- Reference and quote from NASA originally appeared at http://icesat.gsfc.nasa.gov/docs/ICESat_Brochure.pdf, now deleted or moved.
The Greenland and Antarctic ice sheets are an average of 2.4 km (7900 ft) thick, cover 10 percent of the Earth’s land area, and contain 77 percent of the Earth’s fresh water (33 million km3 or 8 million mi3). The Antarctic ice sheet has 10 times more ice than Greenland because of its greater area and average ice thickness. If their collective stored water volume were released into the ocean, global sea level would rise by about 80 m (260 ft).
- Reference and quotes from Professors Andrew Shepherd Duncan Wingham originally appeared August 15, 2009, in an article by Valerie Elliot of the London Times at
http://www.timesonline.co.uk/tol/news/environment/article6797162.ece, titled “Giant glacier in Antarctic is melting four times faster than thought.”
One of Antarctica’s largest glaciers is thinning four times faster than thought ten years ago, it has been found.
Satellite records show that if the melting of the Pine Island Glacier in west Antarctica goes on accelerating at current rates, the main section will have disappeared in 100 years, 500 years sooner than previously thought.
The research showed that the ice surface is dropping at a rate of 16m a year.The faster melting affects 5,400sq km of the glacier, containing enough water to raise world sea levels by 3cm, said Professor Andrew Shepherd of the University of Leeds, a member of the research team. The glacier’s melting could also expose stationary ice behind it to warm seawater, and if that ice were to melt, it could raise sea levels by another 25cm. The research, led by Professor Duncan Wingham at University College London and published in Geophysical Research Letters, is based on satellite observations of the glacier over 15 years. Professor Shepherd said: “Being able to assemble a continuous record of measurements over the past 15 years has provided us with the remarkable ability to identify both subtle and dramatic changes in ice that were previously hidden. “Because the Pine Island Glacier contains enough ice to almost double the Intergovernmental Panel on Climate Change’s best estimate of 21st-century sea level rise, the manner in which the glacier will respond to the accelerated thinning is a matter of great concern.” Professor Shepherd said: “This is unprecedented in this area of Antarctica. We’ve known that it’s been out of balance for some time, but nothing in the natural world is lost at an accelerating exponential rate like this.”
- New Ice Island at Pine Island Glacier : Image of the Day. Published at EarthObservatory.NASA.gov.
The longest and fastest moving glacier in West Antarctica calved a new iceberg in July 2013. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument—built by Japan’s Ministry of Economy, Trade, and Industry for NASA’s Terra satellite—acquired this image of two widening cracks along an edge of the Pine Island Glacier (PIG) in Antarctica. To the west of the cracks—in the image, north is to the upper right—a new 720-square-kilometer (280-square-mile) ice island was formed.
- Ocean currents speed melting of Antarctic ice: A major glacier is undermined from below. Reported at ScienceDaily.com.
June 27, 2011 — Stronger ocean currents beneath West Antarctica’s Pine Island Glacier Ice Shelf are eroding the ice from below, speeding the melting of the glacier as a whole, according to a new study in Nature Geoscience. A growing cavity beneath the ice shelf has allowed more warm water to melt the ice, the researchers say — a process that feeds back into the ongoing rise in global sea levels. The glacier is currently sliding into the sea at a clip of four kilometers (2.5 miles) a year, while its ice shelf is melting at about 80 cubic kilometers a year — 50 percent faster than it was in the early 1990s — the paper estimates.”More warm water from the deep ocean is entering the cavity beneath the ice shelf, and it is warmest where the ice is thickest,” said study’s lead author, Stan Jacobs, an oceanographer at Columbia University’s Lamont-Doherty Earth Observatory.
In 2009, Jacobs and an international team of scientists sailed to the Amundsen Sea aboard the icebreaking ship Nathaniel B. Palmer to study the region’s thinning ice shelves — floating tongues of ice where landbound glaciers meet the sea. One goal was to study oceanic changes near the Pine Island Glacier Ice Shelf, which they had visited in an earlier expedition, in 1994. The researchers found that in 15 years, melting beneath the ice shelf had risen by about 50 percent. Although regional ocean temperatures had also warmed slightly, by 0.2 degrees C or so, that was not enough to account for the jump.
