Rise in the sea level

The rise in the sea level can be caused by multiple and complex factors.

The Sea level rose approximately 120 Mètre S since the peak of the last Glaciation, there is approximately 18 000 years. The increase especially took place until 6 000 years before today. Since 3 000 years before today, and this until the beginning of the 19th century, the sea level practically did not move, increasing only by 0,1 to 0,2 millimetre per annum. Since 1900, it increases by 1 with 3 mm per annum. Since 1992, satellite altimetry starting from TOPEX/Poseidon indicates a rate of rise in approximately 3 mm per annum.

The rise in the sea level can be a consequence Climate warming through two principal processes: the dilation of sea water (since the oceans are heated), and cast iron of the terrestrial ices. It is provided that climate warming will cause significant growths of the sea level during the twenty and unième century.

Highlights

Local level and level eustatic

The Local Average Niveau of the Sea (NMLM) is defined like the height of the sea compared to a point of reference on ground, and on average over a sufficiently long period of time (one month, one year) so that the value is independent of the fluctuations caused by the waves and the tides. One must also adjust the variations of the NMLM to take into account the vertical movements of the Earth, which can be of the same order (some mm/an) that changes of the sea level. Certain earthmovings occur because of an isostatic adjustment of the coat due to the cast iron of the Inlandsis at the end of the last Glaciation: indeed, the weight of an ice cap cause a drop in the subjacent ground and when the ice melts, the ground rebounds (postglacial Rebond). The atmospheric pressure, the oceanic currents and the changes of temperature of the oceans can also affect the NMLM.

The eustatic variations “” (in opposition to the local variations) relate to the deterioration of the total level of the sea, such as the changes of volume of the water of the oceans and the changes of volume of the oceanic basins.

Short-term and periodic changes

There are many factors which can produce short-term changes (of a few minutes in 14 month) on the sea level.

Longer-term changes

Varied factors can affect the volume and the mass of the oceans, driving with long-term changes of the level eustatic of the sea. The two primary influences are the Température (because the volume of the Eau depends on the temperature, according to the laws of the Thermodynamique), and the Masse of water captive of the grounds such as fresh water of the rivers, the lakes, the glaciers, the icecap of the poles. On scales of geological times , changes in form of the oceanic basins and distribution grounds/seas affects the sea level.

Estimates by the observation give that the rise in the sea level due to the increase in the temperature, in the recent decades, is of approximately 1 mm/an. Studies by the observation and the models of the loss of mass of the glaciers and the polar icecap indicate a contribution of the rise in the sea level, on average over the 20th century, of 0,2 with 0,4 mm/an.

Glaciers and icecaps

Each year, approximately 8 mm of water, coming from the surface of the oceans, fall down on the Antarctic and the Inlandsis of the Greenland in the form of snowfalls. If no ice turned over in the oceans, the sea level would thus lose 8 mm per annum. Although the same quantity of water, roughly, turns over to the ocean in the form of icebergs and of cast iron of the ice of the coasts, the scientists do not know which of these quantities of water - leaving towards the poles or while returning - is tallest. The difference between the entering ice and the outgoing ice is called the weight breakdown and is important because it is it which causes the changes in the total level of the sea.

The barriers of ice floating at sea surface do not change, when they found, the sea level. Same manner, cast iron of the ice of the north pole (icecap) which consists of drift ice does not contribute to the increase in the sea level. However, as it is fresh water, its cast iron causes only one very small increase in the sea level, and which is so small that she is in general neglected. One can however affirm that if the barriers of ice found, there are good lucks that the ice caps of Greenland and the Antarctic found too date= February 2007 .

The scientists miss information on stocks of water of the Earth and their evolution. Between 1910 and 1990, their changes contributed to – 1,1 to +0,4 mm/an. If all the Glacier S and the icecap founded, the rise in the sea level would be of approximately 0,5 Mr. the cast iron of the Inlandsis of the Greenland would produce 7,2 m of rise in the level, and the cast iron of the ice cap of the the Antarctic would produce 61,1 of it; Mr. The collapse of the immobilized interior tank of the ice cap of the Western Atlantic would increase the level of 5 with 6 Mr.

