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Image Above: Animation of ground-based lasers and the Global Positioning Satellite fleet measuring the shape of the Earth, including global sea level. Image Above: Visualization of Greenland's fastest glacier, Jakobshavn Isbrae, revealing the retreat of the glacier's calving front over the past six decades. Image Above: Time-lapse visualization showing the collapse of Antarctica's Larsen Ice Shelf in 2002. Image Above: Theoretical image showing areas in the state of Florida that would be affected by a one meter rise in sea level.
Throughout Eartha€™s history sea level has constantly changed and, indeed, it is these very changes that generate most of the geological record!
Geology has left us many clues to how the environment has changed over time and whether the sea was higher or lower than it is today.
Sea level, or a€?mean sea levela€™ as it is sometimes known, is the average height of the oceana€™s surface between high and low tide.
Scientists refer to it as the equipotential surface of the worlda€™s oceans, which means that its level is affected by the strength of gravity (or, more technically, a€?gravitational accelerationa€™) around the Earth. Variations in the gravitational acceleration are themselves caused by variations in the internal density of the Earth. Changes in tides and wave conditions over time are averaged out to determine a a€?still water levela€™ that can be used to identify whether the sea level has changed and also the height of the land above sea level.
In the UK, height above sea level is measured from the a€?Ordnance Datuma€™, which is the mean sea level at the tide gauge bolt Newlyn Pier, Cornwall. Because the surface of the land also moves up and down over long periods of time, sea level changes may be described as a€?relativea€™ or a€?absolutea€™. Relative changes may be observed even though the absolute height of the oceans remains the same. It is important to realise that when earth scientists talk about a rise in mean global sea level (what we call a€?eustatica€™ sea level), local changes may be quite different. During the last ice age, lots of sea water was stored in ice sheets and glaciers and sea level was, on average, more than 130 metres lower than it is today. But these sea level changes, related to the growth and melting of ice sheets, happen relatively quickly, taking tens of thousands to hundreds of thousands of years. We would have very little if any of our sedimentary rocks were it not for the fact that sea levels rise and fall!
Sea level rises may be caused by ice on land melting and running into the sea, adding to the total amount of water in the sea.
Note that there is no direct effect on sea level when sea-based ice melts, because sea-ice is already part of the ocean system. There is, however, a significant indirect effect of Arctic ice melting, which is that the albedo changes.
Albedo is the ability of a surface to reflect sunlight, and ice and snow are very good at reflecting the warming rays of the sun.
As the Arctic ice melts, polar regions will warm even more quickly because the Arctic ocean will now absorb the incoming energy. A eustatic sea level change occurs when there is a global change in the amount of water stored in the oceans, or a change in the geometry of the ocean basins which alters the volume of water they can hold. When the sea level changes in response to the amount of water stored in ice caps this is called glacial-eustasy. If the two main ice caps a€” Greenland and Antarctica a€” melted, then it is calculated that the oceans would rise by 66 metres. A change in the temperature of sea water also contributes to a change in sea level because sea water expands at higher temperatures.
As the atmosphere becomes warmer, the oceans will absorb some of the heat and increase in volume, which in turn leads to higher sea levels. The most famous of these is the collision of the Indian and Eurasian plates that formed the Himalaya Mountains. One relevant consequence of the collision is that a lot of continental crust was inserted under Tibet, leaving a larger ocean basin and therefore lower global sea-levels. During cold periods some of the oceana€™s water is evaporated and stored in ice caps or mountain glaciers, meaning a lower sea level. During warmer periods sea levels rise as the ice melts and once again is added to the volume of the oceans. Over the past 100 years the Eartha€™s climate has warmed a little less than 1A°C, and as temperatures rise thermal expansion of water will add to sea level rise.
The Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) projected that global sea level will rise by up to 60 cm by 2100 due to global warming. With ~10% of the world population living in low-elevation coastal zones, figuring out what is truly causing the seas to rise in some areas is an area worthy of study.


