Sea Level Rise in Tahiti

Figure 1. The port in Pape'ete and surrounding landscape as seen from the Aremiti 2 ferry. (Credit: Emma Van Scoy)

Introduction
Rising sea levels are an imminent threat to island nations around the globe, especially small  islands in the Pacific. Even the largest of the French Polynesian islands, Tahiti, is under threat of losing coastline. The Intergovernmental Panel on Climate Change’s 5th Assessment Report published in 2013 describes the primary contributors to sea-level change as (1) the expansion of the ocean as it warms due to increased atmospheric temperatures, and (2) the transfer of water currently stored on land as ice, to the ocean[1]. Post-industrial anthropogenic input is currently contributing to increasing atmospheric temperatures. Toward the end of the last ice age, anthropogenic input was not a large factor in rising sea levels. Changes and rates of change in sea level also vary between global regions. In the case of the Pacific, global warming related processes such as shifting surface winds, expansion of warming ocean water, and the water volume increase due to melting glaciers can affect established ocean currents, which are responsible for variations in sea level between different regions. Tahiti is located at a considerable distance from major former ice sheets and is characterized by slow and regular land-subsidence rates[2].


The Bølling Warming occurred 14,600 years ago, and marked the end of the last ice age[3]. Since that time, ocean height has risen by 120 meters to its current level[4]. This increase has not been constant. Several sea level records suggest that the glacioeustatic rise following the Last Glacial Maximum (LGM) was characterized by brief periods of extremely rapid sea-level rise. Sea-level increase has been punctuated by rapid accelerations caused by massive freshwater outburst floods from the ice caps[5]. The exact chronology, origin and consequences of these ice-sheet melting episodes remain unclear. However, these short-term bursts of freshwater influx probably disturbed oceanic thermohaline circulation and global climate during the last deglaciation[6]. It is important to understand these past episodes of sea level rise in order to learn more about the potential collapse of large ice sheets in response to recent climate change.


Evidence of past changes in sea level in French Polynesia has been obtained from coral core samples gathered on reefs around Tahiti. The corals that build the reefs in the South Pacific act as natural archives that indicate sea level variations and previous climates. Sea-level rise over the last deglaciation can be reconstructed using U-Th dating from cores that were drilled from Tahitian coral reefs[7]. Coral is very sensitive to sea level change, so fossilized corals are excellent indicators of sea-level change over time, providing information dated back thousands of years[8]. Tahitian reefs are ideal models to reconstruct the deglacial sea level rise and short term events that occurred between the Last Glacial Maximum and the present day since Tahiti is far away from major ice sheets and can therefore provide an accurate average of sea levels across the globe[9]. Using data obtained from fossilized coral samples as well as geophysical simulations, Milne and his colleagues have identified the source of the most recent accelerated rise in sea levels, demonstrating that the Antarctic ice cap was responsible for up to 50% of these increases.


Local sea-level variations in French Polynesia are due to three phenomena that generally work to transform volcanic islands into atolls: erosion, sinking, and subsidence/drift[10]. Erosion is directly related to tropical rains and their intensity, as well as local vegetation cover, as it transports material from higher to lower altitudes through surface runoff and rivers. Sinking is a fast-occurring phenomena caused by the weight of the island which bends the seafloor during and after its formation, and therefore does not play a major role for extinct volcanoes[11]. Finally, subsidence is related to the cooling of the drifting plate, which increases the plate’s density, causing a slow sinking of the plate and any mass located on it at a rate of about 1 mm per year[12]. Subsidence has the greatest impact on high islands, like Tahiti.


The transition from a volcanic island to an atoll is considered relatively fast in geological timescales, taking only a few million years (1 mm of sinking per year causes a sinking of 1,000 m per million of years). It is estimated that Tahiti will be an atoll in about two million years (its highest elevation being 2,241 m) and will look like the Gambier Islands[13]. Today, the subsidence rate is estimated at 0.25 mm/year, and Tahiti consequently observes a relative sea-level rise independent of global trends, making the addition of global sea-level rise a greater concern. The net sea level rise rate is estimated at 2.51 mm/year (Figure 2), which would represent a 0.82 feet rise over the next hundred years.

