Changes in sea level. A sad acceleration: the level of the oceans is rising even faster than previously thought. Methods for measuring ocean level. Satellite altimetry

And other factors. Distinguish between "instantaneous", tidal, average daily, average monthly, average annual and average long-term sea levels.

Under the influence of wind waves, tides, heating and cooling of the sea surface, fluctuations in atmospheric pressure, precipitation and evaporation, river and glacial runoff, the sea level is constantly changing. The mean long-term sea level is independent of these sea surface fluctuations. The position of the mean long-term sea level is determined by the distribution of gravity and the spatial unevenness of hydrometeorological characteristics (water density, atmospheric pressure, etc.).

The constant mean long-term sea level at each point is taken as the initial level from which the land heights are measured. To measure the depths of seas with low tides, this level is taken as zero depth - the mark of the water level from which the depths are measured in accordance with the requirements of navigation. In Russia and most other countries of the former USSR, as well as in Poland, the absolute heights of points on the earth's surface are measured from the average long-term level of the Baltic Sea, determined from zero of the tide gauge in Kronstadt.

Notes (edit)

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Ouroborus
Abstraction level

See what "World Ocean Level" is in other dictionaries:

GOST 31170-2004: Vibration and noise of machines. The list of vibration, noise and power characteristics subject to declaration and control during testing of machines, mechanisms, equipment and power plants of civil ships and means of developing the world's oceans at the stands of supplier factories- Terminology GOST 31170 2004: Vibration and noise of machines. The list of vibration, noise and power characteristics subject to declaration and control during testing of machines, mechanisms, equipment and power plants of civil ships and facilities ... ... Dictionary-reference book of terms of normative and technical documentation

Ocean level- Sea level is the position of the free surface of the World Ocean, measured along a plumb line relative to some conventional reference point. This position is determined by the law of gravity, the moment of rotation of the Earth, temperature, tides and others ... ... Wikipedia

level- LEVEL, heed, husband. 1. The horizontal plane, the surface as a boundary, the height is measured from to the swarm. W. water in the river. 2. The degree of magnitude, development, significance of which n. Cultural y. U. life (the degree of satisfaction of the population with material and ... ... Ozhegov's Explanatory Dictionary

Sea level- A graph showing fluctuations in the level of the World Ocean over the past 550 million years Sea level position of the free surface of the World Ocean, measured by about ... Wikipedia

sea level- the position of the free surface of the World Ocean, tending to be located perpendicular to the resultant of all forces applied to the mass of water. Changes in the position of surface levels are manifested in sea level fluctuations. * * * SEA LEVEL… … encyclopedic Dictionary

SEA LEVEL- the position of the undisturbed surface of the World Ocean, tending to be perpendicular to the direction of the resultant of all forces (mainly gravity) applied to the mass of water. The sea level is subject to fluctuations in relation to the conditional beginning ... ... Marine encyclopedic reference

Water level- wrecks and lakes a x, the position of the free surface of the water of rivers and lakes relative to some constant horizontal surface; as such a surface is taken or some arbitrary height plane, ... ...

Ocean bed- one of the main elements of the relief and geological structure of the seabed of the World Ocean. Covers its abyssal part (see Abyssal) minus the mid-oceanic ridges. It is characterized by the development of a typical oceanic crust. ... ... Great Soviet Encyclopedia

THE AVERAGE LEVEL OF THE EARTH'S LITHOSPHERE SURFACE- the level at which the entire solid earth's surface would be located if it were perfectly flat. Currently corresponds to a depth of about 2.4 km below the present. the average level of the World Ocean. Geological Dictionary: in 2 volumes. M .: Nedra. ... ... Geological encyclopedia

Erosion basis- the level of the pool into which the water flow enters. General (or main) B. e. sea level. Local (or temporary) B. e. flowing lakes, places where the tributary flows into the main river, as well as outcrops of solid rocks that slow down the deep ... Great Soviet Encyclopedia

Books

War of the Sea and Land, Kovalevskaya Alexandra Vikentievna. The distant future ... On the eve of the Third World War, the best scientists of the planet founded Submarine Colonies in the depths of the World Ocean. The nuclear nightmare of the global apocalypse has thrown the inhabitants away ...

