Space weather and extreme geomagnetic activity

Space weather is a natural hazard that threatens the continuous and safe operation of modern technological systems. Our exposure to space weather is a direct result of the global reach of many of these technologies and our growing reliance on interconnected space- and ground-based hardware and networks. However we only have about fifty years of space-based measurements of the Earth’s neighbourhood to give us clues on what we can expect from space weather. Even the global, ground-based, geomagnetic record, which follows changes in space weather, only stretches back continuously for some 160 years. The Sun, the driver for space weather, has magnetic activity cycles of around eleven years. This therefore gives us access to only relatively few ‘seasons’ of direct space observations from which to determine the worst space weather that we could experience. However, quantifying the extremes in geomagnetic activity, from the geomagnetic record, would be an important step forward in assessing just how severe space weather could get.