In his 1999 book, "Catastrophe," David Keys pieces together scientific and historical evidence that a global event - likely an enormous volcano eruption somewhere in the Pacific - thousands of years ago ushered in the modern world as we now know it. Surveying the data from ancient tree-rings, Arctic ice cores and written accounts from Roman, Chinese and Japanese historians, Keys places the eruption in about 535 A.D. Over the next several hundred years, Keys postulates, the resulting changes in rainfall patterns and global and regional temperatures led to a cascade of events that culminated in the toppling of empires, the birth of others, the introduction of the bubonic plague to Europe and the birth of the Islamic religion.

Clearly, the weather can play an important role in human affairs - and vice versa. FRONTIERS takes a look at events - some subtle, some literally Earth shattering

Click on an image below to learn about great moments in global climate change: