We are at the mercy of autumn and it's getting colder. Are we moving towards an ice age, one of the readers wonders.
The fleeting Danish summer is behind us. The leaves are falling from the trees, the birds are flying south, it's getting darker and, of course, colder too.
Our reader Lars Petersen from Copenhagen has begun to prepare for the cold days. And he wants to know how seriously he needs to prepare.
"When does the next ice Age? I learned that glacial and interglacial periods alternate regularly. Since we live in an interglacial period, it is logical to assume that the next ice age is ahead of us, right? he writes in a letter to the Ask Science section (Spørg Videnskaben).
We in the editorial office shudder at the thought of the cold winter that lies in wait for us at that end of autumn. We, too, would love to know if we are on the verge of an ice age.
The next ice age is still far away
Therefore, we addressed Sune Olander Rasmussen, lecturer at the Center for Basic Ice and Climate Research at the University of Copenhagen.
Sune Rasmussen studies the cold and gets information about past weather, storms, Greenland glaciers and icebergs. In addition, he can use his knowledge in order to fulfill the role of "foreteller of ice ages."
“In order for an ice age to occur, several conditions must coincide. We cannot accurately predict when the ice age will begin, but even if humanity did not further influence the climate, our forecast is that the conditions for it will develop in the best case in 40-50 thousand years,” Sune Rasmussen reassures us.
Since we are still talking to the “Ice Age predictor”, we can get some more information about what these “conditions” are in question in order to understand a little more about what the Ice Age actually is.
What is an ice age
Sune Rasmussen relates that during the last ice age the earth's average temperature was a few degrees cooler than it is today, and that the climate at higher latitudes was colder.
Much of the northern hemisphere was covered in massive ice sheets. For example, Scandinavia, Canada and some other parts North America were covered with a three-kilometer ice shell.
The huge weight of the ice cover pressed the earth's crust a kilometer into the Earth.
Ice ages are longer than interglacials
However, 19 thousand years ago, changes in the climate began to occur.
This meant that the Earth gradually became warmer, and over the next 7,000 years, freed itself from the cold grip of the Ice Age. After that, the interglacial period began, in which we are now.
In Greenland, the last remnants of the shell came off very abruptly 11,700 years ago, or to be exact, 11,715 years ago. This is evidenced by the studies of Sune Rasmussen and his colleagues.
This means that 11,715 years have passed since the last ice age, and this is a completely normal interglacial length.
“It's funny that we usually think of the ice age as an 'event', when in fact it's just the opposite. The middle ice age lasts 100 thousand years, while the interglacial lasts from 10 to 30 thousand years. That is, the Earth is more often in an ice age than vice versa.
“The last couple of interglacials lasted only about 10,000 years each, which explains the widely held but erroneous belief that our current interglacial is nearing its end,” says Sune Rasmussen.
Three Factors Influence the Possibility of an Ice Age
The fact that the Earth will plunge into a new ice age in 40-50 thousand years depends on the fact that there are small variations in the orbit of the Earth around the Sun. Variations determine how much sunlight hits which latitudes, and thereby affects how warm or cold it is.
This discovery was made by the Serbian geophysicist Milutin Milanković almost 100 years ago and is therefore known as the Milanković cycle.
Milankovitch cycles are:
1. The orbit of the Earth around the Sun, which changes cyclically about once every 100,000 years. The orbit changes from nearly circular to more elliptical, and then back again. Because of this, the distance to the Sun changes. The farther the Earth is from the Sun, the less solar radiation our planet receives. In addition, when the shape of the orbit changes, so does the length of the seasons.
2. Tilt earth's axis, which fluctuates between 22 and 24.5 degrees in relation to the orbit of rotation around the Sun. This cycle spans approximately 41,000 years. 22 or 24.5 degrees - it seems not such a significant difference, but the tilt of the axis greatly affects the severity of the different seasons. How more Earth tilted, the greater the difference between winter and summer. The Earth's axial tilt is currently at 23.5 and is decreasing, which means that differences between winter and summer will decrease over the next thousand years.
3. The direction of the earth's axis relative to space. The direction changes cyclically with a period of 26 thousand years.
“The combination of these three factors determines whether there are prerequisites for the beginning of the ice age. It is almost impossible to imagine how these three factors interact, but with the help of mathematical models we can calculate how much solar radiation is received by certain latitudes at certain times of the year, as well as received in the past and will receive in the future,” says Sune Rasmussen.
Snow in summer leads to ice age
Summer temperatures play a particularly important role in this context.
Milankovitch realized that for the ice age to start, summers in the northern hemisphere would have to be cold.
