grew and at the same time in China, according to chronicles, there was a minimum number of severe winters. Cold temperatures and heavy snowfalls are observed
in the XII-XIV centuries. During this period, Cambodia, the Mediterranean, Central America and East Africa were wetter.
In the 12th century. cooling began, reaching its maximum at the beginning of the 18th century. It was called the Little Ice Age. We join the opinion of A. S. Monin and Yu. A. Shishkov that this term in use is unauthorized. It reflects the exclusivity of the cooling, and in fact it was only one of several cold snaps that occurred after the climatic optimum, however, due to its proximity to the modern era, this cooling has been well studied on the basis of chronicles and instrumental methods.
The most convincing indicators of changes in climatic conditions in historical times are changes in the position of glaciers and the level of the snow line. Mountain glaciers naturally grow when the amount of solid precipitation increases as a result of lengthening cold seasons or when ablation (melting and evaporation) decreases. Studies of modern glaciers have shown that they do not immediately respond to climate change, but lag for several years and the duration of the lag depends on the size of the glacier, geographical location and topography of the subglacial surface.
After the warm early Middle Ages in the Alps, already in the 13th century. The size of glaciers began to increase. The advance of glaciers is observed not only in the Alps, Scandinavia and Iceland, but also in North America. It especially intensified in the second half of the 16th century. and at the turn of the 16th and 17th centuries. This is evidenced by the remains of moraines and dendrochronological data.
Over the course of several centuries, the glaciers of the Alps changed their area. The maximum advance of alpine glaciers, associated with cooling, occurred at the turn of the 16th and 17th centuries. This is indicated by the remains of buried settlements and mine workings. At the beginning of the 18th century. Glacier growth was observed in Iceland, Norway and Northern Sweden. According to many sources, glacial advances were noted in 1720 (Alps, Scandinavia, USA, Alaska), 1740-1750 (Iceland, Scandinavia, Alaska), 1820 and 1850. (northern Sweden, Iceland). The advance of glaciers in Europe was especially strong in 1750.
V. Brinkmann compiled a generalized graph illustrating the number of maximum glacier advances in the northern hemisphere from 1550 to 1900. Maximum glacier advances occurred in 1610, 1650, 1710, 1750, 1810-1820, 1850, but at the beginning of the 20th century. There is a significant decrease in the area of glaciers.
Climate fluctuations are evidenced not only by pulsating changes in the area of mountain glaciers, but also by the state of the ice situation in the Arctic Ocean, North and Baltic Seas. There is numerous indirect evidence indicating different temperature regimes and degrees of cooling during the Little Ice Age. For example, in 1300-1350. Icelanders completely abandoned the cultivation of grain crops. There are references in chronicles to harsh winters and cool summers in Rus' in 1454, in the mid-16th and early 17th centuries.
In the XIII-XIV centuries. Weather variability increased and a strong cooling occurred. Many countries experienced harsh winters, heavy snowfalls, as well as severe droughts and catastrophic floods. The ice cover of the polar seas has increased significantly. Greenland and Iceland were covered with ice, and in northern Norway, agricultural work completely stopped due to unfavorable climatic conditions.
The next cold wave arrived around the middle of the 16th century. For this time, there are chronicle reports of harsh and long winters in Europe, in particular, the formation of ice cover in the Gulf of Genoa, the freezing of olive trees in France and Italy, and the decline of viticulture in France.
Cooling occurred not only in Europe, but also on other continents. Ancient Chinese chronicles and written documents from other Asian countries indicate cold periods of 1200-1600. According to T. Yamamoto, the advance of glaciers according to radiocarbon dating occurred in 1430 ±80 years, but the maximum cooling occurred in the period 1750-1850. At this time, summer and winter temperatures were 1 - 2 °C lower than in the modern era.
There is no doubt that corresponding changes in temperature and humidity also occurred in tropical latitudes. Indirect evidence of this is the change in river levels during the Little Ice Age.
The Little Ice Age was followed by warming, which began at the end of the 19th century. It manifested itself especially strongly in the 20-30s of the 20th century, when signs of intense warming appeared in the Arctic. According to N.M. Knipovich, the water surface temperature in the Barents Sea in 1919-1928. turned out to be almost 2°C higher than in 1912-1918. According to instrumental observations, in the 1930s the temperature in temperate and high latitudes increased by 5°C compared to the beginning of the century, and in Spitsbergen - even by 8-9°C.
