It's being described by the scientists who wrote it as a "clarion bell" - a report warning the world that unprecedented and immediate change is needed to prevent a climate catastrophe. (Click to subscribe for more Channel 4 News videos. www.youtube.com/channel4news?sub_confirmation=1) A report by the Inter-Governmental Panel on Climate Change for the United Nations says we need to act without delay to prevent the destruction of coral reefs and stop sea levels rising by as much as ten centimetres. If that happened large parts of the world could become uninhabitable.