Climate change is now 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 Wednesday. In a fresh report, the International Union for Conservation of Nature (IUCN) revealed that shifts due to the changing climate now imperil a full third of the 252 UNESCO-listed natural sites around the globe. The report "reveals the damage climate change is wreaking on natural World Heritage, from shrinking glaciers to coral bleaching to increasingly frequent and severe fires and droughts," IUCN Director-General Bruno Oberle said in a statement. nl/rjm/spm