The changes of climate of the 20th century, starting from the studied models, would contribute of – 0,2 and 0,0 mm/an for the Antarctic (result of the increase in precipitations) and from 0,0 to 0,1 mm/an for Greenland (because of the change as well of precipitations as of the overflow). The estimates suggest that Greenland and the Antarctic contributed to a rise in 0,0 to 0,5 mm/an during the 20th century and that it would be the result of one long-term adjustment since the end of the last glaciation.

The current increase in the sea level observed by the marigraphs, of approximately 1,8 mm/an, is in the interval of estimate starting from the factors above but of active research continue in this field. Uncertainty in terms of terrestrial water stocks is particularly large.

Since 1992, satellite programs TOPEX and JASON provided measurements of the change of the sea level. The current data are available. These data show an average rise in 2,9±0,4 mm/an. However, because of the great short-term variability of the sea level, this recent increase does not mean a long-term acceleration inevitably.

Geological influences

At certain times of long the History of the Earth, the continental drift had laid out the grounds following of the configurations very different from that of today. When most of the earth's crust was close to the poles, the study of the rocks showed, during the Ice Age, of the levels of sea unusually low, because there were many polar grounds on which snow and the ice could accumulate. Contrary, for the periods when the emerged grounds gathered around the equator, the Ice Age had much less effect on the sea level. However, during most of the geological time, the long-term level of the sea was higher than today (see the graph opposite). It is only at the border of the Permien and of the Trias, approximately 250 million years ago, that the long-term level of the sea was lower than today.

An assumption based on the plate tectonics could explain fluctuations of the level of the oceans of great amplitude on very the long run. Indeed, it is known that the continental lithosphere (which is formed on the level of the zones of subduction) increases since the origin of geological times because of its weak density which does not enable him to disappear in the depths from the asthenosphere. Thus, the continents increasing, oceanic surfaces are reduced, which tends to increase the level of the oceans since the beginning of the history of the Earth. In addition, when it occurs an orogenesis (by collision), the obstruction continental is reduced because the continental lithosphere is found compressed (while rising), and not spread out. That brings logically to the extension of oceanic surfaces, therefore with a generalized marine regression. Thereafter, once completed orogenesis (fine of collision of plates), it is the erosion which becomes dominating. The continental matter torn off with the new mountains is then involved at the bottom of the oceans, causing the slow rise of the level of those and the invasion of littoral continental surfaces (Transgression marinades generalized).

This assumption would make it possible to explain the sedimentary cycles of great duration which occurred on the level of sedimentary basins currently located at a too high altitude (> 100 m) to be due to climatic causes. One can take in example the Paris basin of which the essence of sedimentation occurred in Mézozoïque, between orogenesis hercynienne (border Permien/Trias) and alpine orogenesis. Within the framework of this assumption, each orogenesis (Precambrian, calédonienne, hercynienne and alpine) correspondent with collisions of plates would have involved continental compressive regroupings and, consequently, the fall of the oceanic level and generalized marine regressions, whereas the intermediate periods (correspondent with fractionations of plates) would have made it possible the erosive phenomena to involve great quantities of continental matter at the bottom of the oceans, causing the rise of their level and the generalized marine invasions. These last would then have allowed the sedimentary cycles observed in the basins currently located at altitudes much higher than 100 Mr.

During the glacial/interglacial cycles on the few million years Before the present, the sea level varied about hundred meters. That is due mainly to the growth and the decrease of the Inlandsis (mainly in the northern hemisphere) supplied with the evaporated water of the sea. The thaw of the ice caps of Greenland and the Antarctic led to a rise in the sea level of approximately 70 meters.

The evaluations of the rise in the sea level starting from satellite altimetry by since 1992, give approximately 2,8 mm/an. They exceed those obtained by the marigraphs. It is not known if that represents an increase over the last decades, if it is normal variability, or, if there are problems of Calibration satellites. In 2001, the TRE declared that measurements had detected a nonsignificant acceleration the current speed of rise in the sea level. More recent work can call that in question; for example Church and White, 2006.

Based on the data obtained by the Marigraph S, the speed of the rise in the total average sea level during the 20th century is in a fork which goes from 0,8 to 3,3 mm/an, with a mean velocity of 1,8 mm/an. Recent studies of the Roman wells with Caesarea and Roman Piscinae in Italy indicate that the sea level had remained rather constant since a few hundred years before our era until a few hundred years ago.

