Consequences Of Polar ice Melting & Rising Sea levels
November 3, 2006 21 Comments
by : Abdul Azeem Khan
A big enough rise of global temperatures would eventually melt the world’s glaciers and ice caps, and indeed a retreat of mountain glaciers since the 19th century was apparent in some regions. That would release enough water to raise the sea level a bit. Worse, beginning in the 1960s, several glacier experts warned that part of the Antarctic ice sheet seemed unstable. If the huge mass slid into the ocean, the rise of sea level would wreak great harm, perhaps within the next century or two. While that seemed unlikely (although not impossible), by the 1980s scientists realized that global warming would probably raise sea level enough to damage populous coastal regions. Rising global temperatures make the sea warmer. As liquids warm they expand. This means that without any more water entering the sea, it is getting deeper. The second effect is that the increased temperature will make Antarctica start to melt. As the ice warms, it melts, putting more water into the sea. If all of Antarctica melts sea levels would rise by 55 meters, although it would take a very large temperature rise for this to happen.
ICE MELTING, GLOBAL SEA LEVELS AND FLOODS
Glaciologists, the scientists who study how ice behaves in seriously large quantities, have a special interest in floods. They even have their own word, jökulhlaup (from Icelandic), to describe the spectacular outbursts when water builds up behind a glacier and then breaks loose. An example was the 1922 jökulhlaup in Iceland. Some seven cubic kilometers of water, melted by a volcano under a glacier, had rushed out in a few days. Still grander, almost unimaginably grand, were floods that had swept across Oregon toward the end of the last ice age when a vast lake dammed behind a glacier broke loose. In the 1940s, after decades of arguing, geologists admitted that high ridges in the Oregon “scablands” were the equivalent of the little ripples one sees in mud on a streambed, magnified ten thousand times, shown in figure-1 below.
Figure-1 Plucking in the Scablands had similar effects, but on a far larger scale. This scoured channel is in Oregon, 150 meters above the Columbia River. The Columbia River filled its valley 150 meters deep and the overflow was still capable of doing this.
By the 1950s, glaciologists were accustomed to thinking about catastrophic regional floods. Also within their purview was flooding on a far grander, but much slower, scale. Since the heroic polar explorations of the late 19th century the world had known that great volumes of water are locked up in ice sheets. If there were substantial melting of the Greenland ice cap, and especially of the titanic volume of ice that buries Antarctica, the water released would raise the oceans in a tide that crept higher and higher for centuries. It had happened before — geologists identified beaches far above the present sea level, cut by waves in warmer periods when the Earth was entirely free of ice. In the last warm interglacial period, some 130,000 years ago, even though most of Antarctica had remained ice-covered, the sea level had been about six meters (20 feet) higher than at present. The next time that happened, sea water would swamp coastal regions where a good fraction of the world’s population now lived. All this became familiar to anyone who followed scientific discussions of global warming.1
Global sea level and the Earth’s climate are closely linked. The Earth’s climate has warmed about 1°C (1.8°F) during the last 100 years. As the climate has warmed following the end of a recent cold period known as the “Little Ice Age” in the 19th century, sea level has been rising about 1 to 2 millimeters per year due to the reduction in volume of ice caps, ice fields, and mountain glaciers in addition to the thermal expansion of ocean water. If present trends continue, including an increase in global temperatures caused by increased greenhouse-gas emissions, many of the world’s mountain glaciers will disappear. For example, at the current rate of melting, all glaciers will be gone from Glacier National Park, Montana, by the middle of the next century (figure. 2). In Iceland, about 11 percent of the island is covered by glaciers (mostly ice caps). If warming continues, Iceland’s glaciers will decrease by 40 percent by 2100 and virtually disappear by 2200.
Grinnell Glacier in Glacier National Park, Montana; photograph by Carl H. Key, USGS, in 1981. The glacier has been retreating rapidly since the early 1900’s. The arrows point to the former extent of the glacier in 1850, 1937, and 1968. Mountain glaciers are excellent monitors of climate change; the worldwide shrinkage of mountain glaciers is thought to be caused by a combination of a temperature increase from the Little Ice Age, which ended in the latter half of the 19th century, and increased greenhouse-gas emissions.
