Sea Levels Rising in Parts of Indian Ocean; Greenhouse Gases Play Role, Study Finds

Newly detected rising sea levels in parts of the Indian Ocean, including the coastlines of the Bay of Bengal, the Arabian Sea, Sri Lanka, Sumatra and Java, appear to be at least partly a result of human-induced increases of atmospheric greenhouse gases, says a study led by the University of Colorado at Boulder.

The study, which combined sea surface measurements going back to the 1960s and satellite observations, indicates anthropogenic climate warming likely is amplifying regional sea rise changes in parts of the Indian Ocean, threatening inhabitants of some coastal areas and islands, said CU-Boulder Associate Professor Weiqing Han, lead study author. The sea level rise -- which may aggravate monsoon flooding in Bangladesh and India -- could have far-reaching impacts on both future regional and global climate.

The key player in the process is the Indo-Pacific warm pool, an enormous, bathtub-shaped area of the tropical oceans stretching from the east coast of Africa west to the International Date Line in the Pacific. The warm pool has heated by about 1 degree Fahrenheit, or 0.5 degrees Celsius, in the past 50 years, primarily caused by human-generated increases of greenhouse gases, said Han.

"Our results from this study imply that if future anthropogenic warming effects in the Indo-Pacific warm pool dominate natural variability, mid-ocean islands such as the Mascarenhas Archipelago, coasts of Indonesia, Sumatra and the north Indian Ocean may experience significantly more sea level rise than the global average," said Han of CU-Boulder's atmospheric and oceanic sciences department.

A paper on the subject was published in Nature Geoscience. Co-authors included Balaji Rajagopalan, Xiao-Wei Quan, Jih-wang Wang and Laurie Trenary of CU-Boulder, Gerald Meehl, John Fasullo, Aixue Hu, William Large and Stephen Yeager of the National Center for Atmospheric Research in Boulder, Jialin Lin of Ohio State University, and Alan Walcraft and Toshiaki Shinoda of the Naval Research Laboratory in Mississippi.

While a number of areas in the Indian Ocean region are showing sea level rise, the study also indicated the Seychelles Islands and Zanzibar off Tanzania's coastline show the largest sea level drop. Global sea level patterns are not geographically uniform, and sea rise in some areas correlate with sea level fall in other areas, said NCAR's Meehl.

The Indian Ocean is the world's third largest ocean and makes up about 20 percent of the water on Earth's surface. The ocean is bounded on the west by East Africa, on the north by India, on the east by Indochina and Australia, and on the south by the Southern Ocean off the coast of Antarctica.

The patterns of sea level change are driven by the combined enhancement of two primary atmospheric wind patterns known as the Hadley circulation and the Walker circulation. The Hadley circulation in the Indian Ocean is dominated by air currents rising above strongly heated tropical waters near the equator and flowing poleward, then sinking to the ocean in the subtropics and causing surface air to flow back toward the equator.

The Indian Ocean's Walker circulation causes air to rise and flow westward at upper levels, sink to the surface and then flow eastward back toward the Indo-Pacific warm pool. "The combined enhancement of the Hadley and Walker circulation form a distinct surface wind pattern that drives specific sea level patterns," said Han.

The international research team used several different sophisticated ocean and climate models for the study, including the Parallel Ocean Program -- the ocean component of NCAR's widely used Community Climate System Model. In addition, the team used a wind-driven, linear ocean model for the study.

"Our new results show that human-caused changes of atmospheric and oceanic circulation over the Indian Ocean region -- which have not been studied previously -- are the major cause for the regional variability of sea level change," wrote the authors in Nature Geoscience.

Han said that based on all-season data records, there is no significant sea level rise around the Maldives. But when the team looked at winter season data only, the Maldives show significant sea level rise, a cause for concern. The smallest Asian country, the Maldives is made up of more than 1,000 islands -- about 200 of which are inhabited by about 300,000 people -- and are on average only about five feet above sea level.

The complex circulation patterns in the Indian Ocean may also affect precipitation by forcing even more atmospheric air down to the surface in Indian Ocean subtropical regions than normal, Han speculated. "This may favor a weakening of atmospheric convection in the subtropics, which may increase rainfall in the eastern tropical regions of the Indian Ocean and increase drought in the western equatorial Indian Ocean region, including east Africa," Han said.

The new study indicates that in order to document sea level change on a global scale, researchers also need to know the specifics of regional sea level changes that will be important for coastal and island regions, said NCAR's Hu. Along the coasts of the northern Indian Ocean, seas have risen by an average of about 0.5 inches, or 13 millimeters, per decade.

"It is important for us to understand the regional changes of the sea level, which will have effects on coastal and island regions," said Hu.

The study was funded by a number of organizations, including NCAR, the National Science Foundation, NASA and the U.S. Department of Energy. University of Colorado at Boulder (2010, July 13). Sea levels rising in parts of Indian Ocean; Greenhouse gases play role, study finds. ScienceDaily. Retrieved July 15, 2010, from http://www.sciencedaily.com­ /releases/2010/07/100713101412.htm

Coral atolls hold on despite sea-level rise

Some South Pacific coral atolls have held their own or even grown in size over the past 60 years despite rising sea levels, research showed Thursday.Some scientists worry that many of the tiny, low-lying islands throughout the South Pacific will eventually disappear under rising sea levels.But two researchers who measured 27 islands where local sea levels have risen 4.8 inches (120 millimeters) - an average of 0.08 inch (2 millimeters) a year - over the past 60 years, found just four had diminished in size.The reason: Coral islands respond to changes in weather patterns and climate, with coral debris eroded from encircling reefs pushed up onto the islands' coasts by winds and waves.Professor Paul Kench of Auckland University's environment school and coastal process expert Arthur Webb of the Fiji-based South Pacific Applied Geoscience Commission, used historical aerial photographs and high-resolution satellite images to study changes in the land area of the islands.While four had gotten smaller, the other 23 had either stayed the same or grown bigger, according to the research published in the scientific journal Global and Planetary Change.The shape-shifting islands changed their size through what the pair describe as ocean shoreline displacement toward their lagoons, lagoon shoreline growth or extensions to the ends of elongated islands.Kench said it had been assumed that islands would "sit there and drown" as sea levels rise. But as the sea rises, the islands respond."They're not all growing, they're changing. They've always changed ... but the consistency (with which) some of them have grown is a little surprising," he told The Associated Press on Thursday.Tuvalu, a coral island group that climate change campaigners have repeatedly predicted will be drowned by rising seas, has its highest point just 14 feet (4.5 meters) above sea level. The researchers found seven of its nine islands had grown by more than 3 percent on average over the past 60 years.In 1972, Cyclone Bebe dumped 346 acres (140 hectares) of sediment on the eastern reef of Tuvalu, increasing the area of Funafuti, the main island, by 10 percent. Another island, Funamanu, gained 1.1 acres (0.44 hectares) or nearly 30 percent of its previous area.A similar trend was found in Kiribati, where three main islands also "grew." Betio expanded by 30 percent (89 acres or 36 hectares), Bairiki by 16.3 percent (14 acres or 5.8 hectares), and Nanikai by 12.5 percent (2 acres, or 0.8 hectares).On World Environment Day in 2008, Kiribati President Anote Tong warned parts of his island nation were already being submerged, forcing some of Kiribati's 94,000 people living in shoreline village communities to be relocated from century-old sites.Worst case scenarios showed Kiribati would disappear into the sea within a century, he said at the time.But Kench said the study shows the islands are coping with sea-level change, with higher waves and water depth supplying sand and gravel from coral reefs."In other words, they (the islands) are slowly moving ... migrating across their reef platforms," he said. "As the sea-level conditions and wave conditions are changing, the islands are adjusting to that."But he warned an accelerated rate of sea-level rise could be "the critical environmental threat to the small island nations," with "a very rapid rate of island destruction" possible from a water depth beyond a certain threshold. That threshold is unknown.Australian sea level oceanographer John Hunter said the findings "are good news and not a surprise.""Coral islands can keep up with some sea-level rise, but (there's also) ocean warming ... and ocean acidification ... that are certainly problematic for the corals. Sea-level rise can actually make the islands grow - as it apparently is doing," said Hunter, who did not participate in the study.While coral might adjust to ocean warming, ocean acidification "will probably be the death knell of the coral reefs," leaving coastal management by humans as the only way of retaining and rebuilding atolls, said Hunter, a researcher at the University of Tasmania's Antarctic Climate and Ecosystems Cooperative Research Center.Commenting on the findings, New Scientist magazine noted, "Erosion of island shorelines must be reconsidered in the context of physical adjustments of the entire island shoreline, as erosion may be balanced by progradation on other sectors of shorelines."

