A "Carrington" type event would wipe out just about anything that wasn't seriously hardened. We have no idea at all how common a CME of this magnitude happens. The only reason we noticed the Carrington event was because it was during the early days of the use of telegraphs. Prior to that, there was really not much of any way to detect them.
For those who are interested in information about solar weather without the hype, visit SolarHam. It's geared more towards Ham Radio operators, but they have great info there.
