The sun is waking up from a long quiet spell. Last week it sent out the strongest flare for four years, and scientists are warning that earth should prepare for an intense electromagnetic storm that, in the worst case - could be a “global Katrina” - costing the world economy $2,000bn.

Senior officials responsible for policy on solar storms – also known as space weather – in the US, UK and Sweden urged more preparedness at the annual meeting of the American Association for the Advancement of Science in Washington.

“We have to take the issue of space weather seriously,” said Sir John Beddington, UK chief scientist. “The sun is coming out of a quiet period, and our vulnerability has increased since the last solar maximum [around 2000].”

“Predict and prepare should be the watchwords,” agreed Jane Lubchenco, head of the US National Oceanic and Atmospheric Administration. “So much more of our technology is vulnerable than it was 10 years ago.”

A solar storm starts with an eruption of super-hot gas travelling out from the sun at speeds of up to 5m miles an hour. Electrically charged particles hit earth’s atmosphere 20 to 30 hours later, causing electromagnetic havoc. Last week’s solar storm may have been the biggest since 2007, but it was relatively small in historical terms. [ FT.COM ]