Ancient tree rings help predict extreme solar storms

Severe space weather can leave a lasting mark in tree rings, offering clues that might help scientists prepare for future disruptive events that threaten communication satellites and astronauts. 

Amy Hessl, a geography professor at West Virginia University’s Eberly College of Arts and Sciences, is leading research that examines how ancient tree rings record evidence of extreme space weather, such as geomagnetic storms and solar radiation bursts.

Tracing space weather through tree rings

Space weather includes a range of phenomena, such as the geomagnetic storms that produce auroras near the poles. These events can sometimes be intense enough to disrupt modern technology. According to Hessl, ancient tree rings have provided evidence of such extreme occurrences in the distant past. 

“If one of these events were to happen today and you were on a high latitude flight flying to Norway, you’d probably receive your lifetime dose of radiation on the plane,” Hessl explained. “And if you were in space, it potentially could kill you.”

Hessl recently received over $202,000 in funding from the National Science Foundation to further investigate the connection between tree rings and space weather. Her research focuses on how solar energetic particles interact with the Earth’s atmosphere, producing radiocarbon that is absorbed by trees. 

As trees grow, they use carbon from the atmosphere to form their rings, effectively preserving a record of past solar activity. By analyzing these tree rings, researchers can trace back significant events, such as the rare and severe “Miyake events.”

Extreme solar storms recorded in trees

Miyake events are characterized by rapid increases in atmospheric radiocarbon and have been detected in tree rings dating back centuries. The first of these events, occurring in 774 AD and 993 AD, was identified 12 years ago. Since then, scientists have discovered seven more events over the past 14,000 years. 

“Some of these events were really extreme and would be incredibly disruptive to our telecommunications system now,” Hessl said. “It’s a very rare event, but it’s not out of the question. We’re dependent on satellites, and if it did happen again, it would probably wipe out most of our telecommunications, taking 15 years to recover. It’s that powerful.”

While most solar energetic particle events originate from solar flares, some particles also come from galactic cosmic rays outside the solar system, often triggered by supernova explosions. 

Although the sun is considered the primary source of Miyake events, Hessl hopes that tree ring data from around the world can help the scientific community pinpoint the exact causes and assess the severity of these occurrences.

Interpreting tree ring data

Interpreting radiocarbon levels in tree rings is not always straightforward. “Until recently, scientists have assumed that trees take up radiocarbon evenly,” Hessl noted. “We’ve been treating trees as if they’re scientific instruments. But they’re not. They’re potentially very biased in the way they take up the radiocarbon.” 

To improve the accuracy of the data, Hessl and her team are investigating why different species of trees, or trees in different locations, might absorb radiocarbon differently. Understanding these variations can help scientists better assess how reliable these natural recorders are.

Research into Miyake events also suggests that some trees store carbon and allocate it at a later time, making them less consistent as recorders of past atmospheric conditions. 

To address these inconsistencies, Hessl is collaborating with Maria Carbone from Northern Arizona University and Rachael Filwett from Montana State University. 

Together, they are studying how different tree species record atmospheric radiocarbon on an annual basis, focusing on three locations in the U.S. with wood that dates back to the last three major Miyake events.

Comparing tree species for consistency

Hessl’s team is comparing three species with different strategies for wood production: the long-lived bristlecone pine from Utah, the deciduous bald cypress in North Carolina, and oak trees preserved in the riverbeds of Missouri. 

The bristlecone pine, the longest-living tree species in the world, has been particularly important in constructing a timeline of past radiocarbon levels. “They live for several thousand years and they’re the backbone of what we know about past radiocarbon in the atmosphere,” Hessl explained.

The research involves taking core samples the size of a pencil – or cross sections if the tree is dead – and using a technique called cross-dating to confirm the year each ring formed. 

By matching tree rings with known Miyake events, the team can examine how different species record these extreme events. However, Hessl expects variations in how well different trees capture the details of these episodes.

Preparing for future space weather events

The goal of this research is to better understand the magnitude and timing of past space weather events and to assess the reliability of trees as recorders of atmospheric radiocarbon. 

“We’re trying to define how extreme those events were,” Hessl said. “When did they occur, exactly? How long did the radiocarbon last in the atmosphere? We need to be sure we’re using reliable recorders, so that’s what we’re trying to figure out.”

By studying how different trees record past events and how they respond to radiocarbon changes today, Hessl hopes to prepare for potential future space weather events that could threaten critical infrastructure, including communication networks. 

Rare, extreme solar storms

While a Miyake event is considered rare and unlikely, Hessl emphasizes the importance of preparation. 

“Some stuff gets a little overblown, but we saw what happened during the pandemic in terms of initial panic,” she noted. 

“So it’s very reasonable to try and figure out what the upper end bookmark of these things are, and then communicate that to the IT community so our technologies can be protected.”

In conclusion, Hessl’s research into tree rings and their ability to record severe space weather provides a window into understanding rare but potentially catastrophic solar events. 

By looking to the past, scientists hope to better prepare for the future, ensuring that modern technology is more resilient to the powerful forces of space weather.

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