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Sea Level - Full Concert - 02/11/77 - Capitol Theatre (OFFICIAL)
Sea Level - Full Concert - 02/11/77 - Capitol Theatre (OFFICIAL)
Published: 2015/01/06
Channel: Rock on MV
What Is Sea Level, Anyway?
What Is Sea Level, Anyway?
Published: 2017/10/23
Channel: Tom Scott
Sea Level "Storm Warning" (1978)
Sea Level "Storm Warning" (1978)
Published: 2010/07/15
Channel: 120jours2Sodom
What is Sea Level?
What is Sea Level?
Published: 2013/11/25
Channel: minutephysics
Sea Level - Cats on the coast (full album)
Sea Level - Cats on the coast (full album)
Published: 2013/10/26
Channel: Don Quixote
Sea Level - On the Edge (full album)
Sea Level - On the Edge (full album)
Published: 2013/10/27
Channel: Don Quixote
Sea Level - Grand Larceny - 2/11/1977 - Capitol Theatre (Official)
Sea Level - Grand Larceny - 2/11/1977 - Capitol Theatre (Official)
Published: 2014/09/23
Channel: Rock on MV
Sea Level - Grand Larceny
Sea Level - Grand Larceny
Published: 2015/06/25
Channel: Fernando Anselmo
This incredible animation shows how deep the ocean really is
This incredible animation shows how deep the ocean really is
Published: 2017/04/04
Channel: Tech Insider
That
That's Your Secret Sea Level
Published: 2013/01/11
Channel: Mutters Log
Sea Level - Tidal Wave
Sea Level - Tidal Wave
Published: 2014/04/24
Channel: Music, Memories & Everything in between
South Florida
South Florida's Rising Seas - Sea Level Rise Documentary 2017
Published: 2017/09/07
Channel: Interesting Facts
Sea Level - Shake A Leg - 2/11/1977 - Capitol Theatre (Official)
Sea Level - Shake A Leg - 2/11/1977 - Capitol Theatre (Official)
Published: 2014/09/23
Channel: Rock on MV
SEA LEVEL - LIVING IN A DREAM 1978
SEA LEVEL - LIVING IN A DREAM 1978
Published: 2009/08/09
Channel: Daniela Flores
Expert explains Future Sea Level Rise (2017)
Expert explains Future Sea Level Rise (2017)
Published: 2017/04/04
Channel: Climate State
The Ocean is Way Deeper Than You Think
The Ocean is Way Deeper Than You Think
Published: 2016/11/11
Channel: RealLifeLore
Earth Under Water Worldwide Flooding Sea Level Rise (SLR)
Earth Under Water Worldwide Flooding Sea Level Rise (SLR)
Published: 2013/08/09
Channel: Climate State
Humanity and a Million Years of Sea Level Change - Dr Nicholas Flemming
Humanity and a Million Years of Sea Level Change - Dr Nicholas Flemming
Published: 2014/09/18
Channel: GreshamCollege
The World After Sea-Level Rise
The World After Sea-Level Rise
Published: 2017/01/24
Channel: The Daily Conversation
சென்னைக்கு காத்திருக்கும் மிகப்பெரிய ஆபத்து ! முழுவதும் கடலில் மூழ்கும் அபாயம் ! ISRO | Sea level
சென்னைக்கு காத்திருக்கும் மிகப்பெரிய ஆபத்து ! முழுவதும் கடலில் மூழ்கும் அபாயம் ! ISRO | Sea level
Published: 2017/11/19
Channel: Top News - Tamil
What the Earth would look like if all the ice melted
What the Earth would look like if all the ice melted
Published: 2015/02/18
Channel: BI Science
Sea Levels - Fact & Fiction
Sea Levels - Fact & Fiction
Published: 2014/07/15
Channel: 1000frolly
Google Earth Sea Level Rise
Google Earth Sea Level Rise
Published: 2014/12/14
Channel: David Sadoff
Sea Level "Midnight Pass" (1978)
Sea Level "Midnight Pass" (1978)
Published: 2010/09/23
Channel: 120jours2Sodom
Sea level rise: Miami and Atlantic city fight to stay above water
Sea level rise: Miami and Atlantic city fight to stay above water
Published: 2017/03/20
Channel: The Guardian
What
What's your elevation above or below sea level?
Published: 2017/03/07
Channel: MashUp Math
Future Sea Level Rise: Top 10 Countries In Danger
Future Sea Level Rise: Top 10 Countries In Danger
Published: 2015/07/30
Channel: The Daily Conversation