Other factors not mentioned when the threat of climate change induced sea level rise is discussed are non–climate-related anthropogenic processes. Sadly, even after presenting the facts given above, the authors just can't resist reaching into the scaremonger's bag for some old and discredited examples of supposed AGW induced sea rise. Furthermore, a recent study by Auckland University geographer Paul Kench has shown that many low-lying Pacific islands are growing, not sinking. It seems that using an inappropriate time step in their model led to inconsistencies in their results. To be fair, Nicholls and Cazenay admit that estimating sea level change is a total crap shoot.
Part of sea level change may, indeed, be caused by human activity, but not because of anthropogenic global warming.
There is also an interesting analysis in the August 2010 National Geographic in the section on the blue hole caves of the Bahamas.
I note that the sea level is not rising an equal amount throughout all of the oceans and is decreasing in some areas and increasing in others. Since this data was provide by satellite readings, were these graphs properly corrected for the anomalies that were recently reported?
They just recently learned the Moon has areas that are denser and areas that are not as dense as the rest of the Moon.
Planet Health Report gives the amount of time it takes for the global average seal level to rise 1 inch. One inch may not seem like much, but every inch of sea level rise covers 50-100 inches of beach.
If the glacial ice covering Greenland were to melt, sea level would rise 20 feet (6 meters)! When a doctor or nurse takes your pulse and your temperature, she or he is "checking your vital signs." These measurements are called "vital," because they are all-important signs of your health.
The area of the Arctic Ocean covered by sea ice is only 66% as large at the end of summer 2009 as in 1979.
Jonathan Overpeck and others have a paper Paleoclimatic Evidence for Future Ice-Sheet Instability and Rapid Sea-Level Rise in Science (24 March 2006) that suggests that sea level rise due to anthropogenic climate change could occur much faster than people have previously expected.
Also, Jonathan Overpeck‘s lab also has a visualization of the consquences of sea level rise for the US and the world. The ice sheet problem today very much resembles the ozone problem of the early 1980s, before researchers recognized the Antarctic ozone hole, Oppenheimer and Alley have written. But then the ozone hole showed up, and scientists soon realized a second, far more powerful loss mechanism was operating in the stratosphere; the solid surfaces of ice cloud particles were accelerating the destruction of ozone by chlorine.
Now glaciologists have a second mechanism for the loss of ice: accelerated flow of the ice itself, not just its meltwater, to the sea.
Three words immediately put you in the newly baptized place instead of reading three pages.Submitted by de dilla on Saturday, August 13, 2011"Salish Sea" . Abdalati will introduce the topic of sea level change, the techniques and technology used to study it, and the implications of such change. Nerem will summarize what is known about sea level based on satellite and ground-based observations, and introduce the factors that contribute to fluctuations in sea level. Miller will discuss the implications of global sea level change and new research capabilities that are being directed at understanding these implications. Alley will discuss the implications of large-scale sea level change on coastal regions and related environments.
And these gradual changes have generated the enormously thick sequences of sedimentary rocks that record the long history of geological time. Sea levels are rising today not only because significant parts of the land-based ice is melting, but also because ocean waters are warming and therefore expanding.
Ice floats because it is less dense than water and because it displaces an equivalent mass of water there is no increase in sea level as it melts a€“ in just the same way a cold drink does not overflow the glass as the ice cubes it contains melt.
This is known as an isostatic sea level change and it causes a relative sea level change as it is the land rising, not the amount of water increasing.
The cause of this rise is twofold: expansion of ocean waters as they warm and additional water from glaciers melting. Nicholls and Anny Cazenav, global sea levels have risen throughout the 20th century but key uncertainties remain.
Ground subsidence due to oil and groundwater extraction, or reduced sediment supply to river deltas caused by dam building, are more frequently to blame. The most dramatic subsidence effects have been caused by drainage and groundwater fluid withdrawal; over the 20th century, coasts have subsided by up to 5 m in Tokyo, 3 m in Shanghai, and 2 m in Bangkok. The people of the Maldives have, in the past, survived a higher sea level of about 50–60 cm. Damming and rerouting rivers diminishes water flowing to the sea; over-pumping buried aquifers and draining oil fields can cause subsidence.