If the winters are snowy and most of the northern hemisphere is covered in snow, then the temperatures and hours of sunshine in the summer determine whether the snow is allowed to remain all summer.
“If the snow does not melt in the summer, then little sunlight penetrates the Earth. The rest is reflected back into space in a snow-white veil. This exacerbates the cooling that began due to a change in the orbit of the Earth around the Sun,” says Sune Rasmussen.
“Further cooling brings even more snow, which further reduces the amount of absorbed heat, and so on, until the ice age begins,” he continues.
Similarly, a period of hot summers leads to the end of the Ice Age. The hot sun then melts the ice enough so that sunlight can again reach dark surfaces like soil or the sea, which absorb it and warm the Earth.
Humans are delaying the next ice age
Another factor that is relevant to the possibility of an ice age is the amount of carbon dioxide in the atmosphere.
Just as snow that reflects light increases the formation of ice or accelerates its melting, the increase in carbon dioxide in the atmosphere from 180 ppm to 280 ppm (parts per million) helped bring the Earth out of the last ice age.
However, ever since industrialization began, people have been pushing the CO2 share further all the time, so it's almost 400 ppm now.
“It took nature 7,000 years to raise the share of carbon dioxide by 100 ppm after the end of the ice age. Humans have managed to do the same in just 150 years. It has great importance whether the Earth can enter a new ice age. This is a very significant influence, which means not only that an ice age cannot begin at the moment,” says Sune Rasmussen.
We thank Lars Petersen for the good question and send the winter gray T-shirt to Copenhagen. We also thank Sune Rasmussen for the good answer.
We also encourage our readers to submit more scientific questions to [email protected]
Did you know?
Scientists always talk about the ice age only in the northern hemisphere of the planet. The reason is that there is too little land in the southern hemisphere on which a massive layer of snow and ice can lie.
With the exception of Antarctica, the entire southern part of the southern hemisphere is covered with water, which does not provide good conditions for the formation of a thick ice shell.
Climatic changes were most clearly expressed in periodically advancing ice ages, which had a significant impact on the transformation of the land surface under the body of the glacier, water bodies and biological objects that are in the zone of influence of the glacier.
According to the latest scientific data, the duration of glacial eras on Earth is at least a third of the entire time of its evolution over the past 2.5 billion years. And if we take into account the long initial phases of the origin of glaciation and its gradual degradation, then the epochs of glaciation will take almost as much time as warm, ice-free conditions. The last of the ice ages began almost a million years ago, in the Quaternary, and was marked by an extensive spread of glaciers - the Great Glaciation of the Earth. The northern part of the North American continent, a significant part of Europe, and possibly Siberia as well, were under thick ice sheets. In the Southern Hemisphere, under the ice, as now, was the entire Antarctic continent.
The main causes of glaciation are:
space;
astronomical;
geographical.
Cosmic Cause Groups:
change in the amount of heat on Earth due to the passage solar system 1 time/186 million years through the cold zones of the Galaxy;
change in the amount of heat received by the Earth due to a decrease in solar activity.
Astronomical groups of causes:
change in the position of the poles;
the inclination of the earth's axis to the plane of the ecliptic;
change in the eccentricity of the Earth's orbit.
Geological and geographical groups of causes:
climate change and the amount of carbon dioxide in the atmosphere (increase in carbon dioxide - warming; decrease - cooling);
change in the direction of ocean and air currents;
intensive process of mountain building.
Conditions for the manifestation of glaciation on Earth include:
snowfall in the form of precipitation at low temperatures with its accumulation as a material for building up a glacier;
negative temperatures in areas where there are no glaciations;
periods of intense volcanism due to the huge amount of ash emitted by volcanoes, which leads to a sharp decrease in the supply of heat (sun rays) to earth's surface and causes a global decrease in temperature by 1.5-2ºС.
The oldest glaciation is the Proterozoic (2300-2000 million years ago) in the territory South Africa, North America, Western Australia. In Canada, 12 km of sedimentary rocks were deposited, in which three thick strata of glacial origin are distinguished.
Established ancient glaciations (Fig. 23):
on the border of the Cambrian-Proterozoic (about 600 million years ago);
late Ordovician (about 400 million years ago);
Permian and Carboniferous periods (about 300 million years ago).
The duration of ice ages is tens to hundreds of thousands of years.
Rice. 23. Geochronological scale of geological epochs and ancient glaciations
During the period of maximum distribution of the Quaternary glaciation, glaciers covered over 40 million km 2 - about a quarter of the entire surface of the continents. The largest in the Northern Hemisphere was the North American Ice Sheet, reaching a thickness of 3.5 km. Under the ice sheet up to 2.5 km thick was the whole of northern Europe. Having reached the greatest development 250 thousand years ago, the Quaternary glaciers of the Northern Hemisphere began to gradually shrink.
