The investigation of natural global catastrophes

Two historical sub-critical global catastrophes (one in the 6th Century, the other in 14th Century) are discussed. It is argued that natural events that cause the death of more than 25% of the global population are more frequent than commonly supposed, averaging roughly once a millennium. Further the events of the two historical case studies have many common features that have lessons for any preparations for future global catastrophes of both natural and anthropogenic origin. It is further concluded that because, by definition, the catastrophe effects the whole world it follows effective action to combat their impact will require significant extraterrestrial capabilities.