Most of the current global land ice mass is located in the Antarctic and Greenland ice sheets (table 1). Complete melting of these ice sheets could lead to a sea-level rise of about 80 meters, whereas melting of all other glaciers could lead to a sea-level rise of only one-half meter.
Climate-related sea-level changes of the last century are very minor compared with the large changes in sea level that occur as climate oscillates between the cold and warm intervals that are part of the Earth’s natural cycle of long-term climate change.
During cold-climate intervals, known as glacial epochs or ice ages, sea level falls because of a shift in the global hydrologic cycle: water is evaporated from the oceans and stored on the continents as large ice sheets and expanded ice caps, ice fields, and mountain glaciers. Global sea level was about 125 meters below today’s sea level at the last glacial maximum about 20,000 years ago (Fairbanks, 1989). As the climate warmed, sea level rose because the melting North American, Eurasian, South American, Greenland, and Antarctic ice sheets returned their stored water to the world’s oceans. During the warmest intervals, called interglacial epochs, sea level is at its highest. Today we are living in the most recent interglacial, an interval that started about 10,000 years ago and is called the Holocene Epoch by geologists.
Sea levels during several previous interglacial were about 3 to as much as 20 meters higher than current sea level. The evidence comes from two different but complementary types of studies. One line of evidence is provided by old shoreline features (figure. 3). Wave-cut terraces and beach deposits from regions as separate as the Caribbean and the North Slope of Alaska suggest higher sea levels during past interglacial times. A second line of evidence comes from sediments cored from below the existing Greenland and West Antarctic ice sheets. The fossils and chemical signals in the sediment cores indicate that both major ice sheets were greatly reduced from their current size or even completely melted one or more times in the recent geologic past. The precise timing and details of past sea-level history are still being debated, but there is clear evidence for past sea levels significantly higher than current sea level.
Figure-3. Wave-cut terraces on San Clemente Island, California. Nearly horizontal surfaces, separated by step-like cliffs, were created during former intervals of high sea level; the highest terrace represents the oldest sea-level high stand. Because San Clemente Island is slowly rising, terraces cut during an interglacial continue to rise with the island during the following glacial interval. When sea level rises during the next interglacial, a new wave-cut terrace is eroded below the previous interglacial terrace. Geologists can calculate the height of the former high sea levels by knowing the tectonic uplift rate of the island. Photograph by Dan Muhs, USGS.
If Earth’s climate continues to warm, then the volume of present-day ice sheets will decrease. Melting of the current Greenland ice sheet would result in a sea-level rise of about 6.5 meters; melting of the West Antarctic ice sheet would result in a sea-level rise of about 8 meters (table 1). The West Antarctic ice sheet is especially vulnerable, because much of it is grounded below sea level. Small changes in global sea level or a rise in ocean temperatures could cause a breakup of the two buttressing ice shelves). The resulting surge of the West Antarctic ice sheet would lead to a rapid rise in global sea level. Reduction of the West Antarctic and Greenland ice sheets similar to past reductions would cause sea level to rise 10 or more meters. A sea-level rise of 10 meters would flood about 25 percent of the U.S. population, with the major impact being mostly on the people and infrastructures in the Gulf and East Coast States (figure. 4). 2 World wide it will affect all the countries in the low lying areas like Bangladesh, Maldives and costal cities thought the world.
Figure- 4. Red shows areas along the Gulf Coast and East Coast of the United States that would be flooded by a 10-meter rise in sea level. Population figures for 1996 (U.S. Bureau of the Census, unpublished data, 1998) indicate that a 10-meter rise in sea level would flood approximately 25 percent of the Nation’s population.
ARTIC ICE MELTING
The Arctic is being severely affected by global warming, according to a scientific study released in 2004. The four-year-long study, known as the Arctic Climate Impact Assessment, was produced by the Arctic Council, consisting of the eight countries that ring the Arctic Ocean along with scientists and members of indigenous groups living in the Arctic. The study found that the average temperature in the Arctic rose nearly 1°C (2°F), almost twice the rate as the rest of the world, in the past few decades. The average winter temperature rose nearly 2°C (4°F), while parts of Russia and Alaska saw average winter temperatures rise 8°C (11°F) since the 1970s.
