(FILES) This file photo taken on November 20, 2014, shows an aerial view of the Great Barrier Reef off the coast of the Whitsunday Islands, along the central coast of Queensland. - Climate change has become the biggest threat to UN-listed natural world heritage sites like glaciers and wetlands, and has pushed Australia's Great Barrier Reef into "critical" condition, conservationists said December 2, 2020. (Photo by Sarah LAI / AFP)