Before Neogene period throughout the Earth - an even warm climate - in the area of \u200b\u200bthe islands of Svalbard and Franz Josef Land (according to paleobotanical finds of subtropical plants) at that time there were subtropics.
Reasons for the cooling of the climate:
the formation of mountain ranges (Cordillera, Andes), which isolated the Arctic region from warm currents and winds (uplift of mountains by 1 km - cooling by 6ºС);
creation of a cold microclimate in the Arctic region;
cessation of heat supply to the Arctic region from warm equatorial regions.
By the end of the Neogene period, northern and South America connected, which created obstacles to the free flow of ocean waters, as a result of which:
equatorial waters turned the current to the north;
the warm waters of the Gulf Stream, cooling sharply in northern waters, created a steam effect;
precipitation of a large amount of precipitation in the form of rain and snow has increased sharply;
a decrease in temperature by 5-6ºС led to the glaciation of vast territories (North America, Europe);
a new period of glaciation began, lasting about 300 thousand years (the frequency of glacier-interglacial periods from the end of the Neogene to the Anthropogen (4 glaciations) is 100 thousand years).
Glaciation was not continuous throughout the Quaternary period. There is geological, paleobotanical and other evidence that during this time the glaciers completely disappeared at least three times, giving way to interglacial epochs when the climate was warmer than the present. However, these warm epochs were replaced by cooling periods, and glaciers spread again. At present, the Earth is at the end of the fourth era of the Quaternary glaciation, and, according to geological forecasts, our descendants in a few hundred-thousand years will again find themselves in the conditions of an ice age, and not warming.
The Quaternary glaciation of Antarctica developed along a different path. It arose many millions of years before the time when glaciers appeared in North America and Europe. Apart from climatic conditions this was facilitated by the high mainland that existed here for a long time. Unlike the ancient ice sheets of the Northern Hemisphere, which disappeared and reappeared, the Antarctic ice sheet has changed little in its size. The maximum glaciation of Antarctica was only one and a half times greater than the current one in terms of volume and not much more in area.
The culmination of the last ice age on Earth was 21-17 thousand years ago (Fig. 24), when the volume of ice increased to approximately 100 million km3. In Antarctica, glaciation at that time captured the entire continental shelf. The volume of ice in the ice sheet, apparently, reached 40 million km 3, that is, it was about 40% more than its present volume. The boundary of the pack ice shifted to the north by approximately 10°. In the Northern Hemisphere 20 thousand years ago, a giant Panarctic ancient ice sheet was formed, uniting the Eurasian, Greenland, Laurentian and a number of smaller shields, as well as extensive floating ice shelves. The total volume of the shield exceeded 50 million km3, and the level of the World Ocean dropped by at least 125m.
The degradation of the Panarctic cover began 17 thousand years ago with the destruction of the ice shelves that were part of it. After that, the "marine" parts of the Eurasian and North American ice sheets, which lost their stability, began to disintegrate catastrophically. The disintegration of the glaciation occurred in just a few thousand years (Fig. 25).
Huge masses of water flowed from the edge of the ice sheets at that time, giant dammed lakes arose, and their breakthroughs were many times larger than modern ones. In nature, spontaneous processes dominated, immeasurably more active than now. This led to a significant renewal of the natural environment, a partial change of the animal and flora, the beginning of human dominance on Earth.
The last retreat of the glaciers, which began over 14 thousand years ago, remains in the memory of people. Apparently, it is the process of melting glaciers and raising the water level in the ocean with extensive flooding of territories that is described in the Bible as a global flood.
12 thousand years ago the Holocene began - the modern geological epoch. The air temperature in temperate latitudes increased by 6° compared to the cold Late Pleistocene. Glaciation took on modern dimensions.
In the historical epoch - approximately for 3 thousand years - the advance of glaciers occurred in separate centuries with low air temperature and increased humidity and were called small ice ages. The same conditions prevailed in recent centuries last era and in the middle of the last millennium. About 2.5 thousand years ago, a significant cooling of the climate began. The Arctic islands were covered with glaciers, in the countries of the Mediterranean and the Black Sea on the verge of a new era, the climate was colder and wetter than now. In the Alps in the 1st millennium BC. e. glaciers moved to lower levels, cluttered mountain passes with ice and destroyed some high-lying villages. This epoch is marked by a major advance of the Caucasian glaciers.
The climate at the turn of the 1st and 2nd millennium AD was quite different. Warmer conditions and the lack of ice in the northern seas allowed the navigators of Northern Europe to penetrate far north. From 870, the colonization of Iceland began, where at that time there were fewer glaciers than now.