How much is sea level rising? Climate Change Impact on Mumbai & Kolkata
How much is sea level rising? Climate Change Impact on Mumbai & Kolkata
Published: 2017/10/25
Channel: Interesting Top 10s In Hindi
EXCLUSIVE: Rising Sea Level in Chennai: Necessary action will be taken soon - O.Panneerselvam
EXCLUSIVE: Rising Sea Level in Chennai: Necessary action will be taken soon - O.Panneerselvam
Published: 2017/11/20
Channel: Thanthi TV
Sea level Meaning
Sea level Meaning
Published: 2015/04/23
Channel: SDictionary
Climate Huckster Al Gore Utterly Embarrassed, Can
Climate Huckster Al Gore Utterly Embarrassed, Can't Explain Why Sea Levels Aren't Rising
Published: 2017/08/03
Channel: The PolitiStick
Estimates of Sea Level Rise by 2100 Have Tripled in the Past Few Years
Estimates of Sea Level Rise by 2100 Have Tripled in the Past Few Years
Published: 2017/06/26
Channel: TheRealNews
Paris Climate Challenge 2015 - The Sea Level Fraud
Paris Climate Challenge 2015 - The Sea Level Fraud
Published: 2015/12/20
Channel: 1000frolly
2050 | half of chennai will be under the sea ISRO report | tamil news | tamil news today | redpix
2050 | half of chennai will be under the sea ISRO report | tamil news | tamil news today | redpix
Published: 2017/11/16
Channel: Red Pix 24x7
Sea level rise
Sea level rise
Published: 2014/07/18
Channel: ABCTVCatalyst
Jim Hansen: Hell Will Break Loose - Ice Melt, Sea Level Rise and Superstorms
Jim Hansen: Hell Will Break Loose - Ice Melt, Sea Level Rise and Superstorms
Published: 2016/09/17
Channel: Climate State
The Secret to Rising Sea Levels - Thermal Expansion
The Secret to Rising Sea Levels - Thermal Expansion
Published: 2012/07/17
Channel: AsapSCIENCE
Climate, Sea Level, and Superstorms
Climate, Sea Level, and Superstorms
Published: 2017/11/20
Channel: YaleClimateConnections
Glacier Change and Sea Level Rise (live public talk)
Glacier Change and Sea Level Rise (live public talk)
Published: 2017/02/11
Channel: NASA Jet Propulsion Laboratory
400+ U.S. Cities
400+ U.S. Cities 'Guaranteed' To Be Lost To Sea Level Rise
Published: 2015/10/16
Channel: Secular Talk
Sea level rise - fact & fiction: John Englander at TEDxBocaRaton
Sea level rise - fact & fiction: John Englander at TEDxBocaRaton
Published: 2014/06/12
Channel: TEDx Talks
Largest Glacier East Antarctic may add to Sea Level Rise (Totten Glacier)
Largest Glacier East Antarctic may add to Sea Level Rise (Totten Glacier)
Published: 2017/11/02
Channel: Climate State
NASA
NASA's Earth Minute: Sea Level Rise
Published: 2015/08/26
Channel: NASA Climate Change
NASA: Rising sea levels more dangerous than thought
NASA: Rising sea levels more dangerous than thought
Published: 2015/08/27
Channel: CNN
Miami
Miami's Real Estate Market is Benefiting from Rising Sea Levels (HBO)
Published: 2017/03/14
Channel: VICE News
Two cities, two very different responses to rising sea levels
Two cities, two very different responses to rising sea levels
Published: 2015/07/02
Channel: PBS NewsHour
What is Sea Level Rise? | Ocean Wise
What is Sea Level Rise? | Ocean Wise
Published: 2017/11/17
Channel: Ocean Wise
THE OCEANS ARE RISING - The Facts About Sea-Level Change - Does Al Gore Own Ocean Front Property?
THE OCEANS ARE RISING - The Facts About Sea-Level Change - Does Al Gore Own Ocean Front Property?
Published: 2017/09/03
Channel: Oppenheimer Ranch Project
Below Sea Level   Official
Below Sea Level Official
Published: 2016/02/04
Channel: leeanna rinker education office
Sea level rise change predictions
Sea level rise change predictions
Published: 2016/08/16
Channel: Tech Insider
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WIKIPEDIA ARTICLE