Based on geological data, the total mean level of the sea can have increased with a mean velocity of approximately 0,5 mm/an during the 6 000 last years and with a mean velocity from 0,1 to 0,2 mm/an during the 3 000 last years. Since the Last glacial maximum, there is approximately 20 000 years, the sea level rose of 120 m (with an average of 6 mm/an) resulting from the important cast iron Inlandsis. A fast increase took place between 15 000 and 6 000 years before the present at a mean velocity of 10 mm/an which because an increase of 90 m; consequently, during the time since 20 000 years before the present (by excluding the fast increase between 15 and 6 thousand years), the mean velocity was of 3 mm/an.

A significant event was the Cast iron 1A Impulse, when the sea level increased by 20 m over 500 years there is approximately 14 200 years. It is a speed of 40 mm/an. Recent studies suggest that the primary source of the molten ice was the the Antarctic, and it is perhaps what because the impulse of southern cold - > northern marked by the Renversement of the Cold of Huelmo/Mascardi of the Southern hemisphere, which preceded the recent Dryas by the Northern Hemisphere. The rise relative in the sea level to specific places is often from 1 to 2 mm/an higher or lower than the total average. Along the semi-Atlantic coasts states-uniennes and Gulf, for example, the sea level rises roughly 3 mm/an.

Rise in the sea level in the future

In 2001, the Third Evaluation report of GIEC predicted that, from here 2100, the Climate warming will lead to a rise in the sea level from 9 to 88 cm. Up to now, no significant acceleration the speed of rise in the sea level was detected at the 20th century Thereafter, J.A. Church and NR. J. White found an acceleration of 0,013 ± 0,006 mm/an ².

One does not expect that the future rise in the sea level, like the recent increase, is overall uniform (details below). Certain areas show a rise substantially more important than the total average (and in much of case, more than twice the average), and others a fall. However, the models diverge with regard to the probabilities from change from the sea level.

Intergovernmental panel on the consequences of the climate change

Results of the chapter on the sea level of the Third Evaluation report of the GIEC (TRE) (authors John A. Church and Jonathan Mr. Gregory) are given below.

The sum of these components indicates a speed of eustatic rise in the level in the sea (correspondent to a change of the volume of the ocean) since 1910 until in 1990 which goes from - 0,8 to 2,2 mm/an, with a central value in 0,7 mm/an. The upper limit is close to the upper limit observed (2,0 mm/an), but the central value is smaller than that observed (1,0 mm/an), i.e. the sum of the components is skewed downwards in comparison with the observational evaluations. The sum of the components indicates an acceleration from only 0,2 (mm/an) /siècle, in a fork of - 1,1 to +0,7 (mm/an) /siècle, in agreement with the observational conclusion of nonthe acceleration of the rise in the sea level during the 20th century. The speed estimated of this rise because of the anthropogenic climate changes since 1910 until in 1990 (starting from studies of models of thermal expansion, glaciers and the ice caps) goes from 0,3 to 0,8 mm/an. It is very probable that the warming of the 20th century contributes significantly to the rise observed, through the thermal expansion of and considerable loss sea water of the ices of the grounds.

An also interesting article is that of Arendt and Al which estimates the contribution of the glaciers of Alaska at 0,14±0,04 mm/an between the middle of the years 1950 and the middle of the years 1990 with an increase of 0,27 mm/an in the medium and the end of the year 1990.

Contribution of Greenland

Krabill and Al consider the contribution total of the Greenland at least 0,13 mm/an in the years 1990. Joughin and Al measured a doubling the speed of Jakobshavn Isbræ between 1997 and 2003. It is about the largest glacier of discharge system of Greenland; it only drains with him 6,5% of the Inlandsis, and it is thought that it is responsible for the increase the speed of rise in the sea level in 0,06 mm/an, or, roughly speaking, of 4% of the increase this speed during the 20th century. In 2004, Rignot and Al estimated the contribution of the south-west of Greenland to 0,04±0,01 mm/an.

