Solar storms hit Earth regularly, most without any noticeable effect on daily life. But a powerful one, the kind that arrives maybe a few times per solar cycle, can disrupt power grids, knock out GPS accuracy, black out radio communications, and push the aurora borealis as far south as Texas. A truly extreme event, on the scale of the 1859 Carrington Event, could cause trillions of dollars in damage and take months or years to fully recover from.
What actually happens depends on the storm’s intensity. NOAA rates geomagnetic storms on a G1 to G5 scale, and the difference between a G1 and a G5 is the difference between a flickering light and a regional blackout.
How Solar Storms Reach Earth
A solar storm begins when the sun ejects a massive cloud of charged particles, called a coronal mass ejection (CME), into space. These clouds travel at hundreds to thousands of kilometers per second. When one is aimed at Earth, it typically arrives in one to three days.
When that cloud of solar plasma reaches Earth, it slams into the planet’s magnetic field. If the magnetic orientation of the incoming material opposes Earth’s field, the two can connect through a process called magnetic reconnection. This opens a pathway for solar energy to pour into Earth’s magnetosphere. That energy gets stored in the stretched magnetic tail on Earth’s nightside, then released in bursts that send charged particles streaming toward the poles, lighting up the aurora and driving electrical currents through the upper atmosphere and down into the ground.
What Happens to the Power Grid
The most consequential effect of a major solar storm is what it does to electrical infrastructure. As the storm drives fluctuating currents in Earth’s upper atmosphere, those changes induce electric fields in the ground below. Long, high-voltage transmission lines act like antennas, picking up these ground-level electric fields and channeling quasi-DC currents, called geomagnetically induced currents (GICs), through the power grid. These currents flow to ground through substation transformers that are grounded on the high-voltage side.
The problem is that transformers are designed for alternating current, not the steady push of DC. When GICs exceed about 30 amps, they drive the transformer’s magnetic core into a lopsided saturation on each cycle. This generates unusual electrical harmonics, increases internal heating, and forces the transformer to consume far more reactive power than normal. During the May 2024 geomagnetic storm, researchers in New Zealand measured these effects directly and found that reactive power consumption rose in a straight line once GIC levels crossed that 30-amp threshold. Extrapolating to a Carrington-level event, they estimated that just 19 of the most affected sites in New Zealand’s grid would need an additional 200 to 350 megavolt-amperes reactive of generation capacity to compensate.
At a G5 (extreme) level, NOAA warns of widespread voltage control problems, protective systems tripping incorrectly, and the possibility of complete grid collapse in some regions. Transformers can suffer permanent damage from overheating, and large high-voltage transformers are custom-built components that take months to manufacture and deliver. A study published in the journal Space Weather estimated that a severe geomagnetic storm could cause $1 to $2 trillion in economic damage in the first year, comparable to a “global Hurricane Katrina.” Notably, direct losses from the power outage itself account for only about 49% of the total cost. The rest comes from cascading effects on supply chains, transportation, water treatment, and every other system that depends on electricity.
GPS, Satellites, and Radio Communications
A solar storm supercharges Earth’s ionosphere, the electrically active layer of the upper atmosphere that GPS signals must pass through. Under calm conditions, a standard GPS receiver can pinpoint your location to within a meter. During a severe storm, that error can balloon to tens of meters or more. In some cases, the ionosphere becomes so turbulent that GPS receivers lose their lock on satellite signals entirely. Near the equator, a phenomenon called ionospheric scintillation makes this problem especially acute, even for more advanced dual-frequency receivers.
Satellites in orbit face their own risks. Charged particles from the storm can build up static on spacecraft surfaces, interfering with electronics and causing orientation errors. Operators may need to make corrections from the ground, and tracking accuracy degrades. At G5 levels, NOAA notes that satellites can experience extensive surface charging, along with problems in communication uplinks and downlinks. The increased drag from a heated, expanding upper atmosphere can also alter satellite orbits, which is a particular concern for large satellite constellations in low Earth orbit.
