Experts say the sun is reaching a peak in its 10-year activity cycle, putting the Earth at greater risk from solar storms.
Power grids, communications and satellites could be knocked out by a massive solar storm in the next two years, scientists warn.
Mike Hapgood, a space weather specialist at the Rutherford Appleton Laboratory near Didcot, Oxfordshire, said: "Governments are taking it very seriously. These things may be very rare but when they happen, the consequences can be catastrophic."
He warned that solar storms are increasingly being put on national risk registers used for disaster planning, alongside other events like tsunamis and volcanic eruptions.
There is 12% chance of a major solar storm every decade - making them a roughly one-in-100-year event. The last major storm was more than 150 years ago.
The threat comes from magnetically-charged plasma thrown out by the sun in coronal mass ejections.
Like vast bubbles bursting off the sun's surface, they send millions of tons of gas racing through space that can engulf the Earth with as little as one day's warning.
They trigger geomagnetic storms which can literally melt expensive transformers in national power grids.
Satellites can be damaged or destroyed and radio communications - including with jet airliners - could be knocked out.
Teams of scientists in North America and Europe monitor the sun and issue warnings to governments, power companies and airline operators.
In 1989, a solar storm was blamed for taking out the entire power network in Quebec, Canada, which left millions without electricity for nine hours.
The largest was known as the Carrington event in 1859, when British astronomer Richard Carrington observed a large solar eruption that took just 17 hours to reach the Earth's atmosphere.
It caused the aurora borealis - or Northern Lights - to be seen as far south as the Caribbean ( via news.sky.com ).