During this period, the retreat of glaciers is observed. In the Alps, glaciers have retreated by 1000-1500 m. Glaciers are retreating in Norway, Sweden, Iceland, Greenland and Spitsbergen. The area of mountain glaciers is decreasing (Caucasus, Pamir, Tien Shan, Altai, Sayan Mountains, Himalayas). The area of glaciers in Africa and the South American Cordillera has greatly decreased. At the same time, many ice islands in the Arctic are disappearing and permafrost and thermokarst phenomena are degrading. Ice conditions in the Arctic improved from 1924 to 1945 and the ice area decreased by approximately 1 million km2.
In the 40s of the XX century. The warming process gave way to cooling, which intensified in the 60s. However, in the mid-60s, average temperatures in the northern hemisphere reached temperatures in the late 10s. During the 1970s, there was a trend towards a significant increase in average annual temperatures. According to M.I. Budyko, in the northern hemisphere, the decrease in temperature ended in the mid-60s and was replaced by an increase in temperature, which accelerated in the early 70s. Research in recent years has shown that for the period 1964-1977. the increase in average annual global temperatures was 0.2-0.3 °C per decade. The greatest increase is typical for high latitudes. According to Budyko, north of 72.5° N. w. rate of temperature rise for 1964-1975. equal to 0.9 °C over 10 years for annual averages and 1.3 °C over 10 years for averages for the cold half-year. Consequently, secular temperature changes were accompanied by strong changes in the mean meridional gradient.
Many authors, including Angell and Korshover, Barnett, Painting, Walsh, based on an analysis of data on air temperature and at various latitudes of the northern hemisphere, unequivocally recognize that the cooling that occurred until the mid-60s was replaced by warming. The development of the 70s warming in the southern hemisphere, and in particular in Antarctica, was noted by Damon and Kuhnen. A. S. Grigorieva and L. A. Strokina analyzed data on temperature fluctuations in the oceanic waters of the northern hemisphere. Changes in water temperature in the Barents Sea and the North Atlantic Ocean are in good agreement with fluctuations in average air temperature, but lag somewhat behind them. This lag can be explained by the high heat capacity of ocean waters.
However, it should be noted that temperature fluctuations in the South Atlantic, North Pacific Ocean and other places do not show a tendency for temperatures to increase in the 70s. This appears to be related to the global system of sea currents.
Observations of the state of the ice situation in the polar regions, at the boundaries of sea ice and mountain glaciers make it possible to draw conclusions not only about the trend of temperature changes, but also about its impact on natural conditions. At the same time, as M.I. Budyko notes, the boundaries of sea ice not only strongly depend on air temperature, but, in turn, they influence the thermal regime of the atmosphere. At high latitudes above the ice-free ocean surface, the air temperature drops only a few degrees below 0°C as the ocean gives off a lot of heat. When the surface of the ocean is covered with ice, the air temperature drops tens of degrees below zero.
According to E. S. Rubinshtein and L. G. Polozova, sea ice cover in the Atlantic sector of the Arctic began to decrease in the 20s of the 20th century. This process in the Barents Sea continued until the mid-50s, after which the ice cover began to increase. The secular variation of ice cover in the Greenland and Barents Seas, calculated by A. S. Grigorieva, shows that the decrease in the area of ice cover occurred after 1920 and reached its maximum value in the mid-50s. In the early 60s, the ice area increased again, but after 1970 it began to decrease significantly. According to R. Sanderson, from 1969 to 1974, ice cover in the Arctic decreased. Similar data are available for the southern hemisphere.
Along with changes in the thermal regime of the atmosphere, the amount of precipitation fluctuates. O.A. Drozdov and A.S. Grigorieva note that during the era of the greatest warming that occurred in the 30s, the number of droughts in zones of insufficient moisture in Eurasia and North America increased significantly. In particular, this is indicated by the drop in the level of the Caspian Sea and the decrease in the full flow of rivers.
Thus, during the 20th century. There were two periods of warming and cooling. The warming that began in late 1969 is currently underway, and temperatures tend to rise further.
Indo-Europeans of Eurasia and the Slavs Gudz-Markov Alexey Viktorovich
Chapter 1. Glacier retreat to the north. Revitalizing life in Eurasia
The retreat of the fourth and last Würm glaciation in the history of the Earth began in the 18th millennium BC. e. However, Northern Europe remained shackled by an ice shell, the thickness of which reached two kilometers, for another ten millennia. A frozen sea of blue ice rested on the northern spurs of the Alps and Carpathians.
On the slopes of the Ural ridge, a powerful tongue of ice reached the heart of the Eurasian plain. The mountain peaks of the Pyrenees, Apennines, Balkans, Caucasus, and Central Asia were covered with huge ice caps, sending cold-freezing streams of ice and snow into the deep valleys surrounding them. From Middle England to the Middle Dnieper and further to the Pacific Ocean, the Eurasian continent was surrounded by a wide belt of tundra. The Arctic cold scorched the waters and shores of the Mediterranean, Black and Caspian Seas with piercing cold. And in Southern Europe, in Asia Minor, in the vast expanses of Central Asia and Siberia, the ocean of taiga stretches like evergreen pine needles.