The study attributed the rising temperatures to increased emissions of carbon dioxide and other greenhouse gases, mainly due to the burning of fossil fuels throughout the world. The study found that as a result of the warming there was widespread melting of glaciers and sea ice and a shortening of the snow season. The report found that the average annual extent of sea ice in the Arctic had decreased by nearly 1 million sq km (386,000 sq mi) since 1974, an area nearly equal to that of Texas and New Mexico. The melting was expected to worsen global warming by increasing the amount of dark land that absorbs Sunlight thus warms the planet. (Figure-5)
The study warned that a number of problems could result from the increased warming. Glacial and snow melt and increased river runoff would add more freshwater to the oceans, potentially affecting ocean circulation such as the Gulf Stream, which is principally responsible for Europe’s moderate weather (see Ocean and Oceanography). Reductions in the amount of sea ice were also expected to shrink habitat for polar bears, seals, some seabirds, and other species, while climate change could also affect food sources, migratory routes, and breeding grounds for caribou and reindeer herds.
The Arctic warming could have mixed results for mining, petroleum extraction, and other industries. On the one hand, the warming could open sea lanes year-round so that ships could transport more natural resources, and less sea ice could enable petroleum companies to increase offshore drilling for oil. On the other hand, the melting of the permafrost could damage roads, pipelines, and other facilities built to extract and transport natural resources.
Finally, the report warned of increased health problems, such as cancer and cataracts, for the Arctic’s human population, due to increased exposure to ultraviolet radiation from the Sun. Increased exposure is expected as a result of the depletion of the ozone layer in the stratosphere, the upper atmosphere, caused by global warming. Although global warming causes temperatures to rise in the troposphere, the lower atmosphere, it has the reverse effect on the stratosphere, causing lower temperatures and an increase in atmospheric ice crystals. Ozone molecules, which absorb harmful ultraviolet radiation, adhere to the surface of these ice crystals, creating an ozone hole that allows ultraviolet radiation to reach the surface of the Earth. 3
Figure-5 ARTIC ICE LOSS 2003-1979 COMAPRISON
ANTARTIC ICE MELTING
The largest remaining piece of one of the largest icebergs ever observed began to crumble on October 28, 2005, after running aground off Antarctica’s Cape Adare(figure-6). The B-15A iceberg is the main body of the B-15 iceberg, which broke from the Ross Ice Shelf in March 2000. When it first formed, the massive berg measured 270 kilometers long by 40 kilometers wide (170 by 25 miles), making it about the size of the state of Connecticut. By November 5, 2005, the berg had dwindled to a still respectable 110 by 20 kilometers (70 by 13 miles).This is not the first time that B-15A has shed pieces. Several pieces broke off between 2000 and 2005; but unlike previous events, the iceberg broke in several locations in October 2005. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua and Terra satellites captured the iceberg’s break-up in the above series of images. On October 27, there was no sign, no faint cracks or lines, that indicated that the iceberg was under stress. But a few hours later, MODIS captured the upper right image, showing that two slivers (the largest of which merited its own name, B-15M) had broken from the berg. By November 1, the lower left half of B-15A had broken away to form B-15N, and several smaller pieces had been chiseled off both sides of B-15A.The currents that pulled the iceberg apart tugged B-15A around Cape Adare, leaving its daughter bergs behind. On November 4, the shrinking berg was moving out of the Ross Sea on the East Wind Drift, an ocean surface current that circles Antarctica counterclockwise. The iceberg’s departure was, no doubt, a relief to denizens of the Ross Sea region. From 2000 to 2003, the iceberg lurked off Ross Island, the location of the U.S. Antarctic Program’s McMurdo Research Station 4
Many scientists finds a substantial risk that warming from projected emissions of greenhouse gases during the next 100 years will cause the gradual disintegration of the West Antarctic Ice Sheet (WAIS), which would remake coastlines everywhere. In the most likely scenario the loss of land-based ice into the ocean would occur over the next five to seven centuries, but could become inevitable in as little as 100 years.
The complete collapse of WAIS would cause sea level to rise rapidly, at ten times the rate of the recent past. Eventually, all of South Florida and more than a quarter of Louisiana would be permanently submerged, as would significant portions of all coastal cities including 15% of Washington DC. In Florida, Louisiana, South Carolina, Virginia, New York, and New Jersey, areas where about ten percent or more of the current population live would be permanently lost, according to a previous report of the National Academy of Sciences.
