The Open Philanthropy Project has included geomagnetic storms in its list of global catastrophic risks of potential focus.
To be honest, I hadn’t heard of them either. But when I was consulting for GiveWell last fall, program officer Howie Lempel asked me to investigate the risks they pose. (Now I’m an employee of GiveWell.)
It turns out that geomagnetic storms are caused by cataclysms on the sun, which fling magnetically charged matter toward earth. The collisions can rattle earth’s magnetic field, sending power surges through electrical grids. The high-speed particles can also take out satellites critical for communication and navigation. The main fear is that an extreme storm would so damage electrical grids as to black out power on a continental scale for months, even years. The toll of such a disaster would be tallied in economic terms, presumably in the trillions of dollars. It would also be measured in lives lost, since all the essential infrastructure of civilization, from food transport to law enforcement, now depends on being able to plug things in and turn them on (NRC 2008, pp. 11–12).
Having examined the issue, especially its statistical aspects, I am not convinced that this scenario is as likely as some prominent voices have suggested. For example, as I will explain in a later post, Riley’s (2012) oft-cited estimate that an extreme storm—stronger than any since the advent of the modern grid—has a 12%-per-decade probability looks like an unrepresentative extrapolation from the historical record. I put the odds lower. My full report has just been posted, along with data, code, and spreadsheets.
Worth noting that studying the effect of damage to GPS systems was not considered in the Open Philanthropy report (beyond a mention that it is beyond the scope of the report), but GPS going down could be very bad indeed, given power grids' and supply chains' near-total dependence on it: https://www.nytimes.com/2021/01/23/opinion/gps-vulnerable-alternatives-navigation-critical-infrastructure.html . On the plus side, an emergency backup system for GPS has already been mandated by U.S. law, but it sounds from the NYT article like it's been 3 years and the government and business interests still can't agree on who's going to pay for it. Might be a good topic for some political advocacy.
David Denkenberger also points to this paper reporting evidence of two extremely large solar storm events in AD 774 and 993, the larger being "five times stronger than any instrumentally recorded solar event": https://www.nature.com/articles/ncomms9611. On that basis he predicts "~10% chance of loss of industrial civilisation this century."