A Carrington-level solar storm today could knock out the power grid

In late summer of 1859, telegraph operators across Europe and North America watched their instruments come alive in ways no one could explain. Sparks jumped from equipment, paper caught fire, and some lines kept transmitting even after their batteries were disconnected. Overhead, curtains of aurora usually confined to polar skies glowed as far south as the Caribbean. The cause was the most intense geomagnetic storm ever recorded, and its arrival in an age of copper wires foreshadowed a hazard that has only grown as civilization wired itself together.

The episode is named for Richard Carrington, the English astronomer who, on September 1 of that year, became the first person to observe a solar flare, a sudden brightening on the face of the Sun. What followed offers a template for understanding one of the few natural events capable of disrupting modern life on a continental scale.

The chain reaction that reaches Earth

A storm of this kind begins with a coronal mass ejection, an enormous cloud of magnetized plasma flung off the Sun. In 1859 the cloud reached Earth in roughly 17.5 hours, an unusually fast transit that suggests an earlier eruption had cleared the path ahead of it. When such a cloud slams into the planet’s magnetic field, it sets off a geomagnetic storm that ripples through the upper atmosphere and drives electric currents deep into the ground and along any long conductor stretched across the landscape.

On the modern scale used by forecasters, the 1859 event would have rated a G5, the highest category, and studies of ice cores suggest it was at least twice as strong as any other storm in roughly 500 years, according to a historical review from the National Oceanic and Atmospheric Administration. The telegraph network was the only electrical infrastructure of consequence at the time, so the damage, while dramatic, was limited. A society that had built almost nothing electrical simply had little for the storm to break.

Why a repeat would hit harder today

The vulnerability now runs through the power grid, and the mechanism is specific. A severe geomagnetic storm induces slow, direct-current-like flows known as geomagnetically induced currents in the long transmission lines that move electricity between cities. Those currents can push the large transformers at the heart of the grid into a state of magnetic saturation, causing them to overheat. In the worst case the heat damages the transformer permanently, as detailed in a space-weather assessment from NOAA’s satellite and information service.

That single point of failure is what makes the scenario serious. High-voltage transformers are enormous, expensive and largely custom-built, and spares are not sitting in warehouses in the numbers a widespread failure would demand. Replacing many of them at once could take a long time, which is why one influential worst-case study warned that full recovery from a Carrington-level event might stretch across years rather than weeks. Experts remain divided on how severe the real-world damage would be, and estimates vary widely, but the direction of the risk is not in dispute: the more electrified and interconnected the grid, the more a great storm can reach.

Satellites face their own version of the threat. A strong storm heats and swells the upper atmosphere, increasing the drag on spacecraft in low orbit and complicating the tracking that keeps them from colliding. The same charged particles can scramble sensitive electronics, degrade solar panels and interfere with the radio signals that satellite navigation and communication depend on. Airlines flying polar routes reroute during major events to avoid radiation exposure and communication blackouts, a quiet, routine sign of how far the effects extend.

How often the Sun throws a punch this hard

Events of Carrington’s magnitude are rare, but they are not unheard of, and near-misses have occurred within living memory. A powerful storm in March 1989 collapsed the electrical grid serving Quebec, plunging millions into darkness in the middle of winter and demonstrating that induced currents can bring down a modern network. In July 2012 an eruption at least comparable to 1859 tore across the orbit Earth had occupied only days earlier, missing the planet in what amounted to a cosmic coincidence of timing, as noted in the record of the 1859 storm and its modern analogues. Had it arrived a week sooner, it would have struck a fully wired planet head-on.

The frequency of the very largest storms is difficult to pin down precisely, because the reliable record is short and the extreme cases are few. Estimates for a Carrington-scale event range from roughly once a century to once every several centuries, uncertain enough that the honest answer is that no one knows exactly when the next one will come. What forecasters do agree on is that the Sun follows an approximately 11-year cycle of rising and falling activity, and that the biggest storms cluster near the peaks of those cycles.

Watching the Sun to buy time

The defense against such an event is not to stop the storm but to see it coming. Space-based observatories monitor the Sun continuously, spotting flares and coronal mass ejections as they erupt, and spacecraft stationed between Earth and the Sun measure the incoming solar wind to give forecasters warning that ranges from hours to a day or two. That window, though short, is enough for grid operators to take protective steps, such as reducing loads and reconfiguring the network to limit how far induced currents can travel.

Hardening the grid against geomagnetic currents, stockpiling spare transformers and improving forecast accuracy all reduce the potential damage, and utilities and governments have moved in that direction over the past two decades. The 1859 storm remains the benchmark against which every plan is measured, a natural experiment that showed, in an age of telegraph wires, what a restless Sun is capable of sending toward a planet that has since plugged nearly everything into the wall.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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