The largest solar flare in 12 years was just recorded.


The sun’s been a bit of a show-off lately. On the heels of its magnificent total eclipse last month, yesterday it produced the biggest solar flare recorded in the last 12 years. This and other flares in recent days have caused a radio blackout and “shock arrivals” of radiation from the sun, according to NASA, as part of a geomagnetic storm expected to continue for the next few days. (Two more mid-level solar flares have been reported so far today.)

Radio blackouts and shocks of radiation sound kinda scary, and previous solar flares have caused problems like transformer explosions and widespread mobile-phone outages. So of course we wondered: What does all of this mean for our health? The good news, experts say, is probably not much.

First things first, what is a solar flare? According to NASA, it’s a sudden and intense flash of brightness that occurs when magnetic energy built up in the solar atmosphere is released. High-energy particles and a burst of ultraviolet rays are released into space, and in a few days time, can reach the Earth’s atmosphere.

NASA also says that these powerful bursts of radiation are nothing to worry about from a health perspective. “Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground,” the space agency said in a statement today, “however—when intense enough—they can disturb the atmosphere in the layer where GPS and communications signals travel.”

Dale Gary, PhD, distinguished professor of physics at NJIT’s Center for Solar-Terrestrial Research, agrees with NASA’s reassuring statement. “There are potential health effects for anyone exposed to that high-energy radiation, but actually we are protected because those rays and particles get absorbed into our atmosphere,” says Gary.

People on airplanes flying at high altitudes over the poles might be at increased risk for some of this radiation, Gary continues, and he says that occasionally, flight routes are changed during periods of unusual solar activity to protect against this. But for anyone on the ground, he says, there’s not much to worry about.

In addition to a large dose of radiation, however, solar flares also cause fluctuations in magnetic fields, which can reach the earth’s surface. “These take a couple days to get here, but when they arrive they can interact with our magnetosphere,” says Gary. “That can induce currents in our power lines, and when that happens, transformers can blow or power outages can occur.”

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According to National Geographic, scientists predict that one of these strong storms will hit our planet tomorrow, September 8. People in high-latitude regions may also be treated to brilliant auroras, or visible lights in the sky, over the next few days.

Still, these storms probably won't cause any health problems—except that there could be safety issues if the power goes out, Gary says. GPS and traffic-light outages could make for risky driving, for example, or hospitals could theoretically lose access to health data.

Not everyone is convinced that solar flares are harmless, however. A 2014 study published in the journal Stroke found a link between geothermal storms and stroke risk among people in New Zealand, Australia, the United Kingdom, France, and Sweden. The study compared 11,453 hospital reports with daily geomagnetic activity over a 23-year period, and found that geomagnetic storms were associated with a 19% increased risk of stroke overall, and a 27% increased risk among adults under 65.

The study could not show a cause-and-effect relationship, and the researchers—from the Aukland University of Technology, the University of Aukland, the University of Oxford, and other institutions—did not have detailed information for all participants about their traditional cardiovascular risk factors. But they speculate that magnetic fluctuations could have an effect on blood pressure, heart rate, blood clotting ability, or circadian rhythms, any of which could have an effect on stroke risk.

Gary, for what it's worth, has his doubts. “The change in magnetic field we're talking about is really small," he says: "If you think of the magnetic field that causes your compass needle to point north, we’re talking about a tenth of a percent of that fluctuation." Those tiny changes are amplified by our giant power grid, he says, but they’re unlikely to have an effect on an individual human body.

Even if the study's assumptions are correct, geomagnetic storms only accounted for less than 3% of all strokes during the study’s timeframe. Considering nearly 17 million strokes occur around the world every year, however, that’s almost half a million people. “Although the effect of geomagnetic activity alone is modest,” the authors wrote in their paper, “in combination with other risk factors, it could be extremely important.”

The authors suggest that geomagnetic storm warnings be announced along with weather reports, and that doctors and patients should pay closer attention to controlling conventional risk factors for stroke during the days leading up to these types of solar events. These actions, they say, may reduce stroke incidence on a global level.