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This marker indicating sea level is situated between Jerusalem and the Dead Sea.

Mean sea level (MSL) (often shortened to sea level) is an average level of the surface of one or more of Earth's oceans from which heights such as elevations may be measured. MSL is a type of vertical datum – a standardised geodetic reference point – that is used, for example, as a chart datum in cartography and marine navigation, or, in aviation, as the standard sea level at which atmospheric pressure is measured to calibrate altitude and, consequently, aircraft flight levels. A common and relatively straightforward mean sea-level standard is the midpoint between a mean low and mean high tide at a particular location.[1]

Sea levels can be affected by many factors and are known to have varied greatly over geological time scales. The careful measurement of variations in MSL can offer insights into ongoing climate change, and sea level rise has been widely quoted as evidence of ongoing global warming.[2]

The term above sea level generally refers to above mean sea level (AMSL).

Measurement[edit]

Sea level measurements from 23 long tide gauge records in geologically stable environments show a rise of around 200 millimetres (7.9 in) during the 20th century (2 mm/year).

Precise determination of a "mean sea level" is difficult to achieve because of the many factors that affect sea level.[3] Sea level varies quite a lot on several scales of time and space. This is because the sea is in constant motion, affected by the tides, wind, atmospheric pressure, local gravitational differences, temperature, salinity and so forth. The easiest way this may be calculated is by selecting a location and calculating the mean sea level at that point and use it as a datum. For example, a period of 19 years of hourly level observations may be averaged and used to determine the mean sea level at some measurement point.

To an operator of a tide gauge, MSL means the "still water level"—the level of the sea with motions such as wind waves averaged out—averaged over a period of time such that changes in sea level, e.g., due to the tides, also get averaged out. One measures the values of MSL in respect to the land. Hence a change in MSL can result from a real change in sea level, or from a change in the height of the land on which the tide gauge operates.

In the UK, the Ordnance Datum (the 0 metres height on UK maps) is the mean sea level measured at Newlyn in Cornwall between 1915 and 1921. Prior to 1921, the datum was MSL at the Victoria Dock, Liverpool.

In Hong Kong, "mPD" is a surveying term meaning "metres above Principal Datum" and refers to height of 1.230m below the average sea level.

In France, the Marégraphe in Marseilles measures continuously the sea level since 1883 and offers the longest collapsed data about the sea level. It is used for a part of continental Europe and main part of Africa as official sea level. Elsewhere in Europe vertical elevation references (European Vertical Reference System) are made to the Amsterdam Peil elevation, which dates back to the 1690s.

Satellite altimeters have been making precise measurements of sea level[4] since the launch of TOPEX/Poseidon in 1992. A joint mission of NASA and CNES, TOPEX/Poseidon was followed by Jason-1 in 2001 and the Ocean Surface Topography Mission on the Jason-2 satellite in 2008.

Height above mean sea level[edit]

Height above mean sea level (AMSL) is the elevation (on the ground) or altitude (in the air) of an object, relative to the average sea level datum. It is also used in aviation, where some heights are recorded and reported with respect to mean sea level (MSL) (contrast with flight level), and in the atmospheric sciences, and land surveying. An alternative is to base height measurements on an ellipsoid of the entire Earth, which is what systems such as GPS do. In aviation, the ellipsoid known as World Geodetic System 84 is increasingly used to define heights; however, differences up to 100 metres (328 feet) exist between this ellipsoid height and mean tidal height. The alternative is to use a geoid-based vertical datum such as NAVD88.

