Watch this out: Sea Level Change during 1993-2007

Hmmmm. Interesting. I’m convinced. I am going up the 3000 foot elevation of Mt. McKinley and camp out. Will someone awaken me when the water gets to the 2000 foot mark.

Nobody wants to put a thermostat on the Sun, We could put a thermostat on the Sun and set it to -10 degrees and create a new ice age, that would freeze Hell over. That would have a lot of benefits, the chicken littles who are running around saying the sky is falling, couldn’t get to hell.

John, your comment is entirely emotional, yet the map reported by Dr Ghulam from NASA is observational. You don’t need to hide on a mountain somewhere, but nations of the world do need to start to plan for significant sea level rise. This has happened many times in Earth history- just look at the limestones in St Louis, and understand they were formed when the sea covered much of the central USA.

You can read the text below, extracted from my book on The Coast () for some background on sea level rise.

Kusky, T.M., 2008, The Coast , Facts on File, Hazardous Earth Set.
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Pub. Date: coming soon!
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Sea level has risen and fallen by hundreds of feet many times in Earth history, and it is presently slowly rising at about one foot per century, but may be accelerating from the effects of global warming. The causes of sea level rise and fall are complex and operate on vastly different time scales. These include growth and melting of glaciers, changes in the volume of the mid ocean ridges, thermal expansion of water from global warming, and other complex interactions of the distribution of the continental landmass in mountains and plains during periods of faulting, mountain building, and basin forming activity. It is important to separate the local effects of the rising and sinking of the land known as relative sea level changes, from global changes in sea level that are referred to as eustatic events.
The fastest changes in sea level are caused by instantaneous geologic catastrophes such as meteorite impacts into the ocean, but luckily these types of events do not happen often. Seasonal changes can blow or move water to greater heights on one side of a basin, and lower on another side, cause water to expand and contract with changes in temperature causing small changes in sea level. Climate changes can cause glaciers and ice caps to melt and reform causing sea levels to rise and fall on time scales of hundreds to thousands of years. Longer term climate variations related to variations in the orbit of the Earth around the Sun can lengthen the time scale of sea level changes related to climate change to hundreds of thousands of years for individual cycles. Plate tectonics also influences sea level changes, but on much longer time scales than climate variations. If the process of sea floor spreading and submarine volcanism becomes accelerated in any geologic time period, the volume of material that makes up the mid-ocean ridge system will be larger, and this extra volume of elevated sea floor will displace an equal amount of sea water and raise sea levels. This process typically operates with time variations on the order of tens of millions of years. An even longer-term variation in sea levels is caused by the motions and collisions of continents in supercontinent cycles. When continents collide, large amounts of continental material are uplifted above sea level, effectively taking this material out of the oceans, making the ocean basins bigger and lowering sea levels. When continents rift apart, the opposite happens, more material is added to the ocean basins, and sea levels rise on the continents. These slow tectonic variations can change sea levels on time scales of tens to hundreds of millions of years.
Rising sea levels cause the shoreline to move landward, whereas a sea level fall causes the shoreline to move ocean-ward. With the present sea level rise, coastal cliffs are eroding, barrier islands are migrating (or being submerged if they were heavily protected from erosion), beaches are moving landward, and estuaries are being flooded by the sea. At some point in the not too distant future, low-lying coastal cities will be flooded under several feet of water, and eventually the water could be hundreds of feet deep. Cities including New Orleans, New York, Washington, Houston, London, Shanghai, Tokyo, and Cairo will be inundated, and the world’s nations need to begin to plan how to handle this inevitable geologic hazard.
About seventy percent of the world’s sandy beaches are being eroded. The reasons for this erosion include rising sea levels, increased storminess, decrease in sediment transport to beaches from the damming of rivers, and perhaps shifts in global climate belts. Construction of sea walls to reduce erosion of coastal cliffs also causes a decreased supply of sand to replenish the beach, so also increases beach retreat. Pumping of ground water from coastal aquifers also results in coastal erosion, because pumping causes the surface to subside, leading to a relative sea level rise.
When sea level rises beaches try to maintain their equilibrium profile, and move each beach element landward. A sea level rise of 1 inch is generally equated with a landward shift of beach elements of more than four feet. Most sandy beaches world-wide are retreating landward at rates of 20 inches – 3 feet per year, consistent with sea level rise of an inch every ten years.

