On Sept. 2nd 1859, a huge coronal mass ejection (CME) slammed into Earth's magnetic field. Campers in the Rocky Mountains woke up in the middle of the night, thinking that the glow they saw was sunrise. Cubans read their morning paper in the predawn hours by the red light of the brilliant auroral display. Earth was bombarded by particles so energetic, they altered the chemistry of polar ice.
The geomagnetic storm intensified and electrified telegraph lines, shocking operators, setting installations on fire and taking the emerging Victorian Internet offline. Fortunately that represented most of technology sensitive to such events. Its cause was a huge solar flare witnessed the day before by British astronomer Richard Carrington. His observation marked the discovery of solar flares and created the field of space weather.
Studies suggest a similar storm would cause a $1 to $3 trillion dollars of infrastructure damage - including much of the electric grid - and require four to ten years for complete recovery. It is likely that most satellites in near orbit would be taken out. We talk about the technologies that impact us the most, but pull the plug even for a week and your mindset changes.
The question is how often do these huge CMEs happen? We haven't seen auroral displays of this magnitude since and our electrical and electronic infrastructure became increasingly more more vulnerable with increasing scale and complexity. Society managed to dodge a bullet. On July 23, 2012, a CME similar in size to the Carrington event was recorded. It wasn’t aimed at the Earth, so no problem… at least that time. One of the reasons for studying space weather is to provide an early warning system to prepare the grid for local space weather events. As the grid is redesigned some, but probably not enough, effort is going towards making it more robust to large geomagnetic storms.