In the 10th century, the Normans, led by Eirik the Red, discovered the southern tip of a huge island, the shores of which were overgrown with thick grass and tall shrubs, they founded the first European colony here, and this land was called Greenland, or “green land” (which is by no means now say about the harsh lands of modern Greenland).
By the end of the 1st millennium, mountain glaciers in the Alps, the Caucasus, Scandinavia, and Iceland also retreated strongly.
The climate began to seriously change again in the 14th century. Glaciers began to advance in Greenland, the summer thawing of soils became more and more short-lived, and by the end of the century, permafrost was firmly established here. The ice cover of the northern seas increased, and attempts made in subsequent centuries to reach Greenland by the usual route ended in failure.
From the end of the 15th century, the advance of glaciers began in many mountainous countries and polar regions. After the relatively warm 16th century, harsh centuries came, which were called the Little Ice Age. In the south of Europe, severe and long winters often repeated, in 1621 and 1669 the Bosphorus froze, and in 1709 the Adriatic Sea froze along the shores.
In the second half of the 19th century, the Little Ice Age ended and a relatively warm era began, which continues to this day.
Rice. 24. The boundaries of the last glaciation
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Rice. 25. Scheme of the formation and melting of the glacier (along the profile of the Arctic Ocean - Kola Peninsula - Russian Platform)
Great Quaternary glaciation
Geologists have divided the entire geological history of the Earth, which has been going on for several billion years, into eras and periods. The last of these, which continues to this day, is the Quaternary period. It began almost a million years ago and was marked by the extensive distribution of glaciers on the globe - the Great Ice Age of the Earth.
Thick ice caps covered the northern part of the North American continent, a significant part of Europe, and possibly Siberia as well (Fig. 10). In the southern hemisphere, under the ice, as now, was the entire Antarctic continent. There was more ice on it - the surface of the ice sheet rose 300 m above its current level. However, Antarctica was still surrounded on all sides. deep ocean, and the ice could not move north. The sea prevented the growth of the Antarctic giant, and the continental glaciers of the northern hemisphere were spreading to the south, turning flowering spaces into an icy desert.
Man is the same age as the Great Quaternary glaciation of the Earth. His first ancestors - ape people - appeared at the beginning of the Quaternary period. Therefore, some geologists, in particular the Russian geologist A.P. Pavlov, proposed calling the Quaternary period Anthropogenic (in Greek, "anthropos" - a man). Several hundred thousand years passed before man took on his modern appearance. The onset of glaciers worsened the climate and living conditions of ancient people who had to adapt to the harsh nature around them. People had to lead a settled way of life, build dwellings, invent clothes, use fire.
Having reached the greatest development 250 thousand years ago, the Quaternary glaciers began to gradually shrink. The Ice Age was not unified throughout the Quaternary. Many scientists believe that during this time the glaciers completely disappeared at least three times, giving way to interglacial epochs, when the climate was warmer than the present. However, these warm epochs were replaced by cooling periods, and glaciers spread again. Now we live, apparently, at the end of the fourth stage of the Quaternary glaciation. After the liberation of Europe and America from under the ice, these continents began to rise - this is how the earth's crust reacted to the disappearance of the glacial load that had been pressing on it for many thousands of years.
The glaciers “left”, and after them, vegetation, animals spread to the north, and, finally, people settled. Since the glaciers retreated unevenly in different places, humanity also settled unevenly.
Retreating, the glaciers left behind smoothed rocks - "ram's foreheads" and boulders covered with hatching. This hatching is formed from the movement of ice on the surface of the rocks. It can be used to determine in which direction the glacier moved. The classic area of manifestation of these traits is Finland. The glacier retreated from here quite recently, less than ten thousand years ago. Modern Finland is the land of countless lakes lying in shallow depressions, between which low “curly” rocks rise (Fig. 11). Here everything reminds of the former greatness of glaciers, their movement and huge destructive work. Close your eyes and you immediately imagine how slowly, year after year, century after century, a powerful glacier creeps here, how it plows its bed, breaks off huge blocks of granite and carries them south, towards the Russian Plain. It is no coincidence that it was while in Finland that P. A. Kropotkin thought about the problems of glaciation, collected a lot of disparate facts and managed to lay the foundations for the theory of the ice age on Earth.
There are similar corners at the other "end" of the Earth - in Antarctica; not far from the village of Mirny, for example, is the "oasis" of Banger - a free ice-free land area of 600 km2. When you fly over it, small chaotic hills rise under the wing of the aircraft, and between them bizarrely shaped lakes snake. Everything is the same as in Finland and ... it doesn't look like it at all, because in Banger's "oasis" there is no main thing - life. Not a single tree, not a single blade of grass - only lichens on the rocks, and algae in the lakes. Probably, the same as this "oasis" were once all the territories recently freed from under the ice. The glacier left the surface of the “oasis” of Bunger only a few thousand years ago.