Mass Loss from Alaskan Glaciers Overestimated? Previous Melt Contributed a Third Less to Sea-Level Rise Than Estimated

The melting of glaciers is well documented, but when looking at the rate at which they have been retreating, a team of international researchers steps back and says not so fast.

Previous studies have largely overestimated mass loss from Alaskan glaciers over the past 40-plus years, according to Erik Schiefer, a Northern Arizona University geographer who coauthored a paper in the February issue of Nature Geoscience that recalculates glacier melt in Alaska.
The research team, led by Étienne Berthier of the Laboratory for Space Studies in Geophysics and Oceanography at the Université de Toulouse in France, says that glacier melt in Alaska between 1962 and 2006 contributed about one-third less to sea-level rise than previously estimated.
Schiefer said melting glaciers in Alaska originally were thought to contribute about .0067 inches to sea-level rise per year. The team's new calculations put that number closer to .0047 inches per year. The numbers sound small, but as Schiefer said, "It adds up over the decades."
While the team looked at three-fourths of all the ice in Alaska, Schiefer noted, "We're also talking about a small proportion of ice on the planet. When massive ice sheets (such as in the Antarctic and Greenland) are added in, you're looking at significantly greater rates of sea-level rise."
Schiefer said the team plans to use the same methodologies from the Alaskan study in other glacial regions to determine if further recalibrations of ice melt are in order. These techniques use satellite imagery that spans vast areas of ice cover.
Previous methods estimated melt for a smaller subset of individual glaciers. The most comprehensive technique previously available used planes that flew along the centerlines of selected glaciers to measure ice surface elevations. These elevations were then compared to those mapped in the 1950s and 1960s. From this, researchers inferred elevation changes and then extrapolated this to other glaciers.
Two factors led to the original overestimation of ice loss with this method, Schiefer said. One is the impact of thick deposits of rock debris that offer protection from solar radiation and, thus, melting. The other was not accounting for the thinner ice along the edges of glaciers that also resulted in less ice melt.
Schiefer and his colleagues used data from the SPOT 5 French satellite and the Japanese ASTER instrument on NASA's Terra satellite and converted the optical imagery to elevation information. They then compared this information to the topographical series maps of glacial elevations dating back to the 1950s.
While the team determined a lower rate of glacial melt during a greater than 40-year span, Schiefer said other studies have demonstrated the rate of ice loss has more than doubled in just the last two decades.
"With current projections of climate change, we expect that acceleration to continue," Schiefer said. This substantial increase in ice loss since the 1990s is now pushing up the rise in sea level to between .0098 inches and .0118 inches per year -- more than double the average rate for the last 40 years.
Working on the Alaskan glacial melt revision with Schiefer and Berthier were Garry Clarke of the University of British Columbia, Brian Menounos of the University of Northern British Columbia and Frédérique Rémy of the Université de Toulouse. E. Berthier, E. Schiefer, G. K. C. Clarke, B. Menounos & F. Rémy. Contribution of Alaskan glaciers to sea-level rise derived from satellite imagery. Nature Geoscience, 2010; 3 (2): 92 DOI: 10.1038/ngeo737

Sea Level in Israel Has Been Rising and Falling Over the Last 2,500 Years

The sea level in Israel has been rising and falling over the past 2,500 years, with a one-meter difference between the highest and lowest levels, most of the time below the present-day level. This has been shown in a new study supervised by Dr. Dorit Sivan, Head of the Department of Maritime Civilizations at the University of Haifa. "Rises and falls in sea level over relatively short periods do not testify to a long-term trend. It is early yet to conclude from the short-term increases in sea level that this is a set course that will not take a change in direction," explains Dr. Sivan.

The rising sea level is one of the phenomena that have most influence on humankind: the rising sea not only floods the littoral regions but also causes underground water salinization, flooded effluents, accelerated coastal destruction, and other damage.

According to Dr. Sivan, the changing sea level can be attributed to three main causes: the global cause -- the volume of water in the ocean, which mirrors the mass of ice sheets and is related to global warming or cooling; the regional cause -- vertical movement of the earth's surface, which is usually related to the pressure placed on the surface by the ice; and the local cause -- vertical tectonic activity. Seeing as Israel is not close to former ice caps and the tectonic activity along the Mediterranean coast is negligible over these periods, it can be concluded that drastic changes in Israel's sea levels are mainly related to changes in the volume of water.

In the present study, in light of earlier studies, research student Ayelet Toker and Dr. Sivan, set out to examine Israel's sea level over the past 2,500 years, based on data deduced from many coastal archaeological findings. They made a careful selection of findings that have been reliably and accurately dated, and first focused on findings that were excavated by the Antiquities Authority in Acre of the Crusader period. These revealed that the sea level during the Crusader period -- just 800 years ago -- was some 50-90 centimeters lower than the present sea level.

Findings from the same period at Caesarea and Atlit reinforced this conclusion. When additional sites were examined from periods before and after the Crusader period, it was revealed that there have been significant fluctuations in sea level: During the Hellenistic period, the sea level was about 1.6 meters lower than its present level; during the Roman era the level was almost similar to today's; the level began to drop again during the ancient Muslim period, and continued dropping to reach the same level as it was during the Crusader period; but within about 500 years it rose again, and reached some 25 centimeters lower than today's level at the beginning of the 18th century.

"Over the past century, we have witnessed the sea level in Israel fluctuating with almost 19 centimeters between the highest and lowest levels. Over the past 50 years Israel's mean sea level rise is 5.5 centimeters, but there have also been periods when it rose by 10 centimeters over 10 years. That said, even acute ups and downs over short periods do not testify to long-term trends. An observation of the sea levels over hundreds and thousands of years shows that what seems a phenomenon today is as a matter of fact "nothing new under the sun," Dr. Sivan concludes.

Rising seas 'clue' in sunken world off Orkney

Among the many structures found submerged was this apparent table with four supports

A unique discovery of submerged man-made structures on the seabed off Orkney could help find solutions to rising sea levels, experts have said.

They said the well preserved stone pieces near the island of Damsay are the only such examples around the UK.

It is thought some of the structures may date back thousands of years.

Geomorphologist Sue Dawson said that people have survived and adapted in the past and it is that adaption to climate change that needs to be learned from.

One of the team, archaeologist Caroline Wickham-Jones, of the University of Aberdeen, said of their freezing investigations under the December seas off Orkney: "We have certainly got a lot of stonework. There are some quite interesting things. You can see voids or entrances.

The really interesting thing about this bay is the stories relating to things under the sea and sea-level change. Our ancestors were dealing with similar problems to ourselves and we'd like to see how they coped with it

Caroline Wickham-Jones
Archaeologist
"There's this one feature that is like a stone table - you've got a large slab about a metre and a half long and it's sitting up on four pillars or walls so the next thing we need to do is to get plans and more photographs to try and assess and look for patterns.

"The quality and condition of some of the stonework is remarkable. Nothing like this has ever been found on the seabed around the UK."

