Sea Level Rise and Small Islands

 As the earth warms, ice caps and glaciers melt, sea level rise is inevitable. Dr Anjani Ganase, marine scientist, wonders what is the monitoring and management plan for our islands’ coasts; urgently needed especially for low-lying communities around Tobago

Although the impact of sea level rise as a result of global warming is less obvious to us on island ecosystems in the tropics, temperature rises in the polar regions result in very visible changes to the landscape and environment. For years, we have seen images of the lone polar bear on an isolated iceberg adrift. More recently, images of waterfalls cascading off the glacial cliffs and huskies wading through ice melt on a balmy 22 degree day remind us that the changes are accelerating. Ninety percent of sea level rise recorded in the last 40 years resulted from a combination of melting glacial ice from the poles, rapidly melting ice sheets from Greenland (just under 2 million km² of it) plus the expansion of the oceanic bodies of water as they continue to warm and absorb heat from the atmosphere. The rate of sea level rise has nearly doubled in the last 17 years (1993 – 2010, 3.2mm/ year) of the last century  (1901 – 2010, 0.19 mm/ year) and the rate is expected to continue to increase unless we effectively curb carbon emissions (IPCC AR 5).  

Low lying coral cays along the Belize Barrier Reef are at risk of drowning with sea level rise. Photo by Anjani Ganase

Sea level rise is expected to displace over 500 million people around the world who live on the coasts. Animated maps have revealed the horrifying inundations of parts of major cities, including New York City, Miami, Amsterdam, Sydney and Mumbai with 2 – 4 degrees rise in global temperature. Yet, less discussed are the island nations around the world most vulnerable to sea level rise, precisely because as the ocean rises, there is nowhere to relocate. Island nations that are especially vulnerable are the low-lying coral atolls that are mere metres above sea level - Kiribati and the Maldives.  Before the end of the century, many of the islands will be unliveable, with some islands being completely inundated by rising waters. Governments of these countries need to make the hard decision to relocate their whole population to another country, where their home, culture and identity will be at risk of being subsumed.

Wave action at the natural pool in Aruba. Photo by Anjani Ganase

Trinidad and Tobago is among the 57 small island developing states that will be impacted by sea level rise, and while we are not the most vulnerable, we still have much to lose. Although many Caribbean islands like Trinidad and Tobago do not expect to experience such extreme impacts of sea-level rise, populations will be displaced, infrastructure and natural habitat will be damaged in the absence of proper planning and management of our coastal zones. Global forecast maps highlight areas such as Bon Accord, Port of Spain, Icacos and Mayaro as being most vulnerable to sea-level rise. While most future scenarios for sea-level rise predict a greater than 0.5-metre increase in the average global sea level change by 2100, there will be significant regional variations as a result of geography, ocean currents and even spatial variations in gravity that may exacerbate or lessen the impact of sea-level rise. These regional and more dynamic effects make it difficult to predict the impacts locally, and therefore real time observations of sea level trends are recommended along with a management plan.  

While a half metre rise may not appear to be much, just imagine the ocean as a bathtub being filled up; it becomes more damaging when you add the effects of the extreme tidal states and weather events. Imagine a storm event on a King tide, where storm surge waves off Buccoo easily pass over the top of the reef into the Lagoon to batter low-lying Bon Accord. Imagine extreme flooding in Port of Spain and southwest Tobago and Mayaro as the rain water has no where to run off because the sea water has already flooded the drainage system of downtown Port of Spain or the wetlands of Mayaro. For some of us, we don’t have to imagine, it is something that has been experienced. Remember the October 2018 flooding on the Caroni, affecting residents of Oropune and Green Vale.

Salt-water intrusion is one of the effects of sea level rise. As salt water penetrates further inland, it may change the condition of soils and agriculture, as it floods ground water and sewage systems. Think about southwest Tobago. Coastal erosion is likely to occur at some beaches and will put at risk any building and road infrastructure too close to the shoreline. Think about the beach erosion and the undermining of the road along Grange Bay. For Tobago, like many Caribbean islands that rely on their coastal and marine ecosystems and beaches to boost their economic sector through tourism, the impacts of sea-level rise will also have an economic impact if not addressed.

Fortunately, there are guidelines to manage sea level rise; proper management of the coastline with strict regulations is required. Ideally, we need to allow this dynamic zone between the sea and land to adapt naturally to oceanic changes as much as possible until the climate stabilises. Infrastructure ought to be set back from the shoreline; and a buffer zone must be established in low-lying areas to accommodate oceanic impacts. The equally important aspect of coastal zone management is the conservation of protective ecosystems, such as coral reefs and mangroves that buffer storm surge and encourage coastal accretion. These ecosystems work more effectively compared to hard engineering, such as sea walls that often fail in the long term and even cause erosion downstream. Complementary to this is the need to monitor local changes in sea level rise, and to develop strategies for adaptive management. 

 

Calm shores of Englishman’s Bay. Photo by Anjani Ganase

References:

Leatherman SP, Beller-Simms N. Sea-level rise and small island states: an overview. Journal of Coastal Research. 1997 Oct 1:1-6.

Church, J.A., P.U. Clark, A. Cazenave, J.M. Gregory, S. Jevrejeva, A. Levermann, M.A. Merri eld, G.A. Milne, R.S. Nerem, P.D. Nunn, A.J. Payne, W.T. Pfeffer, D. Stammer and A.S. Unnikrishnan, 2013: Sea Level Change. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.