The Quaternary glacier also extended to the territory of the Russian Plain. Here, the movement of ice slowed down, it began to melt more and more, and somewhere in the place of the modern Dnieper and Don, powerful streams of melt water flowed from under the edge of the glacier. Here passed the border of its maximum distribution. Later, on the Russian Plain, many remnants of the spread of glaciers were found, and above all, large boulders, like those that were often encountered on the path of Russian epic heroes. In thought, the heroes of old fairy tales and epics stopped at such a boulder before choosing their long road: right, left or go straight. These boulders have long stirred the imagination of people who could not understand how such colossi ended up on a plain among dense forests or endless meadows. They came up with various fabulous reasons, and there was a “global flood”, during which the sea allegedly brought these stone blocks. But everything was explained much more simply - a huge flow of ice with a thickness of several hundred meters cost nothing to “move” these boulders a thousand kilometers.
Almost halfway between Leningrad and Moscow there is a picturesque hilly-lake region - the Valdai Upland. Here, among the dense coniferous forests and plowed fields, the waters of many lakes splash: Valdai, Seliger, Uzhino and others. The shores of these lakes are indented, they have many islands, densely overgrown with forests. It was here that the border of the last distribution of glaciers on the Russian Plain passed. It was the glaciers that left behind strange shapeless hills, the depressions between them were filled with their melt waters, and subsequently the plants had to work hard to create good living conditions for themselves.
About the causes of the great glaciations
So, glaciers on Earth were not always. Even in Antarctica, coal has been found - a sure sign that it was warm and humid climate with rich vegetation. At the same time, geological data testify that the great glaciations were repeated on Earth repeatedly every 180-200 million years. The most characteristic traces of glaciation on Earth are special rocks - tillites, that is, the petrified remains of ancient glacial moraines, consisting of a clay mass with the inclusion of large and small hatched boulders. Individual thicknesses of tillites can reach tens and even hundreds of meters.
The causes of such major climate changes and the occurrence of the great glaciations of the Earth are still a mystery. Many hypotheses have been put forward, but none of them can yet claim the role of a scientific theory. Many scientists have been looking for the cause of the cooling outside the Earth, putting forward astronomical hypotheses. One of the hypotheses is that glaciation arose when, due to fluctuations in the distance between the Earth and the Sun, the amount of solar heat received by the Earth changed. This distance depends on the nature of the Earth's movement in its orbit around the Sun. It was assumed that glaciation occurred when winter fell on aphelion, i.e., the point of the orbit most distant from the Sun, at the maximum elongation of the earth's orbit.
However, recent studies by astronomers have shown that a change in the amount of solar radiation hitting the Earth alone is not enough to cause an ice age, although such a change should have its consequences.
The development of glaciation is also associated with fluctuations in the activity of the Sun itself. Heliophysicists have long found out that dark spots, flares, prominences appear periodically on the Sun, and even learned how to predict their occurrence. It turned out that solar activity changes periodically; there are periods of different duration: 2-3, 5-6, 11, 22 and about a hundred years. It may happen that the climaxes of several periods of different durations will coincide, and solar activity will be especially great. So, for example, it was in 1957 - just in the period of the International Geophysical Year. But it may be the other way around - several periods of reduced solar activity will coincide. This can cause the development of glaciation. As we will see later, such changes in solar activity are reflected in the activity of glaciers, but they are unlikely to cause a great glaciation of the Earth.
Another group of astronomical hypotheses can be called cosmic. These are assumptions that the cooling of the Earth is influenced by various parts of the Universe that the Earth passes through, moving in space along with the entire Galaxy. Some believe that the cooling occurs when the Earth "floats" parts of world space filled with gas. Others are when it passes through clouds of cosmic dust. Still others argue that "space winter" on Earth happens when the globe is in apogalactia - the point furthest from that part of our Galaxy where the most stars are located. At the present stage of the development of science, it is not possible to support all these hypotheses with facts.
The most fruitful hypotheses are those in which the cause of climate change is assumed to be on the Earth itself. According to many researchers, the cooling that causes glaciation may occur as a result of changes in the location of land and sea, under the influence of the movement of the continents, due to a change in the direction of sea currents (for example, the Gulf Stream was previously deflected by a land ledge that stretched from Newfoundland to the Green Islands). cape). There is a widely known hypothesis according to which, during the epochs of mountain building on Earth, large masses of continents that rose up fell into higher layers of the atmosphere, cooled down and became places for the birth of glaciers. According to this hypothesis, epochs of glaciation are associated with epochs of mountain building, moreover, they are conditioned by them.
