• an aperiodic series of Miyake events ...

... Often, we point to the Carrington Event of 1859 as the worst-case scenario for solar storms. The 774-75 AD storm was at least 10 times stronger; if it happened today, it would floor modern technology. Since Miyake’s initial discovery, she and others have confirmed five more examples (12,450 BC, 7176 BC, 5259 BC, 664-663 BC, 993 AD). Researchers call them “Miyake Events.”

... For each of the confirmed Miyake Events, researchers have found matching spikes of 10Be and 36Cl in ice cores. These isotopes are known to trace strong solar activity. Moreover, the 774-75 AD Miyake Event had eyewitnesses; historical reports of auroras suggest the sun was extremely active around that time.

... The 1989 flare was not very big compared to the 1859 Carrington Event. Had the Carrington Event happened in 1989, the entire North American power grid could have gone down.

Satellites are even more vulnerable to solar storms. They’re just floating up in space, totally exposed. The influx of particles can flip bits in a satellite’s memory and scramble it. The particles can also cause a satellite to send out spurious signals. Or they can straight-up fry its electronics.

That’s why solar storms are dangerous. If satellites or the power grid went down, that would throw society into chaos. Most phones and communications equipment would no longer work. People would be floundering without information. The loss of power would be especially harrowing. It would disrupt our ability to distribute food, to cool and heat our homes, to provide medical care. We wouldn’t recover for weeks—perhaps months. Many people could die.

And the really scary thing is that the 1859 Carrington event is itself small potatoes compared to truly epic solar storms that scientists have recently discovered.
. . .
... if Mikaye events did result from solar storms, they were truly massive storms—with the potential to cause equally massive damage.

Here are some numbers for perspective. The atomic bomb that leveled Hiroshima in 1945 released the energetic equivalent of 15,000 tons of TNT. Well, the Carrington Event of 1859 released the equivalent of 660 billion Hiroshima bombs.

And the Miyake events of 774 and 993 were five times bigger than the Carrington Event. Scientists now know of an event from 14,300 years ago that was twice as big as those. We’re talking 6.7 trillion Hiroshima bombs.

The most recent occurred just over 1,000 years ago in 993 CE. Researchers believe these events occur rarely – but at somewhat regular intervals, perhaps every 400 to 2,400 years.

The most powerful known Miyake event was discovered as recently as 2023 when Bard and his colleagues announced the discovery of a carbon-14 spike in fossilised Scots pine trees in Southern France dating back 14,300 years. The spike they saw was twice as powerful as any Miyake event seen before, suggesting these already-suspected monster events could be even bigger than previously thought.
. . .
Miyake events, however, are a different beast – causing blasts of particles at least ten times larger than the Carrington event. In fact, so small was the Carrington event by comparison that any spike of carbon-14 it produced barely shows up in tree rings at all. In March, a study found a very subtle hint of carbon-14 from the Carrington event, but nothing compared to a Miyake event. "It doesn't show up", says Pearson. "Either that means there's something different [going on], or [Miyake events are] on a much greater scale than the Carrington event. That's where the potentially dramatic side lies. If they are events like the Carrington event but just on a larger scale, we need some serious mitigation strategies as quickly as possible."

A Miyake Event Would Cripple Modern Society

Unfortunately, Miyake events also carry an ominous promise to disrupt the future. In the face of a Carrington-level event, our modern telecommunications systems would collapse. Chaos would ensue.

But remember, the Carrington event was relatively minor. Faced with a surge of high-energy particles characteristic of a Miyake event—one powerful enough to leave its mark in the rings of trees—the induced current would flood the thousands of satellites that encircle Earth, crippling them for months and possibly years. Power grids would topple immediately, leaving anything reliant on electricity, like lights, electric vehicles, and ventilators, inoperable. Astronauts would undoubtedly receive lethal doses of radiation, and even people on board airplanes could encounter dangerous levels.

E3 induces low-frequency (quasi-dc) currents in transmission lines and bulk power system
transformers that have grounded wye windings. The flow of these geomagnetically induced
currents (GIC) in transformer windings can cause magnetic saturation of transformer cores,
which causes the transformers to generate harmonic currents, absorb significant quantities
of reactive power, and experience additional hotspot heating in windings and structural
parts. Potential impacts of E3 on the electric power grid include voltage collapse (regional
blackout), protective equipment misoperation due to harmonics, and transformer damage
due to additional hotspot heating. Additionally, certain sensitive power electronics-based
loads, for example uninterruptible power supplies, may be prone to disruption or damage
due to harmonic voltage distortion that is transferred from the transmission system to
medium-voltage and low-voltage systems.
. . .
Assessing the potential impacts of E3 on the bulk power system is similar to assessing the
impacts of geomagnetic disturbance (GMD) events; however, there are some important
distinctions. First, the E3 E-fields are much shorter duration than GMD events, generally
lasting up to 100’s of seconds (refer to Figure 1) as compared with hours or days with a
GMD event. Secondly, E3 E-field levels can be an order of magnitude higher than a severe
GMD event. Because of these important distinctions, the methods used to assess the
potential impacts of E3 can differ from those used to assess severe GMD events. Lastly, the
results of E3 assessments should never be used to quantify the effects of a severe GMD
event and vice versa, as the two phenomena should always be considered separately.

• And Gamma-ray Bursts ...

There is a very good chance (but no certainty) that at least one lethal GRB took place during the past 5 billion years close enough to Earth as to significantly damage life. There is a 50% chance that such a lethal GRB took place within two kiloparsecs of Earth during the last 500 million years.

The Ordovician mass extinction 450 million years ago may have been caused by a GRB. Estimates suggest that approximately 20–60% of the total phytoplankton biomass in the Ordovician oceans would have perished in a GRB, because the oceans were mostly oligotrophic and clear. The late Ordovician species of trilobites that spent portions of their lives in the plankton layer near the ocean surface were much harder hit than deep-water dwellers, which tended to remain within quite restricted areas. This is in contrast to the usual pattern of extinction events, wherein species with more widely spread populations typically fare better. A possible explanation is that trilobites remaining in deep water would be more shielded from the increased UV radiation associated with a GRB. Also supportive of this hypothesis is the fact that during the late Ordovician, burrowing bivalve species were less likely to go extinct than bivalves that lived on the surface.

A case has been made that the 774–775 carbon-14 spike was the result of a short GRB, though a very strong solar flare is another possibility.

Gamma-ray bursts (GRBs) pose significant threats to Earth's biosphere and geosphere if occurring sufficiently nearby, primarily through atmospheric disruption and subsequent ecological cascades. The high-energy gamma radiation ionizes atmospheric nitrogen and oxygen, producing nitrogen oxides (NO_x) that catalytically destroy stratospheric ozone (O_3). For a long GRB at approximately 10 kiloparsecs (kpc), models predict a global ozone reduction of up to 38%, with localized depletions exceeding 70% at mid-latitudes, persisting above 10% for about seven years and full recovery taking 10-12 years. This depletion allows increased penetration of solar ultraviolet-B (UVB) radiation, elevating surface UV fluxes by factors of 2-16 times the annual average in affected regions.