Geophysicist Richard Bates, from the Scottish Oceans Institute, said: "We've got other sites down on the south coast of England where we have got submerged landscapes, meso-neolithic landscapes as we have here but what we haven't got anywhere else is actual structures.

"I don't say that's unique - that we'll never find that anywhere else, but so far we haven't seen such things before."

In general Scotland's mainland has been getting higher - but the surrounding islands have been sinking.

Sue Dawson, a geomorphologist from the University of Dundee, has been studying how and why the coast line is constantly changing.

She said: "One of the key premises behind a lot of the study of the past is that the past is a key to the present and the future.

"So we can look to times when maybe environmental changes have been much more rapid and much more catastrophic in some instances and people have survived and adapted and it's that adaption to climate change is one of the key things that we need to get to grips with."

The experts said the seabed around Orkney may be littered with man-made structures.

Experts believe this could be a submerged grave headstone
Richard Bates added: "We can look at the terrestrial landscape around here and see how man's occupied that.

"Pretty much anywhere in Orkney you can see a vista which has part of man within it, ancient man in the environment.

"The similar case is going to be in this drowned landscape so the few places we have seen so far are the biggest features but we expect to see much more as we dissect that landscape in finer and finer detail."

And they believe that while looking at an uncertain future it may pay to look into the past.

Caroline Wickham-Jones said: "The really interesting thing about this bay is the stories relating to things under the sea and sea-level change. Our ancestors were dealing with similar problems to ourselves and we'd like to see how they coped with it."

'Cryo-egg' to predict sea levels

The 'Cryo-Egg' must endure thousands of metres of ice pressure
A hi-tech "cryo-Egg", which will help predict sea levels changes, is to be created by experts at Bristol university.

The device will be sunk into the depths of the Greenland ice sheet before beaming back data about how frozen water is moving into the sea.

The university won £225,000 from the government-funded Natural Environment Research Council to build the egg.

"The engineering challenges for cryo-egg are vast," said Dr Jemma Wadham.

Uncharted landscape

Project leader and geographical scientist Dr Wadham added: "In addition to the need to survive crushing by ice and extreme cold, the probe must be able to communicate with scientists on the surface through kilometres of ice.

"This will be the first goal of the project, and is the focus of the current funding".

Glacial ice moves around so any cables linking the probe to the surface would eventually snap.

The only solution for the development team will be to employ wireless communication.

The wireless cryo-egg - whose name is derived from cryogenics, the study of low temperatures - will be developed over two years and is also intended to monitor the Antarctic and its largely uncharted subterranean landscape.

BBC

Earth's Polar Ice Sheets Vulnerable to Even Moderate Global Warming; New Orleans, Much of Southern Florida, Expected to Be Permanently Submerged

A new analysis of the geological record of the Earth's sea level, carried out by scientists at Princeton and Harvard universities and published in the Dec. 16 issue ofNature, employs a novel statistical approach that reveals the planet's polar ice sheets are vulnerable to large-scale melting even under moderate global warming scenarios. Such melting would lead to a large and relatively rapid rise in global sea level.

According to the analysis, an additional 2 degrees of global warming could commit the planet to 6 to 9 meters (20 to 30 feet) of long-term sea level rise. This rise would inundate low-lying coastal areas where hundreds of millions of people now reside. It would permanently submerge New Orleans and other parts of southern Louisiana, much of southern Florida and other parts of the U.S. East Coast, much of Bangladesh, and most of the Netherlands, unless unprecedented and expensive coastal protection were undertaken. And while the researchers' findings indicate that such a rise would likely take centuries to complete, if emissions of greenhouse gases are not abated, the planet could be committed during this century to a level of warming sufficient to trigger this outcome.

The study was written by Robert Kopp, who conducted the work as a postdoctoral researcher in Princeton's Department of Geosciences and Woodrow Wilson School of Public and International Affairs; Frederik Simons, an assistant professor of geosciences at Princeton; Jerry Mitrovica, a professor of geophysics at Harvard; Adam Maloof, an assistant professor of geosciences at Princeton; and Michael Oppenheimer, a professor of geosciences and international affairs in Princeton's Woodrow Wilson School.

As part of the study, the researchers compiled an extensive database of geological sea level indicators for a period known as the last interglacial stage about 125,000 years ago. Polar temperatures during this stage were likely 3 to 5 degrees Celsius (5 to 9 degrees Fahrenheit) warmer than today, as is expected to occur in the future if temperatures reach about 2 to 3 degrees Celsius (about 4 to 6 degrees Fahrenheit) above pre-industrial levels.

"The last interglacial stage provides a historical analog for futures with a fairly moderate amount of warming; the high sea levels during the stage suggest that significant chunks of major ice sheets could disappear over a period of centuries in such futures," Kopp said. "Yet if the global economy continues to depend heavily on fossil fuels, we're on track to have significantly more warming by the end of century than occurred during the last interglacial. I find this somewhat worrisome."

Oppenheimer added, "Despite the uncertainties inherent in such a study, these findings should send a strong message to the governments negotiating in Copenhagen that the time to avoid disastrous outcomes may run out sooner than expected."

Previous geological studies of sea level benchmarks such as coral reefs and beaches had shown that, at many localities, local sea levels during the last interglacial stage were higher than today. But local sea levels differ from those in this earlier stage; one major contributing factor is that the changing masses of the ice sheets alter the planet's gravitational field and deform the solid Earth. As a consequence, inferring global sea level from local geological sea level markers requires a geographically broad data set, a model of the physics of sea level, and a means to integrate the two. The study's authors provide all three, integrating the data and the physics with a statistical approach that allows them to assess the probability distribution of past global sea level and its rate of change.

The researchers determined through their analysis that there is a 95 percent probability that, during the last interglacial stage, global sea level peaked more than 6.6 meters (22 feet) above its present level. They further found that it is unlikely (with a 33 percent probability) that global sea level during this period exceeded 9.4 meters (31 feet).

Sea levels during the last interglacial stage are of interest to scientists and important to policymakers for several reasons. Most notably, the last interglacial stage is relatively recent by geological standards, making it feasible for climate scientists to develop a credible sea level record for the period, and is the most recent time period when average global temperatures and polar temperatures were somewhat higher than today. Because it was slightly warmer, the period can help scientists understand the stability of polar ice sheets and the future rate of sea level rise under low to moderate global warming scenarios.

The findings indicate that sea level during the last interglacial stage rose for centuries at least two to three times faster than the recent rate, and that both the Greenland and West Antarctic ice sheet likely shrank significantly and made important contributions to sea level rise. However, the relative timing of temperature change and sea level change during the last interglacial stage is fairly uncertain, so it is not possible to infer from the analysis how long an exposure to peak temperatures during this stage was needed to commit the planet to peak sea levels.

Sea Level Is Rising Along US Atlantic Coast, Say Environmental Scientists

An international team of environmental scientists led by the University of Pennsylvania has shown that sea-level rise along the Atlantic Coast of the United States was 2 millimeters faster in the 20th century than at any time in the past 4,000 years.

Sea-level rise prior to the 20th century is attributed to coastal subsidence. Put simply, land is being lost to subsidence as the earth continues to rise in response to the removal of the huge weight of ice sheets during the last glacial period. Using sediment cores from the U.S. Atlantic coast, researchers found significant spatial variations in land movement, with the mid-Atlantic coastlines of New Jersey, Delaware and Maryland subsiding twice as much as areas to the north and south. Coastal subsidence enhances sea-level rise, which leads to shoreline erosion and loss of wetlands and threatens coastal populations.

Researchers corrected relative sea-level data from tide gauges using the coastal-subsidence values. Results clearly show that the 20th-century rate of sea-level rise is 2 millimeters higher than the background rate of the past 4,000 years. Furthermore, the magnitude of the sea-level rise increases in a southerly direction from Maine to South Carolina. This is the first demonstrated evidence of this phenomenon from observational data alone. Researchers believe this may be related to the melting of the Greenland Ice Sheet and ocean thermal expansion.

