Despite more than three centuries of occasional human impact on Caroline Island, it is one of very few remaining near-pristine tropical islands. The United Nations rated the atoll with a 'Human Impact Index' rating of 1 in 1998, making it one of the most unspoiled islands in the world. Its undisturbed state has led to a proposal that it be designated a World Heritage Site and a Biosphere Reserve. Caroline was visited in 1965 by the Pacific Ocean Biological Survey Program, in 1974 by the Line Island Expedition, and in 1988 and 1991 by the United Nations Environment Programme (UNEP) Wildlife Conservation Unit. A 1991 Kiribati Government expedition, comprising personnel of the Wildlife Conservation Unit and officials of the Ministry of Line and Phoenix Islands Development, agreed that with the exception of South Islet, Long Islet, and Nake Islet, the Caroline Atoll islets should become Wildlife Sanctuaries.