What an “S-Class” Solar Superflare would Mean (and What We Actually Know), By Professor X

There is a tendency, when discussing solar storms, to drift either into complacency or melodrama. On the one hand, they are treated as technical curiosities — interesting to space physicists, but of little practical consequence. On the other, they are inflated into civilisation-ending catastrophes. The reality, as is often the case, sits in an uncomfortable middle ground. It is neither trivial nor apocalyptic. It is, rather, a problem of modern dependence meeting an old and only partially understood natural force.

The recent paper in Journal of Geophysical Research: Space Physics contributes to a growing recognition that the Sun is capable of producing events larger than those typically considered in infrastructure planning. The language sometimes used — "S-class" flares, or superflares — does not refer to an official classification system but to events exceeding the familiar X-class scale by an order of magnitude or more. This is not speculation drawn from distant stars alone; it is anchored in evidence that our own Sun has produced, and may again produce, eruptions at the upper end of that range. What remains uncertain is not the possibility, but the timing. Suggestions of a specific year, such as 2027, should be treated as indicative of an elevated phase in the solar cycle rather than a precise forecast. The Sun does not publish a schedule.

To understand the risk, one must separate the visually dramatic from the materially consequential. Solar flares themselves, bursts of electromagnetic radiation, can disrupt radio communications almost immediately. But the more serious threat lies in the associated coronal mass ejection — a vast cloud of magnetised plasma that, if directed toward Earth, can interact with the planet's magnetic field. The crucial variable is orientation. A southward magnetic field in the incoming plasma couples efficiently with Earth's magnetosphere, allowing energy to pour in. When that happens, the consequences move rapidly from the upper atmosphere into the systems on which modern life depends.

The closest historical analogue is the Carrington Event. Telegraph systems failed, operators received shocks, and auroras were visible at latitudes where they had no business appearing. That event, however, occurred in a world that was only lightly electrified. Its modern significance lies not in what it did, but in what it would do now. The intervening century and a half have seen the construction of an electrical and informational infrastructure of extraordinary reach and, in certain respects, fragility.

The most immediate vulnerability is the power grid. Long transmission lines, by virtue of their length, act as collectors of geomagnetically induced currents during a strong solar storm. These currents are not part of the system's design parameters. They flow into transformers, driving them into saturation, generating heat, and in severe cases causing permanent damage. Unlike many other components, large transformers are not easily replaced. They are specialised, expensive, and often manufactured to order with long lead times. A sufficiently strong and widespread event could therefore produce not just a blackout but a prolonged disruption, measured in weeks or, in extreme scenarios, months.

Satellites represent a second point of vulnerability. They operate in an environment that is directly exposed to the effects of solar activity. High-energy particles can damage electronics, degrade solar panels, and interfere with onboard systems. At the same time, the heating of the upper atmosphere during a storm increases drag on low-Earth orbit satellites, altering their trajectories. The result is not necessarily the wholesale destruction of satellite constellations, but a period of degraded performance and increased failure rates. Given the extent to which navigation, communications, and timing systems depend on these platforms, even partial disruption would have cascading effects.

Communications themselves are not immune. High-frequency radio, still used in aviation and maritime contexts, can be rendered temporarily unusable. Navigation systems that rely on stable ionospheric conditions can lose accuracy. The internet, often imagined as a diffuse and therefore resilient network, depends in practice on physical infrastructure — data centres, cables, and the power that sustains them. It would not vanish, but it would degrade, unevenly and unpredictably, as underlying systems faltered.

It is important, however, to resist the drift into exaggeration. Even a very large solar event would not strip away the atmosphere or render the planet uninhabitable. The direct biological effects at ground level would be minimal. The risk is not to life in the immediate sense but to the systems that sustain contemporary life at scale. It is a risk of interruption rather than annihilation, but interruption in a context where continuity is assumed.

What distinguishes the present from the past is not simply technological dependence but the degree of interconnection. Energy, communications, logistics, and finance are now tightly coupled. A disruption in one domain propagates into others. A power outage affects data centres; data centre failures affect communications; communication failures affect coordination of recovery efforts. The system does not fail in a single, isolated way. It degrades across multiple fronts, with feedback effects that are difficult to predict in detail.

This brings us back to the question of probability. The current solar cycle is moving toward its peak, and with that comes an increased likelihood of significant solar activity. But increased likelihood is not certainty. The historical record suggests that extreme events are rare on human timescales, even if they are inevitable over longer periods. The difficulty lies in planning for something that is both unlikely in any given year and potentially disruptive when it occurs. It is precisely the kind of risk that is easy to acknowledge in the abstract and difficult to prioritise in practice.

The more measured conclusion is therefore also the more disquieting. The Sun is capable of producing events that would stress modern infrastructure in ways that have not yet been fully tested. The systems on which contemporary societies depend are, in certain respects, not designed with those upper bounds in mind. There is no imminent certainty of disruption, but there is a clear exposure. The question is not whether such an event would end civilisation — it would not — but whether it would reveal, in a compressed and inconvenient form, the extent to which that civilisation depends on conditions it does not control.Top of FormBottom of Form

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2025JA034977