Figure 2. Mean Sea Level Trend in Pape'ete, Tahiti[14].


Figure 3. Topography of Tahiti: A Landsat satellite image taken in 2001 showing the islands of Tahiti in true color[15].

Tahiti is a volcanic island that has ten mountain summits over 1,500 meters high, and three over 2,000 meters high. It is host to French Polynesia’s highest peak, Mont Orohena, which reaches 2,241 meters above sea level[16]. Because the mountain peaks are at a relatively high elevation, most of inland Tahiti will be safe from rising seas. However, as seen in Figure 3, a reasonable portion of the coastline is surrounded by a shallow lagoon, and the coasts and beaches along the outer edge of the island are vulnerable to sea-level rise[17]. Most of the city of Pape’ete lies between 0 to 600 inches above sea level[18]. The elevation gradient is gradual up until 600 inches (50 feet), and then the gradient increases rapidly[19]. However, the incline is not consistent due to the volcanic nature of the island. Currently, Tahiti has 120 miles (193 km) of coastline with a land area of 403 square feet (1,045 sq km)[20]. With such a limited amount of inhabitable land, sea level rise will have large impact along the coast of the island, as near-shore shallow lagoon depths will increase. The coastal bathymetry and topography of Tahiti are crucial to how the island will hold up against rising sea levels.


Strong tropical lows and cyclones are rare in French Polynesia since the waters in this area of the Pacific are relatively cold. Tahiti is currently most prone to experience cyclones from November to March, but the storm systems that form in the region usually pass south of the island[21]. There is an expected poleward expansion of the reach of storm tracks, however, which would likely contribute to a dampening of sea level rise in the mid to low latitudes. Considering this shift in weather patterns accompanying climate change, Tahiti is expected to experience fewer storms and perhaps decreasing effects of sea-level rise over time, though there is still a great deal of uncertainty in terms of future impacts[22].

 

Sea-level Rise and the Tourism Industry in French Polynesia

Since 1990, tourism has played an important role in the economy of French Polynesia, representing up to 78% of the country’s total income (Figure 4). In 2011, 162,776 tourists visited French Polynesia, staying an average of 14.1 nights (Figure 5) and spending a total of 39.5 billion XPF (459 million USD), which represents about 3.5 times the income originating from the exportation of local products. Around 2,700 companies related to tourism, such as hotels, restaurants, bars, and transportation services, employ an estimated 10,000 people out of the 267,000 inhabitants[23].


Figure 4. Evolution of the number of tourists in French Polynesia per year: 1996 to 2014. The number of tourists in French Polynesia has fluctuated by more than 100,000. The number currently stands at 164,393, about two thirds of its maximum, recorded in 2001, at about 258,000.[24]


Figure 5. Profit from tourism in French Polynesia from 1997 to 2011. More than 68% of French Polynesia’s total income has come from tourism since 1997, reaching a peak of 78% of the country's total income in 2009[25].

Figure 6. Tourism in French Polynesia in numbers. The number of tourists has steadily increased from 2010 to 2012. This increase paired with a minor decrease in the number of rooms has raised the bed occupancy to 57% in 2012, which should translate to an increase in the rooms’ owners’ net income. No significant change was recorded in the length of stay[26].

Out of all expenses, tourists spend the most, about 56% of their budget, on housing (Figure 7). Six out of ten tourists come to French Polynesia as part of a package tour and stay for an average of 8.9 days, compared to a stay of around 18.4 days for those who do not opt for a package tour. Despite a shorter stay, package tourists spend about 40% more than other tourists and make up for 71% of the total income in the tourism sector[27].

Tourism belongs to the employment sector that pays the highest wages, with an average of 316,600 XPF (3,672 USD) per month, followed by industry, at 290,000 XPF (3,370 USD). In comparison, construction pays 225,600 XPF (2,622 USD) and agriculture, 190,000 XPF (2,208 USD). The minimum wage in French Polynesia is currently 250,000 XPF (2,905 USD) for 169 work hours, which translates to an hourly wage of 885 XPF (10.25 USD)[28]; and 19.7% of the population was reported to have an income below the poverty line in 2009[29]. Since the majority of the total salary is concentrated in the tertiary sector, in which services related to tourism belong (Figure 8), tourism can be considered among the most important to the standard of living in French Polynesia.