In low-lying countries like Bangladesh land loss would be much higher. “The good news is that collapse of WAIS is not imminent, but the bad news is that warming gases emitted during the next century could make collapse of WAIS inevitable thereafter. Society simply cannot afford to ignore long term consequences and take such a high-risk roll of the dice”, said Dr. Michael Oppenheimer, author of the peer-reviewed article and an atmospheric physicist with the Environmental Defense Fund (EDF). “Once the ice sheet begins to disintegrate, there will be no turning back”.
WAIS is composed of ice streams, vast rivers of land-based ice that end at floating ice shelves. Opinions vary on the degree to which the ice shelves impede the movement of WAIS toward the ocean. Ocean warming of only a few degrees, which is expected to occur in the next hundred years, could cause one or more of the floating ice shelves surrounding West Antarctica to thin and eventually disintegrate. Since ice shelves float, their disintegration does not increase sea level. But if the flow of WAIS into the ocean increased as a result, global sea level would rise. Rapid collapse of smaller ice shelves along the Antarctic Peninsula in recent years raises the possibility that WAIS’ ice shelves may be quick to disintegrate once they have been thinned by warming.
Other but less likely scenarios including:
1) The continued melting of some of the floating ice shelves accompanied by an increase of the land-based ice due to additional precipitation;
2) The very fast collapse of WAIS with duration of as little as 250 years. The article largely rules out a catastrophic collapse within less than a century.
Several other recent findings add to concerns regarding the stability of WAIS: WAIS, as well as the entire Antarctic Ice Sheet, may already be losing ice and could be a contributing factor to the four to ten inches of sea-level rise that has occurred in the last hundred years.
WAIS may be inherently unstable and primed for collapse by climate changes of the distant past, according to a recent model of the ice sheet. Global warming could accelerate this process. It has been suggested that WAIS disappeared entirely at least once during a previous epoch when Earth was a few degrees warmer than today.
Considerable melting is already occurring on the undersides of some of WAIS’ ice shelves due to contact with the ocean, as indicated by recent measurements. An ocean warming of only a few degrees could cause these ice shelves to thin significantly. In contrast, some earlier studies suggested WAIS’ large ice shelves would remain intact until an atmospheric warming of 15 degrees Fahrenheit had occurred.
Significant warming of the deep ocean around Antarctica is likely to occur during the next century if Earth warms about 4 degrees Fahrenheit, rather than taking several centuries as some have thought. Warmer waters in the deep ocean around Antarctica would lead to increased melting under some of the floating ice, particularly in the vicinity of Pine Island Bay in the southeast Pacific sector of WAIS.(figure-7)
At other locations, unpredictable changes in ocean circulation may increase or decrease melting. “Reductions of greenhouse gases must begin now to insure our planet’s future. The potential for unprecedented loss of coastal regions should move policy makers to take swift and responsible action against global warming”, said Dr. Oppenheimer. “In addition, it is imperative that governments increase support for research to reduce uncertainty over the response of WAIS to global warming”. 5
Figure-7 The Antarctic Peninsula is the northernmost extension of Antarctica, reaching beyond the Antarctic Circle toward South America. Shown here are Adélie penguins, which live much of their lives on the pack ice or in the waters adjoining the peninsula, returning to the land to breed.
Scientists from the British Antarctic Survey (Bas) say the rise in sea levels around the world caused by the melting may have been under-estimated. It is thought that over 13,000 sq km of sea ice in the Antarctic Peninsula has been lost over the last 50 years.
The findings were announced at a Climate Change Conference in Exeter. Professor Chris Rapley, director of (Bas), told the conference that Antarctica could become a “giant awakened”, contributing heavily to rising sea levels. Melting in the Antarctic Peninsula removes sea ice that once held back the movement of glaciers. As a result, glaciers flow into the ocean up to six times faster than before.
The other region in the continent affected by the changes is West Antarctica, where warmer sea water is thought to be eroding the ice from underneath. In 2001, the Intergovernmental Panel on Climate Change (IPCC) predicted the average global sea level would rise by between 11cm (4.3in) and 77cm (30.3in) by 2100 – but forecast that Antarctic’s contribution would be small. Over the past five years, studies have found that melting Antarctic ice caps contribute at least 15% to the current global sea level rise of 2mm (0.08in) a year.