Causes of Changing Sea Levels
The average position of the median sea level may appear to rise or fall with respect to the land surface to an observer on a shoreline, and this is called relative sea level rise or fall. However, it is difficult for the observer on the local shoreline to know if the height of the water is changing, or if the height of the continent is rising or falling. In many places plate tectonics causes areas of the crust to rise slowly out of the sea, or sink gradually downwards below sea level, while the water level is actually staying at the same height. The weight of glaciers or sedimentary deposits can also cause local shorelines to sink, or to rise if the weight if removed. Therefore geologists need a way to differentiate between local changes in relative sea level, and true global sea level changes. This is a difficult problem and is best done by obtaining accurate ages on the time of sea level rise and fall, and correlating these changes with other places around the world. This has been done through many years of study, and now there is a fairly well established curve of global sea level heights going back in geological time. Local or apparent changes in sea level are called apparent sea level, whereas global changes in the height of sea level are called eustatic sea level changes.

Short-Term Climate Changes
Minor changes in sea level of up to about a foot (30 cm) happen in many places in yearly seasonal cycles. Many of these are caused by changes in the wind patterns, as the sun alternately heats different belts of the ocean, and the winds blow water from one side of the ocean to the other. When water is heated in the summer months it also expands slightly, accounting for sea level changes of an inch (2.5 cm) or so. Thermal expansion associated with global warming may raise sea levels about 12 inches (30 cm) by 2050, and 20 inches (50 cm) by 2100. Seasonal development of regional high and low pressure systems that characterize some areas also change sea levels on short time scales. High pressure areas, such as the Bermuda high that often develops over the central Atlantic in the summer lowers local sea levels because the high atmospheric pressure (weight) pushes sea levels lower than in other times.
Other climate phenomena change sea levels more dramatically. For instance, the irregular El Niño event where changes in atmospheric heating cause a warm current to move from the western Pacific to the eastern Pacific can raise sea levels off the coast of Peru (and sometimes as far as California) by up to 2 feet (60 cm), enough to cause enhanced erosion, landslides, and cause considerable damage to the coastal environment in South America. The El Niño phenomenon is described in the following sidebar.

Long-Term Climate Effects
Many changes in the Earth’s climate that control relative sea level are caused by variations in the amount of incoming solar energy, which in turn are caused by systematic changes in the way the Earth orbits the Sun. These systematic changes in the amount of incoming solar radiation caused by variations in Earth’s orbital parameters are known as Milankovitch Cycles, after the Serbian mathematician Milutin Milankovitch who first clearly described these cycles. These changes can affect many Earth systems, causing glaciations, global warming, dramatic sea level changes, and changes in the patterns of climate and sedimentation.
Astronomical effects that influence the amount of incoming solar radiation include minor variations in the path of the Earth in its orbit around the Sun, and the inclination or tilt of its axis causing variations in the amount of solar energy reaching the top of the atmosphere. These variations are thought to be responsible for the advance and retreat of the Northern and Southern Hemisphere ice sheets in the past few million years, and the associated huge sea level changes. In the past two million years alone, the Earth has seen the ice sheets advance and retreat approximately 20 times. The climate record as deduced from ice-core records from Greenland and isotopic tracer studies from deep ocean, lake, and cave sediments suggest that the ice builds up gradually over periods of about 100,000 years, then retreats rapidly over a period of decades to a few thousand years. These patterns result from the cumulative effects of different astronomical phenomena.
Several movements are involved in changing the amount of incoming solar radiation. The Earth rotates around the Sun following an elliptical orbit, and the shape of this elliptical orbit is known as its eccentricity. The eccentricity changes cyclically with time with a period of 100,000 years, alternately bringing the Earth closer to and farther from the Sun in summer and winter. This 100,000-year cycle is about the same as the general pattern of glaciers advancing and retreating every 100,000 years in the past two million years, suggesting that this is the main cause of variations within the present day ice age.
The Earth’s axis is presently tilting by 23.5°N/S away from the orbital plane, and the tilt varies between 21.5°N/S and 24.5°N/S. The tilt changes by plus or minus 1.5°N/S from a tilt of 23°N/S every 41,000 years. When the tilt is greater, there is greater seasonal variation in temperature.
Wobble of the rotation axis describes a motion much like a top rapidly spinning and rotating with a wobbling motion, such that the direction of tilt toward or away from the Sun changes, even though the tilt amount stays the same. This wobbling phenomenon is known as precession of the equinoxes, and it has the effect of placing different hemispheres closest to the Sun in different seasons. Presently the precession of the equinoxes is such that in the Earth is closest to the Sun during the Northern Hemisphere winter. This precession changes with a double cycle, with periodicities of 23,000 years and 19,000 years.
Because each of these astronomical factors act on different time scales their effects are combined in a more complex cycle. Each of these factors interact in a complicated way, known as Milankovitch cycles, after a Serbian (Milutin Milankovitch) who first analyzed them in the 1920s. Using the power of understanding these cycles, it is possible make predictions of where the Earth’s climate is heading, whether into a warming or cooling period, and whether sea levels will rise or fall, or if some regions may experience desertification, glaciation, floods, or droughts.
Present data shows that temperatures were about 2-3 degrees C cooler at the height of the glacial advances 12,000 years ago than they are today, and that temperatures may warm an additional 3-4 degrees C by the year 2100. If this warming occurs as predicted, then large amounts of the glacial ice on Antarctica and Greenland will melt, raising sea levels dramatically. Many scientists predict sea levels will rise at least a foot (0.3 m) by 2100, others predict more. It is likely that the sea level rise will continue past the year 2100, with at least 16 feet (5 m) over the next few centuries. When this happens, most of the world’s large port cities will be partly to largely underwater and world civilizations will have needed to find ways to move huge populations to higher ground. There is a current debate about how much humans are contributing to global warming and the consequent sea level rise. Most data suggest that human induced warming is about or slightly less than one degree over the past 100 years, but that warming is superimposed on the longer-term cycles described above. What is not known is how these long-term natural cycles may change. Warming may continue, or the natural cycles may reverse, or other sudden catastrophic cooling events may occur, such as a volcanic eruption on the scale of Tambora in Indonesia in 1815 that lowered global temperatures by about 1 degree.