Figure 7. Individual expenses by type of tourism. Tourists, regardless of their means of transport or travel plans, spend the majority of their money on lodging, four times more than any other expenses[30].

Figure 8. Distribution of the total salary between the primary, industry, construction and tertiary sectors. 84% of the total salary in French Polynesia comes from the tertiary sector, containing the majority of the services related to tourism[31].

Although the island of Tahiti is in no danger of immediate submersion, the effects of sea-level rise have the potential to greatly impact the local economy. The data discussed here provide a sense of the importance of the role that the tourism industry plays on the largest French Polynesian island containing the capital city, a major international airport, and roughly half of the total population[32].

With the coastal areas of the island drawing tourists with visions of a tropical paradise combined with the difficulty of building further inland, the large number of hotels and resorts along the coast will be the front line for future erosion and loss of shoreline to sea-level rise. The response of the tourism industry to these environmental challenges will be critical to the future economic stability of French Polynesia.

 

Field Interviews in French Polynesia

Residential insight into the sea level rise situation and the tourism industry was gathered through personal interviews conducted in Tahiti and Rangiroa. Considering the difficult nature of observing such gradual shifts in sea level, storm surge was used within the interviews as a representation of areas vulnerable to the effects of higher sea levels. The coast of Tahiti has a gradual coastline elevation gradient, and areas with shallow continental shelf slopes will allow a greater storm surge, which significantly raise the apparent local sea level for the duration of a storm[33].

In Pape'ete, Tahiti an employee of Ferry Aremiti, a ferry company providing transportation among various French Polynesian islands, was willing to discuss sea-level rise and the effects of storm surge[34]. She was aware of the sea level rise situation on a larger, regional scale but was not quite certain how these changes might impact Tahiti. As expected, she said long term changes were not noticeable, but she was also able to provide information on past storms. During the Ouni storm, Pape'ete was put on red alert and roads were flooded for a couple of days. Many boats headed out to sea for safety, and Aremiti was temporarily shut down with only one exception, which was to evacuate people from Moorea. The employee had heard that the storm destroyed over-water bungalows at hotels in Bora Bora, but she was not sure whether any bungalows in Tahiti were affected.

Figure 9. View of Aremiti Ferry terminal and Pape’ete waterfront from Aremiti 2. (Credit: Emma Van Scoy)

Further anecdotal information regarding the sea level situation in Tahiti was gathered through interviewing an employee of Tahiti Cruise and Vacation at their main office in Pape’ete[35]. She acknowledged that sea level rise was an issue but was not immediately concerned for Tahiti and was unsure of the time scale of the issue. She mentioned the same storm, Ouni, along with another named Oli, recalling that the sea level did flood the waterfront port area. Although Tahiti Cruise and Vacation was not directly affected since the company does not have a boat, the employee mentioned that Aremiti, whose offices are located within the same building, had to close temporarily. She was also able to speak about tourists and over-water bungalows, mentioning that the bungalows are very popular in Bora Bora but not as desired in Tahiti. One explanation was that many tourists coming to Tahiti only book one or two nights on the island, since many are from cruise ships and others wish to then travel to other islands during their trip.


Figure 10. Seawall on the shoreline of the MaiTai Hotel in Rangiroa, FP, built to protect the bungalows against increasing wave action and height during storms. (Credit: Julian Honma)

While the current sea level in Tahiti does not present a severe threat or require immediate action, other French Polynesian islands provide an opportunity to examine contrasting situations and potential adaptations. Rangiroa is the largest atoll in the Tuamotus, a group of islands to the northeast of Tahiti[36]. Given the low elevation and narrow width of the atoll (Figure 11), any short or long term change in sea level produces more visible results. A chance to speak with the director of the MaiTai Hotel in Tevaiohie shed light on the effects of sea level on tourism in Rangiroa[37]. The MaiTai is located directly on the lagoon, and the director was certainly aware and concerned about changes in sea level. She cited the topography of the island as one reason for concern, specifically mentioning the lack of mountains in contrast with Tahiti. Although she explained that the hotel’s location provided protection from tsunamis, a local concern, she did mention that indirect effects of such events increase the sea level temporarily.