Rising sea levels are not only a problem in tropical regions, but also a very serious threat to Europe. At the UN Climate Conference (COP23), which was held in Bonn last year, a warning was sounded about the consequences of rising average temperatures on the planet. Melting polar glaciers and rising sea levels threaten to flood large coastal areas, especially in the Netherlands, Belgium and Greece. It is expected that by 2100 the water level in the world's oceans may rise from 40 cm to a meter. These are the latest projections by the Intergovernmental Panel on Climate Change (IPCC).

Preventive measures are possible, but very costly. The impact of climate change could cost the island nation of Fiji $ 4.5 billion over 10 years to minimize damage from rising ocean levels, according to a World Bank report released during COP23. This amount is comparable to Fiji's GDP.

As sea levels rise unevenly in different parts of the planet, the Fiji situation should be a warning to Europe and other regions.

According to the European Environment Agency, since 1993, the level of the world's oceans has risen by 3 millimeters per year, which means that over the past quarter of a century, the water on the planet has risen by more than 7 cm.In total, over the past century, the water level in the ocean has risen by 19.5 cm, but this process was uneven, and the problem is that in last years the situation has deteriorated sharply.

How much water in the world's oceans will rise in the coming years depends entirely on efforts to combat global warming. While Europe still has time to prepare for the "flood", and for many European cities this problem is not relevant at all, but alarming signals still sound.

Thus, the authorities of Venice are engaged in the installation of 57 protective barriers against floods to prevent flooding in the lagoon, on which the pearl of the Adriatic is located. The project has already spent 5.5 billion euros. Veterans of sea flood control, the Dutch have also responded to the threat by inventing houseboats. In the UK, £ 1.8bn has been set aside to protect London and its suburbs in the face of the threat posed by water arriving through the Thames Estuary over the next 100 years. At the same time, the south of England regularly suffers from winter floods. Barcelona, Istanbul, Dublin, and entire regions in Belgium and the Netherlands were also under threat.

All of this means that European politicians and lawmakers must act immediately to prevent a catastrophe. The approach to solving the problem is twofold. On the one hand, it is the construction of barriers to protect coastal areas from water. And on the other - and this is no less important - while there is time, it is necessary to minimize the damage to the environment, as a result of which the level of the world ocean continues to rise. Both of these measures require constant updating of information on the evolution of the coastline.

The Copernicus Program provides vital information to combat climate problems. “Observing water levels in the world's oceans is key to tracking the world's climate change,” says Jean-Noel Tepo, Copernicus Program Manager. “It is important that policymakers and policymakers have a comprehensive understanding of climate change and how it affects different aspects of life on the planet.” That is why the Copernicus program monitors not only the water level in the oceans, but also the formation sea ice, sea temperature and moisture content on the mainland (in the soil). “An integrated approach to what we call 'water rotation' is important for us, because it helps us track the evolution of the planet's climate.”

Large-scale infrastructure projects in the future will certainly take into account the rise in sea levels

One of the organizations providing information to the Copernicus Climate Change Monitoring Program is the French research institute CLS, which is engaged in observations of the development of the sea. As noted by Gilles Larnicole, head of oceanography at CLS, a key role for the organization is to ensure the accuracy and reliability of the collected data, which is extremely important for subsequent decision-making. “Whenever a new harbor or large structure appears on the coastline, its construction must take into account the projected water level in the world's oceans,” says Gilles Larnicole. "The IPCC model is central to this issue, but it is also important to cross-check the information with other sources, such as the data that the CLS collects."

Observations of world ocean levels have become such an important indicator of global warming that last year's UN Climate Conference devoted two whole days to this problem. The Paris Agreement, which limits the temperature rise of the planet to 1.5-2 ° C until the end of the 21st century, was signed by 194 countries. Jean-Noel Tepo, head of the Copernicus program, believes that there is reason for optimism: “The goal is difficult, but if countries adhere to their commitments to achieve it, reducing harmful emissions into the atmosphere, it will be possible to minimize the effect of climate change, limiting the rise in temperatures to an acceptable level, and, as a consequence, reducing the rise in water levels in the oceans. "

World ocean level is a common reference point for all, with which you can measure the height of land areas, as well as the depth of water basins around the globe. This became possible due to the peculiarity of our planet, where continents are only islands in the endless expanses of the World Ocean.