By the 14th millennium BC. e. The lands of modern Denmark, Germany, Poland, Southern Lithuania, parts of Northern Russia and Siberia were freed from under the ice cover. The glacier retreating into the Arctic left huge lakes everywhere and piles of huge boulders scattered everywhere. The contours of the northern seas emerged from under the ice. Following the retreating glacier, mammoths, woolly rhinoceroses, and reindeer moved north. To the south of them, on the vast Eurasian expanses, herds of wild horses, bulls, deer, and bison grazed. They were constantly hunted by hyenas, bears, and cave lions. The mammoths and woolly rhinoceroses that reached the north of the continent soon died and now remind of themselves only through fossilized frozen remains preserved by permafrost.
In the XIV–XI millennium BC. e. The final, Gothic, phase of the last (Würm) glaciation of the Earth has passed. From century to century, the rocks of Northern Britain and Scandinavia, polished by ice and cold, became more and more clearly visible. The sun rescued them from icy captivity, which lasted almost a hundred thousand years. Following the retreating glacier, the tundra, scorched by the arctic cold, was lined with a boundless green carpet. And after it, the taiga crossed the Carpathian and Alpine barriers. Year after year, she pushed further north, towards the steaming cold of the Arctic, dwarf birches torn by the prickly winds and shapeless, spreading pines, clinging to the death to the thawing earth with light yellow crooked trunks. Following the persistent green dwarfs, the seas of coniferous forests advanced in living waves to the north.
For ten thousand years, a gigantic ice sheet slid meter by meter from Europe.
The planet was thawing, the climate was softening. The continent was covered with mixed forest. Its fragrant, delicate green canopy hid the earth from the piercingly cold air currents from the north. Glacial lakes were filled with life, their marshy shores were overgrown with lush grasses. Silent unwitting wanderers, eternal companions of the glacier - boulders, fragments of distant northern rocks, gloomy uninvited guests in Europe - were dressed in moss and grew into the turf. In northern Eurasia, warmed by the sun, oak groves, spreading lindens, and elms were added from century to century.
But in the 9th millennium BC. e. Europe still fully felt the cold of the receding Arctic ice. The steep cliffs of Britain and Scandinavia, polished almost to a mirror shine by the salty waves of the Atlantic, blue ice floes and cruel winds, said goodbye for an endlessly long time to the vast sparkling ice field creeping to the north.
During the 9th–6th millennium BC. e. The forest-tundra of Northern Europe is overgrown with mixed forest. The canopy of the forests was filled with many red deer, boars, fur-bearing animals, and a rich feathered world. Europe was turning into a hunting paradise. The climate became milder from century to century.
Freed from ice captivity, the Baltic took on its modern shape. The waters of Lake Ladoga made their way to the Gulf of Finland and formed a new river - the Neva. The land that existed between Britain and the continent gradually sank more and more into the depths of the sea. The resulting English Channel separated the islands of the British archipelago from Europe. The Black Sea for a long time remained a lake connected to the Caspian Sea, but its breakthrough by the waters of the Bosphorus Isthmus was approaching, and around the 5th millennium BC. e. this event happened. Europe was taking on its modern shape.
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“At present it is difficult to look into the depths of time and draw a consistent course of the distribution of land and water in different geological eras. Such attempts, in the absence of the necessary data, inevitably contain a certain amount of fantasy, and if, for the reasons stated above, they are difficult to refute, then for the same reason they cannot be proven.”
A.K. Leonov. "Regional Geography"
We are now living in the Quaternary period. Otherwise it is called the Anthropocene, the era of man. Today, many scientists believe that humans appeared on Earth during the last Ice Age.
Long periods of time when the climate throughout the Earth was cold and dry, and large areas of land were covered by a thick shell of glaciers, are a characteristic feature of our Quaternary period.
This shortest modern period of the Cenozoic lasts about 0.7–1 million years. Despite the understandable “closeness,” the history of the Quaternary period today causes such heated debates and serious disagreements that other geological eras, tens and hundreds of millions of years distant from us, do not know.
For example, the boundaries separating the Quaternary period from the previous Tertiary period were repeatedly revised: in the specialized literature one can find a variety of dates relating to its duration - from 500 thousand years to 5 million! By the way, for comparison, we note that the age of the Earth as a planet is now estimated at 4.5 billion years.