When referring to geographic features such as mountains on a topographic map, variations in elevation are shown by contour lines. The elevation of a mountain denotes the highest point or summit and is typically illustrated as a small circle on a topographic map with the AMSL height shown in metres, feet or both.

In the rare case that a location is below sea level, the elevation AMSL is negative. For one such case, see Amsterdam Airport Schiphol.

Difficulties in use[edit]

To extend this definition far from the sea means comparing the local height of the mean sea surface with a "level" reference surface, or geodetic datum, called the geoid. In a state of rest or absence of external forces, the mean sea level would coincide with this geoid surface, being an equipotential surface of the Earth's gravitational field. In reality, due to currents, air pressure variations, temperature and salinity variations, etc., this does not occur, not even as a long-term average. The location-dependent, but persistent in time, separation between mean sea level and the geoid is referred to as (stationary) ocean surface topography. It varies globally in a range of ± 2 m.

Historically, adjustments were made to sea-level measurements to take into account the effects of the 235 lunar month Metonic cycle and the 223-month eclipse cycle on the tides.[5]

Dry land[edit]

Sea level sign seen on cliff (circled in red) at Badwater Basin, Death Valley National Park

Several terms are used to describe the changing relationships between sea level and dry land. When the term "relative" is used, it means change relative to a fixed point in the sediment pile. The term "eustatic" refers to global changes in sea level relative to a fixed point, such as the centre of the earth, for example as a result of melting ice-caps. The term "steric" refers to global changes in sea level due to thermal expansion and salinity variations. The term "isostatic" refers to changes in the level of the land relative to a fixed point in the earth, possibly due to thermal buoyancy or tectonic effects; it implies no change in the volume of water in the oceans. The melting of glaciers at the end of ice ages is one example of eustatic sea level rise. The subsidence of land due to the withdrawal of groundwater is an isostatic cause of relative sea level rise. Paleoclimatologists can track sea level by examining the rocks deposited along coasts that are very tectonically stable, like the east coast of North America. Areas like volcanic islands are experiencing relative sea level rise as a result of isostatic cooling of the rock which causes the land to sink.

On other planets that lack a liquid ocean, planetologists can calculate a "mean altitude" by averaging the heights of all points on the surface. This altitude, sometimes referred to as a "sea level", serves equivalently as a reference for the height of planetary features.

Change[edit]

Local and eustatic[edit]

Water cycles between ocean, atmosphere and glaciers

Local mean sea level (LMSL) is defined as the height of the sea with respect to a land benchmark, averaged over a period of time (such as a month or a year) long enough that fluctuations caused by waves and tides are smoothed out. One must adjust perceived changes in LMSL to account for vertical movements of the land, which can be of the same order (mm/yr) as sea level changes. Some land movements occur because of isostatic adjustment of the mantle to the melting of ice sheets at the end of the last ice age. The weight of the ice sheet depresses the underlying land, and when the ice melts away the land slowly rebounds. Changes in ground-based ice volume also affect local and regional sea levels by the readjustment of the geoid and true polar wander. Atmospheric pressure, ocean currents and local ocean temperature changes can affect LMSL as well.

Eustatic change (as opposed to local change) results in an alteration to the global sea levels due to changes in either the volume of water in the world's oceans or net changes in the volume of the ocean basins.[6]

Short term and periodic changes[edit]

Melting glaciers can cause a change in sea level

There are many factors which can produce short-term (a few minutes to 14 months) changes in sea level. Two major mechanisms are causing sea level to rise. First, shrinking land ice, such as mountain glaciers and polar ice sheets, is releasing water into the oceans. Second, as ocean temperatures rise, the warmer water expands.[7]

