The most serious space weather event in history happened in 1859. It is known as the Carrington event, after the British amateur astronomer Richard Carrington, who was the first to note its cause: "two patches of intensely bright and white light" emanating from a large group of sunspots. The Carrington event comprised eight days of severe space weather.

There were eyewitness accounts of stunning auroras, even at equatorial latitudes. The world's telegraph networks experienced severe disruptions, and Victorian magnetometers were driven off the scale. [...]

According to the NAS report, a severe space weather event in the US could induce ground currents that would knock out 300 key transformers within about 90 seconds, cutting off the power for more than 130 million people. [...] The truly shocking finding is that this whole situation would not improve for months, maybe years: melted transformer hubs cannot be repaired, only replaced. "From the surveys I've done, you might have a few spare transformers around, but installing a new one takes a well-trained crew a week or more," says Kappenman. "A major electrical utility might have one suitably trained crew, maybe two." Within a month, then, the handful of spare transformers would be used up. The rest will have to be built to order, something that can take up to 12 months.

Even when some systems are capable of receiving power again, there is no guarantee there will be any to deliver. Almost all natural gas and fuel pipelines require electricity to operate. Coal-fired power stations usually keep reserves to last 30 days, but with no transport systems running to bring more fuel, there will be no electricity in the second month.

With no power for heating, cooling or refrigeration systems, people could begin to die within days. There is immediate danger for those who rely on medication. Lose power to New Jersey, for instance, and you have lost a major centre of production of pharmaceuticals for the entire US. Perishable medications such as insulin will soon be in short supply.

Hurricane Katrina's societal and economic impact has been measured at $81 billion to $125 billion. According to the NAS report, the impact of what it terms a "severe geomagnetic storm scenario" could be as high as $2 trillion. And that's just the first year after the storm. The NAS puts the recovery time at four to 10 years.

Previously, previously.