Rignot and Kanagaratnam produced a complete study and a chart of the glaciers of discharge system and basins of Greenland. They found an acceleration glacial considerable below 66° NR into 1996 which was propagated until 70° NR in 2005; and that the speed of losses of the ice cap during this decade increased by 90 to 200 km ³ /an; that corresponds to a rise in the sea level from 0,25 to 0,55 additional mm/an.

In July 2005, it was reported that the Kangerdlugssuaq glacier, on the east coast of Greenland, moved towards the sea three times more quickly than in the previous decade. Kangerdlugssuaq has approximately 1000 m of thickness, 7,2 km broad, and drains approximately 4% of the ice cap of Greenland. Measurements of Kangerdlugssuaq in 1988 and 1996 showed it moving at a speed between 5 and 6 km/an. In 2005 it moved with 14 km/an.

According to the Evaluation of the Impact of the Climate of the Arctic of 2004, the climatic models provide that the local warming in Greenland will exceed 3 degrees Celsius during this century. In the same way, the models of ice cap provide that such a warming will start the long-term thaw of the ice cap, leading to the complete thaw of the Inlandsis of Greenland over several millenia, from where will result from it a rise in the sea level in approximately seven meters.

Effects of the permafrost and snow line

The snow line is the lowest altitude for which the minimum layer of snow in the year covers more than 50% of surface. That varies approximately 5 500 meters above the sea level at the equator up to the level even of the sea to 65 degrees of Northern or Southern Latitude (according to the effects of the regional improvement of the temperature). The Pergélisol appears then with the sea level and extends more deeply under the sea in direction from the pole. The thickness of permafrost and the height of the ice-barriers of Greenland, like the Antarctic, mean that they are largely invulnerable with a fast cast iron. The Greenland culminates with 3 200 meters, the annual average temperature is there less 32 °C. Therefore, even an increase projected in 4 °C leaves it well in lower part of the melting point of the ice. Number 28 of December 2004 of the review Frozen Ground contains a very significant plan of the affected zones of the permafrost of the Arctic. The zone continues permafrost includes all Greenland, the north of the Labrador, the Territoires of the North-West, the north of Fairbanks in Alaska, and most of north east of the Siberia in the north of the Mongolia and the Kamchatka. The continental ice above permafrost has few chances to melt quickly. As most of the ice caps of Greenland and the Antarctic extends above the snow line and/or base the zone permafrost, they cannot melt in a time much shorter than several millenia; thus it is not very probable that they contribute significantly to the rise in the sea level in the century which comes.

Polar ice

The sea level could increase so more polar ice founded. However, in comparison with the heights of the Ice Age, there is today very few continental Inlandsis which remains to be melted. It is estimated that if all Antarctic founded, that would contribute to more than 60 meters of rise in the sea level, and if it were Greenland, that would make more than 7 meters. The small glaciers and the icecaps could contribute to approximately 0,5 meters. Although this last figure is much small pus that for the Antarctic or Greenland, this thaw could arrive relatively quickly (during the century which comes), while the cast iron of Greenland would be slow (perhaps 1500 years, if it thawed out completely at the fastest speed) and the cast iron of the Antarctic even slower.

In 2002, Rignot and Thomas found that the ice caps of the Western Antarctic and Greenland lost mass, whereas the ice cap of the Antarctic East was probably in balance (although, as regards the ice cap of the Antarctic East, they are not able to determine if the weight breakdown were positive or negative). Kwok and Comiso also discovered that the anomalies of temperature and pressure around the Western Antarctic and on the other side of the Peninsula of the Antarctic were correlated with the El Niño recent.

In 2004, Rignot and Al found a proof of a contribution accelerated to the rise in the sea level coming from the Western Antarctic. The data showed that the ice cap of the Western Antarctic of the sector of the Mer of Amundsen lost 250 kilometers ice cube each year, which had 60% of more than of accumulation of precipitations in the zones of collecting. That only was sufficient to raise the sea level of 0,24 mm/an. Moreover, speeds of dilution of the glaciers studied in 2002 and 2003 had exceeded the values measured with the beginning of the year 1990. The base of the glaciers was several hundred meters more in-depth than than one had known front, showing the ways of evacuation of the ice coming moreover further in the grounds from the sub-polar basin of Byrd. Thus the ice cap of the Western Antarctic could not be as stable as it had been supposed.