It was those vegetation munching, flatulent mammoths :-) Thanks for the interesting information regarding the caves in the Bahamas. Earth's rotation, the shape of the ocean floor and the placement of the continents, tidal effects and the wind probably all have a greater impact. When ice on land, such as mountain glaciers or the ice sheets of Greenland or Antarctica, melts, that water contributes to sea level rise. The flat-topped, slightly dipping spit of land coming into the right-hand side of the picture in the middle distance is a remnant of raised beach. Despite nearly stable sea levels over the past 3,000 years, a number of low-lying and island nations have seized on the imminent flood as a reason to demand reparations from developed nations.
Spatial patterns in sea-level trends mainly result from nonuniform ocean warming and salinity variations, although other factors also contribute, including the solid Earth response to the last deglaciation and gravitational effects and changes in ocean circulation due to ongoing land ice melting and freshwater input. The bottom line is this: if you live in a coastal region you had best be willing to adapt to changing sea levels.
At the same time uplift and subduction, changing wind and currents, erosion and the deposit of sediments all play a larger, natural part. Sounds like verification for the timing of glacial and interglacial periods as well as confirmation that sea-level rise was higher during the last interglacial. As the temperature of the ocean goes up, the ocean actually expands, even without adding any water from the melting ice!
Chemists had shown that chlorine gas would, in theory, destroy ozone, but no ozone destruction had yet been seen in the atmosphere.
In reality, most of the areas in the world that are suffering from inundation are threatened because of human actions, but not global warming. The rate of sea level rise over much of the last 6,000 years has been an almost-imperceptible 1.4 millimeters per year (about 6 inches per century). This is partly because of the normal action of plate tectonics, the movement of Earth's crustal plates.
South of Bangkok, subsidence has led to substantial shoreline retreat of more than 1 km, leaving telegraph poles standing in the sea. On the contrary, there is firm morphological evidence of a significant sea level fall in the last 30 years. Clark withdrew their letter, “Constraints on future sea-level rise from past sea-level change,” from publication in the journal Nature Geoscience. If you want to live on an island paradise, you need to accept that every 50 to 100 years a cyclone will come along and try to erase it from the map. So when climate change alarmists start ranting about the inexorable rise of the world's oceans, realize that it is just another scare tactic being used to frighten the uninformed public—sea level shenanigans meant to promote the warmist agenda.
While the magnitude of the problem remained uncertain, only a few countries restricted the use of chlorofluorocarbons, mainly by banning their use in aerosol sprays.
Damming and rerouting of rivers combined with over-pumping of ground water has led to subsidence in many areas—in other words, the seas are not rising, the land is sinking. IPCC AR4 projections suggest appreciable regional variability around the future global mean rise by 2100 in response to nonuniform future ocean warming, but agreement between the models is poor. Morner, who has worked extensively in the Maldives and has repeatedly stated that the local sea level has not changed significantly in decades (see “New perspectives for the future of the Maldives”).
This sea level fall is likely to be the effect of increased evaporation and an intensification of the NE-monsoon over the central Indian Ocean. That paper presented projections of future sea-level rise based on simulations of the past 22,000 years of sea level history using a simple, empirical model linking sea level rise to global mean temperatures. No one knows whether the exceptionally strong warmings around the ice will continue apace, whether the ice accelerations of recent years will slow as the ice sheets adjust to the new warmth, or whether more glaciers will fall prey to the warmth. Since the early 1990s, sea level rise (SLR) has been measured by high-precision altimeter satellites.
And, as glacial ice melts, a great burden is removed from the continental land mass supporting it. One of their main conclusions was that the model's results supported the projections of sea level rise reported in the Fourth Assessment Report (AR4) of the IPCC. He termed that Phenomenon "Raised Beaches" He observed that phenomenon all over the South American Continent and the Pacific Ocean. Naturally, to climate change alarmists, this suggests that SLR is accelerating because of warming climatic conditions.



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