Changes in sea level

The sea level is constantly changing due to many factors. Among them, the most important are human activities and volcanic activity.

Oscillations of ocean waters can be of two types:

Periodic- fluctuations occur as a result of ebb and flow.
Non-recurrent- arise as a result of tsunamis, typhoons, cyclones, hurricanes.

Also, fluctuations are distinguished by duration:

Short- are regulated by the ebb and flow and last exactly 6 hours 12.5 minutes.
Long- occur over many hundreds of years, and are associated with a global change in the volume of water in the ocean.

Rice. 1. Fluctuations in the level of the World Ocean over the past 200 thousand years.

The first long-term or secular changes in ocean water fluctuations occurred during the historical glaciation of the planet - during this period, the ocean level decreased by 200 m. With the gradual melting of glaciers, it began to rise. In the near future, it is predicted to rise by another 30 cm, which may entail a serious environmental threat to all life on the planet.

M. G. Deev,
Cand. geogr. Sci., Senior Researcher, Department of Oceanology, Moscow State University. M.V. Lomonosov

Methods for measuring ocean level.
Satellite altimetry

Sea level is measured at gauging stations, which are equipped at coastal hydrometeorological stations. The simplest level measurement device is water meter, which is rigidly fixed in the ground in such a way that at the lowest position of the level in this place, the zero mark of the reading scale is always in the water. Hydraulic structures in the form of piers, moorings, dams, breakwaters are often used to secure water-measuring rails.

Scheme
satellite altimetry

Continuous registration of level fluctuations is performed at hydrometeorological stations equipped with tide gauges - level recorders of various types. The designs of most of these devices can be divided into two types: float and hydrostatic. The float tide gauge registers the level of the float floating in a special well connected to the sea by a horizontal pipe. The vibrations of the float, suspended with a counterweight on a flexible wire or cable, are transmitted to the measuring wheel, and from it to the writing device, which draws a curve of the level fluctuations on the tape.

Methods for installing tide gauges: in a well on the bank (a), on a pile foundation (b)

The design of the hydrostatic tide gauge is based on the principle of the well-known aneroid barometer. Sensitive sensors of such devices, most often placed on the bottom of reservoirs, react to fluctuations in hydrostatic pressure that occur with changes in sea level. The sensors of stationary models of such tide gauges are installed in wells or on underwater structures of hydraulic structures, and the recording part of the device is located in the booth of the water gauge post. Some models of hydrostatic tide gauges are designed for autonomous work... In them, the measuring and recording parts of the device are mounted in one waterproof case, and the structure is installed on the bottom.
Observations of the behavior of the World Ocean level at coastal stations and posts cannot give a complete picture of its fluctuations, since they are carried out only in a narrow coastal strip. In the open ocean, there are likely to be numerous level imbalances caused by uneven density distribution, large currents, and other similar causes.
Measurement of absolute level marks in the open ocean became possible only with the beginning of the use of radio altimeters installed on artificial earth satellites. The technique for measuring distances from a space object to the earth's surface began to be developed in the 70s of the last century and was named satellite altimetry. Satellite methods make it possible to continuously monitor the level surface of the World Ocean.
There are several options for calculating satellite orbits for conducting geodetic and other high-altitude measurements of the earth's surface. Consider a program called iso-route satellite imagery that well illustrates the basic principles of satellite altimetry.

Saint Petersburg. Kronstadt. Pavilion(tide gauge is installed in it ) and a water meter, which it is fair to call the number 1 rail in the country, - Kronstadt tide stock. The heights in Russia are counted from the “zero” of the Baltic Sea.

