The age of humanity compared to the age of the Earth is negligible. It is difficult for us to comprehend the speed with which the geological processes of our planet are taking place. It took millions of years for oceans to form on Earth. Even taking a bath takes time, so imagine how much time has passed for the huge basins that occupy two-thirds of the planet's surface to fill with water. Scientists have calculated that the level of the world's oceans was rising by only 1 millimeter per year. Of course, this process did not proceed uniformly. At the same time, various geological processes took place, tectonic plates rose and fell, continents and islands went under water, new ones formed. Forests grew and died, living organisms developed, the climate changed. From point of view human life the whole thing was awfully slow. If you had landed on Earth about 2.5 billion years ago, when the world's oceans were filling up, you could have lived your entire life from birth to death without noticing that something was happening.
Nevertheless, "global floods" occurred, and more than once. Geologists study rocks that look like a layer cake, where layers of marine sediments alternate with layers of purely “land” ones. Modern coastline in in general terms took shape about 6-10 thousand years ago. And 20 thousand years ago, this line was 100 meters lower than the current figure. At the bottom of the North Sea, forests grew, there were swamps and tundra, there were mouths of great years, and, apparently, a person lived. This was not only the case in Europe. Scientists have discovered on the Atlantic shelf of the United States at a depth of one hundred meters peat deposits, bones and teeth of mammoths, ancient human sites. And then the ice age ended, the melting of glaciers began, the ocean level began to rise steadily by almost 1 cm per year. This went on for several millennia, until about the 4th millennium BC there was relative constancy. This does not mean that the ocean level remains at the same level. He continues to hesitate. From 200 BC to 1000 AD, the level remained relatively stable. Then a warm period began, called the Medieval climate anomaly, and until the 15th century, the ocean level increased at a rate of about 0.5 mm per year. Then came the period of cooling again - the Little Ice Age - and relative constancy. Since the 19th century, an active rise in the level of the world ocean up to 2 mm per year began again. This is associated with the next warming.
Oddly enough, it is much easier for scientists to measure prehistory than it is for the last couple of thousand years. Ocean level fluctuations from 1 to 4 meters are difficult to fix, as they are superimposed on the movements of tectonic layers and water level drops associated with tides, waves, surges. What happened in the recent past is almost unmeasurable. If we judge the sea level by the coastal relief, we have to take into account the strength of the surf, the density of the rocks and other conditions. And judging by the deposits (wood, peat, shells of mollusks, corals), it must be borne in mind that during storms, waves can throw detrital material to a height of up to 8 meters per open areas ocean coast.
Mollusks can also live at different depths, by the shells of which scientists determine the age of the deposits. There is also such a curious case. In Australia, geologists have discovered a terrace at a height of 5-7 meters. It had a significant number of shell remains, according to which the age of the terrace was dated to about 5 thousand years. However, in the course of the work of archaeologists, it turned out that the site of ancient people was located on this terrace, and fragments of shells were food waste. And the terrace is actually much older and was formed in one of the interglacial periods about 40 thousand years ago.
The study of fluctuations in the level of the world ocean is now given a lot of attention. great importance. This is interesting not only from a scientific point of view, but also purely from a practical point of view. If you look at a map of the Earth, you can see how much territory is below sea level. Many coastal areas are located in the risk zone. So, a quarter of the Netherlands would have gone under water, if not for powerful dams. However, there are cases when storms drive water to the coast, and it overflows through dams, flooding vast territories. Amsterdam could go under water in the next 150 years if sea levels rise by 1-2 meters.
The well-known constantly sinking Venice can actually sink if the water level rises another meter. Also, St. Petersburg is in danger, where in last years increased flooding is noted. Despite the protective structures and the Thames Barrier protecting against tides, London is also not immune from flooding. Hamburg is located a hundred kilometers from the sea, but the position at the mouth of the Elbe makes it likely that it will go under water when the ocean level rises by 2 and a half meters. In China, the flood protection system is rather poorly developed, so the rise of water even by one and a half meters can threaten many millions of residents of Shanghai, Hong Kong, Guangzhou, Shenzhen. Things are no better in North America. New Orleans and so often suffers from storms and floods. Hurricane Katrina destroyed almost half of the city, and this could happen again. New York is in no less danger. During storms, the coastal part of the city falls into the flood zone, and in order for it to be completely flooded, the water must rise by 3 meters. With this rise in sea level, flooding also threatens San Francisco and Los Angeles.