Changes in Water / Ice Volume
Global sea levels are currently rising, partly as a result of the melting of the Greenland and Antarctica ice sheets. We are presently in an interglacial stage of an ice age, and sea levels have risen nearly 400 feet (120 m) since the last glacial maximum 20,000 years ago, and about 6 inches (15 cm) in the past 100 years. The rate of sea level rise seems to be accelerating, and may presently be as much as an inch (2.5 cm) every 10 years. If all the ice on both ice sheets were to melt, global sea levels would rise by another 230 feet (70 m), inundating most of the world’s major cities, and submerging large parts of the continents under shallow seas. The coastal regions of the world are densely populated, and are experiencing rapid population growth. Approximately 100 million people presently live within 3.2 feet (1 m) of the present day sea level. If sea level were to rise rapidly and significantly, the world would experience an economic and social disaster of a magnitude not yet experienced by the civilized world. Many areas would become permanently flooded or subject to inundation by storms, beach erosion would be accelerated, and water tables would rise.
The Greenland and Antarctic ice sheets have some significant differences that cause them to respond differently to changes in air and water temperatures. The Antarctic ice sheet is about ten times as large as the Greenland ice sheet, and since it sits on the South Pole, Antarctica dominates its own climate. The surrounding ocean is cold even during summer, and much of Antarctica is a cold desert with low precipitation rates and high evaporation potential. Most melt-water in Antarctica seeps into underlying snow and simply refreezes, with little running off into the sea. Antarctica hosts several large ice shelves fed by glaciers moving at rates of up to a thousand feet per year. Most ice loss in Antarctica is accomplished through calving and basal melting of the ice shelves, at rates of 10-15 inches (25-38 cm) per year.
In contrast, Greenland’s climate is influenced by warm North Atlantic currents, and by its proximity to other landmasses. Climate data measured from ice cores taken from the top of the Greenland ice cap show that temperatures have varied significantly in cycles of years to decades. Greenland also experiences significant summer melting, abundant snowfall, has few ice shelves, and its glaciers move quickly at rates of up to miles per year. These fast-moving glaciers are able to drain a large amount of ice from Greenland in relatively short amounts of time.
The Greenland ice sheet is thinning rapidly along its edges, loosing an average of 15-20 feet (4.5-6 m) in the past decade. In addition, tidewater glaciers and the small ice shelves in Greenland are melting an order of magnitude faster than the Antarctic ice sheets, with rates of melting between 25-65 feet (7-20 m) per year, a rate that is apparently increasing. About half of the ice lost from Greenland is through surface melting that runs off into the sea. The other half of ice loss is through calving of outlet glaciers and melting along the tidewater glaciers and ice shelf bases.
These differences between the Greenland and Antarctic ice sheets lead them to play different roles in global sea level rise. Greenland contributes more to the rapid short-term fluctuations in sea level, responding to short-term changes in climate. In contrast, most of the world’s water available for raising sea level is locked up in the slowly-changing Antarctic ice sheet. Antarctica contributes more to the gradual, long-term sea level rise.