It is not known whether the melting is the result of a natural event or the result of global warming.
Professor Rapley said that if this was natural variability, it might be expected to be taking place in only a handful of places. However, studies had shown that it was happening in all three major ice streams in West Antarctica, he added. Several major sections of Antarctic ice have broken off in the past decade. 6
Recent Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery analyzed at the University of Colorado’s National Snow and Ice Data Center revealed that the northern section of the Larsen B ice shelf, a large floating ice mass on the eastern side of the Antarctic Peninsula, has shattered and separated from the continent. The shattered ice formed a plume of thousands of icebergs adrift in the Weddell Sea. A total of about 3,250 km2 of shelf area disintegrated in a 35-day period beginning on 31 January 2002. Over the last five years, the shelf has lost a total of 5,700 km2, and is now about 40 percent the size of its previous minimum stable extent.
Ice shelves are thick plates of ice, fed by glaciers, that float on the ocean around much of Antarctica. The Larsen B shelf (figure 8,9) was about 220 m thick. Based on studies of ice flow and sediment thickness beneath the ice shelf, scientists believe that it existed for at least 400 years prior to this event, and likely existed since the end of the last major glaciation 12,000 years ago .
For reference, the area lost in this most recent event dwarfs Rhode Island (2717 km2) in size. In terms of volume, the amount of ice released in this short time is 720 billion tons, enough ice for about 12 trillion 10 kg bags.
This is the largest single event in a series of retreats by ice shelves in the Peninsula over the last 30 years. The retreats are attributed to a strong climate warming in the region. The rate of warming is approximately 0.5 degrees Celsius per decade, and the trend has been present since at least the late 1940s. Overall in the Peninsula, extent of seven ice shelves has declined by a total of about 13,500 km2 since 1974. This value excludes areas that would be expected to calve under stable conditions.7
Figure-8 View to the broken ice shelf south of the Seal Nunataks. Photo courtesy of Pedro Skvarca, Instituto Antártico Argentino, 13 March 2002.
Figure -9 Mapping the new ice front line towards Cape Foyn. Photo courtesy of S. Tojeiro, Fuerza Aerea Argentina, 13 March 2002.
ARTIC RESEARCH OF UNITED STATES:
The following discussion is drawn in part from the Science Plan for the Study of Environmental Arctic Change (SEARCH) program, a
research program sponsored by the Interagency Arctic Research Policy Committee. The Science Plan was prepared by the former SEARCH Project Office,
Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle. In addition to U.S. SEARCH efforts, the International Study of Arctic Change (ISAC)—the international umbrella for SEARCH—has led to first discussions of coordination of research on environmental change in the Arctic among many interested nations. Observed changes in the atmosphere, in the oceans, and on land in the Arctic are affecting virtually every part of the Arctic and now have potential impacts, both direct and indirect, on human society. These changes include a decline in sea-level atmospheric pressure. Other observed environmental changes include:
• Reduced sea ice extent [3% per decade (Parkinson et al. 1999)] and thickness [–42% in the last 25 years (Rothrock et al. 1999)].
• Shift in the balance between Atlantic and Pacific waters and changes in salinity and temperature (e.g. Morison et al. 2000). The revealing changes in upper ocean temperatures and salinities are five times the RMS variability in the 1970s and exceed extreme values measured in the corresponding locations
in the previous 50 years (EWG 1997, Steele and Boyd 1998).
• Sea level rise in the Russian Arctic. There are 2- to 20-cm increases in sea level in the Russian marginal seas over a 50-year period, with interannual variations on the same order (Pavlov 2001). Proshutinsky et al. (2001) argue that this is driven by changes in atmospheric forcing of the barotropic circulation.
• Permafrost warming (0.5°C) and thawing in the intermittent permafrost region of Alaska (Osterkamp and Romanovsky 1999) and warming and thawing of permafrost in the Russian Arctic (Pavlov 1994) since the late 1980s.
• Decreasing permafrost temperatures in eastern Canada (Wang and Allard 1995).
