During the second week of November this year (2025) there were four X-class solar flares over a period of six days. These caused a severe geomagnetic storm on Earth, with auroras visible as far south as Florida in the US and Austria in Europe. Although a pretty sight in itself, it is a worrying sign of the Earth’s weakening geomagnetic field.
Solar flares, geomagnetic storms, and auroras
A solar flare usually happens in active sunspot regions where there is significant opposite magnetism in nearby areas. When this magnetic tension “snaps”, intense electromagnetic radiation is emitted. A strong enough solar flare can even eject plasma from the sun’s corona, referred to as a coronal mass ejection (CME). When such a CME is directed at Earth, it will arrive about one to three days later, depending on its speed and exact direction.
Normally the Earth’s magnetic field, or geomagnetic field, will divert most of this plasma around the Earth. However, depending on the speed and density of the CME, part of it may penetrate into the Earth’s atmosphere. One consequence of this is a geomagnetic storm, i.e., a disturbance in the geomagnetic field. Strong geomagnetic storms can cause disruptions in radio communication or navigation systems, affect the electrical grid or other technology, and even have an impact on human health.
Another consequence of Earth-directed CMEs is that auroras are visible in the night sky. However, normally this is restricted to high latitudes such as Alaska and Canada in North America or Scandinavia and Siberia in Eurasia.
The November 2025 event
The intensity of a solar flare can be measured, and is expressed on a logarithmic scale, just like earthquakes. Furthermore, this scale is divided into classes, with the highest (most intense) class referred to as class X. However, because the scale is logarithmic, the difference in intensity going from, e.g., an X4 to an X5 solar flare is not additive, but multiplicative.
During the second week of November 2025, four Earth-directed X-class solar flares ranging from X1.2 to X5.1 happened within a period of six days. They all occurred in the same active sunspot region. The image below shows these four events, with the active sunspot region moving eastward from the center of the sun’s disk as seen from Earth as the sun rotates around it’s own axis.
All four of these solar flares caused a CME, some of which combined on their way to Earth. This caused a sequence of geomagnetic storms, the first one being “severe”, or 4 on a scale of 5. The image below shows the progression of the geomagnetic storms caused by the first three solar flares. The fourth solar flare caused only a minor geomagnetic storm (not shown here), mostly due to the fact that the active sunspot region had already moved away towards the sun’s eastern limb.
As a consequence of these geomagnetic storms, auroras were observed as far south as Florida in the US and Austria in Europe. Although severe geomagnetic storms are not common, they are not an unusual event either. However, seeing auroras that far south is highly unusual, and appears to be a sign of Earth’s weakening geomagnetic field.
A weakening geomagnetic field
Recent measurements indicate that Earth’s magnetic field is weakening at an unprecedented pace. Estimates range from 10% to 20% of field strength loss over the past two centuries. Moreover, this weakening is happening at an increasing rate.
A weakening of the geomagnetic field is a natural phenomenon that has happened multiple times in Earth’s past (over geological time scales), and is often associated with a magnetic pole excursion or even complete flip. However, the consequence is that during such an event life on Earth becomes increasingly vulnerable to intense solar activity. Especially with our highly technology-dependent modern society, it has been suggested that a continued weakening of the geomagnetic field, combined with a very large (e.g., X10 or larger) Earth-directed solar flare, could literally send us back to the stone age.
In short, although auroras at low latitudes are certainly an enjoyable celestial display, it is also a stark reminder of what is going on with the geomagnetic field, and how its weakening makes us increasingly vulnerable. Some scientists say it’s not a matter of if, but when…
Update: In January of 2026 another (even stronger) geomagnetic storm occurred. In fact, it was the strongest in more than 20 years, as the result of just one single X1.95 solar flare. Auroras were visible as far south as Florida in the US and Germany and the Netherlands in Europe. It is rather unusual for a single low-X-class flare to produce such strong effects, unless the geomagnetic field strength is really significantly reduced.