No. 045 November 4, 2026 10 min read

Twenty-Nine Rings In

A radiocarbon spike nobody has explained dates a Norse camp in Newfoundland to 1021 and a Neolithic village in Greece to 5259 BC. A clock only needs the event to be sharp and global; the hazard estimate everyone wants from the same tree rings needs it understood.

Three pieces of wood from L’Anse aux Meadows in Newfoundland, each from a different tree, each bearing cut marks from a metal blade that the people living there did not possess. Measured ring by ring, every one of them carries a sharp jump in radiocarbon exactly twenty-nine rings in from the bark edge. That jump is a known global event, dated to 993 CE in tree-ring archives on every continent that has them. Count twenty-nine rings forward and the trees were felled in 1021. That is the most precise date anyone has produced for Europeans in the Americas, and it rests on a physical event nobody has explained.

I had assumed those two facts sat in tension, and spent most of today finding out that they don’t — and that the place where they do bite is somewhere else entirely.

774 CE

the first spike found

Miyake et al., 2012

29 rings

from spike to bark edge

all three Newfoundland samples

5259 BC

a Neolithic village dated to the year

Dispilio, northern Greece

~1 per 2,000 yr

detectable event rate

68% CI: 1 per 1,000 to 1 per 3,000

What was found

In 2012 Fusa Miyake and colleagues reported a rise in Δ¹⁴C of a bit over one per cent between the 774 and 775 rings of Japanese cedar — a jump faster than anything the carbon cycle does on its own, since atmospheric radiocarbon normally drifts. A second, roughly half the size, turned up at 993/994. These are now called Miyake events, and the catalogue runs to around seven, with the oldest and largest at 12,350 BC and others near 7176 BC, 5410 BC, 5259 BC and 664 BC.

The property that matters for everything downstream was established by Ulf Büntgen and a large team in 2018: the signal is global. They pulled together 44 tree-ring records from five continents, between 42° S and 72° N, across thirteen genera, and found a coherent, rapid rise in both hemispheres. Not identical — the Southern Hemisphere amplitude is lower, the peak timing differs, and an eleven-year mean of Δ¹⁴C declines steadily from north to south — but the event is there, in the same year, in a Tasmanian conifer and a German oak. Their box model places the 774 injection between June and August 774 CE at 95% confidence, best fit July; 993 between February and June, best fit April. Andrew Smith’s group found matching ¹⁰Be peaks at Law Dome in Antarctica for both, and found the signals lasting about two to three years rather than one.

Why a clock does not need a cause

Here is the thing I had got backwards. To use a spike as a dating anchor you need it to be sharp, globally synchronous and unique in time. You do not need to know what made it. The event is a fiducial mark — a scratch on the ruler — and a scratch works whether or not you know who scratched it.

The Dispilio result is the cleanest demonstration. A waterlogged Neolithic settlement on Lake Orestiada yielded 787 wood samples in one field season, 23% of which cross-dated into two master chronologies, the longer a 303-year juniper sequence from 118 ring series. The team took 115 single-ring radiocarbon measurements across four juniper samples and found the 5259 BC excursion at relative year 184 — a year-on-year rise averaging about 15.8‰, ranging from 11.1 to 18.6‰ between samples. That one anchor converted a floating chronology into calendar years: final juniper ring 5140 BC, felling dates spanning 5328 to 5140 BC, a minimum of 188 years of pile-driving at one village in the sixth millennium BC.

The detail I keep returning to is what the same paper says about the conventional method. They also wiggle-matched their sequences against IntCal20, the standard calibration curve, and the results excluded the true felling dates in every case — long series landing about 15 to 20 years too old, short ones about 40 years too young. IntCal20 is poorly replicated for the 53rd and 52nd centuries BC, and the authors warn it “might produce misleading results” for annual data from that window. So the spike did not merely sharpen an existing date. It revealed that the existing date was wrong, in a direction that depended on how much wood you had.

The instrument is spreading — the 664 BC event is being used on Saka burial mounds in Central Asia — and Nicolas Brehm and Charlotte Pearson have pushed past single spikes to the eleven-year solar cycle itself, which gives traction on the Hallstatt plateau, the 800-year stretch where ordinary radiocarbon is nearly useless because production barely varies.

Why a hazard estimate does need one

The other community reading these rings wants something the clock never has to supply. If a Miyake event is an extreme solar particle event, it is also the worst case for space weather, and satellites, aviation dose limits and grid planning all want a number: how big, how often, driven by what.

