How tree rings help scientists understand disruptive extreme solar storms

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 across the planet. When these particles hit Earth’s atmosphere, they create a radioactive form of carbon that trees absorb and store in their wood.  

A study published this week in New Phytologist shows that trees don’t all record this carbon in the same way. Understanding those biological differences is key to interpreting Earth’s history of extreme space weather. 

The study, co-authored by Northern Arizona University researchers, reviews how trees take up, store and use carbon and how these processes can affect the timing and strength of the radiocarbon “spikes” left behind by past solar storms, known as Miyake events.  

“Although tree rings are one of our best tools for reading Earth’s history, they’re not perfect instruments,” said West Virginia University scientist Amy Hessl, lead author of the paper. “This paper shows how tree biology shapes the stories they tell.” 

Evidence of these ancient solar storms, far more powerful than anything measured in the modern era, show up in tree rings throughout the world. Previously, 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. 

This study explains why. Trees don’t instantly turn atmospheric carbon into wood. Instead, they may store it for months or even years before using it. Different tree species grow at different times of year and live in different climates, and they vary in how they manage their stored carbohydrates. These biological quirks can shift how radiocarbon appears in tree rings. That allows scientists to better determine when and how intense these storms were not only helping them produce more accurate reconstructions of past events but also helping them refine estimates of how strong future solar storms could be. 

“Understanding how trees acquire carbon from the atmosphere, store it for future use and then use it to grow new wood is critical,” said Mariah Carbone, an associate research professor in the Center for Ecosystem Science and Society and Department of Biological Sciences at NAU and last author on the paper. “The biology determines how faithfully the atmospheric signal is preserved.” 

It also potentially opens up the use of carbon dating in other fields. 

“It’s amazing that one way to improve our understanding of solar storms and solar physics is to better understand tree growth processes, which in turn is critical for improving how we use radiocarbon for carbon dating,” said Andrew Richardson, Regents’ professor in Ecoss and the School of Informatics, Computing, and Cyber Systems. “This study has a lot of implications for applications of carbon dating in fields such as archaeology, for example, as well as the use of radiocarbon in tree rings to reconstruct historical patterns of atmospheric radiocarbon.” 

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 our technology-dependent society today. Modern satellites, communications networks and astronauts are vulnerable to the same kinds of particle storms that left their signatures in trees thousands of years ago.