"There is universal agreement that sea level will rise as a result of global warming but by how much, when and where it will have the most effect is unclear," said Benjamin P. Horton, assistant professor in the Department of Earth and Environmental Science at Penn. "Such information is vital to governments, commerce and the general public. An essential prerequisite for accurate prediction is understanding how sea level has responded to past climate changes and how these were influenced by geological events such as land movements."

The study provides the first accurate dataset for sea-level rise for the U.S. Atlantic coast, identifying regional differences that arise from variations in subsidence and demonstrate the possible effects of ice-sheet melting and thermal expansion for sea level rise.

The results appear in the Dec. 1 issue of the journal Geology. The study was supported by the National Science Foundation, the Thouron Family and the University of Pennsylvania.

The study was performed by Simon E. Engelhart and Horton of the Department of Earth and Environmental Science at Penn, Bruce C. Douglas of the International Hurricane Research Center at Florida International University, W. Richard Peltier of the Department of Physics at the University of Toronto and Torbjörn E. Törnqvist of the Department of Earth and Environmental Sciences and the Tulane/Xavier Center for Bioenvironmental Research at Tulane University Adapted from materials provided by University of Pennsylvania.

Sea Level Could Rise from 0.75 to 1.9 Meters This Century

A new scientific study warns that sea level could rise much faster than previously expected. By the year 2100, global sea level could rise between 75 and 190 centimetres, according to a paper published in the Proceedings of the National Academy of Sciences.

The authors, Martin Vermeer of Helsinki University of Technology in Finland and Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany, based their analysis on measurements of sea level and temperature taken over the past 130 years. In those data they identified a strong link between the rate of sea level rise and global temperature.
"Since 1990 sea level has been rising at 3.4 millimetres per year, twice as fast as on average over the 20th Century," says Stefan Rahmstorf. Even if that rate just remained steady, this would already lead to 34 centimetres rise in the 21st century. "But the data show us clearly: the warmer it gets, the faster sea level rises. If we want to prevent a galloping sea level rise, we should stop global warming as soon as possible," adds Rahmstorf.
The link between the rate of sea level rise and global temperature was originally proposed by Rahmstorf in an article in the journal Science in 2007. The new study refines this idea. It adds a second term to the equation in order to capture the short-term response of sea level, leading to greater physical realism as well as a much greater precision. Vermeer and Rahmstorf also added the latest data sets, including satellite measurements up to 2008 and a correction for water storage in man-made reservoirs, which overall lowers global sea level by 3 centimetres.
Their results show that even for a relatively low greenhouse gas emissions scenario with just 2 degrees Celsius warming over the 21st century, sea level is likely to rise by more than one meter. Their highest scenario, with over 4 degrees Celsius warming over the 21st century, would lead to over 1.4 meters of sea level rise by 2100. When the full set of emissions scenarios and estimated uncertainties are considered, waters may rise by anything between 75 centimetres and 1.9 metres by the year 2100 -- consistent with another recent estimate of an upper limit of 2 metres, based on consideration of ice sheet dynamics.
"More noteworthy even than the very high figures for sea level rise is the almost clockwork precision by which, on climatic time scales, temperature drives sea level rise," says Martin Vermeer. The results of the study also demonstrate the quality of the existing sea level and temperature time series used, "painstakingly constructed from measurements at stations around the globe for well over a century," Vermeer notes.
The projected rise is about three times as much as estimated in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change in 2007, which did not fully include the effects of ice loss from Greenland and Antarctica. To avoid such a large sea level rise, which would be an existential threat to many large coastal cities as well as a number of small island nations, drastic and rapid cuts in greenhouse gas emissions will be required.
The study finds that delays in emissions reductions will come at a high cost, since early emissions cuts are much more effective in limiting sea level rise than later cuts. The emissions reductions needed to keep sea level rise below 1 meter will likely be considerably more ambitious than those needed to limit global warming to 2 degrees Celsius, a policy goal now supported by many nations. Adapted from materials provided by Potsdam Institute for Climate Impact Research (PIK), via AlphaGalileo.

North Carolina Sea Levels Rising Three Times Faster Than In Previous 500 Years, Study Finds

An international team of environmental scientists led by the University of Pennsylvania has shown that sea-level rise, at least in North Carolina, is accelerating. Researchers found 20th-century sea-level rise to be three times higher than the rate of sea-level rise during the last 500 years. In addition, this jump appears to occur between 1879 and 1915, a time of industrial change that may provide a direct link to human-induced climate change.

The results appear in the current issue of the journal Geology.
The rate of relative sea-level rise, or RSLR, during the 20th century was 3 to 3.3 millimeters per year, higher than the usual rate of one per year. Furthermore, the acceleration appears consistent with other studies from the Atlantic coast, though the magnitude of the acceleration in North Carolina is larger than at sites farther north along the U.S. and Canadian Atlantic coast and may be indicative of a latitudinal trend related to the melting of the Greenland ice sheet.
Understanding the timing and magnitude of this possible acceleration in the rate of RSLR is critical for testing models of global climate change and for providing a context for 21st-century predictions.
"Tide gauge records are largely inadequate for accurately recognizing the onset of any acceleration of relative sea-level rise occurring before the 18th century, mainly because too few records exist as a comparison," Andrew Kemp, the paper's lead author, said. "Accurate estimates of sea-level rise in the pre-satellite era are needed to provide an appropriate context for 21st-century projections and to validate geophysical and climate models."
The research team studied two North Carolina salt marshes that form continuous accumulations of organic sediment, a natural archive that provides scientists with an accurate way to reconstruct relative sea levels using radiometric isotopes and stratigraphic age markers. The research provided a record of relative sea-level change since the year 1500 at the Sand Point and Tump Point salt marshes in the Albemarle-Pamlico estuarine system of North Carolina. The two marshes provided an ideal setting for producing high-resolution records because thick sequences of high marsh sediment are present and the estuarine system is microtidal, which reduces the vertical uncertainty of aleosea-level estimates. The study provides for the first time replicated sea-level reconstructions from two nearby sites.
In addition, comparison with 20th-century tide-gauge records validates the use of this approach and suggests that salt-marsh records with decadal and decimeter resolution can supplement tide-gauge records by extending record length and compensating for the strong spatial bias in the global distribution of longer instrumental records.
The study was funded by the National Oceanic and Atmospheric Administration Coastal Ocean Program, North Carolina Coastal Geology Cooperative Program, U.S. Geological Survey and National Science Foundation.
The study was conducted by Kemp and Benjamin P. Horton of the Sea-Level Research Laboratory at Penn, Stephen J. Culver and D. Reide Corbett of the Department of Geological Sciences at East Carolina University, Orson van de Plassche of Vrije Universiteit, W. Roland Gehrels of the University of Plymouth, Bruce C. Douglas of Florida International University and Andrew C. Parnell of University College Dublin.
Adapted from materials provided by University of Pennsylvania.

Rising Sea Levels Are Increasing Risk Of Flooding Along South Coast Of England

A new study by researchers at the University of Southampton has found that sea levels have been rising across the south coast of England over the past century, substantially increasing the risk of flooding during storms.

The team has conducted a major data collection exercise, bringing together computer and paper-based records from across the south of England, from the Scilly Isles to Sheerness, to form a single data set of south coast sea levels across the years.

Their work has added collectively about 150 years worth of historic data to the existing record of English Channel sea-level change and extended the data along the south coast. Their findings are published in the latest edition of the journal Continental Shelf Research.

The data shows that both average sea levels and extreme sea levels have been rising at a similar rate through the 20th Century. The rate of rise is in the range 1.2 to 2.2 mm per year, with 1.3 mm per year recorded at Southampton.