The parameters of the satellite iso-route orbit with a radio altimeter are selected so that each successive orbit ( track) shifted relative to the previous one by some constant value. After a certain number of turns ( cycle) the satellite enters the route of the first track, after which the whole cycle is repeated again. In 1992, according to the TOPEX / Poseidon program, a satellite with two radio altimeters (altimeters) was launched into a near-earth orbit with an altitude of 1336 km with an inclination of 66 ° to the equatorial plane to study the circulation and topography of the World Ocean surface. In 2001, the second satellite of this program, Jason-1, was launched into the same orbit. The distance between adjacent tracks at the equator is 300 km, the duration of one cycle is 10 days. During this time, the Earth's surface is covered with a regular rhombic grid of satellite paths, along which measurements are repeated about 36 times a year.

The graph shows the change in ocean level (in mm, on a vertical scale)
according to TOPEX / Poseidon satellite altimetry data in the 90s - early 2000s.

In satellite altimetry, the sea surface height is calculated relative to the geoid surface by the measured satellite height above the sea and the orbital altitude of the satellite itself - taking into account corrections related to the instrumental accuracy of altimeters, the state of the sea surface, signal transmission through the dense layers of the atmosphere, and some others. As a result, the average height of the sea surface is obtained, which is the calculated value obtained by averaging the altimetric measurements of one or several satellites, which is the closest to the undisturbed ocean surface. The accuracy of such measurements is about 5 cm.

World ocean level in the past and today.
Dynamic topography

Periodically repeating level fluctuations with periods of the order of 15-25 thousand years, caused by ice sheets and leading to changes in the global volume of water in the ocean, are called eustatic. The last major glaciation in the history of the Earth (Würm) reached its greatest development about 18 thousand years ago. Then, at the peak of glaciation, the ocean level, due to the concentration of large volumes of water in the glaciers, dropped, according to various estimates, by 65-125 m relative to the current state. Note that a decrease in the level by one hundred meters in the current boundaries of the World Ocean corresponds to the withdrawal of about 36 million km3 of liquid water, which all goes into solid state and forms the ice sheet on the continents. When the ice begins to melt, the melt water returns to the ocean, which is manifested in a gradual rise in its level.

Changes in the level of the World Ocean over the past 800 thousand years

In the 8-10 thousand years that followed the peak of the Wurm glaciation, the ocean level rose relatively evenly with an average speed of 8-9 m per thousand years. In the last 6 thousand years, there has been a gradual slowdown in the growth of the level, and in the last millennium the rise was about one meter. At present, the nature of the Earth and its climatic system are in conditions of typical interglacial, the optimum of which has already been passed. With a high degree of probability, it can be assumed that under such conditions, secular level fluctuations of the order of ± 1 m per thousand years (on average 1 mm / year) are a normal phenomenon in the history of the Earth.
To assess the current state of the World Ocean level, data from satellite altimetry measurements and vast arrays of oceanographic observations are used, which can be used to calculate the topography of the steric level. Single level measurements (both satellite and terrestrial) reflect the height deviations introduced by the influence of wind waves, swell, tides and other short-term effects. When averaging mass measurements, all short-period and random disturbances of the level surface are excluded, leaving only the level heights due to constant long-term factors. The water surface topography obtained with this procedure, formed under the influence of dynamic reasons, among which one can distinguish latitudinal irregularity of heating of the ocean surface, the influence of large stationary centers of atmospheric action, as well as the largest links of oceanic circulation, is called dynamic topography.
The processing of satellite altimetry data using the TOPEX / Poseidon program has made it possible to obtain the first topographic map of the middle level of the oceans, created from direct measurements. The largest deviations of the dynamic level are from –110 to +130 cm, i.e. on average, tens of centimeters above and below the surface of the geoid.
The highest level is observed in the northern tropical region of the western Pacific Ocean, south of the Japanese Islands. The lowest dynamic level marks are located on the northern periphery of the Southern Ocean, in the 60s southern latitude. In each of the oceans *, the level differences from the tropics to high latitudes are two (Atlantic Ocean) - two and a half (Pacific Ocean) meters. The level of the Pacific Ocean is the highest at all latitudes, the level of the Atlantic Ocean is the lowest, the difference is on average 60-65 cm, the level of the Indian Ocean is in an intermediate position.
Steric level calculations based on annual average temperatures and salinity sea water in these oceans, have shown that the differences in the topography of the "altimetric" and "steric" levels almost do not go beyond the limits of errors allowed in the calculations of both. This means that the main reason for the deviations of the average undisturbed level of the oceans from the surface of the geoid is determined by the difference in the density of oceanic waters, that is, the differences in temperature and salinity, on which the density depends. The higher the temperature and lower the salinity of sea water, the lower its density and vice versa. A decrease in density leads to an increase in volume, and therefore to an increase in level. It is interesting that the excess of the Pacific Ocean level in the Northern Hemisphere is mainly determined by the reduced salinity of its waters, and in the temperate latitudes of the Southern Hemisphere - by their increased temperature.