The climate can also change significantly as a result of a change in the tilt of the earth's axis and the movement of the poles, as well as due to fluctuations in the composition of the atmosphere: there is more volcanic dust or less carbon dioxide in the atmosphere, and the Earth becomes much colder. IN Lately scientists began to associate the appearance and development of glaciation on Earth with the restructuring of atmospheric circulation. When, under the same climatic background of the globe, too much precipitation falls into individual mountainous regions, then glaciation occurs there.
A few years ago, American geologists Ewing and Donn put forward a new hypothesis. They suggested that the Arctic Ocean, now covered in ice, thawed at times. In this case, increased evaporation occurred from the surface of the Arctic sea, which was free from ice, and the flows humid air headed for the polar regions of America and Eurasia. Here, above the cold surface of the earth, from wet air masses heavy snows fell, which did not have time to melt over the summer. Thus, ice sheets appeared on the continents. Spreading, they descended to the north, surrounding the Arctic Sea with an ice ring. As a result of the transformation of part of the moisture into ice, the level of the world's oceans dropped by 90 m, the warm Atlantic Ocean ceased to communicate with the Arctic Ocean, and it gradually froze. Evaporation from its surface ceased, less snow began to fall on the continents, and the nutrition of glaciers deteriorated. Then the ice sheets began to thaw, decrease in size, and the level of the world's oceans rose. Again, the Arctic Ocean began to communicate with the Atlantic Ocean, its waters warmed up, and the ice cover on its surface began to gradually disappear. The cycle of development of glaciation began from the beginning.
This hypothesis explains some facts, in particular, several advances of glaciers during the Quaternary period, but it also does not answer the main question: what is the cause of the Earth's glaciations.
So, we still do not know the causes of the great glaciations of the Earth. With a sufficient degree of certainty, we can only talk about the last glaciation. Usually glaciers shrink unevenly. There are periods when their retreat is long delayed, and sometimes they advance rapidly. It is noted that such oscillations of glaciers occur periodically. The longest period of alternation of retreats and advances lasts for many centuries.
Some scientists believe that climate change on Earth, which is associated with the development of glaciers, depends on the relative position of the Earth, the Sun and the Moon. When these three celestial bodies are in the same plane and on the same straight line, the tides on Earth increase sharply, the circulation of water in the oceans and the movement of air masses in the atmosphere change. Ultimately, there is a slight increase in rainfall and a decrease in temperature around the globe, which leads to the growth of glaciers. Such an increase in the moistening of the globe is repeated every 1800-1900 years. The last two such periods were in the 4th c. BC e. and the first half of the fifteenth century. n. e. On the contrary, in the interval between these two maxima, the conditions for the development of glaciers should be less favorable.
On the same basis, it can be assumed that in our modern era, glaciers must retreat. Let's see how glaciers actually behaved in the last millennium.
Development of glaciation in the last millennium
In the X century. Icelanders and Normans, sailing along the northern seas, discovered the southern tip of an immensely large island, the shores of which were overgrown with thick grass and tall shrubs. This impressed the sailors so much that they named the island Greenland, which means "Green Country".
Why, then, was the most icy island on the globe so flourishing at that time? Obviously, the peculiarities of the then climate led to the retreat of glaciers, the melting of sea ice in the northern seas. The Normans were able to pass freely from Europe to Greenland on small ships. Settlements were founded on the coast of the island, but they did not last long. The glaciers began to advance again, the "ice cover" of the northern seas increased, and attempts to reach Greenland in subsequent centuries usually ended in failure.
By the end of the first millennium of our era, the mountain glaciers in the Alps, the Caucasus, Scandinavia and Iceland also strongly receded. Some passes, previously occupied by glaciers, became passable. The lands freed from glaciers began to be cultivated. Prof. G. K. Tushinsky recently examined the ruins of the settlements of the Alans (ancestors of the Ossetians) in the Western Caucasus. It turned out that many buildings dating back to the 10th century are located in places that are now completely unsuitable for habitation due to frequent and destructive avalanches. This means that a thousand years ago, not only glaciers "moved" closer to the mountain ridges, but avalanches did not descend here either. However, in the future, winters became more severe and snowy, avalanches began to fall closer to residential buildings. The Alans had to build special avalanche dams, their remnants can still be seen today. In the end, it turned out to be impossible to live in the former villages, and the highlanders had to settle down in the valleys.
The beginning of the 15th century was approaching. Living conditions became more and more severe, and our ancestors, who did not understand the reasons for such a cold snap, were very worried about their future. Increasingly, records of cold and difficult years appear in the annals. In the Tver Chronicle one can read: “In the summer of 6916 (1408) ... but then the winter was hard and very cold, snowy too much”, or “In the summer of 6920 (1412) the winter was very snowy, and therefore in the spring it was the water is great and strong." The Novgorod Chronicle says: “In the summer of 7031 (1523) ... the same spring, on Trinity Day, a large cloud of snow fell, and snow lay on the ground for 4 days, but the stomach, horses and cows froze a lot, and the birds died in the forest ". In Greenland, due to the onset of cooling by the middle of the XIV century. ceased to be engaged in cattle breeding and agriculture; the connection between Scandinavia and Greenland was broken due to the abundance of sea ice in the northern seas. In some years, the Baltic and even the Adriatic Sea froze. From the 15th to the 17th century mountain glaciers advanced in the Alps and the Caucasus.
The last great advance of glaciers dates back to the middle of the last century. In many mountainous countries they have advanced quite far. Traveling in the Caucasus, G. Abikh in 1849 discovered traces of the rapid advance of one of the Elbrus glaciers. This glacier has invaded a pine forest. Many trees were broken and lay on the surface of the ice or stuck through the body of the glacier, and their crowns were completely green. Documents have been preserved that tell about frequent ice landslides from Kazbek in the second half of the 19th century. Sometimes, because of these landslides, it was impossible to drive along the Georgian Military Highway. Traces of rapid advances of glaciers at this time are known in almost all inhabited mountainous countries: in the Alps, in the west of North America, in Altai, in Central Asia, as well as in the Soviet Arctic and Greenland.
With the advent of the 20th century, global warming begins almost everywhere. It is associated with a gradual increase in solar activity. The last maximum solar activity was in 1957-1958. During these years there was a large number of sunspots and extremely strong solar flares. In the middle of our century, the maxima of three cycles of solar activity coincided - eleven-year, secular and supersecular. It should not be thought that the increased activity of the Sun leads to an increase in heat on the Earth. No, the so-called solar constant, that is, the value showing how much heat comes to each section of the upper boundary of the atmosphere, remains unchanged. But the flow of charged particles from the Sun to the Earth and the overall impact of the Sun on our planet is increasing, and the intensity of atmospheric circulation throughout the Earth is increasing. Streams of warm and humid air from tropical latitudes rush to the polar regions. And this leads to a rather sharp warming. In the polar regions, it warms up sharply, and then it gets warmer throughout the Earth.
In the 20-30s of our century, the average annual air temperature in the Arctic increased by 2-4°. Border sea ice moved to the north. Northern sea route became more passable for sea vessels, the period of polar navigation was extended. The glaciers of Franz Josef Land, Novaya Zemlya and other Arctic islands have been retreating rapidly over the past 30 years. It was during these years that one of the last Arctic ice shelves, located on Ellesmere Land, collapsed. In our time, glaciers are retreating in the vast majority of mountainous countries.
A few years ago, almost nothing could be said about the nature of temperature changes in the Antarctic: there were too few meteorological stations and there were almost no expeditionary studies. But after summing up the results of the International Geophysical Year, it became clear that in the Antarctic, as in the Arctic, in the first half of the 20th century. the air temperature rose. There are some interesting pieces of evidence for this.
The oldest Antarctic station is Little America on the Ross Ice Shelf. Here, from 1911 to 1957, the average annual temperature increased by more than 3°. On Queen Mary Land (in the area of modern Soviet research) for the period from 1912 (when the Australian expedition led by D. Mawson conducted research here) to 1959, the average annual temperature increased by 3.6°C.
We have already said that at a depth of 15-20 m in the thickness of snow and firn, the temperature should correspond to the average annual temperature. However, in reality, at some inland stations, the temperature at these depths in the wells turned out to be 1.3-1.8° lower than the average annual temperatures over several years. Interestingly, the temperature continued to drop as one went deeper into these boreholes (up to a depth of 170 m), while usually the temperature of the rocks becomes higher with increasing depth. This unusual temperature drop in the ice sheet is a reflection of the colder climate of those years when snow was deposited, now at a depth of several tens of meters. Finally, it is very indicative that the extreme boundary of the distribution of icebergs in the Southern Ocean is now located 10-15 ° south of latitude compared to 1888-1897.
It would seem that such a significant increase in temperature over several decades should lead to the retreat of the Antarctic glaciers. But this is where the "difficulties of Antarctica" begin. They are partly due to the fact that we still know too little about it, and partly due to the great originality of the ice colossus, which is completely different from the mountain and arctic glaciers we are used to. Let's try to figure out what is happening now in Antarctica, and for this we will get to know it better.
