Powerful solar storms are an imperfectly understood threat to the world's power grids, but one with the potential for economic damage so catastrophic that the estimated $100-200 million it would cost annually to deploy an operational space-weather warning system could be trivial by comparison.

In a “perfect storm” scenario, when a high-power coronal mass ejection (CME) of charged particles slams into Earth at a time when the delicate balance operators try to maintain in electric power grids is precarious, the resulting damage could take a decade to repair at a cost very roughly estimated by the National Academies of Science as high as $1 trillion.

In recent congressional testimony and a public forum in Washington, space-weather experts caution that the 1859 solar storm observed by British astronomer Richard Carrington is only the most powerful one detected so far. That storm took down parts of the growing U.S. telegraph network, starting fires in the process and subjecting some telegraph operators to electric shock.

Recent calculations suggest there is a 6-12% chance of another storm at that level in any given year. But since there were no networks of long electric wires crisscrossing the planet before the 19th century, there is really no way to know precisely how bad “the Carrington event” really was, according to Tom Mahony, senior advanced systems manager at Ball Aerospace.

“We've only had 150 years to observe these events,” he says. “We're projecting this as a 100-year event when we've only observed it for 150 years. We have geological records that go back millennia.”

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