A third of World Heritage sites are in critical condition, warns UNESCO in a study published on Thursday. The biodiversity of protected sites is more threatened than ever. The ultimate protection of endangered species in the world, these sites classified as World Heritage are particularly weakened, first and foremost by climate change, warns UNESCO. A third of them are in critical condition, warns the United Nations in a study published on Thursday. Incidentally, UNESCO is alerting the states to protect these 1,157 classified natural and cultural sites. Because although they represent less than 1 % of the Earth's surface, these areas are, on the other hand, home to more than a fifth of the world's wealth of mapped species: that is, more than 75,000 species of plants and more than 30,000 species of mammals, birds, fish, reptiles and amphibians, according to the study.