Plate Tectonics, Supercontinent Cycles, and Sea Level
Movement of the tectonic plates on Earth causes the semi-regular grouping of the planet’s landmasses into a single or several large continents that remain stable for a long period of time, then disperse, and eventually come back together as new amalgamated landmasses with a different distribution. This cycle is known as the supercontinent cycle. At several times in Earth history, the continents have joined together forming one large supercontinent, with the last supercontinent Pangea (meaning all land) breaking up approximately 160 million years ago. This process of supercontinent formation and dispersal and re-amalgamation seems to be grossly cyclic, perhaps reflecting mantle convection patterns, but also influencing sea level, climate, and biological evolution.
The basic idea of the supercontinent cycle is that continents drift about on the surface until they all collide, stay together, and come to rest relative to the mantle. The continents are only one-half as efficient at conducting heat as oceans, so after the continents are joined together, heat accumulates at their base, causing doming and breakup of the continent. For small continents, heat can flow sideways and not heat up the base of the plate, but for large continents the lateral distance is too great for the heat to be transported sideways. The heat rising from within the Earth therefore breaks up the supercontinent after a heating period of several tens or hundreds of millions of years, the heat then disperses and is transferred to the ocean/atmosphere system, and continents move away until they come back together forming a new supercontinent.
The supercontinent cycle has many effects that greatly affect other Earth systems. First, the break-up of continents causes sudden bursts of heat release, associated with periods of increased, intense magmatism. It also explains some of the large-scale sea level changes, episodes of rapid and widespread orogenesis, episodes of glaciation, and many of the changes in life on Earth.
Sea level has changed by hundreds of meters above and below current levels at many times in Earth history. In fact, sea level is constantly changing in response to a number of different variables, many of them related to plate tectonics. The diversity of fauna on the globe is closely related to sea levels, with greater diversity during sea level high stands, and lower diversity during sea level lows. For instance, sea level was 1,970 feet (600 m) higher than now during the Ordovician Period, and the sea level high stand was associated with a biotic explosion. Sea levels reached a low stand at the end of the Permian Period, and this low was associated with a great mass extinction. Sea levels were high again in the Cretaceous.

Changes in Mid-Ocean Ridge Volume
Sea levels may change at different rates and amounts in response to changes in several other Earth systems. Local tectonic effects may mimic sea level changes through regional subsidence or uplift, and these effects must be taken into account and filtered out when trying to deduce ancient, global (eustatic) sea level changes. The global volume of the mid-ocean ridges can change dramatically, either by increasing the total length of ridges, or changing the rate of seafloor spreading. The total length of ridges typically increases during continental break-up, since continents are being rifted apart and some continental rifts can evolve into mid-ocean ridges. Additionally, if seafloor spreading rates are increased, the amount of young, topographically elevated ridges is increased relative to the slower, older topographically lower ridges that occupy a smaller volume. If the volume of the ridges increases by either mechanism, then a volume of water equal to the increased ridge volume is displaced and sea level rises, inundating the continents. Changes in ridge volume are able to change sea levels positively or negatively by about 985 feet (300 m) from present values, at rates of about 0.4 inches (1 cm) every 1,000 years.

Changes in Continental Area
Continent-continent collisions can lower sea levels by reducing the area of the continents. When continents collide, mountains and plateaus are uplifted, and the amount of material that is taken from below sea level to higher elevations no longer displaces seawater, causing sea levels to drop. The on-going India-Asia collision has caused sea levels to drop by 33 feet (10 m).
Other things, such as mid-plate volcanism, can also change sea levels. The Hawaiian Islands are hot-spot style mid-plate volcanoes that have been erupted onto the seafloor, displacing an amount of water equal to their volume. Although this effect is not large at present, at some periods in Earth history there were many more hot spots (such as in the Cretaceous Period), and the effect may have been larger.
The effects of the supercontinent cycle on sea level may be summarized as follows. Continent assembly favors regression, whereas continental fragmentation and dispersal favors transgression.