And that's just big cities, but the entire coastal area will also suffer. Namely, in this zone, for example, 50% of the population of the United States lives, more than half of the population of Japan, 75% of the population of Norway and Portugal, and in general, more than half of all the inhabitants of the planet. That is why it is so important for scientists to study the detailed picture of global sea level fluctuations in order to understand current situation and be able to predict changes in the future.
Borislav Bilyavskaya
Today it is no longer a secret to anyone that global warming resulted in an increase in the level of the oceans. But, despite the most modern equipment and a large number of data, scientists still cannot get a unified picture of sea level dynamics on a global scale.
Only one thing is known for sure: since the middle of the 19th century, the sea level has been constantly rising, and since 1993 this phenomenon has become alarming.
In 2015, this topic was raised repeatedly: there were many scientific works, according to which, the rise in the level of the World Ocean over the past 20 years. The overall rate of increase from 1993 to 2014 is about 2.6-2.9 millimeters per year with an error of plus or minus 0.4 millimeters. At the same time, NASA stated that this effect is additional, from which the ocean receives more than 90% of the heat.
A new study conducted by specialists from the Joint Institute for Research in the field of sciences environment(USA), did not add optimism. The main conclusion of the large-scale work, which lasted 25 years, is this: global sea level is not rising steadily; its growth is gradually accelerating. And if this trend continues, then previous forecasts for the rise of water in the World Ocean - 30 centimeters by 2100 - can be safely multiplied by at least two.
Recall that since the end of 1992, the level of the World Ocean has been measuring international system TOPEX/Poseidon satellites. The authors of the study analyzed the data of these devices, and with them the information received from three satellites"families" Jason, the first of which began work in 2001. These space oceanographic laboratories measure the topography of the surface of the oceans.
In addition, data from ground-based tide sensors and climate simulations were taken into account.
Experts have calculated that the rate of sea level rise is increasing by about 0.08 millimeters per year (on top of the fact that every year the water rises by 3 millimeters). If everything remains as it is, by the end of the century, the oceans will rise by at least 10 millimeters annually and will add another 60-65 centimeters compared to today's mark.
Moreover, as noted by the head of the scientific group, Professor Steve Nerem (Steve Nerem), all the estimates given in this work, although higher than the previous ones, are still very modest.
According to him, the main reason for this growth is still the same -. Exacerbates the situation: because of this, the temperature of air and water increases.
Sea level rise occurs, according to experts, in two ways. First, warming water is expanding, and this "thermal expansion" of the oceans has already raised global water levels by about 3-4 centimeters over the past 25 years. Secondly, water from melting glaciers flows into the waters of the World Ocean, which also raises its level.
Volcanic activity also contributes, albeit relatively small. Earlier, the Nerema team found out that the volcanic eruption is 25 years old, so now the experts are also guided by these indicators in order to minimize errors.
As already mentioned, the indicators of satellite altimeters (altimeters) were also checked against ground data on tides. The authors explain that this information is extremely important: due to the presence of water in the oceans, tides can become more dangerous for residents of coastal areas.
By analyzing and summarizing huge amounts of data, it is possible to build the latest and most accurate climate models. They will help not only to make forecasts for the future and assess the scale ecological disaster, to which we are approaching, but also to predict possible natural disasters for individual regions, experts conclude.
By the way, in 2016, an American climatologist that the melting of glaciers will raise sea levels by at least one meter by 2100, and if the signatory countries do not comply with it, then by all five meters. Some colleagues dismissed his claim as baseless, but now their arguments seem to be melting faster than the ice of Antarctica.
It is always interesting to imagine very improbable, but in principle real things. What would happen if all the ice on Earth, which is more than 20 million cubic kilometers, melted?