• Below-average Northern Hemisphere snow cover in recent years by reductions in spring snow cover since the mid-1980s (Robinson et al. 1993, 1995).
• Decreasing mass of small Arctic glaciers (Dyurgerov and Meier 1997, Dowdeswell et al. 1997).
• Drying trend, increased forest fires (Oechel and Vourlitis 1996, Stocks 1991), and southern pest infestations in Alaska.
• Long-term increase in river runoff (Petersen et al. 2003).
• Large increase in Bering Sea jellyfish populations.According to Brodeur et al. (1999) the biomass of large jellyfish in the Bering Sea has soared in the 1990s.
• Whale migrations shifting with decreased ice extent (Tynan and DeMaster 1997, Treacy 1998).
• Increase in Barents Sea cod size with temperature increases (Bogstad and Gjosaeter 1994,Brander 1994). 8
Polar Ice melting has also a very immense effect on circulations of ocean currents movements. As more and more fresh water is poured into the warmer seas the circulation patterns of ocean currents are in danger which in turn can have fare reaching effects on our earths climate and temperature patterns. 9
Also the vast population of penguins, polar bears, seagulls and other species living in the Polar Regions (figure-10) are also endangered as retreat of the ice shelves is making life more and more difficult for these animals which has resulted in major decrease in their population in the last few years. More recently in 2004, the Ice berg B-15A began to drift north, trapping sea ice in McMurdo Sound. The excess sea ice stranded penguins, which could not reach open water and return with food for their young. 10
Rising sea level would allow saltwater to penetrate farther inland and upstream. The resulting saltwater intrusion could harm aquatic plants and animals, as well as threaten human water supply (IPCC 1998). Salinity has been found to decrease seed germination in a variety of wetland species and to decrease recruitment of seed bank species (Baldwin et al 1996). Already, higher estuarine salinity has been cited as a cause of declining oyster harvests in Chesapeake and Delaware Bays, and as a cause of wetland loss in Louisiana, Florida, and Maryland, and in Louisiana, cypress swamps are becoming open lakes due to increasing salinity (IPCC 1998). Increasing salinity could cause an advance of marine species and a retreat of freshwater species in remaining fresh water reservoirs
Figure-10 There are more Adelie penguins than any other penguin species. They live in the Deep South and as such frequently have to cross many kilometers of ice still bound to the continent or islands to reach land in the spring where they can build their nests
Global Climate is an extremely fragile phenomenon. Nature has kept it in a perfect balance for thousands of years which has enabled this planet to sustain intelligent life form, but recent emissions of toxic gases and other environmental degradation done by anthropogenic activities is effecting this balance which could have disastrous consequences. Polar Ice caps hold most of the water available on the planet frozen, but if this water melts then it will be a disaster for every one, animals and humans alike. Sea level rise due to melting will spell destruction for everyone living in costal areas worldwide. If temperatures climbed a few degrees, as most climate scientists now considered likely, the sea level would rise simply because water expands when heated. This is almost the only thing about global change that can be calculated directly from basic physics. The additional effects of glacier melting are highly uncertain. The rough best guess for the total rise in the 21st century was perhaps half a meter. While such a rise will not be a world disaster, by the late 21st century it will bring significant everyday problems, and occasional storm-surge catastrophes, to populous coastal areas from New Orleans to Bangladesh. More likely than not, low-lying areas where tens of millions of people live will be obliterated. Entire island nations are at risk. Then it will get worse. Even if humanity controls greenhouse emissions enough to halt global warming, the heat already in the air will work its way gradually deeper into the oceans, so the tides will continue to creep higher, century after century. So every possible effort must be done and every possible step must be taken to stop global warming and reduce the anthropogenic activities that are effecting our environment.
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2. Sea Level and Climate,
3. Microsoft Encarta 2006.
5. Nature Reports Possible Sea Level Rise of 13 to 20 Feet Due to Climate Change, http://healthandenergy.com/sea_level_rising.htm
6. Antarctic’s ice melting faster,
7. Larsen B Ice Shelf Collapses in Antarctica, http://nsidc.org/iceshelves/larsenb2002/index.html
8. VOLUME-19 “Artic Research Of United States” FALL/WINTER 2005
9. Ocean Currents and Climate,
10. NASA Satellite imagery of B-15A glacier,
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