Coastal engineering expert Professor Robert Nicholls, of the University's School of Civil Engineering and the Environment, who conducted the study, comments: "While these changes seem small, over a century they accumulate and substantially increase the risk of flooding during storms, unless there have been corresponding upgrades to flood defences. A water level that had an average likelihood of occurring once every 100 years in 1900 now has an average likelihood of occurring on average every 10 to 25 years, depending on the site considered. As sea levels continue to rise and probably accelerate, this increase in the likelihood of flooding will continue."

The most significant extension to the records is that of sea level changes at Southampton where the record now begins in 1935.

Paper-based records at St Mary's on the Isles of Scilly, Weymouth, Southampton and Newhaven have been used to greatly extend existing computer-based records, while the records at Devonport and Portsmouth have both been extended and corrected for pervious errors of interpretation.

This new data is feeding into ongoing efforts to increase the understanding and management of flooding.

The work was conducted by Professor Robert Nicholls, Dr Neil Wells from the University's School of Ocean and Earth Science based at the National Oceanography Centre, Southampton and Dr Ivan Haigh, formerly of the University of Southampton and now at the University of Western Australia.

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Adapted from materials provided by University of Southampton, via EurekAlert!, a service of AAAS.

How Will Future Sea-Level Rise Linked to Climate Change Affect Coastal Areas?

The anticipated sea-level rise associated with climate change, including increased storminess, over the next 100 years and the impact on the nation's low-lying coastal infrastructure is the focus of a new, interdisciplinary study led by geologists at The Florida State University."Our hypothesis is that the historic storm record, which extends back only about 150 years, isn't a reliable indicator of true storm frequency, but the long-term geologic record is," said Joseph F. Donoghue, an associate professor of geology at Florida State University and the study's lead investigator. "This project is crucial because the rates of change in environmental parameters predicted for the near future are much greater than those of the past several millennia. For example, some of the worst-case sea-level rise scenarios predicted for the near future have not been experienced by the coastal system for more than 8,000 years."Funding for the research comes from a three-year, $1.03 million grant from the Strategic Environmental Research and Development Program (SERDP), an environmental science and technology initiative headed by the U.S. Department of Defense and administered in partnership with the Department of Energy and the U.S. Environmental Protection Agency.By 2012, the study is expected to produce methodologies and models that help coastal planners and managers in all low-lying coastal regions better understand, address and mitigate the near-future effects of sea-level rise -- an especially critical issue for the Sunshine State. The research team will perform its field work along the Gulf of Mexico coast in Northwest Florida, a region of the Florida Panhandle distinguished by rare coastal lakes, which harbor sediments that form an environmental record dating back thousands of years."We have decided to focus our field work on the Northwest Florida coast for several reasons besides its proximity to Florida State," Donoghue said. "In terms of major coastal infrastructure, the area has Eglin Air Force Base, one of the largest air bases in the U.S. In addition, the central Panhandle coast has natural features, including coastal lakes, that lend themselves particularly well to the kind of work we want to do."That work will employ a variety of possible scenarios for both sea level change and increased "storminess" -- more storms and more intense storms. Using models of coastal systems that include elements such as barrier islands, wetlands, estuaries and coastal groundwater supplies, the researchers will combine the various sea level and storm scenarios in multiple ways to gauge the potential effects.Florida State University geologist Steve Kish, a co-leader of the study, is responsible for gathering and interpreting the remote sensing data. To lay the groundwork, he has sought and found maps, photos and other records dating back about 150 years that show the evolution of the Northwest Florida coast. The documents reflect surprising rates of change for the coastline in the last two decades, including a retreat landward averaging about six to 10 feet per year.Meanwhile, a fast start on the field work has yielded significant early findings."We have been collecting sediment cores from some of the coastal lakes in Walton County," Donoghue said. "These lakes are unique. They are relatively long-lived, possibly 4,000 to 6,000 years old. Their bottom sediments contain a long, continuous record of coastal environmental conditions, including the occurrence of major storms. The lakes are situated behind barrier dunes, breached only during large storms that carry in marine water and overwash sand. As a result, the lake floors have a chemical and sedimentologic 'signature.'"The researchers are analyzing the lake sediment cores using radiocarbon dating, stable isotope analyses and standard sedimentologic measurements. They hope to obtain a long-term -- several thousand years -- geologic record of storm occurrence for the region."This long geologic record of storm frequency will be compared with the 150-year-old historic storm record," Donoghue said. "Using the geologic record to run our climate models would give us greater confidence in the model results, which we then would use to predict the near-future climate for the coastal region."Florida State University

Climate Change Influences The Size Of Marine Organisms: Big Advantage For The Small

The ice is melting, the sea level is rising and species are conquering new habitats. The warming of the world climate has many consequences. Researchers now report that climate change influences the size of aquatic organisms.

For a long time scientists have observed the biological consequences of global climate change. One of the most famous symptoms is the shift of habitats from the equator further north or further south. More recent studies show that not only the habitats but also the size of organisms is affected.
Dr. Martin Daufresne of the HYAX Lake Ecosystem Laboratory in Aix-en-Provence, France, as well as Prof. Ulrich Sommer and Dr. Kathrin Lengfellner of the Leibniz-Institute of Marine Sciences (IFM-GEOMAR) in Kiel have shown that global warming leads to reduced body size of organisms in the ocean and in freshwater. Very different organisms showed this tendency: bacteria, plankton-algae, zooplankton and fishes in the North and Baltic Sea and in French rivers.
Three mechanisms seem to play a role in this process.
First: The proportion of smaller species grows.
Second: The proportion of smaller individuals grows within one species.
Third: The animals reach sexual maturity with smaller body size.
“This development affects the functioning of the whole eco-system: The body size is decisive for what animals can eat and by whom they are eaten. A shift to smaller species and individuals within the fish population could lead to a reduction of zooplankton because small fish will eat less fish and more zooplankton. This could pave the way fvor massive and unpleasant algal blooms. Furthermore, with smaller fish the economic value of fishery declines”, explains Prof. Sommer.
The bacteria, algae and zooplankton were examined in experiments of Baltic Sea plankton as part of the German Research Foundation-programme AQUASHIFT. The results about fish size are based on long term measurements in the North Sea, the Baltic Sea and in French Rivers.
Journal reference:
Daufresne et al. Global warming benefits the small in aquatic ecosystems. Proceedings of the National Academy of Sciences, 2009; DOI: 10.1073/pnas.0902080106
Adapted from materials provided by Leibniz Institute of Marine Sciences (IFM-GEOMAR).

Declining Aral Sea: Satellite Images Highlight Dramatic Retreat

New Envisat images highlight the dramatic retreat of the Aral Sea’s shoreline from 2006 to 2009. The Aral Sea was once the world’s fourth-largest inland body of water, but it has been steadily shrinking over the past 50 years since the rivers that fed it were diverted for irrigation projects.

By the end of the 1980s, it had split into the Small Aral Sea (north), located in Kazakhstan, and the horse-shoe shaped Large Aral Sea (south), shared by Kazakhstan and Uzbekistan.
By 2000, the Large Aral Sea had split into two – an eastern and western lobe. As visible in the images, the eastern lobe retreated substantially between 2006 and 2009. It appears to have lost about 80% of its water since the 2006 acquisition, at which time the eastern lobe had a length of about 150 km and a width of about 70 km.
The sea’s entire southern section is expected to dry out completely by 2020, but efforts are underway to save the northern part.
The Kok-Aral dike, a joint project of the World Bank and the Kazakhstan government, was constructed between the northern and southern sections of the sea to prevent water flowing into the southern section. Since its completion in 2005, the water level has risen in the northern section by an average of 4 m.
As the Aral Sea evaporated, it left behind a 40 000 sq km zone of dry, white salt terrain now called the Aral Karakum Desert. Each year violent sandstorms pick up at least 150 000 tonnes of salt and sand from the Aral Karakum and transport it across hundreds of km, causing severe health problems for the local population and making regional winters colder and summers hotter. In an attempt to mitigate these effects, vegetation that thrives in dry, saline conditions is being planted in the former seabed.
In 2007, the Kazakhstan government secured another loan from the World Bank to implement the second stage, which includes the building of a second dam, of the project aimed at reversing this man-made environmental disaster.
Envisat acquired these images on 1 July 2006 and 6 July 2009 with its Medium Resolution Imaging Spectrometer (MERIS) instrument while working in Full Resolution Mode to provide a spatial resolution of 300 m.
Adapted from materials provided by European Space Agency.

Close Relationship Between Past Warming And Sea-level Rise

A team from the National Oceanography Centre, Southampton (NOCS), along with colleagues from Tübingen (Germany) and Bristol presents a novel continuous reconstruction of sea level fluctuations over the last 520 thousand years. Comparison of this record with data on global climate and carbon dioxide (CO2) levels from Antarctic ice cores suggests that even stabilisation at today's CO2 levels may commit us to sea-level rise over the next couple of millennia, to a level much higher than long-term projections from the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC).

Little is known about the total amount of possible sea-level rise in equilibrium with a given amount of global warming. This is because the melting of ice sheets is slow, even when temperature rises rapidly. As a consequence, current predictions of sea-level rise for the next century consider only the amount of ice sheet melt that will occur until that time. The total amount of ice sheet melting that will occur over millennia, given the current climate trends, remains poorly understood.
The new record reveals a systematic equilibrium relationship between global temperature and CO2 concentrations and sea-level changes over the last five glacial cycles. Projection of this relationship to today's CO2 concentrations results in a sea-level at 25 (±5) metres above the present. This is in close agreement with independent sea-level data from the Middle Pliocene epoch, 3-3.5 million years ago, when atmospheric CO2 concentrations were similar to the present-day value. This suggests that the identified relationship accurately records the fundamental long-term equilibrium behaviour of the climate system over the last 3.5 Million years.
Lead author Professor Eelco Rohling of the University of Southampton's School of Ocean and Earth Science based at NOCS, said: "Let's assume that our observed natural relationship between CO2 and temperature, and sea level, offers a reasonable 'model' for a future with sustained global warming. Then our result gives a statistically sound expectation of a potential total long-term sea-level rise. Even if we would curb all CO2 emissions today, and stabilise at the modern level (387 parts per million by volume), then our natural relationship suggests that sea level would continue to rise to about 25 m above the present. That is, it would rise to a level similar to that measured for the Middle Pliocene."
Project partners Professor Michal Kucera (University of Tübingen) and Dr Mark Siddall (University of Bristol), add: "We emphasise that such equilibration of sea level would take several thousands of years. But one still has to worry about the large difference between the inferred high equilibrium sea level and the level where sea level actually stands today. Recent geological history shows that times with similarly strong disequilibria commonly saw pulses of very rapid sea-level adjustment, at rates of 1-2 metres per century or higher."
The new study's projection of long-term sea-level change, based on the natural relationship of the last 0.5 to 3.5 million years, differs considerably from the IPCC's model-based long-term projection of +7 m. The discrepancy cannot be easily explained, and new work is needed to ensure that the 'gap is closed'.
The observed relationships from the recent geological past can form a test-bed or reality-check for models, to help them achieve improved future projections.
The project was funded by the Natural Environment Research Council (UK) and the Deutsche Forschungs-Gemeinschaft (Germany).
The authors are Eelco Rohling (NOCS), Katharine Grant (NOCS), Mike Bolshaw (NOCS), Andrew Roberts (NOCS), Mark Siddall (University of Bristol), Christoph Hemleben (University of Tübingen) and Michal Kucera (University of Tübingen).
.
Journal reference:
Rohling et al. Antarctic temperature and global sea level closely coupled over the past five glacial cycles. Nature Geoscience, June 21, 2009; DOI: 10.1038/ngeo557
Adapted from materials provided by National Oceanography Centre, Southampton (UK).National Oceanography Centre, Southampton (UK) (2009, July 7). Close Relationship Between Past Warming And Sea-level Rise. ScienceDaily. Retrieved July 8, 2009, from http://www.sciencedaily.com­ /releases/2009/06/090622103833.htm

Close relationship between past warming and sea-level rise

In a paper in Nature Geoscience, a team from the National Oceanography Centre, Southampton (NOCS), along with colleagues from Tübingen (Germany) and Bristol presents a novel continuous reconstruction of sea level fluctuations over the last 520 thousand years. Comparison of this record with data on global climate and carbon dioxide (CO2) levels from Antarctic ice cores suggests that even stabilisation at today's CO2 levels may commit us to sea-level rise over the next couple of millennia, to a level much higher than long-term projections from the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC).Little is known about the total amount of possible sea-level rise in equilibrium with a given amount of global warming. This is because the melting of ice sheets is slow, even when temperature rises rapidly. As a consequence, current predictions of sea-level rise for the next century consider only the amount of ice sheet melt that will occur until that time. The total amount of ice sheet melting that will occur over millennia, given the current climate trends, remains poorly understood.The new record reveals a systematic equilibrium relationship between global temperature and CO2 concentrations and sea-level changes over the last five glacial cycles. Projection of this relationship to today's CO2 concentrations results in a sea-level at 25 (?5) metres above the present. This is in close agreement with independent sea-level data from the Middle Pliocene epoch, 3-3.5 million years ago, when atmospheric CO2 concentrations were similar to the present-day value. This suggests that the identified relationship accurately records the fundamental long-term equilibrium behaviour of the climate system over the last 3.5 Million years.Lead author Professor Eelco Rohling of the University of Southampton's School of Ocean and Earth Science based at NOCS, said: "Let's assume that our observed natural relationship between CO2 and temperature, and sea level, offers a reasonable 'model' for a future with sustained global warming. Then our result gives a statistically sound expectation of a potential total long-term sea-level rise. Even if we would curb all CO2 emissions today, and stabilise at the modern level (387 parts per million by volume), then our natural relationship suggests that sea level would continue to rise to about 25 m above the present. That is, it would rise to a level similar to that measured for the Middle Pliocene."Project partners Professor Michal Kucera (University of Tübingen) and Dr Mark Siddall (University of Bristol), add: "We emphasise that such equilibration of sea level would take several thousands of years. But one still has to worry about the large difference between the inferred high equilibrium sea level and the level where sea level actually stands today. Recent geological history shows that times with similarly strong disequilibria commonly saw pulses of very rapid sea-level adjustment, at rates of 1-2 metres per century or higher."The new study's projection of long-term sea-level change, based on the natural relationship of the last 0.5 to 3.5 million years, differs considerably from the IPCC's model-based long-term projection of +7 m. The discrepancy cannot be easily explained, and new work is needed to ensure that the 'gap is closed'.The observed relationships from the recent geological past can form a test-bed or reality-check for models, to help them achieve improved future projections.National Oceanography Centre, Southampton (UK)