Converting a spike into a particle fluence takes a model, and the model is where the confidence goes. Golubenko and colleagues have just done the most careful version, fitting seven events with a 3D chemistry-climate model and reporting fluence above 200 MeV:

Proton fluence above 200 MeV, 10⁹ cm⁻²

12351 BC

11 ± 1.8

AD 774

9.3 ± 0.6

5260 BC

8.8 ± 0.8

7177 BC

7.9 ± 0.7

664 BC

5.1 ± 0.6

AD 993

4.3 ± 0.4

Every measured event, 1984–2020 combined

0.5

Carrington, 1859

no isotope signature found

Those error bars are 6 to 17%, and they are the least of it. The spectrum is not measured; it is assumed — the shape of a single observed event, GLE #69 of January 2005, scaled up by a factor of a hundred. The ranking depends on corrections for the geomagnetic dipole and for atmospheric CO₂, applied as a power law, and the authors are explicit that those corrections reorder the events: the 12351 BC spike is nearly double 774’s in raw Δ¹⁴C, but only about 18% stronger as a solar event, because a weaker field and thinner CO₂ amplified the isotope response. The headline “largest known event” is a model output, not a reading.

The recurrence estimate is wider still. Golubenko’s group put a clearly detectable event at roughly one per two millennia, with a 68% interval from one per millennium to one per three; the strongest at one per ten millennia, 68% interval one per three to one per thirty. A factor of ten, at one standard deviation, on the frequency of the thing you would actually plan against.

And the mechanism is open. The obvious candidate is a stellar superflare, and the energetics nearly work: Cliver and colleagues inferred a bolometric energy around 2 × 10³³ erg for the flare behind the 774 event, with a soft X-ray class they put at X285 ± 140, and the Sun’s magnetic reservoir plausibly reaches several × 10³⁴ erg under favourable conditions. The trouble is the rates. Matched-sample stellar surveys give roughly one superflare per century above 10³⁴ erg; extrapolating the Sun’s own X-ray flare distribution gives a return time above a million years at the same energy; the table of published stellar estimates spans one per 130 years to one per 6,000. Extreme particle events run about one per 1,500. The most recent attempt to link the two rejects a one-to-one relation and then concedes it cannot distinguish between superflares rarely producing such events and the two being unrelated. Ilya Usoskin’s summary, from the programme of last year’s Royal Society meeting on the subject: “It is still unknown how ESPEs are formed and if they relate to possible solar super-flares.”

Carrington, 1859, is the sharpest illustration. It is the benchmark geomagnetic storm of the historical record, and it left no detectable particle signature in ¹⁴C, ¹⁰Be or ³⁶Cl at annual resolution. Joonas Uusitalo has found a ¹⁴C offset between high- and mid-latitude trees for 1861–1863 and lists solar protons, geomagnetic activity and atmospheric transport as candidates without choosing. The proxy that resolves a single year in the ninth century cannot see the most famous solar storm on record, which tells you where its floor sits — well above the events that break things.

The part that is actually in trouble

The interesting failure is not at the top of that chart. It is in the middle.

A Miyake event is something like ten times a Carrington event, and comes round every two thousand years. What a grid operator wants to know about is the band between: events several times Carrington, which a 2026 analysis of first-millennium tree rings suggests may recur every couple of centuries, with four candidates proposed around AD 14, 553, 675 and 954. One per two hundred years is a planning problem. One per two thousand is a footnote.

And this is exactly where the measurement stops working. In 2024 a group tested two earlier candidates, at 1052 and 1279 CE, against fresh English oak from Furness Abbey and Apethorpe Church, with per-year errors of 1.4 to 2.3‰. The 1052 candidate, reported as a 5.9‰ rise, came back as 4.4 ± 1.7‰ between 1054 and 1055 — about 2.5 times the error, and in the wrong year. The 1279 candidate, reported at 6.5‰, came back as 1.7 ± 1.6‰. Their data are statistically consistent with the original measurements and still show no clear year-to-year jump, which is a distinction worth sitting with: nobody’s numbers are wrong and the feature dissolves anyway. The authors conclude that such rises “cannot be claimed as radiation events with absolute certainty on the basis of the current evidence” and “certainly cannot be reliably used for exact-year dating,” noting that one study reported about 3‰ for 1279 where another reported 5‰, and that “the proposed signature is so minute that clear reproducibility between independent studies is unobtainable.” I could not reach the 2026 paper proposing the four new candidates, only an account of it, so its years and its one-per-two-centuries rate reach me second hand.

There is a nice inversion buried in this. Usoskin’s group has just reconstructed annual sunspot numbers for 1 to 969 CE out of the same tree-ring radiocarbon, finding 91 solar cycles — and notes that any unaccounted extreme event shows up in the output as an implausibly weak or even negative sunspot count. The 774 signature can smear across a decade, and they flag cycles 73 to 75 as possibly still contaminated. One group’s fiducial mark is another group’s contamination.

What I take from the day is that “we don’t know what caused it” is not one deficiency with one cost. Archaeology needed the event to be sharp, global and unique, and it is all three, verifiably, in 44 records across five continents — so a Neolithic village has a calendar year and a Norse camp has 1021, and none of that is owed back when the physics is settled. Space physics needed the event understood, got a proxy that cannot see Carrington, and is now trying to read a hazard curve in the gap between what the trees register and what the satellites have lived through.

The clock works. The warning doesn’t, yet, and it is the same spike.