Glacial and thermal periods have alternated many times in geological history. Over the last billion years, warm eras have been replaced three times by glacial ones, accompanied by the development of continental glaciations in high latitudes and the establishment of a humid climate in non-glacial areas. We are apparently living at the beginning of the last Laurasian Ice Age, which began about 20–30 million years ago.
Over the past 700 thousand years, glaciations have occurred on our planet at least 7–8 times. Over the past 100 thousand years, profound changes have taken place in the history of our planet. The interglacial period that preceded the glaciation (Mikulino) ended approximately 70–75 thousand years ago. After this, the “first frost” struck. Throughout Europe the climate became wet and cold. This date is considered the beginning of the last Valdai (Vistula) glaciation.
Neither glacial eras nor interglacials were uniform; they were divided into colder and warmer ones. These changes can be illustrated using the examples of Europe and North America. The development of climate from the Mikulino interglacial to the present time looks approximately as follows (processed according to K. Butzer, 1974):
A). Developments in Europe
75,000 years ago - end of the interglacial, beginning of cooling
75,000–64,000 - cold climate, glacier growth
65,000–60,000 - slight warming, glacial retreat in Scandinavia
60,000–40,000 - first glacial maximum; cold climate, the frontal line of glaciers advances to the southern coast of the Baltic
40,000–20,000 - significant climate fluctuations, maximum warming before the 37th and 30th millennia, in between the preservation of a cold climate
20,000–13,000 - second ice maximum, maximum distribution of glaciers
13,000–12,000 - warming, rapid retreat of glaciers
12,500 years ago significant climate fluctuations
12,000–11,300 - small but unstable warming, frequent temperature fluctuations
11,300–10,200 - slight cooling, local growth of glaciers
b). Developments in North America
75,000 years ago - end of the interglacial, significant cooling, appearance and growth of cover glaciers
75,000–60,000 - cooling, growth of glaciers, but in the 65th millennium warming, partial retreat of glaciers
60,000–50,000 - first ice maximum, glacier front approaches the Great Lakes
50,000–44,000 - very noticeable warming and significant retreat of glaciers
44,000–41,000 - severe cooling, maximum expansion of glaciers
41,000–33,000 - some warming
33,000–29,000 - relatively strong cooling, new advance of glaciers
29,000–23,000 - warming, glacier retreat
23,000–12,800 - cooling, second ice maximum, sharp temperature fluctuations, maximum glaciation before the 19th millennium
12,800–11,500 - strong and very rapid warming, glaciers are rapidly retreating, a period of temperate climate begins
11,500–10,000 - some cooling again; slight growth of glaciers, which, however, are far from reaching their previous volumes
When comparing the history of glaciation in Europe and North America, one is struck by a fairly precise correspondence between the cold and warm periods. Oscillations during the transition to the post-glacial era are also synchronous. All this indicates that ice ages are unlikely to be caused by some local causes; rather, we must talk about their global origin.
It was established that about 20 thousand years ago the last ice sheet of the northern hemisphere reached its greatest extent: the area of glaciation was approximately twice the modern area. The volume of ice was then three times greater than in our time. Glaciation lasted 60 thousand years and ended approximately 12–13 thousand years ago.
The Anthropocene is divided into the Pleistocene and Holocene (last post-glacial time). The Holocene began approximately 13–11 thousand years ago and continues to this day. This period also accounts for the bulk of the history of modern humanity.
Currently, there is no consensus among scientists about the most recent glaciation, and discussions arise on this issue every now and then.
The essence of one of them is this: what is our present time - the interval between two great glaciations, or is there no threat of a new ice age to humanity?
We are undoubtedly interested in the fact that during glaciations, huge masses of water in just a few thousand years - almost instantly - are taken from the oceans and accumulated in glaciers on the continents. Transforming into a solid state, they occupy vast areas of land in the form of ice and compressed snow.
All this leads to the drying of the shelf and, naturally, to a decrease in the level of the World Ocean, which causes the emergence of specific “bridges” between continents (Africa and Europe, Asia and North America, Africa, as well as Australia). It is quite clear that this last circumstance played an important role in the settlement of ancient people.
At that time, ice sheets covered the entire territory of what is now Canada, and in other places extended from Scandinavia and Scotland to the southern regions of Great Britain. The territories of Ireland and France merged with Great Britain into a single continental region. The last glaciation dramatically changed the landscape of Europe and had a strong impact on its climate.
Since the total amount of water in the nature of the globe does not change (it is approximately 1 billion 390 million cubic kilometers), it is quite clear that the decrease in water levels in the oceans (the World Ocean accounts for about 96.5% of water) is associated with its conversion to ice . As for the total ice reserves on Earth, they amount to more than 30 million cubic kilometers.