Sea rise from Antarctic ice melt overestimated

While a collapse of the West Antarctic ice sheet will have devastating impacts on global sea levels, a study published Thursday found the anticipated impact has been seriously overestimated.Using new measures of the ice sheet's geometry, British and Dutch researchers predict its collapse would cause sea levels to rise by 3.2 meters (11 feet) rather than previous estimates of five to seven meters.However, the study published in the journal Science found that even a one meter rise in sea levels would be significant enough to weaken the Earth's gravity field in the southern hemisphere and affect the Earth's rotation.That rotational shift would cause water to pile up in the northern oceans and could result in dramatic regional differences in sea levels, with the largest rise on the east and west coast of the United States."The pattern of sea level rise is independent of how fast or how much of the (Western Antarctic Ice Sheet) WAIS collapses," said lead author Jonathan Bamber of the University of Bristol in England."Even if the WAIS contributed only a meter of sea level rise over many years, sea levels along North America's shorelines would still increase 25 percent more than the global average."Antarctica holds about nine times the volume of ice as Greenland and is considered a sleeping giant when it comes to sea levels.The western ice sheet is of particular concern because enormous sections sit in inland basins on bedrock that is entirely below sea level.Vast floating ice shelves currently limit ice loss to the ocean but scientists fear the sheet could collapse if the floating ice shelves break free.The study authors based their predictions on the assumption that only ice on the downward sloping and inland-facing side of the basins would be lost while ice grounded on bedrock that is above sea level or slopes upward would survive.Researchers do not know how quickly the shelf would collapse. But if such a large amount of ice melted steadily over 500 years it would raise sea levels by about 6.5 millimeters per year.That's about twice the current rate due to all sources."Though smaller than past predictions, the scale of the fully manifested instability is enormous," cautioned Erik Ivins of the California Institute of Technology in an accompanying article."The total mass gained by the oceans ... would be roughly equal to the mass showered to Earth by the impact of about 2000 Halley-sized comets."Further complicating the situation is the fact that Greenland seems to be losing as much or more ice than Antarctica, even though it doesn't have the same unstable configuration."Greenland needs only half the mass loss rate of Antarctica to have an equivalent effect on polar motion due to its less polar position," he wrote.Even "more ominous" are the current accelerations of ice flow into the Amundsen Sea Embayment in Antarctica, he wrote."Should the ice sheet grounding line migrate farther inland, ice resting on bedrock well below sea level could become unstable."

Ice sheet melt threat reassessed

A 3.3m sea level rise will still have a devastating impact on coastal areas The collapse of a major polar ice sheet will not raise global sea levels as much as previous projections suggest, a team of scientists has calculated.Writing in Science, the researchers said that the demise of the West Antarctic Ice Sheet (WAIS) would result in a sea level rise of 3.3m (10 ft). Previous estimates had forecast a rise in the region of five to six metres. However, they added, the rise would still pose a serious threat to major coastal cities, such as New York. "Sea level rise is considered to be the one of the most serious consequence of climate change," lead author Jonathan Bamber told the Science podcast. "A sea level rise of just 1.5m would displace 17 million people in Bangladesh alone," he added. "So it is of the utmost importance to understand the potential threats to coastlines and people living in coastal areas." Threat reassessedProfessor Bamber, from the University of Bristol's Glaciology Centre, said that the WAIS posed "potentially one of the most serious threats".The ebb and flow of sea level rise The world has three ice sheets, Greenland, East Antarctica and West Antarctica, but it is the latter that is considered most vulnerable to climatic shifts. "It has been hypothesised for more than 30 years now that the WAIS is inherently unstable," he explained. "This instability means that the ice sheet could potentially rapidly collapse or rapidly put a lot of ice into the oceans." When the idea first emerged in the late 1970s, it was estimated that global sea level would rise by five metres if the WAIS collapsed. Current projections suggest that a complete collapse of WAIS would result in an increase of up to six metres. But Professor Bamber said that no-one had revisited the calculation, despite new data sets becoming available, and scientists developing a better understanding of the dynamics in the vast ice sheets. The original estimates were based on "very basic ice thickness data", he explained. "Ice thickness data gives you information about the depth of the bedrock underneath the ice sheet. "Over the past 30 years, we have acquired much more ice thickness data over the whole of Antarctica, particularly over West Antarctica. "We also have much better surface topography. Those two data sets are critical in determining two things." The first was knowing the volume of ice that could contribute to sea level rise, and the second was a better understanding of the proportion of WAIS that was potentially susceptible to this instability. Instead of assuming that the entire WAIS would collapse, causing sea level to rise by up to six metres, Professor Bamber and colleagues used models based on glaciological theory to simulate how the 2.2 million-cubic-km ice sheet would respond. "Our reassessment of West Antarctica's contribution to sea level rise if the ice sheet was to collapse is about 3.3 metres," he said. "That is about half of the value that has been quoted up until now."The team's study also calculated what regions were likely to experience the biggest increases in sea level. "Sea level rise is not uniform across the world's oceans, partly as a result of disruptions to the Earth's gravity field," explained Professor Bamber. "It turns out that the maximum increase in sea level rise is centred at a latitude of about 40 degrees along the Atlantic and Pacific seaboards of North America." This would include cities such as San Francisco and New York. These areas could expect increases of one-and-a-quarter times the global average, the team estimated. In other words, if the global average was one metre, then places like New York could expect to see a rise of 1.25m. Responding to Professor Bamber's paper in Science, British Antarctic Survey science leader Dr David Vaughan described the findings as "quite sound". "But for me, the most crucial question is not solely about the total amount of ice in West Antarctica, because that might take several centuries to be lost to the ocean," he told BBC News. "The crucial question is how much ice could be lost in 100-200 years; that's the sea level rise we have to understand and plan for. "Even with this new assessment the loss of a fraction of WAIS over those timescales would have serious consequences and costs that we've only really just begun to understand."

Threat from West Antarctica less than previously believed

The potential contribution to sea level rise from a collapse of the West Antarctic Ice Sheet (WAIS) have been greatly overestimated, according to a new study published in the journal Science. Scientists estimate global sea level would rise 3.3 metres, not five or six, as previously thought. The Atlantic and Pacific seaboards of the US, even in the case of a partial collapse, would experience the largest increases, threatening cities such as New York, Washington DC and San Francisco.Long thought of as the sleeping giant with respect to sea level rise, Antarctica holds about nine times the volume of ice of Greenland. Its western ice sheet is of particular interest to scientists due to its unusual below-sea level topography, which is believed to make it inherently unstable. But the area's potential contribution to sea level has been greatly overestimated, according to new calculations. Professor Jonathan Bamber at Bristol University, lead author of the study, said: "There's a vast body of research that's looked at the likelihood of a WAIS collapse and what implications such a catastrophic event would have for the globe. Yet all of these studies have assumed a five- to-six-metre contribution to sea level rise. Our calculation shows those estimates are much too large, even on a thousand year timescale." Jonathan Bamber, Professor in Physical Geography, at the University's School of Geographical Sciences is currently a Visiting Fellow at the University of Colorado at Boulder's Cooperative Institute for Research in Environmental Sciences, or CIRES. Instead of assuming a complete disintegration of the whole WAIS, Bamber and colleagues used models, based on glaciological theory, to simulate how the massive ice sheet would respond if the floating ice shelves fringing the continent broke free. Vast ice shelves currently block the WAIS from spilling into the Weddell and Ross Seas, limiting total ice loss to the ocean. According to theory, if these floating ice shelves were removed, sizeable areas of the WAIS would become, in effect, undammed, triggering an acceleration of the ice sheet towards the ocean and a "rapid" inland migration of the grounding line, the point where the ice sheet's margins meets the ocean and begins to float. The most unstable areas of the WAIS are those grounded below sea level on bedrock with negative bedslope, where the bedrock slopes downwards inland. Once undammed, these areas would quickly become buoyant, forming new floating ice shelves further inland and, in time, precipitating further break up and collapse. For their calculations, the researchers assumed that only these areas would collapse and contribute to sea level rise. In contrast, they assumed areas grounded above sea level, or on bedrock that slopes upwards inland, would likely retain substantial ice masses. Professor Bamber said: "Unlike the world's other major ice sheets – the East Antarctic Ice Sheet and Greenland – WAIS is the only one with such an unstable configuration." Just how "rapid" a collapse of the WAIS would be is largely unknown. Though if such a large mass of ice steadily melted over 500 years, as suggested in an early study, it would add about 6.5 millimetres per year to sea level rise: twice the current rate due to all sources. Professor Bamber added: "Interestingly, the pattern of sea level rise is independent of how fast or how much of the WAIS collapses. Even if the WAIS contributed only a metre of sea level rise over many years, sea levels along North America's shorelines would still increase 25 per cent more than the global average."Regional variations in sea level would be largely driven by the redistribution of ice mass from the Antarctic continent to the oceans, according to the study. With less mass at the South Pole, Earth's gravity field would weaken in the Southern Hemisphere and strengthen in the North, causing water to pile up in the northern oceans. This redistribution of mass would also affect Earth's rotation, which in turn would cause water to build up along the North American continent and in the Indian Ocean. The study was conducted with support from the National Environmental Research Council (NERC) and in collaboration with Delft University of Technology in the Netherlands and the University of Durham.