Global ocean conveyor

Exceeding the level is a visible sign, literally lying on the surface. But there are other properties, as it were, excessive in one ocean and insufficient in the other. For example, the content of biogenic substances (silicates and phosphates) in the North Pacific Ocean is 2-3 times higher than their concentration in the waters of the North Atlantic. The opposite picture is observed in the distribution of dissolved carbonates and oxygen, the concentration of which is highest in the Atlantic Ocean and gradually decreases towards the northern part of the Pacific. These and some other similar facts lead to the conclusion about the existence of an interoceanic exchange of properties in the form of a global circulation that permeates the space of three oceans - from the North Atlantic across the Indian Ocean to the northern latitudes of the Pacific Ocean. According to modern concepts, such a closed circulation exists, it consists of surface and deep oppositely directed flows, it was called the global ocean conveyor belt.

Factors of changes in the level of the World Ocean.

The widespread elevation of the Pacific Ocean level indicates the presence of a constant horizontal pressure gradient, which is aimed at leveling the levels and bringing them into equilibrium. Under the influence of this gradient, from the "highest" region of the Pacific Ocean through the straits of the Indonesian seas to the southwest, a stream of warm waters moves, which through the Indian Ocean, skirting the southern tip of Africa, go out into the Atlantic. Further along the coasts of the two Americas, these waters cross the Atlantic Ocean to its northwestern region. There, due to intensive evaporation, surface waters become saline and thickened, which leads to their convective immersion. Having reached depths of 2000-3000 m, they mix with cold waters coming from the Arctic basin, and begin to form a deep, oppositely directed branch of the global circulation. Crossing the Atlantic Ocean from north to south, deep waters flow into the Circumpolar (Western Winds) Current, which is carried east along the coast of Antarctica. In the South Pacific, in front of the Drake Passage, deep waters turn north and, following in this direction, reach the Aleutian Islands region, where, being less dense relative to local deep waters, they slowly rise to the upper surface layers, closing the "conveyor belt".

Profile conveyor

This movement is extremely slow and is not recorded by any instruments. The period of complete exchange of the waters of the Atlantic and Pacific oceans in the flow of the global oceanic conveyor is estimated to be on the order of many hundreds to one and a half thousand years. Throughout this long journey, there is a slow continuous exchange of heat, salts, nutrients, gases with the surrounding waters. Changes in the Earth's climatic system, expressed in the redistribution of heat and moisture, exacerbation of atmospheric processes, violation of weather regimes in certain regions, can affect the movement of the "conveyor" in the form of changes in the characteristics of the transferred properties, as well as the intensity of transfer.
So, using the example of the global oceanic conveyor, we can conclude that very small but long-term differences in the position of the ocean level are able to excite a stable circulation of waters and processes of interoceanic exchange of properties that maintain global dynamic equilibrium in the World Ocean.

Global oceanic conveyor "full face". Warm streams are shown in red, cold streams are shown in blue.

Map of areas on Earth at greatest risk of being flooded due to rising sea levels. Areas that will go under water if the sea rises six meters are marked in red

American climatologists have found that the rise in the average level of the world's oceans on Earth due to global warming is slowly accelerating. According to data obtained using satellite measurements over the past 25 years, the rate of sea level rise every year increases by an average of 0.084 millimeters per year, scientists write in Proceedings of the National Academy of Sciences.