Figure 11. Panoramic view of the width of Rangiroa near the MaiTai Hotel. The lagoon is to the right and the Pacific ocean is on the left. (Credit: Emma Van Scoy)

Given the concerns that come from having a waterfront business in an area with rising sea-levels and occasional storm surge, the hotel actually built a sea wall in 2013 to protect their waterfront, which includes bungalows, a pool, and a restaurant in close proximity to the water’s edge (Figure 10). Despite the precaution, the water level did rise above the wall in September 2013, leaving more than a foot of sand in the pool, damaging parts of the newly built wall, and destroying the lower part of the hotel’s wooden pier. She went on to say that during the most recent storm the water level rose more quickly, removing sand from the beach, destroying a small bridge, and reaching the front row of bungalows. The director had clearly been thinking about the reality of ongoing sea level concerns, and at one point she acknowledged that at some point the hotel will disappear. However, for the time being, she described the ways in which the hotel strives to reduce its impact on the surrounding environment. The MaiTai received the Earth Check Silver Award, in recognition of steps taken to preserve resources and involvement in social actions in the area, such as trash clean-ups. Additionally, although overwater bungalows frequently appeal to tourists, she made it clear that the lack of these structures at the MaiTai is a fully intentional decision. The hotel is committed to not building the bungalows due to the damage sustained by coral during construction.


Despite the differences between the current sea-level rise situations in Tahiti and Rangiroa, one common thread came through in almost all personal interviews. Multiple people mentioned feeling relatively uninformed about the current and expected changes in sea level. Although multiple sources mentioned that the government made information available, it was commonly expressed that personal knowledge was inadequate for a full understanding of the situation, even on islands where sea level rise is considered a more imminent concern.

 

Julian Honma, Boston College
Karissa Parker, Boston University
Emma Van Scoy, Warren Wilson College
2014

 

References

[1]  Intergovernmental Panel on Climate Change (IPCC). 2013. Climate Change 2013: The Physical Science Basis. Sea Level Change. Accessed 16 February 2014. http://www.ipcc.ch/

[2]  Camoin G.F., Iryu Y., McInroy D. and the Expedition 310 Project Team. 2005. The last deglacial sea level rise in the South Pacific: offshore drilling in Tahiti (French Polynesia). IODP Scientific Prospectus 310.

[3]  Deschamps, P., Durand, N., Bard, E., Hamelin, B., Camoin, G., Thomas, A., Henderson, G., Okuno, J., & Y. Yokoyama. 2012. Ice-Sheet Collapse and Sea-Level Rise at the Bølling Warming 14,600 Years Ago. Nature. 483: 559-564.

[4]  Deschamps et al., 2012.

[5]  Deschamps, P. 2012. "Exceptional rise in ancient sea levels revealed." Institut de Recherche pour le Développement (IRD). Science Daily. Accessed 21 February 2014. www.sciencedaily.com

[6]  Manabe, S. & R.J. Stouffer. 1995. Simulation of abrupt climate change induced by freshwater input to the North Atlantic Ocean. Nature. 378: 165–167.

[7]  Deschamps et al., 2012.

[8]  Milne, G. A., Gehrels, W. R., Hughes, C. W.& M.E. Tamisiea. 2009. Identifying the causes of sea-level change. Nature Geoscience. 2: 471–478.

[9]  Deschamps,. 2012.

[10]  L’État en Polynésie Française. “Environnement naturel”. 2013. Accessed 10 March 2014. http://www.polynesie-francaise.pref.gouv.fr/Presentation-de-la-PF/Geographie-Climat/Environnement-naturel

[11]  L’État en Polynésie Française, 2013.

