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. — AFP pic GENEVA, Dec 2 — 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 today.