Periodic sea level changes
Diurnal and semidiurnal astronomical tides 12–24 h P 0.2–10+ m
Long-period tides    
Rotational variations (Chandler wobble) 14-month P
Meteorological and oceanographic fluctuations
Atmospheric pressure Hours to months −0.7 to 1.3 m
Winds (storm surges) 1–5 days Up to 5 m
Evaporation and precipitation (may also follow long-term pattern) Days to weeks  
Ocean surface topography (changes in water density and currents) Days to weeks Up to 1 m
El Niño/southern oscillation 6 mo every 5–10 yr Up to 0.6 m
Seasonal variations
Seasonal water balance among oceans (Atlantic, Pacific, Indian)    
Seasonal variations in slope of water surface    
River runoff/floods 2 months 1 m
Seasonal water density changes (temperature and salinity) 6 months 0.2 m
Seiches
Seiches (standing waves) Minutes to hours Up to 2 m
Earthquakes
Tsunamis (generate catastrophic long-period waves) Hours Up to 10 m
Abrupt change in land level Minutes Up to 10 m

Recent changes[edit]

For at least the last 100 years, sea level has been rising at an average rate of about 1.8 mm (0.1 in) per year.[8] Most of this rise can be attributed to the increase in temperature of the sea and the resulting slight thermal expansion of the upper 500 metres (1,640 feet) of sea water. Additional contributions, as much as one-quarter of the total, come from water sources on land, such as melting snow and glaciers and extraction of groundwater for irrigation and other agricultural and human needs.[9]

Aviation[edit]

Pilots can estimate height above sea level with an altimeter set to a defined barometric pressure. Generally, the pressure used to set the altimeter is the barometric pressure that would exist at MSL in the region being flown over. This pressure is referred to as either QNH or "altimeter" and is transmitted to the pilot by radio from air traffic control (ATC) or an automatic terminal information service (ATIS). Since the terrain elevation is also referenced to MSL, the pilot can estimate height above ground by subtracting the terrain altitude from the altimeter reading. Aviation charts are divided into boxes and the maximum terrain altitude from MSL in each box is clearly indicated. Once above the transition altitude, the altimeter is set to the international standard atmosphere (ISA) pressure at MSL which is 1013.25 hPa or 29.92 inHg.[10]

See also[edit]

References[edit]

  1. ^ What is "Mean Sea Level"? (Proudman Oceanographic Laboratory).
  2. ^ Solomon et al., Technical Summary, Section 3.4 Consistency Among Observations in IPCC AR4 WG1 2007; Hegerl et al., Executive summary, Section 1.3: Consistency of changes in physical and biological systems with warming in IPCC AR4 SYR 2007.
  3. ^ US National Research Council, Bulletin of the National Research Council 1932 page 270
  4. ^ "Evaluating models of sea state bias in satellite altimetry". Journal of Geophysical Research. NASA. 99 (C6): 12581. 1994. Bibcode:1994JGR....9912581G. doi:10.1029/94JC00478. Roman Glazman Greysukh, A. M., Zlotnicki, V.
  5. ^ "Stonehenge pt 3". www.celticnz.co.nz. Retrieved 2017-02-18. 
  6. ^ "Eustatic sea level". Oilfield Glossary. Schlumberger Limited. Retrieved 10 June 2011. 
  7. ^ "Global Warming Effects on Sea Level". www.climatehotmap.org. Retrieved 2016-12-02. 
  8. ^ Bruce C. Douglas (1997). "Global Sea Rise: A Redetermination". Surveys in Geophysics. 18 (2/3): 279–292. Bibcode:1997SGeo...18..279D. doi:10.1023/A:1006544227856. 
  9. ^ Bindoff, N.L.; Willebrand, J.; Artale, V.; Cazenave, A.; Gregory, J.; Gulev, S.; Hanawa, K.; Le Quéré, C.; Levitus, S.; Nojiri, Y.; Shum, C.K.; Talley, L.D.; Unnikrishnan, A. (2007). "Observations: Oceanic Climate Change and Sea Level" (PDF). In Solomon, S.; Qin, D.; Manning, M.; Chen, Z.; Marquis, M.; Averyt, K.B.; Tignor, M.; Miller, H.L. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. 
  10. ^ US Federal Aviation Administration, Code of Federal Regulations Sec. 91.121

External links[edit]

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