A solar storm is an event in which activity on the Sun interferes with the Earth's magnetic field. Because the Sun is so far away, many people believe that solar storms are not capable of causing very much damage, but they can in fact be quite devastating. Research in the early 2000s created a number of potential worst case scenarios which illustrated the destructive power of solar storms, including scenarios showing that powerful nations in the developed world could be brought to their knees for a decade or more by a storm of large magnitude.

Solar storms occur as a result of events such as solar flares and coronal mass ejections. These events generate a so-called “solar wind,” a gust of charged particles which can slam into the Earth's magnetic field in hours if the solar wind happens to be traveling in the direction of Earth. The collision can generate quite a light show as a geomagnetic storm erupts, and the storm can last for several days under the right conditions.

The most severe solar storm in recorded history occurred in 1859. Known as the Carrington Event, this solar storm caused electromagnetic disruptions all over the world, including auroras over the equator and interruption of scientific devices which relied on the Earth's magnetic field to function properly. Lesser storms were also recorded in 1958, 1989, and 2000, and these events were associated with interruptions of the electrical grid and damage to satellites.

Concerns about solar storms revolve around their ability to disrupt electrical systems. A severe solar storm could effectively knock out the electricity grid across a large swath of the world, which would have very serious consequences, as it would be necessary to replace large portions of the grid. Solar storms can also disrupt communications and satellites, and they can be very dangerous for astronauts if astronauts happen to be in the way of the solar wind.

A solar storm can also involve the introduction of tremendous amounts of radiation, which is dangerous for many living organisms. The disruption of the Earth's magnetic field can also be damaging for some organisms. Some animals, for example, appear to be sensitive to magnetic fields and they could become disoriented in a solar storm.

Due to concerns about solar storms, a number of agencies monitor solar activity for signs of events which could trigger a solar storm. Periodically, warnings or advisories may be issued to alert people to events which could cause disruption such as interference with radio signals. In the event of a major solar storm, however, there is little that could be done to prepare or prevent damage.