The last ice age brought about the appearance of the woolly mammoth and a huge increase in the area of glaciers.
But it was only one of many that have cooled the Earth throughout its 4.5 billion years of history.
The consequences of warming
The last ice age brought about the appearance of the woolly mammoth and a huge increase in the area of glaciers. But it was only one of many that have cooled the Earth throughout its 4.5 billion years of history.
So, how often does the planet go through ice ages, and when should we expect the next one?
The main periods of glaciation in the history of the planet
The answer to the first question depends on whether you mean the big glaciations or the small ones that occur during these long periods. Throughout history, the Earth has experienced five long periods glaciations, some of which lasted for hundreds of millions of years. In fact, even now, the Earth is going through a large period of glaciation, and this explains why it has polar ice.
The five main ice ages are the Huronian (2.4-2.1 billion years ago), the Cryogenian glaciation (720-635 million years ago), the Andean-Saharan (450-420 million years ago), the late Paleozoic glaciation (335-260 million years ago) and the Quaternary (2.7 million years ago to the present).
These major periods of glaciation may alternate between smaller ice ages and warm periods (interglacials). At the beginning of the Quaternary glaciation (2.7-1 million years ago), these cold ice ages occurred every 41,000 years. However, in the last 800,000 years, significant ice ages have appeared less frequently - about every 100,000 years.
How does the 100,000 year cycle work?
Ice sheets grow for about 90,000 years and then begin to melt during the 10,000 year warm period. Then the process is repeated.
Given that the last ice age ended about 11,700 years ago, perhaps it's time for another one to begin?
Scientists believe that we should be experiencing another ice age right now. However, there are two factors associated with the Earth's orbit that influence the formation of warm and cold periods. Considering how much carbon dioxide we emit into the atmosphere, the next ice age won't start for at least another 100,000 years.
What causes an ice age?
The hypothesis put forward by the Serbian astronomer Milyutin Milanković explains why there are cycles of ice and interglacial periods on Earth.
As the planet revolves around the Sun, the amount of light it receives from it is affected by three factors: its inclination (which ranges from 24.5 to 22.1 degrees in a cycle of 41,000 years), its eccentricity (changing the shape of the orbit around of the Sun, which fluctuates from a near circle to an oval shape) and its wobble (one complete wobble occurs every 19-23 thousand years).
In 1976, a landmark paper in the journal Science presented evidence that these three orbital parameters explained the planet's glacial cycles.
Milankovitch's theory is that orbital cycles are predictable and very consistent in a planet's history. If the Earth is going through an ice age, then it will be covered in more or less ice, depending on these orbital cycles. But if the Earth is too warm, no change will occur, at least in regards to the growing amount of ice.
What can affect the warming of the planet?
The first gas that comes to mind is carbon dioxide. Over the past 800,000 years, carbon dioxide levels have fluctuated between 170 and 280 parts per million (meaning that out of 1 million air molecules, 280 are carbon dioxide molecules). A seemingly insignificant difference of 100 parts per million leads to the appearance of glacial and interglacial periods. But carbon dioxide levels are much higher today than they were in past fluctuations. In May 2016, carbon dioxide levels over Antarctica reached 400 parts per million.
The earth has warmed up so much before. For example, during the time of the dinosaurs, the air temperature was even higher than now. But the problem is that in modern world it is growing at a record pace because we have released too much carbon dioxide into the atmosphere in such a short time. In addition, given that emission rates are not declining to date, it can be concluded that the situation is unlikely to change in the near future.
The consequences of warming
The warming caused by the presence of this carbon dioxide will have big consequences, because even a small increase average temperature Earth can bring dramatic changes. For example, the Earth was on average only 5 degrees Celsius colder during the last ice age than it is today, but this has led to a significant change in regional temperature, the disappearance of a huge part of the flora and fauna, and the appearance of new species.
If global warming lead to the melting of all the ice sheets of Greenland and Antarctica, the level of the oceans will rise by 60 meters, compared with today's figures.
What causes great ice ages?
The factors that caused long periods of glaciation, such as the Quaternary, are not as well understood by scientists. But one idea is that a massive drop in carbon dioxide levels could lead to cooler temperatures.
So, for example, according to the uplift and weathering hypothesis, when plate tectonics leads to the growth of mountain ranges, new unprotected rock appears on the surface. It is easily weathered and disintegrates when it enters the oceans. Marine organisms use these rocks to create their shells. Over time, stones and shells take carbon dioxide from the atmosphere and its level drops significantly, which leads to a period of glaciation.
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