This is almost 2/3 of all fresh water, which is equal to the flow of all the rivers of the globe over 600–700 years.
Currently, the earth's glaciers (including underground ice) account for up to 14 percent of the land surface. Ice sheets almost completely cover the entire continent - Antarctica - and the largest island on Earth - Greenland. At the same time, ice shelves (about 7 percent of the surface of the World Ocean) and their fragments - icebergs (20 percent of the ocean area), as well as perennial and seasonal sea ice, float on vast areas of oceans and seas.
Thus, about 21 percent of the Earth's surface is now occupied by ice and glaciers.
Therefore, we have to assume that we live in... an ice age, apparently between two glacial maxima. As already noted, during the previous glacial maximum, that is, 20-18 thousand years ago, land and sea ice covered 43 percent of the Earth's surface.
A very important phenomenon called glacioisostasy is associated with glaciations. The fact is that an ice dome several hundred meters thick (in some areas of Antarctica the thickness of the ice today reaches 3–4 kilometers), squeezing the earth’s crust with its enormous weight, causes it to sag. An ice mass 2 kilometers thick pushes the earth's crust approximately 700 meters.
During interglacial periods, when, for example, the glacial load in northern Europe disappeared, the earth's crust began to straighten and within a few thousand years returned to its equilibrium position.
Thus, glacioisostatic movements led to significant changes in the outlines and depths of marginal seas in northern Europe.
For example, back in the 18th century, the observant Finnish bishop Erik Sorolainen noted that the seashores of his homeland were “growing”... Since then, scientists have carried out hundreds of measurements and observations. They were able not only to determine the rate of modern land uplift in areas of former glaciers, but also to calculate this rate in the era of ice melting, separated from us by millennia.
In the initial stage of glacier melting, which, according to modern data, occurred 13–11 thousand years ago, in the area of the current Norwegian Oslo station, the rate of land rise reached almost 5 centimeters per year. Over a thousand years, Scandinavia has risen by more than 45 meters.
Apparently, a fairly powerful glacier was melting at a rapid pace at that time, and then it slowed down.
Subsequently, for example, 6–8 thousand years ago, the rate of uplift decreased by almost half and reached 25 meters per millennium. The glacier completely melted, but the earth's crust continued to rise, albeit even more slowly. It is currently rising at a rate of 9 meters per millennium, that is, less than a millimeter per year. And in just the era that began with the melting of the glaciers and continues to this day, the Scandinavian shield rose by 500–600 meters, but some researchers even put the figure at 700 meters!
Moreover, it turned out that the rise of Scandinavia is uneven. Back in the 18th century, it was noted that the coasts of Northern Sweden were rising, and those of Southern Sweden were falling. In other words, part of the territory that was the sea becomes land, and part of the land turns into a shelf literally before our eyes. In the north of the Gulf of Bothnia, the rate of rise is 1 centimeter per year: the Baltic shelf comes to the surface. But in another area of the Baltic, near Copenhagen, the land is sinking at a rate of about 1 millimeter per year, and there is a slow but constant elusive advance of the sea.
As a result, the Baltic Sea is changing its shape. Since it is the youngest in the world (it arose about 16 thousand years ago), it has been established that the Baltic acquired its main contours only 4–5 thousand years ago.
During this time, which is insignificant from the point of view of geology, the Baltic Sea went through several stages in its development, differing from each other in climatic, geological and hydrological conditions, fauna and flora, and also, naturally, the outlines of its coast. The Baltic was sometimes a lake, sometimes a sea, the south of Scandinavia was sometimes connected by land with the European continent, sometimes disconnected from it, etc.
Is it possible for the destruction of cities and islands in this area in ancient times and even antiquity?
The history of the North Sea shows that yes.
For example, in the 1st millennium AD, a vast territory was under its waters, as chronicles and legends of past years colorfully tell.
In the past, many islands disappeared in the waves of the North Sea. Perhaps among them were the legendary islands of Is, Lyonesse, and Avalon, about which ancient Celtic legends tell. But it is no longer legends, but documentary stories that say that many former islands of the North Sea have become the current shoals and banks. At the end of the 11th century, the area of Heligoland was 90 square kilometers, now it is only 0.6 square kilometers. Underwater archaeological research has shown that on the shelf bordering Heligoland on all sides, there are traces of some ancient structures...
Shelf boundaries are not determined by depth alone. The average depth of the world shelf today is considered to be 132 meters, although there are areas lying at a depth of several hundred meters.
For example, off the coast of Antarctica, the shelf is located at depths of up to 500 meters. Most likely, the earth's crust here caved in under the terrible pressure of the ice that currently covers Antarctica.
