A solar superstorm like the one in 1859 could knock out power grids for months

In the late summer of 1859, the Sun hurled a burst of charged particles at Earth that lit up the night sky as far south as the tropics and set telegraph equipment sparking on multiple continents. Scientists now use that event as the benchmark for the worst kind of space weather a modern society might face. The reason it still commands attention is simple: the technology of 1859 was a handful of telegraph wires, while today’s grids, satellites, and communications networks are vastly more powerful and far more vulnerable to the same forces.

A storm on that scale is rare, on the order of a once-in-a-century event, but it is not hypothetical. Researchers who study geomagnetic hazards warn that a direct hit from a comparable eruption could damage the heavy equipment that regional power grids depend on, and some of that equipment cannot be swapped out quickly. That combination is what turns a brief solar outburst into the possibility of outages measured not in hours but in weeks or months.

The night the telegraph caught fire in 1859

The storm is named after Richard Carrington, the British astronomer who watched an intense solar flare erupt just before Earth’s magnetic field was thrown into chaos. According to the detailed historical record of the event, telegraph operators reported sparks leaping from their equipment, pages catching fire, and lines that kept working even after their batteries were disconnected, carried by the electrical currents the storm induced in the wires. Auroras normally confined to polar skies were seen near the equator, and in some places people could reportedly read a newspaper by their light in the middle of the night. In an age of telegraphs the damage was startling but limited; the concern is what the same currents would do to a grid that now carries continent-spanning loads.

What a coronal mass ejection does to Earth

The engine behind such a storm is a coronal mass ejection, a vast cloud of magnetized plasma flung off the Sun. When one is aimed at Earth, it can slam into the planet’s magnetic field and set off a geomagnetic storm, the kind of event tracked by NOAA’s Space Weather Prediction Center. These eruptions rise and fall with the Sun’s roughly 11-year activity cycle, becoming more frequent around the peak of each cycle. Most storms produce nothing worse than vivid auroras and minor radio interference. A rare few, arriving fast and carrying an intense, well-aligned magnetic field, can drive powerful electric currents deep into the ground and into anything conductive stretched across it, including long-distance power lines.

Why transformers are the weak point

The heart of the danger is the high-voltage transformer, the appliance-sized-to-house-sized units that step electricity up and down as it moves across the grid. A severe geomagnetic storm induces currents that can flow into these transformers, overheating their cores, tripping protective systems, and in the worst cases physically damaging them. That matters because the largest transformers are not stock items; they are custom-built, expensive, and often carry lead times of many months, which is precisely why a storm-driven outage could persist far longer than an ordinary blackout. A U.S. Geological Survey analysis warned that an event on the Carrington scale could adversely affect electric-power transmission systems and lead to blackouts spanning entire regions rather than single neighborhoods, with cascading failures rippling across interconnected networks.

The regions most exposed

Not every part of a country faces the same risk, because the currents that reach the surface depend on the rock beneath it. To map that variation, USGS scientists built a nationwide model of the geoelectric fields a Carrington-scale storm would generate, drawing on decades of magnetic data and measurements of the Earth’s electrical conductivity. The peer-reviewed study behind that map found that the eastern and midwestern United States would be most affected, because the bedrock there conducts the storm’s currents in ways that push more energy into the power system. Those same regions hold many of the nation’s largest population centers and most critical infrastructure, which sharpens the stakes of a direct hit.

How a 100-year storm is monitored today

The scientists who study these hazards are careful to keep the risk in proportion. A USGS geophysicist described Carrington-class storms as “100-year-type events,” rare but genuinely consequential, and noted that an intense storm could be more hazardous than the power industry is currently prepared for. Modern defenses rest heavily on early warning: a network of ground-based magnetic observatories and space-based sensors tracks solar activity continuously, giving grid operators a window, sometimes only tens of minutes to a day, to reduce loads and protect equipment before the worst of a storm arrives. Utilities can take steps such as adjusting power flows, reconfiguring how current moves through the network, and postponing maintenance when a major storm is forecast, measures that can blunt the damage even if they cannot eliminate it. Long-term resilience planning also increasingly includes stockpiling spare transformers and standardizing designs, so that if several are lost at once the replacement timeline is measured in weeks rather than the many months a bespoke unit can require.

Recent activity has served as a reminder that the Sun remains capable of surprises. During strong storms in the mid-2020s, auroras appeared far outside their usual range and caused only minor disruptions, such as brief high-frequency radio blackouts, precisely because they fell short of Carrington intensity. The lesson researchers draw is not that a catastrophe is imminent but that preparation matters: mapping the vulnerable regions, hardening the most exposed transformers, and maintaining the forecasting networks that would provide crucial hours of warning. The 1859 storm endures as a benchmark because it shows what the Sun is capable of, and because it forces a modern, electrified world to reckon with a threat that predates the grid by billions of years.

This article was produced with AI assistance and reviewed by Morning Overview editors.

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