The UK must make immediate plans to cope with a massive solar 'superstorm', the Royal Academy of Engineering has said.
The Sun is constantly sending bursts of radiation and other particles towards the Earth, and such 'solar weather' already affects satellites, radio waves and communications networks.
But roughly once a century massive eruptions on the Sun cause so-called 'superstorms' of charged plasma and radiation to hurtle towards us, and could cause large amounts of damage to modern technology.
The last recorded superstorm was in 1859, when the 'Carrington event' caused visible auroras around the world, of a type which are normally just seen at the poles.
The RAE said another storm of this scale was "inevitable", and warned that aspects of the UK's modern infrastructure were not all prepared to cope.
It said that a superstorm "will degrade the performance of the electricity grid, satellites, GPS systems, aviation and possibly mobile communications".
The report added that there was a risk that air passengers and crew could be subject to a one-off dose of radiation which might raise the risk of cancer.
The Academy called for radiation alerts to be placed on the ground, in space and in aircraft to "minimise and quantify the risk".
"Consideration should also be given to classifying solar superstorms as radiation emergencies for air passengers and crew, although the radiation levels concerned are borderline," it said.
About 10% of satellites would be temporarily shut down by the storm.
Most could be brought back online quickly, the report said, but global navigational satellite systems like GPS could still be shut down for up to three days.
The Academy recommended that the UK upgrade communications networks to function without GPS for short periods, particularly those used by emergency services.
"Such a loss of navigational aids could potentially affect aircraft and shipping," the report added. "Today's aircraft navigation systems are not wholly dependent on GNSS and their use is generally backed up by other navigation aids; it is important that these alternative navigation options remain available in the future."
But it added that in many areas, the UK is "well advanced" compared to other nations.
The National Grid has already taken measures to protect against disruption from space weather, it said. While some power cuts would occur, the grid's "lattice network" structure meant it could withstand the storm better than, for instance, Canada, which is more fragile.
It said:
"The National Grid has already taken measures to harden the electricity grid against such disruption and has an active mitigation strategy in place. This should be continued, combining appropriate forecasting, engineering and operational procedures."
The Academy called for the creation of a UK Space Weather Board to oversea plans to protect against the worst effects of solar storms.