Earth was once hit by an extreme solar storm that would devastate human civilisation if it happened today, tree rings show.
Scientists were able to piece together the solar storm from ancient tree rings that were found in the French alps, and showed evidence of a dramatic spike in radiocarbon levels some 14,300 years ago. That spike was the result of a massive solar storm, the biggest ever found by scientists.
If a similar event happened today, it could knock the power grid offline for months and destroy the infrastructure we rely on for communications, scientists have warned. The researchers behind the new study have urged that the extreme nature of the newly discovered event should be a warning for the future.
“Extreme solar storms could have huge impacts on Earth. Such super storms could permanently damage the transformers in our electricity grids, resulting in huge and widespread blackouts lasting months,” said Tim Heaton, professor of applied statistics in the School of Mathematics at the University of Leeds. “They could also result in permanent damage to the satellites that we all rely on for navigation and telecommunication, leaving them unusable. They would also create severe radiation risks to astronauts.”
Further work is needed to ensure that the world is protected from similar events happening again, scientists said. And more research is required to actually understand how and why they might happen.
Scientists have found nine extreme solar storms, or Miayake Events, that happened in the last 15,000 years. The most recent of them happened in the years 993 AD and 774 AD, but the newly found one was twice as powerful as those.
Researchers do not know exactly what happened during those Miyake Events, and studying them is difficult because they can only be understood indirectly. That makes it difficult for scientists to know how and when they might happen again, or if it is even possible to predict them.
“Direct instrumental measurements of solar activity only began in the 17th century with the counting of sunspots,” said Edouard Bard, professor of climate and ocean evolution at the Collège de France and CEREGE. “Nowadays, we also obtain detailed records using ground-based observatories, space probes, and satellites.
“However, all these short-term instrumental records are insufficient for a complete understanding of the Sun. Radiocarbon measured in tree-rings, used alongside beryllium in polar ice cores, provide the best way to understand the Sun’s behaviour further back into the past.” 
The largest solar storm that scientists were able to actually observe and study happened in 1859, and is known as the Carrington Event. It caused vast disruption to society, destroying telegraph machines and creating a bright aurora so bright that birds behaved as if the Sun was rising.
The Miayake Events like the newly found storm would have been vastly more powerful, however. They were discovered by slicing ancient trees that are becoming fossils into tiny rings, and then analysing the radiocarbon that was present in them.
Their work is published in a new article, ‘A radiocarbon spike at 14,300 cal yr BP in subfossil trees provides the impulse response function of the global carbon cycle during the Late Glacial’, in the journal The Royal Society’s Philosophical Transactions A: Mathematical, Physical and Engineering Sciences.
