This is the second post in a series about geomagnetic storms as a global catastrophic risk. A paper covering the material in this series was just released.
My last post raised the specter of a geomagnetic storm so strong it would black out electric power across continent-scale regions for months or years, triggering an economic and humanitarian disaster.
How likely is that? One relevant source of knowledge is the historical record of geomagnetic disturbances, which is what this post considers. In approaching the geomagnetic storm issue, I had read some alarming statements to the effect that global society is overdue for the geomagnetic “Big One.” So I was surprised to find reassurance in the past. In my view, the most worrying extrapolations from the historical record do not properly represent it.
I hasten to emphasize that this historical analysis is only part of the overall geomagnetic storm risk assessment. Many uncertainties should leave us uneasy, from our incomplete understanding of the sun to the historically novel reliance of today’s grid operators on satellites that are themselves vulnerable to space weather. And since the scientific record stretches back only 30–150 years (depending on the indicator) and big storms happen about once a decade, the sample is too small to support sure extrapolations of extremes.
Nevertheless the historical record and claims based on it are the focus in this and the next post. I’ll examine four (kinds of) extrapolations that have been made from the record: from the last “Big One,” the Carrington event of 1859; from the July 2012 coronal mass ejection (CME) that might have caused a storm as large if it had hit Earth; a more complex extrapolation in Kappenman (2010); and the formal statistical extrapolation of Riley (2012). I’ll save the last for the next post.