Tree rings offer insight into devastating radiation storms

Rings from trees that are thousands of years old have shed light on a mysterious, unpredictable and potentially devastating kind of astrophysical event that could affect everyday life. 

A University of Reading meteorology professor teamed up with scientists from the University of Queensland in Australia to apply cutting edge statistics to data from millennia-old trees in order to find out about huge bursts of cosmic radiation, also known as ‘Miyake Events.’ 

They occur around once every thousand years but it is unclear what causes them. 

Dr Benjamin Pope, from the University of Queensland’s Maths and Physics department, said: “The leading theory is that they are huge solar flares.

“We need to know more, because if one of these happened today, it would destroy technology including satellites, internet cables, long-distance power lines and transformers.

“The effect on global infrastructure would be unimaginable.”

Enter the humble tree ring.

First author UQ undergraduate maths student Qingyuan Zhang developed software to analyse every available piece of data on tree rings.

Zhang said: “Because you can count a tree’s rings to identify its age, you can also observe historical cosmic events going back thousands of years.

“When radiation strikes the atmosphere it produces radioactive carbon-14, which filters through the air, oceans, plants, and animals, and produces an annual record of radiation in tree rings.

“We modelled the global carbon cycle to reconstruct the process over a 10,000-year period, to gain insight into the scale and nature of the Miyake Events.”

The common theory until now has been that Miyake Events are giant solar flares.

“But our results challenge this,” Mr Zhang said.

“We’ve shown they’re not correlated with sunspot activity, and some actually last one or two years.

“Rather than a single instantaneous explosion or flare, what we may be looking at is a kind of astrophysical ‘storm’ or outburst.”

Dr Pope said the fact scientists don’t know exactly what Miyake Events are, or how to predict their occurrence, is very disturbing.

“Based on available data, there’s roughly a one per cent chance of seeing another one within the next decade.

“But we don’t know how to predict it or what harms it may cause.

“These odds are quite alarming, and lay the foundation for further research.”

The research is published in Proceedings of the Royal Society A.

Mathew Owens, Professor of Space Physics at the University of Reading, said: “The paper describes a really powerful new tool that the community can used to better understand (possible) extreme space weather events in the tree-ring records. 

“What's surprising is that some of the radiocarbon events seems to be last more than a year (when we'd expect a typical space weather event to last a few days, at most), and that the events don't appear to occur in sync with the solar cycle (which modern space weather generally does). 

“This shows that there's still a lot to learn about the radiocarbon data and space weather in the past."