The local geology offered one explanation. On the same cruise, a group led by Adrian Jenkins, a researcher at British Antarctic Survey and study co-author, sent a robot submarine beneath the ice shelf, revealing an underwater ridge. The researchers surmised that the ridge had once slowed the glacier like a giant retaining wall. When the receding glacier detached from the ridge, sometime before the 1970s, the warm deep water gained access to deeper parts of the glacier. Over time, the inner cavity grew, more warm deep water flowed in, more melt water flowed out, and the ice thinned. With less friction between the ice shelf and seafloor, the landbound glacier behind it accelerated its slide into the sea. Other glaciers in the Amundsen region have also thinned or widened, including Thwaites Glacier and the much larger Getz Ice Shelf.
One day, near the southern edge of Pine Island Glacier Ice Shelf, the researchers directly observed the strength of the melting process as they watched frigid, seawater appear to boil on the surface like a kettle on the stove. To Jacobs, it suggested that deep water, buoyed by added fresh glacial melt, was rising to the surface in a process called upwelling. Jacobs had never witnessed upwelling first hand, but colleagues had described something similar in the fjords of Greenland, where summer runoff and melting glacier fronts can also drive buoyant plumes to the sea surface.
In recent decades, researchers have found evidence that Antarctica is getting windier, and this may also help explain the changes in ocean circulation. Stronger circumpolar winds would tend to push sea ice and surface water north, says Jacobs. That in turn, would allow more warm water from the deep ocean to upwell onto the Amundsen Sea’s continental shelf and into its ice shelf cavities.
Pine Island Glacier, among other ice streams in Antarctica, is being closely watched for its potential to redraw coastlines worldwide. Global sea levels are currently rising at about 3 millimeters (.12 inches) a year. By one estimate, the total collapse of Pine Island Glacier and its tributaries could raise sea level by 24 centimeters (9 inches).
The paper adds important and timely insights about oceanic changes in the region, says Eric Rignot, a professor at University of California at Irvine and a senior research scientist at NASA’s Jet Propulsion Laboratory. “The main reason the glaciers are thinning in this region, we think, is the presence of warm waters,” he said. “Warm waters did not get there because the ocean warmed up, but because of subtle changes in ocean circulation. Ocean circulation is key. This study reinforces this concept.”
The study received funding from the US National Science Foundation and the UK National Environment Research Council.
- Greenhouse Effect and Sea Level Rise.
Online summary of the Cost of Holding Back the Sea following a more conventional web format with link to pdf of other Reports that Deal With the Implications of Rising Sea Level and What We Can Do About It. Titus, J.G., R.A. Park, S.P. Leatherman, J.R. Weggel, M.S. Greene, P.W. Mausel, S. Brown, C. Gaunt. M. Trehan, and G. Yohe. 1991. Greenhouse Effect and Sea Level Rise: The Cost of Holding Back the Sea.” Coastal Management 19:171-210. This web page provides the final text as submitted to the journal in response to the peer review. Only minor editing changes were made in the published version.
The Cost of Holding Back the Sea
James G. Titus, Richard A. Park, Stephen P. Leatherman,
J. Richard Weggel, Michael S. Greene, Paul W. Mausel,
Scott Brown, Cary Gaunt, Manjit Trehan, and Gary Yohe
Previous studies suggest that the expected global warming from the greenhouse effect could raise sea level 50 to 200 centimeters (2 to 7 feet) in the next century or two. This article presents the first nationwide assessment of the primary impacts of such a rise on the United States: (1) the cost of protecting ocean resort communities by pumping sand onto beaches and gradually raising barrier islands in place; (2) the cost of protecting developed areas along sheltered waters through the use of levees (dikes) and bulkheads; and (3) the loss of coastal wetlands and undeveloped lowlands. The total cost for a one meter rise would be $270-475 billion, ignoring future development.
We estimate that if no measures are taken to hold back the sea, a one meter rise in sea level would inundate 14,000 square miles, with wet and dry land each accounting for about half the loss. The 1500 square kilometers (600-700 square miles) of densely developed coastal lowlands could be protected for approximately one to two thousand dollars per year for a typical coastal lot. Given high coastal property values, holding back the sea would probably be cost-effective.
