The Impact of Rising Sea Levels on the Bahamas

by Larry Smith

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.

Comments

[Glenn K]

Pilkey knows what he talking about. The last IPCC report was inaccurate and didn't include the Greenland or Antartic because of disagreements over the magnitude and the rate of melt in these areas. The world's media then reported that the IPCC had actually lowered it's sea level rise from the previous report in 2000. Of course nothing was further from the truth, all they had done was change the way they made their prediction. If you add back in possible melting from those areas the sea levels rise dramatically as Pilkey and others are now predicting.

[Nicolette Bethel]

Again, thanks Larry!

[Pieter Hale]

Have you come across any shaded elevation maps of New Providence?
Contour line maps are harder to read.
People probably would like to see one before they buy property that might be near or below sea level!

Also, I’m curious about how many islands will be formed within NP if sea level goes up a bit.

[larry smith]

check this out...

http://flood.firetree.net/

[Tim]

Scientific exploration requires critical skepticism.

Let me say first, I am an environmentalist. I believe doing all we can to preserve and protect our environment is essential to a healthy world.

I also am NOT a believer in Anthropogenic Global Warming (AGW), - NO I am not a holocaust denier, nor do I believe the world is flat - but I do believe in Climate Change. There is no observable evidence to confirm supposed consensus that man is responsible for any kind of warming trend, which for the past 12 years has actually been more of a cooling trend, nor can the suggested course of action of the 'Alarmists' effectively fix anything - at least not according to their own information.

Taking the example of the rise of sea levels, lets look at what other good scientists can tell us about it. Those not motivated to follow the dogma of AGW.

In sea level rise theories, the melting ice caps are the most signifcant role player. The Arctic cap loses ice in the summer, but no one bothers to mention that we only began collecting data on it in 1979, at the end of the second-coldest period in the Arctic in a century. The ice had to be abnormally expanded then.

it's also floating ice, and melting it and doesn't change sea level at all. And, for all the headlines about loss of ice in Greenland, which does contribute to rising sea levels, the mean temperature there was much higher from 1910 through 1940. Between then and the late 1990s, temperatures in southern Greenland — the region where ice is melting — declined sharply.

Around the world, in Antarctica, for the last few decades, average temperatures across the continent have been going down. Snowfall has increased, resulting in more continental ice. In fact, every modern computer simulation of 21st century climate has Antarctica continuing to accrete ice.

Also, While today's balance between the icecaps and global sea level has been relatively steady since about 1000 B.C., it would be careless to assume that this is the Earth's natural state and that it should always be this way. What could happen to climate naturally in the next few thousand years? If the Earth continued to warm and break from ice age conditions, some of the remaining ice caps could melt. On the other hand, climate might swing back into another ice age. (In fact, some of the environmentalists now worried about global warming were worried about another ice age in the 1960s and 1970s.)

In either case, such a change in climate would take thousands of years to accomplish. Note that it has taken 18,000 years to melt 60% of the ice from the last ice age. The remaining ice is almost entirely at the north and south poles and is isolated from warmer weather. To melt the ice of Greenland and Antarctica would take thousands of years under any realistic change in climate. In the case of the East Antarctic Ice Sheet, which accounts for 80% of the Earth's current ice, Sudgen argues that it existed for 14,000,000 years, through wide ranges in global climate. The IPCC 2001 report states "Thresholds for disintegration of the East Antarctic ice sheet by surface melting involve warmings above 20° C... In that case, the ice sheet would decay over a period of at least 10,000 years." The IPCC is the United Nations' scientific committee on climate change; its members tend to be the minority that predicts global warming and its statements tend to be exaggerated by administrators before release. Given that the IPCC tends to exaggerate the potential for sea level rise, it is clear that no scientists on either side of the scientific debate on global warming fear the melting of the bulk of Antarctica's ice. Consider also this abstract of an article by Jacobs contrasting scientific and popular understanding:

'A common public perception is that global warming will accelerate the melting of polar ice sheets, causing sea level to rise. A common scientific position is that the volume of grounded Antarctic ice is slowly growing, and will damp future sea-level rise. At present, studies supporting recent shrinkage or growth depend on limited measurements that are subject to high temporal and regional variability, and it is too early to say how the Antarctic ice sheet will behave in a warmer world.'

How much concern should we have about the 20% of world ice outside the East Antarctic Ice Sheet? Some sources have recently discussed the "possible collapse" of the West Antarctic Ice Sheet (WAIS). It is suggested that this sheet (about 10% of Antarctic ice) could melt in the "near term" (a usefully vague phrase) and raise sea level 5 to 6 meters. Current understanding is that the WAIS has been melting for the last 10,000 years, and that its current behavior is a function of past, not current climate. The abstract of an article by Alley and Whillans addresses this:

"The portion of the West Antarctic ice sheet that flows into the Ross Sea is thinning in some places and thickening in others. These changes are not caused by any current climatic change, but by the combination of a delayed response to the end of the last global glacial cycle and an internal instability. The near-future impact of the ice sheet on global sea level is largely due to processes internal to the movement of the ice sheet, and not so much to the threat of a possible greenhouse warming. Thus the near-term future of the ice sheet is already determined. However, too little of the ice sheet has been surveyed to predict its overall future behavior."

The suggestion that humans have the power to turn planetary warming into cooling is a scientific absurdity. We have neither the technology, the means, the money, nor the political will to do this.

Consider the Kyoto Protocol, a "baby step" in the fight against global warming. It "requires" the U.S. to reduce its emissions of carbon dioxide to seven percent below 1990 levels by 2008-2012. Requirements vary by a percent or so for most other signatories such as Canada and the EU nations. Yet if every nation of the world met its Kyoto targets, the amount of warming that would be prevented is .07 degrees Celsius per half-century — an amount too small to even measure, as average surface temperatures fluctuate by about twice that much from year to year.

And there is so much more science out there that goes against or is different than what the 'consesus' scientists argue. I believe we should mitigate to the highest degree possible our actual impact on the environment. Pollution and CO2 emissions are harmful, even if in some instances highly exaggerated. My point is don't simply trust one argument, or one theory just because someone has labelled it consensus, there is always another side, and if, as I stated at the start, there is no critical skepticism, the truth will not be known.

For more on 'Consensus Science' read this article by Michael Creighton:
http://www.crichton-official.com/speech-alienscauseglobalwarming.html

[larry smith]

http://www.pbs.org/wgbh/nova/extremeice/program.html

[Lil Tangerine]

Pieter Hale

flood.firetree.net/?ll=25.0554,-77.3956&z=5&m=14

Looks like about 10.