National Geographic created a series interactive maps, which demonstrate what catastrophic consequences would occur on our planet. The melted ice, which would have entered the oceans and seas, would have led to a sea level rise of 65 meters. It would engulf cities and countries, changing the general appearance of continents and coastlines, wiping out entire populations.
Scientists believe it will take about 5,000 years for temperatures to rise enough to melt all the ice on Earth. However, a start has already been made.
Over the past century, the temperature on Earth has increased by about 0.5 degrees Celsius, and this has led to a sea level rise of 17 cm.
If we continue to burn coal, oil and gas reserves, the average temperature on our planet will reach 26.6 degrees Celsius instead of today's 14.4 degrees Celsius.
So let's see what will become of the continents...
In Europe, cities like London and Venice will be under water. It will also flood the Netherlands and most of Denmark. The Mediterranean Sea will expand and increase the size of the Black and Caspian Seas.
In Asia, China and Bangladesh will be flooded, and more than 760 million people will be under water. Among the destroyed cities will be: Karachi, Baghdad, Dubai, Calcutta, Bangkok, Ho Chi Minh City, Singapore, Hong Kong, Shanghai, Tokyo and Beijing. The coast of India will also decrease significantly.
In North America, the entire Atlantic coastline in the US will disappear along with Florida and the Gulf Coast. In California, the hills of San Francisco will turn into islands, and the California Valley will become a huge bay.
In South America, the Amazonian lowland and the Paraguay river basin will become the straits of the Atlantic Ocean, wiping out Buenos Aires, coastal Uruguay and part of Paraguay.
Compared to other continents, Africa will lose less land mass due to rising sea levels. However, rising temperatures will lead to the fact that most of it will become uninhabitable. In Egypt, Alexandria and Cairo will be flooded by the Mediterranean Sea.
Australia will have a continental sea, but it will lose most of the narrow coastal strip where 4 out of 5 Australians live.
In Antarctica, what was once land ice will no longer be ice or land. This will happen because under the ice there is a continental relief, which is below sea level.
What does Antarctica look like without ice?
Antarctica is the largest ice sheet in the world, but what is under it?
Scientists from NASA have shown the surface of Antarctica, which has been hidden under a thick layer of ice for more than 30 million years. In a project called BedMap2, researchers calculated the total amount of ice in Antarctica to predict sea level rise in the future. To do this, they needed to know the underlying topography, including wide valleys and hidden mountain ranges.
Some of the most impressive discoveries in Antarctica were the deepest point of all continents, the valley below the Byrd Glacier, which is located at a distance of 2780 meters below sea level. The scientists also received the first detailed images of the Gamburtsev Mountains, which are under a 1.6-kilometer layer of ice.
The new map is based on surface elevation, ice thickness and base topography, which were taken using land, air and satellite surveys. The scientists also used radar, sound waves, and electromagnetic instruments to map.
The level of the World Ocean is undergoing constant changes associated with both the activity of underground volcanic activity and human activity. Research by scientists has shown that the volume of the ocean and the configuration of its shores during geological history undergone continuous changes that will continue to occur in the future. Even maps have been drawn up, which give the position and contours of the continents, as they will become in millions of years.
Not far from Naples, on the shore of the bay, there are the remains of a colonnade and the ruins of an ancient temple dedicated to Serapis, the god of dying and reborn nature, can be seen. The choice of a place for the construction of the temple was not made by the ancient Romans by chance: warm sulfuric springs are beating from the ground here. Long before the beginning of our era, crowds of pilgrims came here to worship the deity and to bathe in the warm springs, famous for their healing properties throughout the Roman Republic. Time did not spare the elegant architectural structure. As a result of earthquakes and wars, the temple turned into a ruin, but before that it was destroyed by the sea.
From year to year, it came closer and closer to the bases of the columns, to the buildings of the term (warm baths) and threatened to flood the healing springs themselves. A dam had to be built along the shore to block the path of sea water. But no tricks of the builders and sacrifices of the priests could save the doomed temple.
The sea covered the pedestal of the colonnade with sand, spread widely over the courtyards of the buildings, and finally the salty sea water mixed with the healing water of the springs. The Temple of Serapis lost its charm and glory and was soon abandoned.