The environmental consequences of doing so, however, may not be acceptable. Although the most common engineering solution for protecting the ocean coast–pumping sand–would allow us to keep our beaches, levees and bulkheads along sheltered waters would gradually eliminate most of the nation’s wetland shorelines. To ensure the long-term survival of coastal wetlands, federal and state environmental agencies should begin to lay the groundwork for a gradual abandonment of coastal lowlands as sea level rises.
SUMMARY AND CONCLUSIONS<
We estimate that shoreline retreat from a one meter rise in sea level would cost the United States 270 to 475 billion dollars. Like all cost estimates involving unprecedented activities, our estimates ignore the impacts we could not readily quantify and those we can not foresee, and hence, are almost certainly too low. But policymakers are accustomed to “soft” estimates, and we see no reason to believe that our underestimates are any worse than the norm.
Table 9 summarizes our calculations. Thirty six thousand square kilometers (fourteen thousand square miles) of land could be lost from a one meter rise, with wet and dry land each accounting for about half the loss. For a few hundred billion dollars, fifteen hundred square kilometers (six to seven hundred square miles) of currently developed land could be protected, but the loss of coastal wetlands would be that much greater.
At the national level, protecting developed coastal areas appears to be cost-effective. The cumulative figure would be spread over one hundred years; even at the end of the century, the annual cost of protection on barrier islands would be about $2,000 for a quarter-acre lot–hardly a welcome prospect for coastal property owners but nevertheless one well worth bearing in order to maintain the property. The cost of protecting developed mainland areas would be only about one-tenth as great.
The fact that it may be cost effective to protect property does not necessarily imply that it would be in the interest of society to do so. We must also consider the loss of natural shorelines and coastal wetlands that would result. Our results suggest that up to a point, the objectives of protecting wetlands and coastal property may be compatible. Abandoning developed areas would increase the area of surviving wetlands by only 5 to 10 percent–but at great cost. By contrast, limiting coastal protection to areas that are already densely developed (and allowing currently-undeveloped areas to flood) would increase the area of surviving coastal wetlands by 40 to 100 percent, depending on how much the sea rises.
However, estimates in areal losses understate the differences in environmental impacts for the various policy options. Although a substantial loss would occur even if developed areas were abandoned, most of today’s wetland shorelines would still have wetlands; the strip would simply be narrower. By contrast, protecting all mainland shorelines could result in wetlands being confined to a small number of isolated reserves, a situation that humanity has already imposed on many terrestrial species.
Our results are consistent with the hypothesis of a 1987 study by the National Academy of Engineering that shore protection will be cost-effective for most developed areas (Dean et al., 1987). From the perspective of civil engineers, that study concluded that little action is necessary today because shore protection structures can be erected rapidly compared with the rate of sea level rise. However, the speed with which communities could build these structures is small comfort to the birds and fish whose habitat would be destroyed by doing so.
Sea level rise is an urgent issue for coastal environmental planners for the very reason that it lacks urgency for directors of public works. If environmentalists do not lay the necessary groundwork today to institutionalize a gradual abandonment of the coastal plain as sea level rises, the public will almost certainly call upon engineers to protect their homes in the years to come.
- Quote from “NASA – Is Antarctica Melting?” by Erik Conway,
NASA/Jet Propulsion Laboratory, summarizes compelling evidence that ice in
Antarctica is melting.
… measurements from the Grace satellites confirm that Antarctica is losing mass 11. Isabella Velicogna of JPL and the University of California, Irvine, uses Grace data to weigh the Antarctic ice sheet from space. Her work shows that the ice sheet is not only losing mass, but it is losing mass at an accelerating rate. “The important message is that it is not a linear trend. A linear trend means you have the same mass loss every year. The fact that it’s above linear, this is the important idea, that ice loss is increasing with time,” she says. And she points out that it isn’t just the Grace data that show accelerating loss; the radar data do, too. “It isn’t just one type of measurement. It’s a series of independent measurements that are giving the same results, which makes it more robust.”