High-frequency radio, used by aviation, maritime, and military communications, can go completely dark during an extreme event. NOAA’s scale warns that HF radio propagation may be impossible in many areas for one to two days during a G5 storm. Low-frequency radio navigation systems can also drop out for hours.
Radiation Exposure for Airline Passengers
Solar storms also produce bursts of energetic particles that increase radiation levels at high altitudes and latitudes. For people on the ground, Earth’s atmosphere provides ample shielding, and the added exposure is negligible. But for passengers and crew on high-altitude polar routes, the dose can be meaningful.
A CDC study examining flight attendant radiation exposure during solar particle events found that the largest storms produced dose rates at cruising altitude of 240 to 480 microsieverts per hour during the first three hours, tapering off afterward. For context, a single chest X-ray delivers about 20 microsieverts. A transatlantic flight from London to Los Angeles during one of the studied events delivered an estimated dose of 90 microsieverts, while a Paris to San Jose route came in at 202 microsieverts. These are small numbers in the context of a single flight, but they matter for pregnant crew members and frequent fliers who accumulate exposure over time. Airlines can reduce risk by rerouting flights to lower latitudes or altitudes during major events.
The Carrington Event: What a Worst Case Looks Like
The benchmark for an extreme solar storm remains the Carrington Event of September 1859. During that storm, brilliant red auroras were visible to within 18 degrees of the geomagnetic equator, meaning people in the tropics could see them. Colorful auroral displays of all types persisted below 50 degrees latitude for roughly 42 hours during the strongest phase. Ship logs from across the Atlantic recorded vivid skies through the night.
The world’s telegraph network, then about 200,000 kilometers of wire, was severely disrupted. Ionospheric currents were so powerful that magnetometers went off-scale. Many telegraph lines were unusable for eight hours or more, causing real economic damage at a time when telegraphy was the backbone of long-distance communication. Some telegraph operators reported that their equipment continued to work even after they disconnected the batteries, powered by the induced currents alone.
If a Carrington-scale storm struck today, the consequences would be far more severe simply because modern civilization depends on a vastly more complex electrical and electronic infrastructure than existed in 1859.
How Much Warning We Get
Earth’s primary early warning system is the DSCOVR satellite, positioned at a gravitational balance point about 1.5 million kilometers sunward. DSCOVR measures the solar wind directly and provides 15 to 60 minutes of advance warning before a storm’s effects reach Earth. That window is narrow, but it is enough time for power grid operators to take protective action.
Coronal mass ejections can also be spotted leaving the sun one to three days before arrival using solar observatories, but the critical details, particularly the magnetic orientation that determines how severely the storm will interact with Earth’s field, can only be measured when the cloud reaches DSCOVR.
How Grids Prepare and Protect Themselves
Utilities and grid operators have several tools to reduce damage. On the hardware side, certain transformer designs are inherently more resistant to GICs. Three-phase transformers with a three-limbed core design handle DC currents better than other configurations. Series capacitors installed on transmission lines can block GICs as a side benefit of their primary function. Replacing older electromechanical protective relays with modern microprocessor-based versions reduces the risk of unnecessary shutdowns triggered by GIC-induced harmonics.
Operationally, when a storm warning arrives, grid managers can increase their reserve generation capacity, adjust protective relay settings to prevent false trips, and preemptively take the most vulnerable equipment offline. These steps sacrifice some efficiency and capacity in the short term but can prevent catastrophic, long-lasting damage to irreplaceable components.
Where We Are in the Solar Cycle
The sun follows an approximately 11-year activity cycle. Solar Cycle 25, the current cycle, was forecast to peak around July 2025, with an average intensity similar to the previous cycle. During peak years, the likelihood of strong geomagnetic storms increases substantially. NOAA estimates that G5 events occur about four days per solar cycle on average, while G3 and G4 storms are far more common, with roughly 130 and 60 days of activity per cycle, respectively. The May 2024 storm, which reached G5 and produced aurora visible across much of the continental United States, was a reminder that extreme events are rare but not hypothetical.