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"Warning" about
Global Warming

Science Mysteries


Global Warming Predictions - Main Menu


2. Global Warming & Rising Oceans

Quotations from an article by By Jeffrey Chanton

Rising Oceans

Global sea level rise is caused by two factors. One is the delivery of water to the ocean as land ice melts, such as mountain glaciers and polar icecaps. Current evidence of global warming includes the widespread retreat of glaciers on 5 continents. For example:

  • The ice cap on Mount Kilimanjaro may be gone in 20 years. About 1/3 of Kilimanjaro's ice field has disappeared in the last 12 years and 82% of it has vanished since it was first mapped in 1912.
  • Sea ice in the Arctic Ocean is thinning.
  • Massive Antarctic ice sheets have collapsed into the sea with alarming rapidity.

The second factor is the thermal expansion of water within the oceans. As the temperature of the waters in the oceans rises and the seas become less dense, they will spread, occupying more surface area on the planet. Increased temperature will accelerate the rate of sea level rise.

Since the end of the last ice age, 18,000 years ago, sea level has risen by over 120 meters.

  • Geological data suggests that global average sea level may have risen at an average rate of 0.1 to 0.2 mm/yr over the last 3000 years.
  • However, tide gauge data indicate that the global rate of sea level rise during the 20th century was 1 to 2 mm/yr.

Along relatively flat coastlines, such as those of the Atlantic, or coastlines bordering fertile, highly populated river deltas, a 1 mm rise in sea level causes a shoreline retreat of about 1.5 meters. We are already seeing evidence of shoreline retreat in the U.S.:

  • Along the marshy Gulf Coast of Florida, the effects of sea level rise can be observed in the number of dead cabbage palms at the seaward edge of the salt marsh.
  • Along the Atlantic Coast of the USA, erosion is narrowing beaches and washing out vacation houses. As sea level rises and coastal communities continue to grow and pump water from aquifers, salt water intrusion into groundwater will become a greater problem.

Low-lying Pacific island nations will be inundated or the rising sea level will invade their drinking water aquifers.

  • Tuvalu comprises nine coral atolls between Australia and Hawaii. Their highest point is 5 meters (15 feet) above seal level. As sea level has risen, Tuvalu has experienced lowland flooding. Saltwater intrusion is adversely affecting drinking water and food production. Tuvalu's leaders predict that the nation will be submerged in 50 years. In March 2002, the country's prime minister appealed to Australia and New Zealand to provide homes for his people if his country is washed away, but the plight of this nation is being ignored.
  • Other threatened island nations include the Cook Islands and the Marshall Islands. During the last decade, the island of Majuro (Marshall Islands) has lost up to 20 per cent of its beachfront.

In addition to island nations, low-lying coastal countries are threatened by rising sea level. A 1 meter rise in sea level would inundate half of Bangladesh's rice land. Bangladeshis would be forced to migrate by the millions. Other rice growing lowlands which would be flooded include those of Viet Nam, China, India and Thailand. Millions of climate refugees could be created by sea level rise in the Philippines, Indonesia and Egypt.

The 10 warmest years on record have been since 1983 and the 7 warmest years on record have been since 1990. If business continues as usual, our current rate of fossil fuel consumption indicates that the carbon dioxide content of the air will double by 2100.

  • This doubling will enhance the greenhouse effect and result in a 1 to 5 degree Centigrade increase in global temperature.
  • Land areas will warm more rapidly than the global average as the temperature of oceanic areas will be moderated by the heat capacity of water.
  • Warming will also be greatest at higher latitudes, for in the past, climate change has affected the earth's polar regions to the greatest extent.
  • Humidity effects, included in the heat index, will exacerbate warming effects.

 

Source: http://www.actionbioscience.org/environment/chanton.html

The effect of oceans rising up to 14m has been illustrated online by British software engineer Alex Tingle. He has used National Aeronautics and Space Administration data and Google Earth technology:

Impact of oceans rise by 14m on Florida, USA
Source: Google Earth http://flood.firetree.net/?ll=27.2839,-80.7275&z=10&m=14&t=1

It has been predicted that if global warming continues, the world's major ice shelves will melt by 2100, causing oceans to rise by between 7m and 14m.

In The Bulletin magazine, Dr Flannery says the Arctic ice cap has entered "a death spiral" that will see it melt away entirely in summer within the next five to 15 years.

He says if the Greenland ice sheet collapses, oceans will rise by about 6m. "And that could happen surprisingly quickly," he says. "The Larsen B ice shelf on the Antarctic Peninsula . . . had been stable for 12,000 years, yet it shattered to fragments over just a few weeks."

Flood Maps

---

Answers to Sea Level Rise Locked in Ice

Imagine the 48 states and maybe half of Mexico covered with ice and you have Antarctica. (Related: Understanding polar ice).It is a continent of about 5.4 million square miles, which makes it about one and a half times as large as the USA’s 48 contiguous states.

Ice, averaging 1.6 miles deep, covers 97.6 percent of Antarctica, giving it 90 percent of the world’s ice and 70 percent of all of the globe’s fresh water – in the form of ice. If all of this ice melted, sea levels around the world would rise by about 200 feet.