By the way, the volume of this ice during the last glaciation was even greater.
Antarctica's fresh ice now makes up 90 percent (more than 27 million cubic kilometers) of the Earth's total ice mass. New data shows that this giant ice sheet began to form much earlier than researchers had expected until relatively recently. Mountain-valley glaciers in West Antarctica began to form 40–50 million years ago. Since then, the glaciation of Antarctica has never been interrupted.
The melting of glaciers and the filling of the World Ocean with water served as the basis for the appearance of legends about the “great flood”, which scientists, ethnographers and folklorists recorded among the most diverse peoples of the Earth, in Europe and Asia, America and Australia, Africa and Oceania. By the way, the Bible also speaks about the global flood, and its word, for example, was believed unquestioningly in the Middle Ages. Only a heretic or a pagan could doubt the Holy Scriptures.
And therefore, medieval science had to dress up in the garb of religion. Philosophers, mathematicians, and logicians created their works in the form of commentaries on biblical texts. And the beginnings of the Earth sciences - medieval hydrography, geology, oceanology arose as a kind of commentary on the stories about the global flood, with which God, according to the Bible, punished the human race for its sins. Sea shells are found on the tops of high mountains: isn’t this proof that the waters of the flood covered “all the high mountains that are under the whole sky,” as the Bible says.
However, gradually it became clear to most critically thinking scientists that the history of the flood as it is presented in the Bible, to put it mildly, does not entirely correspond to reality... Firstly, Noah’s ark could not accommodate “two of all living creatures.” Secondly, water could not cover the highest mountains of the entire planet. And thirdly, the human race could not have originated from the three descendants of the righteous Noah. And the advent of the 19th century - the “era of great historical discoveries”, which continues to this day - brought the sensational discovery of texts that served as the basis for the biblical story of the flood...
But we are somewhat distracted from our story...
So, a complex of very different data that makes it possible to restore the general patterns of the Late Pleistocene glaciation closest to us has shown that the slow initial development of ice sheets (25–20 thousand years ago) was replaced by their rapid growth and their subsequent degradation (12–10 thousand years ago ).
The melting of glaciers that once covered northern Europe, most of North America, and vast territories of Antarctica, that is, the liberation of certain vast areas of the Earth from former continental ice, naturally caused a significant rise in the current level of the World Ocean.
Today, the majority of scientists dealing with this problem - geologists, glaciologists, geomorphologists, oceanologists - do not have a common opinion about the levels of depression of the World Ocean during the era of the most recent glaciation.
Modern glacial massifs of the Arctic and Antarctic, as well as mountain glaciers, bind such an amount of water that if all this ice melted at once and the water poured into the oceans, their level would rise by many tens of meters, and huge coastal territories (their area is commensurate or even exceeds the territory of the current CIS) would be under water, including many of the world's largest port cities.
However, despite the continuing debate about the level of the World Ocean, one trend can be noticed: an increase in the depths from which it is necessary to count when reconstructing the ancient land that existed during the last glaciation.
The times are not so far away when it was considered “firmly established” that the level of the World Ocean during the era of the last glaciation was 90 meters lower than today. Then new facts forced scientists to name the figure 110 meters. The latest series of discoveries made during deep drilling, studying coral structures, the distribution of freshwater fish, etc., again forced us to reconsider the established level.
Now even the most cautious researchers call the value 140–150 meters. Many domestic and foreign scientists believe that the level of the World Ocean was 180–200 meters lower than today.
This means that, when reconstructing the outlines of islands and continents during the last glaciation, we must consider as former land everything that is covered with light blue paint on modern maps of the seas or is limited by an isobath of 200 meters!..
So, the departure of the last glacier, which increased the water level in the World Ocean by 150–200 meters, showed us that it plays a very important role in the life of our planet.
It takes millions of years for a glacier to melt. But today glaciers are disappearing right before our eyes. And this is confirmed by indisputable facts - photographs.
Jokulsarlon, Iceland. 2009. A 360-kilogram block of ice, doomed to death, glistens in the moonlight on a winter Icelandic beach. The tide carried her into the lagoon formed by a retreating glacier. Balog calls such glacier fragments ice “diamonds.”
It seems to me that glaciers are alive. They look like wild animals. Previously, people were afraid of them, like wolves - the only difference was that one glacier could immediately devour an entire village. By the end of the 19th century, everything changed: residents of northern countries came up with the idea of using glaciers as bait for tourists. For example, in Switzerland it was possible to go to the middle of the Rhone Glacier through a tunnel (it was cut down every summer!), the entrance to which was located a stone's throw from the Belvedere Hotel. Perhaps very soon the glaciers will disappear altogether - they will “die out”, like many animals. But for now they are here - alive.
