September 1859, May 2024: two solar storms that defined their era, separated by 165 years and all the difference between a pre-electric civilization and a hyper-connected one. Comparing these two events is the best way to grasp both the physics of extreme storms and what the future has in store if another one hits in 2026 or beyond.
Carrington, 1-2 September 1859
On the morning of 1 September 1859, British amateur astronomer Richard Carrington was sketching a sunspot group from his villa in Redhill, south of London. During his session, two extraordinarily intense bright points appeared inside the group - he had just witnessed the first solar flare ever observed in visible light. The event lasted about five minutes.
Seventeen hours later, the associated coronal mass ejection reached Earth. The ensuing geomagnetic storm has no equal in the instrumental era. Auroras were seen as far south as Cuba, Hawaii, and Singapore - down to about 23° geographic latitude, where they are normally never visible. The sky was bright enough to read a newspaper at night in some regions. Telegraph operators across the United States and Europe reported induced currents so strong that their lines worked without batteries, powered solely by the storm. Several fires were reported in telegraph offices.
May 2024, 10-12 May
One hundred and sixty-five years later, between 10 and 12 May 2024, a succession of at least four coronal mass ejections from active region 13664 hit Earth. The resulting geomagnetic storm was classified G5 (Kp 9) - the strongest event since October-November 2003 ("Halloween storms"). Auroras were visible to the naked eye from Marseille, Toulouse, and Nice in France, from Florida and Texas in the US, and from southern Italy and Spain in Europe. For the first time since solar cycle 19 (1957-1959), tens of thousands of French observers saw an aurora from their balcony.
Technological side: 24-48 hours of GPS RTK service disruption used by North American precision agriculture, temporary degradation of Starlink satellites, HF communication outages, transpolar flight rerouting. Insurance estimates exceed $500 million of cumulated impact.
Physical comparison
| Carrington 1859 | May 2024 | |
|---|---|---|
| Estimated Kp | ~10 (off modern scale) | 9 (saturation) |
| Dst minimum | ~-850 nT (reconstruction) | -412 nT (measured) |
| Aurora southern limit | Cuba, Hawaii (~22°N) | Marseille, Florida (~28-30°N) |
| Peak duration | ~24 hours | ~12 hours |
| Estimated CME speed | 2,000 km/s | 1,800 km/s |
| Sun-Earth transit time | 17 h 40 min | ~22 hours (4 CMEs) |
In reconstructed geomagnetic intensity, Carrington remains roughly twice as intense as May 2024. It stays the absolute reference of the instrumental era for the worst reasonable scenario.
What May 2024 proved
May 2024 turned several truths from academic hypotheses into operational facts. First: modern infrastructures are sensitive to events much less extreme than Carrington. You don't need a hypothetical G10 to disrupt services or lose hardware - a moderate G5 is enough to drive several hundred million dollars of global impact. Second: the operational forecast chain has 30 to 60 minutes of usable lead time, no more. Once DSCOVR sees the CME crossing L1 with known polarity, the storm is on Earth within the hour. Third: public communication has become a quality dimension. Operators who alerted users early kept their reputation; those who communicated after the fact took critical pushback.
What if Carrington happens in 2026?
Not a hypothetical question. Solar climate models suggest a Carrington-class event has roughly 10 to 15 % probability per decade. Cycle 25, more active than expected, doesn't reduce that probability - it marginally raises it. If a modern Carrington hit in 2026, consequences would be markedly heavier than in 1859, for two reasons: higher infrastructure sensitivity (continental power grids, LEO constellations, connected agriculture) and cross-dependency between those infrastructures (a regional power blackout disrupts comms, which disrupts emergency coordination, etc.).
Individual preparedness is limited but not nil. For an aurora observer: have your Pulsar alerts configured on your city's Kp threshold, your spot scouted and your gear ready - on this kind of event the window is measured in hours and the app notifies you before social-media rumours catch up. For a household: a battery lamp, some water, a hand-crank radio - the same prep as for a major storm. For a critical-system operator: have a safe-mode protocol documented and tested.