Fortunately, even the most drastic scientific scenarios for global warming don’t envision Antarctica warming enough to directly melt all of this ice for at least hundreds of years, if ever. In fact, one of the first effects of a warmer climate could be more snow for Antarctica, which would more than make up for melting ice. This would happen because warm air carries more water vapor to turn into snow.

Still, we can’t be sure all of Antarctica’s ice is going to stay frozen as the world’s climate warms, whether naturally or because of gasses humans are adding to the atmosphere.  While straightforward melting isn’t going to send water from Antarctica’s ice washing through the streets of New York City and London, nature may have other ways of putting water from some of the ice into the world’s oceans.

The weak spot could be the West Antarctic Ice Sheet. But even under the worst scenario with much likelihood of happening, ocean-front property owners won't have to worry about water from Antarctica any time soon.

Scores of scientists, technicians, and others are now living in tents and huts on that part of the ice, trying to determine just how much a threat it is to the world’s coastal areas. Antarctica’s "summer" from November into February is the research season on The Ice.

The Transantarctic Mountains separate the West Antarctic Ice Sheet from the much larger East Antarctic Ice Sheet. The West Antarctic sheet covers the part of Antarctica south of the Pacific Ocean inland to the mountains and contains about 11 percent of the ice that sits on the continent.

Water from a melted West Antarctic sheet could push global sea levels as much as 20 feet higher than they would otherwise be.  Scientists say the West Antarctic sheet is more likely to collapse than the large East Antarctic sheet because its bottom is mostly below sea level. East Antarctica’s ice is mostly grounded above sea level.

Ice moves slowly – a few feet a year - toward the edges of Antarctica much in the way pancake batter spreads out as you pour it on a griddle. Much of the West Antarctic sheet’s ice moves onto the Ross and Ronne ice shelves, which are floating on the ocean. These range from around 4,000 feet thick where they are connected to the ice sheet to around 600 feet thick at the ocean end. The Ross Ice Shelf stretches about 450 miles from the ice sheet to the ocean and is about 600 miles wide. The Ronne Ice Shelf is a little smaller.

If these shelves melted, as they could in a warmer world, ocean water would be able to lap directly at the bottom of the ice sheet, undermining it and allowing large chunks of ice to fall into the sea to melt.

The shelves could melt while the main ice sheet stays frozen solid because the are in warmer parts of Antarctica and because sea water eats at them from the bottom as well as the edges.

Many scientists feel the key to figuring out how likely the West Antarctic sheet is to collapse any time in the next 200 years lies in the rivers of ice called "ice streams." Instead of moving toward the sea like one huge glacier, West Antarctica’s ice moves in streams; rivers of ice running between banks of ice.

Jack Williams, USATODAY.com
McMURDO STATION, Antarctica, Jan. 19, 1999

 

Heat from the Earth below warms the bottom of the ice sheets to around 30 degrees Fahrenheit, enough to melt ice that’s under great pressure there.

Right now scientists aren’t sure whether the total amount of Antarctic ice is increasing or decreasing, but either way, it’s close to being in balance. Icebergs, sometimes huge icebergs, are always breaking off, or "calving" from, the ice shelves. At the same time, snow falling on Antarctica is replacing the ice that floats away in the icebergs.

Those who study the West Antarctic Ice Sheet have many opinions about what it’s likely to do. But, "one outcome that may be put aside for the moment, because no convincing model of it has been presented, is a sudden collapse that causes a level rise in the coming century," says Michael Oppenheimer of the Environmental Defense Fund.

Oppenheimer is not among the scientists working on The Ice, but wrote an article for the journal "Nature" last May summing up the state of West Antarctic Ice Sheet.
No matter what happens, he says, "it would take at least several hundred years for the ice to melt. It’s not something that’s going to happen overnight."

Rising water

About the worst scenario those who study the ice see is for a warmer climate to cause the Ross Ice Shelf to quickly grow thinner and disintegrate. Without it, the Ice Sheet begins collapsing and melting ice causes global sea levels to rise as much as 20 feet in 250 to 400 years.

Another possibility is that the ice sheet is inherently stable. Under this scenario, the over-the-ice streams slow down, which reduces the amount of ice going into the ocean. The extra snow falling on Antarctica from warmer air more than makes up for the melting ice and actually slows sea level rise.

Oppenheimer thinks the most likely scenario is for melting to gradually increase during the coming century with the Ross Ice Shelf finally gone in about 200 years. During this time the Antarctic contributes up to seven or so inches a century to global sea-level increase as warmer air continues adding more ice to Antarctica.

But, other effects including the expansion of ocean water as it warms up, increase sea levels by much more. With the Ross Ice Shelf gone, the West Antarctic Ice Sheet begins collapsing, which takes another 500 to 700 years. During this period, melting Antarctic ice adds around 20 to 50 inches a century to global sea levels.

This seems like a long time away. Why worry about it now?

"My son is six months old, Oppenheimer says. "Assuming he has children when he's 30, and his children live 75 to 80 years, my grandchildren will be here" when a melting of the West Antarctic Ice Sheet could begin affecting the world. "The grandchildren of people living today will be affected. We have an obligation to them."

(Originally published in 1999. Re-published in 2004 with minor editing)
Source:
http://www.usatoday.com/weather/resources/coldscience/aiceshet.htm


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