New Antarctic seabed sonar images reveal clues to sea-level rise

Most comprehensive seabed image of Amundsen Sea EmbaymentMotorway-sized troughs and channels carved into Antarctica's continental shelves by glaciers thousands of years ago could help scientists to predict future sea-level rise according to a report in the journal Geology this month (May).Using sonar technology from onboard ships, scientists from British Antarctic Survey (BAS) and the German Alfred Wegener Institute (AWI) captured the most extensive, continuous set of images of the seafloor around the Amundsen Sea embayment ever taken. This region is a major drain point of the West Antarctic Ice Sheet (WAIS) and considered by some scientists to be the most likely site for the initiation of major ice sheet collapse.The sonar images reveal an 'imprint' of the Antarctic ice sheet as it was at the end of the last ice age around 10 thousand years ago. The extent of ice covering the continent was much larger than it is today. The seabed troughs and channels that are now exposed provide new clues about the speed and flow of the ice sheet. They indicate that the controlling mechanisms that move ice towards the coast and into the sea are more complex than previously thought. Lead author Rob Larter from British Antarctic Survey said, "One of the greatest uncertainties for predicting future sea-level rise is Antarctica's likely contribution. It is very important for scientists and our society to understand fully how polar ice flows into the sea. Indeed, this issue was highlighted in 2007 by the Intergovernmental Panel on Climate Change (IPCC). Our research tells us more about how the ice sheet responded to warming at the end of the last ice age, and how processes at the ice sheet bed controlled its flow. This is a big step toward understanding of how the ice sheets are likely to respond to future warming.' Issued by British Antarctic Survey Press Office: British Antarctic Survey media contact: Linda Capper, Tel: +44 (0)1223 221 448; email: http://mail.niot.res.in/cgi-bin/openwebmail/openwebmail-send.pl?sessionid=prince*mail.niot.res.in-session-0.142247773241611&folder=INBOX&page=1&sort=date&keyword=&searchtype=subject&action=composemessage&message_id=%3Cgtq06q%2B5rf6%40eGroups.com%3E&compose_caller=read&to=LMCA%40bas.ac.uk; mobile 07714 233744Alfred Wegener Press Office contact: Margarete Pauls, Tel: +49(471) 4831-1180; email: http://mail.niot.res.in/cgi-bin/openwebmail/openwebmail-send.pl?sessionid=prince*mail.niot.res.in-session-0.142247773241611&folder=INBOX&page=1&sort=date&keyword=&searchtype=subject&action=composemessage&message_id=%3Cgtq06q%2B5rf6%40eGroups.com%3E&compose_caller=read&to=Margarete.Pauls%40awi.deJacqueline Martin, Tel: +49(471) 4831-1112; email: http://mail.niot.res.in/cgi-bin/openwebmail/openwebmail-send.pl?sessionid=prince*mail.niot.res.in-session-0.142247773241611&folder=INBOX&page=1&sort=date&keyword=&searchtype=subject&action=composemessage&message_id=%3Cgtq06q%2B5rf6%40eGroups.com%3E&compose_caller=read&to=Jacqueline.Martin%40awi.deInterview opportunities with BAS science contact: Dr Rob Larter, Tel: +44 (0)1223 221573; email http://mail.niot.res.in/cgi-bin/openwebmail/openwebmail-send.pl?sessionid=prince*mail.niot.res.in-session-0.142247773241611&folder=INBOX&page=1&sort=date&keyword=&searchtype=subject&action=composemessage&message_id=%3Cgtq06q%2B5rf6%40eGroups.com%3E&compose_caller=read&to=RDLA%40bas.ac.ukInterview opportunities with AWI science contact: Dr Karsten Gohl, Tel: +49(471)4831-1361; email: http://mail.niot.res.in/cgi-bin/openwebmail/openwebmail-send.pl?sessionid=prince*mail.niot.res.in-session-0.142247773241611&folder=INBOX&page=1&sort=date&keyword=&searchtype=subject&action=composemessage&message_id=%3Cgtq06q%2B5rf6%40eGroups.com%3E&compose_caller=read&to=Karsten.Gohl%40awi.deNotes for editors: Pictures: computer generated animation of the sea floor; stills and broadcast-quality footage of BAS ship RRS James Clark Ross in the Southern Ocean are available from the BAS Press OfficeBackground For the past 20 years scientists studying the Greenland and Antarctic ice sheets have used a range of technologies, including satellite images, ice-penetrating radar and other techniques to monitor the movement of ice as it flows from Antarctica's interior towards the coast.Science teams often work in remote and extreme locations to measure change in their attempts to understand their likely contribution to global sea-level rise. This work is the result of a collaboration between scientists onboard two research cruises in 2006 – Jan-Feb BAS ship RRS James Clark Ross; Feb-Mar onboard AWI ship RV Polarstern. Ship-borne research cruises provide crucial information about Antarctica's ice sheet and climate history. This data combined with that from other satellite and ground-based studies help provide answers to big environmental questions that are relevant to people all over the world.The area of the Amundsen Sea embayment surveyed was 9950 km2. This is equal to - •Nearly half the size of Wales (20,799 sq.km) •Nearly the size of Yorkshire (11,903 sq.km, since 1991) •Larger than Norfolk and Suffolk combined (9172 sq.km) In the western Amundsen Sea embayment three 17-39 km wide troughs extend seaward from the modern ice shelf front. This is roughly with width of the English Channel. Individual streamlined features carved into the seabed are about as wide as a motorway. Ice sheet The Antarctic ice sheet retreated to near its present limit around 10 thousand years ago. It is the layer of ice up to 5000 m thick covering the Antarctic continent. It is formed from snow falling in the interior of the Antarctic which compacts into ice. The ice sheet slowly moves towards the coast, eventually breaking away as icebergs which gradually melt into the sea. The ice sheet covering East Antarctica is very stable, because it lies on rock that is above sea level and is thought unlikely to collapse. The West Antarctic is less stable, because it sits on rock below sea level. Ice shelf An ice shelf is a thick (100-1000 m), floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are found in Antarctica, Greenland and Canada only. Glacier Just as rivers collect water and allow it to flow downhill a glacier is actually a "river" of ice. A glacier flows much more slowly than river. Rivers of ice within ice sheets account for most of the drainage into the oceans.Continental shelf The relatively shallow (generally up to 200 meters) seabed surrounding a continent where the depth gradually increases before it plunges into the deep ocean. Around Antarctica the continental shelf is up to 1600 m deep as a result of millions of years of glacial erosion. The deepest parts of the Antarctic continental shelf are near the present ice margin and depths generally decrease offshore.The Cambridge-based British Antarctic Survey (BAS) is a world leader in research into global environmental issues. With an annual budget of around £45 million, five Antarctic Research Stations, two Royal Research Ships and five aircraft, BAS undertakes an interdisciplinary research programme and plays an active and influential role in Antarctic affairs. BAS has joint research projects with over 40 UK universities and has more than 120 national and international collaborations. It is a component of the Natural Environment Research Council. More information about the work of the Survey can be found at: www.antarctica.ac.uk