Meanwhile, the sea continued to advance. The bases of the columns went into the coastal sand for two and a half meters, piles of debris lay on the stone slabs of the floors, the water slowly arrived. Centuries passed. In the XIII-XIV centuries, the sea level reached its limit, the columns were flooded with water by 6 meters.
As you know, Naples is located near one of the greatest volcanoes in the world - Vesuvius; all the surroundings lie in the area of active volcanic activity, the manifestation of which was the hot springs of the temple of Serapis. In 1538, there was another earthquake and a strong outpouring of lava, after which the ruins began to rise from the water. The sea receded. TO early XIX For centuries, the ruins stood on land, and the revived warm springs again began to attract those who were thirsty for healing.
Looking in these surroundings at the stones and burnt-out grass heated by the hot sun, it is hard to believe that 400 years ago the whole area was at the bottom of the sea. Now this is evidenced only by historical records and many holes drilled in the columns by sea molluscs-stone-borers. The famous German biologist, Professor K. Keller, who visited the ruins of the temple at the end of the last century, reports that he easily removed several whitened shells of these mollusks from the passages in the columns.
The case of the Temple of Serapis is far from unique. There are many other architectural structures that have been swallowed up by the sea. The discovery of many fossil remains of marine animals high above the ocean level indicates that almost any area of modern land was once, or even several times, the bottom of the sea.
Sometimes the advance (transgression) or retreat of the sea (that is, its regression) has only a local character. They result from relatively small tectonic movements earth's crust and do not affect adjacent parts of the coast. However, there is irrefutable evidence that during the geological history of the Earth, the transgressions and regressions of the ocean were of a global nature, with the water level either rising by 150–180 meters compared to the current one, or falling 200–300 meters below it.
G. Lindberg, a well-known Soviet scientist and specialist in the study of the sea, writes the following about this: “The facts of the location of sea terraces at an altitude of up to 1000 or more meters above sea level are well known. They irrefutably prove the vertical movements of the land. But at the same time, the facts of the relative uniformity of the location of sea terraces over a considerable length of coasts are also well known, not only within one sea, but also within a number of seas and even on the coasts of other continents.
As an example, G. Lindberg gives data on the location of six main horizons of marine terraces along the Atlantic coast of Patagonia ( South America) and in Europe along the shores of the Mediterranean, Black and Caspian Seas. The heights of all these horizons surprisingly coincide with each other, which means that their surfaces were formed simultaneously and at the same level of the ocean.
Large rivers, after flowing into the sea, usually have a deep and far-reaching continuation of the channel, often with the formation of a real delta on the seabed. These underwater valleys cannot form deep under water, therefore, they owe their origin to the flowing water of rivers and arose during a period of lowering of the ocean level.
The causes of ocean level change are different. On the one hand, this is the result of the movement of the earth's crust. Let's imagine that in any place there will be a subsidence of the seabed. The water will immediately fill the cavity, and general level the ocean will be lower.
The German scientist A. Penk calculated that as a result of the sinking of the bottom of the Mediterranean Sea, the water level in the World Ocean dropped by 12 meters. It has been established that as a result of bottom subsidence, the Bering, Okhotsk, Japan and East China Seas, many deep-sea trenches Pacific Ocean. It is clear that their formation caused a drop in the water level in the ocean. It is also possible reverse processes, when the seabed in some areas begins to rise and thereby causes transgression. Increased volcanic activity under water with lava outpouring also contributes to the rise of the ocean level. However, with all these processes, the volume of water in the ocean does not change.
Can the volume of the ocean change at all? It turns out that such changes may have happened, apparently, more than once. It is known that part of the hydrosphere, water shell of our planet, is in a solid state in the form of glaciers. Imagine that under the influence of some reasons, the ice of Antarctica suddenly melts, the volume of which is 25 million cubic kilometers! Immediately, the ocean level will rise by 40 meters, most of the largest cities world, the most densely populated parts of the continents, as well as many islands.
Such melting can occur as a result of increased solar activity or under the influence of the movement of the mainland, covered with glaciers, to lower latitudes.