Subsidence of Coastal Environments
Natural geologic subsidence is the sinking of land relative to sea level or some other uniform surface. Subsidence may be a gradual barely perceptible process, or it may occur as a catastrophic collapse of the surface. Subsidence occurs naturally along some coastlines, and in areas where ground water has dissolved cave systems in rocks such as limestone. It may occur on a regional scale, affecting an entire coastline, or it may be local in scale, such as when a sinkhole suddenly opens and collapses in the middle of a neighborhood. Other subsidence events reflect the interaction of humans with the environment, and include ground surface subsidence as a result of mining excavations, ground water and petroleum extraction, and several other processes. Compaction is a related phenomenon, where the pore spaces of a material are gradually reduced, condensing the material and causing the surface to subside. Subsidence and compaction do not typically result in death or even injury, but they do cost Americans alone tens of millions of dollars per year. The main hazard of subsidence and compaction is damage to property. Subsidence can also result in more sinister long-term effects. Many coastal cities are experiencing slow subsidence so that surfaces once above sea level sink to many feet below sea level over hundreds of years. This phenomenon results in putting cities including Venice, New Orleans, and many others below sea level. In the case of New Orleans the subsidence has resulted in the surrounding wetlands to have sunk below sea level, placing the city—now partly below sea level—much closer to the coast than when it was built. Subsidence has therefore contributed greatly to the increased damage to the city from recent hurricanes, and continues to place the city at ever-increasing risk.
Subsidence and compaction directly affect millions of people. Residents of New Orleans live below sea level and are constantly struggling with the consequences of living on a slowly subsiding delta. Coastal residents in the Netherlands have constructed massive dike systems to try to keep the North Sea out of their slowly subsiding land. The city of Venice, Italy has dealt with subsidence in a uniquely charming way, drawing tourists from around the world. Millions of people live below the high-tide level in Tokyo. The coastline of Texas along the Gulf of Mexico is slowly subsiding, placing residents of Baytown and other Houston suburbs close to sea level and in danger of hurricane induced storm surges and other more frequent flooding events. In Florida, sinkholes have episodically opened up swallowing homes and businesses, particularly during times of drought.
The driving force of subsidence is gravity, with the style and amount of subsidence controlled by the physical properties of the soil, regolith and bedrock underlying the area that is subsiding. Subsidence does not require a transporting medium, but it is aided by other processes such as ground water dissolution that can remove mineral material and carry it away in solution, creating underground caverns that are prone to collapse.
Natural subsidence has many causes, all of which may operate in the coastal environment. Dissolution of limestone by underground streams and water systems is one of the most common, creating large open spaces that collapse under the influence of gravity. Ground water dissolution results in the formation of sinkholes, large, generally circular depressions caused by collapse of the surface into underground open spaces.
Earthquakes may raise or lower the land suddenly, as in the case of the 1964 Alaskan earthquake where tens of thousands of square miles suddenly sank or rose three to five feet, causing massive disruption to coastal communities and ecosystems. Earthquake – induced ground shaking can also cause liquefaction and compaction of unconsolidated surface sediments, also leading to subsidence. Regional lowering of the land surface by liquefaction and compaction was widespread in the magnitude 6.9 Kobe Japan earthquake of 1995.
Volcanic activity can cause subsidence, as when underground magma chambers empty out during an eruption. In this case, subsidence is often the lesser of many hazards that local residents need to fear. Subsidence may also occur on lava flows, when lava empties out of tubes or underground chambers. The eruption of Krakatoa in Indonesia in 1883 was associated with rapid collapse of the coastal caldera, and the sea rushed into the exposed magma chamber, generating a huge tsunami that killed 36,000 people in nearby coastal villages.
Some natural subsidence on the regional scale is associated with continental scale tectonic processes. The weight of sediments deposited along continental shelves can cause the entire continental margin to sink causing coastal subsidence and a landward migration of the shoreline. Tectonic processes associated with extension, continental rifting, strike slip faulting, and even collision can cause local or regional subsidence, sometimes at rates of several inches (7-10 cm) per year.
Human-Induced Subsidence
Several types of human activity can result in the formation of sinkholes or cause other surface subsidence phenomena. Withdrawals of fluids from underground aquifers, depletion of the source of replenishment to these aquifers, and collapse of underground mines can all cause surface subsidence. In addition, vibrations from drilling, construction or blasting can trigger collapse events, and the extra load of buildings over unknown deep collapse structures can cause them to propagate to the surface, forming a sinkhole. These processes reflect geologic hazards caused by human’s interaction with the natural geologic environment.

