Ancient Tree Rings Suggest the Sun Can Unleash Far Bigger Storms

Studies of the world's oldest trees suggest the sun is capable of storms far bigger than anything recorded by modern satellites, and researchers are now trying to work out how often storms of an in-between scale might strike. The evidence comes from "Miyake events" — sudden spikes in carbon-14, a radioactive form of carbon produced in the atmosphere and later locked into a tree's growth rings, that appear when Earth is hit by an intense burst of solar particles.

The first Miyake event was found in 2012, when researcher Fusa Miyake examined a Japanese cedar from Yakushima Island and found carbon-14 had jumped by about 12 parts per thousand between AD 774 and 775 — roughly 20 times the normal variation. The spike later turned up in trees from North America and Europe and in beryllium-10, another radioactive isotope, preserved in ice cores. A nearby supernova or gamma-ray burst was ruled out as too distant, tracing the spike back to the sun.

Even the 1859 Carrington event, the most powerful solar storm in recorded history — it set telegraph lines on fire across Europe and North America and pushed auroras into the tropics — was not intense enough to leave a carbon-14 signature. Researchers calculate that a storm ten times larger than Carrington, a so-called superflare, is needed to do that. Six Miyake events are now confirmed, occurring roughly every 2,000 years; the largest, dated to 12,350 BC, was found in 2023 in fossil Scots pine from the French Alps.

Scientists still have a "missing middle": modern instruments record ordinary storms in detail, while tree rings preserve only the most extreme Miyake events. In a new paper in Communications Earth & Environment, researchers including Michael Dee of the University of Groningen combined eight high-resolution carbon-14 tree-ring records spanning AD 1 to 970 — five newly measured from European oak in Germany and France — to search for storms in that gap.