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Title: The impact of rising sea levels on the Bahamas
Date: 02 March 2010
Source/Author: Bahama Pundit/Larry Smith
Category: International

 

 

Arguably, our most valuable national asset is the shoreline - the transition zone between land and sea that surrounds our islands. So we should all be acutely aware of what is happening to the coast that could affect our investments and quality of life.

Over the millennia, shorelines have advanced and retreated as sea levels rose or fell over a range of some 500 feet. The difference today is that there are now millions of people living on densely developed shorelines around the world, so even a relatively small change in sea level can have a big impact.

Sea levels have been rising since the end of the last ice age, about 10,000 years ago. Measurements from around the world show a rise of almost 20 centimeters since 1880 - about eight inches - and if this gradual pace continues, we can expect a rise of another foot above current sea level by the end of this century.

That's right in the middle of the range projected by the UN's Intergovernmental Panel on Climate Change (IPCC) in 2007. But unfortunately, the rise won't be constant. In fact, scientists say the rate of increase is accelerating as the world gets warmer, and they are not sure how long the ice sheets on land will survive.

In 2007 the IPCC did not factor melting ice sheets into their projections. Their report provided a conservative forecast for sea level rise from thermal expansion of the oceans and from the melting of mountain glaciers, but didn't assign numbers to the contribution from melting ice sheets because of the uncertainties involved.

In the last century, sea level rise was mostly due to thermal expansion (if you heat 50 gallons of water to 100 degrees Fahrenheit you will have roughly 51 gallons). But in recent years, scientists have determined that the Greenland ice sheet and the Arctic Ocean pack ice are rapidly falling apart. And the latest studies show that the West Antarctica ice sheet is also melting.

In fact, planners in Rhode Island and Miami-Dade County have concluded that a minimum of a three- to five-foot sea level rise should be anticipated by 2100. A California report assumes a possible 4.6-foot rise by 2100, while the Dutch assume a 2.5-foot rise by 2050 in the design of their tidal gates. In the Bahamas, a three-foot rise would affect 11 per cent of our land area, without taking account of storm surges. And the World Bank says this would lead to a 5 per cent loss in GDP. 

According to Dr Orrin Pilkey, professor emeritus at Duke University in North Carolina, "A number of studies examining recent ice sheet dynamics have suggested that an increase of seven feet or more is not only possible, but likely. Certainly, no one should be expecting less than a three-foot rise in sea level this century."

Pilkey is one of the world's leading coastal geologists, famous for his battles with the US Army Corps of Engineers. His recently published book, The Rising Sea, co-written with Rob Young, director of the Programme for the Study of Developed Shorelines, argues that without thoughtful planning, the economic and human consequences of sea level rise will be disastrous.

"Governments and coastal managers should assume the inevitability of a seven-foot rise in sea level," Pilkey says. "This number is not a prediction. But we believe that seven feet is the most prudent, conservative long-term planning guideline for coastal cities and communities, especially for the siting of major infrastructure."

He is convinced that the continued development of many low-lying coastal areas — including much of the US east coast — is foolhardy and irresponsible. In our region, Miami and New Orleans will be heavily impacted by sea level rise, and it is clear that we face hard and controversial choices, including abandoning storm-damaged property, changing where and how we build, and setting coastal management policies that make sense.

This theme was taken up recently by local coastal expert Neil Sealey during a public meeting at the Bahamas National Trust. Sealey is a former lecturer at the College of the Bahamas who has written several textbooks on regional geography. His talk focused on climate change and beach erosion in the Bahamas. 
 
"Sea level rise by itself won't destroy our beaches," he said. "They simply retreat and build up in a new position. The problem arises when something is done to the beach to stop it adjusting. And our low-lying land already floods during storms, so we don't have to wait for sea level rise to make the right decisions."

Apart from their commercial value (to tourism and fisheries), beaches and mangroves protect the coast from flooding and storm damage, so we should do everything possible to preserve them. But casuarinas, seawalls, roads and other structures along the shore promote erosion and should be removed wherever possible, Sealey said. 

"Seawalls scour beaches and eventually get undermined, so they have to be rebuilt at more cost," he said. "Beach replenishment is similarly costly and temporary. If we study the consequences of shoreline infrastructure, the clear lesson is - don't build along the shore. This is a critical problem for the Bahamas. We need to restore dunes and wetlands, create buffer zones along the coast, remove invasives and monitor developments as they proceed." 

He called for the Bahamas to set up a regime to govern shoreline conservation and development throughout the islands as Barbados did some 15 years ago. And the new Planning and Subdivision Bill that is expected to become law this summer does contain some protections along these lines. 

Specifically, it prohibits construction within "significant wildlife habitat, wetland, woodland or area of natural or scientific interest;  significant corridor, coastline or shoreline of the ocean or a lake; or significant natural corridor, feature or area." It also designates areas that should not be developed, for reasons of "flooding, erosion, subsidence, instability, conservation or other environmental considerations."

But in the Bahamas, the consequences of sea level rise extend far beyond the shore and are a complex problem, especially where infrastructure is concerned. 

For example, the Lynden Pindling airport now being redeveloped at great expense will flood as the water table rises in response to higher sea level. The College of the Bahamas in Oakes Field is barely a foot above sea level and already floods when it rains, so this will only get worse. In fact, experts say that inland inundation and salinisation will become huge issues because our groundwater is tidal and directly linked to sea level.

And of course, these forecasts do not take account of storm surges or other coastal effects. So they give only a partial picture of vulnerability. The message for decision makers is that sea level rise is real and will only get worse. 

The more pessimistic forecasts point out that melting of the West Antarctica ice sheet will raise sea level by 16 feet, while melting of the Greenland ice sheet will add another 20 feet. The question is, how long will it take for this to happen? If global warming continues unabated, scientists fear we could reach a tipping point that would lead to a rapid loss of ice.

The ramifications of a major sea level rise are massive. Agriculture will be disrupted, water supplies will turn salty, storms and flood waters will reach further inland, governments will be disrupted and millions of environmental refugees will be created. For example, 15 million people live at or below three feet elevation in Bangladesh alone.

But even if we ignore such catastrophic predictions, Bahamians will undoubtedly feel the effects of sea level rise in the next decades. According to Pilkey, (writing for an American audience) we should prohibit the construction of high-rises and major infrastructure in vulnerable areas. And we should seek to relocate damaged buildings and infrastructure away from these shorelines rather than rebuilding in the same place. 

You may not know it, but the Bahamas does have a national climate change policy which acknowledges our vulnerabilities (it was formulated in 2005 and is available on the BEST Commission website). But it seems that this recognition is only just beginning to percolate through the labyrinth of government - otherwise, why would we keep investing millions to rebuild seawalls around the country, among other contradictory practices.

Implementation of this policy rests heavily on the development of a national land use plan, something which is prescribed by the new Planning and Subdivision Bill. The policy calls for a coastal zone management authority; adaptation strategies for agriculture; promotion of energy efficiency, alternative fuels and green vehicles; updating building codes and planning guidelines; working with insurers on risk management; protecting freshwater resources; forests and other vital ecosystems; and educating the public. 

Interestingly, the policy makes some of the same points that Professor Pilkey makes—we should assess the feasibility of relocating vulnerable settlements and infrastructure and prevent future development in vulnerable areas.

Meanwhile, Philip Weech, of the BEST Commission, and Arthur Rolle, of the Met Office, are developing computer models to better understand the impacts we can expect from sea level rise and climate change.

http://www.bahamapundit.com/2010/03/the-impact-of-rising-sea-levels-on-the-bahamas.html

 

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