The importance of considering the pressures of climate change and ocean acidification in a broader context of anthropogenic pressures. The aim is to show how future threats initially take root in the current issues of “unsustainable development”, that is to say, non-viable development, illustrated in particular by the strong deterioration of coastal ecosystems and uncontrolled urbanization. In this case, climate change and ocean acidification play the role in the acceleration of pressure on the living conditions of insular communities.
The case of the coral archipelago of Kiribati (Central Pacific) illustrates this point. Focus is put on the effects of climate change only, since the effects of ocean acidification are for the moment too complex to determine in the specific case of Kiribati. A brief assessment of the natural constraints and socio-economic changes of the last two centuries can explain what pressures the country is currently facing, and in what manner climate change will amplify them. With the questionable future of these areas and island populations, this demonstrates the major importance of overlapping the physical (climatic and chemical processes, ecosystems, etc.) and human dimensions (cultural relationship to resources and risk, development patterns, etc.) in order to understand these systems in their geographical and historical complexity. In other words, their vulnerability to future environmental changes not only depends on the evolution of the climate/ocean relationship. This basic reasoning is a fundamental step towards understanding vulnerability in all its dimensions, but also to imagine strategies of adaptation that can be locally relevant, consistent and realistic in their implementation.
Like Tuvalu and the Maldives, Kiribati mainly comprises atolls whose evolution depends on the responses of corals to changes in weather and sea conditions. Its exclusive economic zone (EEZ) is vast(3.5 million km²) and contrasts with the modesty of its land area (726km²), which is also fragmented into a large number of islands. On an atoll, the dominant element is the lagoon, enclosed by a ring of reef islands that are generally less than 1km² in area. They are also not inhabitable on their entire surface due to the presence of mudflats and mangrove swamps, to the strong instability of their coastlines and to very low altitudes in some parts. Summits mainly culminate around 3 to 4m, so the risk of submersion remains very high. As they are young (between 2000 and 4000 years), made of sand and coral debris and exposed to marine process., their soils are poor and vegetal resources weakly diversified. Water is scarce, brackish (2-3g salt/L) and very sensitive to climatic fluctuations. Water comes from rainfall that infiltrates to form a shallow groundwater lens (from 1 to 2m) proportional in size to the islands. In the southern atolls of Kiribati, the presence of water becomes uncertain during droughts related to El Niño episodes, which can last up to 2 years.
At a human level, three thousand years of history have shaped a territorial organization based on a dual strategy: to ensure that each family has access to a (low) diversity of land and marine resources, and to rationally manage these resources. The delimitation of the islands into transversal strips connecting the lagoon to the ocean allowed each family to exploit the different environments. The habitation was generally located at a distance of 20 to 60 meters from the lagoon coast, sheltered from swell. In the interior, coconut and pandanus trees (wood, palms and fruit) were grown and in very low areas, taro could be found. Families also used to share the operation of fish traps on the ocean side and fish ponds in the sheltered areas. They additionally used to collect shellfish on the foreshore of the muddy lagoon. Island communities made food and coconut provision in anticipation of harsh weather conditions. This system supported an access of the population to a diversified diet and attenuated food crises related to fluctuations in the different resources. Nowadays this ancestral approach is hardly used anymore, especially in the most populated urbanized islands(e.g., the South Tarawa Urban District).
Within less than two centuries, Kiribati has experienced five major transformations:
1. The regrouping of habitations into villages in the rural atolls and into urban areas in Tarawa Atoll.
2. The concentration of political power in the capital of the Tarawa atoll, abandoning the self-management system specific to each atoll.
3. The replacement of a rich and complex traditional law by simplistic written law.
4. The replacement of a subsistence economy by a market economy.
5. the disintegration of the traditional land tenure system.
A population boom in the atoll-capital also characterises the last decades, mainly due to progress made in the field of health. The strong population growth of Kiribati – from 38,000 in 1963 to over 103,000 in 2010 – representing + 171% – is mainly concentrated in the urban district of South Tarawa. This island is now home to half the country’s population on only 2% of the territory, with an average population density of 3125 inhabitants per km2. This
situation is the cause for (i) a rapid degradation of ecosystems and resources, (ii) a loss of identity and cultural connection to the environment, and (iii) a high population exposure to sea-related hazards due to the settlement of flood-prone and unstable areas, and (iv) a growing dependence towards international aid and food imports.
Finally, all of these transformations, put into the perspectives of weakening of coral reefs, coastal erosion, marine inundation, scarcity of water resources, etc., can largely explain the vulnerability of Kiribati to climate change and ocean acidification.
Their intrinsic characteristics, both physical and anthropogenic, place the small islands in the forefront of threats associated with climate change and ocean acidification. However their situation poses more universal issues in the sense that, ultimately, the major amount of coastlines of the world are also threatened by extreme weather and marine events and by the progressive deterioration of the living conditions of ecosystems and human communities. Hence, contrary to what might have been a priori believed, small islands do not present such marginal situations. Consequently they have important lessons to teach, including the three main issues that emerge.
Firstly, the vulnerability of coastal areas to future environmental change does not only depend on rising sea level and intensification of extreme events. Although this review demonstrates that these two pressure factors are very important, they are often the only ones to be blamed in vulnerability assessments carried out in coastal areas. The analysis based on these factors only is therefore too biased as it does not take into account the consequences of global warming nor ocean acidification which are capable of weakening the core of the resource systems of island territories, in particular the fundamental links of the food chain at the coast (coral reefs, for example) as well as offshore (phytoplankton, for example).
Secondly, this vulnerability does not only depend on pressures related to nature, such as the occasional hazards as well as the more gradual changes in environmental conditions. Anthropogenic factors will also play a decisive role in the future of the islands and, in a larger sense, of their coasts. Knowing that climate change and ocean acidification are genuine threats – it would be irresponsible and dangerous to deny it – the extent of tomorrow’s difficulties are closely related to both current unsustainable occupation of land area and exploitation of resources.
Finally, if immediate proactive policies could be triggered for the readjustment of territories, for environmental protection and for the modification of the relationship between human communities and their economies and the marine and coastal resources, a major step forward would be made towards adaptation to climate change and ocean acidification. The identification of anthropogenic pressure factors presently at work finally provides many clues for imagining and starting to implement adjustments to environmental changes. Human responsibilities are powerful levers that must be used to reduce future threats.