Paul Singer, billionaire, says that the greatest threat to the world today is an electromagnetic pulse.
http://www.cnbc.com/id/101875747
"(A natural EMP event) today would cause a massive disruption to the electric grid, possibly shutting it down entirely for months or longer, with unimaginable consequences," Singer wrote. "Only two years ago, the sun let loose with a Carrington-magnitude burst, but the position of the earth at the time prevented the burst from hitting it. The chances of additional events of such magnitude may be far greater than most people think."
Carrington refers to a solar storm in 1859 that caused telegraph systems to fail around the world.
http://www.cnbc.com/id/101875747