The severity of space weather varies as the Sun follows a consistent 11-year cycle of changing solar activity. The next cycle peak is expected between 2013 and 2015. Extreme geomagnetic events are nevertheless relatively rare, with return period estimates ranging from between 100 and 200 years to up to 500 years. (1) Less severe events are more frequent and often occur on an annual basis. The cumulative impact of milder disturbances should not be underestimated, however, particularly as our dependency on power increases and power infrastructure in some countries fatigues with age.
There have been several recorded historical instances of severe space weather events throughout human history. However, the three most extreme recorded events occurred before the widespread use of electricity. The Carrington event in 1859 is regarded as the most extreme solar event on record. Although electricity use was limited at the time, several telegraph lines around the world were overloaded (in North America particularly), triggering fires and ultimately causing a breakdown in service.
More recently, a less intense geomagnetic storm affected Canadian systems in 1989, triggering a blackout that affected nine million people and causing economic losses of up to CAD2 billion. Although this event did not cause any permanent damage to transformers in the network, several relays were tripped and the grid transitioned from normal operations to complete shutdown in a mere 90 seconds. It took more than nine hours to restore services. Transformers also suffered minor damage in the U.S. state of New Jersey and in the United Kingdom.
In October 2003, meanwhile, solar storms caused a blackout in Sweden for around one hour and minor disturbances were experienced in North America. Unusually, 12 transformers were damaged and taken out of commission in the low geomagnetic latitude country of South Africa during this event. A Japanese satellite valued at more than USD600 million was also permanently damaged.
1. Return periods for extreme solar events are difficult to estimate given large-scale electricity grids have only existed since the late 1800s.