The global warming, how and why it began?

What caused rapid global warming initially before man began burning fossil fuels for energy and power?

• Causing sea levels to rise quickly, causing the ancient coastal cities of Alexandria and Skara Brae to become submerged?

• Answer:

  This is a question about paleoclimatology. There is a really great video lecture on the subject by Richard Alley (Google 'biggest climate control knob'). There are a number of famous 'hot periods' over the last 20,000 and, generally, we have good explanations for what caused each them and, importantly, we know why they aren't the cause of the current rapid warming we are facing now. A good example is the Holocene climatic optimum, which occurred around 9,000 to 5,000 years ago. The cause was predictable changes in the earths orbit (Google 'milankovitch cycles' to find out more). Also, it is important to note that the other warming we have seen over the last 20,000 years has not been as rapid as the warming we are seeing now, contrary to the statement in the question.