In 2005, one announced that, between 1992 and 2003, the Eastern Antarctic had thickened at a mean velocity of 18 mm/an, while the Western Antarctic showed a total thinning of 9 mm/an, associated with an increased precipitation. A profit of this size is sufficient to slow down the rise in the sea level of 0,12±0,02 mm/an.

Effects and stakes of the rise in the sea level

On the basis of projection indicated above, report/ratio TRE of the GIEC ( IPCC TAR ) WG II notes that one can expect that the current and future change of the climate has various impacts on the coastal systems; including a coastal erosion accelerated, an exacerbation of the occurrence and width of the Flood S, marine invasions due to the storms, the inhibition of elementary production processs, changes in the characteristics and the water quality of surface and of the Subterranean water (Salinisation), more losses of properties and littoral habitats , of the losses of Resource S and social values Cultural them and, decline of the quality of the Ground and water, economic losses (Agriculture, Aquiculture, Tourism, Leisure S) and bound and services of Transport S (the littorals are often bordered of important or vital infrastructures for national transport). Potential losses of life belong to the impacts quoted by the GIEC.
Les model projects regional and local differences important in the relative changes of the marine level. The impacts will also vary according to the capacities of ecological Résilience of the ecosystem S and thus depending on the biogeographic zones and their health condition.

The statistical data on the impacts of the rise in the marine level on the man are rare. A study (number of April 2007 D “Environment and Urbanization” ) recalls that 634 million people lives in coastal sectors with less than 10 meters above the sea level. And two thirds of the cities of more than five million people are located in coastal sectors of lowlands. It is in many countries (ex: France, even Observatory of the littoral/IFEN) the littorals which urbanize most quickly and which are touched by the Périurbanisation.
Une most of the chemical factories , of the Refinery S, large the Port S strategic, of the powerplants, in particular nuclear most powerful are built there. It is as on atolls vulnerable to the immersion as one made many nuclear tests (Moruroa, Marshall Islands, of which the atoll of Enewetak…)
Ce on the littorals as one are as remained of many invaluable and threatened natural environments (for example expensively bought by the Conservatoire of the littoral in France); They shelter an important part of the natural reserves and world Biodiversité. Many reefs are likely not to be able to grow rather quickly to adapt to a rise of water, especially if this one becomes more turbide and polluted because of an increase in erosion, which seems to be already the case. All these resources are threatened by the rise of the oceans.

Do the islands run?

The evaluations of the GIEC suggested that the deltas and the small island states could be particularly vulnerable to the rise in sea level. The relative rise in the sea level (caused most of the time by depression) causes the substantial ground loss in some deltas. However, the changes of the sea level were not yet the cause of losses environmental, humane, or economic substantial in the small island states. The preceding declarations say that the parts of the insular nations of Tuvalu “were inserted” because of the rise in the sea level. However, the following reviews suggested that the ground losses had in fact be the result of erosion during and after the cyclones Gavin, Hina, and Keli of 1997. The islands in question were not populated. Reuters reports that other Pacifiques islands face a serious risk, of which the island of Tegua in Vanuatu. He affirms that the data of Vanuatu do not show any clear rise in the sea level, and are not corroborated by data of measurement of tide. The data of measurement of tide of Vanuatu show a clear rise in approximately 50 millimetres of 1994 to 2004. The linear regression of this short-term sequence suggests a speed of rise in approximately 7 mm/an, although there is a considerable variability and that it is difficult to evaluate the exact threat which weighs on the islands by using a sequence with if short term. According to Patrick J. Michaels, skeptic on climate warming: “in fact, the sectors such as the island of Tuvalu show substantial declines of the sea level for this period”.

Many options were proposed which could assist the insular nations to enable them to adapt to the rise in the sea level.

