Thresholds Database > Society: possible collapse of atoll communities

Background

Atolls are rings of coral reefs enclosing a lagoon (Barnett and Adger 2003). Islets around the rim of the reef have a mean height of approximately 2 metres above sea-level. There are five countries worldwide that are made up solely of low-lying atolls; Kiribati, the Maldives, the Marshall Islands, Tokelau and Tuvalu with a combined population of approximately 416,000 people. Kiribati, the Maldives and Tuvalu are official "Least Developed Countries" in the United Nations system.



Atolls generally have high population densities, meaning that a single event will affect large numbers of people. Fresh water reserves are usually limited and the islands are susceptible to erosion. An increase in sea-surface temperature would pose the greatest long-term risk to atoll morphology since coral is highly sensitive to sudden changes in SST.



With a mean annual warming of 2oC or higher predicted by 2050 and 3oC by about 2080, a sea-level rise of between 9 and 88 cm is predicted by 2100 (Houghton et al. 2001). Atoll countries are particularly vulnerable to sea-level rise because of their high ratio of coastline to land area, relatively high population densities and low level of available resources for adaptive measures (as measured by national income per capita) (Barnett and Adger 2003).

Alternate Regimes

1. Functioning island societies with productive agricultural and fishing industries

2. Destruction of coral and atolls no longer able to support resident populations of people

Mechanism

Atoll communities are not expected to remain sustainable with the combined impact of projected sea-level rise, projected increases in coral bleaching episodes and with additional stressors such as increased land-based pollution (Barnett and Adger 2003). The most likely impacts on atoll societies are increases in flooding events, with freshwater aquifers becoming increasingly contaminated with saline water from storm surges and seepage and decreasing productivity from agriculture and artisanal fishing.


Social Thresholds: At some, (as yet) unknown point in time, it is expected that the atoll environment will no longer be able to support a functioning society (provision of food, water, cost of flood mitigation).

Ecological thresholds: Severe and frequent disturbances as a result of the sea level rise is expected to reduce the resilience of the coral reef and severely impede it's growth rate.

Management Decisions in Each Regime