The Carrington Event was the correct answer in the first part.
CME - coronal mass ejection
Should we be concerned? - With the increasing reliance on GPS for navigation and the fact that last year, 40 of the 49 Starlink satellites launched by Space X were destroyed by a solar flare, it's understandable to feel a little concerned.
Currently, there are four satellite constellations and two regional systems orbiting the Earth, all fully interoperable. This means that users can determine their position by picking up signals from any combination of satellites belonging to any of the systems. However, despite the multitude of satellites available, they are all subject to the same solar influences, and under the right conditions, there is potential for some of them to be compromised. I found this interesting article on the subject.
The Electronic Navigational Chart will come to the fore as the world's leading portfolio of official paper charts the ADMIRALTY Standard Nautical Charts (SNCs) which are the world's most trusted and widely used official paper charts ceases to produce paper charts by late 2026 (there is a rumour that this may be extended a second time to 2030). Most commercial vessels use an ENC system with great effect, particularly the Electronic Chart Display and Information Systems (ECDIS). ECDIS may have just a GPS input or many sensor inputs, including radar, GYRO, Anemometer, Echo Sounder, and Navtex, to name a few. In order to satisfy SOLAS and the IMO, if you intend to to use an ECDIS, there has to be redundancy should there be a failure of some nature. If an ECDIS computer fails, it is a simple case of turning to a backup system (some vessels carry 3 or more). If the onboard GPS transponder fails, yes you guessed it - switch to a backup. What if the orbiting GPS satellites are destroyed? Switch to a backup? Surely if the CME has taken out one system because it was in the way of the CME track, then the other satellites we might switch to will also be at risk. What do we do in that instance? ECDIS being the clever bit of kit it is will switch to DR mode until it can pick up signals from any of the various constellation satellites remaining.
Great for the commercial world, what does the leisure industry do to cope with this failure? EECDIS is not a small system and is very expensive, using up space that small vessels don't have. While paper charts are available from IMRAY and other providers, the leisure industry is being encouraged to move more towards paperless navigation. Some of you may have radar and or echo sounders that you could use to help navigate should your GPS fail and you are relatively close to the coast. For those of you a little further offshore, you may consider brushing up on your astro navigation skills. Those without radar could rely on an echo sounder and a handheld compass.
Although there are promising studies and papers on emerging terrestrial GPS navigation systems, I couldn't find a functioning global system. I would be happy to be emailed with information if you know of any systems available to the general public, either current or upcoming. I also couldn't find a SOLAS type-approved chart plotter-sized device that could be incorporated for the leisure industry. Perhaps this is a gap in the market for an enterprising company willing to get into discussions with the IMO and International Hydrographic Organisation?
If the HSE or MAIB were conducting a risk assessment, they would ask whether the risk was foreseeable and what was done to mitigate it. While a paper portfolio is not cheap, takes up space and there is a need to know how to use it, for now it may be a worthwhile backup.