Earlier today (Australian time) two coronal mass ejections from the sun travelling at different speeds towards hit our planet at around the same time, triggering a very strong geomagnetic storm.
For reference, this was measured to trigger a Kp=8 storm, where the Kp values are on a scale from 0 to 9, so it was pretty big. In fact, it was big enough that spaceweather.com reported that it triggered auroras so extensive they were visible from mid-latitude locations such as England and Germany.
Spaceweather.com also mention that it was big enough that it might have squashed the Earth's protective magnetic field enough to expose geostationary satellites to the solar wind and interplanetary medium. In short words, this means that some satellites risk getting fried due to this storm. We'll find out in a few days.
Geomagnetic storms of this magnitude happen from time to time, and usually don't cause big problems. However, larger events can occur that can cause considerable problems for our big-infrastructure oriented civilisation.
Another big geomagnetic storm hit in March 1989 and caused considerable damage to electricity distribution in Canada as the changing magnetic field induced current flows in the long-distance electricity distribution cables, causing some really big transformers to melt, and causing havoc with satellites.
This event showed how our modern infrastructure is prone to damage by solar events. Indeed, there are now measures taken to reduce this kind of damage by shutting power distribution down during intense geomagnetic storms so that no transformers melt. However, damage to satellites is difficult to prevent.
However, the 1989 storm was small in comparison to what the sun can throw at us.
In 1859 the most intense geomagnetic storm ever recorded occurred and has become known as the Carrington Event.
That solar storm was so intense that aurorae were observed in such low latitudes as the Caribbean, and were so bright in the Rocky Mountains in America that gold miners got up and began to prepare breakfast.
The electric currents induced by the magnetic flux were so intense that they enabled inter-continental telegraph lines (the Internet of the 19th century) to keep working with out their power source, while others gave operators shocks.
We have since discovered that events the size of the Carrington Event occur about every 500 years.
Both the 1989 and Carrington events would create havoc with our vast number of communications and location satellites such as GPS and geostationary satellite telephone systems if they occurred today.
Even low-earth-orbit systems like Iridium and Globalstar would not be immune as the radio interference would potentially prevent their operation by interfering with satellite-ground and satellite-satellite communications. There are also more sinister problems for low-earth-orbit satellites. First, the outer parts of the atmosphere heat up and increase the pressure, and thus drag, which can cause the satellites to lose altitude, which is bad for all sorts of reasons. Second, the Van Allen radiation belts become more active, which can cause problems for satellites.
A repeat of the Carrington Event today would likely damage or destroy a significant number of satellite, as well as causing wide-spread blackouts.
In short, that part of our infrastructure which we like to consider to be immune to disaster, i.e., satellite communications and location services, are in fact prone, and science informs us that it is only a matter of time before such an event occurs.
My point in all this is that infrastructure is fragile in various ways, and forms a single point of failure.
This is why the Serval Project is working to enable existing cell phones to keep communicating when deprived of their supporting infrastructure, so that at least local communications will remain possible in the face of almost any situation, without the capability placing a cost-burden on society.