Do trees remember solar storms?

Nature often reminds us of our fragility and smallness on Earth, even more so if we stop to reflect on our insignificant role in the universe. Despite our anthropocentric vision, we are very far from controlling our entire environment. An example is large solar flares that can change our lives in the blink of an eye.

Geomagnetic storms are caused by the interaction between a solar flare or coronal mass ejection and the Earth’s magnetic field. These types of storms cause a disturbance in the Earth’s magnetic field, which produces spectacular aurora borealis, but can also cause global and devastating effects on our species.

In a society as dependent on technology as today’s, a large electromagnetic storm could take us months or years back to pre-technological life, as they could affect, among other things, communications, navigation systems and electrical networks, infrastructure.

For example, the so-called Carrington event, the largest geomagnetic storm in recent memory, destroyed most of the telegraph systems in the northern hemisphere in 1859. Documents from that time report sightings of the northern lights in southern places like Madrid or Rome.

Fortunately, still limited communications meant that this phenomenon did not have very important consequences. But have these events happened before? How can we know when and where they happened? Let’s find out!

Space record on earth

Despite the fact that right now we can most suffer from its consequences, geomagnetic storms have happened throughout history. How can we know? We have a historical record that we owe to photosynthesis.

In this process, plants take up atmospheric carbon in the form of CO₂, which they combine with water to produce organic matter using energy from sunlight. Some of this organic matter is used to form the cells that form the structure of the plant.

Thus, trees that can be hundreds or thousands of years old record everything that happens around them and store this information in the forest. They are even capable of reflecting an increase in the extremely rare radioactive isotope C¹⁴. This isotope is formed by bombardment with cosmic rays in contact with N¹⁴ atoms in the upper part of the earth’s atmosphere.

By analyzing the C¹⁴ content of the growth ring cells of very old trees, we could track when these events occurred. The unusual increase in C¹⁴ is usually associated with huge emissions of solar cosmic radiation.

In this way, scientists have been able to date cosmic ray magnification events, also called Miyake events. Among them stands out one that happened between 774 and 775, ten times more important than what happened in 1859 and was discovered in 2012 by a group of Japanese researchers led by Fusa Miyake. However, the authors did not link the origin of these cosmic rays to a solar flare or any other possible source.

Relationship between Miyake events and the solar cycle

A recent study by University of Queensland researcher Benjamin Pope casts doubt on the association of these C¹⁴ peaks with solar flares due to their inconsistency with our star’s activity cycles. This group of scientists collected all available data on the Miyake events and created a new software for your analysis.

The events reconstructed by Fusa Miyake’s team do not fit with the 11-year solar cycle, the time period when the Sun is at its most magnetic. Geomagnetic storms usually occur during solar maximum, while Miyake events do not have a clear connection. The second discrepancy may be the duration of the phenomena, while the 774-775 event appears to last for several years, the 1859 Carrington event only lasted one or two days.

In any case, the task of predicting when Miyake’s next event will take place remains an open one. And, just as important, there is still a long way to go to find out when and with what intensity past events occurred. Only by examining their regularities can we find mechanisms by which we can further reduce our fragility in nature.

Gabriel Sangueza Barreda, Forest Ecology Researcher, University of Valladolid and Miguel Garcia Hidalgo, Research Fellow, University of Valladolid

This article was originally published on The Conversation. Read the original.

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