Ground Water Extraction
The extraction of ground water, oil, gas, or other fluids from underground reservoirs can cause significant subsidence of the land’s surface. In some cases the removal of underground water is natural. During times of severe drought, soil moisture may decrease dramatically and drought-resistant plants with deep root systems can draw water from great depths, reaching a hundred feet or more (many tens of meters) in some cases. In most cases, however, subsidence caused by deep fluid extraction is caused by human activity.
This deep subsidence mechanism operates because the fluids that are extracted served to help support the weight of the overlying regolith. The weight of the overlying material places the fluids under significant pressure, known as hydrostatic pressure, that keeps the pressure between individual grains in the regolith at a minimum. This in turns helps prevent the grains from becoming closely packed or compacted. If the fluids are removed, the pressure between individual grains increases and the grains become more closely packed and compacted, occupying less space than before the fluid was extracted. This can cause the surface to subside. A small amount of this subsidence may be temporary, or recoverable, but generally once surface subsidence related to fluid extraction occurs, it is non-recoverable. When this process occurs on a regional scale the effect can be subsidence of a relatively large area. Subsidence associated with underground fluid extraction is usually gradual but still costs millions of dollars in damage every year in the United States.
The amount of surface subsidence is related to the amount of fluid withdrawn from the ground and also to the compressibility of the layer that the fluid has been removed from. If water is removed from cracks in a solid igneous, metamorphic, or sedimentary rock, then the strength of the rock around the cracks will be great enough to support the overlying material and no surface subsidence is likely to occur. In contrast, if fluids are removed from a compressible layer such as sand, shale or clay, then significant surface subsidence may result from fluid extraction. Clay and shale have a greater porosity and compressibility than sand, so extraction of water from clay rich sediments results in greater subsidence than the same amount of fluid withdrawn from a sandy layer.
One of the most common causes of fluid extraction related subsidence is the over-pumping of ground water from aquifers. If many wells are pumping water from the same aquifer the cones of depression surrounding each well begin to merge, lowering the regional ground water level. Lowering of the ground water table can lead to gradual, irreversible subsidence.
Surface subsidence associated with ground water extraction is a serious problem in many parts of the southwestern United States, and in coastal cities such as New Orleans. Many cities such as Tucson, Phoenix, Los Angeles, Salt Lake City, Las Vegas, and San Diego rely heavily on ground water pumped from compressible layers in underground aquifers.
The San Joaquin Valley of California offers a dramatic example of the effects of ground water extraction. Extraction of ground water for irrigation over a period of fifty years has resulted in nearly thirty feet (9 m) of surface subsidence. Parts of the Tucson Basin in Arizona are presently subsiding at an accelerating rate, and many investigators fear that the increasing rate of subsidence reflects a transition from temporary recoverable subsidence, to a permanent compaction of the water-bearing layers at depth.
The world’s most-famous subsiding city is Venice, Italy. Venice is sinking at a rate of about one foot per century, and much of the city is below sea level or just above sea level, and prone to floods from storm surges and astronomical high tides in the Adriatic Sea. The city has subsided more than ten feet since it was founded near sea level. These aqua altas (meaning high-water in Italian) flood streets as far as the famous Piazza San Marco. Venice has been subsiding for a combination of reasons, including compaction of the coastal mud that the city was built on. One of the main causes of the sinking of Venice has been ground water extraction. Nearly 20,000 ground water wells pumped water from compressible sediment beneath the city, with the result being the city sunk into the empty space created by the withdrawal of water. The Italian government has now built an aqueduct system to bring drinking water to residents, and has closed most of the 20,000 wells. This action has slowed the subsidence of the city, but it is still sinking, and this action may be too little too late to spare Venice from the future effects of storm surges and astronomical high tides.
Mexico City is also plagued with subsidence problems caused by ground water extraction. Mexico City is built on a several thousand foot thick sequence of sedimentary and volcanic rocks, including a large dried lake bed on the surface. Most of the ground water is extracted from the upper 200 feet of these sediments. Parts of Mexico City have subsided dramatically, whereas others have not. The northeast part of the city has subsided about 20 feet (6 m). Many of the subsidence patterns in Mexico City can be related to the underlying geology. In places like the northeast part of the city that are underlain by loose compressible sediments, the subsidence has been large. In other places underlain by volcanic rocks, the subsidence has been minor.
The extraction of oil, natural gas, and other fluids from the Earth also may result in surface subsidence. In the United States, subsidence related to petroleum extraction is a large problem in Texas, Louisiana, and parts of California. One of the worst-cases of oil field subsidence is that of Long Beach, California, where the ground surface has subsided 30 feet (9 m) in response to extraction of underground oil. There are approximately 2,000 oil wells in Long Beach, pumping oil from beneath the city. Much of Long Beach’s coastal area subsided below sea level, forcing the City to construct a series of dikes to keep the water out. When the subsidence problem was recognized and understood, the city began a program of re-injecting water into the oil field to replace the extracted fluids and to prevent further subsidence. This re-injection program was initiated in 1958, and since then the subsidence has stopped, but the land surface can not be pumped up again to its former levels.
Pumping of oil from an oil field west of Marina del Ray along the Newport-Ingelwood fault resulted in subsidence beneath the Baldwin Hills Dam and Reservoir, leading to the dam’s catastrophic failure on December 14, 1963. Oil extraction from the Inglewood Oil field resulted in subsidence related slip on a fault beneath the dam and reservoir, which was enough to initiate a crack in the dam foundation. The crack was quickly expanded by pressure from the water in the reservoir, which led to the dam’s catastrophic failure at 3:38 P.M. on December 14th, 1963. Sixty five million gallons of water were suddenly released, destroying dozens of homes, killing five people, and causing 12 million dollars in damage.

