Would a sea level rise gravely endanger low-lying coral atolls?
Regarding atolls and sea level rise, the most important fact was discovered by none other than Charles Darwin. He realized that coral atolls essentially “float” on the surface of the sea. When the sea rises, the atoll rises with it. They are not solid, like a rock island. They are a pile of sand and rubble. There is always material added and material being lost. Atolls exist in a delicate balance between new sand and coral rubble being added from the reef, and atoll sand and rubble being eroded by wind and wave back into the sea or into the lagoon. As sea level rises, the balance tips in favor of sand and rubble being added to the atoll. The result is that the atoll rises with the sea level. Darwin’s discovery also explained why coral atolls occur in rings as in Fig. 1 above. They started as a circular inshore coral reef around a volcanic rock island. As the sea level rose, flooding more and more of the island, the coral grew upwards. Eventually the island was drowned by the rising sea
