Sea Level Rise

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The Netherlands is protected by more than 10,000 miles of dikes, dams, dunes, sluices, and floodgates capable of snapping shut and holding back the sea. It is estimated that without this protection 65 percent of the country would be submerged. Similar coastal defenses may become a universal need 50 to 100 years from now with the impending rise in sea levels.

Huge glaciers of Greenland, which hold enough ice to raise global sea levels by up to 21ft, are reported to be moving at an accelerating rate and dumping twice as much ice into the sea than five years ago. This can flood some of the world's major population centers, including all of Britain's city ports.

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9 to 88 cm Rise Predicted

Rise in sea levels is not only a threat to the smaller islands. More than 70 percent of the world's population lives on coastal plains, and 11 of the world's 15 largest cities are on the coast or estuaries. Sea levels rose between 10 and 20 centimeters (4-8 inches) over the 20th century. During the 21st Century the rise is predicted to be 9 to 88 cm. Even a small amount of rise in sea level is feared to have the following profound effects:

  • Coastal flooding and storm damage
  • eroding shorelines
  • salt water contamination of fresh water supplies
  • flooding of coastal wetlands and barrier islands
  • an increase in the salinity of water
  • will affect beaches, freshwater, fisheries, coral reefs and atolls, and wildlife habitat

28,700,000 Cubic Kilometers of Icecaps

The world’s icecaps and glaciers in various mountain regions of the world, including grounded ice in Antarctica and Greenland, total 28,700,000 cubic kilometers. In the last ice age the total ice volume was about 3 times greater and world sea levels about 120 meters lower. Global temperatures during that period were also 5 degrees C (9 degrees F) lower than today. This is because much of the ocean's water was tied up in glaciers.

Sea levels are rising because of all the greenhouse gasses we have emitted till date and what we are going to emit in future. Melting ice and thermal expansion of the oceans (water expands as it heats up) are expected to contribute equally to this rise.

Rise Patterns

According to climate models, satellite data and hydrographic observations, sea level rise around the world is not exactly uniform. While in some areas it has risen above the global mean rise, in other areas it has actually fallen.

‘Rise Preceded Carbon Dioxide Emission’

There are some studies which suggest that most of the cumulative sea level rise had taken place before the majority of carbon dioxide emissions.

It is pointed out that for the last 20, 000 years rise in sea levels have been the norm and not an exception. The average rate of sea level rise in this period was 60 centimeters per century. The sea level rise for the last 150 years has been constant while there has been a 100-fold rise in man-made carbon dioxide emissions over the same period. It is pointed out that most of the sea level rise had preceded the carbon dioxide emission period. Though available data is limited there are reports of a sea level rise of about 15 centimeters per century around the mid 1800s.

Another theory

Another section of scientists believes is that sea level rise will not be caused by massive Arctic or Antarctica ice melts but by a rise in sea temperature which increases the volume of sea water.

The Arctic region, with the exception of Greenland, comprises mostly floating polar ice in water. The melting of this ice cover would have no effect on the sea level because the ice is already displacing the water it is in. Antarctica, however, contains glaciers or land ice. If this region were to begin to melt, there would be a great increase in sea level because the water stored in these glaciers would then flow into the seas.

Consequences of Sea Level Rise

About one meter of land is lost with every centimeter rise in sea level. The consequences will be:

  • Many will die in extensive floods and efforts to evacuate huge numbers of people will spread diseases. Reduced availability of fresh water will further affect human health.
  • Changes in salinity or loss of ice cover are likely to cause the loss of important biological communities
  • Thousands of species of fish and wildlife which thrive in the coastal areas around the world will be threatened. These species are crucial for the regional economy, culture and quality of life.
  • Healthy coastal habitats, which protect us from the effects of hurricanes and flooding, are in danger because of potential sea level rise.
  • Salt marshes and mangroves, being closest to the sea level, are particularly in danger. Wetlands not only provide habitat for a number of species, but offer economic livelihood to a number of communities. Sea rise will erode the outer boundaries of these wetlands, and with the flooding of dry areas by higher water levels, new wetlands will form inland.
  • Measures are already been taken at the government and personal levels to protect property against the rising sea level. Some of these measures are likely to have adverse effects on the environment and on public use of beaches and waterways.

Cost of Holding Back the Sea: An Example

According to some estimates a one meter rise in sea level would inundate 14,000 square miles. This would cost the United States 270 to 475 billion dollars, excluding some unquantified and unforeseen expenditure. 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.

With continued development of other areas the cost could considerably go up. Coastal erosion is estimated to damage 1500 homes in the US each year for several decades, at a cost to property owners of US$530 million a year. Low lying areas will be the first to be affected, i.e. over the next 60 years. Some other estimates say that a 0.5m sea-level rise by 2100 could cause cumulative impacts to U.S. coastal property of US$20 billion to US$150 billion and that more extensive damage could result if climate change increases storm frequency or intensity.

REFERENCES:

  • Facts and figures on sea level rise
  • Sea level rise
  • Coastal Zones and Sea Level Rise
  • Potential Effects on Water Levels by Glacial Melting
  • Greenhouse Effect and Sea Level Rise
  • The Oceans