Telegraph operators in the northeastern United States reported something really weird on a clear night in September 1859: their equipment was producing sparks, catching fire, and sometimes sending messages without any battery power at all. As far south as Cuba, the aurora borealis could be seen. What had come was a wall of solar plasma, a coronal mass ejection so massive and swift that it caused Earth’s magnetic field to be constricted to the point where every wire connecting towns became an unwanted antenna. The so-called Carrington Event took place over a few days. If it occurred now, the damage would be quantified in failing electricity grids, malfunctioning water treatment systems, and blackouts that would last months over entire continents rather than in melted telegraph lines.
Solar Cycle 25, an approximately eleven-year cycle of growing and declining activity that drives sunspot counts, solar flares, and the coronal mass ejections that silently unnerve grid engineers, is currently at its height. In recent years, the current cycle has been running hotter than expected, resulting in persistent X-class and M-class flares and delivering multiple large CMEs approaching Earth’s magnetosphere. The largest geomagnetic storm in 20 years occurred in May 2024, producing auroras that were visible over most of Europe and North America. While the auroras were stunning to witness, it was unsettling to consider the damage that a slightly greater event might have caused to high-voltage infrastructure.
Since the threat’s dynamics are not apparent, it is worthwhile to comprehend them. Power transmission lines are forced to act like massive antennas when a CME directly hits Earth’s magnetic field, compressing and distorting the magnetosphere. Geomagnetically induced currents, or GICs, are the end result. These currents introduce direct current into systems that are solely intended to use alternating current.
In response to that injected DC, high-voltage transformers—which are already running close to their thermal limits—enter what engineers refer to as half-cycle saturation, consuming reactive power at an accelerated pace and producing heat that they weren’t designed to dissipate. The production and shipping of some of these transformers, which weigh hundreds of tons, takes more than a year. They’re not piling up. Losing multiple at once wouldn’t be a short-term annoyance.
The warning window makes this more difficult to control than most infrastructure issues. The Sun can reach Earth in as short as fourteen hours after a coronal mass ejection, though most require two to three days. Since a southward-pointing magnetic field strikes hardest, the NOAA Space Weather Prediction Center uses data from spacecraft positioned between Earth and the Sun to track these events from the moment they erupt. This allows them to estimate arrival time and, crucially, the magnetic orientation of the incoming plasma.
Before the storm arrives, grid operators can take the most vulnerable transformers down, reduce demand, and transfer loads in advance if they receive that information in a timely manner. That decision-making process, which moves at the speed of the government and utilities, must always function properly.
It’s difficult to ignore the tension in the public discourse surrounding this risk. Depending on the model, the potential damage from a Carrington-scale event has been estimated to be between several hundred billion and a few trillion dollars. Space weather agencies often publish forecasts, and researchers write lengthy warnings. However, investment in hardening the grid against geomagnetic storms is still uneven in most nations, driven more by decisions made by individual utilities than by any unified national standard. The level of readiness is genuine and has increased. The question of whether it is adequate is a separate and really open one, one that the Sun is subtly pressing as it accelerates toward the apex of its cycle.