They are breathing. At the top of the glacier, the snow compacts, turning into ice; at the base, the ice, on the contrary, melts. "The glacier inhales in winter and exhales in summer," says Matthias Huss, a glaciologist at the University of Freiburg in Switzerland. In August, he said, the Rhone River gets a quarter of its water from melting glaciers.
Perhaps very soon the glaciers will disappear altogether - they will “die out”, like many animals. But for now they are here - alive.
Icefjord glacier, Greenland 2008. Warm sea water from the North Atlantic breaks off an iceberg the height of a 15-story building from the glacier.
They are moving. “If a glacier isn't moving, it's standing ice, not a glacier,” explains Dan Fagr, pointing to a white stripe on the horizon in Glacier National Park, Montana, USA. Dan is an environmentalist specializing in global warming issues who has worked at the park for two decades.
There are now 25 active glaciers in Glacier Park, but a century ago there were six times as many - 150. Many of them disappeared even before scientists could map the glaciers. That they were once here is proven by the moraines they left behind - piles of boulders and rubble, that is, unsorted rock fragments that were plowed by moving blocks of ice.
Columbia Glacier, Columbia Bay, Alaska. 2006 When photographer James Balog first photographed the Columbia Glacier, it had already retreated nearly 18 kilometers since 1980. This speed gave Balog the idea for the Extreme Ice Survey: installing cameras near glaciers to document climate change.
Bridge Glacier, British Columbia, 2012: Retreating about one and a half meters per melt season, the 10-kilometre Bridge Glacier in British Columbia's Coast Range is under dual threat from scant snowfall in winter and warmer temperatures in summer. As the glacier melts, the lake at its base increases in size.
They rule nature. 20 thousand years ago, Switzerland was a sea of ice, above which the peaks of the Alps rose in islands. The remaining glaciers grew slightly in the 19th century, at the end of the so-called Little Ice Age. Photographs from 1849 show that the border of the Rhone Glacier at that time was 500 meters lower than it is now.
It was during the Little Ice Age that Swiss scientists managed to collect data on other - past - ice ages. Only then, in the 19th century, did we learn that the Earth’s climate periodically changes greatly. And if humanity had not intervened in natural processes by building factories and cars, a new ice age would have awaited us in one or two millennia. Now the threat is exactly the opposite.
2012 Prince William Sound is clogged with icebergs, indicating that the retreat of the Columbia Glacier is accelerating. In six years, he lost more than three kilometers of ice in length. The height of the glacier has decreased by almost 380 meters compared to 1980 - this is the height of the Empire State Building.
This photo of the Rhone Ice Tunnel was taken in the summer of 2012; in 2009 the ice ended where the fabric cover is now. The glacier is rapidly thinning, losing both length and width. A tourist stands on ice covered with mud and stones that have rolled down the slope.
They are fighting. Glaciers always strive for equilibrium - they maintain a height and mass such that the amount of snow falling on top of the glacier equals the amount of ice melting below. “They are trying to adapt, but it is not easy,” explains Matthias Huss. Weather conditions are different everywhere, so there are still glaciers on Earth that are advancing. But there are very few such persistent ones: in the Alps, for example, not a single one. Half of the local ice melted in the last century - enough water to fill all Swiss lakes. Huss predicts that 80 to 90 percent of Alpine glaciers will disappear by 2100.
Rhone Glacier, Switzerland, 2012. An icy river is drying up in the Alps. In the last century, this majestic glacier, the famous source of the Rhone River, shortened by almost one and a half kilometers. Every summer, the owners of the Belvedere Hotel dig a tunnel into the glacier to allow tourists to walk inside. In recent years, in order for the structure to survive the summer season, it has to be covered with heat-insulating fabric.
Steingletscher, Switzerland, 2006
Steingletcher, Switzerland, 2012. In six years, the shape of the ancient Steingletcher glacier has changed significantly. If the summer months in mountain regions continue to become warmer and drier, many alpine glaciers could lose up to 75% of their mass or disappear altogether by the end of the century, threatening local water resources.
Glacier Bridge, British Columbia, 2009
The Rhone glacier has retreated into the mountains and is now not visible from the valley. Today it ends right above the Belvedere Hotel, and in the summer you can still walk through the tunnel dug through it. To see the glacier in winter, when the road to the hotel is closed, you will have to climb the mountain.
“Of course, Glacier Park would be beautiful without glaciers,” notes Dan Fagr. “And in Switzerland too,” Huss continues, but adds: “Although it personally pains me to watch how these huge and beautiful animals gradually fade away, lose weight and die.”
