LA Times - Coronal mass ejections are caused when the magnetic field in the sun's atmosphere gets disrupted and then the plasma, the sun's hot ionized gas, erupts and send charged particles into space. Think of it like a hurricane — is it headed toward us or not headed toward us? If we're lucky, it misses us. In 1989 on hit Quebec, the power system went from normal operation to failure in 90 seconds. It affected around 6 million people. The impact was reckoned to be $2 billion Canadian in 1989 prices.
A storm in 1859 as the biggest space weather event. We know there were huge impacts on the telegraph, which suggests there would be similarly severe impacts on modern power grids. It's hard to compare it to the 1989 event because of the changes in our technology.
A recent paper [published in February in the journal Space Weather] tried to estimate the chance of having a repeat of 1859 and came up with a value of a 12% chance of it happening in the next 10 years. That's quite a high risk.
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