Compaction-Related Subsidence on Deltas and Passive Margins
Subsidence related to compaction and removal of water from sediments deposited on continental margin deltas, in lake beds, and in other wetlands poses a serious problem to residents trying to cope with the hazards of life at sea level in coastal environments. Deltas are especially prone to subsidence because the sediments that are deposited on deltas are very water-rich, and the weight of overlying new sediments compacts existing material, forcing the water out of pore spaces. Deltas are also constructed along continental shelves that are prone to regional-scale tectonic subsidence, and are subject to additional subsidence forced by the weight of the sedimentary burden deposited on the entire margin. Continental margin deltas are rarely more than a few feet above sea level, so are prone to the effects of tides, storm surges, river floods, and other coastal disasters. Any decrease in the sediment supply to keep the land at sea level has serious ramifications, subjecting the area to subsidence below sea level.
Some of the world’s thickest sedimentary deposits are formed in deltas on the continental shelves, and these are of considerable economic importance because they also host the world’s largest petroleum reserves. The continental shelves are divided into many different sedimentary environments. Many of the sediments transported by rivers are deposited in estuaries, which are semi-enclosed bodies of water near the coast in which fresh water and seawater mix. Near shore sediments deposited in estuaries include thick layers of mud, sand, and silt. Many estuaries are slowly subsiding, and they get filled with thick sedimentary deposits. Deltas are formed where streams and rivers meet the ocean, and drop their loads because of the reduced flow velocity. Deltas are complex sedimentary systems, with coarse stream channels, fine-grained inter-channel sediments, and a gradation seaward to deep - water deposits of silt and mud.
All of the sediments deposited in the coastal environments tend to be water rich when deposited, and thus subject to water loss and compaction. Subsidence poses the greatest hazard on deltas, since these sediments tend to be thickest of all deposited on continental shelves. They are typically fine-grained mud and shale that suffer the greatest water loss and compaction. Unfortunately, deltas are also the sites of some of the world’s largest cities, since they offer great river ports. New Orleans, Shanghai, and many other major cities have been built on delta deposits, and have subsided ten or more feet (several m) since they were first built. Many other cities built on these very compactable shelf sediments are also experiencing dangerous amounts of subsidence. What are the consequences of this subsidence for people who live in these cities, and how will they be affected by increased rates of subsidence caused by damming of rivers that trap replenishing sediments upstream? How will these cities fare with current sea level rise, estimated to be occurring currently at a rate of an inch (2.5 cm) every ten years, with more than 6 inches (15 cm) of rise in the past century? Whatever the response, it will be costly. Some urban and government planners estimate that protecting the populace from sea level rise on subsiding coasts will be the costliest endeavor ever undertaken by humans.

Subsidence Statistics for the 10 Worst-Case Coastal Cities.

City Maximum Subsidence Area Affected Tectonic Environment
Feet (m) square miles (km2)

Los Angeles
(Long Beach) 29.5 (9.0) 20 (50) Oilfield subsidence
Tokyo 14.8 (4.5) 1,170 (3,000) Delta
San Jose 12.8 (3.9) 312 (800) Delta
Osaka 9.8 (3.0) 195 (500) Delta
Houston 9 (2.7) 4,720 (12,100) Oilfield and coastal marsh
Shanghai 8.6 (2.63) 47 (121) Delta
Niigata 8.2 (2.5) 3,237 (8,300) Delta
Nagoya 7.8 (2.37) 507 (1,300) Delta
New Orleans 6.6 (2.0) 68 (175) Delta
Taipei 6.2 (1.9) 51 (130)

