The Carrington event happened in the 1850s because of a Coronal Mass Ejection (CME) on the sun. This video speculates on the effects of a similar event today. For more information see: Coronal Mass Ejections.
“The Doomsday Book” by Marshall Brain lays out this scenario in amazing detail and offers solutions to prevent this doomsday scenario from unfolding. You can pre-order the book today on the pre-order page.