Text: Robert Kanzig Photos: James Balog
The Earth's climate periodically undergoes serious changes associated with alternating large-scale cold snaps, accompanied by the formation of stable ice sheets on the continents, and warming. The last ice age, which ended approximately 11-10 thousand years ago, for the territory of the East European Plain is called the Valdai glaciation.
Systematics and terminology of periodic cold spells
The longest stages of general cooling in the history of the climate of our planet are called cryoeras, or glacial eras lasting up to hundreds of millions of years. Currently, the Cenozoic cryoera has been ongoing on Earth for about 65 million years and, apparently, will continue for a very long time (judging by previous similar stages).
Over the course of eons, scientists have identified ice ages interspersed with phases of relative warming. Periods can last millions and tens of millions of years. The modern ice age is Quaternary (the name is given in accordance with the geological period) or, as is sometimes said, Pleistocene (according to a smaller geochronological division - epoch). It began approximately 3 million years ago and, apparently, is still far from complete.
In turn, ice ages consist of shorter-term - several tens of thousands of years - ice ages, or glaciations (the term “glacial” is sometimes used). The warm intervals between them are called interglacials, or interglacials. We now live precisely during such an interglacial era, which replaced the Valdai glaciation on the Russian Plain. Glaciations, although they have undoubted common features, are characterized by regional characteristics, and therefore are named after a particular area.
Within eras, there are stages (stadials) and interstadials, during which the climate experiences short-term fluctuations - pessimums (cold snaps) and optima. The present time is characterized by the climatic optimum of the sub-Atlantic interstadial.
Age of the Valdai glaciation and its phases
According to the chronological framework and conditions of division into stages, this glacier is somewhat different from the Würm (Alps), Vistula (Central Europe), Wisconsin (North America) and other corresponding glaciations. On the East European Plain, the beginning of the era that replaced the Mikulin interglacial is dated back to about 80 thousand years ago. It should be noted that establishing clear time boundaries is a serious difficulty - as a rule, they are blurred - therefore the chronological framework of the stages fluctuates significantly.
Most researchers distinguish two stages of the Valdai glaciation: the Kalininskaya with maximum ice approximately 70 thousand years ago and the Ostashkovskaya (about 20 thousand years ago). They are separated by the Bryansk Interstadial - a warming that lasted from approximately 45-35 to 32-24 thousand years ago. Some scientists, however, propose a more detailed division of the era - up to seven stages. As for the retreat of the glacier, it occurred over a period of 12.5 to 10 thousand years ago.
Glacier geography and climatic conditions
The center of the last glaciation in Europe was Fennoscandia (including the territories of Scandinavia, the Gulf of Bothnia, Finland and Karelia with the Kola Peninsula). From here the glacier periodically expanded to the south, including onto the Russian Plain. It was less extensive in scope than the previous Moscow glaciation. The boundary of the Valdai ice sheet ran in the northeast direction and at its maximum did not reach Smolensk, Moscow, and Kostroma. Then, on the territory of the Arkhangelsk region, the border sharply turned north to the White and Barents seas.
In the center of glaciation, the thickness of the Scandinavian ice sheet reached 3 km, which is comparable to the glacier of the East European Plain, which had a thickness of 1-2 km. Interestingly, while the ice cover was significantly less developed, the Valdai glaciation was characterized by harsh climatic conditions. Average annual temperatures during the last glacial maximum - Ostashkovo - were only slightly higher than the temperatures of the era of the very powerful Moscow glaciation (-6 °C) and were 6-7 °C lower than today.
Consequences of glaciation
The ubiquitous traces of the Valdai glaciation on the Russian Plain indicate the strong influence it had on the landscape. The glacier erased many of the irregularities left by the Moscow glaciation, and formed during its retreat, when a huge amount of sand, debris and other inclusions melted from the ice mass, deposits up to 100 meters thick.
The ice cover did not advance as a continuous mass, but in differentiated flows, along the sides of which piles of fragmentary material—marginal moraines—formed. These are, in particular, some ridges within the current Valdai Upland. In general, the entire plain is characterized by a hilly-moraine surface, for example, a large number of drumlins - low elongated hills.
Very clear traces of glaciation are lakes formed in hollows plowed by a glacier (Ladoga, Onega, Ilmen, Chudskoye and others). The river network of the region also acquired its modern appearance as a result of the influence of the ice sheet.
The Valdai glaciation changed not only the landscape, but also the composition of the flora and fauna of the Russian Plain, influenced the area of settlement of ancient man - in a word, it had important and multifaceted consequences for this region.