True, a number of experts, especially astronomers, believe that our Sun, like other similar stars, the so-called "yellow dwarfs", is distinguished by a very high radiation stability, which changes little even over 10 billion years.
But we should not forget that even a small and relatively short-term increase in solar radiation cannot but affect the earth's climate.
Eleven-year solar cycles are known! In any case, no one can refute the periodicity of the advance and melting of glaciers over the past 1-2 million years. Obviously, during the Ice Age, the ocean became shallow, since part of the water, evaporating from its surface, accumulated on land in the form of ice. During the interglacial epochs, the level of the ocean rose, and in part this happened already before the eyes of man.
The stories about the global flood, preserved in the traditions of many peoples (including the Bible), apparently reflect the events that really took place at the dawn of human history.
The volume of the ocean and the configuration of its shores have undergone constant changes in the course of geological history, which will continue to occur in the future. Even maps have been drawn up, which give the position and contours of the continents, as they will become in millions of years.
Therefore, the usual geographical map world should not be viewed as a reflection of something permanent and unchanging, but rather as a snapshot of the complex dynamic process of the evolution of our planet.
Approximately 71% of the surface of our planet is covered with water, so the assessment of sea level change is one of the most important tasks that allow scientists to predict further changes in the climate on Earth and the living conditions of people living in different regions of the planet.
Until today, scientists believed that they knew exactly the dynamics of sea level changes. This is a sea level rise of 1.6 cm per decade since 1900. In any case, these are the data provided by the National Oceanic and Atmospheric Administration (NOAA). The main cause of sea level rise is global warming.
The results of a new study published in October in Geophysical Research Letters suggest that scientists have underestimated this value. In some regions, sea level rise is faster than the generally accepted indicator by about 5-28%. Global sea level, according to the authors of the study, has risen by at least 14 centimeters over the past hundred years, and in some regions by as much as 17 centimeters.
The reason for this underestimation was uncovered by scientists from NASA's Jet Propulsion Laboratory and the University of Hawaii at Manoa. Comparing the parameters of the current climate model with sea level measurements in previous years, the team of climate scientists found that readings from coastal tide sensors may not be as representative as thought, and such data cannot be used as a reference. Sensors located at many locations in the Northern Hemisphere have been the primary source of data for global sea level measurements over the past few decades.
“This is not a situation where the data is wrong or the tools are not working properly. For a number of reasons, sea levels do not change in the same way across the planet,” says Philip Thompson, lead researcher. “As it turns out, our data is collected in places where sea levels rise the least rapidly due to global warming.”
Typically, water level measurement stations are stationary. In addition to the water level, such stations can determine and weather region, including wind pressure and speed, factors that often affect sea level measurements.
The only problem in this whole situation is the places where such stations are located. According to the study, most of the stations are located in the Northern Hemisphere, where the ice cover is melting faster than in the Southern Hemisphere.
As it turned out, the sea level changes more strongly not where the main factor in the change in the level of the World Ocean waters operates. In fact, this level rises most actively in places far from this factor. According to one source, melting ice in the Earth's Northern Hemisphere has the greatest effect on rising water levels in the "South Pacific and Equator."
The project team also believes it has discovered a reason why the effects of ice melt may differ from region to region. For example, changes in China may differ significantly from those in the US or Africa. The rate of sea level rise varies from region to region due to additional factors. It can be winds, ocean currents, gravity, tides.
“This is very important because it is likely that the influence of certain winds or currents may be causing the rate of sea level rise to be underestimated,” says Thompson. The scientist says that all this is not an accident, specialists need to change the rate of sea level rise upwards. Climatologists make a variety of forecasts, but most experts agree on one thing - there really is global warming, and it is the reason for the rapid melting of ice in both hemispheres of the Earth. Professor Peter Wadhams of Cambridge, for example, argues that this or next year the Arctic may be completely ice-free, something that has not happened in the last 100,000 years.
This year we see new climate records. For example, every month of this year is the warmest on record. Representatives of NASA say that now ice covers 40% less areas in summer than thirty years ago. If the Antarctic ice sheet continues to melt, then sea levels will rise by 3.6 meters in the future, which will simply wipe out many cities along the coast.