One of the direct consequences of global warming on Earth is the rise in the average sea level, which has been observed since the middle of the 19th century. It is due to thermal expansion ocean water, as well as melting polar ice sheets in Antarctica and Greenland and mountain glaciers. In the 20th century alone, the average sea level rose by 17 centimeters and continues to rise. According to some forecasts, some of the countries located at low altitudes, in particular, the island states in the Pacific Ocean, may be completely submerged in the middle of the 21st century. In order to more accurately assess the possible dynamics of mean sea level in the near future, scientists offer a variety of computer and mathematical models, but so far their results are quite different and cannot be considered sufficiently accurate.

To create a more accurate model describing the dynamics of sea level on the planet, American climatologists led by Robert S. Nerem of the University of Colorado Boulder analyzed the latest satellite data on the dynamics of the mean sea level and found that sea level changes over the past 25 years can be described assuming that its growth occurs with a constant, on average, acceleration. In their work, we used all the available data of altimeters installed on satellites of four oceanographic missions of NASA and the National Oceanic and Atmospheric Administration of the United States: from TOPEX / Poseidon launched in 1992 to the Jason-3 satellite, which was in orbit by the Falcon 9 launch vehicle in January 2016 year. From this data, scientists determined the average speed and average acceleration of mean sea level rise on Earth from 1993 to 2017. At the same time, in their study, the authors did not consider the available data obtained using tide gauges (neither for previous years, nor carried out simultaneously with satellite measurements), which are somewhat inferior in their accuracy and may slightly differ from the results of satellite measurements.

At the same time, in order to determine the effect on sea level only of global climatic changes and to avoid the contribution of local single events (which lead to noticeable fluctuations, but do not reflect general quantitative trends), scientists tried to estimate and subtract from the total dependence the contribution of the two most noticeable events that occurred during this period. The first of these was a series of powerful eruptions of the Philippine volcano Pinatubo, which occurred in the early 90s of the XX century. Due to the release of a huge amount of aerosol particles into the atmosphere, these eruptions had a tangible effect on the Earth's climate - in particular, they led to an increase in the average temperature and an increase in the area of the ozone hole over Antarctica. The second important factor, which also led to the local acceleration of sea level rise, was El Niño - the active phase of cyclical Pacific surface currents, which leads to a significant increase in temperature on Earth; the last such phase was observed in 2015-2016. According to scientists, both of these factors lead to significant local deviations from the general trend associated with climatic changes on the planet, and for a quantitative analysis, the associated fluctuations were subtracted from the general dependence.

Dynamics of changes in the global mean sea level (GMSL) from 1993 to 2017. Blue denotes the original data, red - minus the impact of the Pinatubo eruptions, green - minus the contributions of the Pinatubo and El Niño eruptions

R. S. Nerem et al./ PNAS, 2018

As a result of the analysis of the obtained data, adjusted for the influence of El Niño and the Pinatubo eruptions, climatologists determined the average rate of rise in mean sea level on the planet, which was 2.9 millimeters per year, as well as its acceleration. It turned out that the data on changes in mean sea level over the past 25 years are very well described by the constant acceleration model, and on average, the rate of sea level rise every year increases by 0.084 millimeters per year (the measurement error was about 30 percent).

Based on the average rate of sea level rise, scientists proposed to consider the process uniformly accelerated and based on this model, they made an estimate of the sea level in 2100, which should increase by 65 centimeters compared to 2005. According to the scientists, these results are in qualitative agreement with the data of the most accurate forecasts to date, obtained using computer modeling, but in the future the accuracy of estimates should increase due to the analysis of data over longer periods of time.

Note that recently, New Zealand climatologists, whether the sea level rise is really so dangerous for the Pacific islands. It turned out that even the islands of Tuvalu, for which the risk of being flooded is considered the maximum, over the past 30 years, not only did not decrease in area, but even grew slightly. The area has grown even though the sea level there is rising about twice as fast as the global average.

Alexander Dubov