Scientists have long relied on tree rings to learn about ancient solar storms — rare bursts of high‑energy particles from the Sun that can disrupt satellites, power grids, and communication systems. Among the most important signals held in wood is radiocarbon, an isotope created and absorbed by trees when energetic particles from the Sun or deep space strike the upper atmosphere.
In a new study published in New Phytologist, a research team led by Amy Hessl, Professor of Geography in Eberly College’s Department of Geology and Geography, shows that trees don’t all record this carbon in exactly the same way, and that understanding those biological differences is key to interpreting Earth’s history of extreme space weather.
“For decades, scientists have assumed that all trees record atmospheric radiocarbon evenly,” said Hessl. “Our review suggests that what is happening inside the tree is far more important than we realized.”
Miyake events, ancient solar energetic particle storms far more powerful than anything measured in the modern era, show up in tree rings around the world. But scientists have noticed small differences between trees and species that make it hard to determine exactly when the events happened or how intense they were.
Although Miyake events are extremely rare, evidence from tree rings indicates they have occurred multiple times over the past 14,000 years. By clarifying how and when different tree species record atmospheric radiocarbon, the new study strengthens the foundation for using tree rings to quantify the timing and severity of past solar storms.
The authors synthesized decades of work on carbon uptake during photosynthesis, the storage and turnover of nonstructural carbohydrates, and the timing of wood formation.
They found that trees don’t instantly turn atmospheric carbon into wood. Instead, they sometimes store it for months or even years before using it. Different species grow at different times of year, live in different climates, and vary in how they manage their stored carbohydrates. All of these biological quirks can shift how radiocarbon appears in their rings.
The work is part of a larger National Science Foundation project studying just how extreme past solar storms might have been and what similar events could mean for a modern society reliant on satellites, GPS navigation, and space‑based infrastructure.