[12]  L’État en Polynésie Française, 2013.

[13]  L’État en Polynésie Française, 2013.

[14]  Graph from Tides and Currents data gathered by NOAA.

[15]  Image captured by the Enhanced Thematic Mapper Plus on the Landsat 7 satellite.

[16]  Constantino, N and E. Leshner. 2011. “Tahiti: the Physical Environment.” Sustainability in Polynesian Island Cultures and Ecosystems Atlas. Accessed 15 February 2014. http://www.sea.edu/spice_atlas/tahiti_atlas/the_physical_environment_of_tahiti

[17]  Rosenjun, RJ. 2012. “Earth From Space: A Satellites View of Tahiti.” The Atlantic. Accessed 22 February 2014. http://www.theatlantic.com/technology/archive/2012/06/earth-from-space-a-satellites-view-of-tahiti/258908/

[18]  World Atlas. 2014. “Tahiti.” Accessed 23 February 2014. http://www.worldatlas.com/webimage/countrys/oceania/tahiti.htm

[19]  Global Flood Map: French Polynesia.

[20]  World Atlas, 2014.

[21]  L’État en Polynésie Française, 2013.

[22]  IPCC. 2013.

[23]  Institut de la Statistique de la Polynésie Française. 2013. “L’impact Économique du Tourisme International sur l’Économie Polynésienne.” Accessed 10 March 2014. http://www.ispf.pf/docs/default-source/publi-pf-bilans-et-etudes/PF_Etudes_02_2013_depense_touristique.pdf?sfvrsn=0

[24]  Institut de la Statistique de la Polynésie Française, 2013.

[25]  Institut de la Statistique de la Polynésie Française, 2013.

[26]  Institut de la Statistique de la Polynésie Française. 2013. “French Polynesia at a glance, 2013”. Accessed 10 March 2014. http://www.ispf.pf/

[27]  Institut de la Statistique de la Polynésie Française. 2013. “Les Dépenses Touristiques par But de Séjour en 2011. Accessed 10 March 2014. http://www.ispf.pf/docs/default-source/publi-pf-bilans-et-etudes/PF_Etudes_04_2013_depense_tourist_but_sejour.pdf?sfvrsn=0

[28]  Institut de la Statistique de la Polynésie Française. 2013. “Salaires et Revenus”. Accessed 10 March 2014. http://www.ispf.pf/themes/EmploiRevenus/Salairesetrevenus.aspx

[29]  Institut de la Statistique de la Polynésie Française. 2013. “Niveau de Vie (Pauvreté)”. Acessed 10 March 2014. http://www.ispf.pf/themes/EmploiRevenus/NiveauVie.aspx

[30]  Institut de la Statistique de la Polynésie Française, 2013.

[31]  Institut de la Statistique de la Polynésie Française, 2013.

[32]  CIA World Factbook. 2014. “French Polynesia.” Accessed 10 March 2014. https://www.cia.gov/library/publications/the-world-factbook/geos/fp.html

[33]  Masters, J. 2014. Characteristics of Storm Surges. Weather Underground. Accessed 09 March 2014. http://www.wunderground.com/hurricane/surge_characteristics.asp?MR=1

[34]  Teravaih’, D. 24 March 2014. Employee at Aremeti Ferry. Pape’ete, Tahiti. Personal Interview.

[35]  Shan-Koua, K. 24 March 2014. Employee at Tahitio Cruise and Vacation. Pape’ete, Tahiti. Personal Interview.

[36]  Brash, C. “Tuamotus.” Tahiti & French Polynesia. Lonely Planet Publications, 2006.

[37]  Mosnier, C. 29 March 2014. Director of MaiTai Hotel. Tevaichie, Rangiroa. Personal Interview.

 

How to cite this entry:
Julian Honma, Karissa Parker and Emma Van Scoy. 2014. "Sea Level Rise in Tahiti, French Polynesia." Atlas on Sustainability of Polynesian Island Cultures and Ecosystems. Sea Education Association, Woods Hole, MA. Web. [Date Accessed] <html>