What is the fate of these and other coastal cities that are plagued with natural and human-induced subsidence in a time of global sea level rise? The natural subsidence in these cities is accelerated by human activities. First of all, construction of tall heavy buildings on loose, compactable water-rich sediments forces water out of the pore spaces of the sediment underlying each building, causing that building to subside. The weight of cities has a cumulative effect, and big cities built on deltas and other compactable sediment cause a regional flow of water out of underlying sediments, leading to subsidence of the city as a whole.
New Orleans has one of the worst subsidence problems of coastal cities in the United States. Its rate and total amount of subsidence are not the highest but since nearly half of the city is at or below sea level, any additional subsidence will put the city dangerously far below sea level. Already, the Mississippi River is higher than downtown streets, and ships float by at the second story level of buildings. Dikes keep the river at bay, and usually keep storm surges from inundating the city. However, the catastrophes of Hurricanes Katrina and Rita in 2005, of Hurricane Camile in 1969, and many before this, shows that the levees can not be trusted to hold. Additional subsidence will make these measures unpractical, and lead to greater disasters than Hurricane Katrina. New Orleans, Houston, and other coastal cities have been accelerating their own sinking by withdrawing ground water and oil from compactable sediments beneath the cities. They are literally pulling the ground out from under their own feet.
The combined effects of natural and human-induced subsidence, plus global sea level rise, has resulted in increased urban flooding of many cities, and greater destruction during storms. Storm barriers have been built in some cases, but this is only the beginning. Thousands of miles of barriers will need to be built to protect these cities unless billions of people are willing to relocate to inland areas, an unlikely prospect.
What can be done to reduce the risks from coastal subsidence? First, a more intelligent regulation of ground water extraction from coastal aquifers, and oil from coastal regions, must be enforced. If oil is pumped out of an oil reservoir then water should be pumped back in to prevent subsidence. Sea level is rising, partly from natural astronomical effects, and partly from human-induced changes to the atmosphere. It is not too early to start planning for sea level rises of a few feet (about 2 m). Sea walls should be designed and tested before construction on massive scales. Consideration to moving many operations inland to higher ground should be considered.

Conclusion
Sea level is rising presently at a rate of one foot (0.3 m) per century, although this rate seems to be accelerating. This rising sea level will obviously change the coastline dramatically- a one-foot (0.3 m) rise in sea level along a gentle coastal plain can be equated with a 1,000-foot (300 m) landward migration of the shoreline. What will the world look like when sea levels rise significantly? Many of the world’s low-lying cities, like New York, New Orleans, London, Cairo, Tokyo, and most other cities in the world may look like Venice in a hundred or several hundred years. The world’s rich farmlands on coastal plains, like the East Coast of the United States, northern Europe, Bangladesh and much of China will be covered by shallow seas. If sea levels rise more significantly, like they have in the past then vast parts of the interior plains of North America will be covered by inland seas, and much of the world’s climate and vegetation zones will be shifted to different latitudes.
It is clear that governments must begin to plan for how to deal with rising sea levels, yet very little has been done so far. It is time that groups of scientists and government planners begin to meet to first understand the magnitude of the problem, then to study and recommend which tactics to initiate to mitigate the effects of rising sea levels. Can massive dikes and sea walls be built? Will our cities look like Venice, with abandoned lower levels, submerged subways, and boats in the street? These scenes will probably not become reality for a long time, but these events are inevitable on geological time scales.

I’ve read this in and convinced am I that planetary hydrogen dioxide levels follow periodic trends of typical proportions. In other words, the sea level changes that may have been attributed to global warming, are actually more likely to be a natural, periodic event. This isn’t to say there isn’t some actual global warming, but this article clearly shows that not all warming trends are man made.

The science deniers aren’t going to read that. You can tell that for some people climate change is about not being a wimp(chicken little) and accepting a supernatural judgement from a demon in the earth’s core. The people who don’t accept science are often simple name-calling bullies. The first comment, for example, where he thinks the oceans will rise like a flash flood thousands of feet. He has clearly never gotten an understanding of the scale of Earth.

There is no arguing with observational data. I would like to see this data presented for a larger sampling, i.e. 1900 - present, 1500 - present, 0 -present, and before.

Such a small sample is no more useful than a tide chart, or tomorrow’s weather forcast.

I would rate it 5 stars for the Farmers Almanac. If it is being used for a global warming conversation, it is a sad state of affairs in science.

Thanks for sharing that info, Tim Kusky. It was an interesting read.

Scott K., you are missing a tremendous amount of information by passing this off as a tide chart. The important message is that sea level height has increased nearly everywhere! Tides increase height at one place on the planet by decreasing it elsewhere - a planetary rearrangement of water. In this case, however, the ocean is rising everywhere. A 2-20 cm change in sea level height may not give you or johnh reason for pause, but the implications are important for the global climate system and those of us interested in living on a healthy planet.