Measurements of the sea level by satellite

The evaluations of rise in the sea level by satellite altimetry of give 3,1 + 0,4 mm/an over the period 1993-2003 (Leuliette and others, 2004). That is higher than those obtained by the marigraphs. It is not very clear to know if that represents an increase during the last decades: variability, real differences between the satellites and marigraphs, or problems of Calibration of the satellites. These data show an average increase in the sea level of 2,8±0,4 mm/an. That includes an apparent increase in 3,7±0,2 mm/an for the period of 1999 to 2004. The satellites ERS-1 (July 17th 1991 - March 10th 2000), ERS-2 (April 21st 1995 -), and Envisat (March 1st 2002 -) have also components of calculation of sea surface but of use limited for measurement of the total level of the sea due to a less detailed cover.

TOPEX/Poseidon began their series of measure in 1992, and the scientific expedition was finished in October 2005.
Jason-1, launched the December 7th 2001, took now again its mission, and follows the same trace on the ground.

Since significant variability in the short run of the sea level can occur, to extract total average information from sea level is complex. Moreover, the satellite data have a capacity of recording much shorter than the marigraphs, which proved to claim years of operations to extract from the tendencies.

There is a range of distances which apply:

from 140 to 320 mm: Increase in the sea level in the area of the Pacific of El Niño for the period 1997-1998.
140 mm: Interval of typical variations of the sea level (±70 mm).
100 mm: Precision of the altimeter radar ERS-1 radar.
43 mm: Precision of calculations height of surface of the ocean with T/P .
from 30 to 40 mm: Precision of the altimeter radar of TOPEX and POSEIDON-1 which measures the distance to the surface of the ocean.
from 20 to 30 mm: Precision of the determination height of the orbit of the satellite T/P (amplitude of laser, Doppler effect, GPS).
20 mm: Precision of the altimeter radar of Jason-1 POSEIDON-2.
from 7 to 14 mm: Total average sudden rise of the sea level for period 1997-1998 of EL Niño.
A few mm: Total average measuring accuracy of the sea level after having made the average of the cover over ten days.
10 mm: Stability the orbital heights of T/P over 4 years.
2,8 ±0,4 mm: Average annual total rise in the sea level since 1992 according to T/P .

There is apparently a problem with altimeter ERS-2. Average changes of sea level were compared between the satellites, between 60°N and 60°S, of May 1995 at June 1996:

-4,7 ±1,5 mm/an for ERS-1
-5,6 ±1,3 mm/an for TOPEX
+9,0 ±2,1 mm/an for ERS-2

Continuous comparisons of altimeter are available on http://www7300.nrlssc.navy.mil/altimetry/intercomp.html
The various readings are current variations of the sea level, not of the total level, and thus the comparison applies only to the differences between the values. These data are variations in centimetres; a later transformation is made to reach a resolution of 1 millimetre, resolution necessary for the average studies of the sea level.

The comparisons between T/P and data of the marigraphs of the Pacific Islands prove that the monthly average deviations have a precision 20 Misters.

Moreover, it should be noted that, as the satellite results are partially gauged compared to the readings of the marigraphs, they are not entirely independent sources.

The fort El Niño of 1997-1998 " printed a strong signature on the height of sea surface with semi-latitude of the Eastern Pacific. This signal will be followed to the west during the following decade like Eastern demonstration of the border of the propagations of this event in direction of the extension of the Courant of Kuroshio. "

Other satellites:

Geosat Follow is a mission of altimetry of the American navy which was launched the February 10th 1998. The November 29th 2000, the navy validated the satellite like operational. During its mission, the satellite will be maintained in the orbit of the Exact Mission of Repetition of GEOSAT (SEA) (800 km of altitude, 108 steepnesss, 0,001 of eccentricity, and 100 minutes period). This Exact Orbit of 17 days Repetition (OER) follows the trace on the ground of SEA +-1 km. As for the original GEOSAT SEA, the data will be available for oceanic science by NOAA/NOS and NOAA/NESDIS. Altimeter of radar - at single frequency (13,5 gigahertz) with 35 mm of precision on the height. Let us note that the receiver of the GPS is not functional.

Geosat Follow one @ NOAA/LSA
NAVY GEOSAT FOLLOW one (GFO) ALTIMETRY MISSION
NASA WF Geosat Follow one

Other analyzes of the sea level:

Analysis of the Sea level starting from the altimetry of altimetric ERS
Produced of the multimission Ssalto/Duacs: Combined current data of Topex/Poseidon, Geosat Follow One, Jason-1 and Envisat.

Appendices

Translation

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