The Carrington Event
In September 1859, an enormous solar storm caused worldwide telegraph systems failures, and distorted the Earth's magnetosphere. This "Carrington Event" remains the largest solar storm ever recorded. One may only speculate what the consequences would be, if the event took place today, when the world cannot function properly without electricity and high tech.
Today, the Carrington Event would probably damage the telecommunication satellites orbiting the Earth. For me, this translates into many chess games being interrupted. Plus, I probably wouldn't be able to read the chess.com blogs for a while, which would really piss me off.
For the more serious among us, there is a great article in Scientific American on the possible ways of preparing the world for a possible reocurrence: