Japanese cedar trees, shown here lining the path to Togakushi Shrine in Nagano, Japan, can live to be thousands of years old. Inside, their tree rings reflect the amount of carbon-14 that was in them at the time they formed, minus whatever fraction of those atoms have radioactively decayed in the intervening time. Trees like these provided the key evidence in uncovering the solar storm of 774–775: a storm that may have been even more powerful than 1859’s famed Carrington event. (Credit: Chris 73/Wikimedia Commons)

World’s oldest trees reveal the largest solar storm in history

1859’s Carrington event gave us a preview of how catastrophic the Sun could be for humanity. But it could get even worse than we imagined.

While humanity reckons with many problems here on Earth — war, political turmoil, an ongoing pandemic, all alongside the energy, climate, and water crises — it’s important to remember just how relentless the Universe can be. While earthquakes, tornadoes, volcanoes, hurricanes and other natural disasters haven’t exactly ceased in the meantime, there’s a looming threat for which we’re completely unprepared: a solar storm. Without any mitigations, widespread electrical fires and power station failures could come with damages costing of trillions of dollars, impacting the lives of of billions.

Historically, the largest recorded solar event occurred back in 1859: the Carrington event. But more than a millennium prior to that, an even stronger cosmic event struck Earth. We know this because, back in the years spanning 774–775, there was a tremendous spike in the presence of carbon-14 in Earth’s atmosphere, and the evidence is found in tree rings all across the world. After a full decade investigating the possible causes of this spike, the scientific conclusion we’ve reached is that the Sun…