In 1859 a cloud of magnetised solar plasma crossed 150 million kilometres in less than a day. The Sun has just passed the peak of its latest 11-year cycle. Here is what its storms are, how often they come, and what a big one would cost a wired world.
Between Richard Carrington's flare sighting on 1 Sept 1859 and the start of the strongest geomagnetic storm on record. The fastest coronal mass ejections arrive in 15–18 hours; slower ones take several days.Source: Cliver & Svalgaard 2004; NOAA SWPC
NOAA grades geomagnetic storms G1 to G5 by the planetary Kp index. Over an average 11-year cycle, minor storms come by the hundreds; extreme ones come about four times.
Average frequencies over one ~11-year solar cycle, from the NOAA Space Weather Scales.
Sunspots wax and wane on a roughly 11-year beat. In 2019 an expert panel forecast a weak peak of 115. SILSO's count for Cycle 25 peaked at 161 in October 2024.
Peak 13-month smoothed sunspot number per cycle, SILSO version 2 series (Royal Observatory of Belgium).
Storm intensity is measured as the drop in Earth's equatorial magnetic field (Dst, in nanotesla). May 2024 was the strongest storm in two decades. Even the low estimates put 1859 at more than twice that.
1859 is reconstructed from a single magnetometer at Colaba (Mumbai), so it is an estimated range: ≈ −900 nT (Cliver & Dietrich 2013) to ≈ −1,760 nT (Tsurutani et al. 2003). Others are measured Dst minima.
Grids, satellites and GPS all sit inside the magnetic field that a storm shakes. The damage so far has come from storms well short of 1859.
Québec residents lost power for more than 9 hours in March 1989. The grid collapsed in under a minute after geomagnetically induced currents tripped protection systems.
Hydro-Québec; Boteler 2019New Starlink satellites re-entered after a "minor" storm in Feb 2022 swelled the upper atmosphere and raised drag at their 210 km release altitude.
Fang et al. 2022, Space Weather; NOAA/CIRESModelled economic cost to the US of a Carrington-class storm, with 20–40 million people facing outages of up to 1–2 years.
Lloyd's & AER 2013 · modelledA statistical extrapolation from past storms put the chance of a Carrington-class event at about 12% per decade. Other researchers using different methods estimate lower odds, roughly 4–10%.
A near miss already happened: on 23 July 2012 a Carrington-class CME crossed Earth's orbit at a point Earth had passed about nine days earlier.
Probabilities are modelled estimates, not measurements (Riley 2012; Riley & Love 2017; Baker et al. 2013).
Each dot = 1 percentage point. 12 of 100 decades, on Riley's 2012 estimate.
The biggest storms often hit on the declining side of a cycle. The 2003 Halloween storms came about two years after Cycle 23's maximum.
NOAA's Space Weather Prediction Center posts free watches and warnings by G-level, typically hours to days before a CME arrives.
A 72-hour kit (water, light, medicine, a battery radio) covers grid failures of any cause, solar ones included.
Strong storms can degrade GPS. Systems that depend on GPS timing, such as farming, logistics and finance, need backups.
In May 2024, aurora was seen as far south as about 34° latitude. G4+ alerts are also your best chance to see the lights.
Like this? Get a new data story in your inbox every morning.
One infographic a day — real numbers, real sources. No spam, unsubscribe any time.